CSCE416 Test 1

Which layers in the internet protocol stack does a router process?

Physical, Link, Network

Which is NOT true about packet switching with store-and forward transmission?

Packet incurs transmission delay at each loop

Each packet is transmitted at full link capacity

Host break application layer messages into packets

Routers begin forwarding as soon as it gets packet header.

Routers begins forwarding as soon as it gets packets header

What is the key benefit of P2P architecture

Faster Download

Self scalability

Self Scalability

Which of the following delays vary depending on the network congestion

Propagation delay

Queuing delay

Transmission delay

Nodal-processing delay

Queuing delay

Which of the following services are provided by both TCP and UDP

Congestion control

Inter-process communication

Flow control

Reliable transport

Inter-process communication

Which layers in the Internet protocol stack does a link later switch process

Physical, Link, network

Physial, link, network, transport, application

Physical, link, network, transport

Physical, link

Physical, link

Consider sending packets from a source host to a destination host over a fixed route. Increase in which of the following delays is the most likely indication of an impending packet loss?

Transmission delay

Nodal processing delay

Propagation delay

Queuing delay

Queuing Delay

Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end-to-end delay. Which of these delays are constant and which are variable?

Nodal processing - constant

Transmission delay - constant if packet length is fixed and fixed transmission rate

Propegation delay - constant

Queuing delay - depends on amount of traffic: variable

Routing of datagrams from source to destination is the responsibility of

link layer

transport layer

application layer

network layer

Network Layer

Creating a network application implies writing programs that run on network core devices.

True/False

False

Which of the following is NOT true of client server architecture?

Clients communicate directly with each other

Client initiates contact with the server

Client may be intermittently connected

Client may have dynamic IP address

Clients communicate directly with each other

Which is the prevalent form of switching in the internet.

Circuit Switching

Packet Switching

Packet Switching

Suppose two hosts, A and B are separated by 3 hops and the transmission rate at these hops are 10 Mbps, and 100 Mbps respectively. What would be the average end-to-end throughput between A and B.

10 Mbps

100 Mbps

111 Mbps

1 Mbps

1 Mbps

(BOTTLENECK)

Suppose two hosts, A and B are separated by 2,500 Km and are connected by a direct link of R = 1 Mbps. Suppose the propagation speed oer the link is 2.5x10^5 Km/s. What is the maximum number of bits that will be in the link at any time?

40000

20000

80000

10000

(2.5x10^3/2.5x10^5) = 1x10^-2

1x10^-2110^6= 1x10^4=

10,000

Which of the following is not a reason to choose TCP for file transfer?

File transfer is an elastic application

File transfer is a delay-tolerant application

File transfer needs to be secure

File transfer requires requires reliable delivery

File transfer neds to be secure

Which of the following is NOT an end system?

Router

Server

Laptop

Smartphone

Router

Which is more suitable for loss-tolerant delay-sensitive applications

TCP

UDP

UDP

Suppose two hosts, A and B are separated by 4 hops and the transmission rate at each hop is 1Mbps. Assuming the packet size is 12000 bits, ignoring other delays like propagation delay, what would be the end-to-end delay in transmitting the packet from A to B.

48 ms

24 ms

36 ms

12 ms

12000/1x10^6

12ms * 4 hops = 48 ms

Moving packets from routers input to appropriate router output interface is called

forwarding

routing

Forwarding

What information is used by a process to identify a process running on another host

Host Ethernet Address and Process ID

Host IP Address and Socket Port Number

Host ethernet address and socket port number

Host IP Address and Process ID

Host IP address and Socket port number

Data transfer between neighboring network elements is the responsibility of

link layer

application layer

network layer

transport layer

link layer

What are the five layers in the Internet protocol stack? What are the principal responsibilities of each of these layers?

application: supporting network applications

IMAP, SMTP, HTTP

transport: process-process data transfer

TCP, UDP

network: routing of datagrams from source to destination

IP, routing protocols

link: data transfer between neighboring network elements

Ethernet, 802.11 (WiFi), PPP

physical: bits "on the wire"

Which layers in the Internet protocol stack does a router process? Which layers does a link-layer switch process? Which layers does a host process?

