The animated TECHTip Tutorial is available here.

PWE [Pseudo Wire Emulation] provides, among other things:

• Multi-protocol tunnels - Multi-Protocol Label Switching, GRE [Generic Routing Encapsulation], IPSec [Internet Protocol Security], etc.

• Emulated VC [Virtual Circuit]/channels inside tunnels (above) with multicast features
• Sub IP Layers for SONET or sub-wavelength transmission
• Attachment VC [Virtual Channels] based of Frame Relay model of DLCI [Data Link Connection Identifiers] mapped to emulated (act like) VCs.

DSG-DOCSIS(R) Set-top Gateway uses existing DOCSIS CMTS [Cable Modem Termination System] and RF [Radio Frequency] signals (70-130 MHz - Mega Hertz) to transport (send) Forward Channel Downstream service-system information OOB [Out-Of-Band] messaging to compatible STB [Set-Top Boxes].

OOB messages include:

• CA [Conditional Alerts] - including entitlements

• SI [System Information]
• EPG [Electronic Program Guides]
• EAS [Emergency Alert System]
• Other CATV operator messages

Here are some of the frequencies used in cable modem, cable telephony and cable transmission of television signals.

NOTE: Downstream frequencies overlap for this illustration as CATV operators have very different systems.

5-42 MHz - Mega Hertz - Back Channel

OOB Upstream or Reverse Channel internet and telephony from the customer.

50-860 MHz

Downstream or Forward Channel television channels to the customer.

70-130 MHz0

OOB Forward Channel Downstream service-system information to STB [Set-Top Box] or other devices.

These are some of the systems used in a CATV [Community Antenna TeleVision] system headend. The CMTS [Cable Modem Termination System] is the system used to provide cable modem and cable telephony services. Each CATV operator may also have unique systems such as a Class5 CO [Central Office] for interconnection to telephone companies. The remainder of this tutorial will review some cable modem technologies.

802.1D Spanning Tree protocols are used in a cable modem networks to isolate private bridged networks from each if other. However, spanning tree protocols can divert all traffic to other networks leading to the need for routers to limit traffic flow. Cable modem networks are essentially city-wide ethernet LANS [Local Area Network Systems] that can bridge LAN data like building LANs using HFC [Hybrid (mix of systems) Fiber Coaxial] copper wire instead of twisted-pair wire used by telephone companies. A HFC network is a “hybrid” or mix of coaxial copper wire and optical fiber placing fiber where customer density-population is cost-effective and using copper for existing customers. The Cable Labs is the technical research organization of the CATV industry manages the industry standard DOCSIS [Data Over Cable Service Interface Specification] which provides, among many other things, specifications for Multiple Downstream and Upstream topologies. Please contact the Cable Labs for more information.

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[tags]pwe,docsis,data over cable service interface specification,pseudo wire emulation[/tags]