Question

An SCTP client opens an association using an initial tag of 806, an initial TSN of 14534, and a window size of 20,000. The server responds with an initial tag of 2000, an initial TSN of 670, and a window size of 14,000. Show the contents of all four packets exchanged during association establishment. Ignore the value of the cookie.

Answer 1

The question involves the SCTP protocol where a client and server exchange four packets (INIT, INIT ACK, COOKIE ECHO, COOKIE ACK) using specific initial tags, TSNs, and window sizes for establishing an association during a four-way handshake.

Step-by-step explanation:

The student's question pertains to the establishment of an association in Stream Control Transmission Protocol (SCTP), a reliable, message-oriented transport layer protocol. During the four-way handshake process used to initiate an SCTP association, the following packets are exchanged between the client and server:

1. Packet 1: The client sends an INIT message to the server indicating its initial parameters: initial tag of 806, initial TSN (Transmission Sequence Number) of 14534, and an advertised window size of 20,000 bytes.
2. Packet 2: The server responds with an INIT ACK message including a state cookie. The server's initial parameters are: initial tag of 2000, initial TSN of 670, and an advertised window size of 14,000 bytes.
3. Packet 3: The client responds to the INIT ACK by sending a COOKIE ECHO packet that contains the state cookie.
4. Packet 4: Upon receiving the COOKIE ECHO, the server sends a COOKIE ACK packet to the client, thus completing the four-way handshake and establishing the association.

These packets are crucial for the successful initialization of an SCTP connection, allowing both client and server to synchronize their initial sequence numbers and agree on parameters like the window size for flow control.