Figure 47: 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 48: Connection reuse and a firewall
Table 90: 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
Not checked Checked
Table continues…
TCP/TLS operation overview
March 2015 SIP Software for Avaya 1200 Series IP Deskphones-Administration 293
Comments? infodev@avaya.com
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