# Is it possible to shorten "to-tag" 32 character to 16 character **URL:** \ **Category:** Asterisk SIP\ **Created:** [March 26, 2026, 6:56am UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417 "2026-03-26T06:56:43Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![hhs](https://avatars.discourse-cdn.com/v4/letter/h/5daacb/32.png) [@hhs](https://community.asterisk.org/u/hhs)\ **Post date:** [March 26, 2026, 6:56am UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/1 "2026-03-26T06:56:43Z")
Hi everyone, We have two SIP servers in our setup. One is an Asterisk server that we manage, and the other is a custom SIP server developed by another company. We can successfully initiate calls from the custom SIP server without any issues. However, we are encountering a problem when terminating calls. The issue appears to be related to the **To-tag** value in SIP signaling. Asterisk generates a 32-character To-tag and sends it to the custom server. However, the custom server seems to assume that the To-tag is only 16 characters long. As a result, when it sends a request to terminate the call, it includes only the first 16 characters of the To-tag. Because of this mismatch, Asterisk cannot match the dialog and responds with **“Call does not exist.”** This behavior suggests that the issue originates from the custom SIP server. However, before escalating it to the vendor, I would like to confirm: Is it possible to configure Asterisk to generate a shorter (e.g., 16-character) To-tag? If so, how can this be achieved? Otherwise, we will need to coordinate with the vendor to resolve this incompatibility. Thanks in advance for your help. This is the output: \<— Transmitting SIP response (864 bytes) to UDP:192.168.1.21:5060 —\> SIP/2.0 200 OK Via: SIP/2.0/UDP 192.168.1.21:5060;rport=5060;received=192.168.1.21;branch=z9hG4bK138199868 Via: SIP/2.0/UDP 192.168.1.41:5060;rport=5060;branch=z9hG4bK1654394224319 Record-Route: sip:192.168.1.21;lr Call-ID: TestCallID-172.16.61.61-rm86k4132p014 From: “gorev\_39” sip:2039@sip.navcom-redzone.com;tag=tpo9n24200014 To: “alm\_ans\_1” sip:2621@navcom-aa.com; **tag=3ae456f0-eec2-4703-8610-212d2f280158** CSeq: 1 INVITE Server: Asterisk PBX 20.2.1 Allow: OPTIONS, REGISTER, SUBSCRIBE, NOTIFY, PUBLISH, INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, MESSAGE, REFER Contact: sip:0.0.0.0:5060 Supported: 100rel, timer, replaces, norefersub Content-Type: application/sdp Content-Length: 153 v=0 o=- 0 2 IN IP4 0.0.0.0 s=Asterisk c=IN IP4 0.0.0.0 t=0 0 m=audio 12238 RTP/AVP 8 a=rtpmap:8 PCMA/8000 a=ptime:20 a=maxptime:150 a=inactive \<— Received SIP request (430 bytes) from UDP:192.168.1.21:5060 —\> BYE [sip:2621@navcom-aa.com](mailto:sip:2621@navcom-aa.com) SIP/2.0 v: SIP/2.0/UDP 192.168.1.21:5060;branch=z9hG4bK28452914 v: SIP/2.0/UDP 192.168.1.41:5060;branch=z9hG4bK1654394224319;rport=5060 Max-Forwards: 69 t: alm\_ans\_1 sip:2621@navcom-aa.com:5060; **tag=3ae456f0-eec2-47** f: gorev\_39 sip:2039@sip.navcom-redzone.com;tag=tpo9n24200014 Call-ID: TestCallID-172.16.61.61-rm86k4132p014 CSeq: 2 BYE m: sip:2039@192.168.1.41:5060;transport=udp l: 0 \<— Transmitting SIP response (446 bytes) to UDP:192.168.1.21:5060 —\> SIP/2.0 481 Call/Transaction Does Not Exist Via: SIP/2.0/UDP 192.168.1.21:5060;received=192.168.1.21;branch=z9hG4bK28452914 Via: SIP/2.0/UDP 192.168.1.41:5060;rport=5060;branch=z9hG4bK1654394224319 Call-ID: TestCallID-172.16.61.61-rm86k4132p014 From: “gorev\_39” sip:2039@sip.navcom-redzone.com;tag=tpo9n24200014 To: “alm\_ans\_1” sip:2621@navcom-aa.com;tag=3ae456f0-eec2-47 CSeq: 2 BYE Server: Asterisk PBX 20.2.1 Content-Length: 0 ---
