rcum- stances, we can consider retaining the current level of voice facilities for a while as the system grows. 39.8.2 MSC-to-PPDN links The packet pipes from the MSCs to the PPDN are just as critical for data service as the voice trunks are for voice calls. Unlike the single service of voice calling, wireless data calls come in a variety of rates and service levels. The packet links should be engineered for very low delay on all real-time services, in- cluding video calls. These services should be checked for any excess delay on the MSC- to-PPDN packet pipe. All services should have acceptable delay on these packet pipes. Even the back- ground services, those which can tolerate high delays, should have enough capacity on these links. Each packet service, whether for voice (VoIP), video, still images, or data, should have low enough delay from the MSC to the PPDN. Every packet service has a delay requirement, and the fact that some services allow higher delays is not a license for huge delays from the MSC to the PPDN. After all, the other links in the service chain are going to have delays engineered around the service requirements, and they are probably not expecting an extra delay here. 39.8.3 MSC-to-MSC links Links between MSCs are used for inter-MSC handoffs. Only pairs of MSCs that have dedicated transport links are able to have inter-MSC handoffs. Once these links are full, that pair of MSCs can have no more handoffs. It is important to measure the load these links because their congestion has a direct negative impact on inter-MSC handoffs. If these links are getting full, then it is time to diagnose the reasons and fix them. If cells 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 Increasing Capacity are handing off more than they should, then perhaps some parameters need to be ad- justed. Or pe