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Jul 18 / Greg

Second Line On Cisco ATA 186/188

Cisco ATAs have a second line, but you may have also noticed that there is no phone button template that includes two lines for an ATA 186…interesting. It turns out that the second line on the ATA has a completely seperate MAC address associated with it. To use the second line you add it as if it is its own ATA. The MAC, however, isn’t printed on the ATA…there is a secret trick to calculate the MAC for the second line.

An ATA MAC will appear as:


To figure out what the second line’s MAC is, subtract the first two digits on the left as so:


Then add 01 to the end:


That’s it. Just add a new ATA to the system and use the newly calculated MAC.

There are some caveats. If you want to run two simultanious calls, you can only run certain codecs at the same time:

  • Two simultaneous G.723.1 codecs
  • Two simultaneous G.711 codecs
  • One G.723.1 and one G.711 codec
  • One G.729A and one G.711 codec (G.729A is available on first-come, first-served basis)

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    1. iam8up / Jul 21 2011

      Are you sure the second port will do 729 even if the first port is not using it? Usually the DSP is port specific.

    2. Greg / Jul 21 2011

      They say first come first serve…so I’m going to say I have no idea. hehe. They imply that it will. I don’t have the cycles to test, otherwise I would like to know also.

    3. thepowell2000 / Mar 5 2012

      I learned this one the hard way. I couldn’t figure out where this other phone MAC address was coming from. I kept trying to remove it, but with auto-register turned on it kept coming back. Ah, Cisco was sneaky with this one.

    4. kambizms / Jul 27 2012

      very good

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