Variable length signal units with a maximum size limitation. Plans to increase link speed to T1 and E1 speeds to be able to handle the increased demands required of the SS7 network. The first use of SS7 was not for call setup and teardown, but rather for accessing databases. 800 numbers provided a problem for switches in that they could no longer route based on area code. 800 number dialed, CO switch receives digits and routes the call to a remote database via data link.
Database responds with response message packet.
Database provides routing number for call and billing information. CO switch is then able to route the call in the conventional manner. When 800 number lookups via SS7 proved successful, the network was expanded to include the ability to do call setup, teardown, and other services. Gateways convert national versions of SS7 to ITU-TS versions so that the networks of all nations can interoperate with each other. If a company moved, they had to get a new number.