SIP is increasingly becoming established as the basis for modern real-time communication in IP networks. Unified Communications (UC) and collaboration, IP telephony, video streaming, camera surveillance, intercoms, paging systems, and audio recordings increasingly rely upon SIP and RTP for switching and transmission.
The NAT (Network Address Translation) typically carried out by the access router at the edge of the LAN presents a barrier to SIP communications. This is because of the addresses transmitted during SIP signaling and also because of the dynamically negotiated media sessions and the UDP-based RTP connections that depend upon them.
Restrictive firewall configurations prevent communications even where client/server-side mechanisms such as STUN, ICE and TURN are used to overcome NAT.
The SIP ALG for LCOS detects SIP connections and the RTP-based media streams that they depend upon and transforms these in line with the NAT rules in the access router.
Also, the SIP ALG monitors the bandwidths of the SIP connections and so provides QoS.
