Gbps performance... or not?

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Nov 13th, 2003
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Case study:

Let's say we have a Cisco 7500 series box with GEIP line card (Gigabit Ethernet Interface Processor), and a 1 Gbps WAN link (layer 1 is DWDM) connected to it.

"The GEIP is based on the versatile interface processor 2-50 (VIP2-50) architecture and hence exhibits similar data throughput characteristics. The GEIP has a maximum aggregate throughput of 400 Mbps and a Layer 3 packet switching performance of about 110 Kpps, full duplex."

What maximum aggregate throughput means, at all? Aggregate because it's full-duplex? (200 Mbps in each direction)?

For example, if 1 Gbps link is utilised 100%, that means 1 GB rx + 1 GB tx (full duplex) = 2 GB of traffic, our 7500 box will just handle 400 Mbps? That's 20% of the paid bandwidth because aggregate link throughput is 2 Gbps and hardware throughput is just 400 Mbps?

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tbaranski Thu, 11/13/2003 - 10:32
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Aggregate just means total. The direction of the traffic probably doesn't matter -- I'd imagine it can do 400Mbps in one direction, 200Mbps in both directions, or anything in between.

So you won't get full utilization on a 1Gbit link. The GEIP+ can do 800Mbps, which is better but still won't give you full link utilization.

ligna Thu, 11/13/2003 - 23:55
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So I am still assuming right, paying 1 Gbps WAN link in such a setup is waste of money:

there are a backplane capacity limitations and line card data throughput limitations, even with the GEIP+ (800Mbps) cards. Theoretically and practically you can't get what you're paying for! Why is it called Gigabit Ethernet Interface Processor? If Top-of the line box (7500 series) can't handle it, how it works with 2600s and GE modules there? I love marketing

jasyoung Fri, 11/14/2003 - 08:10
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7500 was top of the line in 1996. It's supposed to be able to connect to and route between a wide variety of low to moderate speed medias like sync serial, async serial, token ring, ethernet, fast and gigabit ethernet, ATM, SONET, FDDI, IBM's ESCON, TDM voice, etc. I think it even used to have a 100VG AnyLAN interface. Its backplane is limited to about 1Gbps (1Gbps per side of the box on 7513) and you're just not going to get any more than that. That was the best of the technology at the time; even the 1Gbps speed is the "upgraded" speed.

The only 2600 that can take a Gigabit Ethernet module is the 2691. It's the very highest-end model of 2600. Also consider that if you stuffed the rest of that 2691 full of interfaces and filled them all with traffic aimed out of the NM-1GE, you still couldn't fill it up, because the rest of the interfaces aren't nearly gigabit speed.

tbaranski Fri, 11/14/2003 - 16:55
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The reason a GE module makes sense for the 7500 series is because the routers are capable of doing well over 100Mbps. So there's a large advantage to a GE module relative to an FE module, even if 100% utilization isn't possible. Given that the bandwidth difference between successive Ethernet flavors has historically been 10x, this type of thing is fairly common. Consider how many low-end routers have FE interfaces but can't route at 100Mbps -- they can do well over 10Mbps, so FE interfaces make sense.


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