Layer 2 Qos (802.1Pq) - NEC Univerge SV9100 Manual

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SV9100 Networking Manual

To enable this type of queuing it is necessary to:

Configure the VoIP equipment to mark its packets with a specific value so that the

switches/routers can identify that it is voice – Called Marking.

Configure the network equipment to recognize the difference between the

different Marked packets – Called Classification. (i.e., informs the router what a

voice packet looks like.

Configure the network equipment to give priority to the packets that have been

classified as voice – Called Priority Queuing.

Layer 2 QoS (802.1pq)

QoS is most commonly implemented at Layer 3 of the OSI model. This layer deals

with IP addresses, and is usually handled by Routers. However, sometimes it is

necessary to implement Layer 2 QoS – usually in large LAN environments with

many IP phones.

Layer 2 devices work with Ethernet frames (encapsulated IP packets) rather than

IP addresses. These devices are usually Switched Hubs (Switches). As the IP

header information is encapsulated, the Switched Hubs cannot reference the

Type of Service

Layer 2 QoS uses the Priority field of the Ethernet frame. This field has three bits

and can have eight possible values (000 to 111 in binary). Some switches can be

configured to prioritize traffic based on these values. This field is available only if

the Ethernet device is configured for VLAN (IEEE 802.1q) operation (VLAN is

outside the scope of this document).

QoS) field in the IP header to determine the priority of a