Linksys RTP300 User Guide - Page 18

Introducing Linksys Analog Telephone Adapters Linksys ATA Connectivity Requirements Linksys ATA Connectivity Requirements A Linksys ATA device can be connected to a local router, or directly to the Internet. Each phone connected to an RJ-11 (analog) port on the Linksys ATA device connects to other devices through SIP, which is transmitted over the IP network. In order to ensure connectivity between the devices connected to its FXS ports, the Linksys ATA device requires the following functionality to be supplied on the network connected to its Ethernet port: • Connection to an IP router with hairpinning support • Connection to an outbound Proxy server When a phone connected to the Linksys ATA device communicates with another phone, it sends a SIP packet onto the internal LAN. The packet is then forwarded to the external LAN or directly to the Internet. The source address and source port on the original packet are assigned by the Linksys ATA device DHCP server. The address and port are translated by the Linksys ATA device using Network Address Translation (NAT) and Port Address Translation (PAT). The packet is then routed back to the internal network on the Linksys ATA device by the local router or the ISP router. Problems can occur with calls between phones connected to the Linksys ATA device when an outbound proxy or a router with hairpinning support is not available. The Linksys ATA device cannot directly connect the two telephone devices, but requires a local or remote router to route the packet back to its destination on the local network from which it originated. The necessary routing can be provided by a router with hairpinning support, or by an outbound SIP proxy, which is typically provided by the Internet Telephony Service Provider (ITSP). When relying on the ITSP for interconnecting phones on the Linksys ATA device, local phones connected to the Linksys ATA device are unable to communicate with each other if the Internet connection is not available for any reason. It is recommended you connect the Linksys ATA device to a local router that provides hairpinning support to prevent this problem. Linksys PAP2T Connectivity As shown in the following figure, the PAP2T has two FXS ports (voice lines 1 and 2). Administrative IVR (Line 1 or Line 2) Line 1 Line 2 PAP2T Linksys ATA Administration Guide Ethernet port IP Router (with hairpinning) or Broadband modem ISP LAN WAN Internet IP ITSP 187420 18