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HDX 7000 Dropping Calls

Occasional Contributor

HDX 7000 Dropping Calls

I have a HDX 7000 that seems to be dropping all calls right around the 45 minute mark. I have searched some other forums and saw some post's about the possible "keep alive" issue but im not sure if thats my issue or not. Anyone know a way to check this?

Message 1 of 4
Polycom Employee

Re: HDX 7000 Dropping Calls

Have you timed it to be exactly 45 minutes? Or is it a perception?


If a preception then other reasons need to be looked at.

network packet loss, congestion, content sent, what are the users doing at that time? there are many variables that the system logs and possibly a Wireshark trace may uncover. Polycom support can assist.


If exactly then there may be a timer on port 1720 closing the port on the firewall. Now, newer versions of the HDX (in 3.0.4 it was defaulted to 2 minutes) send a ‘keep alive’ which will keep the port open..

Below is a more detailed description but it was written for older software.  If you have not upgraded in a while I would advise considering upgrading.


H.323 calls are dropping unexpectedly when dialing through a Network Firewall, Security Device or Router that is configured to close idle TCP Ports.  In these scenarios, calls may drop at a consistent time such as 2 hours or 40 minutes.




Network Security Devices such as Firewalls or Routers with security policies, are typically configured to close TCP and UDP Ports which are no longer in use or have become idle.  This is done to free up port availability for other sessions as well as to protect the internal network from malicious attacks through open sockets.


H.323 devices (Endpoints, Gatekeepers and MCUs) use signaling defined by ITU-T H.225 to establish, maintain and disconnect H.323 calls.  The initial signaling is done through TCP Port 1720.  Once the call is established however, this port is typically not needed until the call is disconnected.  The TCP Port 1720 is considered to be open and active for the duration of the call by H.323 devices.  However, since there is no data flowing through this port during the call, it can be seen as idle by network devices configured to monitor for idle ports.  These idle ports can be closed by a network device that is unaware of the H.323 call state.  These unaware devices are lacking an Application Layer Gateway (ALG) which is designed to understand H.323 call flow.  There may also be configurations within the network device where idle ports are closed regardless if there is an H.323 ALG, to accommodate global security settings.


To help avoid premature port closure, many H.323 devices will periodically send a keep-alive packet on TCP Port 1720..  The goal is to maintain an active port state through a network device configured for port timeout.  The keep-alive procedure used by most Polycom H.323 Devices is per RFC-1122.  The default time of this keep-alive packet has historically been set for 2 hours to satisfy the interpretation of TCP port timeout in RFC-1122.  However, many network devices use a default port timeout value that is much less than 2 hours (typically 30 minutes). 




Polycom HDX and VSX now have the ability to adjust the keep-alive packet interval in order to avoid premature port closure.  Once the timeout value has been determined in the network device responsible for the premature port closure and resulting call disconnection, the HDX or VSX should be configured for a keep-alive interval that is before the timeout interval.


The command is tcp kainterval and must be executed through a Telnet session to the HDX or VSX.  Support of this command was introduced in VSX v9.0.6.1 and HDX v3.0.0.


The syntax is:


tcp kainterval <without a value will return the existing value>  default is 1800 (30 minutes) on HDX v3.0.1 and VSX v9.0.6.1

tcp kainterval <value between 900-9000> in seconds


This will persist across reboots.




Polycom Command Shell

XCOM host:    localhost port: 4121

TTY name:     /dev/pts/0

Session type: telnet

tcp kainterval

2011-07-08 20:56:30 DEBUG avc: pc[0]: uimsg: [C: tcp kainterval]

2011-07-08 20:56:30 DEBUG avc: pc[0]: APPCOM: C: tcp kainterval cmd response is 0


2011-07-08 20:56:30 DEBUG avc: pc[0]: 1800

tcp kainterval 900

2011-07-08 20:57:10 DEBUG avc: pc[0]: uimsg: [C: tcp kainterval 900]

2011-07-08 20:57:10 DEBUG avc: pc[0]: APPCOM: C: tcp kainterval 900 cmd response is 0


2011-07-08 20:57:10 INFO avc: pc[0]: config: tcpkeepalivetime[0]:900

2011-07-08 20:57:10 DEBUG avc: pc[0]: NOTIFY: SYS config tcpkeepalivetime 0 "900

tcp kainterval
2011-07-08 20:57:28 DEBUG avc: pc[0]: uimsg: [C: tcp kainterval]
2011-07-08 20:57:28 DEBUG avc: pc[0]: APPCOM: C: tcp kainterval cmd response is
2011-07-08 20:57:28 DEBUG avc: pc[0]: 900

Sr. Product Support Technician
Message 2 of 4
Occasional Contributor

Re: HDX 7000 Dropping Calls

its been timed to be exactly at the 45 minute mark. maybe a 44 minute and a 43 minute disconnect here and there, but the 45 minute mark seems to be the pattern. from browsing around in other threads i was kind of leaning towards the keep alive issue myself. i will try your resolution and get back to you with results.


thank you very much!

Message 3 of 4
Occasional Contributor

Re: HDX 7000 Dropping Calls

i have adjusted the time for the keep alive setting and still seem to be getting call drops at the 45 minute mark. I have had our network admin take a look at the settings in the firewall for any timers that may exist in closing a connection on port 1720 and there doesnt seem to be any the reference a 45 minute time out.

Message 4 of 4