User's Manual

Figure 51: Incoming/Outgoing with connection reuse
When using UDP, an IP Deskphone behind a firewall must periodically send a request to the
server to maintain an open pinhole in the firewall so that the server can contact the IP
Deskphone when sending requests.
When
using TCP/TLS and connection persistence, it is not necessary to send a SIP_PING to
the server in order to keep a pinhole alive, and the keep-alive mechanism is reduced to a
method which involves significantly less overhead.
The following figure demonstrates how critical it is that the server can communicate directly
with the IP Deskphone through the use of the established TCP connection because it has no
way of getting through the firewall in order to contact port 5060 on the IP Deskphone.
Figure 52: Connection reuse and a firewall
Table 84: Connection timers definitions and allowed values
Parameter
name
Description Default
value
Boundaries
OS Keep-
alive only
Selecting this value causes the
OS
TCP Keep-alive functions to
be used instead of the CRLF
ping/pong mechanism. Some
system deployments may prefer
the lighter weight TCP keep-
alive
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Security
284 SIP Software for Avaya 1200 Series IP Deskphones-Administration September 2013
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