Network device that determines application-level network latency by monitoring option values in a transport layer message

• US 20070195797A1
• Filed: 02/23/2006
• Published: 08/23/2007
• Est. Priority Date: 02/23/2006
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Patel, Alpesh, Appala, Syam
• Granted Patent: US 7,873,025 B2
• Time in Patent Office: Days
• US Class Current: 370/400
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 41/0213 Standardised network management protocols, e.g. simple network management protocol [SNMP]
• CPC Class Codes: H04L 41/5096 wherein the managed service relates to distributed or central networked applications
• CPC Class Codes: H04L 43/0852 Delays
• CPC Class Codes: H04L 43/0864 Round trip delays
• CPC Class Codes: H04L 43/10 Active monitoring, e.g. heartbeat, ping or trace-route
• CPC Class Codes: H04L 43/106 using time related information in packets, e.g. by adding timestamps
• CPC Class Codes: H04L 43/12 Network monitoring probes
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/193 at the transport layer, e.g. TCP related

Abstract

A data processing apparatus in a network receives packet flows that are communicated between a first network node and a second network node, and comprises a clock and latency analysis logic configured for receiving a first data segment that has been communicated from the first node and forwarding the first data segment to the second node; storing a first time value of the clock in association with a first timestamp value obtained from the first data segment; receiving a second data segment that has been communicated from the second node and forwarding the second data segment to the first node; retrieving the first time value based on the first timestamp value; determining a second time value of the clock; and determining a first latency value by computing a difference of the second time value and the first time value. Thus end-to-end packet latency is determined by passively observing timestamp values.

Claims

1. A data processing apparatus, comprising:

a network interface that is coupled to a data network for receiving one or more packet flows that are communicated between a first network node and a second network node;

a processor coupled to the network interface;

a clock coupled to the processor;

latency analysis logic coupled to the processor and comprising one or more stored sequences of instructions which, when executed by the processor, cause the processor to perform;

receiving a first data segment that has been generated by an application hosted on a transport layer protocol and communicated from application and transport layer protocol of the first node and forwarding the first data segment to the second node;

storing a first time value of the clock in association with a first timestamp value obtained from the first data segment;

receiving a second data segment that has been communicated from the second node and forwarding the second data segment to the first node;

retrieving the first time value based on the first timestamp value;

determining a second time value of the clock;

determining a first latency value by computing a difference of the second time value and the first time value.

2. The apparatus of claim 1, wherein the apparatus is logically located in a local area network (LAN) segment that contains the first node.

3. The apparatus of claim 1, wherein the data segments are transport control protocol (TCP) data segments, and wherein the timestamp values are in TCP timestamp option fields.

4. The apparatus of claim 3, wherein the second data segment comprises a TCP acknowledgment bit set and a timestamp echo reply (TSecr) value equal to the first timestamp value.

5. The apparatus of claim 1, wherein the latency analysis logic comprises further sequences of instructions which, when executed by the processor, cause the processor to perform:

receiving a third data segment that has been communicated from the second node to the first node;

storing a third time value of the clock in association with a third timestamp value obtained from the third data segment;

receiving a fourth data segment that has been communicated from the first node to the second node;

retrieving the third time value based on the third timestamp value;

determining a fourth time value of the clock;

determining a second latency value by computing a difference of the fourth time value and the third time value;

determining an end-to-end latency value as;

(first latency value +second latency value/2).

6. The apparatus of claim 1, wherein the latency analysis logic does not alter the first data segment or the second data segment.

7. The apparatus of claim 1, wherein the latency analysis logic comprises further sequences of instructions which, when executed by the processor, cause the processor to perform reporting any of the first latency value, the second latency value, and the end-to-end latency value to a network management element while the first node and the second node communicate subsequent data segments.

8. The apparatus of claim 1, wherein the apparatus is logically located on a network access switch that services the first node and wherein the apparatus is logically located within a VLAN that contains the first node.

9. An apparatus, comprising:

a network interface that is coupled to a data network for receiving one or more packet flows that are communicated between a first network node and a second network node;

a processor coupled to the network interface;

a clock coupled to the processor;

means for receiving a first data segment that has been generated by an application hosted on a transport layer protocol and communicated from application and transport layer protocol of the first node and forwarding the first data segment to the second node;

means for storing a first time value of the clock in association with a first timestamp value obtained from the first data segment;

means for receiving a second data segment that has been communicated from the second node and forwarding the second data segment to the first node;

means for retrieving the first time value based on the first timestamp value;

means for determining a second time value of the clock;

means for determining a first latency value by computing a difference of the second time value and the first time value.

10. The apparatus of claim 9, wherein the apparatus is logically located in a local area network (LAN) segment that contains the first node.

11. The apparatus of claim 9, wherein the data segments are transport control protocol (TCP) data segments, and wherein the timestamp values are in TCP timestamp option fields.

12. The apparatus of claim 11, wherein the second data segment comprises a TCP acknowledgment bit set and a timestamp echo reply (TSecr) value equal to the first timestamp value.

13. The apparatus of claim 9, further comprising:

means for receiving a third data segment that has been communicated from the second node to the first node;

means for storing a third time value of the clock in association with a third timestamp value obtained from the third data segment;

means for receiving a fourth data segment that has been communicated from the first node to the second node;

means for retrieving the third time value based on the third timestamp value;

means for determining a fourth time value of the clock;

means for determining a second latency value by computing a difference of the fourth time value and the third time value;

means for determining an end-to-end latency value as;

(first latency value +second latency value).

