Point To Point w/ SPA-Series ATA

[Sean-T123]

I've been looking at Cisco ATA's to implement a project; but telephony is not my forte'. With two SPA-122 ATA's, is it feasible to setup a private point-to-point hotline? Configuration: Phone / SPA-122 w/Rtr / Media Converter / Fiber / Media Converter / SPA-122 w/Rtr / Phone. There would be no service provider in the middle just a fiber run that I have access to. Static IP's of course with the SPA-122 version with the integral router. I just want to make sure my idea matches the equipment setup I'm envisioning. Any input or advice from those with telephony experience is appreciated. Thanks. Sean

[Dan Lukes]

Well, there are several decisions you did. I don't know they are intentional or not.

Are you wishing to use router capabilities of SPA122 to route traffic beyond hotline VoIP stream ? You may be interested to know that such router is not suitable for high speed lines. I assume your line is 100Mbps or 1Gbps capable. With router part of SPA122 you should not count with more than 20Mbps. You should consider to use dedicated router if you wishing for higher speed. If you decide to use dedicated router you may consider to use SPA112 (ATA with no router embedded) instead of SPA122.

If you are not going to use the line for traffic beyond hotline's VoIP stream you need no router and you may use SPA112 as well.

In all cases, the use of SPA1x2 is raising other questions. The main purpose of ATA adapter (SPA1x2) is to convert VoIP SIP stream to plain old analog phone line. Did you considered to use native SIP phone like SPA3xx that require no such conversion ? The configuration of such kind of phone is almost same as configuration of ATA convertor (SPA1x2) and you will avoid all the problems related to analog line and the conversion of SIP to analog.

According the core of your question, yes, you can make direct calls from phone to phone. You need no switch inbetween. The example configuration is described here:

Configuring IP Dialing on the PAP2

Don't be confused it's for PAP2 device. With the exception of different UI design, the configuration of PAP2, SP112 and SPA30x is the same. Same names and meaning of options, same format of option values.

[Sean-T123]

Thank you Dan; your reply is helpful. I actually did intend to restrict traffic to only between to to ATA's - no outside traffic. Strictly a voice hotline, go offhook on either end and the other end rings. Being limited to 20Mbs is not an issue. Voice needs to be 5x5 and very reliable; bandwidth will not be stressed.

I actually need to go PTSN/VOIP/PTSN - no choice. Usually the signals don't need to go that far. This signal however needs to go a ways farther than possible without fiber. I'm working with a specialized voice switching system designed prior to VOIP. The only telephone out is PTSN and similar.

The configuration info really made the concept come together; now I understand how the port handshaking is created.

Thanks again Dan.

[Dan Lukes · Accepted solution]

your reply is helpful

Just rate usefull responses, but I'm happy to hear it even without rating ;-)

I actually did intend to restrict traffic to only between to to ATA's - no outside traffic. 

Then you need no router, thus you need no SPA122. SPA112 is sufficient to connect analog phone (or analog phone-like device). But unless you need to connect analog phone/device you should consider use of SPA3xx instead (connected by cross-over ethernet cable directly to media convertor, no SPA1x2 necesarry at all).

Strictly a voice hotline, go offhook on either end and the other end rings. Being limited to 20Mbs is not an issue. Voice needs to be 5x5 and very reliable; bandwidth will not be stressed.

     Use G.711a or G.711u codec and the voice quality should be excelent.  It should be suitable for fax/data transfers up to 9600baud as well (but no warranty of it).

     Also, the phone can be configured to dial predefined number automaticaly just because the handset become off-hook is possible. See Explaining Dial Plan Hot Line / Warm Line examples if you like to setup calls with no dialing.