r Comments) in the general SIP-related area. Check the following RFCs for your RFP: RFC-3261 B2BUA as defined in RFC-3261 RFC-1889 (RTP) RFC-2833 (Telephone Event) RFC-2976 (Info) RFC-3204 (MIME Support) RFC-3312 (Preconditions) RFC-3313 (Media Authorization) RFC-3326 (Reason Field) RFC-3327 (Path) RFC-3329 (Security Mechanism) RFC-3420 (Sipfrag) RFC-3262 (PRACK) RFC-3264 (Offer/Answer) RFC-3265 (SUBSCRIBE/NOTIFY) RFC-3311 (UPDATE) RFC-3323 (Privacy) RFC-3325 (Private Extensions) RFC-3372 (SIP-T) RFC-3407 (SDP Simple Capability Declaration) RFC-3428 (SIP Extension for Instant Messaging) RFC-3515 (REFER) RFC-3551 (RTP Profiles for Audio and Video) RFC-3581 (SIP Extension for Symmetric Response Routing) RFC-3608 (Service Route Discovery) RFC-3680 (Event Package Registration) RFC-3840 (Indicating User Agent Capabilities) RFC-3842 (Message Waiting Indication) 168 SIP Trunking RFC-3853 (S/MIME Advanced Encryption) RFC-3891 ('Replaces' Header) RFC-3892 (Referred by Mechanism) RFC-3903 (Event State Publication) RFC-3911 ('Join' Header) RFC-3966 (URLs for Telephone Calls) RFC-4028 (Session Timers) RFC-4566 (SDP) Session Timers Session Timer is a keepalive mechanism for SIP sessions. User Agents (UA) send periodic re-INVITE or UPDATE requests to keep the session alive. The interval for the session refresh requests is determined through a negotiation mechanism. If a session refresh request is not received before the interval passes, the session is considered terminated. You need to check with your SBC vendors to see if it supports following timers: Media supervision/fault timers (initial, subsequent, and max session) Signaling (SIP max session timer) Quality of Service Quality of Service (QoS) is a significant issue in VoIP network. The concept is how to guarantee that packet traffic for a voice or other media connection will not be delayed or dropped due to interference from other lower priority traffic. You need to know how the SBC behaves with latency, jitter, packet loss, and burstiness of the network: Does the product