SBC performs protocol repair.
Refer to the background information in Basic Service Availability - DNS.
- The public internet/ISP receives SIP messages with slight variations in SIP headers, parameter formats etc.
- The SBC repairs the protocol information, discards irrelevant and/or offending information or inserts missing information based on the policy installed by the operator. A common "normalized" SIP message passed to the core network simplifies implementation and supports better interoperability.