SONET Frame (SPE) in STS1, and overheads

1. SONET base rate/line rate (STS1/OC1) is 51.840 Mbps (9 * 90 * 8000 * 8)
   1. the frame is 9 rows * 90 Column (810 Byte)
   2. one frame is transmitted every 125*10^-6 seconds (125 mu second) so in each second 8000 frames are transmitted ( 1000000/125)
   3. 8 bits per byte
2. the first 3 columns contain section overhead and line overhead
   1. first 3 rows of these 3 columns contain section overhead ( 3*3 Bytes)
   2. next 6 rows of theses 3 columns contain line overhead  (6*3 Bytes)
3. The rest ( 9 rows * 87 columns) is called as Synchronous Payload Envelop (SPE), thus the capacity if SPE is
   1. 9 * 87 * 8000 * 8 i.e. 50.112 Mbps
4. STS1 line rate of 51.840 Mbps can accommodate 28 DS1 (1.544 Mbps) and one DS3 (44.736 Mbps)
5. three STS1 combine to form STM1 (51.840 * 3 = 155.52 Mbps)
6. the higher level signals can be obtained by synchronous multiplexing of STS1/OC1 signal, so the Multiples are called of OC-N where N can be 1,3,12,48,192,768,3072. for example STS-48/OC-48 is 2488.320 Mbps (51.840 * 48)
7. if the rate needed (like for ISDN) is higher than the STS1 rate, the STS1 are concatenate to form STSNc signal which will be multiplexed, switched and transported as a single entity, some similarities and difference in STS-3 and STS-3c frames are
   1. Both have the same rate of 155.520 Mbps
   2. transport overhead is same for both
   3. STS-3 has 3 separable payloads while STS-3c has a single payload, thus there is only one set of path overhead needed in case of STS-3c SPE
   4. STS-3 may drop/add part of the payload but STS-3c has to drop entire payload
8. overhead of the DS1 (1.544 Mbps [24 DS0 ie 24 * 64Kbps]1.536 Mbps + overhead) ) signal hierarchy
   1. overhead for DS1 = (1.544 – 1.536)/1.544 * 100 = 0.52 %
9. overhead for  DS2 (6.312 Mbps [96 DS0 ie  96 * 64Kbps] 6.144 Mbps + overhead )
   1. overhead for DS2 = (6.312 – 6.144)/6.312 * 100 = 2.7 %
10. overhead for  DS4 (274.176 Mbps [4032 DS0 ie 4032 * 64Kbps] 258.048 Mbps + overhead )
    1. overhead for DS4 = (274.176 – 258.048)/274.176 * 100 =  5.8 %
11. thus in case of the DS the framing overhead increases as the level/rate increases, and the framing overhead is non linear framing overhead ie the increase in the overhead is increase not by a standard rate
12. SOH section overhead of SONET frame, is used for communication between adjacent network elements like regenerators, first three rows of transport overhead
    1. A1 and A2 framing bytes , indicate a beginning of a STS-1 frame, A1, A2 byte pattern is F6280X, when 4 consecutive error framing patterns have been received an OOF(out of frame) condition is declared, OOF is cleared when the 2 consecutive error free framing patterns have been received.   
    2. C1/J0/Z0 section trace(J0)/section growth(Z0)/STS-1 ID (C1), formerly defined as STS-1 ID, now redefined as either section trace byte in the first STS1 of STS-N, or as a section growth byte in the second through Nth STS-1S
    3. B1 section bit interleaved parity BIP-8 byte, even parity to check transmission error over a regenerator section, defined for only for STS-1 of a STS-N signal, B1 byte is calculated over all the bits of the previous STS-N frame after scrambling, then place it in the B1 byte of the STS-1 before scrambling, this B1 byte is compared with the B1 byte received from the first STS-1 of the next STS-N frame
    4. E1 section orderwire byte, for voice communication between regenerators, defined for first STS-1 of a STS-N frame
    5. F1 section user channel byte, passed from one STE to another and can be read/written at each STE in the line, defined for first STS-1 for a STS-N frame 
    6. D1 D2 D3 section DCC (data communication channel) bytes, 192 Kbps for OAM&P (operations administration maintenance and provisioning) between STE, only allocated for the first STS-1 of the STS-N frame
13. LOH line overhead is for STS-N signals between multiplexers, last 6 rows of transport overhead
    1. H1 H2 STS payload pointer, used to indicate the offset in bytes between the pointer and the first byte of the STS-1 SPE, used in all STS-1 of each STS-N to align the STS-1 transport overhead in in the STS-N, and to perform frequency justification, in case of STS-Nc signals only first pointer byte contain the actual pointer to the SPE, subsequent bytes contain the concatenation indicator (10010011 11111111). also used to detect STS path alarm indication signals (AIS-P)
    2. H3 pointer action byte, in each of the STS-1 of the STS-N, for frequency justification,  the H3 byte is used to carry the extra SPE byte only in the event of negative pointer adjustment, other wise the pointer value is undefined
    3. B2 line bit interleaved parity code (BIP-8) byte, in all the STS-1 in the STS-N, for determining a transmission error over the line, even parity calculated over all the bits of the line overhead and STS-1 SPE of the previous STS-1 frame before scrambling. the value is placed in the B2 byte
    4. K1 K2 Automatic Protection Switching (APS channel) bytes, for protection signaling between LTE for bidirectional APS and for detecting line alarm indication signal (AIS-L) and remote defect indication (RDI) signals
       1. bits 1-4 of K1 has different request types (related to priority and type of switching [forced,manual])
       2. bits 5-8 of K1 indicate the number of channels requested
       3. bits 1-4 of K2 selects the channel number
       4. bit 5 of K2 indicates the architecture
       5. bit 6-8 of K2 indicates modes of operation
    5. D4 to D12 line Data communication channel (DCC) bytes, 576 Kbps message channel from a central location for OAM&P (alarms, maintenance, control, monitoring, administration, remote provisioning and communication) between two LTE. A protocol analyzer is required to access the Line DCC. defined only for first STS-1 of STS-N
    6. S1 synchronization status byte, in the first STS-1 of an STS-N, bits 5 to 8 are allocated to convey the synchronization status of the NE
    7. Z1 Growth, located only in the second through Nth STS-1s of an STS-N, and is allocated for future growth, an OC-1 or STS-1 electrical signal does not contain Z1 byte
    8. M0 STS-1 Remote Error Indication REI-L (formerly called as Line Far End Bit Error, FEBE), the M0 byte is only defined for STS-1 in an OC-1 or STS-1 signal, bits 5 to 8 are for REI-L, which conveys the error count detected by LTE (using B2 line BIP-8) back to its peer LTE
    9. M1 STS-N REI-L, The M1 byte is located in the third STS-1 in an STS-N (N >= 3)
    10. Z2 Growth byte, in the first and second STS-1s of an STS-3 and the first second and fourth through Nth STS-1s of an STS-N , these bytes are for future growth and OC1/STS1 doe not have Z2 
    11. E2 order-wire 64 Kbps voice channel, ignored by the STE like regenerators, used by PTE
14. POH path overhead, added by PTE, as part of SPE until the payload is de-multiplexed at the terminating PTE. Is end to end, and added to DS1 signals when they are mapped into VT, and also for STS-1 payloads that travel end to end. in case of super rate services only one set of POH is contained in the first STS-1 of the STS-Nc
    1. J1 STS path trace byte, repeatedly transmit a 64bytes or 16Byte E.164 format string, used by receiving PTE to verify the continued connection to the intended transmitting terminal, payload independent function
    2. B3 STS path BIP-8 byte, even parity code for determining if a transmission error occurred over a path its value is calculated over all the bits of the previous SPE before scrambling and placed in the B3 byte of the current frame, payload independent function
    3. C2 path signal label byte, for indicating the content of the STS SPE, including the status of the mapped payloads, payload independent function, defined as

