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SPA112 T.38 RE-INVITE SDP with NAT

Hello,

 

We have a customer with a SPA112 on the latest firmware (1.3.3-015).  We are experiencing an issue with T38 RE-INVITES with the SDP, whereby, the SPA is not inserting the public IP address on the c=IN line - it is using the private address.  This ONLY happens on a RE-INVITE when fax is detected.  Normal Voice calls are working fine.  SIP ALG on the firewall is disabled, so the SPA is handling NAT itself with RPORT.

 

Call flow is as follows:

 

IP: 1.2.3.4 is the address of the service provider

IP: 4.5.6.7 is the address of the SPA

 

The Initial INVITE sent from the SPA is:

U 2014/04/29 10:17:12.828587 4.5.6.7:9871 -> 1.2.3.4:5060
INVITE sip:01234567890@1.2.3.4 SIP/2.0.
Via: SIP/2.0/UDP 4.5.6.7:51290;branch=z9hG4bK-33b6f3d1.
From: "4866" ;tag=5e90c75bfeef54feo0.
To: .
Remote-Party-ID: "4866" ;screen=yes;party=calling.
Call-ID: 8c61385f-f81ff7ca@10.10.100.86.
CSeq: 102 INVITE.
Max-Forwards: 70.
Contact: "4866" .
Expires: 240.
User-Agent: Cisco/SPA112-1.3.3(015).
Content-Length: 337.
Allow: ACK, BYE, CANCEL, INFO, INVITE, NOTIFY, OPTIONS, REFER.
Supported: replaces.
Content-Type: application/sdp.
.
v=0.
o=- 127744542 127744542 IN IP4 10.10.100.86.
s=-.
c=IN IP4 4.5.6.7.
t=0 0.
m=audio 5580 RTP/AVP 8 0 2 18 100 101.
a=rtpmap:8 PCMA/8000.
a=rtpmap:0 PCMU/8000.
a=rtpmap:2 G726-32/8000.
a=rtpmap:18 G729a/8000.
a=rtpmap:100 NSE/8000.
a=fmtp:100 192-193.
a=rtpmap:101 telephone-event/8000.
a=fmtp:101 0-15.
a=ptime:20.
a=sendrecv.

 

Note the C=IN line here contains the correct Public IP address for the media to be sent.

 

Once the SPA detects a fax, it RE-INVITES with:

 

U 2014/04/29 10:17:17.867742 4.5.6.7:9871 -> 1.2.3.4:5060
INVITE sip:01234567890@1.2.3.4:5060;transport=udp SIP/2.0.
Via: SIP/2.0/UDP 4.5.6.7:51290;branch=z9hG4bK-ac862738.
From: "4866" ;tag=5e90c75bfeef54feo0.
To: ;tag=gU7tDv3et16aQ.
Remote-Party-ID: "4866" ;screen=yes;party=calling.
Call-ID: 8c61385f-f81ff7ca@10.10.100.86.
CSeq: 103 INVITE.
Max-Forwards: 70.
Contact: "4866" .
Expires: 30.
User-Agent: Cisco/SPA112-1.3.3(015).
Content-Length: 271.
Content-Type: application/sdp.
.
v=0.
o=- 127744542 127744543 IN IP4 10.10.100.86.
s=-.
c=IN IP4 10.10.100.86.
t=0 0.
m=image 23862 udptl t38.
a=T38FaxVersion:0.
a=T38MaxBitRate:14400.
a=T38FaxRateManagement:transferredTCF.
a=T38FaxMaxBuffer:200.
a=T38FaxMaxDatagram:200.
a=T38FaxUdpEC:t38UDPRedundancy.

 

Notice here how the C=IN line has the SPA private IP address.  Because of this, it never receives the T.38 stream.

 

I've attached a full sip trace rather than clog this post :-).

 

The configuration of the SPA for NAT is:

Handle VIA received: No

Insert VIA received: No

Substitute VIA Header: No

STUN Enable: NO

Handle VIA rport: Yes

Insert VIA rport: Yes

NAT Mapping Enable: Yes

NAT Keep Alive Enable: Yes

 

 

As mentioned above, all inbound and outbound calls work absolutely fine.  We only get the problem with T.38 re-invite.

 

 

Anyone else have this issue, any ideas?

 

 

2 REPLIES
New Member

Anyone else experiencing this

Anyone else experiencing this issue?

New Member

Barry,I cannot say for sure

Barry,

I cannot say for sure as I don't have a Cisco T.38 ATA yet (it's in shipping).

However, I can tell you from LOTS of experience with CISCO SPA504Gs that are behind NAT, we experienced very similar problems establishing audio streams until we set the NAT SETTINGS for all of the to YES:

Handle VIA received: Yes

Insert VIA received: Yes

Substitute VIA Header: Yes

Handle VIA rport: Yes

Insert VIA rport: Yes

NAT Mapping Enable: Yes

NAT Keep Alive Enable: Yes

 

We don't typically use STUN:

STUN Enable: NO

 

It might be worth a try.

HTH,

Sean

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