Why OTN Is Becoming More Important

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amitawal 12/5/2012 | 5:04:59 PM

re: Why OTN Is Becoming More Important

Yuu mentioned that OTN and SONET/SDH are both L1. They both use GFP for carrying (encapsulating) Ethernet. So why do you say that OTN is more effficient that SONET/SDH in carrying Ethernet?

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tmmarvel 12/5/2012 | 5:04:58 PM

re: Why OTN Is Becoming More Important

And whether with OTN or SDH, it's still TDM used for sub-packet-layer grooming (e.g. 10G feeds to/from "100G"), to achieve better jitter etc. performance and lower per bit cost than with any packet level switching. So what's the kicker with OTN?

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ross.halgren 12/5/2012 | 5:04:56 PM

re: Why OTN Is Becoming More Important

Packet services have all but killed TDM services at the end-user level (and rightfully so) but TDM is still important at the Service Transport level. Service capacity granularity and security has alot to do with this. Packetisation of services makes sense for the aggregation and switching of relatively low capacity and variable rate services at various levels, from the user-level up to the edge multiplexing and switching level. However, for service transport, where aggregated capacities are at least 1Gbps (or 10Gbps some would say), TDM still has a useful place for the Transport of multiple 1G and 10G service channels over a wavelength multiplexed transport network (from Metro to Long-Haul). This is because for 1-10Gbps service channels, the capacity is sufficiently large compared to the capacity of a wavelength (currently 100Gbps) that its granularity is "manageable" and because TDM separation of service channels provides another level of security for different service providers and high-end users that are sharing the same wavelength. In contrast, TDM has become impractical to manage for lower-level services having a capacity of 64kbps for example (eg, 100G would theoretically support over 1.5 million x 64kbps TDM services).

OTN and GFP / TDM multiplexing of high-capacity channels effectively provides a fully transparent sub-lambda transport layer within a wavelength-switched transport network. Given the above service evolution, OTN has become more important for the multiplexing and switching of 1-10G transport services within 40G and 100G wavelengths and OTN will retain its importance as wavelength capacities increase to 400G, although by then, the minimum transport service granularity is likely to increase to 10Gbps.

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eylons 12/5/2012 | 5:04:54 PM

re: Why OTN Is Becoming More Important

OK, it is well understood that there are tons of circuits out there, and they will probably not disappear in the short term. Ethernet/MPLS/IP is indeed taking over but the very large SONET/SDH installed base will continue to enable TDM leased lines as long as it is profitable.

If we put voice aside, those TDM leased lines are many times Ethernet-over-SONET (or Ethernet-over-SDH) point to point secure and reliable service to enterprise customers. So in this example I would say that EoS service migration to packet solutions is simpler than OTN solutions. Packet solutions today present CoS/QoS as good as SONET/SDH solutions.

- Packet does TDM: with standard circuit emulation protocols (also for high capacity). At mobile networks, Packet does TDM (with SAToP/CESoP/etc.) as common practice

- OTN does packet: true, natively. But… native TDM support is built-in and therefore scaling up packet in OTN is challenging. Enabling 90% packet traffic over OTN – not so cheap and not so easy…

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nelso53 12/5/2012 | 5:04:54 PM

re: Why OTN Is Becoming More Important

Amitawal, the improvements OTN provides over traditional SONET/SDH platforms is phenomenal. Certainly one of the key improvements is scale when compared to legacy technologies like SONET/SDH. Take a closer look at all the capabilities of the respective provisioning platforms and I think you will have your answer.

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OldPOTS 12/5/2012 | 5:04:53 PM

re: Why OTN Is Becoming More Important

Packet over SONET (POS) is the most efficient method to transport packets over SONET systems. It does what ATM took advantage of and used wasted mapping & diagnostic space on SONET. But, other than this, the efficiency differences are very small between POS and other packet techniques, <1% tested under network conditions. About 15% better than pure SONET. And replacing existing SONET equipment (primaily muxes) is a large CAPEX cost.

And POS more importantly addresses the security/separation/COS issue as efficiently as possible!

