Computing and using different path quality metrics for different service classes
Some embodiments provide a method for quantifying quality of several service classes provided by a link between first and second forwarding nodes in a wide area network (WAN). At a first forwarding node, the method computes and stores first and second path quality metric (PQM) values based on packets sent from the second forwarding node for the first and second service classes. The different service classes in some embodiments are associated with different quality of service (QoS) guarantees that the WAN offers to the packets. In some embodiments, the computed PQM value for each service class quantifies the QoS provided to packets processed through the service class. In some embodiments, the first forwarding node adjusts the first and second PQM values as it processes more packets associated with the first and second service classes. The first forwarding node also periodically forwards to the second forwarding node the first and second PQM values that it maintains for the first and second service classes. In some embodiments, the second forwarding node performs a similar set of operations to compute first and second PQM values for packets sent from the first forwarding node for the first and second service classes, and to provide these PQM values to the first forwarding node periodically.
1. A method of quantifying quality of a plurality of service classes provided by a link between first and second forwarding nodes in a wide area network, the method comprising:
at the second forwarding node:
based on packets sent from the first forwarding node for a first service class, computing and storing a first path quality metric (PQM) value for the first service class to quantify the quality of service provided to packets processed through the first service class;
based on packets sent from the first forwarding node for a second service class, computing and storing a second PQM value for the second service class to quantify the quality of service provided to packets processed through the second service class; and
forwarding the first and second PQM values from the second forwarding node to the first forwarding node for the first forwarding node to use to assess the quality of the first and second service classes for forwarding data messages to the second forwarding node, wherein different service classes provided by the link are associated with different quality of service guarantees.
2. The method of claim 1 , wherein computing the first and second PQM values comprises using unique sequence numbers for first and second service classes to compute the first and second PQM values.
3. The method of claim 2 , wherein each sequence number has first and second portions, the first portion comprising a first sequence number that counts in one range, and the second portion comprising a value associated with the service class.
4. The method of claim 3 , wherein the value in the second portion is a DSCP (differentiated service code point) identifier.
5. The method of claim 1 , wherein the PQM values comprise loss values measured by counting number of packets not received at the second forwarding element within each of a plurality of particular time periods.
6. The method of claim 5 , wherein computing the PQM loss value comprises an updating average loss value as packet loss values are counted.
7. The method of claim 5 , wherein counting number of packets not received comprises using unique sequence numbers for each service class to determine whether packets are being received in the correct sequence.
8. The method of claim 1 , wherein the PQM values comprise delay values measured by using time stamps associated with the received packets to determine transit duration for the packets.
9. The method of claim 8 , wherein computing the PQM delay value comprises an updating average delay value as packet delay values are computed.
10. The method of claim 8 , wherein the PQM values further comprise jitter values that express the rate of change in the computed delay values.
11. The method of claim 1 , wherein different PQM values are computed for the first and second service classes in order to treat each service class as an independent logical subpath of the path between first and second forwarding elements.
12. The method of claim 1 , wherein PQM values are computed for the service classes and not for service queues utilized because service queue configurations that are used by a physical network connecting the first and second forwarding nodes, are not known.
13. The method of claim 1 further comprising:
at the first forwarding node:
based on packets sent from the first forwarding node for the first and second service classes, computing first and second PQM values for first and second service classes to quantify the QoS guarantees provided to packets processed through the first and second service classes as the packets are forwarded from the second forwarding node to the first forwarding node; and
forwarding first and second PQM values from the first forwarding node to the second forwarding node for the second forwarding node to use to assess the quality of the first and second service classes for forwarding data messages to the first forwarding node.
14. A non-transitory machine readable medium storing a program for quantifying quality of a plurality of service classes provided by a link between first and second forwarding nodes in a wide area network, the program for execution by at least one processing unit of a second forwarding node and comprising sets of instructions for:
based on packets sent from the first forwarding node for a first service class, computing and storing a first path quality metric (PQM) value for the first service class to quantify the quality of service provided to packets processed through the first service class;
based on packets sent from the first forwarding node for a second service class, computing and storing a second PQM value for the second service class to quantify the quality of service provided to packets processed through the second service class; and
forwarding the first and second PQM values from the second forwarding node to the first forwarding node for the first forwarding node to use to assess the quality of the first and second service classes for forwarding data messages to the second forwarding node, wherein different service classes provided by the link are associated with different quality of service guarantees.
15. The non-transitory machine readable medium of claim 14 , wherein computing the first and second PQM values comprises using unique sequence numbers for first and second service classes to compute the first and second PQM values.
16. The non-transitory machine readable medium of claim 15 , wherein each sequence number has first and second portions, the first portion comprising a first sequence number that counts in one range, and the second portion comprising a value associated with the service class.
17. The non-transitory machine readable medium of claim 16 , wherein the value in the second portion is a DSCP (differentiated service code point) identifier.
18. The non-transitory machine readable medium of claim 14 , wherein the PQM values comprise loss values measured by counting number of packets not received at the second forwarding element within each of a plurality of particular time periods.
19. The non-transitory machine readable medium of claim 18 , wherein computing the PQM loss value comprises an updating average loss value as packet loss values are counted.
20. The non-transitory machine readable medium of claim 18 , wherein counting number of packets not received comprises using unique sequence numbers for each service class to determine whether packets are being received in the correct sequence.