OpenMCU-ru – DSCP Based QoS Packet Tagging Rules for Linux IP Tables

In Ubuntu, the best way to ensure that the firewall is up and running and that your packet filtering or mangling rules are in place any time the network connection comes up, you should create a rule in the /etc/network/if-up.d folder. An alternative approach to that would be to put a “post-up” rule on whatever interface in you /etc/network/interfaces file. From my experience, so that your firewall rules can be easily maintained as well having the ability to make comments for each rule, it’s ideal to take advantage of the iptables-save and iptables-restore functionality.

In order to follow this procedure, the first time you set up the firewall, you will have to manually add all the firewall rules and then issue the iptables-save command. For sake of saving time, I will just provide you with the contents of my config file that can be restored with the iptables-restore < config_file command. Continue reading “OpenMCU-ru – DSCP Based QoS Packet Tagging Rules for Linux IP Tables”

Polycom RealPresence Desktop – Windows QoS Registry Settings

Last week, I had to call Polycom support for two issues. One of which I mentioned in another post (Automatic Gain Control issue) and the other was because I wanted to find out why their user manual showed some QoS settings that my version did not have access to.

After waiting on hold for ten minutes, the first tech support person I reached was a little cocky, arrogant, smart ass of a prick who was less than helpful with either of my support requests. At one point, he literally told me “we can’t control Windows” (which brings up the question, “Well why in the fuck did Polycom even make software in the first place then?”) in regards to my AGC issue even after I told him that I had disabled all of the Windows settings that take control of the audio interface. He also said that you can set up QoS in Windows “somewhere in the network settings” (which turned out to be completely erroneous) without giving an ounce of help or direction.

Towards the end of our call, he was just trying to get me off the phone basically with an answer of “you’re fucked” to all my questions. At that point, I got pissed off and demanded to speak to somebody else. Finally, I got put on the phone with one of their product engineers and they actually addressed my issues. Long story short, the engineer ended up having to do a remote support session and did indeed acknowledge my AGC issue and gave me an explanation of why I couldn’t see the QoS settings mentioned in the manual. It turns out, those settings only show up if you use their provisioning server and they don’t even set the QoS settings in Windows like I needed.
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pcapsipdump – Dump SIP Signalling and RTP Streams Per Call Leg into Separate Pcap Files

For a VoIP administrator, in order to properly diagnose and troubleshoot issues sometimes, you need the ability to go to be able to go back in time and dig deep within packet traces to get to the heart of the problem. Unfortunately, this means following the NSA’s policy and doing blanket data collection if you can handle the disk storage requirements.

Sure if the problem is easily reproducible, then you can either do a SIP trace in your VoIP software to get just the signalling data or if you need the RTP streams too, you can use “tcpdump” to capture the packets and avoid this scenario altogether but that isn’t always the case and using tcpdump certainly does have it’s limitations.

Capture (pcap) files get huge and harder to work with, you have to create filters to find the data you need, the list goes on and on. Of course, there are some helpful switches you can use to try to get around this when trying to capture data for long periods of time but then you still run into the problem of needing to run the application as a daemon, rotating log files, and then you still have to dig extensively for the data you need.
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