OP

PS -Or is this a religious issue for a special case and not the ENTIRE network?? Do a network inventory of the entire used network and try to apply the solution if you think the end is near. Migration will occur, but only as CAPEX is available to service all parts of the network.

I was not origionally a fan of POS, but became so as the networks slowly migrated to more packet links.

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sgan201 12/5/2012 | 5:04:53 PM

re: Why OTN Is Becoming More Important

Hi,

 

When you say OTN, do you refer to GFP-T or GFP-F solution or both??

Thanks.

 

Dreamer

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Sterling Perrin 12/5/2012 | 5:04:52 PM

re: Why OTN Is Becoming More Important

Amitawal,

Some people have already jumped in here, but I'll give you some of what I was thinking about when I made the statements:

1. the ability to scale is one big advantage. OTN is buit for wavelength-level capacaties, and at 100G there is no sonet/sdh standard at all. it is OTN.

2. the ODU0 granularity was built to match 1 GigE traffic, making OTN a fit for 1G, 10G, 100G, and beyond. 1G is a big deal because alot of aggregation networks are being based on 1Gig pipes.

3. ODUflex allows the size of the OTN pipe to be resized to closely match the capacity of whatever data rate is being used. And, with ODUflex with hitless adjustment, the re-sizing will be able to be done dynamically (on the fly) - making OTN look alot like Ethernet.

4. Synchronous vs. Asynchronous: this is a fundatmental difference between sonet and OTN, even though they are both TDM. I'm not sure that this directly contributes to efficiency in packets but it does appear to have an impact on cost.

Sterling

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amitawal 12/5/2012 | 5:04:48 PM

re: Why OTN Is Becoming More Important

My replies are inline:

-Amit

 

1. the ability to scale is one big advantage. OTN is buit for wavelength-level capacaties, and at 100G there is no sonet/sdh standard at all. it is OTN.

[Amit] True. True dream of OTN was line side multi-vendor interop but that hasn't been successful. And I'm wondering why do we lack 100G SONET/SDH standard? More than anything technical, my feeling is that this was not considered as there was so little market traction on STM-256.

2. the ODU0 granularity was built to match 1 GigE traffic, making OTN a fit for 1G, 10G, 100G, and beyond. 1G is a big deal because alot of aggregation networks are being based on 1Gig pipes.

[Amit]Yes. Isn't that inefficient though? The SONET/SDH pipes rarely need to carry full wire speed 1xGE. It is more often a fraction (atleast in the SDH market). Also full GE can be carried in VC4-8v and switched at that granularity as well.

3. ODUflex allows the size of the OTN pipe to be resized to closely match the capacity of whatever data rate is being used. And, with ODUflex with hitless adjustment, the re-sizing will be able to be done dynamically (on the fly) - making OTN look alot like Ethernet. 

[Amit] ODU flex is nothing but SONET/SDH VCAT + LCAS which enable same capability - hitless addition/removal of VC/VT in a VC Group. For bigger granularity, I'm wondering if there could have been a combination of contiguous & virtual concatenation. For example, to carry 4G worth bandwidth, a VC416c x 2v seems much simpler if there was standards direction towards it. Wouldn't this have been much better than evolving a completely different OTN switching? 

4. Synchronous vs. Asynchronous: this is a fundatmental difference between sonet and OTN, even though they are both TDM. I'm not sure that this directly contributes to efficiency in packets but it does appear to have an impact on cost.

[Amit]Note that many of OTN switching equipments also are supporting SONET/SDH switching. So there can't be any cost advantage for omitting supporting synchronization here. On the other hand, it can only lead to more complex ASICs and engg effort thereby increasing cost rather than reducing it. Is the real cost advantage a result of Moore's law or really Synch vs Async? 

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tmmarvel 12/5/2012 | 5:04:43 PM

re: Why OTN Is Becoming More Important

Any actual implementations (GA products / in-service networks) for "ODUflex with hitless adjustment"?

And is this different than SDH VCAT-LCAS (other than capacities)?

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