Router: network, link and physical

Switch: Link and physical

Host: Application, transport, network, link and physical

What information is used by a process to identify a process running on another host?

IP address and Host Port numbers

How many round trips would it take to download a web page that contains 8 embedded objects from the same server? Assume that the page and each of the embedded objects are small and their transmission times are negligible. Answer this question for each of the following versions of HTTP.

Nonpersistent HTTP with no parallel TCP connections

1.Establish TCP connection: 1 roundtrip

2.HTTP request and receive object: 1 roundtrip

3.Takes 2 roundtrips to get the base html file

4.Repeat steps 1 and 2 for each of 8 objects

Takes 16 roundtrips for 8 objects (2 x 8)

5.Total of 18 roundtrips to get the page and objects

How many round trips would it take to download a web page that contains 8 embedded objects from the same server? Assume that the page and each of the embedded objects are small and their transmission times are negligible. Answer this question for each of the following versions of HTTP.

Persistent HTTP with with pipelining

1.Establish TCP connection: 1 roundtrip

2.HTTP request and receive object: 1 roundtrip

3.Takes 2 roundtrips to get the base html file

4.Send requests for objects back to back on the same connection (send request for obj2 before getting obj1)

Takes roughly 1 roundtrip for all objects

5.Total of 3 roundtrips to get the page and objects

How many round trips would it take to download a web page that contains 8 embedded objects from the same server? Assume that the page and each of the embedded objects are small and their transmission times are negligible. Answer this question for each of the following versions of HTTP.

Nonpersistent HTTP with 2 parallel TCP connections

Nonpersistent HTTP with 2 parallel TCP connections

1.Establish TCP connection: 1 roundtrip

2.HTTP request and receive object: 1 roundtrip

3.Takes 2 roundtrips to get the base html file

4.Repeat steps 1 and 2 for the first 4 (out of 8) objects

Takes 8 roundtrips for 4 objects (2 x 4)

5.In parallel, repeat steps 1 and 2 for the second 4 objects

Takes 8 roundtrips for 4 objects (2 x 4)

6.Steps 4 and 5 are done in parallel

Together they take only 8 roundtrips

7.Total of 10 roundtrips to get the page and objects

How many round trips would it take to download a web page that contains 8 embedded objects from the same server? Assume that the page and each of the embedded objects are small and their transmission times are negligible. Answer this question for each of the following versions of HTTP.

Persistent HTTP with without pipelining

1.Establish TCP connection: 1 roundtrip

2.HTTP request and receive object: 1 roundtrip

3.Takes 2 roundtrips to get the base html file

4.Repeat step 2 for each of 8 objects (use same connection)

Takes 8 roundtrips for 8 objects (1 x 8)

5.Total of 10 roundtrips to get the page and objects

Will Web caching reduce the delay for all objects requested by a user or for only some of the objects?

For all objects

Is it possible for an organization's Web server and mail server to have exactly the same alias for hostname (for example foo.com)?

Yes it is possible

What would be the type of resource record that contains the hostname of the mail server?

MX Record

Where does an end host typically send the DNS query to?

Top level domain server

Local DNS Server

Authorative Name Server

Root Name Server

Local DNS Server

Web caching with a hit ratio of 25% reduces the delay in receiving ___ objects requested by user

100%

50%

25%

75%

100% of objects requested

What information is used by a process to identify a process running on another host?

Host IP and Socket Port Number

Which type of DNS resource contains the hostname of email server

NS

A

MX

CNAME

MX

Which of the following is NOT a service provided by DNS?

Mail serving aliasing

Host aliasing

Dynamic IP address allocation

Hostname to IP Address translation

Dynamic IP Address allocation

What is the key problem, which HTTP/2 does not solve that is being addressed by HTTP/3

Small object may have to wait for transmission behind large object

Loss recovery by TCP stalls all object transmissions

Loss recovery by TCP stalls all object transmissions

Which of the following is not a benefit of using a web cache?

