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