Depending from case to case, the record-routing can be avoided, especially if you know the environment and only one server is used between two endpoints. At that moment you can store existing contact in htable and replace it with one having the server ip. You can eventually use uuid to generate the contact to be unique, but not a must.

The logic would be:

- call comes in, store $sht(x=>$ci::a1:contact) = contact uri - store $sht(x=>$ci::a1:ftag) = From tag - replace contact header with one using server ip and send out - store new contact uri as $sht(x=>$ci::a2:contact) - replies comes in, store $sht(x=>$ci::b1:contact) = contact uri - replace contact header with another new one using server ip and send out - store new contact uri as $sht(x=>$ci::b2:contact) - when a request within dialog comes in, based on From tag and $sht(x=>$ci::a1:ftag), you detect the direction and based on that you set the appropriate r-uri using either $sht(x=>$ci::a1:contact) or $sht(x=>$ci::b1:contact) and replace the contact with a2/b2 variants

Alternative to htable is to use database or other storage (e.g., nosql like redis, mongo, ...).

As a matter of fact, upcoming 4.4 includes the topos module which should do what you want here, but due to lack of time caused by some unexpected events, at this moment works properly only for MESSAGE requests. By the time of release I should have the time to fix the dialog routing as well.

Cheers, Daniel

On 20/03/16 02:41, Matthew Harrold wrote:

Thanks for your quick response.

No, you can't remove those headers. They serve an essential
purpose and the endpoints won't consider the requests or responses
valid without them.

It should be theoretically possible to remove some of the via and record-route headers, assuming the contact is also re-written. The end point's (phones) themselves do not need to be aware of anything downstream of the SIP server they're registered too.

See my blog post on this topic:

http://blog.csrpswitch.com/sip-udp-fragmentation-and-kamailio-the-sip-header-diet/

Thanks for the link!

And you certainly can't hide topology this way.

-- Alex


On 03/19/2016 09:26 PM, Marrold wrote:

    Hi,

    Is there any way to remove Via and Record-Route headers from
    requests
    sent to an endpoint and update the contact header, but have
    Kamailio
    statefully remember where the replies need to route?

    I imagine this would involve mangling the packets slightly to
    behave
    similar to a B2BUA.

    My motivations, in order of priority -

    1) Reduce UDP packet size to avoid MTU limitations
    2) Improve interoperability, don't expect end points to be able to
    properly parse / process many via / record-route headers
    3) Hide topology.

    If someone could point me in the right direction in terms of
    configuration or modules, that would be great.

    Thanks


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Thanks for your quick response.

No, you can't remove those headers. They serve an essential purpose and the

endpoints won't consider the requests or responses valid without them.

It should be theoretically possible to remove some of the via and record-route headers, assuming the contact is also re-written. The end point's (phones) themselves do not need to be aware of anything downstream of the SIP server they're registered too.

See my blog post on this topic:

http://blog.csrpswitch.com/sip-udp-fragmentation-and-kamailio-the-sip-header...

Thanks for the link!

On Sun, Mar 20, 2016 at 1:27 AM, Alex Balashov abalashov@evaristesys.com wrote:

Marrold,

No, you can't remove those headers. They serve an essential purpose and the endpoints won't consider the requests or responses valid without them.

See my blog post on this topic:

http://blog.csrpswitch.com/sip-udp-fragmentation-and-kamailio-the-sip-header...

And you certainly can't hide topology this way.

-- Alex

On 03/19/2016 09:26 PM, Marrold wrote:

Hi,

...

Is there any way to remove Via and Record-Route headers from requests sent to an endpoint and update the contact header, but have Kamailio statefully remember where the replies need to route?

I imagine this would involve mangling the packets slightly to behave similar to a B2BUA.

My motivations, in order of priority -

1. Reduce UDP packet size to avoid MTU limitations
2. Improve interoperability, don't expect end points to be able to

properly parse / process many via / record-route headers 3) Hide topology.

If someone could point me in the right direction in terms of configuration or modules, that would be great.

Thanks

---

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-- Alex Balashov | Principal | Evariste Systems LLC 1447 Peachtree Street NE, Suite 700 Atlanta, GA 30309 United States

Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/

---

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I understand intermediate endpoints *expect* these headers, this is why I asked if there's anyway for Kamailio to remember what is removed and essentially re-add them to the response, IE-

SIP request hits edge proxy from internal network > Via and Route headers from intermediate proxies are removed, previous 'path' is stored in memory linked to the dialog > SIP request is forwarded to end point.

End point responds to request via edge proxy > edge proxy looks up existing dialog and reinserts the missing headers > forwards to the next hop.

What I'm asking is theoretically possible, although it may not be RFC compliant or something that Kamailio supports.

Thanks

On Sun, Mar 20, 2016 at 2:40 AM, Alex Balashov abalashov@evaristesys.com wrote:

On 03/19/2016 09:43 PM, Marrold wrote:

It should be theoretically possible to remove some of the via and

...

record-route headers, assuming the contact is also re-written. The end point's (phones) themselves do not need to be aware of anything downstream of the SIP server they're registered too.

No, because intermediate endpoints:

(1) Expect the Route set to remain as configured between the two endpoints;

(2) Expect Vias corresponding to their hop to remain as upstream elements remove theirs in transit.

You can't break SIP like that - terribly sorry! :-)

-- Alex

-- Alex Balashov | Principal | Evariste Systems LLC 1447 Peachtree Street NE, Suite 700 Atlanta, GA 30309 United States

Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/

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That's essentially what I'm hoping for, although I appreciate from an RFC purist perspective it's probably a bit of a nasty hack.

On Sun, Mar 20, 2016 at 2:57 AM, Alex Balashov abalashov@evaristesys.com wrote:

So, you mean some sort of scheme wherein...

(1) Kamailio keeps endpoint A in the dark as to the fact that anything was removed;

(2) Kamailio portrays itself as a UA/origin of all requests?

-- Alex

-- Alex Balashov | Principal | Evariste Systems LLC 1447 Peachtree Street NE, Suite 700 Atlanta, GA 30309 United States

Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/

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