BIT 3554 T1 Study Guide

What is the Internet? Which of the following descriptions below correspond to a "nuts-and-bolts" view of the Internet?

- A collection of billions of computing devices, and packet switches interconnected by links - A "network of networks". - A collection of hardware and software components executing protocols that define the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

When an application uses a TCP socket, what transport services are provided to the application by TCP? Check all that apply.

- Loss-free data transfer. The service will reliably transfer all data to the receiver, recovering from packets dropped in the network due to router buffer overflow. - Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers. - Congestion control. The service will control senders so that the senders do not collectively send more data than links in the network can handle.

How many calls can be carried? Consider the circuit-switched network shown in the figure below, with four circuit switches A, B, C, and D. Suppose there are 20 circuits between A and B, 19 circuits between B and C, 15 circuits between C and D, and 16 circuits between D and A. What is the maximum number of connections that can be ongoing in the network at any one time?

70

Protocols that are part of a distributed network application.

Application layer

The transport layer sits on top of the network layer, and provides its services using the services provided to it by the network layer. Thus it's important that we know what is meant by the network layer's "best effort" delivery service. True or False:

Correct! The network layer's best effort service doesn't really provide much service at all, does it?

This field contains application data that was written into a socket by the sender of this TCP segment.

Data (or payload)

This field contains the number of bytes in the TCP header

Header length field

Check all of the phrases below that state a true property of a local DNS server.

The local DNS server can decrease the name-to-IP-address resolution time experienced by a querying local host over the case when a DNS is resolved via querying into the DNS hierarchy.

Time spent transmitting packets bits into the link.

Transmission delay

Transfer of data between one process and another process (typically on different hosts)

Transport layer

Where is transport-layer functionality primarily implemented?

Transport layer functions are implemented primarily at the hosts at the "edge" of the network.

The sender measures RTTs and uses the current RTT measurement to infer the level of congestion.

delay-based

Access network per-subscriber speeds. Match the access network with the approximate speeds that a subscriber might experience. (Note: if you look these up, do so in the 8E textbook or the slides, or video -- since link access speeds are always increasing over the years). - Ethernet - 4G cellular LTE - 802.11 WiFi - Cable access network - Digital Subscriber Line

- Ethernet: Wired. Up to 100 GBPS per link - 4G cellular LTE: Wireless. Up to 10 MBPS per link - 802.11 WiFi: Wireless. 10's-100's of MBPS per device - Cable access network: Wired. Up to 10's to 100's of MBPS per downstream user - Digital Subscriber Line: Wired. Up to 10's of MBPS per downstream user

Which of the fields below are in a UDP segment header? [Hint: note the use of the word "header" in this question statement. - Internet checksum - Source IP address - Source port number - Destination port number - Upper layer protocol - Sequence number - Length (of UDP header plus payload) - Data (payload)

- Internet checksum - Source port number - Destination port number - Length (of UDP header plus payload)

What is a protocol? Which of the following human scenarios involve a protocol (recall: "Protocols define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt")? - One person asking, and getting, the time to/from another person. - A person reading a book. - A person sleeping. - Two people introducing themselves to each other. - A student raising her/his hand to ask a really insightful question, followed by the teaching acknowledging the student, listening carefully to the question, and responding with a clear, insightful answer. And then thanking the student for the question, since teachers love to get questions.

- One person asking, and getting, the time to/from another person. - Two people introducing themselves to each other. - A student raising her/his hand to ask a really insightful question, followed by the teaching acknowledging the student, listening carefully to the question, and responding with a clear, insightful answer. And then thanking the student for the question, since teachers love to get questions.

Check all of the services below that are provided by the TCP protocol.

- Reliable data delivery. - In-order data delivery - A congestion control service to ensure that multiple senders do not overload network links. - A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. - A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender.

Packet switching versus circuit switching (2). Which of the characteristics below are associated with the technique of circuit switching?

- Reserves resources needed for a call from source to destination. - Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two approaches for implementing this technique. - This technique was the basis for the telephone call switching during the 20th century and into the beginning of this current century.

Which of the characteristics below are associated with a client-server approach to structuring network applications (as opposed to a P2P approach)?

- There is a server that is always on. - There is a server with a well known server IP address. - HTTP uses this application structure.

Which of the characteristics below are associated with a P2P approach to structuring network applications (as opposed to a client-server approach)?

- There is not a server that is always on. - A process requests service from those it contacts and will provide service to processes that contact it.

