CS 372 - Midterm

UDP service - internet protocols

"unreliable" (best effort) data transfer between sending and receiving process - does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee - suitable for multimedia applications

Convert the following units. Your answer should be a whole number with no text in the answer field: 60.76 Kbps = _____ bits per second

60.76 x 1000 = 60,760 60,760

Al Gore invented the internet.

False

An HTTP server maintains client states.

False

Cookies are not a security or privacy concern.

False

Does HTTP preserves state between sessions?

False

FTP is implemented over a pair of UDP connections.

False

FTP is implemented over a single TCP connection

False

HTTP implements caching by use of a UDP check.

False

If there is only one error bit in a segment, it can go undetected.

False

In store-and-forward networks, only one packet may be in transit on a link at any given time.

False

In store-and-forward transmission, a packet switch may begin transmitting the first bits of packet before it has finished receiving that the last bits of the packet.

False

It is acceptable to create two TCP connections on the same server/port doublet from the same client/port doublet.

False

The TCP protocol provides error detection and correction.

False

The TCP protocol provides reliable, connectionless service.

False

The UDP protocol implements congestion control.

False

The UDP protocol implements reliable data transfer.

False

The UDP protocol is connection-oriented.

False

The UDP protocol provides reliable, connectionless service.

False

The following is a valid IP address: 130.154.1.256

False

The following is a valid IP address: 130.154.465.201

False

The internet is a system for connecting computers using a single transmission technology.

False

The organization that manages the .org TLD is known as the Public Internet Organization (PIO).

False

There is a single, central DNS server.

False

Match the event with the TCP receiver action: Arrival of segment that partially or completely fills in gap in received data.

Immediately send ACK, provided that segment starts at the lower end of gap.

Match the event with the TCP receiver action: Arrival of out-of-order segment with higher-than-expected sequence number.

Immediately send duplicate ACK, indicating sequence number of next expected byte.

A simple checksum can detect all 1-bit errors.

True

A simple checksum can detect some 2-bit errors.

True

An FTP server maintains client states.

True

FTP is a peer-to-peer protocol.

True

FTP is implemented over a pair of TCP connections.

True

HTTP implements caching by use of a conditional GET.

True

IMAP maintains the client's entire email directory structure on the client.

True

If a file is up-to-date in your local browser cache, then the use of a proxy server will not save time.

True

If there are 2 bits in error, the errors can go undetected?

True

In one mode, POP3 can download emails to the client, and keep the originals on the mail server.

True

Most packet switches use store-and-forward transmission.

True

SMTP can send additional types of objects Multipurpose Internet Mail Extension / MIME.

True

Sending emails with false "Sender IP" is called "email spoofing".

True

The TCP protocol implements flow control.

True

The TCP protocol is connection-oriented.

True

The UDP protocol provides error detection.

True

The following is a valid IP address: 130.154.1.25

True

The internet is a network of networks.

True

There are 232 (4,294,967,296) unique 32-bit IP addresses (ignoring reserved addresses)

True

What is the benefit of broadband cabling over baseband cabling? Can Broadcast cabling utilize a greater range of frequencies in transferring information. This allows more data to be transferred over this type of cabling.

True

What is the role of physical media in access networks? Do Analog signals relate to bits propagating over/through the physical media.

True

What is the role of physical media in access networks? Is the physical media a physical link in the chain between sender/receiver pairs.

True

What is an application that does NOT have stringent data integrity requirements?

Video streaming

Which of the following is NOT a characteristic of a computer virus?

Viruses are designed to collect information from the user, like keystrokes

Proxy server

a server that takes some of the load off an origin server (e.g. Amazon) Scenario: a user's browser sends all HTTP requests to cache - if object in cache: cache returns object - else, proxy server has to pass the HTTP request to the origin server and the origin server will return it to the proxy, then client.

spyware

a type of malware that infects your computer and attempts to capture various bits of your data or even your passwords and send them back to the attacker through the internet.

As a packet is being constructed and passed "down" to the next layer of the internet protocol stack, a new "header" is added. This process is called ____________

encapsulation

Top-Level Domain (TLD)

example: eecs.oregonstate.edu - eecs: specific computer server that can be contact - edu : TLD

Retransmitting a missing segment before the segment's countdown timer expires is called...

fast retransmission

Two types of physical media

guided media: signals propagate in solid media unguided media: signals propagate freely

Network edge

hosts and applications clients and servers

network security

how computer networks can be attacked intentionally or unintentionally and how we can defend ourselves against that.

A ______________ model uses a central server to setup connection between peers

hybrid

In a ______________ architecture, one host is always on, and other hosts may connect and be handed off amongst themselves by this first host.

hybrid client-server/P2P

ICMP applications

implemented at the network layer, only user interface goes to the application layer.

Reliable data transfer

implemented in the application, transport, internet layers

The TCP sequence numbers are used to implement _________ .

in-order delivery

Worm

installs itself, replicates itself, and sends itself around the internet (attacks the network core)

network core

interconnected routers network of networks

Protocol ___________ allows multiple protocols to work together.

interoperability

Pipelining

sender transmits multiple packets - packets "in-flight" have yet to be acknowledged - receiver might not be able to handle that many packets arriving at the same time benefit : increases network utilization

The TCP sequence numbers are used to implement _________.

reliable data transmission

two main types of HTTP

request, response -ASCII (human readable) Uploading form input: URL method: - uses GET method - input is uploaded in URL field of request line. POST method: input is uploaded to server in the entity body

IP addresses and "root zone" TLDs coordinated by IANA (Internet Assigned Numbers Authority) High-level management of Internet names and addresses handled by ICANN (Internet Corporation for Assigned Names and numbers)

root zone = .uk, .edu, etc

RTT

round-trip time: time for a small packet to travel from client to server and back

HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #3,356. HostA now sends segments of the same application data stream in order: P: 210 bytes Q: 174 bytes R: 115 bytes Suppose the segments arrive at Host B in the order Q, P, and R. What is the acknowledgment number on the segment sent in response to segment R?

segment sent in response to segment R: = 3,356 + (sequence P) + (Sequence Q) + (Sequence R) + 1 = 3,856

IP spoofing

send packet with false source address

The transport layer resides on/in the network ________.

edge

A client-side history of transactions between a client and server using HTTP is called a Cookie.

True

A network is a system for connecting multiple computers using a single transmission technology.

True

TCP uses

- client initiates tcp connection to server, port 80 - server is always listening, accepts tcp connection - http messages are exchanged between client and server - tcp connection closed

Two categories of physical media

- Guided Physical Media include wired communication types such as: Twisted Pair, Coaxial Cable (coax), and Fiber-Optic cable. - Unguided Physical Media is another name for wireless radio communication. Types include: Terrestrial Microwave, Wifi LAN, Wide-Area Networks or WAN (cellular), and Satellite communications.

Applications that use TCP

- HTTP -FTP (file transfer) -SMTP (email) -Telnet (remote login)

Frequency division multiplexing (FDM)

- Achieves multiplexing by using different carrier frequencies - Frequencies must be separated to avoid interference - Receiver can "tune" to specific frequency and extract modulation for that one channel - Useful only in media that can carry multiple signals with different frequencies - high-bandwidth required

Non-persistent HTTP

- At most one object is sent over a TCP connection. - downloading multiple objects requires multiple connections - browsers often open parallel TCP connections to fetch referenced objects Response time: 2*RTT + transit time - one RTT to initiate TCP connection - one RTT for HTTP request and response - file transmission time

Baseband and broadband

- Baseband uses a small part of the wave spectrum and sends only one signal at a time - Broadband uses a larger part of the wave spectrum and uses frequency division multiplexing to send multiple signals simultaneously

What is the goal of caching in HTTP

- Caching prevents excessive requests to the origin server. - Caching prevents additional congestion in the internet - Caching prevents the same information from being repeatedly downloaded - Caching appears to speed up page downloads

What are some reasons for the layering of network protocols?

- Can update the inner workings of a protocol, as long as input/output remain the same - Protocols can be tested independently of one another - The complication of dealing with the intermeshed types of hosts and data is lessened - When maintenance is required at one level, changes do not affect other layers

What are cookies used for?

- Cookies make some web browsing more convenient by saving browsing history - Cookies can save preferences for a news-feed - Cookies can enable targeted advertising - Cookies can save info a shopping cart - Cookies can save your location for weather report

Packet switching cont 2

- Data transmitted in small, independent pieces. source divides outgoing messages into packets and destination recovers original data - Each packet travels independently Includes enough information for delivery, may follow different paths and can be retransmitted if lost

What devices reside on the network edge? (check all that apply)

- End-systems - smartphones - laptops - servers - hosts

What are some tools for implementation of reliable data transfer?

- Error Detection - Timing Message Sequencing - Receipt Acknowledgement

Please select all examples of systems using guided media.

- Ethernet home networks - Cable television/internet - ADSL - Fiber-optic internet

Two ways of dividing the link bandwidth into pieces

- Frequency division multiplexing (FDM) - Time division multiplexing (TDM)

Characteristics of TCP

- Full-duplex operation (bi-directional data flow in the same connection at the same time) - In-order byte stream service (received data same as sent data) - Acknowledgment of bytes received - Retransmission of packets if necessary - Pipelining for efficiency (multiple packets sent at once) - Hurry-up-and-wait (burst of packets sent, then wait for acknowledgment) - Flow-controlled for reliability (sender will not overwhelm receiver) - MSS: Data will be broken up into segments, then reassembled at the receiver

What must an application layer protocol specify?

