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A packet transmission diagnostic system transmits diagnostic packets during a communications session in which data packets are transmitted between a source and destination. The diagnostic packets elicit responses from routers along a path between the source and destination. The elicited responses, i

A packet transmission diagnostic system transmits diagnostic packets during a communications session in which data packets are transmitted between a source and destination. The diagnostic packets elicit responses from routers along a path between the source and destination. The elicited responses, in the form of packets, are used by the diagnostic system to produce one or more packet-delivery metrics for one or more of the routers along a packet transmission path between the source and destination.

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What is claimed is: 1. In a packet network communications system, a method of analyzing packet-delivery performance along intermediate path segments during a communications session between a source and destination for a predetermined application, comprising the steps of: (A) establishing a communic

What is claimed is: 1. In a packet network communications system, a method of analyzing packet-delivery performance along intermediate path segments during a communications session between a source and destination for a predetermined application, comprising the steps of: (A) establishing a communications session between a source and a destination by a call signaling exchange between the source and the destination, the communications session being that period between a call answer signal from the destination and a call termination condition; (B-1) sending data packets between the source and the destination during the communications session; (B-2) sending diagnostic packets from the source during the same packet communication session in which the data packets are transmitted between the source and destination, each diagnostic packet being of same format as data packets delivered during the communications session, each diagnostic packet eliciting a response from a router along a path between the source and destination; and (C) analyzing the responses from routers along at least one path to produce a packet-delivery metric for one or more of the routers along one or more paths between the source and the destination, wherein each diagnostic packet is of the same length as data packets being transmitted in the communications session, each diagnostic packet including: the same user datagram protocol (UDP) destination port number as data packets, the same differential services code point as the data packets, and a real time protocol (RTP) header that is valid for the data being transmitted in the communications session. 2. The method of claim 1 further comprising the step of: (D) obtaining information from the destination through out-of-band signaling and using the information to determine the number of routers between the source and destination. 3. The method of claim 2 wherein the out of band signaling returns the time to live (TTL) value of an RTP packet at the destination, the difference between the TTL value at the destination and the TTL value at the source indicating the number of routers along a path from the source to the destination. 4. The method of claim 2 wherein each diagnostic packet contains a flag in its header, the value of which is modified by each router is passes through and which elicits a response from a router whenever the received value of the flag reaches a threshold. 5. The method of claim 4 wherein the flag is a TTL flag and each router decrements the value of the flag as a packet passes through the router. 6. The method of claim 4 wherein the elicited response is an error response packet that includes a timestamp. 7. The method of claim 5 wherein the elicited response is an Internet control message protocol (ICMP) time exceeded packet that includes a timestamp and the Internet protocol (IP) address of the router sending the ICMP packet as the source address. 8. The method of claim 7 wherein the data packets are media packets. 9. The method of claim 7 wherein the diagnostic packets elicit at least one response from each router along one or more paths between the source and destination. 10. The method of claim 1 further comprising the step of: (E) from the analysis of step (C), identifying one or more routers whose performance is diminished in comparison to one or more other routers delivering said data packets. 11. The method of claim 1 wherein the response elicited by a diagnostic packet is a returned packet that includes a timestamp. 12. The method of claim 1 wherein the data packets are routed on a policy basis and the diagnostic packets include the same policy attributes. 13. The method of claim 12 wherein the policy basis is a quality of service policy. 14. The method of claim 13 wherein the data packets are voice packets. 15. The method of claim 13 wherein the data packets are video packets. 16. The method of claim 13 wherein the data packets are audio packets. 17. The method of claim 14 wherein the data packets are real time protocol (RTP) packets sent over Internet protocol (IP). 18. The method of claim 1 further comprising the step of: (F) signaling an on-hook condition to close the communications session. 19. The method of claim 1 further comprising the step of: (G) transmitting a plurality of diagnostic packets to a router and determining the jitter attributable to the router from timestamps within the elicited packets. 20. The method of claim 1 further comprising the step of: (H) determining the delay from timestamps within elicited packets. 