Session Deletion

[Tanya Shastri <[e-mail]>]

Hi,

Session deletion has not been mentioned explicitly in the draft.

It is not clear to me whether Admin Down could be used for deletion.
So I am not sure which of the following is correct:
- Admin down should be treated as a transitionary state during session
   deletion (Putting a session in Admin Down leads to it being deleted).
- Admin down is a state that a session may be held in.

If Admin down is to be treated as a temporary state then the draft could
include a description on how to transition out of AdminDown state to
complete deletion of the session.
"TABLE 1" below should be valid i.e. Transition out of Admin Down state
or receiving IHY=0 from the other end or on Timer Expiry.

Possible events are: Create, IHY=0, IHY=1, GoAdminDown(Delete), GoAdminUp
TABLE 1: Finite State Machine Transition from Old State to New State,
on the above events. (Interesting cells have a *).
---------------------------------------------------------------------
New state -> |Deleted | Init  | Failing | Down   | UP    | AdminDown|
              |(session|       |         |        |       |          |
Old state    |does not|       |         |        |       |          |
    |         |exist)  |       |         |        |       |          |
    v         |        |       |         |        |       |          |
---------------------------------------------------------------------
Deleted      |        |       | Create  |        |       |          |
(adj does    |        |       |         |        |       |          |
not exist)   |        |       |         |        |       |          |
---------------------------------------------------------------------
Init         |        | IHY=0 |TimerExp |        | IHY=1 | GoAdminDn|
---------------------------------------------------------------------
Failing      |        |       | Create  | IHY=0  |       | GoAdminDn|
              |        |       | IHY=1   |        |       |          |
---------------------------------------------------------------------
Down         |        | IHY=0 |         |        | IHY=1 | GoAdminDn|
---------------------------------------------------------------------
Up           |        |       | IHY=0   |        | IHY=1 | GoAdminDn|
              |        |       | TimerExp|        |       |          |
---------------------------------------------------------------------
AdminDown    |* IHY=0 |       |GoAdminUp|        |       |          |
              |TimerExp|       |         |        |       | IHY=1    |
--------------------------------------------------------------------|

If Admin down is to be treated as a state that a session may be held in
(not just to transition to deleted state) then an extra state may be
needed (Deleting) as shown in the state transition table below.
A session in deleting state could behave similiar to if it were in
AdminDown state (i.e. the diagnostic code could be set to Admin Down
in outgoing BFD control packets).

Possible events are: Create, IHY=0, IHY=1, Delete, GoAdminUp,
                      GoAdminDown(GoAdDn)
TABLE 2: Finite State Machine Transition from Old State to New State.
-----------------------------------------------------------------------|
New state->|Deleted | Init| Failing | Down   | UP    | Deleting | AdDn |
            |(session|     |         |        |       |          |      |
Old state  |does not|     |         |        |       |          |      |
    |       |exist)  |     |         |        |       |          |      |
    v       |        |     |         |        |       |          |      |
-----------------------------------------------------------------------|
Deleted    |        |     | Create  |        |       |          |GoAdDn|
(adj does  |        |     |         |        |       |          |      |
not exist) |        |     |         |        |       |          |      |
-----------------------------------------------------------------------|
Init       | Delete |IHY=0|TimerExp |        | IHY=1 |          |GoAdDn|
-----------------------------------------------------------------------|
Failing    |        |     | Create  | IHY=0  |       | Delete   |GoAdDn|
            |        |     | IHY=1   |        |       |          |      |
-----------------------------------------------------------------------|
Down       | Delete |IHY=0|         |        | IHY=1 |          |GoAdDn|
-----------------------------------------------------------------------|
Up         |        |     | IHY=0   |        | IHY=1 | Delete   |GoAdDn|
            |        |     | TimerExp|        |       |          |      |
-----------------------------------------------------------------------|
Deleting   |* IHY=0 |     |* Create |        |       |* IHY=1   |      |
            |TimerExp|     |         |        |       | GoAdminDn|      |
-----------------------------------------------------------------------|
AdminDown  |        |     |GoAdminUp|        |       |* Delete  |GoAdDn|
-----------------------------------------------------------------------|

Please clarify deletion of a session and which (if) one of the above
approaches is correct.

Also I think it would help to have a state transition table like the ones
above or a state diagram (I guess that is in the works) to explain
section 6.6.6 in the draft.

Thanks,
Tanya