- Message Semantics (meaning) - Rules for message send & response (how, when) - Types of message exchanged - Message Syntax (fields, structure)

What must an application-level protocol specify? (Check all that apply)

- Message response rules - Message sending rules - Message semantics - Types of messages exchanged -Message fields & structure

What are some tradeoffs for the implementation of RDT in TCP

- More packets on the network (because of ACKs) - leading to congestion issues - Additional overhead - Possible delays due to waiting for acknowledgements

Socket programming with UDP

- No "connection" between client and server - Transmitted data may be lost or received out-of-order - no handshaking before sending data - sender explicitly attaches IP destination address and port# to each packet - Receiver extracts sender's address and port number from received packet.

peer to peer

- No always on server - peers are intermittently connected and might change IP addresses - illegally share files (bitTorrent) Pros: scalable & distributive Cons: difficult to manage & not secure Peer-to-peer is a different model. With P2P there is no central authoritative server. End-user machines will find other end-user machines through advertised IP addresses. They will then use their P2P client software to connect and exchange info. Examples include bit-torrent and other file-sharing services.

Why is there a UDP?

- No connection establishment (Which can add to delay) - Simple: No connection state at sender, receiver - Small header size - No congestion control: UDP can blast away as fast as desired

UDP: summary

- No frills, bare bones transport protocol - Best effort service - Basic error detection - UDP segments may be lost or delivered out of order - Connectionless: + No handshaking between UDP sender and receiver + Each UDP segment handled independently of others - UDP use: + Streaming multimedia apps (loss tolerant, rate sensitive) + DNS

Two generals problem

- cannot guarantee that message will be received - cannot guarantee that received message has no errors

How is data transferred through the network?

- circuit switching : dedicated circuit per call [ telephone net ] - packet-switching : data sent through net in discrete "chunks" on shared media

As discussed in the lectures, what are the primary functions of a packet-switched network.

- Packet construction - Packet transmissioon - Packet interpretation

Four sources of packet delay

- Processing delay: check bit errors, determine whether the packet is valid, and determine output link (where to send data to) - Queuing delay : time waiting at output link for transmission - Transmission delay: R = link bandwidth (bps) L = packet length (in bits) transmission delay = L / R - Propagation delay d = length of physical link (in meters) s = propagation speed in medium (~2.5 x 10^8 m/sec) propagation delay = d/s

Other functions of the network core

- Queuing packets - Route discovery - Traffic/congestion control - Retransmitting lost packets - Determining type of data - messages, service requests/responses, files, audio/video

ICMP allows information to be carried between what types of devices (e.g. router to...)?

- Router to Source Host - Source Host to Destination Host - Destination Host to Source Host - Router to Router

What are some responsibilities of the Application Layer?

- Support network applications - Determine destination IP address

The HTTP request message require an extra \r\n at the end of the header Section because:

- The HTTP header must be separated from the entity body. - That's just the way it is

What are characteristics of FDM?

- The spectrum is divided up into bands of frequency - Multiple users can transmit, provided that they use the right frequency

Web caching

- Typically, cache is installed by ISP (university, company, residential ISP) - Cached objects have "expiration" so that they can be refreshed automatically Why web caching? reduce response time for req, reduce traffic on an institution's access link, enables poor providers to effectively deliver content Conditional GET: don't send object if cache has up-to-date cached version specify date of cached copy in HTTP request : If-modified-since<date>

Three major components in Email

- User Agents : compose, read,edit, send e.g. Gmail, outlook, yahoo - Mail Server • mailbox contains incoming messages for user • message queue of outgoing mail messages (emails have to be kept in the mail server as the user agents might not work. so we need a server to store the messages). - SMTP (Simple Mail Transfer Protocol) • defines message transfer rules & formats between mail servers • Client: sending mail • Server: receiving mail user mailbox

What are the components of e-mail?

- User agent (such as an email client, or webmail) - An email protocol - A mail server

Packet switching disadvantages/ downsides

- When many users want to be active at the same time - Packet switching is fine for data that is not time-critical - Excessive congestion causes: packet delay and lost, "jitter" - packet construction creates additional overhead - protocols needed for reliable data transfer congestion control - bandwidth guarantees are needed for audio/video apps

Packet switching cont.

- all streams share network resources - each packet uses full link bandwidth - resources used as needed better utilization, less waste & we can also have a congestion when demands exceed resources

Client server

- always on - fixed/known IP address - serves many clients simultaneously A client will contact a server to download or upload data. The server is always on and listening for incoming requests. A well-known example is the web. Your internet browser is the client, and the websites you visit are the servers. ex: Google, amazon, myspace

SMTP

- application layer protocol uses TCP as it is more reliable - default port is 25 - "push" protocol command/response interaction - commands: plain text - response: status code and phrase messages must be in 7-bit ASCII

Packet "sniffing"

- broadcast media (shared ethernet, wireless) - promiscuous network interface reads/records all packets (e.g., including passwords!) passing by

Typical home network components

- cable or DSL modem - routerr/firewall/ NAT - etherrnet - wireless access point cabled/wireless devices

TCP service - internet protocols

- connection-oriented: setup required between client and server processes - reliable transport between sending and receiving process -flow control: sender won't overwhelm receiver -congestion control: throttle sender when network overloaded -does not provide: timing, minimum bandwidth guarantees

Twisted pair connectors

- connector: same on both ends of the cable; used with hubs, switches - crossover: one of each; direct connection

ICMP has two classes of messages

- error messages - informational messages Ex of error messages: • Destination unreachable router sends when a datagram cannot be delivered to its final destination • Source quench router sends when it has no more queuing space available. • Time exceeded message is sent in two cases 1. router sends when TTL = 0 2. destination host sends when reassembly timer expires before all fragments arrive • Fragmentation required- router sends when datagram too large for outbound network (if "do-not-fragment" flag is set)

Guided Media: fiber optic cable

- glass fiber carrying light pulses, each pulse represents one bit • high-speed operation:- high-speed point-to-point transmission (e.g., 10's-100's Gbps) • low error rate: - immune to electromagnetic noise and other interference BIGGEST PROBLEM: breakage. when a main fiber optic line goes down, an area will lose the internet/ it'll be very slow

end systems(hosts)

- individual computers that initiate requests or provide services e.g. personal computers, cellphones e.g. server computers

Circuit switching fundamentals

- link bandwidth, switch capacity - dedicated resources, no sharing - circuit-like (guaranteed) performance - call setup required *bandwidth = transmission rate (bps)

network structure

- network edge - network core - physical media

ISP's (internet service provider)

- occupy the lowest tier - called access networks cause they provide access to the internet Communication starts with a local or tier 3 ISP, and may traverse many networks, including Tier 1 providers, before it reaches another local network and its destination.

Circuit switching cont.

- pieces allocated to calls - circuit switching can be wasteful, a call might be set up even when two hosts that are talking have nothing to transfer - resource piece idle if not used by owning call - consumers are charged on a per-minute basis

ISO (International Standards Organization)/ OSI reference model

- presentation layer: Allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions - session layer: synchronization, checkpointing, recovery of data exchange -Internet stack "missing" these layers• these services, if needed, must be implemented in the application layer of the Internet protocol stack

Physical media

- provides the required link between sender & receiver - propagates bits between sender/receiver pairs

packet loss

- queue (buffer) has finite capacity - if packet arrives at a full queue, it is dropped (lost) - lost packet may possibly be retransmitted by the previous node, by the source, or not at all

What device reside in the network core?

- routers - switches

Unguided media: wireless radio

- signal carried in electromagnetic spectrum - no physical wire effects of propagation environment (can cause a high error rate) - reflection - obstruction by objects - interference

TCP

- stop and wait protocol, with poor network utilization - TCP will send a burst of packets and then wait for acknowledgement. Utilization for a single TCP packet is poor, so solution is: pipelining: TCP solves this by sending a number of packets, one right after another, and then waiting for an acknowledgement.

UDP use

- streaming multimedia apps (loss tolerant, rate sensitive) - DNS - SNMP

POP3

- uses "download and delete" mode. - Bob cannot re-read e-mail if he changes client -"Download-and-keep": copies of messages on different clients - POP3 is stateless across sessions

Transport protocols

-Provide logical communication between application processes running on different hosts - Run on end systems

A network protocol may do the following (check all that apply):

-Specify actions taken upon message transmission - Specify actions taken upon message receipt - Specify the whether or not information is sent - Specify the order of messages sent and received - Specify the time between sending information. - Specify the form of messages sent and received

What are some examples of guided media?

