which a single router is transmitting packets, each of length L bits, over a single link with transmission rate R Mbps to another router at the other end of the link.

INSTRUCTIONS TO CANDIDATES

ANSWER ALL QUESTIONS

Question 1 

Consider the figure below, in which a single router is transmitting packets, each of length L bits, over a single link with transmission rate R Mbps to another router at the other end of the link.

Suppose that the packet length is L= 12000 bits, and that the link transmission rate along the link to router on the right is R = 10 Mbps.

(a) What is the transmission delay (the time needed to transmit all of a packet's bits into the link)? (b) what is the maximum number of packets per second that can be transmitted by the link?

Question 2

 Computing end-end delay (transmission and propagation delay)

Consider the figure below, with three links, each with the specified transmission rate and link length.

Find the end-to-end delay (including the transmission delays and propagation delays on each of the three links, but ignoring queueing delays and processing delays) from when the left host begins transmitting the first bit of a packet to the time when the last bit of that packet is received at the server at the right. The speed of light propagation delay on each link is 3x10**8 m/sec. Note that the transmission rates are in Mbps and the link distances are in Km. Assume a packet length of 16000 bits. Give your answer in milliseconds.

Question 3

 End to End Throughput and Bottleneck Links

Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 100 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 90 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 60 Mbps per second. You might want to review Figure 1.20 in the text before answering the following questions:

1. What is the maximum achievable end-end throughput (in Mbps) for each of four client-to-server pairs, assuming that the middle link is fair-shared (i.e., divides its transmission rate equally among the four pairs)?

2. Which link is the bottleneck link for each session?

3. Assuming that the senders are sending at the maximum rate possible, what are the link utilizations for the sender links (RS), client links (RC), and the middle link (R)?

Question 4

 The HTTP RESPONSE message

 Consider the figure below, where the server is sending a HTTP RESPONSE message back the client.

Suppose the server-to-client HTTP RESPONSE message is the following:

 

HTTP/1.1 200 OK

Date: Mon, 27 May 2019 19:12:59 +0000

Server: Apache/2.2.3 (CentOS)

Last-Modified: Mon, 27 May 2019 19:13:59 +0000 ETag:17dc6-a5c-bf716880.

Content-Length: 4264

Keep-Alive: timeout=22, max=54 Connection: Keep-alive Content-type: text/html

Answer the following questions:

 

• Is the response message using HTTP 1.0 or HTTP 1.1?

• Was the server able to send the document successfully? Explain

• At what date and time was this response sent?

• When was the file last modified on the server?

• How many bytes are there in the document being returned by the server?

• What is the default mode of connection for HTTP protocol? Is the connection in the reply persistent or nonpersistent?

• What is the type of file being sent by the server in response?

• Does the response message use separate keep-alive messages?

• What is the name of the server and its version ? List the advantages of the server

• What is the timeout value for the response message?

 

The advanced questions below may require you to dig into the HTTP specification [RFC 7231] or other online documents:

 

• Give the default connection timeout for the given

• Should the timeout value be short or long? Give reasons for your choice of

• Is the connection dropped or kept open after the timeout? Can the connection be extended even after timeout? Explain

• What are the maximum number of requests and responses the server has allowed? What happens when the maximum number of requests and responses are sent?

• What is the ETag in the success response message sent? State its

• Will the ETag change if the resource content at this particular resource location changes?

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