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Understanding UDP/TCP relay RRS feed

  • Question

  • Hello,

    I noticed in the monitoring that bad quality calls are usually using TCP relay when users are both external. It seems to me that this is the issue.

    I understand that UDP is usually preferred over TCP and TCP is used in case UDP would fail.

    Could someone explain in which situation the UDP relay is not possible? What makes it sometimes fail and establish the communication in TCP ?

    Regards

    Wednesday, August 3, 2016 5:53 AM

Answers

  • Hi

    UDP is preferred for media traffic, when media is negotiated via SDP you will be able to see the media ports the client and peer endpoint have chosen to pass media over. UDP is a connectionless and a fire and forget transport protocol. TCP checks the connection state and checks whether the data packet has reached the destination. As such TCP is not the best protocol to send media over because it is slower than UDP as a result.

    That said, when you are external, Lync will use both protocols in its delivery arsenal. This is for failback / alternative methods for when the preferred transport protocol fails.

    The main reason TCP will be used is if the Edge server external AV interface is only accepting inbound TCP packets on 50,000 to 59,999 port range. Check your firewall to allow UDP through on the same port range. If you don't want TCP at all, block the range on TCP. However, bear in mind that if UDP fails, there is no alternative then.

    The other problem may be that the external parties internet router may not allow UDP out of their network, some home routers especially the ones that are branded as your provider (managed) discourage the use of UDP both inbound and outbound connections and therefore Lync will negotiate TCP for media delivery instead of UDP

    thanks


    Note: Please remember to `Mark as Answered` a post that answers your question and/or `Vote as Helpful` posts that have helped you. This will help others find answers to similar problems. For more Skype for Business help visit: http://www.skype4b.uk Please note that answers are based on my experience and opinion only and do not necessarily represent the views of my employer.

    Thursday, August 4, 2016 8:10 AM
  • Hi FrancoisCA,

    From Lync side, please make sure the UDP ports(3478, 50000-59999) are opened. Otherwise, you may contact your network team to check why the UDP connection failed. Network Monitor would be a valuable tool to track network issues.

    About the port settings, please refer to the following articles:

    Determine external A/V firewall and port requirements

    Understanding Lync Edge Server Ports


    Best Regards,

    Jessie Yuan


    Please remember to <b>mark the replies as an answers</b> if they help and <b>unmark</b> them if they provide no help.<br/> If you have feedback for TechNet Subscriber Support, contact <a href="mailto:tnmff@microsoft.com"> tnmff@microsoft.com</a>.

    Thursday, August 4, 2016 8:00 AM
  • Completely agree with Mark.

    1. first check if your firewall opened high range ports for TCP/UDP or not.

    2. even though the ports are opened still its unable to failback it could be the endpoint service provider issue where there network may or may not allowed UDP.



    Regards, Rajukb | MCSE (Communication ), MCSA (o365) ,Certified "Lync server 2013 depth support engineer"| This posting is providedwith no warranties and confers no rights. If my reply answers your question please mark as answer/helpful if its helpful.

    Sunday, August 7, 2016 7:37 PM

All replies

  • Deleted
    Wednesday, August 3, 2016 7:36 AM
  • Yeah Lync External SIP sessions does not support UDP you will get better explanation on below article.

    http://blog.unifiedcommunications.eu/07/why-microsoft-use-tpc-instead-of-udp-for-sip/

    Hope this helps.


    Regards, Rajukb | MCSE (Communication ), MCSA (o365) ,Certified "Lync server 2013 depth support engineer"| This posting is providedwith no warranties and confers no rights. If my reply answers your question please mark as answer/helpful if its helpful.

    Wednesday, August 3, 2016 9:51 AM
  • Hello,

    I am talking about the data I find in the section "Media line (Main audio)" in the skype monitoring reports.

    Most of the calls are showing for caller and callee connectivity: "Relay" and for Transport "UDP".

    What makes a call to not use UDP for media?

    Wednesday, August 3, 2016 10:46 AM
  • Hi FrancoisCA,

    From Lync side, please make sure the UDP ports(3478, 50000-59999) are opened. Otherwise, you may contact your network team to check why the UDP connection failed. Network Monitor would be a valuable tool to track network issues.

    About the port settings, please refer to the following articles:

    Determine external A/V firewall and port requirements

    Understanding Lync Edge Server Ports


    Best Regards,

    Jessie Yuan


    Please remember to <b>mark the replies as an answers</b> if they help and <b>unmark</b> them if they provide no help.<br/> If you have feedback for TechNet Subscriber Support, contact <a href="mailto:tnmff@microsoft.com"> tnmff@microsoft.com</a>.

    Thursday, August 4, 2016 8:00 AM
  • Hi

    UDP is preferred for media traffic, when media is negotiated via SDP you will be able to see the media ports the client and peer endpoint have chosen to pass media over. UDP is a connectionless and a fire and forget transport protocol. TCP checks the connection state and checks whether the data packet has reached the destination. As such TCP is not the best protocol to send media over because it is slower than UDP as a result.

    That said, when you are external, Lync will use both protocols in its delivery arsenal. This is for failback / alternative methods for when the preferred transport protocol fails.

    The main reason TCP will be used is if the Edge server external AV interface is only accepting inbound TCP packets on 50,000 to 59,999 port range. Check your firewall to allow UDP through on the same port range. If you don't want TCP at all, block the range on TCP. However, bear in mind that if UDP fails, there is no alternative then.

    The other problem may be that the external parties internet router may not allow UDP out of their network, some home routers especially the ones that are branded as your provider (managed) discourage the use of UDP both inbound and outbound connections and therefore Lync will negotiate TCP for media delivery instead of UDP

    thanks


    Note: Please remember to `Mark as Answered` a post that answers your question and/or `Vote as Helpful` posts that have helped you. This will help others find answers to similar problems. For more Skype for Business help visit: http://www.skype4b.uk Please note that answers are based on my experience and opinion only and do not necessarily represent the views of my employer.

    Thursday, August 4, 2016 8:10 AM
  • Completely agree with Mark.

    1. first check if your firewall opened high range ports for TCP/UDP or not.

    2. even though the ports are opened still its unable to failback it could be the endpoint service provider issue where there network may or may not allowed UDP.



    Regards, Rajukb | MCSE (Communication ), MCSA (o365) ,Certified "Lync server 2013 depth support engineer"| This posting is providedwith no warranties and confers no rights. If my reply answers your question please mark as answer/helpful if its helpful.

    Sunday, August 7, 2016 7:37 PM