-Waveguide cabling (fiber-optic) -Cups with a string connecting them -Twisted pair copper wires -Coaxial cables

Convert the following units. Your answer should be a whole number with no text in the answer field: 6.18 Mbps = _____ Kbps

6,180 Kbps

Suppose there are 62 packets entering a queue at the same time. Each packet is of size 9 MiB. The link transmission rate is 2.1 Gbps. What is the queueing delay of packet number 1 (in milliseconds, rounded to one decimal place, e.g. 0.01234 seconds would be entered as "12.3")

0

The one's complement of 10010110 is

01101001

For the following question, proper hexadecimal format is (0xYYYY) where Y will range in (0-9) or (A-F). Only proper formats will be accepted. Suppose that we send a DNS request with ID #26944. What is the little-endian representation (hexadecimal)? What is the big-endian representation (hexadecimal)? Which representation is required for network communication? (Enter "1" or "2" without quotes)

0x4069 0x6940 2

Suppose that we send a DNS request with ID # 46921. (Note the network order is in big-endian) What is the little-endian representation (hexadecimal)? ________ What is the big-endian representation (hexadecimal)? ________ Which representation is required for network communication? ________

0x49B7, 0xB749, 0xB749

Compute the sum with carry-wraparound (sometimes called the one's complement sum) of the following two numbers. Give answer in 8-bit binary, zero-padded to 8 bits if necessary, with no spaces (e.g. 00101000). Please note this is different than the checksum calculation.NOTE: Canvas will remove any leading zeros from your answer. This will not cause your answer to be marked as incorrect. 00000001 11111111

1

The UDP protocol uses a 16 -bit, ___'s complement of the ___ 's complement sum to compute the checksum

1's 1's

Alice sends message to Bob

1) Alice uses her user agent to compose message and send to [email protected] 2) Alice's user agent sends message to her mail server; message placed in message queue 3) Client side of SMTP opens TCP connection with Bob's mail server 4) SMTP client sends Alice's message over the TCP connection 5) Bob's mail server places the message in Bob's mailbox 6) Bob uses his user agent to read message

Assume a TCP sender is continuously sending 1,034-byte segments. If a TCP receiver advertises a window size of 8,943 bytes, and with a link transmission rate 35 Mbps an end-to-end propagation delay of 23.4 ms, what is the utilization? Assume no errors, no processing or queueing delay, and ACKs transmit instantly. Also assume the sender will not transmit a non-full segment. Give answer in percentages, rounded to one decimal place, without units (e.g. for an answer of 10.43% you would enter "10.4" without the quotes).

4

Transport layer protocols

1. A message (data) is passed from the Application layer to the Transport layer. 2. The Transport layer breaks the message up into data blocks (if necessary). 3. The Transport layer appends a header that contains the source and destination port numbers that correspond to the source and destination processes. 4. These blocks/ports are encapsulated into segments. The segments and their IP addresses are then passed to the Network layer. 5. This process is then reversed at the destination host, where the destination port is used to find the correct process. Upon arrival, the segments must be demultiplexed, or separated, and then delivered to the correct process.

Place the steps in the correct order for a complete e-mail communication.

1. Alice uses her user agent to compose message and sent to Bob's email address. 2. Alice's user agent sends message to her mail server; message placed in message queue. 3. Client side of SMTP opens TCP connection with Bob's mail server. 4. SMTP client sends Alice's message over the TCP connection. 5. Bob's mail server places the message in Bob's mailbox. 6. Bob uses his user agent to read the message.

How long does it take to send a file of 80 KiB from host A to host B over a circuit-switched network? - The link's transmission rate = 1.5 Mbps - Each link uses TDM with 24 slots/sec - 500 ms to establish end-to-end circuit

1. Change KiB to Kb 80 Kib = (80 x 2^10 bytes)* 8 bits per byte = 640 Kib = 655.36 Kb 2. Bandwidth of the circuit 1.5 Mbps/ 24 = 62.5 Kbps 3. Time to send 655.36 Kb/62.5 Kbps + 0.5 s = ~ 11 s

Put the steps in the most correct order for TCP Connection initialization.

1. Client sends segment with SYN set to 1 2. Server sends segment with SYN set to 1 and ACK set to the Client's SeqNum+1 3. Client sends segment with SYN set to 0 and ACK set to the Server's SeqNum+1

We want to know how long it would take to send five 1480-byte packets. Assume the pipeline will accommodate 6000 bytes from sender to receiver at any given time. 1. How many packets will fit in the pipeline? 2. ​​​​​​How many pipelines will it take to deliver the five packets? 3. How long will it take to send the 5 packets? ( ______ ms.) 4. What is the utilization with pipelining? ( ______ % ) 5. What happens if the sender sends information faster than the receiver can process?

1. Floor(6000 / 1480) = 4 packets will fit in the pipeline. We can send the 5th packet when we receive the ACK for the first packet. See diagram below. 2. 2 3. From #2 above, one pipeline will take 23.2 ms. It will take 2 pipelines to send all the data. So the time is 23.2ms * 2 = 46.4 ms (much better than the previous 116ms) 4. Answer: Time spent transmitting = 5*(1.184 + 0.016) = 6ms Total time until finished = 46.4 ms (from above) Utilization = (6 ms / 46.4 ms) * 100 = approx. 12.9%, much better than before! 'NOTE: The reason this looks different from lecture is that, in the lecture slides, there is a continuous stream of packets (infinite packets). In this problem there are a limited number of packets. 5. Packets would be dropped. With a receive window implementation, the receive window size will shrink over time, eventually limiting the sender's output rate to that which can be processed by the receiver (flow control).

DNS services

1. Hostname to IP address translation 2. Web server aliasing- Canonical, alias names 3. Mail server aliasing 4. Load distribution

With a stop-and-wait implementation (no pipelining) subject to the following conditions: - R = 10Mbps - Network end-to-end time (after initial transmission) = 11 ms - ACK packet L = 20 bytes 1. What is the transmission time for one packet 1480-byte packet? (_______ ms) 2. What is the ACK transmission time? (_____ ms) 3. What is the end-to-end time for one packet? (____ ms) 4. How long would it take to send five 1480-byte packets? (_____ ms) 5. What is the utilization? (______ %) 6. How does the receiver handle multiple incoming packets?

1. Initial Transmit = L/R = 1480 * 8 / 10,000,000 = 1.184 ms. 2. ACK transmit = 20 * 8 / 10,000,000 = 0.016 ms 3. First packet total = 1.184 + 11 + 0.016 + 11 = 23.2ms (Just the first packet) 4. 5 * 23.2ms = 116 ms 5. Time spent transmitting = 1.184 + 0.016 = 1.2msTotal time until finished = 23.2 ms (from above)(1.2ms / 23.2 ms) x 100 = approx. 5.2 % 6. An input buffer is filled as data comes in, and the application layer drains the buffer as it needs the data contained therein.

HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB, and HostB immediately acknowledges every packet. Assume that the timeout is the same for all packets. HostB's "window size" is 2000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #140. HostA now sends packets of the same application data stream in order: P (50 Bytes), Q (60 Bytes), and R (100 Bytes). 1. Suppose that packet P is lost, but packets Q and R are received. What is the acknowledgement number in the ACK for packets Q and R?

1. Q: 141, R: 141

A typical HTTP session:

1. The client initiates a TCP connection (creates socket) to server, port 80. 2. The server accepts the TCP connection from the client. 3. HTTP messages (application-layer protocol messages) are exchanged between the browser (HTTP client) and the Web server (HTTP server). 4. The TCP connection may then be closed by the client or server.

Process for DNS

1. client queries root server to find .com DNS server 2, client queries .com DNS server to get amazon.com DNS server 3. client queries amazon.com DNS server to get IP address for www.amazon.com

protocols define

1. format and order of messages sent and received among network entities 2. actions taken on message transmission and receipt

Compute the sum with carry-wraparound (sometimes called the one's complement sum) of the following two numbers. Give answer in 8-bit binary, zero-padded to 8 bits if necessary, with no spaces (e.g. 00101000). Please note this is different than the checksum calculation.NOTE: Canvas will remove any leading zeros from your answer. This will not cause your answer to be marked as incorrect. 10000010 10001111

10,010

The one's complement of 01101001 is

10010110

Compute the sum with carry-wraparound (sometimes called the one's complement sum) of the following two numbers. Give answer in 8-bit binary, zero-padded to 8 bits if necessary, with no spaces (e.g. 00101000). Please note this is different than the checksum calculation.NOTE: Canvas will remove any leading zeros from your answer. This will not cause your answer to be marked as incorrect. 10010110 10010000

100111

How long does it take to send a 10 MiB file from Host A to Host B over a circuit-switched network, assuming: Total link transmission rate = 91.7 Gbps. Network is TDM, with 19 permitted users, each with an equal time slot size. A link connection requires a setup time of 87.1 ms. Your answer should be in miliseconds (ms) with one decimal place, and without the unit (e.g. "140.6" without the quotes)

104.5

Suppose there are 84 packets entering a queue at the same time. Each packet is of size 9 MiB. The link transmission rate is 2.1 Gbps. What is the queueing delay of packet number 4 (in milliseconds, rounded to one decimal place, e.g. 0.01234 seconds would be entered as "12.3")

107.9

How long does it take to send a 19 MiB file from Host A to Host B over a circuit-switched network, assuming: Total link transmission rate = 66.4 Gbps. Network is FDM, with 19 permitted users, each with an equal bandwidth share. A link connection requires a setup time of 62.5 ms. Your answer should be in miliseconds (ms) with one decimal place, and without the unit (e.g. "140.6" without the quotes)

108.1

Suppose there are 4 routers in sequence between Host A and Host B, all of which use store-and-forward routing. What is the total end-to-end delay for a packet originating from Host A with destination Host B, under the following conditions. Each of the link transmission rates are 7.9 Mbps The total distance from Host A to Host B along its path of transmisison is 164.2 km The speed of propagation through the transmission medium is is 2.5 x 108 m/s The packet size is 2 KiB Remember that you must also uplink from Host A to the first router. Give answer in milliseconds, rounded to 1 decimal place, without units (e.g. for 0.12345 seconds you would enter "123.5" without the quotes).

