Voice Over IP

ANOTHER LOOK AT THE VoIP PROTOCOL SUITE

Figure 7-2 shows a more detailed view of the VoIP protocol suite that is used to support the operations in Figure 7-1. Once again, the routers are not processing the VoIP traffic. Their job is to use IP to forward this traffic from user A to user B. In this simple example, three routers operate across four links between the users.

The lower layer protocols and interfaces differ, depending on the placement of the router. On links 1 and 4, the lower layer interfaces with the user nodes and the routers are V.90, HDLC, and LAPM. But, between the routers, on links 2 and 3, these protocols are not executed. They are replaced with another L_1 system, typically a DS1, DS3, or SONET trunk, and the two ATM layers: ...