DRAFT
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Discover the NAT mappings used to communicate with the peer. This could be done with the help of
some external device. For example a server could be deployed on the external network such that the
server will respond to a special NAT-Mapping-Discovery request by sending back a message to the
source IP address/port of the request, where the message will contain the source IP address/port of the
original request. The SPA can send such a request when it first attempts to communicate with a SIP
entity in the public network and stores the mapping discovery results returned by the server.
Communicate the NAT mapping information to the external SIP entities. If the entity is a SIP Registrar,
the information should be carried in the Contact header that overwrites the private address/port
information. If the entity is another SIP UA when establishing a call, the information should be carried in
the Contact header as well as in the SDP embedded in SIP message bodies.
The VIA header in
outbound SIP requests might also need to be substituted with the public address if the UAS relies on it to
route back responses.
Extend the discovered NAT mappings by sending keep-alive packets. Since the mapping is only alive for
short period, the SPA continues to send periodic keep-alive packets through the mapping to extend its
validity as necessary.
Note: NAT Mapping does not have to applied globally on the phone. It can be enabled or disabled per
Extension. Some service providers offer their own solution of NAT traversal; NAT mapping should be
disabled on the SPA-841 for extensions configured for these service providers.
7
Data Networking Features Supported
The SPA-841 supports the following Data Networking Features:
MAC Address (IEEE 802.3)
IPv4 – Internet Protocol Version 4 (RFC 791) upgradeable to v6 (RFC 188
ARP – Address Resolution Protocol
DNS – A Record (RFC 1706), SRV Record (RFC 2782)
DiffServ (RFC 2475) and ToS – Type of Service (RFC 791/1349)
DHCP Client – Dynamic Host Configuration Protocol (RFC 2131)
ICMP – Internet Control Message Protocol (RFC792)
TCP – Transmission Control Protocol (RFC793)
UDP – User Datagram Protocol (RFC768)
RTP – Real Time Protocol (RFC 1889) (RFC 1890)
RTCP – Real Time Control Protocol (RFC 1889)
SRTP - Secure Real Time Control Protocol (RFC XXXX)
8
Configuring and Provisioning Overview
The SPA-841 requires the administrator to ensure that two files are loaded correctly onto the device.
These files are:
•
A firmware file (e.g. SPA841.bin). This file provides the operating system and call processing
functions for the device. Firmware upgrades are explained in Section 13.
