which is a standard method to relay information from a host to a monitoring device. Most equipment that an SP owns and deploys supports SIP trunks for PSTN access support and SNMP-based monitoring. However, because of the complexity of the implementa- tion and the amount of network traffic that can be generated, SNMP might not be a long- term network management solution for SIP trunks. Several new candidates, in the form of XML-based messaging systems, are possible replacements for SNMP-based network monitoring solutions. Chapter 5: Components of SIP Trunks 75 Regardless of the method used for the transport of the status, the specific items that need to be monitored are similar. Some of the typical items monitored by the SP of a SIP trunk service, regardless of what specific piece of equipment is used, are shown here: CPU utilization: What is the average and peak CPU utilization of the various devices involved in the SIP trunking solution? Connectivity: What is the status of the interfaces? Are they UP or DOWN? How much traffic flows across them? Failure, traps, and warnings: Are there any failure, trap, or warning messages sent from any of the components of the SIP trunking solution? Active calls: How many active sessions exist on the component being monitored? This is an important measurement to ensure that the ultimate goal of providing an active SIP trunk services is accomplished. One of the areas that is most problematic with SIP trunk services that is not a major prob- lem with TDM trunk service is the capability to determine if a trunk is "UP." Because of the lack of connectedness of SIP trunks when compared with TDM trunks, there is no definitive way, as there was when monitoring TDM trunks, to determine a trunks active status (for example, if it is "UP"). In the TDM world, a Layer 2 keepalive, such as an SS7 File in Service Unit (FISU) or a Q.921 Layer 2 keepalive would send periodic messages to determine if a trunk was active could accept new calls. If these messages were either received with errors or 