hannel(s) for OAM. So do SONET and SDH. The solution for a LAN is comparatively straight-forward. The network management facility/LAN protocol analyzer becomes just another active station on the LAN. Network management traffic remains as any other revenue-bearing traffic on the LAN. Of course, the network management traffic should not overpower the LAN with message unit quantity that we might call network management overhead. WANs vary in their capacity to provide some form of communicating network man- agement information. X.25 provides certain types of frames or messages dedicated for network control and management. However, these frames/messages are specific to X.25 and do not give data on, say, error rate at a particular point in the network. Frame relay provides none with the exception of flow control and the CLLM, which are specific to frame relay. For a true network management system, a separate network management communication channel may have to be provided. It would have to be sandwiched into the physical layer. However, SNMP (described below) was developed to typically use the transport services of UDP/IP. (See Chapter 11 for a discussion of TCP/IP and related protocols.) It is additional overhead, and care must be taken of the percentage of such overhead traffic compared to the percentage of "revenue-bearing" traffic. Some use the term "in-band" when network management traffic is carried on separate frames on the same medium, and they use the term "out-of-band" when a separate channel or time slot is used such as with E1/T1. 21.6 NETWORK MANAGEMENT FROM A PSTN PERSPECTIVE 21.6.1 Objectives and Functions The term used by Telcordia (Ref. 12) for network management is "Surveillance and Control." The major objectives for network surveillance and control organizations are as follows: Maintain a high level of network utilization Minimize the effects of network overloads Supports the BOC's5 National Security Emergency Preparedness commitment There are three important functions that contribute to attaining th