Avaya X330WAN manual Data Mode

Chapter 4 Operational Concepts and Configuration Examples

enables the TCP Sliding Window mechanism on the sending peer to adjust the window size accordingly, thereby reducing the transmission rate and ultimately reducing the congestion on the X330WAN Rx queues.

Note: WRED is an automatic process and is always enabled. WRED does not include any user-configurable parameters.

The ingress packets exit the queues based on strict priority scheduling. Upon exiting, they are subject to Layer 3 manipulation (routing, Policy-based modification, etc.). The packets are then inserted into one of the four Tx queues per egress Serial interface based on their 802.1p priority. WRED is implemented on the Tx queues similar to the Rx queues. On each Serial interface the packets are transmitted to the line based on strict-priority scheduling between the four queues.

Since WAN traffic can carry data and voice, a means of setting priorities for different types of traffic is required. The X330WAN QoS mechanism on the Serial interfaces operates in the following modes:

•Data mode - Provides no voice support. This is the default mode.

•VoIP mode - Gives precedence to VoIP traffic, while still processing data traffic on the lower priorities.

The mode type is configurable using the (no) voip-queuecommand.

Data Mode

The incoming packets are categorized into the following Rx queues:

•High priority queue - All packets entering via the Serial interface, and LAN Ethernet packets with 802.1p priority 4-7.

•Low priority queue - All packets entering via the Fast Ethernet port, and LAN Ethernet packets with 802.1p priority 0-3.

You can prioritize traffic entering on the Fast Ethernet and FabricFast Ethernet interfaces based on the packet’s DSCP value. You prepare a Policy List which maps the packet’s DSCP value to the 802.1p priority. You then need to activate this new policy list on the ingress direction of either the Fast Ethernet or FabricFast Ethernet interface. The packet’s priority is now changed according to the DSCP value in the incoming packet’s IP header. When using this method, choose the list’s trust to be either DSCP or CoS-DSCP. For more information, refer to "Policy" on page 48.

X330WAN automatically sets the size of the four Tx queues based on the interface bandwidth and the Maximum Transmission Unit (MTU) configured by the user. The default queue size allows a maximum two second delay. The categorization of data into the four Tx queues is based on packet priority. All queues implement head-drop when overflowed, as shown in Figure 4.9 on page 57.

56 Avaya X330WAN User’s Guide