On 6/22/2011 9:45 AM, Michael Picher wrote:
> Which port is your sipXecs system plugged into?  I don't see a port with
> DSCP 46 forced.
>

My sipXecs system is plugged into port 7 on a 3Com 4200G.  Here's the 
configuration for that port:

interface GigabitEthernet1/0/7
  stp edged-port enable
  broadcast-suppression pps 3000
  port access vlan 162
  undo jumboframe enable
  priority-trust cos

I have just changed the configuration to the following, changing the 
priority-trust from cos to dscp:

interface GigabitEthernet1/0/7
  stp edged-port enable
  broadcast-suppression pps 3000
  port access vlan 162
  undo jumboframe enable
  priority-trust dscp

The 3Com switches allow for the automatic setting of the COS to 6 and 
the DSCP to 46 when ports are configured to be a part of the "voice 
vlan."  "Voice VLAN" is a feature of the 3Com 4200 switches.  Our voice 
vlan is 162 and because the port (interface GigabitEthernet1/0/7) is 
already in VLAN 162, I believe its DSCP value is already set to 46 
because when, as a test, I tried to add the "voice vlan enable" command 
to that port, it told me the following:

[4200G]interface GigabitEthernet1/0/7
[4200G-GigabitEthernet1/0/7]voice vlan enable
  Can't enable voice vlan because the port is in voice vlan and auto 
mode has been set!
[4200G-GigabitEthernet1/0/7]

When I look at the status for the voice VLAN, I see the following:

[4200G]display voice vlan status
Voice Vlan status: ENABLE
Voice Vlan ID: 162
Voice Vlan security mode: Security
Voice Vlan aging time: 1440 minutes
Current voice vlan enabled port mode:
PORT                     MODE     COS  DSCP
---------------------------------------------
GigabitEthernet1/0/4     AUTO     6    46
GigabitEthernet1/0/5     AUTO     6    46
GigabitEthernet1/0/6     AUTO     6    46
GigabitEthernet1/0/8     AUTO     6    46
GigabitEthernet1/0/9     AUTO     6    46
GigabitEthernet1/0/10    AUTO     6    46
GigabitEthernet1/0/11    AUTO     6    46
GigabitEthernet1/0/12    AUTO     6    46
GigabitEthernet1/0/13    AUTO     6    46
GigabitEthernet1/0/14    AUTO     6    46
GigabitEthernet1/0/15    AUTO     6    46
GigabitEthernet1/0/18    AUTO     6    46
GigabitEthernet1/0/19    AUTO     6    46
GigabitEthernet1/0/20    AUTO     6    46
GigabitEthernet1/0/21    AUTO     6    46
GigabitEthernet1/0/22    AUTO     6    46
GigabitEthernet1/0/23    AUTO     6    46
GigabitEthernet1/0/24    AUTO     6    46

[4200G]

The voice VLAN is a dynamic VLAN that automatically detects the presence 
of IP phones based on their MAC addresses.  Since the sipXecs server is 
not a Polycom phone, it does not appear in this dynamically updated list.

The following statement is from the 3Com Switch 4200G Family 
Configuration Guide:

In order to improve the transmission quality of voice traffic, the 
switch by default re-marks the precedence of the traffic in the voice 
VLAN as follows:
- Set the CoS (802.1p) precedence to 6.
- Set the DSCP precedence to 46.


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