In DASH (Dynamic, Adaptive Streaming over HTTP), a server divides a video file into chunks that ... (pick best completion from below)

... are stored, each encoded at multiple rates (video quality). The client plays the video chunk-by-chunk, with each chunk requested at encoding rate that fits the available bandwidth at the time.

What is an HTTP cookie used for?

A cookie is a code used by a server, carried on a client's HTTP request, to access information the server had earlier stored about an earlier interaction with this Web browser. [Think about the distinction between a browser and a person.]

What is meant by a cumulative acknowledgment, ACK(n)?

A cumulative ACK(n) acks all packets with a sequence number up to and including n as being received.

What information does the type "NS" resource record hold in the DNS database? Check all that apply.

A domain name and the name of the authoritative name server for that domain.

What information does the type "A" resource record hold in the DNS database? Check all that apply.

A hostname and an IP address.

Lets the sender know that a packet was received correctly at the receiver.

ACK

This field contains the index in the byte stream of the next in-order byte expected at the receiver

ACK number field

What do we mean when we say "HTTP is stateless"? In answering this question, assume that cookies are not used. Check all answers that apply.

An HTTP server does not remember anything about what happened during earlier steps in interacting with this HTTP client.

When an application uses a UDP socket, what transport services are provided to the application by UDP? Check all that apply.

Best effort service. The service will make a best effort to deliver data to the destination but makes no guarantees that any particular segment of data will actually get there.

How is the sending rate typically regulated in a TCP implementation?

By keeping a window of size cwnd over the sequence number space, and making sure that no more than cwnd bytes of data are outstanding (i.e, unACKnowledged). The size of cwnd is regulated by AIMD.

This field contains the Internet checksum of the TCP segment and selected fields in the IP datagram header.

Checksum

Used by sender or receiver to detect bits flipped during a packet's transmission.

Checksum

A message indicating that the sending side is initiating the protocol to terminate a connection.

FIN message

A message sent in response to a request to terminate a connection, ACKing that the side receiving this message is also willing to terminate the connection

FINACK message

Link Transmission Characteristics. Which of the following physical layer technologies has the highest transmission rate and lowest bit error rate in practice?

Fiber optic cable

Routing versus forwarding. Choose one the following two definitions that makes the correct distinction between routing versus forwarding.

Forwarding is the local action of moving arriving packets from router's input link to appropriate router output link, while routing is the global action of determining the source-destination paths taken by packets.

What is the role of an authoritative name server in the DNS? (Check all that apply)

It provides the definitive answer to the query with respect to a name in the authoritative name server's domain.

Transfer of data between neighboring network devices.

Link layer

Lets the sender know that a packet was NOT received correctly at the receiver.

NAK

Delivery of datagrams from a source host to a destination host (typically).

Network layer

HTTP/3: QUIC connection establishment. How many RTTs are needed to establish an HTTP/3 connection (i.e., before data can begin to flow between client and server) using QUIC?

One RTT. Reliability, congestion control, flow control, and security parameters are established in the first two parts of the setup handshake, which takes one RTT.

Transfer of a bit into and out of a transmission media

Physical layer

Time needed to perform an integrity check, lookup packet information in a local table and move the packet from an input link to an output link in a router.

Processing delay

Time need for bits to physically propagate through the transmission medium from end one of a link to the other.

Propagation delay

Time spent waiting in packet buffers for link transmission.

Queueing delay

A general purpose error message used during connection set up or tear down to let the other side know that an error has occurred, and that the referenced connection should be shut down.

RESET message

This field contains the number of available bytes in the TCP receiver's buffer.

Receiver advertised window

Match the functionality of a protocol with the name of a the email protocol (if any) that implements that functionality. Pushes email from a mail client to a mail server. Pulls mail from one mail server to another mail server. Pulls email to a mail client from a mail server.

SMTP, Neither SMTP or IMAP, IMAP

A message from client to server initiating a connection request.

SYN message

A message from server to client ACKing receipt of a SYN message and indicating the willingness of the server to establish a TCP connection with the client.

SYNACK message

This field contains the index in the sender-to-receiver byte stream of the first byte of that data in the payload carried in this segment.

Sequence number

Allows for duplicate detection at receiver

Sequence numbers

This field contains the port number associated with the sending socket for this TCP segment.

Source port number

What approach is taken by a CDN to stream content to hundreds of thousands of simultaneous users?

Store/serve multiple copies of videos at multiple geographically distributed sites.

What is the purpose of the HTTP GET message?

The HTTP GET request message is used by a web client to request a web server to send the requested object from the server to the client.

What is the purpose of a manifest file in a streaming multimedia setting?

To let a client know where it can retrieve different video segments, encoded at different rates

True or False: When multiple UDP clients send UDP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host.

