SS7-MTP Layer 2 protocol

The following table provides a summary of the MTP2 message structure included in this page:

Message format ITU-Q703 arrow_2_forward.gif (1040 octets)
List of  Messages types ITU-Q703 arrow_2_forward.gif (1040 octets)
List of Time-limits ITU-Q703 arrow_2_forward.gif (1040 octets)
List of Primitives of Service ITU-Q703 arrow_2_forward.gif (1040 octets)

MTP2: Message format

MSU (Message Signal Unit) format
- Octet 1: field
bit 8 BIB: Backward Indicator Bit
bits 7-1 BSN: Backward Sequence Number
- Octet 2: field
bit 8 FIB: Forward Indicator Bit
bits 7-1 FSN: Forward: Sequence Number
- Octet 3: field
bits 6-1 LI: Length Indicator
- Octet 4: field
bits 8-1 SIO: Service Information Octet
- Octets 5-n: field
bits 8-1 SIF: Signalling Information Field
- Octets n+1,n+2: field
bits 16-1 CK: Check bits
LSSU (Link Status Signal Unit) format
- Octet 1: field
bit 8 BIB: Backward Indicator Bit
bits 7-1 BSN: Backward Sequence Number
- Octet 2: field
bit 8 FIB: Forward Indicator Bit
bits 7-1 FSN: Forward: Sequence Number
- Octet 3: field
bits 6-1 LI: Length Indicator
- Octets 4-5: field
bits 8-1 SF: Status Field
- Octets 6-7: field
bits 16-1 CK: Check bits

Basic format of SF field in a LSSU:

- Octet 1: field
bits 8-4 Spare
bits 3-1 CBA
CBA Status indication
0 0 0 Status Indication "O": Out of alignment
0 0 1 Status Indication "N": Normal
0 1 0 Status Indication "E": Emergency
0 1 1 Status Indication "OS": Out of Service
1 0 0 Status Indication "PO": Processor Outage
1 0 1 Status Indication "B": Busy
FISU (Fill In Signal Unit) format
- Octet 1: field
bit 8 BIB: Backward Indicator Bit
bits 7-1 BSN: Backward Sequence Number
- Octet 2: field
bit 8 FIB: Forward Indicator Bit
bits 7-1 FSN: Forward: Sequence Number
- Octet 3: field
bits 6-1 LI: Length Indicator
- Octets 4-5: field
bits 16-1 CK: Check bits

MTP2: List of messages

MTP2: List of time-limits

Timer

 Value Designation
T1 40-50 s (64 kbit/s)
500-600 s (4.8 kbit/s)		 Timer "alignment ready"
T1* 300 s
(range 25 - 350 s)		 Bit rate of 1.5 and 2.0 Mbit/s
T2 5-150 s
T2 low = 5-50 s
T2 high = 70-150 s 		Timer "not aligned"
Only for automatic allocation of signalling data links and terminals
T3 1-2 s Timer "aligned"
T4   Proving period timer = 216 or 212 octet transmission time
T4n T4n (64) = 7.5-9.5 s
Nominal value 8.2 s 		Normal proving period at 64 kbit/s
(corresponding to Pn = 216)
T4n T4n (4.8) = 100-120 s
Nominal value 110 s 		Nominal proving period at 4.8 kbit/s
(corresponding to Pn = 216)
T4n* 30 s
(range 3 - 70 s)		 Proving period timer = 216 or 212 octet transmission time
Normal proving period at 1.5 and 2.0 Mbit/s
T4e T4e (64) = 400-600 ms
Nominal value 500 ms		 Emergency proving period at 64 kbit/s
(corresponding to Pe = 212)
T4e T4e (4.8) = 6-8 s
Nominal value 7 s		 Emergency proving period at 4.8 kbit/s
(corresponding to Pe = 212)
T4e* 400 - 600 ms Emergency proving period at 1.5 and 2.0 Mbit/s
T5 80-120 ms Timer "sending SIB"
T6   Timer "remote congestion"
  T6 (64) = 3-6 s Bit rate of 64 kbit/s
  T6 (4.8) = 8-12 s Bit rate of 4.8 kbit/s
T7   Timer "excessive delay of acknowledgement"
  T7 (64) = 0.5-2 s Bit rate of 64 kbit/s - For PCR method, Values less than 0.8 s should not be used
  T7 (4.8) = 4-6 s Bit rate of 4.8 kbit/s

* The timer values that are changed for these high speed signalling links.

MTP2: List of primitives

  Primitives
   

 

 

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updated:  27-Feb-04