Zenith Cable Modem - Zenith At Cogeco in Canada

Zenith At Cogeco in Canada

Cogeco in Canada launched with the 4 Mbit/s, external Rev D cable modem in roughly 1996, and by August 1997 had 2500 subscribers. The network was failing for 3 reasons:

  • The Zenith network is a pure bridged CSMA/CD Ethernet. It has no understanding of the Layer 3 ARP protocol. Thus ARP storms through the layer 2 switches used in the first headend designs would clog the network.
  • The layer 2 switches and layer 3 routers of the time did perform any QOS or rate limiting, thus a 4 Mbit/s input port on the Channelmizer could be flooded with up to 10 Mbit/s of traffic bursts.
  • The Cogeco network contained an unusual reverse path amplifier as part of the retrofit to accommodate return path. This particular amplifier contained a design defect whereby the pad and equalizer plug in modules would literally fall off the circuit board when the device was opened. A thermal incompatibility existed causing the holes for the parts to increase in diameter, while the pins would elongate and become smaller. This fault was documented and proven as a result of Cogeco’s first DOCSIS deployment with the Cisco uBR7246, MC11-FPGA linecard, and IOS 11.3(4)NA, which contained the “flap list.”

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