Embedded Headers Support in 3xx Contact Headers

Overview

The SBC Core supports embedded headers received in Contact headers of a 3xx message. Details of this support include:

Contact header information is used to form the R-URI of the redirected INVITE.
Embedded Route header information is used for determining the egress IPTG and next hop of the redirected INVITE.
- Route header with FQDN or IP Address pointing to the SBC (received FQDN matches configured FQDN of zone on which 3xx is received or received address matches Signaling Ports address) is removed.
- Egress IPTG selection is based on the following criteria in the order shown.
  - Embedded Route header parameters presence.
    - dtg parameter if dtg is present.
    - tgrp parameter if tgrp and trunk-context are present and processTgrpContext is enabled and trunk-context points to the SBC.
    - tgrp parameter if tgrp is present.
  - "skipDTGLookupForRouteHdr” flag.
    - Network Selector Table (NST) lookup (using embedded Route header content and zone on which the 3xx is received) if this flag is disabled (for the IPTG that received the 3xx).
    - PSX/ERE routing analysis (embedded Route header content is used as the called party information) if this flag is enabled.
- Top-most Route Header not pointing to SBC is used for determining the next hop.
Embedded From header information is used as the calling party. Embedded To header is the new To header in the redirected INVITE.
All embedded headers received are present (in non-embedded form) in received order in the redirected INVITE (other than any removed Route header pointing to SBC and headers which replace the ingress INVITE headers).

The “Honor Embedded Headers in 3xx” flag is added to the IP Signaling Profile (IPSP) allowing SBC to handle embedded headers in 3xx Contact headers. This flag is associated with the trunk group that received the 3xx, and is disabled by default.

For configuration details, refer to:

Ensure "Force Re-query for Redirection" flag associated with the specified IPSP is enabled when using this feature.

Embedded PAI Header is present in the redirected INVITE only if “Include Embedded PAI” flag is enabled in this IPSP.

A 3xx with embedded headers over GW-GW is rejected with '403 Forbidden' message when "Honor embedded headers in 3xx" enabled.

Call Flows

The following call flows are supported:

Call Flow 1: C in IP Address format

SBC5K

|

-----INVITE----->|

|

|----INVITE---->

|

|<-----3xx------

|Contact:A;tgrp=Z;trunk-context=non-SBC?Route:SBC-FQDN

| Route:C

| Route:D

|-----ACK------ >

|

SkipDTGLookupForRoute is disabled (default)

Force Re-query for Redirection is enabled

Network Selector Table (NST) needs to have an entry provisioned for C

Egress IPTG is determined based on NST lookup for C

|

Profiles associated with that Egress IPTG are applied

|

INVITE is sent to C

|

|-----INVITE------->

|Request-URI:A;tgrp=Z;trunk-context=non-SBC

|Route:C

|Route:D

Call Flow 2: C in FQDN format