1. Answer the following questions about TCP connection establishment? a. What is

Question

1. Answer the following questions about TCP connection establishment?

a. What is the first segment exchanged?

b. What is the second segment exchanged?

c. What is the third segment exchanged?

.

2. What can you say about the TCP segment in which the value of the control field is one of the following:

a. 000010

b. 010010

.

3. In a TCP connection, the initial sequence number at the client site is 2,171. The client opens the connection, sends only one segment carrying 1,000 bytes of data, and closes the connection. What is the value of the sequence number in each of the following segments sent by the client?

a. The SYN segment?

b. The ACK segment carrying no data?

c. The data segment?

d. The FIN segment?

Explanation / Answer

Question 1

A] The Client sends the first segment, a SYN segment, in which only the SYN flag is set. This segment is for synchronization of sequence numbers. It consumes a single sequence number. SYN carries no real data, but think of it carrying an imaginary byte.

B] The server sends the second segment, a SYN+ACK segment, with 2 flag bits set SYN and ACK. This has a dual purpose. It is a SYN segment for communication in the other direction towards the client and also acts as the acknowledgement for the SYN segment. Consumes a single sequence number.

C] The client sends the third segment, which is an ACK segment. This acknowledges the receipt of the second segment with the ACK flag and acknowledgment number field. ACK, if not carrying any data, consumes no sequence number.

Question 2

A] 000010

The SYN bit is set. This is a SYN segment request to synchronize the sequence numbers.

B] 010001

The ACK and the FIN bits are set. This is a FIN+ACK in response to a received

FIN segment

Question 3

A] The SYN segment- The sequence number in the SYN segment is 2171. The SYN segment consumes one sequence number; the next sequence number to be used is 2172.

B] The ACK segment carrying no data- Enough data not provided as to know the sequence number of the ACK segment from the client, the initial sequence number at the server side should be provided.

C] The data segment- The sequence number in the data segment is 2172 (which represents the sequence number of the first byte). The bytes in the packets are numbered 2172 to 3171. Note that the client sends the data with the second packet (no separate ACK segment).

D] The FIN segment- The sequence number in the FIN segment is 3172. Note that the FIN segment does consume a sequence number

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