11

How long does it take to send a 11 MiB file from Host A to Host B over a circuit-switched network, assuming: Total link transmission rate = 34.1 Gbps. Network is TDM, with 9 permitted users, each with an equal time slot size. A link connection requires a setup time of 89 ms. Your answer should be in miliseconds (ms) with one decimal place, and without the unit (e.g. "140.6" without the quotes)

113.4

Convert the following units. Your answer should be a whole number with no text in the answer field: 146.38 Kbps = _____ bits per second

146.380

Convert the following units. Your answer should be a whole number with no text in the answer field: 149.86 Kbps = _____ bits per second

149860

Convert the following units. Your answer should be a whole number with no text in the answer field: 2 MiB = _____ bits

16,777,216

Convert the following units. Your answer should be a whole number with no text in the answer field: 257 B = _____ bits

2056

A client in a network with a proxy server requests a 4 MiB file from an internet server, fakeservername.com. The network's proxy server has a 2.01 Mbps connection to fakeservername.com. The average response time between the network's proxy server and the internet origin server (including RTT) is 3.8 seconds for a small "header-only" HTTP request/response. The file requested by the client is currently in the proxy server cache, but the proxy server relays the client's request to the internet server with "if-modified since". Assume that transmissions between the proxy and the origin servers are stream (not packets) at full bandwidth, with negligible propagation delay. How much time is saved if the file has not been modified? (Give answer in seconds, without units, rounded to two decimal places, so for an answer of 1.4233 seconds you would enter "1.42" without the quotes.)

16.69

Convert the following units. Your answer should be a whole number with no text in the answer field: 20 KiB = _____ bits

163,840

How many unique network interface hardware addresses are possible (ignoring reserved addresses

16^12 (281,474,976,710,656)

Suppose there are 5 routers in sequence between Host A and Host B, all of which use store-and-forward routing. What is the total end-to-end delay for a packet originating from Host A with destination Host B, under the following conditions. Each of the link transmission rates are 5.8 Mbps The total distance from Host A to Host B along its path of transmisison is 152.6 km The speed of propagation through the transmission medium is is 2.5 x 108 m/s The packet size is 2 KiB Remember that you must also uplink from Host A to the first router. Give answer in milliseconds, rounded to 1 decimal place, without units (e.g. for 0.12345 seconds you would enter "123.5" without the quotes).

17.6

Convert the following units. Your answer should be a whole number with no text in the answer field: 24 B = _____ bits

192

The reserved port for FTP data transfer is port __

20

A client's browser sends an HTTP request to a website. The website responds with a handshake and sets up a TCP connection. The connection setup takes 2 sec, including the RTT. The browser then sends the request for the website's index file. The index file references 9 additional images, which are to be requested/downloaded by the client's browser. How many requests (including the initial request) must be sent by the browser... 1. With non-persistent HTTP? 2. With persistent HTTP?

20 11

The minimum size of a TCP header is ____ bytes. The maximum size of a TCP header is ____ bytes.

20 bytes minimum, maximum is 60 bytes

HTTP Response Codes

200 : OK 301 : Moved permanently : requested object moved 400 : Bad request : req not understood by server 404 : Not found 505 : HTTP version not supported

Given the attached image, and:h Host A converts analog to digital at a = 49 Kbps Link transmission rate R = 5 Mbps Host A groups data into packets of length L = 111 bytes Distance to travel d = 755.5 km Propagation speed s = 2.5 x 108 m/s Host A sends each packet to Host B as soon as it gathers a whole packet. Host B converts back from digital to analog as soon as it receives a whole packet. How much time elapses from when the first bit starts to be created until the conversion back to analog begins? Give answer in milliseconds (ms) to two decimal places, normal rounding, without units (e.g. 1.5623 ms would be entered as "1.56" without the quotes)

21.32

The reserved port for SSH is port __

22

A client in a network with a proxy server requests a 6 MiB file from an internet server, fakeservername.com. The network's proxy server has a 2.16 Mbps connection to fakeservername.com. The average response time between the network's proxy server and the internet origin server (including RTT) is 4.9 seconds for a small "header-only" HTTP request/response. The file requested by the client is currently in the proxy server cache, but the proxy server relays the client's request to the internet server with "if-modified since". Assume that transmissions between the proxy and the origin servers are stream (not packets) at full bandwidth, with negligible propagation delay. How much time is saved if the file has not been modified? (Give answer in seconds, without units, rounded to two decimal places, so for an answer of 1.4233 seconds you would enter "1.42" without the quotes.)

23.3

How many bytes of data are in the "application data" section of a TCP segment with a total length of 2400 bytes and a header length of 8?

2380 2368

The dotted-decimal form of 32-bit internet addresses is composed of 4 decimal numbers, separated by periods. What is range of possible values for each of the four decimal numbers? 0 to _____

255

Convert the following units. Your answer should be a whole number with no text in the answer field: 26.42 Mbps = _____ Kbps

26,420

Given the attached image, and:h Host A converts analog to digital at a = 45 Kbps Link transmission rate R = 3.1 Mbps Host A groups data into packets of length L = 124 bytes Distance to travel d = 957.9 km Propagation speed s = 2.5 x 108 m/s Host A sends each packet to Host B as soon as it gathers a whole packet. Host B converts back from digital to analog as soon as it receives a whole packet. How much time elapses from when the first bit starts to be created until the conversion back to analog begins? Give answer in milliseconds (ms) to two decimal places, normal rounding, without units (e.g. 1.5623 ms would be entered as "1.56" without the quotes)

26.2 ms

Convert the following units. Your answer should be a whole number with no text in the answer field: 26 MiB = _____ bytes

27,262,976

Given the attached image, and:h Host A converts analog to digital at a = 40 Kbps Link transmission rate R = 2.2 Mbps Host A groups data into packets of length L = 115 bytes Distance to travel d = 905.9 km Propagation speed s = 2.5 x 108 m/s Host A sends each packet to Host B as soon as it gathers a whole packet. Host B converts back from digital to analog as soon as it receives a whole packet. How much time elapses from when the first bit starts to be created until the conversion back to analog begins? Give answer in milliseconds (ms) to two decimal places, normal rounding, without units (e.g. 1.5623 ms would be entered as "1.56" without the quotes)

27.04

Convert the following units. Your answer should be a whole number with no text in the answer field: 3 MiB = _____ bytes

3,145,728

If a TCP sender sends packets with sequence numbers 100, 200, and 300, and has several more packets (all of 100 bytes) waiting in the sending buffer, and two ACKs are received back, with ACK numbers 200 and 300, what is the next step for the sender?

300

Convert the following units. Your answer should be a whole number with no text in the answer field: 33.35 Mbps = _____ bits per second

33,350,000 bits

The sequence number of a TCP segment is 768. This segment has a total length of 1400 bytes and a header length of 10 (10 32-bit words). The next segment has the same total length and header length. What is the sequence number of the segment immediately following these two? Assume that the first segment from earlier is received with errors. The second segment is received ok. What is the ACK number for the second segment from earlier?

3488 768

The sequence number of a TCP segment is 768. This segment has a payload data size of 1380 bytes. The next segment also has a payload of 1380 bytes. What is the sequence number of the segment immediately following these two? Assume both segments from earlier are sent and received with no errors. What is the ACK number sent back to the sender in response to the second segment?

3528 3528

Convert the following units. Your answer should be a whole number with no text in the answer field: 47 B = _____ bits

376

If a TCP sender sends packets with sequence numbers 100, 200, and 300, and has several more packets (all of 100 bytes) waiting in the sending buffer, and only one ACK is received, with ACK number 400, the sender should send a packet with sequence number ________,

400

Suppose there are 3 routers in sequence between Host A and Host B, all of which use store-and-forward routing. What is the total end-to-end delay for a packet originating from Host A with destination Host B, under the following conditions. Each of the link transmission rates are 2.1 Mbps The total distance from Host A to Host B along its path of transmisison is 130.4 km The speed of propagation through the transmission medium is is 2.5 x 108 m/s The packet size is 3 KiB Remember that you must also uplink from Host A to the first router. Give answer in milliseconds, rounded to 1 decimal place, without units (e.g. for 0.12345 seconds you would enter "123.5" without the quotes).

47.3

A client's browser sends an HTTP request to a website. The website responds with a handshake and sets up a TCP connection. The connection setup takes 5.6 ms, including the RTT. The browser then sends the request for the website's index file. The index file references 10 additional images, which are to be requested/downloaded by the client's browser. Assuming all other conditions are equal, how much longer would non-persistent HTTP take than persistent HTTP? (Give answer in milliseconds, without units, rounded to one decimal place. For an answer of 0.01005 seconds, you would enter "10.1" without the quotes.)

56

What is the total utilization of a circuit-switched network, accommodating five users with equal bandwidth share, and the following properties: Two users each using 92% of their bandwidth share Two users each using 43% of their bandwidth share One user using 13% of their bandwidth share Give answer in percent, with one decimal place (normal rounding) and no percentage sign (e.g. for 49.15% you would enter "49.2" without the quotes).

56.6

A client's browser sends an HTTP request to a website. The website responds with a handshake and sets up a TCP connection. The connection setup takes 2.6 ms, including the RTT. The browser then sends the request for the website's index file. The index file references 22 additional images, which are to be requested/downloaded by the client's browser. Assuming all other conditions are equal, how much longer would non-persistent HTTP take than persistent HTTP? (Give answer in milliseconds, without units, rounded to one decimal place. For an answer of 0.01005 seconds, you would enter "10.1" without the quotes.)