21. The method of claim 1 further comprising the step of: (I) determining loss from the number of transmitted packets that don't elicit a response. 22. The method of claim 1 wherein the packets are Internet protocol (IP) packets. 23. The method of claim 1 wherein the packets are hypertext transfer protocol (HTTP) packets. 24. In a packet network communications system, a method of analyzing packet-delivery performance along intermediate path segments during a communications session between a source and destination for a predetermined application, comprising the steps of: (A) establishing a communication session between a source and a destination by a call signaling exchange between the source and the destination, the communications session being that period between a call answer signal from the destination and a call termination condition (B-1) sending data packets between the source and the destination during the communications session; (B-2) sending diagnostic packets from the source during the same communication session in which the data packets are transmitted between the source and destination, each diagnostic packet being transmitted in the communications session, each diagnostic packing including: the same user datagram protocol (UDP) destination port number as data packets, the same differential services code point as the data packets, and a real time protocol (RTP) header that is valid for the data being transmitted in the communications session, each diagnostic packet eliciting a response from a router along a path between the source and destination; (C) analyzing the responses from routers along at least one path to produce a packet-delivery metric for one or more of the routers along one or more paths between the source and the destination; and (D) obtaining information from the destination through out-of-band signaling and using the information to determine the number of routers between the source and destination, the out of band signaling returns the time to live (TTL) value of an RTP packet at the destination, the difference between the TTL value at the destination and the TTL value at the source indicating the number of routers along a path from the source to the destination. 25. The method of claim 24 wherein the step of establishing a packet communications session includes the step of: employing call signaling to transmit an off hook signal to the destination and receive an answer signal from the destination. 26. The method of claim 25 wherein the data packets are routed on a policy basis and the diagnostic packets include the same policy attributes. 27. The method of claim 25 wherein the policy basis is a quality of service policy. 28. The method of claim 25 wherein the data packets are voice packets. 29. The method of claim 28 wherein the data packets are real time protocol (RTP) packets sent over Internet protocol (IP). 30. The method of claim 25 wherein the data packets are video packets. 31. The method of claim 25 wherein the data packets are audio packets. 32. An apparatus, having a computer readable storage medium, for analyzing packet-delivery performance along intermediate path segments during a communications session between a source and destination for a predetermined application, comprising: a controller for establishing a communications session between a source and a destination by a call signaling exchange between the source and the destination, the communications session being that period between a call answer signal from the destination and a call termination condition; a diagnostic packet source for sending data packets and diagnostic packets from the source during the same communication session in which data packets are transmitted between the source and destination, each diagnostic packet being of same format as data packets delivered during the communications session, each diagnostic packet eliciting a response from a router along a path between the source and destination; the controller also for analyzing the responses from routers along at least one path to produce a packet-delivery metric for one or more of the routers along one or more paths between the source and the destination, and wherein the diagnostic packet source is for producing each diagnostic packet the same length as data packets being transmitted in the communications session, each diagnostic packet including: the same user datagram protocol (UDP) destination port number as data packets, the same differential services code point as the data packets, and a real time protocol (RTP) header that is valid for the data being transmitted in the communications session. 33. The apparatus of claim 32 wherein the controller is for obtaining information from the destination through out-of-band signaling and to use the information to determine the number of routers between the source and destination. 34. The apparatus of claim 33 wherein the out-of-band signaling returns the time to live (TTL) value of an RTP packet at the destination, and the controller is for suing the difference between the TTL value at the destination and the TTL value at the source to determine the number of routers along a path from the source to the destination. 35. The apparatus of claim 33 wherein each diagnostic packet contains a flag in its header, the value of which is modified by each router it passes through and which elicits a response from a router whenever the received value of the flag reaches a threshold. 36. The apparatus of claim 35 wherein the flag is a TTL flag that each router decrements as a packet passes through the router. 37. The apparatus of claim 35 wherein the diagnostic packet source is for sending a diagnostic packet that elicits a response in the form of an error response packet that includes a timestamp. 