True

The sender infers segment loss from the absence of an ACK from the receiver.

end-end

Which of the following are advantages of using a web cache? Select one or more answers.

- Caching generally provides for a faster page load time at the client, if the web cache is in the client's institutional network, because the page is loaded from the nearby cache rather than from the distant server. - Caching uses less bandwidth coming into an institutional network where the client is located, if the cache is also located in that institutional network.

What is the value of caching in the local DNS name server? Check all that apply.

- DNS caching provides for faster replies, if the reply to the query is found in the cache. - DNS caching results in less load elsewhere in DNS, when the reply to a query is found in the local cache.

Which of the following statements about pipelining are true? One or more statements may be true.

- A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver. - With a pipelined sender, there may be transmitted packets "in flight" - propagating through the channel - packets that the sender has sent but that the receiver has not yet received.

What is the Internet (2)? Which of the following descriptions below correspond to a "services" view of the Internet?

- A platform for building network applications. - A place I go for information, entertainment, and to communicate with people.

What are advantages of implementing transport-layer functionality in QUIC at the application layer? Select all that apply.

- As an application-layer protocol, QUIC can be updated/modified at "app frequency" rather than at the frequency of operating system updates. - QUIC can establish all connection parameters (security, reliability, flow and congestion control)in just one handshake rather than separately in two.

If set, this segment cumulatively ACKs all data bytes up to, but not including, the byte index in the ACK value field of this segment.

ACK bit

Match the name of an Internet layer with unit of data that is exchanged among protocol entities at that layer, using the pulldown menu. Application layer: Transport layer: Network layer: Link layer: Physical layer:

Application layer: Message Transport layer: Segment Network layer: Datagram Link layer: Frame Physical layer: Bit

What is meant by transport-layer demultiplexing?

Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket.

Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission.

Retransmission

What is meant by transport-layer multiplexing?

Taking data from one socket (one of possibly many sockets), encapsulating a data chuck with header information - thereby creating a transport layer segment - and eventually passing this segment to the network layer.

Bits are set at a congested router in a sender-to-receiver datagram, and bits are in the returned to the sender in a receiver-to sender ACK, to indicate congestion to the sender.

network-assisted

True or False: It is possible for two TCP segments with source port 80 to be sent by the sending host to different clients.

True

True or False: It is possible for two UDP segments to be sent from the same socket with source port 5723 at a server to two different clients.

True

Which of the following are changes between HTTP 1.1 and HTTP/2? Note: select one or more answers.

- HTTP/2 allows objects in a persistent connection to be sent in a client-specified priority order. - HTTP/2 allows a large object to be broken down into smaller pieces, and the transmission of those pieces to be interleaved with transmission other smaller objects, thus preventing a large object from forcing many smaller objects to wait their turn for transmission.

Packet switching versus circuit switching (1). Which of the characteristics below are associated with the technique of packet switching?

- Resources are used on demand, not reserved in advance. - Data may be queued before being transmitted due to other user's data that's also queueing for transmission. - Congestion loss and variable end-end delays are possible with this technique. - This technique is used in the internet

Computing Packet Transmission Delay(1). Suppose a packet is L = 1500 bytes long (one byte = 8 bits), and link transmits at R = 1 Gbps (i.e., a link can transmit bits 1,000,000,000 bits per second). What is the transmission delay for this packet?

.000012 secs

DNS functions. Match the function of a server to a given type of DNS server in the DNS server hierarchy. 1) Provides authoritative hostname to IP mappings for organization's named hosts. 2) Replies to DNS query by local host, by contacting other DNS servers to answer the query. 3) Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers. 4) Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu).

1) Authoritative DNS server 2) Local DNS server 3) Top level domain (TLD) 4) DNS root servers

Match the definition/function of an element or approach in a networked streaming video system, with its name. 1) A unit of video, each of which may be encoded at multiple different rates, stored in different files. 2) A file containing the location and encoding rate of files corresponding to video segments in a video. 3) An approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions. 4) A CDN approach that stores content in access networks, close to clients.

1) Chunk 2) Manifest 3) DASH 4) Enter deep

If-Modified-Since. What is the purpose of the If-Modified-Since field in a HTTP GET request message

To indicate to the server that the client has cached this object from a previous GET, and the time it was cached.

True or False: with TCP's flow control mechanism, where the receiver tells the sender how much free buffer space it has (and the sender always limits the amount of outstanding, unACKed, in-flight data to less than this amount), it is not possible for the sender to send more data than the receiver has room to buffer.

True