SI-41 ANSI-41 is a signaling standard for wireless telephony that tells various parts of the wireless world how to communicate with each other. These signaling links almost uni- versally use Signaling System 7 (SS7) for telephone signaling. Chapters 14 and 15 de- scribe the architecture and function of SS7 and ANSI-41. ANSI-41 links are signaling links only; subscriber voice and data go on other facilities. There are two exceptions to this, the short message service (SMS) and its successor, enhanced message service (EMS), which send small packets of user data over ANSI-41, as described in Chap. 20. 5The reality of CDMA is that increasing traffic in one cell decreases the capacity of its neigh- bors, so there is some notion of community capacity we are not addressing here. 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. Telephone Transport Key Telephony Concepts ANSI-41 allows the MSC to communicate with Other MSCs for inter-MSC handoff signal management. The home location register (HLR) for roamer registration. The visitor location register (VLR) for roamer calls. A message center for short message service (SMS). The over-the-air activation function (OTAF) for over-the-air service provisioning (OTASP). This list doubtless will grow as wireless telephone systems add capabilities and fea- tures to meet customer demand. ANSI-41 operates on SS7 networks, which are designed so that each switch and each link run at no more than 40 percent capacity, allowing for one of a pair of redundant facilities to carry the load if one piece of equipment should fail. As a result, transport facilities carrying ANSI-41 systems must be designed and expanded to maintain suffi- cient excess capacity to meet the requirements of SS7. 13.2.3 MSC to MSC Voice and data links are required between MSCs for inter-MSC handoffs. These facili- ties are dedicated to handoff tr