ormance. It is a pity to spend all the money we are spending on radio equipment and other base station equipment only to lose calls because we did not provision enough transport facilities. 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. Measuring System Performance for Growth Measuring System Performance for Growth There are some transport links where overflow is available. Dedicated transport for mobile-to-mobile calls can overflow to the PSTN. Links from the MSC to private net- works may be able to overflow to the PSTN if their facilities are full. However, most transport in our wireless telephone network is critical to system ser- vice. When backhaul links are full, or when links to the PSTN and PPDN are full, ser- vice is denied. If these trunks are too busy, then the system may need more facilities, or it may need service to some of the transport equipment. 39.8.1 MSC-to-PSTN links The voice links from the MSC to the PSTN are critical for voice traffic. When these links are full, voice call traffic is denied all over the wireless system. Blocking voice calls is bad for revenue because it turns away money-making calls and annoys sub- scribers who are paying for wireless service. These voice trunks should be traffic engi- neered for very low blocking. The voice links are full-rate 64-kbps pulse code modulation (PCM), so they can be traffic engineered according to Sec. 23.1. With the very high quantities of these voice trunks, we expect to be able to maintain low blocking and high occupancy during the busy hour. Because of the importance of the voice links to the PSTN, we should be watching their performance. We should have a plan in place if the voice facilities become full. On the other hand, if the voice links from the MSC to the PSTN are never more than 80 percent full, then perhaps we have more facilities than we need. Under these ci