Inter-exchange media types

Wed May 1 06:37:07 UTC 1996

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?
>> 
>> ----------------------------------------------------------------------
>> Hank Nussbacher                  Manager, Internet Technology Programs
>> Telephone: +972 3 6978852        Vnet:     HANK at TELVM1
>> Fax:       +972 3 6978115        Internet: hank at ibm.net.il
>> ----------------------------------------------------------------------
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>> 
>> 
>

-- 
Jeremy Porter, Freeside Communications, Inc.      jerry at fc.net
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