• United States
by Steve Taylor and Larry Hettick

Enabler for voice over cable

Jul 07, 20032 mins

* An underpinning of voice over cable explained

We mentioned recently that Cox Cable says it already has 750,000 customers making and receiving millions of calls per day using its telephone service. Many among us quickly dismiss this significant start as limited to a residential market segment, and one that’s willing to use voice over cable with a level of service that would not be acceptable for business users.

However, cable technology is rapidly maturing – so that the same reliability and quality of service you’ve come to expect from traditional voice services will soon be available for voice over cable.

One of the key ingredients for providing excellent support for voice over cable is the DOCSIS 1.1 specification. According to Cisco’s Andrew Page, in his paper “Business Considerations of a DOCSIS 1.1 Migration,” offering high-quality voice-over-cable services requires support for DOCSIS’s Unsolicited Grant Service (UGS). He explains:

“When a voice-enabled cable modem initiates a VoIP call, a UGS service flow is activated through the packet classification process. This UGS would be configured to assign fixed-sized data grants at periodic intervals to and from that cable modem, without the cable modem having to contend or request bandwidth during a voice call. For the duration of the VoIP call, the UGS would be dynamically activated. Upon completion of the call, the UGS would be torn down, and the cable modem would revert back to its contention-based method of requesting bandwidth. Thus, VoIP packets may be delivered over a DOCSIS 1.1 infrastructure with guaranteed bandwidth and jitter characteristics, providing users with superior telephony service.”

DOCSIS 1.1 offers many other enhancements over basic DOCSIS 1.0, including better VPN support. If you’re interested in beefing up your knowledge of the state of the art for VoIP over cable, we’re supplying links below to Page’s paper, plus another that focuses on availability issues.