Cable modems are not required on servers. If they are implemented, they must meet the requirements in this section.
Cable modem provides two-way services: Data flows downstream from the cable operator’s head end and upstream from the customer’s PC. At the head end, the cable data system is terminated by the cable modem termination system (CMTS), which terminates the upstream and downstream radio frequency (RF), MAC layer, and possibly Layer 3 protocols from the cable side. CMTS provides the internetwork connection between the cable system and the rest of the network at the head end. CMTS can be implemented on a proprietary hardware platform or a PC platform running Windows NT to provide different networking functions such as routing, Quality of Service (QoS) support (such as RSVP), and so on.
Some implementations transmit upstream using narrow-band networks such as ISDN or analog modem, but as cable companies upgrade their networks, an increasing number of RF return modems, for example, two-way modems, are being deployed. Two-way modems are preferred, because they are always connected, perform better, and do not tie up phone lines or require modem banks.
The three current cable modem specifications are:
Industry support for DOCSIS is growing rapidly in North America. In present form, its upper layers fully describe IP traffic encapsulated by 802.3/DIX Ethernet framing. ATM is left for future study.
External Ethernet DOCSIS cable modems provide IEEE 802.1d bridging for one or more Customer Premises Equipment (CPE); a PC attaches to them indirectly through its 10BASE-T network adapter. Integrated cable modems attach directly to the PC over buses such as USB, PCI, and IEEE 1394, and require a vendor-supplied NDIS 5.0 miniport driver. This driver exposes an 802.3/DIX Ethernet adapter interface to the operating system and it interfaces to the cable modem hardware using the appropriate bus (PCI) or bus interface driver (USB or IEEE 1394) at its bottom edge.
In contrast to DOCSIS, both the 802.14 and the DVB/DAVIC efforts are focused on using ATM, typically implementing an ATM adapter interface and using an NDIS 5.0 ATM miniport driver.
Recommended
An integrated cable modem should be used for servers. This recommendation means integrating everything from the cable modem’s physical interface layer, such as an RF coax connector, up through a standard PC 802.3/DIX Ethernet or ATM adapter MAC interface onto a single device. In other words, the software perceives the integrated cable modem as a standard Ethernet or ATM network adapter.
An example of this is a USB-attached DOCSIS implementation that integrates cable modem Physical Media Dependent (PMD), downstream convergence, cable MAC, link security, 802.3/DIX MAC “adapter” filtering, and USB device interface functions in the same box. Similar devices can be implemented that are attached using PCI or IEEE 1394 buses.
Required
For the integrated cable modem, the following network adapter requirements must be met:
For the integrated cable modem exposing an ATM interface, the following requirements must be met as defined in “Network Adapter Requirements” earlier in this chapter:
For the integrated cable modem exposing an Ethernet interface, the following requirements must be met as defined in “Network Adapter Requirements” earlier in this chapter:
Required
Refer to ATM Adapter requirements for ATM-specific requirements if an ATM/cable modem solution is implemented.