Establishment and termination of sctp Association

Like TCP, sctp is also connection-oriented, so there is also an associated handshake process for establishing and terminating. However, the handshake process of sctp is different from that of TCP.

 

Four-way handshake

When a sctp association is established, the following situation occurs (similar to TCP ).

(1) The server must be prepared to accept external associations. This is usually done by calling the socket, bind, and listen functions, called passive open.

(2) The customer actively opens the connection by calling connect or sending a message that implicitly opens the association. This allows the customer sctp to send an init message (initialization ), this message informs the Server customer of the IP address list, initial serial number, start mark of all groups in the Association identified by the user, the number of outgoing streams requested by the customer, and the number of external streams that the customer can pay.

(3) The server uses an init_ack message to confirm the client's init message, it contains the server's IP address list, initial serial number, start ID, number of outgoing streams requested by the server, number of external streams supported by the server, and a status cookie. Status cookie contains all the statuses required by the server to ensure the association is valid. It is digitally signed to ensure its validity.

(4) The customer returns the server's status cookie with a cookie_echo message. In addition to cookie_echo, user data may be bound to the message in the same group.

(5) The server uses a cookie_ack message to confirm that the cookie returned by the customer is correct. This association is established. The message may also contain user data in the same group.

The above exchange process requires at least four groups, so it is called sctp's four-way handshake. Figure 2-6 shows the four segments.

 

Establishment and termination of sctp Association