This Standard is broadly applicable to the evaluation of any equipment that terminates or routes traffic using the Internet Protocol. This Standard can also be used to evaluate media streams or other protocols carried over IP networks. Examples of the types of equipment that can be evaluated using this model include: ? IP-connected endpoints: o IP network devices (such as: user agents@ call agents@ media servers@ media gateways@ application servers@ routers@ switches@ etc.) o IP video (IPTV@ video conferencing@ telepresence@ etc.) o IP phones (including soft phones) o IAF (Internet Aware Fax) ? PSTN-connected devices through IP gateways: o POTS through Voice-over-IP (VoIP) gateways o T.38 facsimile devices and gateways o V.150.1 and V.152 (voiceband data@ VBD) modem-over-IP gateways o TIA-1001 and V.151 textphone-over-IP gateways The IP network model can be used in two ways: ? Test an IP stream under simulated network conditions ? Test an IP stream in real time using hardware emulation of the network model. The IP network model can be used to study and to understand: ? the interaction of different traffic mixes ? the effects of QoS and queuing on different types of traffic ? packet delay variation and packet loss. Whether in software simulation or real-time hardware emulation@ users can select from several test cases specified in this Standard. Users can optionally define their own test cases. This model has the following limitations: ? Some VoIP networks may utilize PSTN at one or both ends of the connection through a media gateway. This model only addresses the IP portion of the network and does not address the PSTN portion of the end-to-end connection. ? The network model represented in this Standard does not model all possible connections that can be encountered between devices. ? This Standard only specifically includes GPON and DSL access technologies. Characteristics of other access technologies such as CATV and wireless are for further study. ? Abnormal events such as link failures and route flaps (and the packet reordering that such events can cause) are not included in this Standard. ? The standard test cases use streams of interfering traffic that were captured on live networks. While realistic@ they are still just examples; users could substitute their own files of interfering traffic. ? The LAN-to-LAN test cases of TIA-921-A are now modeled as two cascaded ANSI/TIA-921-B core-to-LAN segments. See section 6.3. ? The IP network model presented herein is based on an informal survey of anonymous IP service providers and IP network equipment manufacturers in the 2010 timeframe and will continue to evolve as more statistical information becomes available and as the IP network evolves.