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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


Unistim/Unistim with Term id

Term ID MSB (if from phone)




CMD1 Address (Manager) msb 1=phone 0=switch

CMD1 Length includes address


if necessary additional data


CMD2 Address if applicable

CMD2 Length includes address


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]

Capture Filter

You cannot directly filter PROTO protocols while capturing. However, if you know the ["TCP"] port used (see above), you can filter on that one.