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Re: MCI [ATM overhead]
by bajaj＠bellcore.com 21 Mar '96

21 Mar '96

>> There's beginning to be some expectation that there will be a transmission >> capacity crunch in the carrier's Sonet nets, and this ~25% ATM cell tax may >> be looked at carefully as packet over Sonet solutions emerge. > I.e. a dual clearline DS-3 actually carries as much user data as OC-3c ATM. > Which, incidentally, was why SprintLink backbone design is easily expandable > to dual links (that includes carefully considering implications for routing). > Sean presented that design on NANOG a year ago, BTW. Funny thing, the design > is expandable beyond that, too, so OC-3 ATM is already obsolete. > > --vadim Other than the SprintLink design Vadim mentions above, what other alternatives are emerging for high bandwidth IP transport? Is anyone implementing PPP over SONET (RFC 1619)? Shikhar

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Re: MCI [ATM overhead]
by Wolfgang Henke 20 Mar '96

20 Mar '96

johnc(a)msc.edu (John Cavanaugh) writes: > You can find a paper that addresses this question at > > http://www.msci.magic.net/docs/magic/overhead.ps or > fte:ftp.magic.net/pub/magic/overhead.ps > > It covers OC-3c, OC-12c, 100 and 140 Mbps TAXI, and DS3 framing, and > gives the effective bandwidth at each layer. Thank you for the reference. I will certainly check it out. Here is a little table which I hope will help ISPs planning to upgrade bandwidth: SONET (Synchronous Optical Network) speeds given in Mbps nominal w/o Sonet ATM TCP/IP overhead OC-3 STS-3c 155.520 149 122 137 future net backbone OC-12 STS-12c 622.080 599 488 549 OC-48 STS-48c 2488.32 2396 1953 2197 current telco backbone OC-192 STS-192c 9953.28 9585 7813 8788 on single mode fiber or multi mode fiber or CATV 75 ohm coax (the lower speeds) Additions and corrections are welcome. Wed Mar 20 07:56:41 PST 1996 http://www.whnet.com/wolfgang/sonet.html > John Cavanaugh EMail: johnc(a)msc.edu > Minnesota Supercomputer Center, Inc. johnc(a)cray.com > 1200 Washington Ave. S Phone: +1 612 337-3556 > Minneapolis, MN 55415 FAX: +1 612 337-3400 Wolfgang Wolfgang Henke wolfgang(a)whnet.com . http://www.whnet.com/wolfgang/ WH Networks ... ftp.whnet.com /pub/wolfgang 2672 Bayshore Parkway Suite 503 ....... +1 415 390 9316 Mountain View CA 94043 ................... fax +1 415 390 9317

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Re: MCI [ATM overhead]
by Wolfgang Henke 20 Mar '96

20 Mar '96

Jim Forster <forster(a)cisco.com> writes: He's talking about the overhead due to carrying variable length IP packets in fixed length ATM cells. Consequently the last cell of an AAL5 frame will contain 0 - 39(?) bytes of padding, which is wasted bandwidth. Assuming random length distributions (which they're not), the average waste is about 20 bytes per packet. My rough estimate, based on an average packet size of 200 bytes (used to be correct, not sure anymore), is that the waste due to cell padding is about 10%. Due to the highly skewed packet size distribution the actual overhead might vary substantially. Note that this 10% is on top of the ~10% overhead due to the 5 byte ATM cell headers (5/53 ~= 10%), and various other overheads (some of which are also present in frame over Sonet schemes). There's beginning to be some expectation that there will be a transmission capacity crunch in the carrier's Sonet nets, and this ~25% ATM cell tax may be looked at carefully as packet over Sonet solutions emerge. Great. Let's estimate the ATM bandwidth available on an OC-3. With STS-3c SONET at 155.520 Mbps it gets reduced to 149.760 Mbps due to section, line and path SONET overhead. Next we reduce 10% due to 20 bytes lost on average 200 byte long packets due to incomplete ATM cell fills resulting in 134.784 Mbps. Then we need to subtract 9.43% due to ATM headers of 5 bytes in 53 byte packets. Thus we end up with a 122.069 Mbps true information rate which is about 78.5% of the nominal OC-3 capacity. And we still have not raised the issues of wasted reserved bandwidth and routing ease which were recently addressed very eloquently by Vadim Antonov when comparing connection based with packet based transport. Wolfgang Wolfgang Henke wolfgang(a)whnet.com . http://www.whnet.com/wolfgang/ WH Networks ... ftp.whnet.com /pub/wolfgang 2672 Bayshore Parkway Suite 503 ....... +1 415 390 9316 Mountain View CA 94043 ................... fax +1 415 390 9317

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Re: cisco OC3 interfaces
by Dave Morton 20 Mar '96

20 Mar '96

>Gordon, > >The only OC3 interfaces we sell for the 75XX series of routers >are the single mode and multimode versions of the AIP (ATM interface >processor). > >I believe what Dorian is referring to is the use of several of these >routers (actually, they could be 4500s, 4700s, 70x0's or 75xx's) >connected to an ATM switch. Nothing too mysterious. > >If anyone has been discussing other OC3 interfaces with you, they >are potentially in violation of a non-disclosure agreement, and I >would suggest that such conversations shouldn't be happening. Dave, The cat is probably out of the bag wrt the above regardless of any NDAs - if cisco was not working on such a beast they would be pretty silly. Cheers, Dave

