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  • LLDP / QoS / DSCP Settings

    I've been tasked with reviewing and fixing QoS for our ShoreTel phone environment. From my reading I have come across a LOT of material, mostly related to the network itself and not the phones.

    However, I wanted to first start by determining exactly what has been setup on the phones regarding QoS. Our environment is as follows:
    • Mostly IP480 phones
    • Each phone has a dedicated ethernet drop and switch port (No PCs are connect to any phone) and the switch ports are configured to be untagged
    • As such, we do not specify layer2tagging or a vlanid in option 156 of our DHCP server (It's nice having the phone only boot once into the correct VLAN)

    Questions:
    1. I see that some DSCP options are set in Administration > Features > Call Control > Options. These include three different DiffServ values (which we use the defaults). How, exactly, do these values get sent to the phones? Are these pulled when the phone boots and connects to the tftp server? Are there any other conditionals required to cause these values to be applied or not applied?
    2. How do the values in the area mentioned above actually work? Is it that the phone downloads them, then sends them to the switch when the switch checks LLDP?
    3. Are there any other QoS settings handled in the phone settings, or anywhere else, that I should be aware of?
    I'm trying to have 100% understanding of the phones and phone system so I can then move on to how the switches handle QoS.

    Any input or high-level overview is greatly appreciated! Thanks in advance.

  • #2
    This could be an interesting topic. To add awareness....Incorrect QoS can be worse than no QoS and DSCP tagging only works if all the connected parts that need the tags pass and see the tags correctly.


    Questions:
    1. I see that some DSCP options are set in Administration > Features > Call Control > Options. These include three different DiffServ values (which we use the defaults). How, exactly, do these values get sent to the phones? Are these pulled when the phone boots and connects to the tftp server? Are there any other conditionals required to cause these values to be applied or not applied? All of these settings within the director are markers. These markers do nothing without your environment passing what is seen through each layer
    2. How do the values in the area mentioned above actually work? Is it that the phone downloads them, then sends them to the switch when the switch checks LLDP? The server passes the tag to the switches and the switches pass it to the phone.
    3. Are there any other QoS settings handled in the phone settings, or anywhere else, that I should be aware of? almost all the Qos is within the layer 2 and layer 3 infrastructure
    I'm trying to have 100% understanding of the phones and phone system so I can then move on to how the switches handle QoS.
    Lance Paddock
    BTX | Business Telephone eXchange
    1(800) 289-0299

    Comment


    • #3
      If I have read across the internet correctly.. LLDP can specify which VLAN a phone needs to boot into, correct? I'm wondering where those settings are even setup. (I know you can specify that in the DHCP options as well, but that isn't the same as LLDP).

      Comment


      • #4
        LLDP (IEEE 802.1AB) is a vendor agnostic Layer-2 protocol that can do automatic VLAN assignment but there are multiple ways for that to be accomplished.


        Download the attachment below:

        Mitel Network Best Practices image_1198.pdf
        Attached Files
        Last edited by Lance; 01-21-2020, 10:17 AM.
        Lance Paddock
        BTX | Business Telephone eXchange
        1(800) 289-0299

        Comment


        • #5
          So what I have found is the following:
          1. The switch advertises itself via multicast LLDP packets periodically
          2. When the phone boots, it sends a multicast LLDP packet to the switch, telling the switch that it's a phone, etc. Initially the phone's VLAN ID, L2 priority, DSCP values, etc are empty or 0.
          3. The switch then updates its LLDP packet sent to the phone to include specifics related to phones. This includes VLAN ID, L2 priority, DSCP, etc.
          The phone does not appear to echo these settings back (L2 priority, DSCP, etc) until after the DHCP request is made, and after the phone connects to the mitel server.

          I know that the L2 setting, at least, is configured entirely on the switch itself. I'm wondering about the VID and DSCP settings... are these picked up via DHCP or from LLDP?

          Comment


          • #6
            that depends on your broadcast type.

            For example:
            IP 400 Series Phones”
            • LLDP OFF: Director DSCP used for RTP and Signaling
            • LLDP-MED TLV ON with a default of 0: Director DSCP used for RTP and Signaling
            • LLDP-MED TLV ON with a non-zero value: LLDP Value used for RTP. Director DSCP used for Signaling
            All other phone series:
            • LLDP OFF: Director DSCP used for RTP and Signaling
            • LLDP-MED TLV ON with a default of 0: Director DSCP used for RTP and Signaling
            • LLDP-MED TLV ON with a non-zero value: Last setting wins, LLDP first, Director (config file) last
            Lance Paddock
            BTX | Business Telephone eXchange
            1(800) 289-0299

            Comment


            • #7
              Hmm, okay. Lance Do you know which specific value (default of 0 or non-zero) I'm looking for? I have the wireshark LLDP packet, and see a handful of TLV values, but I don't know which one is being referenced.

              As a side note, when I initially setup my phones VLAN I used the command "voice" to specify that the VLAN was for voice. I actually didn't know what that command did. We are using HP switches.

              With the voice command ON, I see that the switch starts sending a "Network Policy" section of the LLDP packet to the phone, which includes the VLAN, P2 Priority, and DSCP value.

              With the voice command OFF, the switch doesn't include these details in the LLDP packet sent to the phone at all.

              In both ON/OFF cases, the phone eventually picks up all the same values:
              • VLAN ID = 0
              • L2 Priority = 5
              • DSCP = 46
              I assume the VLAN ID is 0 because that's the default...telling the phone to NOT tag any of the traffic. We don't set layer2tagging in DHCP option 156 (so it's disabled). Our phones are connected to UNtagged ports on our switch and have a dedicated network drop (no PCs attached). So that makes sense.

              I have to then therefore assume that the voice command is not actually doing anything useful for us as it appears that it's primarily for LLDP, and that the phone isn't actually getting any of its settings from LLDP (but instead, from DHCP).

              Comment


              • #8
                I think I figured it out.

                The value of 0 (default) or non-zero is referring to the DSCP value. I found that I could manually set a DSCP value for the VLAN... and the phone would pick it up and report it via its LLDP multicast packet.

                However, if I did NOT specify a DSCP value, then I found that the phone reverted to the value in Director.

                So I think that, if you specify any value for DSCP explicitly on the switch, that this will override director (at least for the value reported via LLDP multicast packets).

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