Unified Networks IP Stimulus (UNIStim)

Unistim is a Nortel proprietary VOIP protocol. It is a lower level protocol than SIP or most other VOIP protocols. It's important to always think of the phone as a very dumb terminal. Whereas with SIP, the phone has a basic understanding of a phone call,in Unistim the phone knows how to send key press events, display text, flash light, and stream audio. All intelligence is at the switch layer. Like SIP Unistim does use RTP as its audio transport. Nortel has broken up the commands into 6 managers each having a set of phone initiated and switch initiated commands. The managers are Basic, Broadcast, Audio, Key/Indicator, Display, Broadcast. Unistim general layout:

| RUDP Sequence ID MSB | | ... | | ... | | RUDP Sequence ID LSB | | ACK/NAK/Payload | | Unistim/Unistim with Term id | | Term ID MSB (if from phone) | | ... | | ... | | Term ID LSB | | CMD1 Address (Manager) msb 1=phone 0=switch | | CMD1 Length includes address | | CMD1 ID | | if necessary additional data | | ... | | CMD2 Address if applicable | | CMD2 Length includes address | | CMD2 ID | | if necessary additional data | | ... |

Nortel's RUDP:

In a nutshell every payload packet sent from either the switch or the phone has a sequence id. The receiver of the packet must send an ACK back with the sequence id. If the equipment is expecting id 1000 and instead receives 1004 it would send a NAK on packet 1000 and the sender would have to resend all packets beginning with 1000. The phone and the switch have independent sequence numbers.

0xFFFFFFFF has special significance as a sequence number. When a phone starts up it would send 0xFFFFFFFF which the switch would then NAK, except the sequence number of the NAK would be the sequence number the switch wants the phone to use as a starting point. Also if the switch fails over to the backup it would use the 0xFFFFFFFF to signal the phone that a fail-over has occurred and the phone should take appropriate action.


It is my understanding that Unistim is basically an IP adaptation of Nortel's DMS protocol.

Protocol dependencies

Example traffic

Example of multiple commands comming from the switch:


Example of phone sending key press event showing terminal id:



The Unistim dissector is partially functional. Nortel has published a pdf which describes the protocol, but as I have been writing the dissector I have discovered several discrepancies. Some were decipherable but some weren't. There are a few commands which transmit either icon bitmaps or font descriptions which I have chosen to display as hex data.

Preference Settings

None at this time

Example capture file

Display Filter

A complete list of UNISTIM display filter fields can be found in the display filter reference

Show only the UNISTIM based traffic:


Capture Filter

You cannot directly filter UNISTIM protocols while capturing. However, if you know the UDP port used (see above), you can filter on that one.

Capture only the Unistim traffic over the default port (5000):

 udp port 5000

External links

Nortel Phones


Imported from https://wiki.wireshark.org/UNISTIM on 2020-08-11 23:27:05 UTC