19 Mar
2003
19 Mar
'03
11:01 p.m.
I agree with Juha. In my opinion possibility to register and use more
than one contact is very nice feature of SIP and it shouldn't be restricted
this way.
It is also possible that user agents will register more than one
contacts transparently, they may use different port numbers for presence
and instant messaging (SUBSCRIBE,NOTIFY,MESSAGE) and different port
number for voice (INVITE, ACK, BYE). Restricting ser to just one contact
will prohibit such user agents because our registrar doesn't support
callee preferencies yet. On the other hand right now I am not aware of
any user agents using multiple ports this way.
Also user agents capabable of simultaneous use of TCP and UDP might want
to register 2 contacts, one for UDP and one for TCP transport.
If I understood your email correctly, the only problem with unregistered
user agents when IP address changes is that another user agent (which
was assigned IP address of the previously unregistered user agent) will
receive calls not targeted to him. Something like this:
1) UA1 with IP1 registers
2) hang up, UA1 is still registered with IP1
3) another user dials in, gets previsously freed IP1 and starts UA2
4) UA2 registers (with different address of record)
5) UA3 invites UA1 (which is offline already) but the INVITE will be
sent to UA2 (which has now IP1)
I don't know if there is any time window in which a previsously assigned
IP address must not be reassigned, but I assume no.
Such a situation cannot be completely avoided, but the probability that
something like this will happen can be significantly decreased by using
reasonably short expires intervals. Morover I could extend registrar to
either: 1) refuse contacts with too long expires parameter
2) force shorter expires value if the value provided by user
agent is too long.
Shorter expires value will, of course, increase traffic.
What do you think ? Maybe limited expires value could solve your
problem ?
In regards to q parameter: q is preference of contacts (see RFC3261).
This parameter is provided by user agents when registering contacts and
can be assigned value from 0.00 to 1.00, where 0 means the lowest and 1
the highest priority among contacts registered for a single address of
record.
Jan.
On 19-03 17:02, Juha Heinanen wrote:
Ricardo Villa writes:
You are absolutely right about
"exiting" the UA agent (our UA agent works
fine). But not everybody in the network is going to go through the menu and
click "log out" every time. Some people will close it, or some people might
drop their dial-up connection and redial again right away.
even if you close the UA window, it should still unregister. droping of
connection wihtout the user doing so is of course another thing that
very little can be done about.
I am just trying to eliminate this scenario as a
potential problem.
but at the same time you are removing an extremely valuable feature of
sip, i.e., allowing several parallel registrations and forking to them.
may be i didn't understod what the problem actually is. if i have two
registrations for the same uri and one of them is not valid anymore,
then, due to forking, the valid one will receive the requests anyhow.
-- juha
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