Cable modems are neither required nor recommended for PC 97, but if a cable modem is implemented in a PC 97 system, it must meet the requirements defined in this section. For basic requirements for Plug and Play, power management, and driver requirements, see the "PC 97 Design for Network Communications" section later in this chapter.
Cable modems connected to a PC are one component in a system that cable TV operators use to deliver High Speed Cable Data Services (HSCDS) to cable TV customers. HSCDS provides two-way services (data flows both "downstream" from the cable operator's head end and "upstream" from the customer's PC).
Ideally, two-way HSCDS is delivered over 450-MHz and 550-MHz hybrid fiber-coax (HFC) cable TV distribution networks. Most of the current cable TV distribution network in the U.S. is 300-MHz, 350-MHz, and 400-MHz coax branch and tree networks.
In 1996, HSCDS delivery has primarily been confined to trial projects. In these trials, the cable modems used on customer premises are typically external to the PC with their own power supply. These cable modems are essentially IP routers. The cable modem's upstream connection is either a standard "F" coax interface or an ATM interface. The cable modem connection to the PC uses a 10BaseT interface (RJ45) to connect a twisted pair to a standard Ethernet network adapter.
For the next several years, it is expected that external cable modems will be included as part of the HSCDS service by the cable operator, much like set top boxes. In light of that, along with the absence of standards for cable modems, few PC vendors are expected to bundle cable modem hardware with their systems.
PC platform vendors can build PCs that are capable of using external cable modems by including a standard Ethernet network adapter in their PC systems. The PC platform should also have Microsoft TCP/IP software pre-installed.
HSCDS upstream data flow can be implemented on the predominant 300-MHz, 350-MHz, and 400-MHz coax branch and tree cable TV distribution networks by using telephone circuits for the upstream channel. This is a design alternative used today to accomplish HSCDS field trails with existing cable TV networks until more HFC networks are built.
There are a great number of design issues for cable operators as they upgrade their cable TV distribution networks to HFC and begin to deliver HSCDS. Even operators who have existing HFC networks must add equipment to that network in order to begin offering HSDCS. The speeds at which cable TV operators resolve these issues will determine the requirements for cable modems in homes and businesses in two years. Although HSDCS is primarily only in trials today, a majority of the cable operators in the U.S. are working on business plans for delivering HSCDS within the next two years.
PC platform makers must track the rate at which cable TV operators are resolving these issues and what are the best methods. The key design issues for cable modems for PC platform makers are cost, standards, and the evolution of cable modems from external to internal models.
Some cable modem vendors plan to implement the new IEEE 802.14 protocol when it becomes available. It should be well suited to the distances, data rates, and physical plant scenarios for HSCDS on cable TV distribution networks.
For basic requirements for Plug and Play, power management, and driver support, see the "PC 97 Design for Network Communications" section later in this chapter.
19. Support PC 97 requirements for network adapters
| Required |
The following requirements must be met, as defined in the "Network Adapter Basic Features" section earlier in this chapter:
20. Provide platform support for external cable modems
| Recommended |
Plan to support external cable modems by supplying a low-cost Ethernet network adapter as part of a PC until a low-cost internal cable modem becomes available.
21. Provide Ethernet card solution
| Recommended |
PC platform makers providing a standard Ethernet card to connect to an external cable modem can contribute to a low-cost solution at the customer's end for the HSCDS service today.
Cable TV operators are extremely sensitive to the cost of every component it takes to deliver HSCDS over an HFC cable distribution network. For example, operators currently want the cable modem on the customer's site to cost no more than $500. Cable modem vendors are building devices that cost between $395 and $1495.
This cost sensitivity can be understood in the context of what it costs cable TV operators to upgrade their physical plant to deliver HSCDS. Estimates are that cable operators have spent over $500 per customer to build the existing physical plant. Upgrades of coax branch and tree networks to HFC are estimated to cost another $150 to $400 per household.
22. Participate in developing standards
| Recommended |
Microsoft encourages cable modem vendors to contact Microsoft about the devices they are designing. Microsoft wants to work with the cable TV industry in establishing standards for the use of cable modems in HSCDS delivery networks.