ATM meta-signaling is used for dynamic connections. These are made on demand are released when transmission is complete. Both point-to-point and point-to-multipoint configurations can be supported. The alternative to dynamic connections is permanent connections, which are established at the time of installation. A permanent connection is just that; it remains connected all of the time, unless there is a failure. This is analogous to permanent virtual circuits.

Q.2931 defines the signaling messages used to establish, maintain, and release connections at the UNI. The public network will not use Q.2931; it uses SS7 instead. The SS7 protocol supports Q.2931 through the Broadband ISUP protocol (BISUP). Q2931 was derived from the ISDN signaling protocol, Q.931.

ATM will require much more complexity than existing signaling. For example, if a caller initiates a voice call, a signaling message is generated to establish a connection for the voice. If the caller then activates a camera for videoconferencing, another connection must be established for just the video segment of the call. Both connections must be correlated and synchronized.

Broadcast signaling virtual channels support connection establishment for applications where the same data must be sent to multiple destinations. There are two types, general and selective. General allows signaling to be sent to all endpoints at the user interface (not all endpoints within the network). Selective allows the network to broadcast signaling to endpoints which meet a particular service profile. Both general and selective are unidirectional, sent from the network to endpoints at a user interface.

This means that ATM could place significant demand on the existing SS7 network used within the NNI. The BISUP protocol hasbeen defined to support these ATM services and is still evolving. This is also the reason for expanding the capacity of the SS7 links beyond the present 64kbps (in addition to requirements being placed on SS7 to support more database applications.)

Many ATM books may declare that SS7 is not required anymore or that it is unclear what role SS7 will play in the ATM world. However, the RBOCs are already busy planning expansions to their SS7 networks because they envision increased demand on SS7 services. The SS7 network provides much more than connection establishment through the public network. It also supports database access for telephone switches providing Intelligent Network solutions, cellular applications, and now local number portability.

SS7 may remain a mystery to many in the data world mainly because it has always been an obscure telephone company technology. It is best understood by those directly involved with telephone networks (and in many cases not well understood even there). One thing is certain, SS7 is not going away, and ATM signaling will not replace SS7. ATM signaling is designed to meet signaling requirements at the UNI but it does not provide the services required of the NNI.

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