10 Slides to Sonet

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10 Slides to Sonet

  1. 1. SONET The Telecom Source 10 Slide Technology Series
  2. 2. Introduction <ul><li>SONET stands for S ynchronous O ptical NET work </li></ul><ul><li>SONET is a set of coordinated ITU, ANSI and Bellcore standards for high bit-rate fiber optic transmission </li></ul><ul><li>The SONET standard defines a hierarchical set of transmission rates and transmission formats </li></ul><ul><li>The “synchronous” in SONET refers to the method used to perform multiplexing in which all clocks are synchronized </li></ul><ul><li>SONET is predominantly a North American standard </li></ul><ul><li>SDH ( S ynchronous D igital H ierarchy) is the international equivalent of SONET </li></ul>
  3. 3. Overview <ul><li>The SONET hierarchy defines hierarchy levels for transmission </li></ul><ul><li>Each SONET level has an O ptical C arrier (OC) level and a corresponding electrical level transmission frame structure called the S ynchronous T ransport S ignal (STS) </li></ul><ul><li>The base transmission rate for SONET is 51.840 Mbps </li></ul><ul><li>STM ( S ynchronous T ransport M odule) is the SDH equivalent (i.e. international equivalent) of STS </li></ul><ul><li>The base transmission rate for SDH is 155.52 Mbps </li></ul>
  4. 4. SONET Hierarchy STM-64 9953.280 STS-192 OC-192 STM-32 4976.640 STS-96 OC-96 STM-16 2488.320 STS-48 OC-48 STM-12 1866.240 STS-36 OC-36 STM-8 1244.160 STS-24 OC-24 STM-6 933.120 STS-18 OC-18 STM-4 622.080 STS-12 OC-12 STM-3 466.560 STS-9 OC-9 STM-1 155.520 STS-3 OC-3 - 51.840 STS-1 OC-1 SDH Equivalent Line Rate (Mbps) Electrical Level (STS) Optical Level (OC)
  5. 5. SONET Structure – High Level <ul><li>The SONET hierarchy is linear unlike the T-n hierarchy which is non-linear </li></ul><ul><ul><ul><li>For example, 3 x OC-1 bit-rate = OC-3 bit-rate but 28 x DS-1 bit-rate is not equal to DS-3 bit-rate </li></ul></ul></ul><ul><li>SONET is natively a channelized technology </li></ul><ul><ul><ul><li>For example, an STS-3 contains 3 STS-1’s each with a bit-rate of 51.84 Mbps </li></ul></ul></ul><ul><li>STS-1 frames can be concatenated to form a single high bit-rate SONET “channel” </li></ul><ul><ul><ul><li>STS-1 frame concatenation is equivalent to unchannelized DS-n’s </li></ul></ul></ul><ul><ul><ul><li>A concatenated SONET link is referred to as OC-nc or STS-nc (the “c” is for concatenated) </li></ul></ul></ul><ul><ul><ul><li>For example, 3 STS-1 frames can be concatenated to form an STS-3c frame </li></ul></ul></ul><ul><ul><ul><li>An STS-3c frame has a single payload and a bit rate of 155.52 Mbps </li></ul></ul></ul><ul><li>STS/OC-n distinction </li></ul><ul><ul><ul><li>STS frames are the electrical equivalent of the OC levels </li></ul></ul></ul><ul><ul><ul><li>All SONET frame creation, multiplexing and adding of overhead bits is done in the electrical (i.e. STS) domain rather than the optical domain </li></ul></ul></ul>
