What a luck, there are some industry standard protocols such as PacketCable NCS 1.0, MGCP 1.0, and SIP 2.0. Most of these protocols are public.

There are 4 major "session protocols" within the world of VOIP.

	SIP - by IETF - standard - Session Initiation Protocol
	H.323 - by ITU-T standard
	H.248 = Megaco = MGCP - Media Gateway Control Protocol (from Cisco and Telcordia)
	IAX - non standard free proprietary protocol for Asterisk environments

The session protocol is responsible for the seamless forwarding of all dial information and codec negotiating between the gateways (routers or integrated VOIP phones) within the IP network. Click on the links above, to see more information about this complex technology.

Now, as you know something about the session protocols, dont think, you can select one of your choice. You must accept, what your hardware is offering to you. So your hardware and/or software must support at least SIP and H.323. The MAX 6000 cannot talk SIP, but H.323, the MAX TNT and APX can do it with TAOS 11.0.x.

If you call the gateway from a public coinphone (or a public phonebox), you get the question for your PIN. After entering the PIN, you get the question for the dial number. All this is done locally between the PSTN world and your gateway over SS7. After entering the dial number, you hear a new dial tone and then the SIP server is forwarding the dial request from local gateway over the internet to the remote gateway at the other end.

Now the permission must be confirmed and the codec for this single session must be negotiated and the dial number must be transferred to the other gateway. All this is done over a session protocol. If the other end answers the call, the session is established and this information is returned back over the session protocol too.

The session protocol handles each single session from one single ISDN channel of the local E1 (T1) connection to the other single channel of the remote E1 (T1) connection.

you may read the TAOS 11 upgrade documentation with its 312 pages. There is explaned what SIP is and how to configure this protocol.

Believe me, its not easy. But what a luck, the explanation has grown much better than old Ascend docs. One disadvantage of the old MAX 4000 and MAX 6000 docs has been, its was written from profesionals for professionals. It was really hard, to read these manuals as a beginner within an ISP.