Transport Layer

Question 1

Define sliding window - 3 big points

Answer 1

Receiver or destination will not wait for all the bytes for its window size to be received before replying. Receiver will send bytes after every two segments it receives. Benefit: allows the sender to continuously transmit segments. (If the buffer space of the receiver decreases, it will reduce its window size to inform the source to reduce the number of bytes it sends)

Question 2

TCP Header Field: Control bits - describe size of the field, and label the major flags.

Answer 2

6 bits. URG, ACK, PSH, RST, SYN AND FIN

Question 3

Describe the 3-way handshake

Answer 3

Point: The initializing client requests a client-to-server communication session with the server. 2: Server responds with an ACK, and a request a server-to-client communication session. 3: The initiating client ACK the server-to-client communication session.

Question 4

Describe ACK (2 important functions)

Answer 4

ACK flag used in connection establishment and session termination

Question 5

Describe SYN

Answer 5

Synchronize sequence numbers used in connection establishment

Question 6

Describe FIN

Answer 6

No more data from sender and used in session termination.

Question 7

Sequence and ACK numbers - how are they different over the course of handshake.

Answer 7

Sequence and ACK numbers. Client sends a SYN to server (SYN is a seq number 102). Server ACK with + 1 of the seq number (102). Server sends its own sequence number (300). Process is repeated for last step.

Question 7

How many bytes for the UDP Header

Answer 7

8 bytes (64 bits)

Question 8

UDP Header - list the five fields

Answer 8

Source and Destination Port, Sequence Number, Length and Checksum

Question 9

What is a socket pair?

Answer 9

Combination of source IP, source port, or the destination IP and destination port is known as a socket. Sockets enable multiple processes, running on a client, to distinguish themselves from each other. Essentially, a client can throw different source port numbers to do multiple sessions, like requesting something from the file server or web server (https). Both are using the same destination IP server. The transport layer keeps track of the port numbers (source), so they can be forwarded to the correct application.

Question 10

UDP - describe the differences

Answer 10

stateless protocol, connectionless, better delivery protocol.

Question 11

Highlights of TCP

Answer 11

Stateful protocol, provides reliability, flow control, connection oriented protocol. Tracks segments, re-transmits any un-ack data, sends data at an efficient rate. (Tracks the state of the session)

Question 12

Fields of a TCP Header

Answer 12

Source, Destination Port, sequence number, ack number, header length, reserved, control bits, window size, checksum and urgent.

Question 12

TCP Header

Answer 12

20 bytes (160 bytes)