Definitive MPLS Network Designs [Electronic resources] نسخه متنی

Figure 4-2. Telecom Kingland Telephony Transit Logical Architecture

[L2VPN]. If you want to know more about this resource, look up the code in the "References" appendix to find out specific information about the resource.

This voice transit approach offers very significant cost reductions. First and foremost, operational expenses have been reduced significantly because of lower site costs incurred by the much more compact technology of modern soft switches as compared to legacy Class 4 switches. Also, as illustrated in Figure 4-3, a reduction in the number of ports and transmission capacity is achieved. It results from the migration from a mesh topology (where every Class 4 switch had to have separate dedicated connections with every other Class 4 switch with which it was tandem switching) to a cloud topology (where each soft switch only needs to be connected to the MPC locally). Moreover, for voice traffic TK can take advantage of lower bandwidth costs per kbps that can be achieved through multiplexing over the very high-speed MPC.

A total of 64 VoIP trunk gateways are currently deployed. There are four gateways in each of the six Level 1 POPs and two gateways in 20 of the 50 Level 2 POPs.

Because Kingland was an early adopter of IPv6, TK introduced an IPv6 Internet access service to its portfolio a year ago to meet customer demand. TK is also planning to introduce an IPv6 VPN service next year.

Telecom Kingland POP Structure

Each Level 1 POP is composed of two backbone P routers that are connected to several other Level 1 POPs via STM-64 links and that support the STM-16 connections to Level 2 POPs.

In four of the six Level 1 POPs, the P routers are also connected to gateways providing external connectivity such as Internet peering points and gateways to TK's international network.

Each Level 2 POP is made up of two backbone P routers, which support STM-16 connectivity to two Level 1 POPs (or, in a few cases, support STM-1 connectivity to two different P routers of the same Level 1 POP).

Both Level 1 and Level 2 POPs host the edge devices providing customer connection to the MPC. For Enterprise services (as opposed to residential services and wholesale services), this includes the following:

mPE routers (offering IPv4 Internet and Layer 3 MPLS VPN services) that are connected to the two P routers via STM-1 links (or via STM-16 for a few high-speed mPE routers in Level 1 POPs).

Network Access Servers (NASs) and Broadband Access Servers (BASs) supporting remote access to Internet and Layer 3 MPLS VPN services. These devices are separate from the ones used for wholesale services because they offer a higher grade of service imposing different operational practices (such as reduced maintenance windows) and different design rules (such as lower port oversubscription). The NAS and BAS for Internet access are connected to the P routers via dual Gigabit Ethernet switches. The NAS and BAS for access to the Layer 3 MPLS VPN service are connected via dual Gigabit Ethernet switches to the mPE routers.

For wholesale services, the edge devices include a very large number of NASs and BASs also connected to the P routers via dual Gigabit Ethernet switches. The backbones from operators using TK's NAS/BAS wholesale services are connected to the MPC via SDH or Gigabit Ethernet for Internet peering.

For PSTN trunking, the VoIP trunk gateways are dual-attached to two telephony PE routers (also called PE-PSTN) by multiple STM-1 links. In turn, these telephony PE routers are attached to the two P routers in the POP by local STM-16 links.

The Level 1 and Level 2 POP designs are shown in Figures 4-4 and 4-5, respectively.