Browser based soft phone application intermittently fails to launch.

We use a service to route calls for our call center. There are about 100 call center agents and everyday, four or five will have trouble launching the soft phone application. We connect to the call manager and soft phone system via and MPLS.

Sometimes restarting the PC fixes it. Sometimes resetting the browser fixes it, sometimes disabling / re-enabling the NIC fixes it. Sometimes it magically fixes itself.

The attached packet capture image from Wireshark typifies what a TCP stream looks like from a PC experiencing  a failed application launch.

NOTE: In the attached file, the TCP RST flag is not always seen. Many times I only see the TCP re-transmissions or TCP SEQ Out Of Order.

Questions 1: Am I right to believe my problem is, either a reset is being thrown or the other side stops responding for some reason, hense the re-transmissions

Since this is over an MPLS, I am not able to get a capture from the other side.

Question 1. What troubleshooting steps should I take to identify why I am getting these re-transmission, and or Resets.

Question 2: Is it possible that some traffic might be routing out the MPLS, while other is getting lost in the network? If this were possible, and I wanted to capture the packets on the Switch, would I SPAN the both the interface connected to the PC and the Interface connected to the router, or just the router?

Note: I don't have trouble logging into the portal, I have trouble launching the softphone, which uses a browser extension.

Note: We connect to the portal (user authentication and call manager) and establish the soft phone connection over the MPLS.

Note: When the problem is active, it affects all browsers, so switching browsers does not help..

Many Thanks
Robert AdvancedideaAsked:
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Peter SchultzSenior Network AdministratorCommented:
Do you have QoS on the MPLS for SIP/VOiP VLAN ?  Different Bandwith on both ends ?
Robert AdvancedideaAuthor Commented:

Than you for your question. Duplexing, as far as I can 'see", is set correctly from my router to the next hop. We do not manage the MPLS circuit as we do not own it.

Once established the SIP traffic passes to the Vendor without problem; in other words the calls work. There is no specific configuration for QOS or VLAN tagging given in the vendors documentation.

The system had been running for about 1 year without issues. This is a new problem that is very sporadic and not repeatable, with the exception of one user. This one agent, must restart his PC every morning or he will not be able to launch the soft phone application.

Because of how sporadic and non repeatable the issue, i am really looking for ideas on how to troubleshoot it. I am stumped, because i cannot reproduce it at will.

This morning there were two users that could not connect. I switched them over to wireless and they connected. That makes me believe there is a problem with the wire, or switch, but it could also be the NIC or maybe with WinSock -- I'm baffled.
Peter SchultzSenior Network AdministratorCommented:
agreed, not so easy to solve ;)

The one user who has to restart - i would search on that specific machine, too.

Troubleshooting - not easy .... if the problem lies in the network stack - any tcpdump will help. I think there is another option to check. Many MPLS Providers offer packages with "guaranteed" traffic and "optional traffic" - so if you buy 1GBit you'll probably get 400 MBit "guaranteed" and 600 MBit "if available". And furthermore - if you have branch offices with - lets say - 200MBit MPLS and a corporate office with 1GBit MPLS, the corporate office is sending out data at a speed of 1GBit - so if load is high - the branch office will have overload problems.

good hunting ...
Robert AdvancedideaAuthor Commented:
I am closing this ticket. There has been no solution to the problem. It had "magically" resolved itself.

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Robert AdvancedideaAuthor Commented:
There was no repeatable solution developed. Some of the things that worked were switching from wired to WiFi. Switching Browsers, Restarting PC's and resetting WinSock. As of this post, the problem has magically resolved itself. I am giving Peter the points for at least attempting to find a solution.
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