NAT traversal with session border controllers: Difference between revisions

Revision as of 02:44, 26 April 2024

Latest revision as of 14:45, 19 April 2025

Line 20:

In order for the SBC to know which user agent is actually being contacted the SBC can keep a local copy of the user agent's registration. The local copy includes the private IP address and the user's [[URI|SIP URI]] as well as the public IP address included in the IP header that was assigned to the SIP message by the NAT.

Alternatively the SBC can store this information in the forwarded SIP messages. This is displayed in the figure here. The user's contact information is combined in a special format and added as an additional parameter to the contact header. The contact information includeincludes the user's private IP address and SIP URI as well as the public IP address in the IP header of the SIP message. When the registrar receives a request for the user, the registrar will return the complete contact information to the proxy, which will include this information in the SIP message. The SBC can then retrieve this information from the SIP request and use it to properly route the request to the user.

Adding the user agent's contact information to the registered contact information has many advantages. As the SBC does not have to keep local registration information, this solution is simple to implement and does not require memory forto keepingkeep the information. Further, requests destined tofor the user agent do not necessarily have to traverse the SBC that has processed the user agent's registration messages. Any SBC that can reach the user agent can correctly route messages destined to the user agent based on the information included in the SIP request. This advantage applies, however, only in some cases. In case the NAT used in front of the user agent accepts traffic only from the IP addresses which the user agent has contacted previously then only the SBC that has processed the user agent's REGISTER requests will be able to contact the user agent.

The other option is to keep a local copy of the registration information which can, however, increase the processing requirements on the SBC. The SBC will have to manage a local registration database. Beside the memory requirements the SBC will have to replicate this information to a backup system if it is to be highly available. This will further increase the processing requirements on the SBC and increase the bandwidth consumption.