One of the primary purposes of Converged Multiservice Access Platform (CMAP) is to squeeze more technology into crowded headends. Initiated by Comcast, CMAP combines cable modem termination system (CMTS) and edge QAM functions. (For more, click here
and here). CMAP also will help cable operators transition their networks to all-IP.

At a SCTE Rocky Mountain Chapter conference "Engineering for All-IP," Jorge Salinger, VP/Access Architecture with Comcast, discussed some of the benefits of CMAP and its IP capabilities.

Although cable networks today deliver both unicast streams (such as high-speed data and video on demand [VOD]) and multicast streams with switched digital video (SDV), most video is broadcast to multiple service groups. According to Salinger, "We’re developing the CMAP because we’re going to have a lot more unicast and multicast use as compared to broadcasting. Moving forward, both are going to be much more relevant."

Also more relevant will be adaptive bit rate (ABR) technology, used extensively for video streamed over the Internet to optimize it in real time based on the end user’s bandwidth and CPU capacity.

"In the cable industry, (ABR) is new, but we’re starting to use it as well," Salinger noted. “We may be required to send more than one version of a stream because different clients are going to be asking for different rates. If a multicast stream is being transported to a device and the client starts asking for a different rate, CMAP could send a different unicast stream. Existing CMTSs can do it, too, but will require denser architectures. More reasons for CMAP."

Rob Horner, architect/IP Video Systems with Cisco, commented, "A MPEG 2 transport stream is a ‘spray and pray’ approach, based on the source pushing video to a device with clearly defined behavior. But ABR flips that entire model on its head. The client is intelligent, and understands the conditions and the way it’s consuming that video. MPEG 2 is push model. ABR is a pull model."

Besides combining CMTS and edge QAM functions with CMAP, there are other aspects to consider for all-IP networks. Home gateways may play an important role. "Gateways are going to be extensively deployed for video over IP," said Salinger. "CMAP is important but not the only thing to reconfigure the network."

He also mentioned edge caching. Although it isn’t included in the CMAP specifications, "all vendors talking to us are talking about including caching in their implementations," Salinger said.

Comcast is planning a trial of CMAP operational readiness sometime this year and wants to begin testing new CMAP equipment in 2012. "The tools we use to configure CMTSs and edge QAMs will need to be adapted," explained Salinger. "Monitoring tools will have to be adapted. Configuration of the headend will be different. Folks in the field will see signals generated out of one box instead of two."

-Linda Hardesty

The Daily


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