In the last newsletter, we discussed the cloud strata in today's networks. In a typical environment, there is at least IP over ATM/Multi-protocol Label Switching over SONET over dense wave division multiplexing over fiber. In an effort to simplify our lives and to have more efficient networks, there are multiple proposals to eliminate some of the protocol layers. The two that are most often targeted for elimination are ATM and SONET. But the key question is whether we can afford to get rid of these layers.
Let's start with SONET and its international counterpart, SDH - Synchronous Digital Hierarchy. SONET/SDH does indeed add overhead and minimal complexity to the network. For instance, at the OC-3/STM-1 rate of 155.54M bit/sec, there's 150.36M bit/sec left for actual traffic after you subtract the overhead. This amounts to a loss of about 3% of the bandwidth.
So what do you get for this 3%? The ability to use SONET for counter-rotating rings for local access is a network application of SONET that may or may not be useful. But the major benefit that SONET provides is a sophisticated framing structure for operations, administration and maintenance within the network.
This framing structure defines for service providers a sophisticated mechanism for multiplexing multiple slower data streams. These slower streams may be other SONET streams, DS3s, DS1s, or even 64K bit/sec DS0s. Even more importantly, the SONET/SDH layer provides very valuable management hooks for maintenance and performance monitoring on transmission facilities. These hooks, while transparent to the user, are most valuable in providing a high level of service.
Is this feature worth 3%? Absolutely. After all, as we move to the SONET speed ranges, the cost per bit per second for transmission decreases drastically. For the added benefits, it's much better to think of the service as a managed 150M bit/sec service than as a " raw " 155M bit/sec service.
So SONET stays. But what about ATM? We'll tackle that next.
RELATED LINKS
Steve Taylor is President of Distributed Networking Associates and Publisher/Editor-in-Chief of Webtorials.Com. For more detailed information on most of the topics discussed in this newsletter, connect to Webtorials.Com, the first Web site dedicated exclusively to market studies and technology tutorials in the Broadband Packet areas of Frame Relay, ATM, and IP.
Larry Hettick is an independent consultant, with 19 years of experience in telecommunications and data communications marketing and product management for service providers and equipment vendors. He can be reached at larry@larryhettick.com
You can reach the authors at taylor@webtorials.com or larry@larryhettick.com.
Convergence archive
Past newsletters.
Network World's The Edge
SONET still there, but playing quieter
Network World's The Edge, 12/18/00
