Unidirectional path-switched ring (UPSR)/Subnetwork connection protection (SNCP) switching
Overview
Alcatel-Lucent 1850 TSS-5 supports path switched ring applications in accordance with the path protection switching schemes described in Telcordia Technologies GR-1400.
Alcatel-Lucent 1850 TSS-5 performs path switching in response to automatically detected faults in paths and external commands from a WaveStar® CIT or operations system (OS). Alcatel-Lucent 1850 TSS-5 supports UPSR switching for VT1.5 and STS-N signals on OC-N interfaces or SNCP switching for VC-N signals on STM-N interfaces.
Path protection switching functions are available from the WaveStar® CIT System View menu when you select Fault → Protection Switch.
Protection switching priorities
The following table shows the UPSR/SNCP protection switch priorities (in descending order of priority) used by Alcatel-Lucent 1850 TSS-5.
Table 4-2: UPSR/SNCP switch priorities
|
Switch Priorities (Descending Order) |
Source of Request |
|---|---|
|
Clear |
WaveStar® CIT or OS |
|
Lockout |
WaveStar® CIT or OS |
|
Forced |
WaveStar® CIT or OS |
|
Automatic Switch: Signal Failed |
Automatic |
|
Automatic Switch: Signal Degrade |
Automatic |
|
Manual |
WaveStar® CIT or OS |
Automatic path selector criteria
Alcatel-Lucent 1850 TSS-5 performs automatic path switching based on the automatic path selector criteria. The automatic path selector criteria uses the following hierarchy of signal impairments (ordered from top to bottom in increasing signal quality):
-
line/multiplex section LOS, LOF, AIS, path AIS, LOP, and UNEQ (most impaired - worst signal quality)
-
Path BER exceeding a signal fail threshold
-
Path BER exceeding a signal degrade threshold
-
Path-level signal with no impairments.
Important!
Alcatel-Lucent 1850 TSS-5 selects the path-level signal with the best quality.
Unidirectional switching
Unidirectional switching refers to protection switching that is performed in the receive direction only. The transmitting terminal transmits the same path-level signal on two paths. The receiving terminal monitors the two path-level signals independently and chooses one path-level signal as the active path and the other path-level signal as the standby path. Alcatel-Lucent 1850 TSS-5 selects the incoming path-level signal with the best quality (based on the automatic path selector criteria).
Nonrevertive switching
Path switching is nonrevertive. When a protection switch occurs, the receiving terminal selects the signal from the standby path. In nonrevertive switching, when the fault clears the receiving terminal does not switch back to the original path.
UPSR/SNCP architecture
Figure 4-1, UPSR/SNCP path switching example illustrates an example of path protection switching. The path switching is performed in the receive direction. If the active incoming path-level signal fails, the circuit pack chooses the standby path-level signal. In the transmit direction, the circuit pack bridges the same path-level signal to the working and protection paths.
Figure 4-1: UPSR/SNCP path switching example
Path protection rings feed a payload (VT, STS-N or VCN) from the ring entry point, simultaneously in both rotations of the ring, to the signal's ring drop or exit point as shown by traffic AC and CA. This duplication of the signal that enters the ring is called a head-end bridge. The node that drops the signal from the ring monitors both ring rotations and is responsible for selecting the signal that has the highest quality. This function at the ring exit point is called a tail-end switch.