Port Based Priority Example - NEC Electra Elite IPK Programming Manual

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When a network incorporates VLANs, the designer must remember that for a
device on one VLAN to communicate with a device on another VLAN, all
traffic between VLANs must travel across a router or a switch with built-in
layer 3 routing ability. Layer 3 routing is slower than layer 2 switching and can
be a potential traffic bottleneck on the network. Therefore, it is logical to
create a VLAN for voice traffic only.
By enabling layer 2 QoS in the LAN, voice and other time-sensitive traffic can
be given priority when the network is congested.
A workgroup may have all PCs in VLAN 200 and all IP telephone terminals in
VLAN 100, even when PCs are typically connected to the second Ethernet
port on the IP telephone terminals. The port on an Ethernet switch supporting
both the IP telephone and the PC must be configured to allow traffic from both
VLAN 100 and VLAN 200. NEC IP terminals have two Ethernet connections
that can be assigned to different VLANs and QoS priorities.
The IEEE 802.1q VLANs insert a 4-byte tag in the Ethernet frame that
includes both the VLAN Identifier (1~4095) and the user_priority (0~7) field
that is used to assign traffic to a priority queue.
The HUB(8) has high and low priority queues. With Memory Block 1-16-06 set
to NO (default), Memory Block 1-16-07 is used to determine which queue a
frame is assigned, based on the frame IEEE 802.1p priority.
For port-based priority, Memory Block 1-16-06 determines which queue a
frame is assigned, based on the port it enters. When an untagged frame
leaves the HUB(8) ETU, it is assigned a priority based on the assigned queue
and the corresponding memory block for the port it leaves: 1-16-08 for
high-priority queue frames or 1-16-09 for low-priority queue frames.
IEEE 802.1q VLAN tags should be sent only to equipment that supports IEEE
802.1q/p. The insertion of an additional 4 bytes likely can create frames that
are larger than the normal Ethernet maximum frame size. Equipment that
does not support, IEEE 802.1q/p likely cannot respond to frames with tags.
Using Memory Block 1-16-15, the HUB(8) can be configured to send tagged
frames only to those devices that support tags.

Port Based Priority Example

In this example, the HUB(8) is set up to support 2 VLANs:
VLAN Membership
• VLAN 100 (black) – voice traffic for IP telephones A, B, and C,
plus the IPC and MG ETUs.
• Vlan 200 (grey) – data traffic of PCs A, B, and C.
Electra Elite IPK
Advanced Applications