3700 Networking MIDTERM
TCP service
- 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 throughput guarantee, security - connection-oriented: setup required between client and server processes
Suppose there are two links between a source and a destination. The first link has transmission rate 100 Mbps and the second link has transmission rate 10 Mbps. Assuming that the only traffic in the network comes from the source, what is the throughput for a large file transfer.
10 Mbps
Suppose a client sends an HTTP request message with the If-modified-since: header. Suppose the object in a server has not changed since the last time a client retrieved the object. Then the server will send a response message with the status code: - 304 Not modified - 200 Ok - 404 Not found - none of them
304 not modified
Presentation Layer
Allows hosts and applications to use a common language; performs data formatting, encryption, and compression.
OSI Model Layers
Application, Presentation, Session, Transport, Network, Data Link, Physical
A mobile device such as a tablet CANNOT be treated as an end system in the context of networking
False
A user requests a Web page that consists of some text and three images. For this page, the client will send one request message and receive four response messages.
False
ADSL bandwidth is shared
False
Before sending a packet into a datagram network, the source must determine all of the links that packet will traverse between source and destination
False
DNS is organized as a centralized structure in order to provide reliable services
False
DNS servers are organized in a hierarchical structure, and the TLD servers are in the first level
False
Ethernet is a popular residential access technology
False
Flash can aid the http protocol to keep 'state' in web communications
False
HTTP protocol is a "stateful" protocol, which means servers will maintain information about past client requests
False
In BitTorrent, a peer's instantaneous download rate can never exceed its instantaneous upload rate
False
In P2P architecture, there should be a stable always-on server to provide reliable services to network users
False
In P2P file distribution, an entire file should never be divided into chunks in order to provide file integrity
False
In computer networking, data cannot be sent over DSL phone line
False
In computer networking, switches and routers always perform the same functions
False
In computer networking, the transport layer is responsible for the logical communication between hosts
False
In computer networks routers are mainly used to control sending and receiving of messages
False
In computer networks, a packet will never be dropped even the buffer on a router is full
False
Mobile Networks are more flexible than home network, therefore routers should not be used in mobile networks
False
On the sender side of network communications, the data will go through the network layer first and then go through the transport layer
False
The Date: header in the HTTP response message indicates when the object in the response was last modified.
False
With non-persistent connections between browser and origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages
False
What is the data unit sent/received over the Link layer in OSI model? - Message - Datagram - Segment - Frame
Frame
HFC
Hybrid Fiber Coax homes share access network to cable headend unlike DSL which has dedicated access
queuing and loss
If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up
Inter-process Communication
Information sharing between processes to speed up computation, allow modularity, convenience
Which statement is True about the traceroute command? - It traces the routing path of a packet from source to destination - it traces the forwarding path of a packet from source to destination - It traces the storing procedure of a packet from source to destination
It traces the routing path of a packet from source to destination
Which Option Is Not a Networking Protocol? - Pop3 - MBP - TCP - FTP
MBP
P2P architecture
No always-on server; arbitrary end-systems directly communicate; peers request service from other peers, provide service in return to other peers; peers are intermittently connected and change IP addresses
Four sources of packet delay
Nodal Processing, Queueing Delay, Transmission Delay, Propagation Delay
Which type of data cannot be sent over cable network - Video - Text - Audio - None
None
Which device is typically used to connect an Ethernet to an internet service provider (ISP) - Switch - End System - Data Server - Router
Router
Which device is typically used to connect multiple different networks? - switch - DSL - Fiber - Router
Router
Which protocol is used to control data sending and receiving between mail servers in E-mail communications? - FTP - SMTP - POP3 - IMAP
SMTP
Which option is NOT the source of a packet delay in computer networking? - Propogation Delay - Segment delay - Transmission delay - Nodal processing
Segment delay
Bandwidth is actually a metric to describe the capacity of a computer network
True
DNS lookups often involve a combination of recursive and iterative queries
True
Domain name system aims to perform hostname to IP address translation
True
If a POP3 client does not send the `dele` command, copies of the messages that the client has retrieved remain in the mail server
True
In networking can routers and switches forward packets
True
It is possible for a mail client to send e-mail messages over HTTP rather than SMTP
True
Iterated query and recursive query are two different types of query in DNS name resolution
True
Layers four and five of the internet protocol stack are implemented in the end systems but not in the routers in the network core
True
Personal devices such as tablets and cellphones can be treated as end systems in the context of computer networking
True
Routing and Forwarding are the two key network-core functions
True
Two distinct web pages can be sent over the same persistent connection
True
Which option is a type of DNS records? - A - NS - CNAME - all
all
A browser will generate header lines as a function of _____ - browser type and version - user configuration of browser - whether the browser has a cached version of the requested object - all of the above
all of the above
In computer networking, firewall can be deployed in _____ - routers - end systems - servers - all of them
all of them
client/server architecture
always on host permanent IP address data centers for scaling may have dynamic IP addresses do not communicate directly with each other
sockets
analogous to door, sending process shoves message out door sending process relies on transport infrastructure on other side of door to deliver message to socket at receiving process
aside
applications with P2P architectures have client processes & server processes
Physical Layer
bits "on the wire", actually sends the data across the network. The other layers get the data ready to be sent
Local DNS name servers ______ - obtain resource records from Web caches - never cache resource records - cache resource records, but discard them after a period of time that is on the order of a few days - cache resource records and never discard
cache resource records, but discard them after a period of time that is on the order of a few days
Which option is used to maintain User-server states in HTTP protocol? - cookies - flash - memory - buffer
cookies
calculate transmission rate
d[nodal processing] = d[proc] + d[queue] + d[trans] + d[prop]
d trans = transmission delay
d[trans] = L/R
Link Layer
data transfer between neighboring network elements - Ethernet, 802.111 (WiFi), PPP - frame
Protocols
define format, order of messages sent and received among network entities, and actions taken on message transmission receipt
routing
determines source-destination route taken by packets
cable network multiplexing
different channels transmit different frequency bands
What do end systems connect to in Ethernet network?
