at leaves a point-to-point con- nection permanently in place. 4In our old Advanced Mobile Phone Service (AMPS) days, we had about 1.5 handoffs per call, and the 1AESS analog switch that could handle 250,000 landline calls per hour only handled 100,000 cellular calls per hour. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Switching Capacity Switching Capacity components, whereas the subscriber data packets are routed to the landline data net- work, and SMS packets are routed to the SS7 network. The packets still may require processing. The base-station-to-MSC link may be a packet link, but its packets may not be the same format as the speech coder and land- line data network require. Packets are often encapsulated with an extra header to get them between the base station and the MSC. The packet handlers are a queuing system, and we have to know their specific ar- chitecture to do the queuing analysis in Sec. 23.3. The model tells us how likely a packet is to wait longer than some specified time t based on the characteristics of the packets and the queue. The time t is how long we are willing to wait for a packet to get through the packet handler. While this waiting time t may affect a data subscriber's Internet performance, the most important issue in determining t is how quickly packets have to be processed for the speech coding not to have gaps, assuming that the speech data come by packet. We can allow t to be longer only at the expense of lengthening the propagation delay voice calls in the MSC. If we try to make the speech propagation too short, then we run the risk of losing too many packets to queuing delay. 24.5 Speech Coding The speech coding process converts the low-bit-rate speech (QCELP for cdmaOne or cmda2000, AMR for W-CDMA) to standard telephone trunk PCM. Each wireless voice call requires one bidirectional speech handler. Ha