on register (HLR) prior to establishing the call, the HLR can identify the current location of the call in a different LATA. The HLR provides the SS7 network with the temporary listed directory number (TLDN) of the user terminal in a different LATA. The SS7 network can then contact the MSC serving the user terminal through its TLDN, and the call can be connected directly from the callING party's local office to the serving MSC without routing through the LATA of the home MSC. The voice connections from the MSC to the PSTN are full-rate links, 64-kbps pulse code modulation (PCM) links. This is the format the PSTN uses for voice calls at this time, so the conversion from our low-bit-rate packetized voice channel to a full-rate PCM channel takes place in the MSC. The links may be u-law encoded DS-0 links or A-law encoded E-0 links; they are in the form expected by the landline telephone network. The bad news is that all these voice links are full-rate trunks. The good news is that the MSC can be centrally located to have cheap transport available. There may be a tradeoff between backhaul expense and other MSC transport, but the MSC can be placed close to a point of presence (POP) in the PSTN to reduce cost. 2We will be casual and refer to a user terminal being in an MSC region. The user terminal is served by a base station in the MSC region, but we can skip the base station in our discussion of MSC transport. 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. MSC Transport Planning MSC Transport Planning The first job of MSC-to-PSTN facilities provisioning is to figure out the total voice de- mand for the busy-hour for all base stations served by the MSC. We may need to ana- lyze different groups of subscribers and evaluate their behavior and calling patterns to determine what the busy-hour traffic looks like. The mall traffic may be 20,000 erlang