Reduce load on the origin server

Reduce traffic in the core of the internet

Reduces memory access latency on the client host

Reduce traffic on an institution's access link

Reduces memory access latency on the client host

Which of the following is NOT a part of the Uniform Resource Locator (URL)

Object path name

Application protocol

Object Size

Server host name and port number

Object Size

Getting a web page with 6 images with non-persistent HTTP with 3 parallel TCP connection takes ___ round trips

12

8

14

6

6 round trips

2 to get page

2 round trips from each parallel TCP

Which of the following is NOT needed for maintaining state using cookies

Persistent HTTP where server keeps connections open

Cookie file kept on users host

Cookie specific action by server with backend databae

cookie header line in HTTP request messages

Persistent HTTP where server keeps connections open

Creating a network application implies writing programs that run on

End systems

Network core devices

End systems

How many sockets does a TCP server supporting 9 different clients simultaneously need

18

10

11

1

10

How many sockets does a client that communicates simultaneously with 2 UDP servers and 2 TCP servers need

4

2

1

3

3

2TCP + 1UDP

What is the key difference between HTTP/1.1 and HTTP/2?

Transmission order of requested objects

Request Methods

Header fields

Response status codes

Transmission order of requested objects

With non-persistent HTTP

multiple objects can be sent over a TCP connection

At most one object is sent over a TCP connection

At most one object is sent over a TCP connection

Getting a web page with 6 images with persistent HTTP without pipelining takes __ round trips

12

8

10

14

8

Getting a web page containing 6 images with non-persistent HTTP with no parallel TCP connections takes __ round trips

14

8

12

6

14

How many sockets does a UDP server supporting 3 different clients simultaneously need?

4

1

3

2

1

When two processes are communicating, the process that initiates communication is called

Server process

Client process

Client process

Which type of DNS resource record contains the IP address of a hostname

CNAME

A

NS

MX

A

Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and Host B each send a UDP segment to Host C with destination port number 6789. Will both segments be directed to the same socket at C? If so, how will the process at C know that these two segments originated from two different hosts?

Yes,

Source IP Address will know that these two segments originated from two diferent hosts

Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B.

Are all the requests being sent through the same socket at C?

If they are being passed through different sockets, do both sockets have port 80?

No

Yes

Describe why an application developer might choose to run an application over UDP rather than TCP.

No connection establishment

Simple: No connection state at sender, receiver

small header size

no congestion control

UDP can blast away as fast as desired

can function in the face of congestion

Is it possible for an application to enjoy reliable data transfer even when the application runs over UDP? If so, how?

Yes, you would have to implement it yourself. Like using UDP3.

You'd have to establish a handshake connection with UDP that would timeout after no communication.

UDP and TCP use 1s complement sum for their checksums. Suppose you have three 8-bit bytes: 01110000, 01001100, 01010101

•What is the 1's complement sum of these 8-bit bytes? (Note that although UDP and TCP use 16-bit words in computing the checksum, for this problem you are being asked to consider 8-bit summons).

•Give an example error scenario that will be caught by the receiver.

•Give an example error scenario that will not be caught by the receiver.

11101101

Pick one bit that a 0 becomes 1 that will be caught by the receiver in which an error is noticed.

If a 1 and a zero in the same spot of the 8-bits switch to the opposite state. The sum would be the same and no error would be caught

§Suppose Host A sends two TCP segments back to back to Host B over a TCP connection. The first segment has sequence number 90; the second has sequence number 110.

•How much data is in the first segment?

•Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment that Host B sends to Host A, what will be the acknowledgment number?

20 bytes is in the first segment

The acknowledgement number would be 90

In TCP, will the loss of an acknowledgment always result in a retransmission of that packet? Why or why not?

No, because the ACK is acknowledges the next sequence number

Suppose Host A sends 3 TCP segments back to back to Host B over a TCP connection. The sequence numbers of the 1st, 2nd and 3rd segments are 1000,1500,2500 respectively. When the 1st segment arrives at B, in the ACK that B sends to A, what will be the ACK number?

