MPLS and CES circuits

[lars]

Hi there

Is it possible to run a CES (Circuit Emulated Service) over a MPLS network?

I know it's an ATM terminology, but I wonder if it's possible...

Cheers,

Lars Christensen

[romccallum]

hmmmm, you could try to do ATMover MPLS with ATM at each end. That is if you have the correct devices and the correct IOS.

[thammad]

In Cisco, I did not find any code support this feature. However, MPLS Forum (MFA) have approved Implementation Agreement (IA) "Emulation of TDM Circuits over MPLS Using Raw Encapsulationin" November 2004 (MFA 8.0.0)(See http://www.mplsforum.org/tech/TDMoMPLS_IA.pdf). The first annoucement claiming the support for this IA which I found is by RAD (see http://www.tdmoip.com/Article/0,6583,20396,00.html )

Also, this site from RAD contains more information www.tdmoip.org

Note:MFA 4.0.0 http://www.mplsforum.org/tech/tdm_ia_4.0.pdf is discussing TDM Transport over MPLS using AAL1 while MFA 8.0.0 remove the need for AAL1)

I will apreciate if any body confirm if TDM over MPLS is supported in Cisco or not.

[luis.rueda]

Thammad,

The fact is that I asked the same question recently on a Service Provider day, and the answer that Cisco gave me was "not yet"..... the fact is that doing TDM over MPLS is not supported, but TDMoIP is!!!! so basically the solution would be to hook up a 2600/2800/3600/3700/3800 router with the following NM

http://www.cisco.com/en/US/products/hw/routers/ps274/products_data_sheet09186a00802045f5.html

In fact this article talks about CEoIP which is Circuit Emulation over IP wich can then be putten inside your MPLS network.... It is not a final solution, but I belive it's better than nothing.

Hope this helps

[lars]

Ok, that's sounds interesting. I've also found some other equipment that might do well across a MPLS network (again it's TDMoIP... http://www.rad.com/Home/0,6583,953,00.html)

Thank's for the answer anyway. Now I'v got a few different approaches for start off with.

[woli]

sorry to say that is offtopic.

I cannot imagine an "ATM over MPLS".

Having an ATM interface on a router does not mean that this can be used for that ahem creative idea.

ATM interfaces in routers are terminating interfaces.

They do AAL5.

There are ATM CES interfaces in cisco ATM products like the 3600. They do TDM over ATM.

TDM over IP exists as well.

Clearly MPLS over ATM exists, you are a decorated netpro expert in this field.

But ATM over MPLS?

Isn't this like asking for ATM over IP?

Maybe you can bring some light in here,

I do not have an idea what the benefit would be.

[luis.rueda]

You are right when you say Cisco routers only work as terminating circuits, and can only run AAL5, but have you heard of Cell Relay over MPLS, it can get you to transport any type of ATM circuits over an MPLS network.

As long as the benefits I can think of a lot.... for instance how about getting rid of those ATM switches.... also you could have multiple MPLS paths, and do FastReRoute in roder to have protection for the links.....

Also I heard Cisco is planning to do SDHoMPLS thorugh a technique called G-MPLS.

[woli]

I have to admit I have not heard yet of cell relay over MPLS.

I come from the voice side and here a native ATM network so far is the best underlay network I can have for the high demanding tactical voice networks we design.

Yes, it is kind of a religious war, and yes, ATM is vanishing, IP is still coming.

I can see that for the purpose of "getting rid of those ATM switches" is an application of call relay over MPLS.

However as a voice and ATM guy I am too closed-minded to see this too positive.

It is a surrogate for ATM that might be sufficient for ATM data traffic.

All existing voice/video application will suffer noticable changes in performance parameters like delay/jitter. So I am not expecting such a migration to be seamless.

It is to some degree similar to replacing existing PDH lines between branch office PABX systems with circuit emulation over IP: it works, but brings much irritation with it (e.g. need for echo cancellation).

(The switch from ATM to MPLS will be not that glaring than the switch from TDM directly to packet)

About SDHoMPLS: what will be the transport media for this: POS...?

Wolfgang

[woli]

Circuit Emulation Service is a term wellknown in ATM, however not tied to ATM semantically.

It means the ability to transport synchronous data (typically TDM voice) over a network that no longer is circuit switched.

CESoverATM is what can be done on cell switched ATM networks, mostly using AAL1.

CESoverIP can be done with ITU-T Y.1413 TDMoverIP, e.g. with cisco's NM-CEM-T4E1 module.

Another vendor is RAD - they are holding TDMoverIP patents as well. Their mechanism basically is AAL1 circuit emulation in IP.

However all these approaches do not directly connect into MPLS but to IP. MPLS networks will be a very good candidate for long haul CESoverIP WAN topologies.

Whenever doing TDMoverIP clocking and de-jitter will be your major concerns.

Most circuit applications usually use the circuit they are receiving from the central office as a clock reference. With CESoverIP this is no longer possible.

Cisco writes that synchronous receiver and transmitter clocks are "imparative". But where to get these from?

There is an adaptive clocking algorithm in cisco CEoIP which tunes the clock by the average fill level of the dejitter buffer.

Be aware that the default dejitter buffer size is at 60 ms. I just learned this, and it is far beyond the delay value of a TDM line. It can be adjusted between 5 and 500 milliseconds. 60 ms definitely is much too much for standard TDM applications like telephony as with an round-trip delay of more than 35-50 ms echo cancellation becomes imparative.

Wolfgang