User:Avanish12/NEXT GENERATION SONET

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The article will be covered in following three parts:- (1) Introduction (2) Limitations (3) Solutions

(1) Introduction: (a) Limitations of SONET (b) Methods of  Overcoming  The Limitations (Next Generation SONET)

(2) Limitations: (a) Inefficient payload mapping (b) Fragmented payload (c) Moves, adds, and changes delay (d) Path failures (e) Lack of framing protocol (f) Suitability Of SONET For Ethernet Transport (g) Mapping Ethernet Into SONET (a) Inefficient payload mapping: With contiguous concatenation payload sizes of approximately 50 Mbps, 150  Mbps, 600 Mbps, and 2.4 Gbps, and technologies running at 100 Mbps and 1 Gbps, the two do not match closely. These inefficiencies are attributed to concatenation, which has strict payload size restrictions and requires contiguous payload elements. (b) Fragmented payload: As SONET systems are deployed and reconfigured, the payload mapping tends to cause holes in the payload capacity. This phenomenon is similar to that seen in hard drives as files are deleted and added to a computer. The fix for both SONET systems and hard drives is to shut the system down and repack all the contents. This means that the SONET systems are unavailable for customer traffic while performing this fix. Payload mapping algorithms that allow non-contiguous areas would help fix this problem.

(c) Moves, adds, and changes delay: The manual nature for provisioning SONET systems delays the capability of moves, adds, and changes. Days, weeks, and months could be required to add a customer or adjust the bandwidth for existing paths. No automated tools are currently used for these processes.

(d) Path failures: The SONET system is tailored to recognize and recover from hardware and optical failures. However, a logical failure can go undetected and is just as detrimental to communications as a fiber cut. End-to-end protocols are being implemented that can detect any type of loss and isolate the problem segment.

(e) Lack of framing protocol: SONET is a TDM circuit-switched transport. When packet traffic is mapped to a SONET circuit, the payload is transparent to the SONET equipment. As SONET equipment moves to edges of the network (i.e., routers), SONET devices must differentiate between actual packets of data and idle patterns. A framing protocol is not defined in the SONET standards and leads to incompatibilities between vendors.

(f) Suitability Of SONET For Ethernet Transport: The SONET hierarchy is based on a multiple of 51.84 Mbps. The payload was designed to carry the North American digital hierarchy and the European digital hierarchy. As such, the base 10 multiples of Ethernet speeds are not a clean fit into the SONET system. To accommodate Ethernet speeds a new construct is necessary for the SONET payload—the concatenated virtual tributary.

(g) Mapping Ethernet Into SONET: The individual payloads of the virtual tributaries are inverse multiplexed at the source and destination points to form higher speed connections. The nomenclature of VT1.5-7v indicates that seven virtual tributary 1.5s should be combined to form a single 10 Mbps data connection.

(3) Methods of  Overcoming  The Limitations (Next Generation SONET): (a) Virtual Concatenation: n-STS-1’s over multiple paths A channel can be n×STS-1 or nxT1 for any n        Different STS-1’s can follow different path Size match: 10 Mbps over 7 T1, �100 Mbps over 2 STS-1, 1 Gbps over 21 STS-1

SONET Virtual Concatenation:VCAT: Bandwidth in increments of VT1.5 or STS-1 For example: 10 Mbps Ethernet in 7 T1’s = VT1.5-7v�100 Mbps Ethernet in 2 OC-1 = STS-1-2v, �1GE in 7 STS-3c = STS-3c-7v The concatenated channels can travel different paths� Need buffering at the ends to equalize delay All channels are administered together. �Common processing only at end-points.

CREATED BY: AVANISH TYAGI