1000

1501

1500

1001

1500

Suppose UDP sends data bytes 01110000, 01001100, and 01010101 along with the checksum (note that although UDP and TCP use 16-bit words in computing the checksum, for this problem you are being asked to consider 8-bit summands) During the transmission the 1st byte is corrupted and received as 01110111. Can the UDP receiver detect this error?

Yes

In TCP, which of the following header bits would be set in the connection close request segment?

SYN

ACK

URG

FIN

FIN

Suppose Host A sends 3 TCP segments back to back to Host B over a TCP connection. The sequence number of the 1st, 2nd and 3rd segments are 1000,1500, and 2500 respectively. How much data is in the 1st segment

125

1000

500

1500

500 bytes

Suppose UDP sends bytes 01110000, 01001100, and 01010101 along with the checksum. During transmission the 1st and 2nd bytes are corrupted and received as 01110100 and 01001000. Can the UDP receiver detect this error?

No

In TCP will the loss of an ACK always result in a retransmission of a segment?

No

In TCP, which of the header bits would be set in the connection request segment

URG

SYN

ACK

FIN

SYN

UDP uses which of the following fields in the segment header to determine the socket to pass the received data to.

Source port number

destination IP address

Sour IP address

Destination port number

Destination IP address

Destination port number

What functionality does UDP provide beyond what is provided by IP?

Faster communication

Error detection

Inter-process communication

Best effort delivery

Error detection

Inter-process communication

What method does TCP use to estimate the round trip time

Exponential weighted moving average of sample RTT

Under which of the following scenarios does a TCP receiver send an ACK without delay

Arrival of in-order segment with expected sequence number and all data up to expected sequence number already ACKed

Arrival of out-of-order segment higher-than-expected sequence number

Arrival of a segment that partially of completely fills gap

Arrival of in-order segment with expected sequence number and one other segment has ACK pending

Arrival of out-of-order segment higher-than-expected sequence number

Arrival of a segment that partially of completely fills gap

Arrival of in-order segment with expected sequence number and one other segment has ACK pending

Why might an application developer choose UDP over TCP

More secure

No congestion control

Small header size

No connection establishment

No congestion control

Small header size

No connection establishment

Which of the following header fields are common to both UDP and TCP

Acknowledgement number

Checksum

Destination Port Number

Sequence number

Checksum

Destination Port Number

Suppose Host A sends 3 TCP segments back to back to Host B over a TCP connection. The sequence numbers of the 1st, 2nd, and 3rd segments are 1000, 1500 and 2500 respectively. Suppose the 1st segment arrives, 2nd segments is lost, and then the 3rd segment arrives at B. When the 3rd segment arrives at B, in the ACK that B sends to A, what will be the ACK number?

1000

2500

1001

1500

1500

TCP Uses which of the following fields in the segment header to determine the socket to pass the received data to?

Destination IP address

Destination port number

Source IP address

Source Port Number

Destination IP address

Destination port number

Source IP address

Source Port Number

What is the size of UDP header?

16 bytes

8 bytes

12 bytes

20 bytes

8 bytes

Which of the following versions of HTTP use UDP

HTTP/3

HTTP/1.1

HTTP/2

HTTP/1.0

HTTP/3

HTTP/1 (non-persistant HTTP TCP)

HTTP/1.1 (persistant HTTP TCP)

HTTP/2 (non-persistant HTTP TCP)

What would be the checksum computed by UDP if the data bytes are 01110000, 01001100, and 01010101

11101110

11101101

00010001

00010010

11101101

Reliable data deliver is challenging because of which of the following reasons?

Sender has no direct knowledge of network state

Packets may be lost during transit

Sender has no direct knowledge of receiver state

Packets may be reordered during transit

Sender has no direct knowledge of network state

Packets may be lost during transit

Sender has no direct knowledge of receiver state

Packets may be reordered during transit

How does TCP use the estimated round trip time to set the time out interval for retransmission of a segment.

Timeout = Estimated TT + 4*Deviation from Estimated RTT

§TCP waits until it has received three duplicate ACKs before performing a fast retransmit. Why do you think the TCP designers chose not to perform a fast retransmit after the first duplicate ACK for a segment is received?

