Sipura SPA-2100 is a multi-port, all-in-one Analog telephone and fax machine adapter. It has two FXS ports(Analog Telephone Adapter), two Ethernet ports(LAN and WAN) and one power-supply jack. Sipura SPA-2100 supports various protocols including SIP 2.0, TCP/UDP/IP, RTP/RTCP, HTTP, ICMP, ARP/RARP, DNS, DHCP(both client and server), NTP, TFTP, PPPoE, STUN.. It also supports different codecs: G.711, G.723.1, G.729A/B, G.728, G.726, iLBC, T.38.

The Sipura SPA-2100 eliminates the NAT problem by being both a router and a SIP adapter, which allows it to use your public IP address in SIP messages. The most common NAT problem is one-way audio (the other person can hear you, but you can't hear him). If your Sipura SPA-2100 is plugged directly into your DSL/cable modem and you have one public IP address (typical situation), then your Sipura SPA-2100 will use the public IP address (rather than a private IP address that would be assigned if a typical home router was in between the DSL/cable modem and the SIP adapter), which eliminates NAT problems.

The Sipura SPA-2100 also has a couple more relatively minor benefits: T.38 (QoS for faxes), and G.729 works simultaneously on both lines (which means that if you have a typical 128 kbps uplink, you can make two phone calls and browse the Internet all at the same time).