OTN is a technology developed to provide intelligent grooming, management and resiliency in WDM Networks. The main idea is to add SDH/SONET like functionality on circuits over WDM. The technology is gaining quite a bit of traction and mind-share in the telecommunications market and a number of WDM vendors are betting the future on rapid adoption of the technology. A more technical explanation can be found here.
The Telecommunications Market globally needs a mechanism to manage the multiservice, multivendor and multi-carrier transport service offerings. Being able to merge Ethernet, SDH/SONET, Fiber Channel services onto a common manageable infrastructure is very appealing to Carriers across the globe. OTN then also inserts troubleshooting tools within the protocol that Carriers can use as a common set of troubleshooting tools across various Carriers and vendors equipment.
The main issue is that OTN has taken a very long time to develop and might have missed it’s market window.
The reason I mention this is because most of the services we all use are IP based and most of those IP services are over Ethernet (not SDH/Sonet or Fiber Channel). A number of Vendors have started to work towards a solution that packetizes the Optical Layer and relies on Ethernet mechanisms for Operations Administration and Management (OAM).
This Packetization at the Ethernet Layer affords, first and foremost, a far superior grooming capability than OTN due to it’s statistical multiplexing nature. This is regardless of the speeds of Ethernet, 1Gig, 10Gig, 40GigE, 100GigE and even Terabit will all have the same advantages.
One of the main arguments against using native Ethernet over WDM, or bypassing OTN entirely is centered around latency and jitter. While this is a valid concern, a number of new developments in switch technology are mitigating this assertion by putting as much Ethernet intelligence into hardware as possible.
Another argument is the inability of Ethernet to carry SONET/SDH or Fiber channel circuits natively (if they could be carried at all). This is a valid concern and is 100% true; however, the massive Carrier migration to Ethernet Networks lends credence to the assertion that OTN might be too late.
With the rapid packetization of the Optical Layer by using Ethernet natively over WDM, I’m not so sure OTN will have as much traction as previously touted. Of course if a Carrier is forced to carry SDH and Fiber Channel, OTN is a very attractive (if not, necessary) technology to implement.
Let me know what you think.
{ 4 comments… read them below or add one }
John,
I think it is important to point out that OTN technology is very widely deployed. It is in most OEO Optical Transponders which are an element of long distance DWDM systems. What is new to the market is moving that technology to interface modules of routers and switches and providing Optical Network Elements like ROADMs a colored wavelength.
One of the big advantages to OTN framing is the FEC (Forwarding Error Correction). The error correction solves with code some very hard physics problems and yields several db of gain for reach and/or hops.
I think the question of "OTN Interfaces" in routers and switches is a bit different from the question of the OTN standards and technology. There is continual effort on various enhanced FECs with several deployed today. Given that "green field" implementations where you get to start with all new fiber are rather rare I'd expect the OTN technology to be deployed and enhanced significantly for many years.
A good question is, where will it be deployed? I think the answer varies with distance and the topology of the optical network. It is not clear to me that the Ethernet evolution obviates OTN technology.
Fred, you're right….I'm an IP guy and therefore usually overlook the advantages of a FEC.
The main point behind the post (and perhaps not clearly stated) was to question the opinion that OTN has a place in the Access/Service portions of a Carrier's network. I just do not see any advantage of OTN technology in service delivery and I'm seeing a number of Vendors push this (and therefore some Carriers are starting to insist that their Metro boxes be OTN compliant).
From a grooming perspective OTN has clear advantages in mixed use networks (OC-whatever + Fiber Channel + Ethernet) on the long haul, but in the metro or even in the European Country Networks, I just don't see the need…..
Fred, from a FEC perspective you're absolutely right, increasing reach is obviously very useful. I also do see the advantages of OTN from a multiservice grooming perspective in the long haul.
My main point here (obviously not made clearly
) was to counter a number of Vendors claims that Metro/Access gear must evolve to be OTN compliant and to push OTN as a service delivery technology. I just do not see the point of OTN in an IP/Ethernet based service network.
Now that I take a look at the post again, I didn't do a good job of qualifying my statement.
John,
OK now I get your point. And yes I encountered the same thinking when we produced the xGE DWDM interfaces. The target application was metro/regional networks where passive DWDM systems were typically in place. There was always customers in the market asking for OTN framing in these interfaces. In my opinion there was two reasons for those requests:
a) OTN was successful in the long distance optical networks therefore it most be useful here too, and
b)perception that Ethernet alone can NOT be maintained with effective troubleshooting.
I'm afraid we are not past the maintenance of Ethernet perception problem. Awhile ago when EFM (802.3ah) and CFM (802.1ag) were being deployed I searched for tutorials on Ethernet OAM and the enhancements these features provided. I did not find much, reinforcing the perception that Ethernet has little OAM capability, which I don't believe to be the case. Admittedly, the support mechanisms are different than SDH/SONET.
I can't tell you how many times I've heard of point to point xGE WAN Phy deployments only because there it has OAM terminology and features familiar to the operations staff.
Living with Ethernet still has many perception hurdles especially in the carrier market space.
cheers
Fred