Specifications

Chapter 16 - Quality of Service (QoS) IEEE 802.1q
164
Mediatrix 4100
These variables are 1 octet scalar ranging from 0 to 255. The DSCP default value should be
101110. This results in the DS field value of 10111000 (184).
This default value would result in a value of “101” precedence bits, low delay, high throughput, and
normal reliability in the legacy IP networks (RFC 791, RFC 1812). Network managers of legacy IP
networks could use the above-mentioned values to define filters on their routers to take advantage
of priority queuing. The default value is based on the Expedited Forwarding PHB (RFC 2598)
recommendation.
2. Set the value you want to use.
You can find references on DS field under the IETF working group DiffServ. For more information,
please refer to the following RFC documents:
• Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
(RFC 2474)
• An Architecture for Differentiated Services (RFC 2475)
• Assured Forwarding PHB Group (RFC 2597)
• An Expedited Forwarding PHB (RFC 2598)
3. Restart the Mediatrix 4100 so that the changes may take effect.
IEEE 802.1q
The 802.1q standard recommends the use of the 802.1q VLAN tags for Ethernet frames traffic prioritization.
VLAN tags are 4-byte headers in which three bits are reserved for priority indication. The values of the priority
bits shall be provisioned.
The 802.1q standard comprises the 802.1p standard.
It is the network administrator’s responsibility to provision the Mediatrix 4100 with standard and correct values.
 To enable the IEEE 802.1q user priority configuration:
1. In the qosIeee8021q group of the qosMIB, locate the following variables:
• qosSignalingIeee8021qEnable
• qosVoiceIeee8021qEnable
• qosT38FaxIeee8021qEnable
2. Set the value of these variables to enable.
The corresponding user priority configuration is enabled.
3. In the qosIeee8021q group of the qosMIB, locate the following variables:
• qosSignalingIeee8021qUserPriority
• qosVoiceIeee8021qUserPriority
• qosT38FaxIeee8021qUserPriority
These variables are 1 octet scalar ranging from 0 to 7. The 802.1q default priority value should be
6 for both signalling and media packets.
4. Set the value you want to use.
5. Restart the Mediatrix 4100 so that the changes may take effect.
For more information, please refer to the MIB Reference manual.
Note: RFC 3168 now defines the state in which to set the two least significant bits in the TOS byte. On the
other hand, this RFC only applies to TCP transmissions and the bits are thus set to “0” in the Mediatrix 4100.
This has the following effects:
• The TOS values for UDP packets are the same as in the MIB.
• The TOS values for TCP packets are equal to the closest multiple of 4 value that is not greater than the
value in the MIB.