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SMDI Serial Cable - Maximum length ?

Hi all,

I have to install a UNITY Dual-switch integration whit CCM and Ericsson MD110 PBX.

The computer room (where the UNITY server resides) is 3 or 4 floors above the PBX room (where the MD110 resides).

Is there a limitation for the RS232 cable length between the UNITY server serial port, and the PBX?

Thanks for your answer


Cisco Employee

Re: SMDI Serial Cable - Maximum length ?

The maximum supported cable length is directly related to the speed of transmission; the slower the data, the longer the maximimum length.

I'm pretty sure the textbook answer is going to be 50 feet @9600 baud; which is defined in the RS-232 spec. However, your milage may very. If there's a lot of interfence, this length may go down. If evironmental factors are good, the length may go up.

The Unity group has not done any testing on cable length, and there might be other requirements from the PBX. But I think the "safe" answer is 50 feet. Anybody else out there have success with longer distances?


Re: SMDI Serial Cable - Maximum length ?


Black Box sells an RS232 signal extender called Miniture Async Short Range Modem (SRM-5A) (made by RAD) that will extend an RS232 signal out to 2-3 miles at 9600 baud on 24 AWG copper wire. I'm using these extenders on my SMDI link on a Nortel SL-100. My guess is that they would work in your application. The Black Box part number is ME749A-M or ME749A-F (male or female).

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