Ata Connectivity Requirements - Cisco SPA2102 Administration Manual

Introducing Cisco Small Business Analog Telephone Adapters

ATA Connectivity Requirements

NOTE
ATA Connectivity Requirements
Cisco Small Business ATA Administration Guide
For information about the WRP400, see the WRP400 Administration Guide.
An 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 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 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 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 ATA device DHCP server. The address and
port are translated by the ATA device using Network Address Translation (NAT)
and Port Address Translation (PAT). The packet is then routed back to the internal
network on the ATA device by the local router or the ISP router.
Problems can occur with calls between phones connected to the ATA device
when an outbound proxy or a router with hairpinning support is not available. The
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 ATA device, local phones connected to the 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 ATA device to a local router that
provides hairpinning support to prevent this problem.
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