SONET Signal Hierarchy Electrical Optical Data Rate CCITT Signal Signal (Mbps) name STS-1 OC-1 51.84 STS-3 OC-3 155.52 STM-1 STS-9 OC-9 466.56 STM-3 STS-12 OC-12 622.08 STM-4 STS-18 OC-18 833.12 STM-6 STS-24 OC-24 1244.16 STM-8 STS-36 OC-36 1866.24 STM-12 STS-48 OC-48 2488.32 STM-16 SONET Acronyms SONET - Synchronous Optical NETwork STS - Synchronous Transport Signal OC - Optical Carrier (fiber optic standard) STM - Synchronous Transport Module. CCITT name for rates but 51.84 Mbps rate not used. SPE - Synchronous Payload Envelope (the "data" portion of a SONET frame). SDH - Synchronous Digital Hierarchy (as opposed to PDH - Plesiochronous Digital Hierarchy) SONET Features Synchronous - All STS levels above STS-1 are byte multiplexed STS-1 streams with the frames aligned (byte one from all STS-1 streams, byte two from all streams, etc). Designed to carry all the plesiochronous signals (DS-1, DS-3, PDH levels 1 to 4, etc.) Data (SPE or Synchronous Payload Envelope) is found using a pointer. SPE usually starts in one SONET frame and ends in the next. Overhead bytes for operations, administration and Maintenance (OAM) of section, line, and path. Section, Line, and Path Path is the complete communications path from the originator of the data to the consumer. The path may involve a sequence of lines. A line refers to a point-to-point communications link between switching or multiplexing devices (centers). A line may involve a sequence of sections. A section is a length of fiber of copper. Two sections can be connected by a repeater to from a longer "line". SONET STS-1 Frame (9 rows times 90 bytes per row) <--3 bytes--> <------------------87 bytes------------------> +-----------------------------------------------------------+ 9 section | A1 A2 C1 | | overhead | | | bytes | B1 E1 F1 | | A1 to D3 | | | | D1 D2 D3 | | |------------| | | H1 H2 H3 | 87*9 = 783 bytes of data including | | | 9 bytes of path overhead | | B2 K1 K2 | | 18 line | | | overhead | D4 D5 D6 | | bytes | | | H1 to Z3 | D7 D8 D9 | | | | | | D10 D11 D12| | | | | | Z1 Z2 Z3 | | +-----------------------------------------------------------+ 8 bits times 90 bytes per row times 9 rows times 8,000 frames per second equals 51.84 Mbps Data Located With "H" Pointer +-----------------------------------------------------------+ frame n | A1 A2 C1 | | | | | | B1 E1 F1 | previous 9*87 or 783 byte SPE | | | including 9 path overhead bytes | | D1 D2 D3 | | |------------| | | H1 H2 H3 | ------------------+ | | | | | | B2 K1 K2 | v | | | +----------------------------| | D4 D5 D6 | | J1 | | |-----------------+ | | D7 D8 D9 | B3 current | | | 9*87 or | | D10 D11 D12| C2 783 byte | | | SPE | | Z1 Z2 Z3 | G1 including | +--------------------------------------- 9 path ---------+ frame n+1 | A1 A2 C1 | F2 overhead | | | bytes | | B1 E1 F1 | H4 J1 to Z5 | | | | | D1 D2 D3 | Z3 | |------------| | | H1 H2 H3 | Z4 | | | +-----------------------| | B2 K1 K2 | Z5 | | | |----------------------+ | | D4 D5 D6 | | | | | | D7 D8 D9 | following 9*87 or 783 byte SPE | | | including 9 path overhead bytes | | D10 D11 D12| | | | | | Z1 Z2 Z3 | | +-----------------------------------------------------------+ Section Overhead A1, A2: Framing bytes (1111 0110 0010 1000). C1: Identifies STS-1 stream number within an STS-N frame. B1: Parity byte over previous STS-N frame for section level error monitoring. E1: Section level 64 kbps PCM orderwire. F1: User 64 kbps section level channel. D1-D3: 192-kbps data channel for section operations, administration, and maintenance. Line Overhead H1, H2, H3: Pointer to data frame (10-bit pointer plus stuffing byte). B2: Parity byte over previous STS-N frame for line level error monitoring. K1, K2: ASP (Automatic Protection Switching) equipment commands. D4-D12: 576 kbps data channel for line operations, administration, and maintenance. Z1, Z2: Reserved for future use. E2: Line level 64 kbps PCM orderwire. Path Overhead J1: 64-kbps channel repeating 64-byte user controlled string to monitor path integrity. B3: Parity byte over previous STS-N frame for path level error monitoring. C2: STS payload mapping (what is inside). G1: Status byte - Terminal equipment status and path error performance. G2: 64-kbps channel for path user. H4: Multiframe indicator (beginning of multiframe or ATM cell boundary). Z3, Z4, Z5: Reserved for future use. Virtual Tributaries DS-1 (24 64-kbps PCM channels) is VT1.5. Use 3 columns in an STS-1 SPE (3*9 or 27 bytes) to carry the 193 bit DS-1 frame. 4 VT1.5's form a VT group. Can put 7 groups (28 DS-1's) in an SPE (STS-1 payload) CEPT1 (32 64-kbps channels, 1 framing, 1 signaling, 30 PCM) is VT2.0. Use 4 columns in an STS-1 SPE (4*9 or 36 bytes) to carry the 32 byte CEPT1 (level 1 or E1) frame. 3 VT2.0 form a VT group. Can put 7 groups (21 level 1's) in an SPE (STS-1 payload). STS-3 or STM-1 Signal Speed of 155.52 Mbps. Byte interleave three STS-1 frames. STS-1 frame has 9 rows by 90 columns so STS-3 frame has 9 rows by 270 columns. First row begins with nine section overhead byes followed by 261 (3*87) bytes of data: A1, A1, A1, A2, A2, A2, C1, C1, C2, ... Can carry 139.264 Mbps level 4 signal. (1920 64 kbps PCM data streams).