Voice Over IP

UNDUE PROCESSING OVERHEAD

We are beginning to tread into waters that are beyond the subject of this book, but a few more comments can be made. The protocol stack in Figure 7-3 can be improved. The problem is that the backbone is running IP in each node. To get a sense of why this configuration is not efficient, assume that the traffic is coming into router 2's incoming interface on link 2. This router must execute AAL to reassemble the small ATM cells into the PPP and then IP data units. Then, IP performs a route lookup to make a forwarding decision. After these operations, the IP datagram is passed back to PPP, then AAL, ATM, and the outgoing L_1 interface. This process is repeated at each node in the backbone, and the time and resources expended ...