aSince large amounts of traffic on the Net orginates from modems which are typically plugged into terminal servers, which virtually all have ethernet interfaces, very large amounts of internet traffic have MTUs smaller than the 1500. The locations I know of that have FDDI and state the need for large MTUs are the large sites, that often have discount T-3 service provided at by CO-REN or direct federal subsidies. (Also dialup traffic would seem to be the eara of most rapid growth). I know there was some work done at the Sprint Nap at one point doing traffic research, but don't know if it included any type of size historgram. I've had several people assert that FDDI frame sizes are in fact common, or that at least DS-3 connected customers desire this (who are these people again?) I won't say it isn't true, because I don't have any real data, but I don't see any evidence that anyone else has any idea either. (With stuff plugged into the gigaswitch, I don't see a real easy way to find out either, perhaps we could file a FIOA with the NSA :) ) I believe the folowing to be true: 1. If there is little traffic over 1500 MTU, then switched, 100mbps, full duplex ethernet, will be cheaper more scaleable, and perform better than switched full duplex FDDI. A. Ethernet hardware is more common, thus greater economies of scale. B. Cisco's have full duplex ethernet now. C. The FEP card has TWO 100 mbps ports compared to one FDDI. (and costs less) D. I feel certain that far more packets have been switched in Cisco Cat 5000s, that Dec Gigaswitches, because real line networks other than the Internet also use these. Cisco might could provide some sales numbers to compare with Dec if anyone is interested. E. If you have lots of 10mbps switched connections going into the FDDI, you have a addtional overhead, of the translational bridging. I'd still like to see a number that shows I am wrong, even if it is not very meaningful.

Dtatacom tests were performed in the 10/100 setup. Obviously the Fast ethernet switches had an advantage over the FDDI switches since Fast ethernet and conventional ethernet work with the same frame types. FDDI switches on the other hand has to convert ethernet frames to FDDI frames and vice versa. Todays NAPs in most cases are not 10/100 set up. It is more like DS3/100/100 setup where routers are feeding traffic into the Gigaswitch using FDDI and since HSSI and FDDI is using same MTU size, no fragmentation is involved.

--Ismat

On Sun, 28 Apr 1996, Hank Nussbacher wrote:

...

On Thu, 25 Apr 1996 12:34:25 -0400 Curtis Villamizar wrote:

...

For many products, there is a big difference between how many interfaces physically fit in the card cage and how many actually work under a fairly heavy load. Have you tested a 12 port switched 100 Mb/s ethernet under load? The DEC gigaswitch has been tested under load and has held up so far under load. The Cisco 5000 may bridge better than it routes since there is no route change to deal with, but I'd be a bit worried about deploying without stress testing.

The problem for the major exchanges may soon be what to do when the gigaswitch runs out of bandwidth.

Curtis

The Feb 1996 issue of Data Communications ran a benchmark on these switches along with a few others. I will just summerize the Digital and Cisco info that they state:

Cisco Catalyst 5000 - Full duplex Ethernet, half duplex FDDI, full duplex fast Ethernet; Max: 96 Ethernet, 4 FDDI, 50 Fast Ethernet; Price: $22K for chassis, 24 Ethernet ports, 2 FDDI

Digital Gigaswitch - Ethernet, Full Duplex FDDI; Max: 12 Ethernet, 8 FDDI; Price: $21K for chassis, 24 Ethernet ports, 2 FDDI

Benchmarks:

a) % of frames delivered without loss (100% load on 40 ports): Burst size (in 64 byte frames) 24: Cisco 99% DEC 76% 62: Cisco 100% DEC 75% 124: Cisco 100% DEC 65% 372: Cisco 100% DEC 51% 744 Cisco 100% DEC 49%

b) % of frames delivered without loss (64 byte frames, 24 frame bursts on 40 ports): 70%: Cisco: 100% DEC: 81% 80% Cisco 99% DEC 79% 90% Cisco 99% DEC 85% 100% Cisco 99% DEC 75% 150% Cisco 99% DEC 22%

c) Per port thruput: 64 byte frame per second (24 frame bursts on 40 ports) Cisco: 4891 DEC: 4391

d) Latency (microseconds) - 64 byte unidirectional traffic across 100Mb backbone Cisco: 79 DEC 179

Bottom line: The Gigaswitch performed the almost the worst (Fibronics took that honor) and the Cisco performed the best.

Perhaps it is time to revisit the Gigaswitch technology?

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