MTP - SIGNALLING LINK
SIGNALLING LINK: Reliable transfer of signalling messages (signal(ling) units - SU)-s between two directly connected signalling points.
Basic SU formats:
FISU,
LSSU,
MSU
Functions:
- SU delimitation (flag)
- SU alignment (acceptance)
- error detection (CRC-16)
- error correction (retransmission)
- processor outage
- initial alignment
- signalling link error monitoring (SU error rate monitor, alignment error rate monitor)
- flow control - (LSSU messages)
-----------+ MSU +------RC-------+ SU +----DAEDR----+ +--------------
|<------------------| |<----| DAEDT | |
| +---LSC----+LSSU| Reception | | AERM | |
| | IAC |<---| part | | SUERM | |
| | POC |-CI-| Impl. |--I--| | |
| | | +---------------+ | | |
| | | +----CC----+ | Error | | Signalling
Signalling| |Link state| |Congestion| | detection | | data
network | |control | | control | | delimitation| | link
functions | |part | | part | | and | | (Level1)
(Level3) | |Impl. | +----------+ | alignment | |
| | | +------TC-------+ | | |
| | |-CI-| |<----| Impl.
| +----------+ | Transmission | | | |
|-------------------| part | | | |
|--------MSU------->| |-SU->| | |
----------+ +---------------+ +-------------+ +-------------
C - Control
I - Indication
Automaták:
- Link State Control (LSC)
- Link state control states:
- Power off, Out of service, Initial alignment, Aligned not ready,
Aligned ready, Aligned already ???, In service, Processor outage
- Events:
- Power on, Start, Stop, Aligned not possible, Link failure, Alignment complete
FISU, MSU, SIPO, Local processor outage, SIO, SIOS, Local processor recovered,
SIN, SIE, No processor outage,
- Transmitted signals:
- SIOS, SIPO, FISU, MSU
- Initial Alignment Control (IAC)
Első inicalizáláskor, link hiba visszaálláskor. Complelled exchange of
status information between the two signalling points.
- Processor Outage Control (POC)
A vett jelzésüzenetek nem továbbítódnak a 3-as és 4-es rétegek felé.
Adás: LSSU "PO"
Vétel: MSU-k eldobása. Csak a 3. réteg képes kihozni ebből az állapotból.
- Delimitation, Alignment and Error Detection (Receiving) (DAEDR)
- Delimitation, Alignment and Error Detection (Transmitting) (DAEDT)
- Basic Transmission Control (TC)
- Basic Reception Control (RC)
- Preventive Cyclic Retransmission - Transmission Control (PCR-TC)
- Preventive Cyclic Retransmission - Reception Control (PCR-RC)
- Alignment Error Rate Monitor (AERM)
- Signal Unit Error Rate Monitor (SUERM)
- Congestion Control Part (CC)