  6. 6. SONET Structure - STS <ul><li>STS has a frame structure. </li></ul><ul><li>An STS-1 frame </li></ul><ul><ul><ul><li>Consists of 810 bytes (9 rows and 90 columns) </li></ul></ul></ul><ul><ul><ul><li>Is transmitted at 8000 frames per second </li></ul></ul></ul><ul><ul><ul><li>Stores the “overhead” info in the first 3 columns of the frame </li></ul></ul></ul><ul><ul><ul><li>Stores the payload (i.e. the user info) in the other 87 columns </li></ul></ul></ul><ul><li>An STS-n frame </li></ul><ul><ul><ul><li>Consists of 810 x n bytes (9 rows and 90 x n columns) </li></ul></ul></ul><ul><ul><ul><li>Is Formed by byte-wise multiplexing of the “n” STS-1 frames </li></ul></ul></ul><ul><ul><ul><li>Is transmitted at 8000 frames per second </li></ul></ul></ul><ul><ul><ul><li>Stores the “overhead” info in the first 3 x n columns of the frame </li></ul></ul></ul><ul><li>STS-nc frames </li></ul><ul><ul><ul><li>Consist of 810 x n bytes </li></ul></ul></ul><ul><ul><ul><li>Are transmitted at 8000 frames per second </li></ul></ul></ul><ul><li>STS frames are transmitted one row at a time from top to bottom </li></ul>STS-1 Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Columns 1 2 3 4 5 87 88 89 90 1 2 3 4 5 6 7 8 9 Rows Overhead Payload
  7. 7. SONET Structure - Virtual Tributaries <ul><li>Compatibility with lower rate existing digital hierarchies (i.e. T-n and E-n) is achieved via Virtual Tributaries </li></ul><ul><li>Virtual Tributaries </li></ul><ul><ul><ul><li>Allow SONET to carry lower rate info (e.g. DS-1) </li></ul></ul></ul><ul><ul><ul><li>The lower rate (sub-rate) info is mapped into “sections” of an STS-1 frame </li></ul></ul></ul><ul><ul><ul><li>These sections are each called a virtual tributary </li></ul></ul></ul><ul><ul><ul><li>The virtual tributaries are independent of each other </li></ul></ul></ul><ul><ul><ul><li>Each tributary can contain different types of information </li></ul></ul></ul><ul><li>The STS-1 frame is divided into exactly 7 virtual tributary groups (VTG) </li></ul><ul><ul><ul><li>VT types (i.e. VT1.5, VT2, …) cannot be mixed within a single VTG </li></ul></ul></ul><ul><ul><ul><li>Each VTG in an STS-1 frame consists of 108 bytes each (9 rows by 12 columns) </li></ul></ul></ul><ul><ul><ul><li>VT super-frames are possible </li></ul></ul></ul><ul><li>There are four virtual tributary sizes (i.e. VT types) defined in SONET </li></ul><ul><ul><ul><li>A single VTG can carry 4 VT-1.5s. Each is contained in three 9-byte columns (9 rows by 3 columns = 27 bytes). VT1.5 carries enough bandwidth to transport a DS-1 signal. </li></ul></ul></ul><ul><ul><ul><li>A single VTG can carry 3 VT2s. Each is contained in four 9-byte columns (9 rows by 4 columns = 36 bytes). VT2 carries enough bandwidth to transport an E-1 signal. </li></ul></ul></ul><ul><ul><ul><li>A single VTG can carry 2 VT3s. Each is contained in six 9-byte columns (9 rows by 6 columns = 54 bytes). VT3 carries enough bandwidth to transport a DS-1C signal. </li></ul></ul></ul><ul><ul><ul><li>A single VTG can carry 1 VT6. It is contained in twelve 9-byte columns (9 rows by 12 columns = 108 bytes). VT6 carries enough bandwidth to transport a DS-2 signal. </li></ul></ul></ul>
  8. 8. SONET Networks <ul><li>SONET is a fixed bandwidth “trunking” technology </li></ul><ul><li>Service providers can overlay FR, ATM and other technologies on SONET to provide bandwidth on demand types of features </li></ul><ul><li>Service adapters are used to map incoming signals from one service type (e.g. DS-1) to another service type (e.g. VT1.5) for SONET transmission </li></ul><ul><li>Fiber optic links are inherently unidirectional and not full duplex and therefore are generally deployed in pairs </li></ul><ul><li>SONET can be deployed in a point-to-point or ring configuration (ring configurations are much more common than point-to-point) </li></ul>