**Author:** ![omnipbx](https://sea1.discourse-cdn.com/asterisk/user_avatar/community.asterisk.org/omnipbx/32/8839_2.png) [@omnipbx](https://community.asterisk.org/u/omnipbx)\ **Post date:** [March 26, 2026, 8:15am UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/2 "2026-03-26T08:15:14Z")
unset “caller\_name” and use “UUID compliant with RFC 4122“ in “tag” ---
**Author:** ![omnipbx](https://sea1.discourse-cdn.com/asterisk/user_avatar/community.asterisk.org/omnipbx/32/8839_2.png) [@omnipbx](https://community.asterisk.org/u/omnipbx)\ **Post date:** [March 26, 2026, 8:15am UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/3 "2026-03-26T08:15:17Z")
The upstream SIP server uses “SIP compact headers.” You can enable it globally: #sip.conf [general] compactheaders = yes #pjsip.conf [system] compact\_headers=yes However, there’s a 99% chance this won’t solve the problem. The “To” field is limited to 64 bytes on the upstream SIP server. ---
**Author:** ![jcolp](https://sea1.discourse-cdn.com/asterisk/user_avatar/community.asterisk.org/jcolp/32/8848_2.png) [@jcolp](https://community.asterisk.org/u/jcolp)\ **Post date:** [March 26, 2026, 8:21am UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/4 "2026-03-26T08:21:14Z")
> [@hhs](#): > > Is it possible to configure Asterisk to generate a shorter (e.g., 16-character) To-tag? If so, how can this be achieved? There is no configuration option. It’s generated by the PJSIP library internally when creating a SIP dialog. ---
**Author:** ![hhs](https://avatars.discourse-cdn.com/v4/letter/h/5daacb/32.png) [@hhs](https://community.asterisk.org/u/hhs)\ **Post date:** [March 26, 2026, 2:08pm UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/5 "2026-03-26T14:08:27Z")
Is there a way to modify the source code so that it generates a 16-byte unique tag instead of a 32-byte one? If so, which part of the source code should be examined to implement this change? Thanks ---
**Author:** ![jcolp](https://sea1.discourse-cdn.com/asterisk/user_avatar/community.asterisk.org/jcolp/32/8848_2.png) [@jcolp](https://community.asterisk.org/u/jcolp)\ **Post date:** [March 26, 2026, 2:09pm UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/6 "2026-03-26T14:09:33Z")
Having not looked at this I don’t know specifically where, but it would be in the PJSIP library. Not in Asterisk itself. ---
**Author:** ![seanbright](https://sea1.discourse-cdn.com/asterisk/user_avatar/community.asterisk.org/seanbright/32/9799_2.png) [@seanbright](https://community.asterisk.org/u/seanbright)\ **Post date:** [March 26, 2026, 2:24pm UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/7 "2026-03-26T14:24:40Z")
> [@hhs](#): > > This behavior suggests that the issue originates from the custom SIP server. Correct. RFC 3261 places no such restriction on the `to` tag. ---
**Author:** ![system](https://global.discourse-cdn.com/asterisk/original/2X/4/475d0c889911cfb84ac4881ad6df8b523e3f9105.png) [@system](https://community.asterisk.org/u/system)\ **Post date:** [April 25, 2026, 2:24pm UTC](https://community.asterisk.org/t/is-it-possible-to-shorten-to-tag-32-character-to-16-character/112417/8 "2026-04-25T14:24:55Z")
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