Linksys ATA Administration Guide
18
Linksys ATA Connectivity Requirements
Introducing Linksys Analog Telephone Adapters
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).
Line 1
Line 2
Internet
IP Router (with
hairpinning) or
Broadband modem
ITSP
ISP
PAP2T
LAN
WAN
Ethernet
port
Administrative
IVR (Line 1 or
Line 2)
IP
IP
187420
