Where calls go between VoIP endpoints (e.g. SIP trunk to H.323 extension) there are two options: Direct and indirect media. Direct media does not use the server’s routing engine and hence the base capacity concurrent calls will apply.

Direct media is a configurable parameter for VoIP trunks and extensions with a default of active.

Indirect media will occur either where configured, or if direct media is not possible (even if configured). Some causes would be:

• VoIP traffic routed between the LAN1 and LAN2 interface

• Unsuccessful codec negotiation (including silence suppression, DTMF transport as well as basic codec support)

• A VoIP endpoint that does not support direct media

• Mismatch of RTP and SRTP

• Mismatched SRTP or SRTCP security settings such as no common cipher suite. These should be avoided if at all possible due to the limited indirect media SRTP capacity.

• Network Address Translation (NAT) traversal usually associated with Remote Worker phone deployments.

The above should be avoided if at all possible due to the limited indirect media capacity.