57.2

How long does it take to send a 7 MiB file from Host A to Host B over a circuit-switched network, assuming: Total link transmission rate = 81.8 Gbps. Network is FDM, with 12 permitted users, each with an equal bandwidth share. A link connection requires a setup time of 50.2 ms. Your answer should be in miliseconds (ms) with one decimal place, and without the unit (e.g. "140.6" without the quotes)

58.8

A client's browser sends an HTTP request to a website. The website responds with a handshake and sets up a TCP connection. The connection setup takes 2 sec, including the RTT. The browser then sends the request for the website's index file. The index file references 2additional images, which are to be requested/downloaded by the client's browser. How many requests (including the initial request) must be sent by the browser... With non-persistent HTTP? __ requests With persistent HTTP? __ requests

6 4

What is the total utilization of a circuit-switched network, accommodating five users with equal bandwidth share, and the following properties: Three users each using 97% of their bandwidth share Two users each using 8% of their bandwidth share Give answer in percent, with one decimal place (normal rounding) and no percentage sign (e.g. for 49.15% you would enter "49.2" without the quotes).

61.4

What is the total utilization of a circuit-switched network, accommodating five users with equal bandwidth share, and the following properties: Three users each using 98% of their bandwidth share Two users each using 7% of their bandwidth share Give answer in percent, with one decimal place (normal rounding) and no percentage sign (e.g. for 49.15% you would enter "49.2" without the quotes).

61.6

Theoretically, the maximum number of bytes that can be carried in the "application data" section of a UDP segment is

65,527

Given a link with a maximum transmission rate of 87.9 Mbps. Only two computers, X and Y, wish to transmit starting at time t = 0 seconds. Computer X sends fileX (19 MiB) and computer Y sends fileY (340 KiB), both starting at time t = 0. Statistical multiplexing is used, with details as follows: -Packet Payload Size = 1000 Bytes -Packet Header Size = 24 Bytes (overhead) -Ignore Processing and Queueing delays -Assume partial packets (packets consisting of less than 1000 Bytes of data) are padded so that they are the same size as full packets. -Assume continuous alternating-packet transmission. -Computer X gets the transmission medium first. At what time (t = ?) would FileY finish transmitting? Give answer in milliseconds, without units, and round to one decimal places (e.g. for an answer of 0.013777 seconds you would enter "13.8" without the quotes)

65.1

How long does it take to send a 8 MiB file from Host A to Host B over a circuit-switched network, assuming: Total link transmission rate = 86.7 Gbps. Network is FDM, with 9 permitted users, each with an equal bandwidth share. A link connection requires a setup time of 60.9 ms. Your answer should be in miliseconds (ms) with one decimal place, and without the unit (e.g. "140.6" without the quotes)

67.9

Convert the following units. Your answer should be a whole number with no text in the answer field: 87 B = _____ bits

696

Convert the following units. Your answer should be a whole number with no text in the answer field: 903 B = _____ bits

7224

What is the minimum UDP header size?

8 bytes

The reserved port for HTTP is port __

80

Convert the following units. Your answer should be a whole number with no text in the answer field: 89.28 Kbps = _____ bits per second

89,280

HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #1,448. HostA now sends segments of the same application data stream in order: P: 147 bytes Q: 197 bytes R: 313 bytes Suppose that packet P is lost, but packets Q and R are received. What is the acknowledgement number in the ACK for packet R.

= 1,448 + 1 = 1,449

FTP opens an extra connection for a file transfer because:

A control connection can be dedicated and maintained.

HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #3,408. HostA now sends segments of the same application data stream in order: P: 307 bytes Q: 287 bytes R: 265 bytes Suppose that segments P, Q, and R are received, but the acknowledgements for segments P and Q are lost. If there are more segments waiting to be transmitted, what is the sequence number of the next segment transmitted after the ACK for segment R is received?

ACK for next segment transmitted after ACK for R is received: = 3,408 + 307 + 287 + 265 + 1 = 4,268

ACK

ACK's are cumulative. The ACK # is always the next expected byte number. This implies that all previous bytes have been accounted for. If ACK received: • Check to see if ACK includes previously unACK'ed segments - update what is known to be ACK'ed - restart timer if there are outstanding segments

A network that allows a host to connect to the internet is called an __________ network.

Access

A simple checksum can detect all 2-bit errors.

False

Which of the following is NOT a characteristic of "packet sniffing"?

An attacker can "catch-and-kill" the packet, preventing the destination from receiving it

In the Internet protocol stack, the _________- is responsible for assembling user data to be sent.

Application Layer

In the Internet protocol stack, the ___________ is responsible for finding the destination IP address.

Application Layer

Why does the internet require a layered model?

Dealing with complex systems, explicit structure, and modularization. The layered model allows us to have plug in modules that are designed to solve specific problems at different system levels - Modularization eases maintenance and updating of complex system

How can sender know that an error has occurred?

Bit flipped Missing packet Out-of sequence

Error detection in UDP

Can tell if the received data was corrupted during the transfer process. UDP includes length of bytes and segment and header, and ones complement checksum of the entire segment contents

Server X is running Diablo II services on port #4000. Client A is running an application that uses port #450 to request an Diablo IITCP connection to Server X. Client B is running an application that uses port #455 to request an Diablo II TCP connection to Server X. IP addresses: Server X: 152.111.20.36 Client A: 113.13.131.10 Client B: 114.192.111.23 The connection created for Client B is identified by the sockets at the endpoints as follows:

Client b: - IP address: 152.111.20.36 - Port num: 4000 On server X: - IP address: 114.192.111.23 - Port num: 455

In a _______ acknowledgement scheme, a received ACK indicates all segments prior to the ACK'd segment were received.

Cumulative

Which of the following states does the FTP protocol maintain?

Current Directory Earlier Authentication Limit on Concurrent Connections

If a botnet or another large group of hosts is used to execute this attack it is called a _________ attack

DDos

An attack which attempts to make network resources unavailable to legitimate users by flooding a system with illegitimate traffic is called a _________________ attack.

Denial of Service

For de-multiplexing, how is a UDP socket identified?

Destination IP Address Destination Port Number

For de-multiplexing, how is a TCP socket identified?

Destination IP Address Source IP Address Destination Port Number Source Port Number

DNS

Each name consists of a sequence of alphanumeric components separated by periods e.g. www.oregonstate.edu Names are hierarchical, with most significant component on the right -Top-Level Domain (TLD) -Second from right is the domain name within the TLD - Approved by a global authority - uses UDP - DNS domains are logical concepts and need not correspond to physical location of organizations (E.G., chinatoday.com is hosted partly in Beijing, partly in San Francisco)

A connection-oriented protocol in a packet-switched network guarantees a dedicated line - similar to how a circuit-switched network works.

False

What is an application that does NOT have stringent bandwidth requirements?

Email

When a packet is passed down to the next lower layer, it is _____________ into the lower-layer packet.

Encapsulated

Which of the following are application-layer protocols? File Transfer Protocol (FTP) Domain Name Service (DNS) Post Office Protocol v3 (POP3) Internet Protocol (IP) Transmission Control Protocol (TCP) Telnet Secure Shell (SSH) User Datagram Protocol (UDP)

FTP, DNS, POP3, Telnet, Secure shell (SSH)

Which of the following are application-layer protocols?

FTP, DNS, Telnet, Post office protocol v3 (POP3), Secure shell (SSH)

Sending email requires a "pull" protocol to send messages to the recipient's mail service on demand. Receiving mail requires a "push" protocol for the mail service provider to push email into the recipient's inbox.

False, it's the opposite

What is the purpose of fast retransmit? How is it implemented?

Fast retransmit was originated to streamline the process of retransmissions, to increase utilization. If a TCP sender sees three duplicate ACKs (so four ACKs total) for the same segment, it assumes the segment was dropped, and retransmits, even if the countdown timer hasn't expired.

What is an application that does NOT have stringent timing requirements?

File transfer

What transport-layer services are provided by the base TCP protocol? (Check all that apply) Flow control Message security Jitter minimization Connection-oriented service Minimum bandwidth Reliable data transmission Congestion control

Flow control Connection-oriented service Reliable data transmission Congestion control

Fiber optic cable uses wave-length division multiplexing

Frequency division multiplexing can be applied to optical transmission Informally known as color division multiplexing. Receiver separates frequencies using a prism

The ______ application-layer protocol utilizes the TCPtransport-layer protocol.

HTTP

What are some application-layer protocols, and what are they used for?

HTTP Used often for communication of hosted information on the internet (web pages) FTP Used often for transfer of files without a web interface (uploading, etc) SMTP/IMAP/POP3 - Email protocols DNS - Domain name resolution (from www.google.com to 173.194.33.176, etc) SCCP - used in VoIP etc..

Local Area Network (LAN)

Home network can be viewed as LAN but this term usually refers to institutional networks with multiple users , web servers, mail servers

Consider the following: http://www.oregon.gov/SiteCollectionImages/branding/portal/bigfoot.pn

Host name : www.oregon.gov path name: /SiteCollectionImages/branding/portal/bigfoot.png the url is : http://www.oregon.gov/SiteCollectionImages/branding/portal/bigfoot.png The TLD is: GOV

Consider the following: http://www.google.com/images/nav_logo195.png

Host name: www.google.com path name: /images/nav_logo195.png the url is: http://www.google.com/images/nav_logo195.png the tld is : COM

The network layer manages communications from __________.

Host to host

IP addresses

IANA assigns IP network addresses to service providers to be managed hierarchically All applications use IP addresses through the TCP/IP protocol software Domain Name System (DNS) provides translation between symbolic names and IP addresses

How are OSI and ISO related to each other?

