SIP
Sizing SIP trunks is a challenge. IT architects tell Nemertes that as a rule, they budget 80 kbps per trunk to account for additional IP overhead for VOIP. In a one-for-one replacement of TDM PSTN trunks with SIP trunks, bandwidth costs for SIP trunking actually exceeded TDM costs due to the additional overhead required for SIP compared with 64 Kbps channels for TDM voice. Growing use of high-quality compression algorithms such as ITU G.722 and G.729 will allow SIP trunking adopters to reduce bandwidth requirements. As part of enterprise SIP trunking plans, IT managers need to make sure they understand what compression options are supported by both their providers, and their IP-PBX vendors, and what, if any impact compression will have on call quality.
