Cisco Systems uBR7200 manual MC-524, Tod

Configuring Headend Broadband Access Router Features

Telco Return

Cisco uBR7200 series input/output (I/O) controller or applicable port adapter. Upstream data is through a telephone modem typically connected to an analog telephone line. (The telephone modem can be external or internal to a cable modem, or a cable modem card in a PC, based on the third-party cable modem vendor.) Telco return gives cable companies that have not upgraded their cable plants or specific service areas to support two-way RF transmission the ability to offer fast downstream data services via the cable plant and upstream transmission via the PSTN.

Figure 108 illustrates a telco return application.

Figure 108 Telco Return Network Diagram

IP network access

RADIUS dial	Cisco network
	access server
security server

PPPconnection between remote cable modem

and network access server

established following

authentication

PSTN

Upstream

IP network

Headend or hub

DHCP

TFTP

TOD

servers

Cisco uBR7200

series

HFC downstream

including TCD messages

Subscriber

cable modem

25926

Downstream traffic must be precluded by Telephony Channel Descriptor (TCD) messages to enable upstream telco return traffic. TCD messages contain information necessary for the telco return cable modem to access the headend/ISP network access server (for example, a Cisco AS5300 or Cisco AS5800) over the PSTN.

TCD packets contain three critical telco return elements:

•Up to three dial telephone numbers for the telco return cable modem to use when attempting to connect to the headend network access server

•Username or MAC address information

•Authentication password(s)

When connected, the network access server feeds the subscriber username and password to a RADIUS dial security server. Access is granted or denied. When access has been attained, the network server sets up a PPP negotiation and connection.

Cisco IOS Multiservice Applications Configuration Guide

MC-524