Are many ISPs taking advantage of SONET APS protection to provide port or router redundancy on short (metro-area) circuits? Or is it more typical to get two circuits and load-share? Or just not bother?
I know of a few providers that use inter-router APS to protect against router and ADM trib port (mainly router) failures in the core. The optical network side is protected by BLSR or the like. The optical protection options still seem to be much more cost-effective then simply provisioning parallel (but presumably diverse) links between two locations, not to mention that if some load-balancing schema is employed one needs to consider accommodating additional propagation delay incurred on the less optimal path (an ideal application for CoS & TE, perhaps). Inter-router APS proves itself especially useful on trans-oceanic circuits where simply acquiring additional capacity often isn't a viable option, nor is allowing some really expensive circuit to sit idle for 5 or 10 minutes while a router boots and becomes synchronized. As you can imagine, there are lots of interesting issues with inter-router APS and IGP interaction, most of which seem to cast a considerable shadow on its value when considering network availability and convergence in the event of failures. Intra-router APS is much more appealing, assuming stateful port mirroring is implemented, though it doesn't address the main concern of protecting against router failures. Of course, it's definitely better than simply selecting an alternative, presumably less optimal network path simply because a local router becomes unavailable. -danny
Think about it -- are they really provisioning two circuits, leaving one available as a backup? Of course not! This may be a useful feature for voice circuits, where most of the capacity sits idle most of the time. It's worse than useless for data. APS was designed to protect against the failure of the electronics for a single fiber in a cable. Often, a dozen other circuits are "protected" by a single APS. It's a ripoff. Of course, the usual failure mode is backhoe fade, not electronics. In which case, that APS circuit was cut along with the rest. For transoceanic links, diverse APS is even more unlikely, and unless you are paying serious money, you won't be a priority over the other hundred customers that are sharing that APS circuit. Diverse links _are_ the only _real_ protection. You might even get what you pay for.... And in the short term, you at least get twice the bandwidth. WSimpson@UMich.edu Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32
Note that I am not a big fan of APS, but: ----- Original Message ----- From: "William Allen Simpson" <wsimpson@greendragon.com> To: <danny@tcb.net> Cc: "Steve Feldman" <feldman@twincreeks.net>; <nanog@merit.edu> Sent: Tuesday, July 25, 2000 9:04 PM Subject: Re: Sonet protection usage
Think about it -- are they really provisioning two circuits, leaving one available as a backup? Of course not!
This may be a useful feature for voice circuits, where most of the capacity sits idle most of the time. It's worse than useless for data.
APS can be useful for data as well.
APS was designed to protect against the failure of the electronics for a single fiber in a cable. Often, a dozen other circuits are "protected" by a single APS. It's a ripoff.
I think this is a huge oversimplification of APS and how it works. Yes APS allows the **operator** to backup various primaries to a backup. It allows 1:1 which is same as diverse circuits. This is the case of a rope that is **long enough**.
Of course, the usual failure mode is backhoe fade, not electronics. In which case, that APS circuit was cut along with the rest.
If you run your APS primary and backup on the same conduit then APS can not undo bad network design.
For transoceanic links, diverse APS is even more unlikely, and unless you are paying serious money, you won't be a priority over the other hundred customers that are sharing that APS circuit.
Well-engineered trans-oceanic links are laid such that there are at least two conduits running parallel some large distance apart.
Diverse links _are_ the only _real_ protection. You might even get what you pay for.... And in the short term, you at least get twice the bandwidth.
Or you can run 1+1 IP Bonded interfaces and achieve the same effect ;-)
WSimpson@UMich.edu Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32
Bora Akyol wrote:
Note that I am not a big fan of APS, but: ... I think this is a huge oversimplification of APS and how it works. Yes APS allows the **operator** to backup various primaries to a backup. It allows 1:1 which is same as diverse circuits. This is the case of a rope that is **long enough**.
