Voice \ Data Issues

Posted on 2010-03-30
Medium Priority
Last Modified: 2012-05-09
HI experts,

We have a strange problem with what at first appeared to be only the ip-phones\ipt vlans.

The phones are Nortel IP handsets (IP 2002 onwards).

The phones will display server unreachable sometimes during the day and voice calls are choppy or drop.  Sometimes the phone rings by itself on a higher ring tone even when no-one is calling that dn.

The nortel engineer update firmware etc but today I noticed that...

When the phone dropped (sometimes just goes back to NODE: on display), I lost 2 pings to a server.  This suggests that it is not a problem with the phone system but the data network.

QoS is seup and correctly marking voice packets with cos voice dscp ef, the core trusts these mkarking and the distribution layers use acls to qos source and dest, although priority trust from source would work too at this layer.

To explain our setup is quite difficult, I can attach a visso diagram if that helps.

Each distribution switch holds local vlans and then routes off the core for coross campus traffic.


New area 1:
VLAN 3 Router

Core - vlan 3 router vlan
However core also has old networks on that we are in the process of getting rid of, vlan1  data, vlan 2 student, vlan 160 ipt (core prioritises macs of vlan 160 using acls

The prblem seems to happen campus wide but I think one end of the call is always on the old vlan for ipt (vlan 160).

Using wireshark when the phone dropped and I lost 2 pings showed nothing. (Pings are never lost to our servers normally, only when the phone dropped) ps: my pc is not on my phone, I have a dedicated 1gbps connection on another switch.

We use 3com switches, 5500G, 5500-PWR

Any help would be greatly recieved.
Question by:bromley_college
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Author Comment

ID: 29073079
Just to update:

Just now phone lost dial tone but display was still there, this time I didnt lose any pings to server...

Phone then dispalyed NODE - then display went back to normal and dial tone came back.

This problem has been going on a month or more now.

Expert Comment

ID: 29083393
The second update indicates the issue may not be the network but based on your first description the first thing I would ask is if you have spanning tree enabled?  When you look at the switches are you seeing any packet loss?

Author Comment

ID: 29084069
Hi jfrady,

We have stp enabled throughout all new areas, the old area (vlan 1, 160) didnt have it but I have started using it on these old vlans too.

I am not seeing stp issues or packet loss on switch statistics.

I am finding it very difficult to find any information here to help, just now it happened again, phone went (no dial tone) then displayed NODE.  At the same time though rdp session "paused" for about 3 seconds.
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Accepted Solution

jfrady earned 2000 total points
ID: 29085183
You might try disabling STP on your voice VLAN to see if that impacts.  Depending on how it's configured STP can cause traffic to stop flowing whenever a converge happens.

Author Comment

ID: 29087152
The new areas are fine (it seems), they run MSTP within the region.

The old valns run RSTP, so I would either need to disable stp globally per switch or on the ports with the voice vlan on, inc uplinks?

I created a new vlan on my office floor for voice but still the same problem happens, could it be the old vlans on the trunk are the problem, either vlan 1, 2 or 160?

I cannot create a brand new wing for my floor quickly as all devices need preparation (printers etc), then I can remove old vlans.

IIts appears that from the symptoms there must be either a bursty traffic source flooding the vlan or a device issue on the vlan.  All packet tracing so far though has picked up nothing at all.

Expert Comment

ID: 29090410
I thought that STP could be on for the switch overall but enabled or disabled per VLAN.

It's been a while since I have used those switches but I believe you could disable just for the voice vlan.

I agree that either there is some traffic occurring that overruns your voice traffic or a stoppage in the flow of traffic.  If you do not see any floods on the packet trace it would support the idea of traffic flows being interrupted.  

In your update earlier you indicated no packet loss and no lost pings when it occurred.  It's still possible that the issue is not network related.  When the issue occurs does it occur to all phones at the same time?  Is it on internal calls, external calls or both?

I'm not that familiar with the norTel VoIP gear but if it is display related it could be due to multicast issues.  Could also be flapping of some sort.  Is all your VoIP traffic Layer 3?

Author Comment

ID: 29093538
HI jfrady,

I appreciate you taking your time to reply :)

I can't see a way to disable stp just for a vlan for rstp on the old vlans.

When the phones go it is only one or two phones, on each side of call, or in same office.  Problem seems worse in old vllan areas (ground floor east and 2nd floor)  Ground floor west have said they have zero problems (they are on new distribution area, all new vlans, no old vlans).

Sometimes the phone just sits there and then says Server unreachable... or sometimes says NODE and call will drops, or stay active.

Phones also rang by themselves without a call.... very odd.

Problem happens both internal (same switch, different switch) and external.

When packet tracing a phone call, you see phone to signal server, then point to point IP to IP call call, seems ok.  Also noticed that the vlan is not busy (ie no excessive traffic broadcast or multicast reaching vlan devices to flood out.).

Traffic for IPT (VOIP) i assum is layer 3, it does route between all new vlan areas, but even when 2 phones on same switch still have issues, which suggest not a qos problem or network, could be phones or phone system??

Author Comment

ID: 29096277
Disabled stp on the core switch (core is interface for vlan 1, 2 and 160) and so far problem has not re-occurred, early days so will see.

Why do you think stp would have caused it, I didnt see any link flapping issues when it was on?  Could it still be a dodgy switch on the same vlan?

Expert Comment

ID: 29098194
Could be a dodgy switch.  I was thinking spanning tree since it was sporadic.  Traffic flow stops when the tree is re-calculated due to a topology change.  

Author Comment

ID: 29099670
I will leave stp off tomorrow and see if problems re-occur, if not then you are right!

Many thanks jfrady, indded stp does make sense with the intermittency, I just saw that some edge devices are on the core due to it being on the old vlan still for staff.  We cannot move these yet until we redesign the upper floor wing, but when the pc's reboot, sleep etc I guess thats whats triggering the tc notification and stopping traffic flow.

Author Comment

ID: 29194868
Thanks jfrady you were right, will wait until we finish design on upper floor and get core freed up before using stp again.

Expert Comment

ID: 29195245
Super.  Glad it worked out.

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