Framed Structure-Agnostic TDM over Packet (SAToP) is required to detect an incoming AIS alarm in the DS1 SAToP mode. An AIS
alarm indicates a problem with the line that is upstream from the DS1 network element connected to the interface. Framed SAToP
further helps in the detection of a packet drop.
In case of unframed mode of SAToP, data received from the Customer Edge (CE) device is transported ove the pseudowire. If
the Provider Edge (PE) device receives a Loss of Frame (LOF) signal or Remote Alarm Indication (RAI) signal from a CE, the
PE can only transmit the signal that is detected by the CE device. With the introduction of Framed SAToP, when the PE device
receives the LOF or RAI signal, the PE device can detect the alarm for SAToP. Thus, the alarm can be detected earlier in the
network. This helps in enhanced performance.
Note
|
Framing type should be maintained same in all routers end to end.
|
Difference between Framed and Unframed SAToP:
-
For unframed SAToP, the incoming signal is transmitted to the far end. This signal is not analyzed by the PE device. Hence,
no alarm is reported.
-
For framed SAToP, the incoming signal is analyzed but is not terminated. If a LOF or RAI signal is detected, the remote PE
detects the signals and transmits towards the remote CE.
Difference between Framed SAToP and CESoP:
Table 3. Behaviour Difference between Unframed SAToP, Framed SAToP, and CESoP on LOF Alarm
Modes |
Alarm Detected at PE
|
Controller Status at PE
|
Alarm Detected at CE (Remote)
|
Framing Bits Generationat PE (Remote)
|
Framing Bits Terminated at PE (Remote)
|
Unframed SAToP
|
None
|
Up
|
LOF
|
No
|
No
|
Framed SAToP
|
LOF
|
Down (Data path remians up)
|
AIS12
|
Yes
|
No
|
CESOP
|
LOF
|
Down (Data path remians up)
|
AIS
|
Yes
|
Yes
|
Table 4. Behaviour Difference between Unframed SAToP, Framed SAToP, and CESoP on RDI Alarm
Modes |
Alarm Detected at PE
|
Controller Status at PE
|
Alarm Detected at CE (Remote)
|
Framing Bits Generation at PE (Remote)
|
Framing Bits Terminated at PE (Remote)
|
Unframed SAToP
|
None
|
Up
|
RDI
|
No
|
No
|
Framed SAToP
|
RDI
|
Down (data path remains up)
|
RDI
|
No
|
No
|
CESOP
|
RDI
|
Down (data path remains up)
|
RDI
|
M-bit is set into control word
|
Yes
|
Table 5. Behaviour Difference between Unframed SAToP, Framed SAToP, and CESoP on AIS alarm
Modes
|
Alarm Detected at PE
|
Controller Status at PE
|
Alarm Detected at CE (Remote)
|
Framing Bits Generation at PE (Remote)
|
Framing Bits Terminated at PE (Remote)
|
Unframed SAToP
|
AIS
|
Down (data path remains up)
|
AIS
|
No
|
No
|
Framed SAToP
|
AIS
|
Down (data path remains up)
|
AIS
|
No
|
No
|
CESOP
|
AIS
|
Down (data path remains up)
|
AIS
|
L-bit is set into control word
|
Yes
|
Remote Loopback from CE to PE Detection:
Framed SAToP does not detect any loopback.
|
Loopback Detected at PE
|
Controller Status at PE (Remote)
|
Controller Status at CE (Remote)
|
Unframed SAToP
|
No
|
Not in Loopback
|
Loopback
|
Framed SAToP
|
No
|
Not in Loopback
|
Loopback
|
CESOP
|
Yes
|
Loopback
|
Not in loopback
|