ethernet switch
Why layering?
explicit structure allows identification, relationship of complex systems pieces modularization eases maintenance, updating system
In computer networking, the process of moving packets from a router's input to the appropriate router output is defined as _______ . - storing - routing - forwarding - delivering
forwarding
Packet Switching
hosts break application layer into packets forward packets from one router to the next, across links on path from source to destination allows more users to use the network!
Internet Exchange Point (IXP)
hub where the backbone intersects with local and regional networks and where backbone owners connect with one another
Which option is NOT an advantage of web caching? - It can serve as an additional hard drive for end users - it can help to reduce traffic on an institutions access link - it can enable content providers to effectively deliver content - it can help to reduce response time for client request
it can serve as an additional hard drive for end users
Which statement is NOT true about web caching? - it can enable content providers to effectively deliver content - it can help to reduce response time for client request - It cannot be larger than 8g - It can help to reduce traffic on an institutions access link
it cannot be larger than 8g
which of the following servers does not strictly belong to the hierarchical DNS architecture? - Top-level Domain Servers - Local DNS Name Servers - Authoritative DNS servers - Root DNS servers
local DNS name servers
The transfer of an html file from one host to another is _____ . - loss tolerant and time sensitive - loss-intolerant and time sensitive - loss-intolerant and time insensitive - none of the above
loss-intolerant and time insensitive
Application Layer Protocols
messages exchanged e.g. request, response message syntax, fields & how they're dilenated message semantics rules for when and how processes send & respond to messages open protocols: RFC's, HTTP, SMTP
forwarding
move packets from router's input to appropriate router output
For the web application, the user agent is _______ - the users monitor - the users mouse - the users keyboard - none of them
none of them
packet transmission delay = L(bits) / R(bits/sec)
packets of length L, transmission rate R
Which address will be used to direct data to correct process at a node after the data was already forwarded to the node? - MAC - physical - Port - IP
port
client process
process that initiates communication
server process
process that waits to be contacted
Transport Layer
process-process data transfer TCP, UDP - segment
bit
propagates between transmitter / receiver pairs
Which option is NOT a method in HTTP/1.1 ? - GET - PULL - PUT - POST
pull
Two key network-core functions
routing and forwarding
Network Layer
routing of datagrams from source to destination (IP, routing protocols) - datagram
unguided media
signals propagate freely, e.g. radio
Guided Media
signals propagate in solid media: copper, fiber, coax
Which statement is NOT true about CDN (content distribution network)? - stores copies of content at CDN nodes - can deliver video content - subscriber will be directed to the central CDN server to access the requested content - there could be multiple copies for the same content
subscriber will be directed to the central CDN server to access the requested content
Application Layer
supporting network applications (FTP, SMTP, HTTP) - message
Session Layer
synchronization, checkpointing, recovery of data exchange
SMPT is used - to transfer messages from mail server to a user agent - to define the format of message headers - to transfer messages from one mail server to another - all of them
to transfer messages from one mail server to another
In the OSI model, which layer is responsible for the process to process data transfer? - Physical layer - Network layer - Transport layer - Application layer
transport layer
Ethernet
typically used in companies universities etc 10, 100, 1G, 10Gbps transmission rates
UDP service
unreliable data transfer between sending and receiving process
Suppose a DNS resource record has Type=MX. Then - value is the hostname of the mail server that has the alias hostname Name - value is the hostname of the DNS server that is authoritative for Name - value is the IP address of the mail server that has the alias hostname Name - None of them
value is the hostname of the mail server that has the alias hostname Name
physical link
what lies between transmitter and receiver
In networking security, _____ refers to: attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic
DoS
what transport service does an app need?
Data integrity, Timing, Throughput, Security
What is the data unit sent/received over the Network layer in OSI model? - message - segment - datagram - frame
Datagram
