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Cisco CVA122/CVA122E Hardware Installation Guide
OL-0799-02 (05/2001)
Chapter 1
Product Overview
Cisco CVA122/CVA122E Cable Voice Adapter Description
Tips
Information about DOCSIS and EuroDOCSIS requirements and current specifications are
available at the CableLabs web site at http://www.cablelabs.com.
The Cisco CVA122/CVA122E Cable Voice Adapter uses its cable interface to connect to the CMTS over
the Hybrid/Fiber Coax (HFC) cable system. A personal computer (PC) connects to the
Cisco CVA122/CVA122E Cable Voice Adapter through either the Ethernet or USB interface.
The cable voice adapter then acts as an IP bridge, providing Internet access by forwarding traffic
between the PC and the CMTS. Subscribers can use the Cisco CVA122/CVA122E Cable Voice Adapter
to create high-speed, permanent access to the Internet, without the need for telco-based services such
as leased lines.
If supported by the service provider, the Cisco CVA122/CVA122E Cable Voice Adapter can connect to
two PCs by attaching a PC to each interface (Ethernet and USB). In addition, the cable voice adapter’s
Ethernet interface can connect to an Ethernet hub, and additional computers can then be connected to
the hub.
Note
To be complaint with the USB specification, the Cisco CVA122/CVA122E Cable Voice
Adapter does not support networking multiple PCs using a USB bridging hub.
In addition to providing DOCSIS connectivity, the Cisco CVA122/CVA122E Cable Voice Adapter can
optionally provide Voice over IP (VoIP) services, allowing subscribers to make telephone, modem, and
FAX calls over TCP/IP networks such as the Internet. These calls can be made to other VoIP devices,
or to telephone, modem, or FAX devices on the regular telephone network (the Public Telephone
Switched Network, commonly known as PTSN).
The Cisco CVA122/CVA122E Cable Voice Adapter can optionally be configured as an IP router, using
static routes and the RIPv2 routing protocol. When operating in routing mode, the cable voice adapter
can treat its cable, Ethernet, and USB interfaces as separately routable interfaces.
Bridging and routing operations are summarized in the following sections.
Bridging Operations
When acting as a DOCSIS-compliant cable modem, the Cisco CVA122/CVA122E Cable Voice Adapter
provides IP bridging for one or more PCs and other customer premises equipment (CPE). In this mode,
traffic from the cable voice adapter’s Ethernet and USB interfaces is transparently forwarded on to the
cable interface for transmission to the CMTS. Similarly, the cable voice adapter receives traffic on the
cable interface and forwards it to the PCs attached to the Ethernet and USB interfaces.
In bridging mode, the PCs must be assigned IP addresses in the same subnet as the CMTS. Typically, a
Dynamic Host Configuration Protocol (DHCP) server at the headend automatically assigns the IP
addresses to each PC that is authorized to connect to the Cisco CVA122/CVA122E Cable Voice
Adapter.
You can connect a PC directly to the Ethernet port, the USB port, or both ports; if supported by the
service provider, you can also connect an Ethernet hub directly to the Ethernet port and then connect
multiple PCs to the hub. In bridging mode, the Cisco CVA122/CVA122E Cable Voice Adapter supports
a maximum 254 PCs, depending on the maximum number allowed by the CMTS.
By default, one PC is supported for each cable voice adapter. The service provider can change this limit
by changing the MAX CPE parameter in the DOCSIS configuration file. However, the CMTS at the
headend can also enforce its own limit on CPE devices, and the CMTS limit overrides the MAX CPE
