[SIPForum-discussion] General SIP Server Question

[Vivek Batra]

Hi,
Yes, it leads to confusion when you consider both **proxy** and outbound
proxy at the same time.

First of all, should we say it proxy or registrar?? No matters since
different UA manufactures call by different name. E.g., Look at the
configuration of Linksys UAs and Grandstream, you will found it by name
Proxy however in Vodtel, Matrix etc, you will found by name Registrar.
Name of Outbound in UA configurations remain the same.

Now why we need proxy (or registrar) when we have outbound? I believe that
we need because of following:

1. NAT Traversal
2. Support multiple domains (much required in ITSP business)

First requirement can also be served by not having any outbound proxy. We
can have only proxy (or registrar) in the same box only.

But in the second requirement, two separate logic modules are required to
maintain the call control (signaling/ media) which is handled by outbound
proxy and to maintain the location service which is handled by proxy (or
registrar).
In those scenerios, proxy (or registrar) address just acts as tag in the SIP
message which identifies the User Domain. However, it is possible that the
proxy (or registrar) is configured in the same box in which outbound is
configured.

You can see various ITSP's providing this type of service. Suppose you have
company with URL kapanga.com. Now u need SIP number for each employee in
your company. What generally ITSP do in this case is, providing you numbers
like employee1 at kapanga.com, employee2 at kapanga.com etc etc.
Now kapanga.com serves you as proxy server address (or registrar server
address). This address does not need to be resolved by global DNS server
since your ITSP would also provide you Outbound Proxy Address also.

Now you communicate only with the Outbound of your ITSP, however you provide
your domain information in the SIP message (FROM, TO etc). Outbound address
is only used upto netowrk layer. Proxy address (or registrar address) serves
you on application layer.
Doing this, outbound identifes the domain (e.g., Kapanga.com in this case)
it serves.

I hope, this would give some idea however please do give your feedback.

--VB



On Tue, Aug 26, 2008 at 7:47 AM, 杨伟 <shyw13 at gmail.com> wrote:

> Hi, Vivek
>
> I am a little bit confused with case 3.
>
> In case 3, both Proxy address and  outbound proxy address are set. I could
> not any possibility a message will be sent to the Proxy. So it is not used?
>
>
> 2008/8/14, Vivek Batra <vivek7683 at gmail.com>:
>
>> Jerry,
>> Following possibilities are there in each SIP Phone.
>>
>> 1. When you configure only registrar address (or proxy address), SIP phone
>> sends the registration request and call request (INVITE etc) only to
>> registrar/ proxy address configured.
>>
>> 2. When you configure only outbound proxy address in SIP Phone (and not
>> registrar/ proxy address), SIP phone does not sends any registration request
>> however all other messages are send to outbound server only.
>>
>> 3. When you configure both registrar/ proxy and outbound proxy address,
>> all registration request and call request is send to outbound server only on
>> IP layer however the request is sent for specific domain only (which you
>> have been configured as registrar/ proxy address).
>>
>> Difference between case1 and case3 is, you have not set the outbound in
>> case1 while it is in case3. Hence, in cas1, if registrar/ proxy server
>> redirect you to some other domain, SIP Phone tries to send the request to
>> redirected domain only. However, in case3, you have been set the outbound,
>> hence if outbound redirect you to some other domain, then also SIP phone
>> sends the new request to same outbound only which is configured.
>>
>> Hence, the name of SIP entities depends on how you use it!!
>>
>> Cheers!
>> Vivek
>>
>> On Wed, Aug 13, 2008 at 10:45 AM, Jerry Richards <
>> jerryr at tonecommander.com> wrote:
>>
>>> Hello All,
>>>
>>> General question regarding a SIP phone configuration where the phone
>>> communicates with a single SIP server.  Would you agree such a phone need
>>> only configure the following two SIP server entities?
>>>
>>> 1) SIP Registrar (either IP-address or domain-name) to be used inside the
>>> SIP messages for both registration and call-control.
>>>
>>> 2) SIP Proxy (either IP-address or domain-name) to only be used to
>>> identify
>>> where SIP messages are sent.  Basically, this is an Outbound Proxy.
>>>
>>> RFC 3261 uses Proxy and Outbound Proxy and Registrar as if there are
>>> three
>>> entities, so I'm a bit confused.
>>>
>>> Best Regards,
>>> Jerry
>>>
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>>
>>
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