for use in the PSTN. Voice gateways can reside within the access node (serving a local exchange via the V5.2 interface) or at the edge node. Some examples of voice gateways are the: VoATM gateway using ATM adaptation layer 1 (AAL1); VoDSL gateway using ATM adaptation layer 2 (AAL2); and VoIP gateway using H.323 (an ITU recommendation for multimedia applications) or the session initiation protocol SIP. 11.4.6 ROUTERS The backbone and access networks will require the edge node to provide some routing capabilities: routers close to the subscribers will take care of leased-line and IP-based virtual private network (IP-VPN) traffic; Example of resources in a media gateway QoS, incl Service plan adaptation Routing, (business based) Service layer numbering Switching Interconnect AAL1,2,5 Router, Border should MPLS LER gateway Diffserv Multi- trans- SLA, APN parent) IPv4, IPv6 party Echo Canc E.164 Appl. Access Produced packet logic Economy of service Signaling Security Charging Access layers H.248 Development track Ethernet IPsec (mutual dependence Prepaid GTP-U VS. service plan) Charging Others encryption identity Frame relay go to server Protocol store IP, ATM stack Core transport layers Billing Figure 11.12 A more complete view of the MGW resources Edge Nodes label edge routers (LER) and label switch routers (LSR) will handle connectivity toward a multi-protocol label-switching (MPLS) backbone network. egde routers will collect for example xDSL and WLAN traffic. Edge routers can contain LER/MPLS functions. They can be collocated or integrated with MGW. IP multicast routers will provide end users with streaming video or other multimedia applications. 11.5 SUMMARY Finally let us use the fundamental plans to sum up the main tasks of the MGW. The approach is the one presented in Chapter 8. The scope of resources is impressive according to Figure 11.12. In a way it is easier to say what is not included, such as service enablers, application logic. Packet Backbone 12.1 OBJECTIVES The packet backbone is the main solution re