Background: Avaya ASM 6.3.x introduces a new SIP stack, and as part of this additional features are included in the SIP messaging sequence known as headers. The addition of these SIP headers increases the overall size of a the SIP message.
Per RFC 3261 section 8.2.2 under Header Inspection: If a UAS does not understand a header field in a request ( this is, the header field is not defined in this specification or in any supported extension), the server MUST ignore that header field and continue processing the message. A UAS SHOULD ignore any malformed header fields that are not necessary for processing requests.
Based on traces taken at the Acme Session Border controllers, neither the Avaya Session Manger (ASM) nor the ACME Session Border Controllers (SBC)’s were at fault.
Traces at the Acme SBC showed no response to messages sent from the SBC to the SIP carrier.
Call was eventually canceled by the SIP service provider, most likely because after the carrier sent the initial invite the carrier never recieved the 100 trying, 18x message, or 200 OK message, as these messages, depending on call flow may have been greater than the 1500 byte MTU size and therefore dropped by the public carrier network after the SBC but prior to making to the SIP service provider.
