SIP over SCTP

The SBC supports Stream Control Transmission Protocol (SCTP) as a SIP transport. SCTP is an IETF transport-layer protocol providing several enhancements over the Transport Control Protocol (TCP), including:

• Message Orientation—SCTP transports individual messages rather than a continuous byte stream to allow SCTP to separate different signaling messages at the transport layer.
  
  
• Ordered and Unordered Delivery—Assembling received bytes to form signaling messages is performed at the application layer; therefore TCP always delivers an ordered stream of bytes to the application. SCTP can deliver signaling messages to the application as soon as they arrive (when using the unordered service). The loss of a signaling message does not affect the delivery of the rest of the messages, and avoids the head-of-the-line blocking problem in TCP which occurs when multiple higher layer connections are multiplexed within a single TCP connection.
  
  
• Multiple Streams—Missing messages in one stream do not delay the delivery of messages in other streams. A SIP transaction can be considered an application layer connection with multiple transactions running between proxies. The loss of a message in one transaction does not adversely affect the ability of a different transaction to send a message. Thus, if SIP is run between entities with many transactions occurring in parallel, SCTP provides improved performance than SIP over TCP.