prices. A new backhaul plan may be an opportunity to renegotiate some old transport lease contracts. Of course, reconfiguring a backhaul network of 500 cells is an administrative headache and a costly operation. The transport savings has to be significant enough to justify the cost of making the change. We certainly do not recommend doing a global backhaul optimization every time a few cells are added to the system. Rather, revisit- ing the backhaul plan from time to time may uncover cost-saving opportunities. Sumilarly, the thirty-first E-0 requires another E-1, and the seventeenth E-1 may require an- other E-3. 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. Adding Transport Adding Transport 44.2 Adding MSC-to-MSC Capacity As MSCs serve more traffic, they communicate more with their base stations via a backhaul network, they communicate more with the outside world, and they commu- nicate more with each other. The increase in inter-MSC communication means an in- crease in inter-MSC transport requirements. The critical inter-MSC transport need is inter-MSC handoffs. Handoffs require a dedicated link at the DS-1 or E-1 level. If there is no capacity on the link, then there will be no handoffs, and the CDMA air interface will suffer. As we monitor the inter- MSC handoff links, we will see them getting full, and we will know when more capac- ity is required. Mobile-to-mobile calls and roamer terminations are more complicated because they are cost-saving links rather than required transport. If the inter-MSC handoff links are completely full for half an hour each day, then our system is in trouble. However, the most economical solution for mobile-to-mobile calls may be to have significant periods during the day where we are overflowing traffic to the PSTN and paying the per-call charges. It is a cost tradeoff we are managing, the cost of dedicat