dean@pico.oz (Dean Economou) (08/20/90)
I've read in the cisco "Company Backgrounder" that the cisco router uses Multibus. Also, in some postings to this newsgroup I've seen mention of Multibus. Does this mean that the network interface cards for the router are using Multibus I? Thanks, Dean Economou .
BILLW@mathom.cisco.com (WilliamChops Westfield) (08/20/90)
Does this mean that the network interface cards for the router
are using Multibus I?
Yes, that is what it means. The newer AGS+ routers, designed to
handle multiple FDDI rings, MANY ethernets, T3, and so on, also have
another high speed bus (the cBus) that has a continuous throughput of
up to 533 Mbit/S.
To answer the common questions:
1) Isn't Multibus 1 a little slow?
Well, a little. The full bus bandwidth is 160 Mbit/s. This makes it
fine for most interfaces. Also, the cisco architecture avoids copying
data over the multibus whenever possible. With the multiple interface
cards (MCI and SCI cards each have 4 interfaces) a packet incoming on
one interface due to be routed out another interface on that card
never traverses the multbus at all. This explains the difference
between the inter-card and intra-card packet rates that show up in
Scott Bradner's benchmarks, for example. The newer boards (FDDI and
six port ethernet are currently available) use the cBus for their
data transfers to oter cBus boards.
2) Isn't Multibus 1 sort of dead? You can't find the latest interfaces
the way you can get them from 3rd party VMEBus vendors, for example.
This is a small problem. Fortunately, we have enough hardware
expertise to design most of our own interfaces. Unfortunately for our
competitors, the characteristics that make a good (VMEBus, MultiBus 2,
EISA, etc) interface for a computer do not necessarilly make it a good
interface for a router (the primary difference being that a router
rarely looks at the data in a packet). By designing our own boards,
we get to take the application into consideration. Sometimes we even
end up yelling at the chip vendors, who also have a very host-oriented
view of the world.
Bill Westfield
cisco Systems.
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