[Megaco] Glare condition when using embedded descriptors

[John Stock <John.Stock@afc.com>]

Hi all,

I was wondering about handling of this situation:

- Embedded descriptors are used, such that when a user goes offhook, the MG
will provide dialtone and begin digit collection without waiting for
additional signals from the MGC
- A glare condition happens, such that a ring-in on the phone from the MGC
side occurs at the same time as the offhook, such that the MG sends the
offhook notification before receiving the Add command on the ring-in.
- Thus the MG will begin dial tone before getting the Add, and will cease it
when connecting the physical termination to the incoming call.
- The MGC will receive the offhook notification after sending the Add
command for the ring-in, thus sees it simply as a user answering a
terminating call.

My questions are these:

- Is it proper to handle it this way, such that the subscriber is connected
to the incoming call, instead of the alternative which is to block the
incoming call and to provide dial tone and collect digits from the
subscriber for a separate outgoing call?  I believe this is the way it works
with other protocols, such as Q.931 in GR303.
- The odd thing is the brief spurt of dial tone, which may be exacerbated by
any MGC<->MG messaging delay.  Does anyone know anything that's proposed for
handling this?  Though it's probably not a big deal since one would expect
this to happen very very seldomly.  An obvious solution is to not use the
embedded descriptors, however this then of course removes the benefits of
doing such.  Another solution may be to have the MG wait for the Reply to
the offhook before providing dial tone, but this is kind of complex because
the Reply handling may be in a completely different entity and level than
event/signal handling.

Thanks.

John Stock
Systems Engineering
Advanced Fibre Communications
john.stock@afc.com
707-792-6249

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