Applications Overview

The system can be used for a number of edge aggregation applications. Two of the most common are:

• Private line aggregation
• xDSL session termination

Private Line Aggregation

A major application for the ERX edge router is for private line aggregation—the consolidation of multiple high-speed access lines into one access point. See Figure 1-1.

In this application, the service provider can use a single system to offer high-speed access (FT1/FE1 through T3/E3) to thousands of subscribers. The individual subscriber lines can be multiplexed into T3 lines by the service provider and fed into the system. (The system can also accept unchannelized T3 or E3 connections from high-speed users and channelized E1 connections directly into the unit.) Once the traffic is received, the system then handles all IP packet processing, including the assignment of QoS and routing policies. The packets are then routed into the backbone network.

Figure 1-1 Private line aggregation with the ERX system

The system supports a number of access and uplink methods; the most common pairings are listed in Table 1-1.

Table 1-1 Common access/uplink pairings 

Access	Uplink
PPP	ATM, Fast Ethernet, Gigabit Ethernet, or POS
Frame Relay
ATM

xDSL Session Termination

The system supports Broadband Remote Access Server (B-RAS) applications, as shown in Figure 1-2. In this application, the system handles the aggregated output from the digital subscriber line access multiplexers (DSLAMs). Directly connected to the subscriber premises, the DSLAMs handle the copper termination and aggregate the traffic into a higher-speed uplink. The output from the DSLAM is fed into the system through a DS3 or OC3 link.

Figure 1-2 B-RAS application

The system then performs several functions:

• PPP session termination and authentication checking through PAP or CHAP
• Coordination with DHCP servers and local IP pools to assign IP addresses
• Connection to RADIUS servers or use of domain names to associate subscribers with user profile information
• Support for RADIUS accounting to gather detailed billing information
• Application of the user profile to the user traffic flow, which could include QoS, VPN, and routing profiles

The output of the system is typically a high-speed link, such as OC3/STM1 to feed a core backbone router. Virtual routers can also be used to keep the traffic logically separate and to direct packets to different destinations. As shown in Figure 1-2, the packets can be directed to a CLEC, ISP, corporate VPN, or the Internet.

A large number of xDSL protocols are supported, including:

• IP/PPP/ATM
• IP/PPP/Ethernet/ATM
• IP/bridged Ethernet/ATM

See ERX Broadband Access Configuration Guide, Chapter 1, Configuring Remote Access to the ERX System, for information on configuring B-RAS.