Date: Tue, 29 May 2001 22:22:10 -0700 (PDT) From: Tom Samplonius <tom@sdf.com> To: bv@wjv.com Cc: Laurence Berland <stuyman@confusion.net>, Colin Campbell <sgcccdc@citec.qld.gov.au>, Christophe Prevotaux <c.prevotaux@hexanet.fr>, deepak@ai.net, isp@FreeBSD.ORG Subject: Re: OC48 interface Message-ID: <Pine.BSF.4.05.10105292207500.19174-100000@misery.sdf.com> In-Reply-To: <20010530000957.D51041@wjv.com>
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On Wed, 30 May 2001, Bill Vermillion wrote: > > > I'm still learning all this too but from what I've read the opinions > > > are the OC-768 won't happen because SONET is a TDM [Time Division > > > Multiplexing] method and carries a lot of overhead with it. > > > AFAIK TDM isn't frowned upon all that much. It carries overhead > > as far as someone needing to provide clock, but it seems like the > > best way to make truly separate channels in the same band on the > > same fibre/pair/transmitter area. Or CDM, I suppose. Ethernetish > > technologies are better, IMHO, for things where you just want a > > big fat pipe. I guess this is why bandwidth ppl like it, but for > > traditional telco stuff you might want sonet. > > Absolutely - but we have the 'circuit switched' tradition in telco. > A certain cell is associated with a certain link. The electrical > equivalnet of pictures form the early days of telco with poles with > dozens of cross-bars and hundreds of wires. Separate channels is > indeed a ciruit switched philophy. But the world is moving rapidly > to packet-switch, but telcos have a lot of SONET infrastructure. Telcos want to move to packet switching, because they want to oversubscribe the network capacity. At the end of the day, many people want guarrenteed dedicated bandwidth. I see the use of SONET increasing. POS (packet over sonet) links are more and more common on the various backbone providers. Basically POS is PPP over Sonet. SONET is much simpler than ethernet, so it requires PPP for IP encapsulation. The efficiency of such links is very high. Much better than ATM. ... > > > It makes sense. I know that were I have some machines located [in > > > a Level 3 facility] they say their goal is to drop all SONET and > > > become a pure IP transport. > > > I assume by IP u mean ethernet or some similar technology with IP > > running on it, or am I being dense again. > > I'm assuming a lot will be ATM. Ethernot has a lot of overhead > too. I'm just getting my feet wet there, and I've got a DSL link > coming up next week - and it's ATM. PPoA. If it were PPoE you'd > enacapsulate the Ethernet in the ATM and do the reverse at the far > end. Native mode makes more sens. ATM has tons of overhead. About 10 to 15% usually. Ethernet is pretty light in comparision. PPP is basically nothing in comparison. Long haul links are expensive, and most backbones are switching to POS. ATM is disappearing on many backbone networks. Some backbone providers (ie. Teleglobe) refuses to put any IP over ATM. ATM is in significant decline. I'm aware of some regional IP providers who are phasing out all ATM links in favour of PPP links (POS, DS3, etc.). All the OC192 router interfaces that Cisco and Juniper make today are POS, not ATM. I'm sure that Cisco and Juniper are going to be all over OC768 POS too. ATM makes sense for DSL, because usually people want DSLAMs to be simple, so they make the ATM network do the work. I've worked on direct bridged DSL (ethernet over ATM) and PPPoE (PPP over ethernet over ATM) network. The biggest problem with DSL is not the bandwidth, but getting the DSLAM traffic to the IP network. Paying another 5% overhead seems small in comparsion to how difficult your ILEC/CLEC might make this for you. Tom To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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