Because of out of order delivery. We wouldn't be entirely sure if a packet was loss. We can me more confident that the packet is not out of order, and it is actually lost if we wait for a third duplicate ACK.

What happens if network layer delivers data faster than application layer removes data from socket buffers?

receiver controls sender, so sender won't overflow receiver's buffer by transmitting too much, too fast

Q: will 2-way handshake always work in network?

§variable delays

§retransmitted messages (e.g. req_conn(x)) due to message loss

§message reordering

§can't "see" other side

Congestion:

§informally: "too many sources sending too much data too fast for network to handle"

§manifestations:

•long delays (queueing in router buffers)

•packet loss (buffer overflow at routers)

Congestion control versus flow control

Congestion control: Two many senders sending too fast

Flow Control: One sender too fast for one reciever

what happens as original data and original data plus retransmitted data increase ?

as red original data plus retransmitted data increases, all arriving blue pkts at upper queue are dropped, blue throughput -> 0

TCP: from slow start to congestion avoidance

when should the exponential increase switch to linear?

when cwnd gets to 1/2 of its value before timeout.

Suppose the congestion window of a TCP sender was 4 segments long and the threshold is 6 segments. After it receives a new ACK what would be the new congestion window?

6 segments

8 segments

5 segments

7 segments

5 segments

In TCP, which of the following header bits would be set in the response segment sent upon receiving a connection request segment?

URG

ACK

SYN

FIN

ACK

SYN

How does TCP use the estimated round trip time to set the time out interval for retransmission of a segment?

Timeout = Estimated RTT + 4 * Deviation from Estimated RTT

Suppose the congestion window of a TCP sender was 4 segments long and it receives 3 duplicate acks. After that what would be the new threshold.

1 segment

2 segments

8 segments

3 segments

2 segments

In TCP, which of the following header bits could be set in the response segment

ACK

SYN

FIN

URG

ACK

FIN

What functionality does UDP provide beyond what is provided by IP

Inter-process communication

Faster communication

Best-effort delivery

Error detection

Inter-process communication

Error detection

What would be the checksum computed by UDP if the data bytes are 01000000, 01111100, 01010101

11101101

Suppose Host A sends 4 TCP segments back to back to host B over a TCP connection. The sequence numbers of the 1st, 2nd, 3rd and 4th segments are 1500,2500,3000,4500 respectively. How much data is in the 3rd segmnet?

1500 bytes

500 bytes

2000 bytes

1000 bytes

1500 byes

Suppose Host A sends 4 TCP segments back to back to Host B over a TCP connection. The sequence of the 1st, 2nd, 3rd and 4th segments are 1500, 2500, 3000, 4500 respectively. Suppose the 1st segment, then the 3rd segment, and after that the 2nd segment arrives at B. When the 2nd segment arrives at B, in the ACK that B sends to A, what will be the ACK number

4500

3001

2500

3000

4500

If the congestion window of a TCP sender was 4 segments long when a timeout occurred, what would the new congestion window be?

8 segments

2 segments

3 segments

1 segment

1 segment

TCP uses which of the following fields in the segment header to determine the socket to pass the received data to?

Destination port number and IP address

and

Source port number and IP address

Which filed in the TCP header does a receiver use to inform the sender about the number of bytes it is willing to accept without overflowing its buffers?

Send window

Congestion window

Receive window

Ack number

Receive window

Reliable data delivery is challenging because?

Sender has no direct knowledge of network or receiver state and

Packets may be lost or reordered during transit.

Suppose the congestion windows sender is 8 segments and the threshold is 6 segments. After it recieves 8 new ACK,s what would be the new congestion window?

16 segments

14 segments

12 segments

9 segments

9 segments

Suppose Host A sends 4 TCP segments back to back to Host B over a TCP connection. The sequence numbers of the 1st, 2nd, 3rd and 4th segments are 1500, 2500, 3000, 4500 respectively. When the 1st segment arrives at B, in the ACK that B sends to A. What will be the ACK number

1500

2501

1501

2500

2500