Ž . Computer Networks 31 1999 313–326 Two-way broadband CATV-HFC networks: state-of-the-art and future trends Stephen Perkins, Alan Gatherer ) DSPS R & D Center, Texas Instruments, Dallas, TX 75265-5303, USA Abstract Cable modems allow two way digital data transmission between households and a central neighborhood server. In this Ž . overview we briefly describe some of the common characteristics of the Hybrid Fiber Coax HFC operation as presented by Ž . several standards bodies both completed standards and works in progress . This includes a description and comparison of the media access control and physical layer operations of several competing proposals. Our desire is to give a concise but complete picture of the cable modem problem and the proposed solutions. References are provided for readers interested in further investigation. q 1999 Elsevier Science B.V. All rights reserved. Keywords: CATV data networks; Cable modem; DOCSIS; HFC; Hybrid fiber coax; MAC; MCNS; QAM 1. Introduction Cable modems allow transmission and reception of digitally modulated signals over coaxial cables in Ž . a cable television CATV network. CATV networks were originally designed for the one-way broadcast of analog television signals but new modulation schemes and protocols are required to support bi-di- rectional communication. To reduce the cost of equipment, cable companies want mass produced interoperable systems. To this end, the standardization of cable modem systems is occurring in several places. At the time of writing, several proposals have been submitted to different Ž standards organizations. The MCNS Multimedia Cable Network Systems, a limited partnership of ) Corresponding author. Tel.: q1-972-997-5278; fax: q1-972- 997-5693; e-mail: gatherer@ti.com. . Ž cable companies submitted the DOCSIS Data- . Over-Cable Service Interface Specifications pro- Ž posal to the SCTE Society of Cable Telecommuni- . cations Engineers, an ANSI accredited organization w x 6,12,14 and the IEEE 802.14 working group is currently in ballot on a submission to the IEEE 802 w x wx committee 10,11 . Two other bodies, DAVIC 9 Ž Digital Audio and Video Council, a consortium of . w x Ž manufacturers and the ITU 13 International Telecommunications Union, an international multi- . governmental standards organization , have standard- Ž . ized physical layer PHY specifications. While there are multiple standards being presented, the IEEE 802.14 proposal and DOCSIS documents do incorpo- rate the PHYs presented by DAVIC. Finally, several vendors are currently deploying proprietary solu- tions. In this tutorial, our primary goal is to describe the solutions converged on by the above standards organizations. When specific details are given, they 1389-1286r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-7552 98 00272-4