Information Technology Reference
In-Depth Information
relates to the office size and average call volume. As businesses grow, you can consolidate
the multiple analog connections into one or more digital T1 or E1 connections, as shown
in Figure 1-10.
Analog
Connection
Digital
Connection
Home Office
Midsize Office
PSTN
Multiple Analog
Connections
Multiple Digital
Connections
Small Office
Large Office
Figure 1-10
Connections to the PSTN
In the PSTN lies a network of networks, similar to the Internet, which connects offices
from multiple telephony providers together into a massive worldwide network. For all the
telephony providers of the world to communicate together, a common signaling protocol
must be used, similar to the way TCP/IP operates in the data realm. The voice signaling
protocol used around the world is SS7.
SS7 is an out-of-band (CCS-style) signaling method used to communicate call setup, rout-
ing, billing, and informational messages between telephone company COs around the
world. When a user makes a call, the first CO to receive the call performs an SS7 lookup
to locate the number. Once the destination is found, SS7 is responsible for routing the call
through the voice network to the destination and providing all informational signaling
(such as ring back) to the calling device.
Note:
SS7 is primarily a telephony service provider technology. You do not typically
directly interface with the SS7 protocol from a telephony customer perspective.