14. The apparatus of claim 9, wherein the receiving means does not alter the first data segment or the second data segment.

15. The apparatus of claim 9, further comprising means for reporting any of the first latency value, the second latency value, and the end-to-end latency value to a network management element while the first node and the second node communicate subsequent data segments.

16. The apparatus of claim 9, wherein the apparatus is logically located on a network access switch that services the first node and wherein the apparatus is logically located within a VLAN that contains the first node.

17. A packet data router, comprising:

one or more network interfaces that are communicatively coupled to a data network for receiving one or more packet flows that are communicated between a first network node and a second network node;

one or more processors coupled to the network interfaces;

a clock coupled to the one or more processors;

a computer-readable medium comprising one or more stored sequences of instructions which, when executed by the one or more processors, cause the one or more processors to perform;

receiving a first data segment that has been generated by an application hosted on a transport layer protocol and communicated from application and transport layer protocol of the first node and forwarding the first data segment to the second node;

storing a first time value of the clock in association with a first timestamp value obtained from the first data segment;

receiving a second data segment that has been communicated from the second node, wherein the second data segment comprises an acknowledgement of the first data segment and an echo of the first timestamp value;

retrieving the first time value based on the first timestamp value;

determining a second time value of the clock;

determining a first latency value by computing a difference of the second time value and the first time value;

receiving a third data segment that has been communicated from the second node to the first node;

storing a third time value of the clock in association with a third timestamp value obtained from the third data segment;

receiving a fourth data segment that has been communicated from the first node to the second node, wherein the fourth data segment comprises an acknowledgement of the third data segment and an echo of the third timestamp value;

retrieving the third time value based on the third timestamp value;

determining a fourth time value of the clock;

determining a second latency value by computing a difference of the fourth time value and the third time value;

determining an end-to-end latency value as;

(first latency value +second latency value/2).

18. The apparatus of claim 17, wherein the data segments are transport control protocol (TCP) data segments, and wherein the timestamp values are in TCP timestamp option fields.

19. The apparatus of claim 18, wherein the second data segment comprises a TCP acknowledgment bit set and a timestamp echo reply (TSecr) value equal to the first timestamp value.

20. The apparatus of claim 17, wherein the latency analysis logic does not alter the first data segment or the second data segment.

21. The apparatus of claim 17, wherein the apparatus is logically located on a network access switch that services the first node and wherein the apparatus is logically located within a VLAN that contains the first node.

22. A machine-implemented method comprising:

receiving a first data segment that has been generated by an application hosted on a transport layer protocol and communicated from application and transport layer protocol of the first node and forwarding the first data segment to the second node, wherein the data segment is received at a third node that is logically located in the network on a data communication path between the first node and the second node, wherein the third node maintains a local clock;

storing a first time value of the local clock in association with a first timestamp value obtained from the first data segment;

at the third node, receiving a second data segment that has been communicated from the second node to the first node;

retrieving the first time value based on the first timestamp value;

determining a second time value of the local clock;

determining a first latency value by computing a difference of the second time value and the first time value.

23. A method as recited in claim 22, wherein the data segments are transport control protocol (TCP) data segments,

24. A method as recited in claim 22, further comprising the steps performed at the third node of:

receiving a third data segment that has been communicated from the second node to the first node;

storing a third time value of the local clock in association with a third timestamp value obtained from the third data segment;

receiving a fourth data segment that has been communicated from the first node to the second node;

retrieving the third time value based on the third timestamp value;

determining a fourth time value of the local clock;

determining a second latency value by computing a difference of the fourth time value and the third time value;

determining an end-to-end latency value as;

(first latency value +second latency value/2).

25. A method as recited in claim 24, wherein the third node reports any of the first latency value, the second latency value, and the end-to-end latency value to a network management element while the first node and the second node communicate subsequent data segments.

26. A computer-readable tangible storage medium comprising one or more stored sequences of instructions which, when executed by one or more processors, cause the one or more processors to perform:

receiving a first data segment that has been generated by an application hosted on a transport layer protocol and communicated from application and transport layer protocol of the first node and forwarding the first data segment to the second node, wherein the data segment is received at a third node that is logically located in the network on a data communication path between the first node and the second node, wherein the third node maintains a local clock;

storing a first time value of the local clock in association with a first timestamp value obtained from the first data segment;

at the third node, receiving a second data segment that has been communicated from the second node to the first node;

retrieving the first time value based on the first timestamp value;

determining a second time value of the local clock;

determining a first latency value by computing a difference of the second time value and the first time value.

27. The computer-readable medium of claim 26, wherein the data segments are transport control protocol (TCP) data segments.

28. The computer-readable medium of claim 26, comprising further sequences of instructions which, when executed by the one or more processors, cause the one or more processors to perform:

receiving a third data segment that has been communicated from the second node to the first node;

storing a third time value of the local clock in association with a third timestamp value obtained from the third data segment;

receiving a fourth data segment that has been communicated from the first node to the second node;

retrieving the third time value based on the third timestamp value;

determining a fourth time value of the local clock;

determining a second latency value by computing a difference of the fourth time value and the third time value;

determining an end-to-end latency value as;

(first latency value +second latency value/2).

29. The computer-readable medium of claim 28, wherein the third node reports any of the first latency value, the second latency value, and the end-to-end latency value to a network management element while the first node and the second node communicate subsequent data segments.