ers will need to re- quest change of service at the local offices where backhaul connections are terminated. Our logical diagrams show links from base station to MSC, but the reality of the back- haul network is that it is largely composed of leased lines routed through the PSTN. There are three other issues to address in developing IP backhaul network solutions. One is the issue of IP networks versus IP pipes. This is fairly easy to address. Even when the backhaul network is a network, it is a fan-out network, not an interconnected network with alternate routing. As a result, in terms of latency and jitter, it can be con- sidered a single-route packet pipe. The second issue is alternate transport, such as point-to-point microwave transmis- sion. Here, due to the layering of OSI protocols, the problem is relatively simple. The physical layer of the microwave channel does not need to change. It is a matter of putting IP over microwave instead of putting voice circuits over microwave. The prob- lem is analogous to the situation in the landline backhaul network, and IP over mi- crowave solutions have been in use for a number of years. The third issue is the issue of the capacity of the backhaul network. This will be ad- dressed in Chaps. 35 and 44. 19.5 Conclusion This chapter on hybrid voice-data networks completes the picture of voice and data con- vergence. Many books on convergence include video transmission and provide more in- formation about use of the cable TV network as data transport. A brief discussion of the role of video transmission in convergence is appropriate here. Including video data in the convergence picture does realize economy through the sharing of facilities, and video can be packetized for this purpose. For broadcast- quality video, the data rate is much higher than that for telephony, the sensitivity to latency is less (because the transmission is one way, and delay will not be noticed as easily), and the sensitivity to jitter is high. In many situations, such as the download of video clip