How do I choose between a Linksys PAP2 and SPA2100 VoIP adapter?

The PAP2 and the SPA-2100 are both 2-Line Analog Telephone Adapters(ATA) that convert VoIP signaling to an analog voice signal so you can use your traditional telephone devices; i.e. your home phone or business phone system. So which one is right for me? The basic answer lies in the need for a router or the need to minimize bandwidth usage. I'll address these individually.

Router Functionality
The PAP2 only has one Ethernet LAN port while you notice that the SPA-2100 has an additional RJ45 WAN port. The additional WAN port on the SPA-2100 is due to the built-in router. In case your network doesn't have a router (i.e., your computer connects directly to your DSL or cable modem) you will need to use the SPA-2100. If your network has a router you can use either the PAP2 or the SPA-2100 (in this case the WAN port of the SPA-2100 is connected directly to your existing LAN).

One easy way to determine if your DSL or cable modem is also a router is does it have additional Ethernet connections to allow the device to share between multiple computers. If so, you can use either the PAP2 or SPA2100; if not, you must use the SPA2100.

Quality of Service
An important function of the router on the SPA-2100 is providing QOS (Quality Of Service) to the two voice channels, when the SPA2100 is used as your router it guarantees that the voice channels get priority over none real-time data transactions such as file transfer and web page content. If you do heavy streaming of video or audio, ie gaming, etc. we recommend the SPA2100

Keep in-mind that the Ethernet interface on the SPA-2100 is 10BaseT and therefore, will limit your modem data to 10Mbps. Most networks handle 10Mbt connections just fine.

Bandwidth Usage
Both the PAP2 and SPA-2100 support multiple voice compression standards; G.711 (A-law and µ-law), G.726 (16/24/32/40 kbps), G.729 A, and G.723.1 (6.3 kbps, 5.3 kbps) voice coding. The most commonly used voice coder is G.711 because at 64Kbps speed it is the closest thing to a standard voice signal. The downside however is it requires 64Kbps data rate in each direction (transmitting and receiving voice). Once you add the network overhead it requires, you must have sustained data rate of about 100Kbps on both the up and down channels.

In cases where adequate bandwidth is not available or being used by multiple ATAs you can compress the voice using G.726, G.723, or G.729. Because of its quality per compression rate G.729 is becoming more and more popular. The data rate requirement for G.729A is only 8Kbps (12.5% of the G.711). Yes you will gain bandwidth; however, you will also compromise voice quality. Also note that tones cannot be decoded with G.729, and therefore, fax and in-band DTMF can't be used with this compression.

One advantage of the SPA-2100 is concurrent support G.729 on both channels. The PAP2 can only support G.729 on one channel at a time. If you can afford the bandwidth, or if you are using the ATA on an internal network, I recommend you use G.711.

Note: if you are unsure of you download and upload speed of your internet connection go to http://www.speedtest.net/ , click on a test location and it will give you your public IP address as well as your download and upload speed. In most cases expect your download speed to be much faster than your upload.

Ringer equivalence number (REN)
While REN is probably not something that will come into your decision process I want to let you know how it affects your telephone performance. REN is a measurement of how much ringing power certain telephone equipment takes or generates (in this case the ATA generates the ring). From the ATA side REN determines how many telephones can connect to each ATA line and still get them ringing properly.

SPA-2100 Max Ringer load = 3REN
PAP2 Max Ringer load=5REN

In a case where you plan to connect the ATA to a line port on your key system or to a single phone the difference in REN values are meaningless. However, if you trying to drive 3 phones bridged to a single ATA port, REN value can be a factor. You can usually find the REN use value of your telephone on a label on the bottom of the phone.

Need additional help in deciding which ATA works for you, give us a call @ 800-390-1200.