OK, since it "allows" 1:1, taking the same capacity as 2 circuits, why do you think that they charge less than for 2 circuits? Alternatively, since 2 circuits are paid for, why not use both, doubling capacity? My opinion (based on a fair number of years of experience) is that any ISP foolish enough to have bought APS should also ask proof that no other circuit is provisioned for the same APS. Once you've done that, a class action might be in order.... APS is specified to switch a failing circuit over to a backup within 50 milliseconds. It assumes that failure is in a multiplexor. It assumes that most of the circuits will be statistically idle. It assumes that the individual T3 (OC-1) paths are burstable, and can be recombined at the path or section layer. It assumes that 50 milliseconds is short relative to switching time. In short, it assumes voice. Data doesn't look like that at all! If the failure is actually due to the usual circumstances, a lot of data "circuits" fail all at once. There is no chance that they will all be backed up. APS (as sold) is a fraud on the uninformed.
Well-engineered trans-oceanic links are laid such that there are at least two conduits running parallel some large distance apart.
And which are those? I was unaware that any were laid that way. My information is dated on that topic, tho'. (The only one I ever viewed was pre-optical.)
Or you can run 1+1 IP Bonded interfaces and achieve the same effect ;-)
Unless it has vastly improved since I last tried it, bonding does not work well over diverse paths, due to timing differences. WSimpson@UMich.edu Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32
William Allen Simpson wrote:
Bora Akyol wrote:
Well-engineered trans-oceanic links are laid such that there are at least two conduits running parallel some large distance apart.
And which are those? I was unaware that any were laid that way. My information is dated on that topic, tho'. (The only one I ever viewed was pre-optical.)
A note of personal experience on land sonet: about 5 years ago, the last time I personally walked a sonet installation, I discovered that the "ring" that looked so pretty on the engineering diagrams was actually being laid in a single conduit, without even diverse building entrances. Seems the contractor was avoiding costs of right of way acquisition. My report cost the contractor several million in penalties and redesign, and me much pain. And I've never taken a sonet contract since. I'm picky. You should be, too. WSimpson@UMich.edu Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32
At 07:10 AM 07/26/2000 -0400, William Allen Simpson wrote:
My opinion (based on a fair number of years of experience) is that any ISP foolish enough to have bought APS should also ask proof that no other circuit is provisioned for the same APS. Once you've done that, a class action might be in order....
This isn't an issue, when you own the transmission gear (like many NSPs do). -Steve
At 07:10 AM 07/26/2000 -0400, William Allen Simpson wrote:
My opinion (based on a fair number of years of experience) is that any ISP foolish enough to have bought APS should also ask proof that no other circuit is provisioned for the same APS. Once you've done that, a class action might be in order....
This isn't an issue, when you own the transmission gear (like many NSPs do).
Do telcos in the US actually book contention ratio's on protection paths?! After thinking about it, it makes sense. Why else do seemingly minor fibre breaks cause so much disaster [hello Sean!] At COLT on our Metro SDH provided services if we say that its protected then its never overbooked, we do offer unprotected services to carriers. On Gemini and AC-1 they have protected paths, Gemini being the slightly better cable as according to the brochure I have AC-1's US leg comes into the same location [brookhaven?]. Regards, Neil.
I might point out that Global Crossing does lay out their paths as rings including under sea cables. http://www.globalcrossing.com/net_ac1.htm for us to europe http://www.globalcrossing.com/net_pc1.htm for US to japan. SOnet circuits for the most part, are set up as protected rings with full redundancy. Specing APS does not cost the carrier the same as two circuits since each of the SONET circuits are speced with a full protection path. Two circuits would end up with two working and two protect paths using up twice as much SONET capacity. The request for APS usually only effects the connection from the SONET MUX to the router. NOTE the above only applies to SONET circuits not to DWDM lambdas. -jonp On Wed, 26 Jul 2000 07:10:52 -0400, William Allen Simpson <wsimpson@greendragon.com> wrote:
Well-engineered trans-oceanic links are laid such that there are at least two conduits running parallel some large distance apart.
And which are those? I was unaware that any were laid that way. My information is dated on that topic, tho'. (The only one I ever viewed was pre-optical.)
Or you can run 1+1 IP Bonded interfaces and achieve the same effect ;-)
Unless it has vastly improved since I last tried it, bonding does not work well over diverse paths, due to timing differences.
WSimpson@UMich.edu Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32
-- Jonathon N. Plonka VP IP Engineering,Global Crossing jplonka@globalcenter.net
participants (6)
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Bora Akyol
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Danny McPherson
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Jonathon Plonka
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Neil J. McRae
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Steve Meuse
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William Allen Simpson