ISO is a multinational dedicated to the agreement of standards worldwide and the OSI is the model which purpose is to show how to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software."

If a TCP sender sends packets with sequence numbers 100, 200, and 300, and has several more packets (all of 100 bytes) waiting in the sending buffer, and no ACKs are received back, what is the next step for a TCP sender, the sender should send a packet with sequence number ________,?

If countdown timer expires, re-send packet with sequence number 100.

What about RDT is indicated by the two-generals problem?

If there is any possibility of error in the communications channel, it is impossible to guarantee 100% reliable data transfer.

Match the event with the TCP receiver action: Arrival of in-order segment with expected sequence number. One other in-order segment waiting for ACK transmission.

Immediately send single cumulative ACK, ACKing both in-order segments.

Fill in the blanks

In an internet name, what is the highest-priority component? The Top-Level Domain ex: .com, .org, .edu The second-highest priority component? The domain name. ex: oregonstate What are subsequently prioritized components used for? internal host names ex: engr.oregonstate.edu

hybrid

In this model, a central server will exchange connection info with its clients, and then the clients make contact directly with each other. Examples include Skype video conferencing.

Access networks are managed by ____

Internet Service Providers (ISP) Connection to ISP edge routers via telephone lines, cable, cooper coaxial, fiber Wireless (stationary and mobile)

Connection-oriented services TCP - transmission control protocol

Internet's connection-oriented service handshake: prepare for transfer reliable, in-order, byte-stream data transfer flow control: sender won't overwhelm receiver congestion control: senders "slow down sending rate" when network is congested

Connectionless service UDP Service - User Data Protocol

Internet's connectionless service - NO handshake - Unreliable data transfer (fire and forget) - (best effort) data transfer - If a packet is lost, it's lost - No flow control - No congestion control Applications that use UDP must be able to handle missing data. In this case, it's like video streaming services

Traceroute

List of all routers on the computed path from A to B is called the route from A to B traceroute uses UDP with TTL field set and sends to a very unlikely port Finds route via expanding ring search: • when ICMP message arrives, source keeps copy of message • UDP segment eventually arrives at destination host • destination returns ICMP "port unreachable" message (3, 3)

What devices reside on the network edge?Laptops Tablets Printers Smart TVs Desktop Computers Routers Switches

Laptops Tablets Printers Smart TVs Desktop Computers

Please place the following in the order of the OSI layering model.

Layer 1 : Physical layer Layer 2 : Link/Data-link Layer 3: network layer layer 4: transport layer layer 5 : session layer layer 6: presentation layer layer 7: application layer

What are the seven layers in the Open Systems Interconnection (OSI)?

Layer 1 : Physical layer Layer 2 : Link/Data-link Layer 3: network layer layer 4: transport layer layer 5 : session layer layer 6: presentation layer layer 7: application layer

Internet protocol stack

Layer 1: Physical Layer carries actual signals between devices through the physical media ex: cable, wireless, Layer 2: Link layer data transfer between neighboring network elements (node to node transfer) ex: PPP, Ethernet Layer 3: Network layer routing of datagrams from source to destination through the core of the internet ex: IP, routing protocols Layer 4: Transport layer process-process data transfer ex: TCP (reliable data stream), UDP (fast but less reliable) Layer 5: Application layer supporting network applications ex: FTP (File transfer protocol), SMTP (simple mail transfer protocol), HTTP

Modems connect end systems to edge routers via access network media

Legacy, cable, and wireless

What is the minimum necessary information for identifying a process on a remote host?

Local host IP address & Port Number plus Remote host IP address & Port Number

Multimedia in email

MIME allows SMTP to handle foreign characters and images, additional lines in message header declare MIME type

Multiplexing with physical media means

Merging multiple communication streams onto the same medium

ICMP message format

Message format depends on type • Type 8-bit [0 .. 40] (41 .. 255 reserved) • Code 8-bit (sub-type) Checksum • Same as UDP Other information (32-bit units) •Router addresses, etc. Original IP Header + first 8 bytes of data • Original IP header is at least 20 bytes. • Datagram data is used by host to match message to appropriate process.

Persistent HTTP

Multiple objects can be sent over single TCP connection between client and server. - server leaves connection open after sending response - subsequent HTTP messages between same client/server sent over open connection - client sends requests as soon as it encounters a referenced object - as little as one RTT for all the referenced objects

UDP, in order delivery? full duplex service? in order delivery? pipelining? Flow Control? (Yes / No) Congestion Control? (Yes / No) Bandwidth Guarantee? (Yes / No) Reliable Delivery(mostly)? (Yes / No) Jitter Threshold? (Yes / No)

No - Packets may be delivered out of order No - One way service No - Packets may be delivered out of order No pipeline, BUT it is fire and forget (so you can transmit all you want) No - Sender may overwhelm receiver No - Ignores possibility of congestion in the internet. No - no bandwidth guarantees. No - "Fire and Forget" service ("Send it, and, FORGET IT!") No - no jitter threshold.

What transport-layer services are provided by the base UDP protocol? (Check all that apply) Jitter minimization Message security None of these services are provided by UDP Connection-oriented service Congestion control Flow control Minimum bandwidth

None of these services are provided by UDP

What transport-layer services are provided by the base UDP protocol? (Check all that apply) Message security Minimum bandwidth Connection-oriented service Jitter minimization Congestion control None of these services are provided by UDP Flow control

None of these services are provided by UDP

Web page consists of a base HTML-file which includes several referenced objects

Object can be HTML file, JPEG image, etc

Server X is running enigma services on port #2100. Client A is running an application that uses port #437 to request an enigma TCP connection to server X. Client B is running an application that uses port #1296 to request an enigma TCP connection to server X. Use this information to answer the few questions below IP addresses: Server X: 201.64.107.12 Client A: 128.193.51.213 Client B: 128.193.35.127 On Client A: Source IP address and port .On Server X: Destination IP address and port .On Server X: Source IP address and port . 2. Is it OK for Client B to start a second application (running at the same time as the first application) that uses port #213 to request an enigma TCP connection to server X? (True/False) 3. Is it OK for Client A to start a third application (running at the same time as the first and second applications) that uses port #213 to request an enigma TCP connection to server X? (True/False)

On Client A: - Destination IP address and port: 201.64.107.12, 2100 Source IP address and port: - 128.193.51.213, 437 On Server X: Destination IP address and port: 128.193.51.213, 437 Source IP address and port: 201.64.107.12, 2100 2) True 3) False

Server X is running Diablo II services on port #4000. Client A is running an application that uses port #450 to request an Diablo II TCP connection to Server X. Client B is running an application that uses port #455 to request an Diablo II TCP connection to Server X. IP addresses: Server X: 152.111.20.36 Client A: 113.13.131.10 Client B: 114.192.111.23 Client B starts a second application (running at the same time as the first application) that uses the next incremental port number to request an Diablo II TCP connection to Server X. The connection created for Client B is identified by the sockets at the endpoints as follows:

On client b: ip address: 152.111.20.36 port number: 4000 On server X: ip address: 114.192.111.23 port number: 456 (increment by 1)

Server X is running XBox Live services on port #3072. Client A is running an application that uses port #1796 to request an XBox Live TCP connection to Server X. Client B is running an application that uses port #2076 to request an XBox Live TCP connection to Server X. IP addresses: Server X: 201.164.10.123 Client A: 128.193.11.113 Client B: 128.193.45.227 Client B starts a second application (running at the same time as the first application) that uses the next incremental port number to request an XBox Live TCP connection to Server X. The connection created for Client B is identified by the sockets at the endpoints as follows:

On client b: ip address: 201.164.10.123 port number: 3072 On server X: ip address: 128.193.45.227 port number: 2077 (increment by 1)

Connection-oriented demultiplexing

One-to-one relationship between the two end-systems. Incoming segments are directed to just one socket based on these values: source iP address, source port number, destination ip address, destination port number - Server host may support many simultaneous TCP sockets. - Web servers have different sockets for each connecting client. > non-persistent HTTP will have different socket for each request

What are characteristics of TDM?

Only one user may transmit at a time

What are some common usages of ICMP?

PING requests use ICMP messages with echo requested. Traceroute (tracert) uses a series of ICMP messages, each with an incrementing TTL, to trace the path from source to destination. Destination Network Unreachable is extremely common if your internet goes down somewhere. Destination Port Unreachable is common if a web server goes down. Internet Core Routing Algorithms use ICMP to establish paths and active router listings.

What is NOT a characteristic of client-server architecture? -The client initiates communication with a server by sending a request. -All data flows through the server. -A server is always on and waiting for requests. -Peers can connect to each other once initial server contact is made.

Peers can connect to each other once initial server contact is made.

If an HTTP server can send 14 objects over a single TCP connection, this is an example of _______ HTTP.

Persistent

We call a program that is running on a host a _______________

Process

Sockets and connections

Process sends/receives messages to/from its socket. A connection is a socket pair (4-tuple consisting of the client IP address, client port number, server IP address and server port number) that identifies two endpoints.

The transport layer manages communications from __________.

Process to process

Time spent in transit between nodes in a network is called ___________________.

Propagation Delay

What is an application that does NOT have stringent security requirements?

Public records

Application layer protocols

Public-domain protocols: defined in RFCso allow for interoperability e.g., HTTP, SMTP, etc. Proprietary protocols: defined by the application e.g., Skypeo e.g., the app you will create for Project #1

The IMAP e-mail protocol is called a ___protocol.

Pull

The SMTP e-mail protocol is called a ____ protocol.

