CHAPTER 8 Appendix A: Quality of Service (QoS) Setup
55
Type of Service (ToS) is an 8-bit field placed in the IP header to indicate how packets are treated. ToS
determines the relationship between priorities of ingress IP packet traffic and queues. The 3 leftmost
bits possess a priority value ranging from 0 to 7, which implies the importance of a packet. The higher
the value, the more important the packet (default value = 0). By attaching priority value to packets,
users are enabled to classify and place them into different queues. The screen above allows users to
configure the transmission priority (= queue) for packets with different priorities.
Assumed that the priority mode for ETH1 and ETH4 are “ToS”, then both ports should apply the “ToS
Field Priority Setup”. Moreover, ETH1 and ETH4 share common settings, rather than have their own.
8.2.2. Scheduling Algorithm for Ingress Traffic – Reading Data From Queues to TDM
Interface
After QoS setup for ingress traffic is complete, the following process is to configure the Scheduling
Algorithm for ingress traffic, which determines how packets are polled out of the queues and
transmitted to TDM interfaces. If more than one of the queues for a port contains packets, then a
transmission scheduling algorithm determines which queue should be transmitted first. Here, TDMoE
card supports two scheduling algorithm taking charge of reading data from queues to TDM interface:
Strict Priority (SP) and Weight Round Robin (WRR). The mechanisms and setup screens are shown
below.
SLOT 2 TDMoE === Scheduling Algorithm === 13:37:16 12/31/2009
ARROW KEYS: CURSOR MOVE, TAB: ROLL OPTIONS
ETH1: SP
ETH2: SP
ETH3: SP
ETH4: SP
NOTE:
SP: Strict Priority.
WRR: Weighted Round Robin.
<< Press ESC key to return to previous menu >>
(VT-100 Terminal Path: Main Menu > (S) System Setup > (C) Qos Setup > (B) Transmission
Scheduling > (B) Scheduling Algorithm)
Strict Priority (SP): When a port applies SP Algorithm, it suggests packets/frames will be delivered
from queues to that port in a strict order. Whenever packets are to be forwarded, the system will
transmit packets starting from the highest priority queue. For TDMoE card, each port includes 4 queues.
The hierarchy of all the queues is: queue 3 is considered with highest priority, queue 2 is prior to queue
1, and Queue 0 has the lowest priority, i.e. queue3>queue 2>queue 1>queue 0. For example, queue 3,
queue 2 and queue 1 all contain 4 packets. All 4 packets of queue 3 should be transmitted before any of
those in queue2 or queue 1 are. Before queue 1 sends packets, all the packets in queue 2 should be
delivered.
Yet, if you configure the scheduling algorithm as WRR, there is one last step to go, i.e. setup the WRR
Weight Ratio, as shown below.
SLOT 2 TDMoE === WRR Weight Setup === 14:24:08 12/31/2009
ARROW KEYS: CURSOR MOVE, Please Input: 0~100, BACKSPACE to edit
P0 queue P1 queue P2 queue P3 queue
Weight: 007% 013% 027% 053%
NOTE: The sum of weights must equal 100
<< Press ESC key to return to previous menu >>
(VT-100 Terminal Path: Main Menu > (S) System Setup > (C) Qos Setup > (B) Transmission
To Next Page
Loading...
Need help?
General
