Upstream Transmissions; Voice Operations - Cisco uBR924 Installation Manual

Cisco uBR924 Cable Access Router Description

Upstream Transmissions

The data transmitted in the upstream direction (from the user to the network) is typically much less than
that on the downstream direction, so a smaller bandwidth is allocated to it. The upstream transmissions
share a 200 kHz-wide to 3.2 MHz-wide channel in the 5 to 42 MHz range, providing a bandwidth of up
to 10 Mbps.
Depending on the quality of the physical plant and the CMTS used at the headend, users on a single
downstream can be allocated across several upstreams to ensure a responsive network. Service
providers can allocate different upstream bandwidths depending on the services purchased by a
subscriber. For example, a subscriber purchasing basic home service might be allocated a 128 kbps
upstream, while businesses purchasing premium services might be allocated a 384 kbps upstream.
The Cisco uBR924 router receives the upstream data from the CPE devices to which it is connected. It
modulates this data for transmission on the coaxial cable system to the CMTS. The CMTS then routes
the data to the appropriate destination (local server, Internet, and so forth) through its WAN interfaces.
All DOCSIS cable modems use a request/grant mechanism to obtain bandwidth on the upstream. The
CMTS grants the bandwidth according to the requestor's level of service, ensuring that the cable modem
is not exceeding the maximum bandwidth for upstream transmissions that has been specified by the
subscriber's service agreement.
End-to-end throughput varies based on the design and loading of network components, the
Note
mix of traffic, the processing speed and interface of the host server(s), the processing
speed and local Ethernet performance of the subscriber's computer, as well as other
parameters. Because the network can be configured to support multiple levels of service
with different performance requirements, the subscriber's service level agreement also
affects throughput. DOCSIS also specifies fundamental performance limitations to ensure
that the majority of subscribers experience good performance, rather than permitting a few
users to consume the entire capacity.

Voice Operations

When using a voice-enabled Cisco IOS image, the Cisco uBR924 cable access router supports
Voice over IP (VoIP), which transmits voice and fax calls over a TCP/IP network such as the Internet.
Depending on the services purchased from the cable service provider, subscribers can place and receive
calls without using the local exchange carrier.
The router supports two simultaneous voice and fax calls from each subscriber site, but multiple
telephones and fax devices can be connected to each of the router's two VoIP telephone lines (provided
the 5 REN limit for each telephone line is not exceeded). Telephones at each subscriber site must
support touch-tone dialing; rotary dialing is not supported, nor are special telephone features such as
call waiting, forwarding, and conferencing.
Subscribers can connect standard telephones and fax machines to the Cisco uBR924 router; IP
telephones are not required. Depending on the voice network set up by the service provider, subscribers
can place calls to numbers that are in the existing telco network; the called party does not have to be
using VoIP telephone service.
Fax devices—standard Group III and computer-based Group III machines up to 14,400
Note
baud—are supported in Cisco IOS Release 12.0(5)T and higher voice-enabled images. In
general, fax/modem cards are not supported over VoIP links.
Cisco uBR924 Router Hardware Installation Guide
1-10
Chapter 1 Product Overview
OL-0338-01 (3/2000)