Tom Randstrom Mon, 02/23/2009 - 08:01
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SONET defines interface standards at the physical layer of the OSI seven-layer model.

Marvin Rhoads Fri, 03/06/2009 - 05:01
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Note that, while SONET is accurately described as being a "Layer 1" (physical layer) protocol, it's not "just" a physical/electrical specification like, say, Category 5 Unshielded Twisted Pair (Cat 5 UTP). The SONET specifications and protocols include a number of methodologies for multiplexing of signals (DS-x through OC-n speeds) into trunks, protection of traffic on those trunks, etc. SONET trunks typically operate at speeds ranging from OC-48 (~2.5 Gbps) to OC-768 (~40 Gbps). They use path and ring protection methodologies such as Bidirectional Line Switched Ring (BLSR) to ensure reliable traffic transmission in the event of equipment or line faults.

When lower speed non-SONET inputs are carried over a SONET backbone, the packets (or cells or frames) are wrapped or encapsulated into a SONET specification signal for transmission across the SONET backbone and through any intermediate nodes until it reaches its destination. Typically there is not intelligent signaling between those tributary stream technologies and the SONET signaling. (There has been some development work along those lines such but I don't believe it's ever gained any widespread adoption.)

Hope this helps. Please rate the post if it does.

Tom Randstrom Mon, 02/23/2009 - 08:43
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SONET is designed to transport many protocols and interface speeds over a common infrastructure. The current SONET multiplexers (such as ONS 15454) can support services carried via DS-1/DS-3, OC-N, Ethernet (10/100/1000Mbps), Fiber Channel, etc.

Hope this helps!

Cisco ONS 15454 Data Sheet

rayroyaleverest Mon, 02/23/2009 - 10:07
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How would I use SONET without a technology such as ATM or Frame Relay?


Tom Randstrom Mon, 02/23/2009 - 10:23
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You can transport ATM and/or Frame Relay (as well as Ethernet, etc) over SONET within DS-n or OC-Nc circuits.

SONET is like a highway (SONET network). It has multiple lanes (STS/VT) to carry the traffic. Trucks (ATM) and cars (Frame Relay) can travel over the same highway in their own lanes. The on/off ramps (SONET Muxes) allow the traffic to enter and leave the highway.

I am not sure if my analogy will help you or not.


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