  9. 9. SONET Rings <ul><li>A SONET ring is a collection of more than 2 SONET network elements (nodes) forming a closed loop </li></ul><ul><li>SONET ring architectures can be described by 3 basic attributes </li></ul><ul><ul><ul><li>Number of fibers per link (2-fiber vs. 4-fiber) </li></ul></ul></ul><ul><ul><ul><li>Direction of signal (unidirectional vs. bidirectional) </li></ul></ul></ul><ul><ul><ul><li>Level of switch protection (line switching vs. path switching) </li></ul></ul></ul><ul><li>SONET ring nomenclature uses abbreviations </li></ul><ul><ul><ul><li>ULSR – unidirectional line switched ring </li></ul></ul></ul><ul><ul><ul><li>BLSR – bidirectional line switched ring </li></ul></ul></ul><ul><ul><ul><li>UPSR – unidirectional path switched ring </li></ul></ul></ul><ul><ul><ul><li>BPRS – bidirectional path switched ring </li></ul></ul></ul><ul><ul><ul><li>Each of the above options can be 2-fiber or 4-fiber </li></ul></ul></ul><ul><li>Of the 8 possible ring architectures, only 3 are generally used in practice </li></ul><ul><ul><ul><li>2-fiber unidirectional path switched (2-fiber UPSR) </li></ul></ul></ul><ul><ul><ul><li>2-fiber unidirectional line switched (2-fiber ULSR) </li></ul></ul></ul><ul><ul><ul><li>4-fiber bidirectional path switched (4-fiber BPSR) </li></ul></ul></ul>Node 1 Node 2 Node 4 Node 3 SONET Ring
  10. 10. SONET Rings …cont’d <ul><li>2-fiber vs. 4 fiber </li></ul><ul><ul><ul><li>2-fiber rings have 2 physical fibers between each pair of nodes </li></ul></ul></ul><ul><ul><ul><li>4-fiber rings have 4 physical fibers between each pair of nodes </li></ul></ul></ul><ul><li>Unidirectional vs. bidirectional </li></ul><ul><ul><ul><li>In unidirectional rings, information flow between 2 nodes (node 1 to node 2 or node 2 to node 1) always travels in a single direction </li></ul></ul></ul><ul><ul><ul><li>Unidirectional rings use a loop (or pair of loops) for working traffic and the other loop (or pair of loops) for protection </li></ul></ul></ul><ul><ul><ul><li>In bidirectional rings, information flow between 2 nodes (node 1 to node 2 or node 2 to node 1) travels in 2 (opposite) directions </li></ul></ul></ul><ul><ul><ul><li>Unidirectional and bidirectional rings are indistinguishable physically </li></ul></ul></ul><ul><li>Line switching vs. path switching </li></ul><ul><ul><ul><li>Line switching and path switching are forms of protection switching </li></ul></ul></ul><ul><ul><ul><li>Line switching works by switching traffic to the protection fiber at both end of a span in the event of a failure </li></ul></ul></ul><ul><ul><ul><li>Path switching works by sending traffic along both the working and protection fibers in the event of a failure and allowing the receiver the select the best signal </li></ul></ul></ul><ul><ul><ul><li>Path switching can occur at the STS-1 or VT level as opposed to only the OC-n level for line switching </li></ul></ul></ul>
  11. 11. Typical SONET Network ADM ADM TM TM D+R ADM D+R MN MN MN MN DSC DSC ADM ADM DSC TM (Terminal Multiplexer) - an end-point SONET device that converts from SONET to non-SONET format ADM (Add/Drop Multiplexer) - aggregates or splits (grooms) SONET traffic on to one of two SONET links DCS (Digital Cross-Connect) – similar to the ADM but can interconnect a large number of STS-n links MN (Matched Nodes) – used to interconnect SONET rings and provide an alternative path in case of failure D+R (Drop and Repeat Nodes) – used to send duplicate copies of signals along alternate paths
  12. 12. The Telecom Source www. thetelecomsource .com Info@ thetelecomsource .com

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