Multiple AoR reachabiliTy InformatioN Indication
|Document||Charter||Multiple AoR reachabiliTy InformatioN Indication WG (martini)|
|Title||Multiple AoR reachabiliTy InformatioN Indication|
|IESG||Responsible AD||Gonzalo Camarillo|
|Charter edit AD||(None)|
|Send notices to||(None)|
The MARTINI working group is chartered to specify a means by which an entity that is authoritative for SIP URIs can dynamically register reachability information for multiple Addresses of Record ("AORs") with a service provider. The SIP protocol [RFC 3261 and its extensions] supports multiple means of obtaining the connection information necessary to deliver out-of-dialog SIP requests to their intended targets. When a SIP Proxy needs to send a request to a target AOR within its domain, it can use a location service to obtain the registered contact URI, together with any associated path information [RFC 3327], and build a route set to reach the target UA(s). The SIP REGISTER method can be used to register contact URIs and path information. SIP-outbound [RFC 5626] enhances this mechanism to cater for UAs behind NATs and firewalls. When a SIP UA or Proxy needs to send a request to a target for which it is not authoritative, the UA/Proxy can use RFC3263 procedures for using DNS to resolve the next-hop connection information. In practice, many small and medium-sized businesses use a SIP-PBX that is authoritative for tens or hundreds of SIP AoRs. This SIP-PBX acts as a registrar/proxy for these AoRs for clients hosted by the SIP-PBX. UAs register with the SIP-PBX on behalf of the AoRs concerned. A SIP Service Provider (SSP) provides SIP peering/trunking capability to the SIP PBX. The SIP-PBX must be reachable from the SSP so that the SSP can route inbound SIP requests for the AoRs addressed to the SIP PBX, routing these requests to the SIP-PBX itself for onward delivery to registered UAs. Experience has shown that existing mechanisms are not always sufficient to support SIP-PBXs for small/medium businesses. Since a single SSP may support multiple thousands of such SMB SIP-PBX's, it is impractical and cost-prohibitive to manually provision their IP addresses in every SIP node along paths to those SIP-PBXs. Furthermore, IP addresses can be dynamically assigned and therefore can potentially change relatively frequently. In current deployments, dynamic reachability mechanisms based on the SIP REGISTER method are commonly used. Effectively, a single REGISTER request registers the AoR of the SIP-PBX, so that any out-of-dialog request targeted at a SIP URI for which the SIP-PBX is authoritative can be delivered from the SSP to the SIP-PBX. However, implementations of this mechanism vary in details, leading to interoperability issues between SIP-PBXs and SSPs, and the need for equipment to support different variants. The task of this working group is to to standardize a multiple-AoR registration mechanism for SIP that can be widely deployed by service providers at large scale. The solution will support AoRs with E.164 addresses at a minimum, although support for other classes of AoRs may be included. The solution will utilize existing SIP mechanisms to the extent possible, although it is anticipated that small protocol extensions are likely to be required, and hence a standards track (rather than BCP) deliverable is expected. The solution will accommodate existing SIP extensions relating to registration (e.g., Path, Service-Route [RFC 3608] and SIP-outbound) by ensuring that they are not precluded from use in the context of multiple AoR registrations. The solution will incorporate a compatibility mechanism to ensure a deterministic outcome when interworking with entities that do not support multiple AoR registration. The working group will coordinate with SIP Forum and other industry groups on requirements and will coordinate its work with other IETF working groups including DRINKS and SIPCORE.