38. The apparatus of claim 36 wherein diagnostic packet source is for sending a diagnostic packet that elicits a response in the form of an Internet control message protocol (ICMP) time exceeded packet that includes a timestamp and the Internet protocol (IP) address of the router sending the ICMP packet as the source address. 39. The apparatus of claim 38 wherein the data packets are media packets. 40. The apparatus of claim 38 wherein the diagnostic packet source is for sending diagnostic packets that elicit at least one response from each router along one or more paths between the source and destination. 41. The apparatus of claim 32 wherein the controller is for identifying one or more routers along a path between the source and destination whose performance is diminished in comparison to one or more other routers delivering said data packets. 42. The apparatus of claim 32 wherein the diagnostic packet source is for sending a diagnostic packet that elicits a response in the form of a returned packet that includes a timestamp. 43. The apparatus of claim 32 wherein the data packets are routed on a policy basis and the diagnostic packet source is for sending a diagnostic packet that includes the same policy attributes. 44. The apparatus of claim 43 wherein the policy basis is a quality of service policy. 45. The apparatus of claim 44 wherein the data packets are voice packets. 46. The apparatus of claim 45 wherein the data packets are real time protocol (RTP) packets sent over Internet protocol (IP). 47. The apparatus of claim 44 wherein the data packets are video packets. 48. The apparatus of claim 44 wherein the data packets are audio packets. 49. The apparatus of claim 32 wherein the controller is for signaling an on-hook condition to close the communications session. 50. The apparatus of claim 32 wherein the controller is for transmitting a plurality of diagnostic packets to a router and to determine the jitter attributable to the router from timestamps within the elicited packets. 51. The apparatus of claim 32 wherein the controller is for determining a delay metric from timestamps within elicited packets. 52. The apparatus of claim 32 wherein the controller is for determining loss from the number of transmitted packets that don't elicit a response. 53. The apparatus of claim 32 wherein the diagnostic packets source is for sending Internet protocol (IP) packets. 54. The apparatus of claim 32 wherein the diagnostic packet source is for sending hypertext transfer protocol (HTTP) packets. 55. In a packet network communications system, an apparatus, having a computer readable storage medium, for analyzing packet-delivery performance along intermediate path segments during a communications session between a source and destination for a predetermined application, comprising: a controller for establishing a communications session between a source and a destination by a call signaling exchange between the source and the destination, the communications session being that period between a call answer signal from the destination and a call termination condition; a diagnostic packet source for sending data packets and diagnostic packets from the source during the same communication session in which data packets are transmitted between the source and destination, each diagnostic packet being of the same length and format as data packets being transmitted in the communications session, each diagnostic packet including: the same user datagram protocol (UDP) destination port number as data packets, the same differential services code point as the data packets, and a real time protocol (RTP) header that is valid for the data being transmitted in the packet communications session, each diagnostic packet eliciting a response from a router along a path between the source and destination; a controller for analyzing the responses from routers along at least one path to produce a packet-delivery metric for one or more of the routers along one or more paths between the source and the destination; and the controller also for obtaining information from the destination through out-of-band signaling and to use the information to determine the number of routers between the source and destination, the difference between the TTL value at the destination and the TTL value at the source indicating the number of routers along a path from the source to the destination. 56. The apparatus of claim 55 wherein the data packets are routed on a policy basis and the diagnostic packet source is for sending diagnostic packets that include the same policy attributes. 57. The apparatus of claim 56 wherein the diagnostic packet source is for sending diagnostic packets wherein the policy basis is a quality of service policy. 58. The apparatus of claim 55 wherein the data packets are voice packets. 59. The apparatus of claim 58 wherein the data packets are real time protocol (RTP) packets sent over Internet protocol (IP). 60. The apparatus of claim 55 wherein the data packets are video packets. 61. The apparatus of claim 55 wherein the data packets are audio packets. 62. The apparatus of claim 55 wherein source and destination are diagnostic elements, the source diagnostic element is for signaling to the destination diagnostic element the TTL value at the source, the destination diagnostic element configured to determine the number of hops between the source and destination by the difference between the TTL value at the source and the received TTL value and to signal the number of hops to the source diagnostic element. 63. The apparatus of claim 55 wherein the source diagnostic element is for transmitting diagnostic packets to elicit response from routers without regard to TTL value.