2 Dec
2004
2 Dec
'04
9:16 p.m.
Hi all!
This is a "request for comments" and I would be happy If you give me
your opinions. And maybe we could see some of the results in ser. :-)
When configuring ser (editing the ser.cfg), IMO a big problem is the
mixture of routing logic and NAT traversal. Every time I think about
routing policies (inbound, outbound, in-dialog, out-dialog ...) I always
have to take care about the NAT traversal. ser.cfg would be much easier
to handle if we do not have to take care about NAT traversal. Therefore,
already several companies use dedicated NAT traversal devices which
will be configured as outbound proxy in the user agents (eg. Jasomi Peer
Point).
I want to use another ser instance as dedicated outbound proxy - that is
NAT traversal and nothing more (maybe some kind of protection using the
permissions and pike modules). AFAIK this is not possible with current
ser out-of-the-box. If this is wrong, please correct me and ignore the
rest of this email.
I came up with 2 solutions for this problem:
1. Using the "Path:" header as described in RFC3327
2. Enhance ser to rewrite the Contact: in the outbound proxy, store the
real contact, and forward to the main proxy.
Now, a bit more detailed for the follwing setup:
UA1 -- OBProxy -- mainProxy -- ..... UA2
1.
During registration, the OBP adds an "Path:" header with its SIP URI to
the REGISTER message. The mainProxy does not only save the AOR and the
Contact: URI, but also the Path: headers. If the main proxy "lookup()"
the contact of UA1, it also retrieves the stored Path and creates the
Route: headers. Therefore, the OBP stays always in the signaling path
for out-dialog transactions. To stay also in the signaling path for
in-dialog transaction, RecordRoute will be used (as usual).
Advantages: The OBProxy does not have to save()/lookup(), therefore no
kind of storage is required. Will be needed for 3GPP.
Disadv: The UA has to send keep-alive messages (CRLF) to keep the NAT
binding alive.
Todo: save() must also save the "Path", lookup() must retrieve the
"Path" and add it to the "Route". Adding the Path header can be done
by
a new function or using "subst/append_hf".
2.
The outbound proxy receives a REGISTER with e.g.
Contact: <sip:klaus@10.0.0.4:5060>.
First it uses fix_nated_contact: =>
Contact: <sip:klaus@1.2.3.4:4321>.
Then it creates a new contact URI which uses the fixed contact as
username and the IP Address of the OBP as domain part, e.g:
Contact: <sip:klaus%401.2.3.4%3A4321@5.6.7.8>
Then, the outbound proxy saves in the location table the fixed contact
and the modified contact (instead of the AOR) and then it forwards the
modified REGISTER to the mainProxy.
Now, the main proxy will store <sip:klaus%401.2.3.4%3A4321@5.6.7.8> as
contact for the AOR of UA1. Thus, if the main proxy makes a "lookup()",
it will forward the requests to the OBP. Then the OBP also makes a
lookup and retreives the fixed contact address.
Todo: create a new "save_obp" function which rewrites the contact and
stores the fixed and new contact (instead of fixed contact and AOR).
What do you think about this? (I prefer Version 1)
I think this will be a good enhancement to ser and should not be that
hard to implement.
regards,
Klaus