1. Copyright 1999, S.D. Personick. All Rights Reserved. Telecommunications Networking II Lecture 37 Topics in 21st Century Networking: Cable Modems

2. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Modems What is the opportunity we are trying to address? -Utilize existing coaxial cable television infrastructure (that reaches most residences) to provide high speed internet access

3. Copyright 1999, S.D. Personick. All Rights Reserved. Why do we want to utilize existing infrastructures? Because the cost of installing a new infrastructure that can reach a broad base of potential customers would not be recovered during a period in which the number of actual customers is still small. I.e., you can’t make a credible business case for building a new infrastructure.

4. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Distribution Infrastructure Head End Super Trunk (cable or fiber) Distribution Node Trunk Drops to homes

5. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Distribution Infrastructure Head End Super Trunk (cable or fiber) Distribution Node Trunk Drops to homes Issues: noise, interference, distortion

6. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Modem Architecture Head End Router Cable modem Home LAN Trunk Super Trunk To the Internet TV sets Drop

7. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Modem Architecture Each cable modem shares a 6MHz channel on a cable system with a number of other cable modems. The data rate that can be delivered downstream (toward the customer) is roughly 6MHz x 3-6 bits per second per Hz of bandwidth ~ 18-36 Mbps The upstream (toward the head end router) communication can be done over the cable or using a telephone line

8. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Modem Architecture Technical/Engineering issues: The downstream communication data rate is much higher than upstream communication data rate…a problem for TCP connections Ingress noise, poor condition of cable plant and customers’ inside cabling

9. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Modem Architecture Practical issues Traditional cable engineering, installation and maintenance processes are not compatible with the complexity of cable modem/Internet technology

10. Copyright 1999, S.D. Personick. All Rights Reserved. Cable Modem Architecture Business issues Internet service providers want cable modem broadband access service to be unbundled from the provision of Internet services that utilize broadband access