Re: WAN Ethernet

"Michelot" <mhostettler@xxxxxxxx> wrote in message news:1147119794.553651.221390@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Bonjour Stephen,

> So, your bandwidth is twice you need.

SONET/SDH APS requires twice the bandwidth as well due to the protect
circuit.

Yes, you're right, it's view like that at the client side. Now, the
provider can use the protected path to carry a low priority traffic,
which can be removed by a upper priority traffic, in case of failure.

The thing is, the rates customers pay for protected circuits are based on the premise that both paths are dedicated to that circuit. If the telco is using the protect path for someone else's unprotected circuit, they effectively get to sell the same bandwidth twice.

> And, if there is a problem, you can't distinguish if it is from you
> (client
> layer) or from the provider (server layers).

Of course you can. If a circuit goes down, you see it on the routers.

...and you don't have traces to know if the problem comes from the
transport network, or from the access to the transport network. I
understood that it was CE routers, and not PE routers. So you need to
join the POPs.

A customer doesn't care where the error is, exactly; knowing that doesn't get their bits through. Since they're paying for the circuit from CE to CE, when it goes down they just call the telco and yell until it's back up again. What does colocating CE equipment in the CO/POP help with?

The SLAs are typically the same for "unprotected" circuits as for
"protected" ones.

SLAs depend on the statistical duration of the service interruption,
and this duration must be better when there is a protection (switching
less than 50 ms in case of failure).

True, but irrelevant. I can get the same SLA (say, 99.9999% uptime) on an unprotected circuit as a protected one. The credits might not be the same, and the number of times you invoke it may be different, but the other terms will be identical. The sales people don't care, and management doesn't either; they price their circuits with the assumption they'll have to pay the maximum credit, and if they don't it's just extra profit.

The "client" has no control over availability in either
case, just credits for SLAs not being met. However, in my experience,
buying an SLA will not appreciably change the actual availability, but it
will often increase the circuit cost more than the maximum credit you can
recover, so buying an SLA is usually counterproductive.

It depends on the client. A correct SLA contract include the penalty
rates, and the client can ask to apply those each time the SLA is not
respected. Today, there are some tools to measure that precisely, at
the client side.

Measurement isn't the issue. The issue is that every telco I've dealt with caps the maximum credit you can receive, so that even if the circuit is down 100% of the time, you still pay 60-80% of the monthly fee (depending on how good you are at negotiating with their salesperson).

No, it's not, but as consumers we don't care. All I care about is that
my bits get from point A to point B for the lowest cost. I'll handle
reliability myself, since I can do a better job than the telco can
(speaking from experience).

Long distance providers have MNT devices highly capable. This don't
avoid the protections at the client level, to still improve the QoS,
and protect the access.

Designing a protected transport network is a real job.

Doing it right requires hiring talented people and buying good equipment, both of which are expensive. It's a lot more profitable to provide mediocre service.

One of the problems is, at least in the US, that the "working" and
"protect" paths are often provisioned through the same ROW -- if not
the same fiber bundle. When you lose one, you usually lose the
other, so APS buys you nothing in most cases.

It's not really the case in rings.

You might want to study some high-profile fiber cuts in the US. There have been several cases where tunnel explosions/fires have cut off entire cities from the phone/data network; ditto for train derailments (Sprint put all their fiber next to railroad tracks, since they were owned by Southern Pacific Railroad, and other carriers use that fiber too). You'd think nobody but the telco ops folks would notice, but they make the headlines every few months because both sides of a ring were put in the same ROW.

My favorite is an incident in Houston where one guy trenching with a backhoe managed to cut _every single copper and fiber cable_ going into a CO which also happened to be the tandem for that side of town. About a million people were without phone service for nearly a week. Apparently the CO only had a single entrance, so from the far side of the road where the two sides of the rings met over to the CO wall, they were vulnerable. Backhoes are drawn like magnets to such mistakes, and they're all over the place if you look closely.

S

--
Stephen Sprunk "Stupid people surround themselves with smart
CCIE #3723 people. Smart people surround themselves with
K5SSS smart people who disagree with them." --Aaron Sorkin


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