Polycom SIP 2.2.2 - Manual (Page 209)

Configuration Files
A - 97
This configuration attribute is defined as follows:
Attendant <attendant/>
The Busy Lamp Field (BLF) / attendant console feature enhances support for
a phone-based attendant console.
Attribute
Permitted
Values
Default Interpretation
nat.ip dotted-decima
l IP address Null IP address to advertise within SIP signaling - should
match the external IP address used by the NAT device.
nat.signalPort 1024 to 65535 Null If non-Null, this port will be used by the phone for SIP
signaling, overriding the value set for
voIpProt.local.signalPort
in sip.cfg.
nat.mediaPortStart 1024 to 65535 Null If non-Null, this attribute will be used to set the initially
allocated RTP port, overriding the value set for
tcpIpApp.port.rtp.mediaPortRangeStart
in sip.cfg.
Refer to RTP <rtp/> on page A-54 .
nat.keepalive.interval 0 to 3600 Null If non-Null (or 0), the keepalive interval in seconds. This
parameter is used to set the interval at which phones will
send a keep-alive packet to the gateway/NAT device to
keep the communication port open so that NAT can
continue to function as setup initially.
The Microsoft Live Communications Server 2005
keepalive feature will override this interval. If you want to
deploy phones behind a NAT and connect them to Live
Communications Server, the keepalive interval received
from the Live Communications Server must be short
enough to keep the NAT port open. Once the TCP
connection is closed, the phones stop sending keep-alive
packets.
Note These attributes are available on SoundPoint IP 600 and 601 phones (with an
attached Expansion Module) only.