Push

Time spent waiting for the transmission medium to become available is called ____________.

Queueing Delay

What are some examples of unguided media?

Radar Broadcast wireless Bat sonar Human speech

Throughput

Rate(bits/sec) at which bits are actually being transferred between sender/receiver - instantaneous: rate at given point in time - average: rate over longer period of time

TCP Fast transmit

Receipt of duplicate ACKs indicate loss of segments - Sender usually pipelines segments - If segment is lost, there will likely be many duplicate ACKs. fast retransmit: - resend segment before timer expires - better performance

What are the key points of a Selective Repeat retransmission scheme?

Selective repeat retransmission will keep a countdown timer for each un-ACK'd segment. When the protocol calls for a retransmission, it will only re-transmit un-ACK'd segments individually, rather than a bulk dump of all un-ACK'd segments.

TCP acknowledgement numbers

Receiver acknowledges all correct segments received. - Error segments are not acknowledged at all "acknowledgement number" field contains the number of the next byte expected

The minimum necessary information for identifying a process on a remote host would be (check all that apply):

Remote host IP Remote port number

What is the minimum necessary information for identifying a process on a remote host?

Remote host IP address & Port Number

What devices reside in the network core?

Routers Switches

Two key functions of packet-switching

Routing: determines source-destination route taken by packets Forwarding: move packets from router's input to appropriate router output

push/pull protocol

SMTP is a Push protocol IMAP is a Pull protocol POP3 is a Pull protocol.

TCP sequence numbers

Segments are sent as a stream of bytes: - Not separated into records, data types, etc. - Protocol keeps count of data bytes sent + For each segment, protocol puts byte stream number of first byte in segment's data into "sequence number" field Sender keeps a copy of each segment until acknowledged by receiver (for possible retransmission) Sender's segment also has "acknowledgement number" - TCP is full-duplex. Data can flow in both directions simultaneously - Typical (nothing to ACK) segment has a bogus number in the "acknowledgement number" field

sender protocol and receiver protocol

Sender protocol: - accepts messages from application socket - breaks messages into data blocks - encapsulates blocks/ports into segments - passes segments/addresses to network layer Receiver protocol: - accepts segments from network layer - re-assembles data blocks into messages - passes messages to sockets at application layer

TCP retransmission

Sender sets a count-down timer for each segment sent - If timer expires before ACK received... re-send - If segment error, ACK will never arrive Receiver can detect and discard duplicates - If ACK is delayed (Arrives after re-send) - If ACK is lost

HostA has established a TCP connection with HostB in a remote network. HostA is sending segments to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #1,059. HostA now sends segments of the same application data stream in order: P: 284 bytes Q: 255 bytes R: 125 bytes What is the sequence number on segment R?

Seq num for R: = 1,059 + Segment P + Segment Q +1 = 1,059 + 284 + 255 + 1 = 1,599

HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #4,874. HostA now sends segments of the same application data stream in order: P: 190 bytes Q: 127 bytes R: 440 bytes What is the sequence number on segment Q?

Sequence number on segment Q : = 4,874 + (sequence P) + 1 = 4,874 + 190 + 1 = 5,065

What is the first step for the use of cookies in the HTTP request/response procedure?

Server responds to the initial client request, and includes in this response a request to use cookies.

What aspects of RDT does the UDP protocol implement?

Simple error detection.

What is another name for a host IP address and port number?

Socket/endpoint

Path MTU discovery

Source can determine path MTU - smallest MTU on path from source to destination

Functions of packet-switching networks

Source host (edge) : Packet construction - encode/package data at source Routers(core): packet transmission - send packet from source to destination Destination(edge): Packet interpretation - unpack/decode data from packet at destination - acknowledgement receipt

How layering works

Starting at the Source, data is passed down through the layers until it reaches the physical layer and is transmitted to the next node in the network. Each layer appends a header to the data, may perform other tasks, and then passes the data along.

If I want to be fair about my usage of internet resources, I would use the ___ protocol.

TCP

If I want to be reasonably sure the recipient received my transmitted information, I would use the ____ protocol.

TCP

In the internet, an application-level protocol implemeting email service would most likely utilize ___ as its transport-layer protocol.

TCP

In the internet, an application-level protocol implemeting email service would most likely utilize ______ as its transport-layer protocol.

TCP

In the internet, an application-level protocol implemeting web browsing would most likely utilize ____- as its transport-layer protocol.

TCP

The FTP application-layer protocol utilizes the ____ transport-layer protocol.

TCP

The SMTP application-layer protocol utilizes the _____ transport-layer protocol.

TCP

HTTP uses the ___ transfer-layer protocol at port __

TCP, 80

What is the key point of a cumulative acknowledgement scheme?

The ACK you receive is for the next expected byte number. This means that an ACK for byte #N means that all bytes (N-1, N-2, ... 1) have already been received.

What is the Domain Name System (DNS) application-layer protocol used for and what transport-layer protocol does it make use of?

The DNS protocol uses UDP, and is used to resolve human-friendly word-based web addresses into Network-layer IP addresses and alias web and mail servers.

How is an ICMP message carried?

The ICMP message is in the payload of the IP datagram. The format of the information in the payload depends on the type of ICMP message being sent.

What is reliable data transfer?

The ability to guarantee that a transmitted message was received, and it was received as it was sent (without errors).

Which of the following best describes reliable data transfer in the internet (using networking terminology)?

The ability to send and receive information that you are reasonably sure is what was sent, without losing any information.

What is the purpose of the TCP countdown timer?

The countdown timer is used in RDT to help determine if a packet has dropped. TCP will retransmit a packet, and restart the timer, upon a timer interrupt.

If an IPv4 datagram had to traverse 15 routers to reach its destination host, and I set the IPv4 header TTL field to 10, what would happen?

The datagram would be dropped by the 10th router in the path, and that router would send an ICMP Type 11 (Time Exceeded), Code 0 (TTL expired in transit) message back to the sending host.

A client-side piece of data which is used to keep track of transactions between a client and server is called a cookie.

True

Constraints

The software for each layer depends only on the services of the software provided by neighboring layers (well-defined interfaces) The software at layer n at the destination receives exactly the same protocol message sent by layer n at the sender (consistency) - These constraints mean that protocols within a protocol stack can be: tested independently and modified/replaced independently

____________________ is the rate at which bits are actually transferred between sender/receiver.

Throughput

definition of Transmission delay

Time spent being placed on the transmission medium limited by the transmission protocol

Definition of processing delay

Time spent processing header information. Checking bit errors and deciding outport link.

definition of Propagation delay

Time spent traveling on the physical medium

definition of Queueing delay

Time waiting for the transmission medium

Identifier

To receive messages, process must have an identifier. How to identify a process? have an identifier that consists of IP address and port number (called a socket/endpoint)

Time spent being placed on the transmission medium is called _____________________.

Transmission Delay

In the Internet protocol stack, the ____________ is responsible for process-to-process communication.

Transport Layer

If I were going to implement a lossy VoIP connection, I would use the ____ protocol.

UDP

In the internet, an application-level protocol implemeting live-streaming video would most likely utilize _________ as its transport-layer protocol.

UDP

Connectionless demultiplexing

UDP socket identified by destination (iP address, port number) When host receives UDP segment: check destination port number and directs UDP segment to socket with that port number.

In the HTTP protocol, an object is addressable by its ____

URL

Each object is addressable by a ..

Uniform Resource Locator (URL)

Communication via guided media is complex enough by itself, but communication via unguided (wireless) media is even more complicated. What are some additional difficulties of wireless networking?

Wireless signals are more vulnerable to interference and noise. Wireless signals may be blocked, especially by metal. Wireless signals attenuate with distance. Wireless signals may reflect and interfere with other wireless signals. Wireless signals may reflect and interfere with other wireless signals.

A third party intercepting a packet and downloading its information before it is sent onward toward its destination is called _______________

a packet sniffer

TCP, full duplex service?

Yes, for example Telnet, which echoes back every character.

TCP, connection oriented?

Yes, implemented by a 3-way handshake at start of connection.

TCP, in order delivery? pipeling? Flow Control? (Yes / No) Congestion Control? (Yes / No) Bandwidth Guarantee? (Yes / No) Reliable Delivery(mostly)? (Yes / No) Jitter Threshold? (Yes / No)

Yes, via sequence numbers in tcp header information Yes, though pipeline is limited by congestion and flow control Yes, receiver advertises a window size, and sender limits output accordingly. Yes, implemented by restricting pipeline size based on receipt of acknowledgements (or lack thereof) No bandwidth guarantees. Yes - Acknowledgement for delivery of packets No - no jitter threshold.

Botnet

a group of virus-infected computers acting in concert to achieve some nefarious task. - used for spam, distributed denial of service (DDos) attacks

Layering

each layers implements a service - via its own internal-layer actions - relying on services provided by layer above/below

HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #2,475. HostA now sends segments of the same application data stream in order: P: 116 bytes Q: 225 bytes R: 179 bytes Suppose the segments arrive at Host B in the order Q, P, and R. What is the acknowledgment number on the segment sent in response to segment Q?

acknowledgement number sent in response to Q: = 2,475 + 1 = 2,476

protocol

allows entities to talk to one another in a defined manner.

