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What Are the Similarities Between SPA112 and SPA122 ATA's?
In a nutshell they are both:

• A Two Port ATA (Analog Telephone Adapter)
  Each port is independently configurable with a different SIP VoIP account, or service.
  This essentially gives you two separate VoIP services (or lines) in one box. You connect one telephone for each VoIP account or line enabled. Or, you can configure it to use one line as a telephone, and the other line as a FAX line.
• Both ATA's use the same firmware versions. (at least they do at the time of this article). Therefore, all functionality is essentially the same, except for special features enabled in the SPA122 that are not enabled in the SPA112.

So, if you are looking for a DIY 2-port VoIP ATA, either of these two ATA's will do the job.

Really, that's the bottom line of what these ATA's have in common. They are basically the same.... except...

The Real Difference Between the SPA112 and SPA122
The real difference between these two boxes lies in what the SPA122 can do, that the SPA112 can't do.

SPA112
SPA112_back_Large1.jpg (11.61 KiB) Viewed 11176 times

SPA122
SPA122_image4_back1.jpg (13.52 KiB) Viewed 11176 times

In a nutshell, the SPA122 is the SPA112 + the following features added:

• A built-in NAT-Router.
• A built-in DHCP Server, with DHCP IP address reservation capability.
• An extra "Ethernet port" for connecting to a PC, or LAN Switch.
• Port Forwarding for devices behind its Firewall (when enabled as a NAT-Router).
• QOS - Upstream flow control. (giving your VoIP calls upstream priority through its Internet port) QOS is only enabled when in NAT-Router Mode (not available in Bridge Mode).
• DMZ option - (for those who just can't quite figure out port forwarding)
• Bridge Mode - Allows the SPA122 to function just like SPA112 + the extra Ethernet switch port.
  Bridge Mode is minus DHCP and NAT functionality. (it's all about the firmware)

Bottom line, the SPA122 is a full fledged 2-port Ethernet switch and NAT-Router with a built-in 2-Port VoIP ATA, that also has the option of Bridge Mode, for when you don't need NAT-Router functionality (then it's really just like the SPA112 plus the Yellow Ethernet port).

So, which one do you pick?
Well, I have both. But, if I had to make a choice based on personal network circumstances, I would decide based on the following:

Pick the SPA112 when:

• You already have a network NAT-Router and just want to configure your very own VoIP ATA for a DIY VoIP service.

Pick the SPA122 when:

• You don't have a NAT-Router. The SPA122 will function as your NAT-Router and VoIP adapter in one box. Then, add an Ethernet Switch behind it (4-port or 8-port, etc.) and you can use this as your main network NAT-Router-Firewall and DHCP server with port-forwarding capability, and VoIP QOS as a bonus.
• You want the flexibility to occasionally use it behind an existing NAT-Router (in Bridge Mode).

For a few extra pounds, the SPA122 offers the most flexibility and the best of both worlds.