user manual

Configuring Headend Broadband Access Router Features
Telco Return
MC-524
Cisco IOS Multiservice Applications Configuration Guide
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
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.
IP network access
RADIUS dial
security server
Upstream
Subscriber
cable modem
HFC downstream
including TCD messages
25926
Cisco uBR7200
series
DHCP
TFTP
TOD
servers
Cisco network
access server
PPP connection between
remote cable modem
and network access server
established following
authentication
Headend or hub
PSTN
IP network