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LMP Question: TE link FSM
I have some problems with the TE FSM in draft-ietf-ccamp-lmp-01.txt.
There are 4 combinations of CC UP/Down and None/Some Data Channels
Allocated, but only 3 states in the FSM. Also, the TE Link Events should
be related to whether the links are allocated to the TE, not whether
they are currently carrying data. Transition 4 is shown but the note
indicates it should not happen.
Here is a proposal for a modified TE Link FSM.
11.2.1. TE Link States
An LMP TE link can be in one of the states described below. Every
state corresponds to a certain condition of the TE link and is
usually associated with a specific type of LMP message that is
periodically transmitted to the far end via the associated control
channel or in-band via the data links.
Down: There are no control channels available and no data
links are allocated to the TE link.
Empty: At least one control channel is available and no data
links are allocated to the TE link.
Up: This is the normal operational state of the TE link. At
least one primary CC and one or more data-bearing links
is
required to be operational between the nodes sharing
the TE
link.
Degraded: In this state, all primary CCs are down, but the TE link
still includes some allocated data links.
11.2.2. TE Link Events
Operation of the LMP TE link is described in terms of FSM states and
events. TE Link events are generated by the packet processing
routines and by the FSMs of the associated primary control
channel(s) and the data links. Every event has its number and a
symbolic name. Description of possible control channel events is
given below.
1 : evCCUp: First active CC goes Up.
2 : evDCUp: One or more data channels are UP and
LinkSummaryAck message has been received
acknowledging the TE link configuration.
3 : evDCDown: Last data channel of TE link has been removed.
4 : evCCDown: Last active CC goes Down.
5 : evReconfig: Successful TE reconfiguration, LinkSummaryAck
message
6 : evReconfigFail: Unsuccessful TE reconfiguration attempt,
LinkSummaryNack
message
11.2.3. TE Link FSM Description
Figure 4 illustrates operation of the LMP TE Link FSM in a form of
a state transition diagram.
+--------+
| |
| Down |
| |
+--------+
| ^
1| 4|
| |
v |
+--------+
| |<---+
| Empty | | 6
| |----+
+--------+
| ^
2| 3|
| |
v |
+--------+ 1 +--------+
| |------>| |<---+
| Deg | | Up | | 6
| |<------| |----+
+--------+ 4 +--------+
| ^
| |
+---+
5
Figure 4: LMP TE Link FSM
In the above FSM, the sub-states that may be implemented when the
link verification procedure is used have been omitted.
Regards,
George R. Young
edgeflow Inc.
329 March Rd., Kanata, ON, Canada, K2K 2E1
phone: +1 613-270-9279 Ext 287
fax: +1 613-270-9268