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cisco OC3 interfaces
by Dave O'Leary 20 Mar '96

20 Mar '96

Gordon, The only OC3 interfaces we sell for the 75XX series of routers are the single mode and multimode versions of the AIP (ATM interface processor). I believe what Dorian is referring to is the use of several of these routers (actually, they could be 4500s, 4700s, 70x0's or 75xx's) connected to an ATM switch. Nothing too mysterious. If anyone has been discussing other OC3 interfaces with you, they are potentially in violation of a non-disclosure agreement, and I would suggest that such conversations shouldn't be happening. dave Date: Tue, 19 Mar 1996 11:02:19 -0500 (EST) >From: Gordon Cook <gcook(a)tigger.jvnc.net> Reply-To: cook(a)cookreport.com To: Dorian Kim <dorian(a)cic.net> Cc: David Miller <david(a)dirigo.mint.net>, Jasper(a)cloud9.net, inet-access(a)earth.com, nanog(a)merit.edu Subject: Re: MCI I am told that Cisco has an OC-3 interface to its 75XX series of routers. If so why would you need a cluster of routers around each ATM switch?

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Re: MCI [ATM overhead]
by Paul Ferguson 20 Mar '96

20 Mar '96

At 07:51 PM 3/19/96 -0800, Jim Forster wrote: > >There's beginning to be some expectation that there will be a transmission >capacity crunch in the carrier's Sonet nets, and this ~25% ATM cell tax may >be looked at carefully as packet over Sonet solutions emerge. > I think it will be critically important, especially in long-haul interconnect scenarios. Historically speaking, as providers have replaced congested links with faster ones, they have also become quickly congested. And since these high-speed long-haul links are not cheap, you can bet that these organizations want to get the most bang-for-the-buck. I can't imagine that ~25% bandwidth overhead would be acceptable, especially when more efficient alternatives exist. Nice synopsis, Jim. - paul

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Re: MCI [ATM overhead]
by avg＠postman.ncube.com 20 Mar '96

20 Mar '96

Jim Forster <forster(a)cisco.com> wrote: >He's talking about the overhead due to carrying variable length IP packets >in fixed length ATM cells. ... >There's beginning to be some expectation that there will be a transmission >capacity crunch in the carrier's Sonet nets, and this ~25% ATM cell tax may >be looked at carefully as packet over Sonet solutions emerge. Given the bimodailty of IP traffic size distribution (about 40% of packets are small, like TCP ACKs or telnet/rlogin keystrokes) the ATM "cell tax" is closer to 32%. I.e. a dual clearline DS-3 actually carries as much user data as OC-3c ATM. Which, incidentally, was why SprintLink backbone design is easily expandable to dual links (that includes carefully considering implications for routing). Sean presented that design on NANOG a year ago, BTW. Funny thing, the design is expandable beyond that, too, so OC-3 ATM is already obsolete. --vadim

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Re: MCI [ATM overhead]
by jogden＠merit.edu 20 Mar '96

20 Mar '96

If we are going to talk about ATM overhead when doing TCP/IP don't we need to talk about the overhead of partially filled ATM cells? Won't that cost you about 1/3 of your available bandwidth? -Jeff Ogden Merit

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Re: MCI
by rcraig＠cisco.com 19 Mar '96

19 Mar '96

At 12:29 96/3/19, Wolfgang Henke wrote: ... >I have assembled a list of several best effort packet routers including >known research efforts: > >http://www.whnet.com/wolfgang/giga.html The list shows the 75xx as doing about 80mbps, which is incorrect. I've been doing extensive testing in a realistic testbed with a three HSSI, two FDDI configuration, and I get 160mbps without difficulty. The aggregate throughput at the moment is limited, not by the unit under test, but by the generators I'm using. I've just acquired some more powerful ones, so should be able to stress the box a bit more. The results I anticipate will approach Product Marketing's numbers ;-) Robert.

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Re: MCI
by Paul Ferguson 19 Mar '96

19 Mar '96

At 12:54 PM 3/19/96 -0500, Gordon Cook wrote: > >Arun Welch wrote: > >Yup. There's work in progress to put IP directly on SONET, which should save >people with OC-3c backbones from paying the ATM penalty. > >Cook: would you please give a pointer to whom they are and what one reads >or looks at to get up to speed? (ie IP over sonet) > RFC-1619, 'PPP over SONET/SDH'. - paul >********************************************************************* >Gordon Cook, Editor & Publisher Subscriptions: Individ-ascii $85 >The COOK Report on Internet Individ. hard copy $150 >431 Greenway Ave, Ewing, NJ 08618 USA Small Corp & Gov't $200 >(609) 882-2572 Corporate $350 >Internet: cook(a)cookreport.com Corporate Site Lic. $650 >http://pobox.com/cook/ for new COOK Report Glossary of Internet terms >********************************************************************* > -- Paul Ferguson || || Consulting Engineering || || Reston, Virginia USA |||| |||| tel: +1.703.716.9538 ..:||||||:..:||||||:.. e-mail: pferguso(a)cisco.com c i s c o S y s t e m s

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