MetaRouters
 PAGE  5











Voice and Video

Isochronous traffic such as voice and video is different from data.

  • Data traffic is bursty. Current routers take advantage of this fact and use buffers to statistically multiplex the traffic.

  • Voice and video traffic is periodic. Periodic traffic reduces the available buffering and link bandwidth. This increases the probability of blocking and accelerates the onset of congestion.

The key to designing a terabit router for voice, video, and data is to minimize the congestion by minimizing fabric blocking, output port blocking, hierarchical blocking, and maximizing broadcast efficiency.

  • Fabric Blocking: The links in multi-stage switching networks are shared. Some paths through the network can block other paths. Two paths through an eight port Butterfly network can block the other six ports. This blocking multiplies the effect of isochronous traffic. A MetaRouter based on 12 port routers reduces fabric blocking by a factor of six over a Butterfly network by spreading the traffic over six equivalent paths.

  • Output Port Blocking: Packets have a certain probability of colliding at the same router output port.

    • This probability runs away. The more packets there are trying to exit the same port at the same time, the greater the probability that packets will collide at the output port. The more packets collide, the more packets are delayed.

    • This probability compounds with each router traversed.

    The larger the module fanout and the fewer rows in the network, the lower the probability of a collision, the smaller the congestion, and the larger the effective voice and video bandwidth of the network. The probability that a packet will traverse a 532 port MetaRouter based on 12 port routers without a collision is 0.57 while the probability that a packet will traverse a 512 port Banyan or Butterfly network is 0.0037. The probability that a packet will traverse the MetaRouter is more than a factor of 100 greater.

  • Hierarchical Blocking: Many networks are organized in a hierachical manner. Only a certain proportion of the traffic can travel up through the hierarchy. This assumes a locality in the traffic. Unfortunately, Internet traffic has little locality.

  • Broadcast Efficiency: The larger the module fanout and the fewer rows in the network, the more efficient the broadcast and the less internal bandwidth consumed. A 64 port Butterfly requires 63 links to multicast a signal while a 64 port MetaRouter based on 12 port routers requires 6 links. This is  fewer links by a factor of 10.

 





















Home   Opportunity   About Terabit   MetaRouters  1  2  3  4  5  6   Contact Us   Site Map