This section overviews basic cable architectures associated with each of the main service types—data, voice, and video—and discusses Cisco products used in the deployment of these services. Cisco solutions make it possible for cable service providers to augment existing HFC infrastructures and introduce two-way cable IP data, voice, and video services. Since all services employ an IP-based backbone, much of the initial investment required can be leveraged among multiple services.
Basic Broadband Access Architecture
To evolve an existing HFC network for two-way services, the architecture for the cable network needs to have the following components:
• The high-speed network backbone transports data, voice, and video to external networks which support these applications
• The headends pass data, voice, and video between the backbone and hub/HFC network. Centralized equipment such as provisioning servers, OSS servers, and billing support system servers typically reside at the headend. If the cable service provider offers voice services, call gateways and call agent software are required at the headend
Reference Information Page
Cable IP Network Architecture Description 12-1
How to Get More Complete Product, Solution, Network Management, and Cisco IOS Software Information
12-4
Helpful Cisco Web Sites 12-4
Cisco Systems Overview 12-6
• The hubs/HFC network connect the subscriber premises to the
headend/backbone infrastructure. They convert the traditional digital packets (seen in the headends and on the backbone) into the RF format used to transmit the information through the fiber coaxial portions of the plant
• DOCSIS or EuroDOCSIS-compliant CPE reside at the customer premises and convert the RF data streams generated at the hub and carried over the HFC network into the usable data, voice, and video information supplied to the end-user. Examples of CPE include cable modems (CMs), set-top boxes (STBs), multimedia terminal adapters (MTAs), and VoIP telephones
High-Speed Network Backbone
A high-speed digital backbone network connects the network of a large cable operator to the rest of the world (in very large cable service provider networks, backbones also are used to carry data between different regions of the cable IP infrastructure). The backbone connects to other networks such as the PSTN, other cable system backbones, and Internet connection points. See Overview, page viii, for illustration of a large multiservice network.
Headend
The principle role of the headend is to bring external services—satellite video, off-the-air video, Internet data, and voice—into the cable operator’s access network. In some instances, several headends will be used in each region, each with somewhat different roles in voice, video content, and Internet connectivity. Typically, headends
Cable IP Network Architecture Description CH A P T E R 12 R EFEREN C E IN FO R M A T IO N
traffic between external sources and the internal network. Multiservice networks might also contain the Cisco ONS 15454 or Cisco ONS 15327, part of the Cisco Complete Optical Multiservice Edge and Transport (COMET) product portfolio. These products bring the capacity of the metropolitan market up to par with the core and overcome what has been referred to as a “services bandwidth barrier” that strands capacity in the core from reaching the end customer. Cisco Catalyst® switches can be used to route local traffic between the gigabit switch router and the servers—OSS, billing system servers, and so on—located at the headend. If a cable service provider chooses to offer voice services, a key component of the headend is the telephony gateway. This component gives the broadband network the ability to interoperate with the PSTN. Other elements in the headend include: IP/MPEG remuxes, MPEG compressors, analog receivers, satellite receivers/scramblers, and descramblers.
Hub/HFC Network
Hubs contain equipment that converts between the backbone format and the format required for a particular data, voice, or video access network. Internal components of the hub include modulators, receivers, scramblers/descramblers, remuxes, codecs, and cache servers. Hubs may additionally receive off-the-air video streams in analog format or digital video from satellite feeds.
At the center of the Cisco two-way hub architecture is the Cisco CMTS/router— the Cisco uBR7100 Series in small operations, Cisco uBR7200 Series in small-, mid- to large-sized operations, or the Cisco uBR10012 in large operations. The Cisco CMTS/router connects subscribers on the HFC plant to the backbone network through both local area network (LAN) and wide area network (WAN) interfaces. If traffic demands are high, more than one CMTS/router may be required based on the CMTS platform chosen. In some instances, a Cisco 10000 Series may be used to aggregate traffic before it is passed to the headend.
Multiservice networks must accommodate a mix of network support features based on packet type. Data is bursty, requiring error-free, high-bandwidth service on an occasional basis. Voice is time-sensitive, requiring a small amount of bandwidth all the time, and precise metering to assure quality reception. Video is both bandwidth-hungry and time-sensitive, requiring high bandwidth at a steady rate. Unlike data, both voice and video can accommodate low error rates with little impact on perceived quality.