The payload (non-header portion) of a transport-layer segment is the data from the ______________ layer.

application

At the transport layer, what is the payload?

application data

Sockets

are a "door" to the services provided by the transport layer. Sockets are created by and associated with an application process running on the host. Two socket types for two transport services: - UDP : the unreliable datagram - TCP : the reliable byte stream

Cookies

are bits of client state that are shared with the originating server, and possibly with 3rd-party websites. They enable things like shopping carts and directed advertising. Four components of cookies: 1. cookie header line of HTTP response message 2. cookie header line in HTTP request message 3. cookie file kept on user's host, managed by user's browser 4. back-end database at Web site How cookies work: - when initial HTTP requests arrives at site, site creates : unique ID and entry in backend database for ID

DoS

attackers make resources (server, bandwidth) unavailable to legitimate traffic byoverwhelming resource with bogus traffic

What cookies can provide:

authorization, shopping carts, recommendations, user session state (web e-mail) cookies permit sites to learn a lot about you, you may be giving your name and e-mail to sites malware/spyware cannot reside in cookies.

A ______________ is a group of computers all controlled for a common objective, possibly by an infection in the system, used cooperatively to process and/or send information in mass amounts (DDoS, distributed computing).

botnet

If your computer becomes infected, you may be enrolled in a ________ and used in _______ attack(s) against other hosts without your knowledge.

botnet(s), DDoS attack(s)

What units are used for transmission rate?

bps

What units are we using for network bandwidth?

bps

How reliable is reliable data transfer?

can take steps to make physical layer more reliable, but there will always be problem (congestion in core, etc). small steps: - Error detection - Acknowledgement - Sequencing - Timing (flow/congestion control) - Retransmission - Fairness

IP can detect a variety of errors including

checksum, TTL expires, no route to destination network. IP discards datagrams with certain types of problems. If an error occurs, IP will discard the datagram. Some errors can be reported using ICMP.

A ____________-switched network has a dedicated circuit through which information is sent, whereas a _____________-switched network sends information in "chunks" through a network on shared media

circuit, packet

A TDM-based network is a ______________ network

circuit-switched

client/server model

client host requests/receives service from a server that is "always on" e.g. web browser (client), web server, email client/server

Socket programming with TCP

client must contact server: server process must first be running, server must have created socket that welcomes client's contact - when contacted by client, server TCP creates new socket for server process to communicate with that particular client > allow server too talk with multiple clients > source port numbers used to distinguish clients

In a ___________ architecture, one host is always on, and other hosts may connect and be continually serviced by this first host.

client-server

In a _____________ architecture, one host is always on, and other hosts may connect and be continually serviced by this first host.

client-server

A _____________ has dedicated service provider

client-server model

physical media

communication links

A pair of sockets is called a __________

connection

TCP

connection-oriented: • handshake (exchange of control messages) initializes sender/receiver state before data exchange point-to-point: • one sender, one receiver • full duplex (bi-directional data flow in same connection) in-order byte steam: • cumulative byte count • acknowledgement of bytes received pipelined: • CP congestion and flow control • send & receive buffers flow controlled: • sender will not overwhelm receiver • MSS: maximum segment size

The network layer resides on/in the network ________.

core

Difference between HTTP 1 and HTTP 2

data and headers are separated in HTTP 2. This allows HTTP 2 connections to send headers and data in multiplexed/interleaved fashion

Lower layer services required by the application layer protocols

data integrity, timing, bandwidth and security

Packet switching

data sent through net in discrete "chunks" (packets) of media - 'virtual' connections and many machines accessing the network at the same time - The job of the network core, is to forward all of those packets through the network to the correct destination.

Circuit switching

dedicated circuit per call - With circuit switching, a physical connection, or circuit, is setup over some part of the network. - data is transferred between just two machines. In other words, all of the bandwidth is dedicated to two machines for a period of time. Then another set of machines will talk.

Application layer

defines types of messages exchanged (requests, response), messages syntax (what fields are included in messages), messages semantics (meaning of information in fields) how to talk to a remote host and what happens when the packages come in

Demultiplexing at receiving host

demultiplexed: separated apart segments are demultiplexed and delivered received segments to correct socket. How it works? - Host receives IP datagrams, each datagram has source IP address and destination IP address. - Has source, and destination port number Host then uses IP addresses and port numbers to direct segment to appropriate socket.

UDP checksum

detect "errors" (e.g., flipped/ lost bits) in transmitted segment sender: - start checksum = 0 - compute checksum : one's complement of sum of segment contents as 16 bit int receiver: -compute checksum of received segment - compare computed checksum to segment checksum field. if equal, no error detected. If not equal, error detected and discard packet.

DNS records

distributed database storing resource records (RR) type A : used to identify IP addresses type NS: host name of the authoritative name server of the domain type CNAME: real name of the server type MX: .. ttl : returns the num of seconds for objects to remain in cache

Statistical multiplexing in FDM

each host gets same bandwidth (continuously) - a limited number of hosts get exclusive use of one slot or one channel - if a host is idle, its bandwidth is wasted

Statistical multiplexing in TDM

each host gets same slot (periodically) - a limited number of hosts get exclusive use of one slot or one channel - if a host is idle, its bandwidth is wasted

Flow control is intended primarily to ..

keep a TCP sender from overwhelming a receiver's buffer.

Socket

logical connection between processes running on hosts, it is created by and associated with an application on the localhost. an application process uses a socket to send/ receive messages to/from another application process.

peer to peer model

minimal or no use of dedicated server we want to transfer data as quick as possible and not store them on our servers e.g. skype or bitTorrent

multiplexed

mixed together in a sending queue. sent out in the order they were received Multiplexing means to combine, or mix-together. De-multiplexing means to separate out again.

Multiplexing at sending hosts

multiple processes can be running at the same in host. gather all those data from multiple sockets, create segments and encapsulate segments with header multiplexed : mixed together

Merging multiple communication streams into the same media is called _________?

multiplexing

The internet core is a _______________ network

packet-switched

A __________________ model connects hosts to each other without the use of dedicated services

peer-to-peer

In a __________ architecture, no one host is always on, but hosts may connect amongst themselves in an on-demand fashion.

peer-to-peer

If an HTTP server can send 2 objects over a single TCP connection, this is an example of ______ HTTP.

persistent

A program running on a host is called a ______

process

The transport layer manages communications from _______ to ________

process to process

Processes communicate

process: a program running within a host - Processes inside a single host communicate using inter-process communication (managed by OS). - Processes communicate by exchanging messages (managed by protocols). Client process: process that initiates communication Server process: process that waits to be contacted

nodal delay

processing delay + queuing delay + transmission delay + propagation delay

The POP3 e-mail protocol is called a ___l protocol.

pull

Statistical multiplexing

refers to the way in which packet-switched networks share network resources - sequence of A & B does not have fixed pattern - Transmission medium is shared on demand (if a host is idle, its bandwidth is available to others)

TCP flow control - sliding window

sender won't overflow receiver's buffer by transmitting too much, too fast 1. sender transmits one segment 2. receiver specifies window size (specifies how many bytes in the data stream can be sent) 3. sender limits unACKed data to "receive window"

demultiplexed

separated out and recombined into the original byte stream

HTTP is stateless

server maintains no information about past client requests

KEEP-ALIVE in HTTP 1.0

specifies persistence (keep the connection open) since 1.1, all connections default to persistent

__________ is designed to act like a server, and can distribute data from an infected computer to a remote host upon request.

spyware

Radio link types

terrestrial microwave, LAN, wide-area, satellite with satellite, you can get signal out in the country where no other network is possible

End-to-end delay (nodal delay)

total time from initiating send from source to completed "receive" at destination

FTP (file transfer protocol)

transfer file to/from remote host TCP control connection port 21 TCP data connection port 20 After transferring one file, server closes TCP data connection. TCP control stays on. FTP server maintains "state": • current directory, earlier authentication • limit on concurrent connections

The __________ layer manages communications from process to process.

transport

The transport layer requires some network layer services

transport layer: logical communication between processes network layer: logical communication between hosts - packet addressing, route computation, packet forwarding

ICMP informational messages

triggered by request • Echo request/reply - Sent to ICMP software on any host/router - In response to a request, the ICMP software is required to send an ICMP echo reply message. • Address mask request/reply - Broadcast when a host boots- Router replies with the mask used in that subnet • Router path MTU discovery - Distributed path discovery

Guided media

twisted-pair cooper wire - rate depends on thickness and distaance - make up 99% of wired connections - may pick up intereference ("noise")

The transport layer

two types of connection: connection and connectionless connectionless UDP : fire and forget, best-effort, fastest way to send data connection TCP : Slower, reliable

The DNS application-layer protocol utilizes the ____ transport-layer protocol.

udp

__________ are designed to destroy files or cause a computer malfunction.

viruses

Malware

when your computer/device gets attacked, it's normally due to a software that gets installed somehow - virus: self-replicating infection by receiving/executing object, usually corrupt files on a host - worm: self-replicating infection that executes itself as it travels around a network (attacks the network core) -spyware: can record keystrokes, websites visited upload info to collection sites

IMAP

• Keep all messages in one place: the server • Allows user to organize messages in folders • IMAP keeps user state across sessions

Three mail access protocols

• POP: Post Office Protocol [RFC 1939] authorization (agent <-->server) and download • IMAP: Internet Mail Access Protocol [RFC 1730] manipulation of stored messages on server, more complex • HTTP: gmail, Hotmail, Yahoo! Mail, etc.

Sequence vs ACK#

• Sequence# is the number (in the data stream) of the first byte of the sent segment • ACK# is the number of the next byte expected by the receiver.

Applications that use UDP

• streaming media • Teleconferencing • DNS (Domain Name Service) • Internet telephony