What was the inter-packet gap between pings? Were they pushing right up against each other, with some wanting to go out while others were still being output? What other traffic was the router trying to pump out, if any? I'm thinking you would need to have packets queued up waiting to go out to see the benefits.
Priscilla At 11:33 PM 10/1/01, Chuck Larrieu wrote: >A couple of weeks ago there were a couple of discussions on this board about >using multiple T1's to improve data throughput. If memory serves, there were >two possible ways to do this: 1) per packet load sharing and 2) PPP >multilink > >for no particular reason I decided to do a little study on PPP multilink. >Well, OK, I do have two particular reasons - an upcoming Lab and a customer >who is asking about this. > >So, I build a scenario as follows: > > serial0 token ring >R6--------R5-----------R4 > |--------| > serial1 > >to test throughput, I used extended ping, with multiple pings and various >size payloads, from a loopback on R4 to a loopback on R6. > >the routing protocol was EIGRP, done to assure per packet routing between R6 >and R5 as a control. > >My results were interesting, to say the least. unexpected, but so consistent >that there is no question, in my mind, anyway, about some of the assumptions >many of us make about various load sharing and multiplexing options. > >a summary of the results are using the Cisco router reporting of >min/avg/max round trip times - the middle number is the one to watch. > >packet size PPP multilink single serial link configured as PPP >multilink > >1000 24/24/132 20/20/104 > >1500 28/29/52 24/27/112 > >500 16/19/64 12/13/104 > >64 12/14/60 4/7/104 > >note that in every case, the single link, configured for PPP multilink, is >SIGNIFICANTLY faster than the dual link. > >Interesting. So I constructed some further experiments, using extended ping, >multiple packets of variable size - range 64 to 1500: > > PPP multilink per packet load share single T1 > > 8/17/136 4/17/136 4/17/144 > >these figures are from over 15,000 pings per scenario, so it is not a case >of random chance here. there is no difference whatsoever between the results >of a single serial link, per packet load sharing over two serial links, and >PPP multilink. what is most surprising is that a single serial connection >proves JUST AS FAST as a dual serial connection. > >Now what I conclude from this is an opinion that multiple T1's DO NOT really >do much for you in terms of more bandwidth. At least for the kinds of data >flows I am able to generate in the lab. Furthermore, PPP multilink is >actually harmful to throughput. So I gotta ask - is load sharing really >adding anything to the mix? Really? In real world scenarios and data flows, >where is it that you are gaining anything? > >Lastly, I set up a final scenario in which I sent 5000 byte packets. this >means fragmentation and reassembly would occur, because the MTU on all wan >interfaces is 1500 bytes. Here are the results when pinging 5000 times using >a 5000 byte payload: > >single serial link: 64/66/168 > >per packet load share: 64/64/168 > >ppp multilink: 48/52/172 > >note here that the load sharing scenario is slightly faster than the single >serial link, and that the ppp multilink is FAR AND AWAY faster that the >other two. I suspect the reason for this is efficiencies gained under the >multilink scenario when fragmenting and reassembling the oversized payloads > >In any case, I hope this presentation will lead to some good discussion of >bandwidth and results. would it be fair to suggest that peoples' efforts to >solve what they perceive as bandwidth issues by implementing multiple WAN >links is really a study in fruitless activity? > >Maybe I should have set up some IPX scenarios? > >Chuck ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=21697&t=21623 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