       Bits 1-4	Bits 5-8	Status
       0000	0000	Unequipped
       0000	0001	equipped
       0000	0010	VT structured STS-1 SPE (VT pointer changes to accommodate the asynchronous relationship between DS-1 signals and the VT super-frame)
       0000	0011	Locked VT mode (tributary signal is fixed with respect to SPE)
       0000	0100	Asynchronous mapping for DS3 (44.736 Mbps)
       0001	0010	Asynchronous mapping for DS4NA (139.264 Mbps)
       0001	0011	Mapping for ATM
       0001	0100	Mapping for DQDB (distributed queue dual bus)
       0001	0101	Asynchronous mapping for FDDI

    4. G1 path status byte, for conveying back path terminating status and performance to an originating STS PTE, payload independent function. thus the duplex path in it entirely can be monitored from either end, or from any point along the path.
       1. bits 1 to 4 are for STS Path REI-P (formerly called as path FEBE [far end bit error]), bits 5,6, and 7 for STS Path RDI (remote defect indicator), bit 8 is undefined currently

          Bits 1- 4	STS Remote Error Indicator - Path
          bits 5-7	STS Remote Defect Indicator - Path	Trigger and Interpretation
          111	AIS-P ,LOP-P	remote defect
          110	UNEQ–P, TIM-P	remote connectivity defect
          101	AIS-P, LOP-P	remote server defect
          100	AIS-P, LOP-P	remote defect
          011	no defects	no remote defect
          010	PLM-P, LCD-P	remote payload defect
          001	no defects	no remote defect
          000	no defects	no remote defect

    5. F2 path user channel byte, for communication between PTE, eg in a DQDB F2 carry DQDB layer mgmt info, thus its a application specific function
    6. H4 Virtual Tributary (VT) multi-frame indicator, application specific function, generalized multi-frame indicator for payload containers, currently used for VT structure payload
    7. Z3 Z4 Z5 reserved for future functions   

SOH,LOH,POH

A1 framing	A2 framing	J0/Z0/C1	J1 STS path trace
B1 (BIP-8)	E1 orderwire	F1 user	B3 (BIP-8)
D1 dcc	D2 dcc	D3 dcc	C2 path signal label
H1 pointer	H2 pointer	H3 pointer action (-ve justification)	G1
B2 (BIP-8)	K1 APS	K2 APS	F2
D4 dcc	D5 dcc	D6 dcc	H4
D7 dcc	D8 dcc	D9 dcc	Z3
D10 dcc	D11 dcc	D12 dcc	Z4
S1/Z1 (sync and growth)	M0 or M1/Z2 (REI-L, growth)	E2 orderwire	Z5

 

Reference:

http://www.techfest.com/networking/wan/dks1/dks1.htm#A8

http://www.tek.com/Measurement/App_Notes/SONET/overheads.pdf