Multiplex communications – Diagnostic testing – Loopback
Reexamination Certificate
1998-10-28
2002-10-15
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Diagnostic testing
Loopback
C370S352000, C370S401000
Reexamination Certificate
active
06466548
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a packet switched network used for transmitting audio data, video data or any other delay sensitive data, and more particularly to a hop by hop loopback system that locates quality of service problems in the packet switched network.
Conversations between two or more people include constant acknowledgements. If the conversation is face to face, the acknowledgement can be either visual or audible. Visual acknowledgements are typically in the form of body motions such as a head nod, hand motion, or facial expression. Audible acknowledgements typically come in the form of words or noises such as “I see”, “ok”, “yes”, “um hum”, etc. Phone conversations also require constant acknowledgements. Since phone conversations are not conducted face to face, these acknowledgements must be given audibly.
Packet switched networks, such as the Internet, are used for conducting telephone calls. Audio signals from a telephone are converted into voice packets by an originating gateway. The voice packets are then transmitted over the packet switched network to a destination gateway that converts the voice packets back into voice signals that are output to a destination telephone. Delay is a particular problem in packet switched networks that disrupts the interaction and feedback in telephone conversations.
For example, if the network has a lot of delay, audio feedback can be misinterpreted. A person completing a statement over the phone may wait for an acknowledgement such as “ok”, “yes”, “I see”, “uh hum”, etc. The packet switched network can delay the voice packets containing the acknowledgement. The delayed acknowledgement may be misinterpreted as confusion, apathy, or rudeness. While in fact, an immediate acknowledgement was given by the listener. If audio signals are delayed too long, the speaker may go onto another subject. When the audio packets do arrive, the-speaker does not know what part of the conversation the listener was responding to. These network delays result in disjointed and confusing conversations.
Utilities currently exist that can identify end to end network delay. End to end delay is generally defined as the time it takes a packet to go from an originating telephony gateway endpoint to a destination telephony gateway endpoint. One way to measure end to end delay is to put loopback interfaces into the gateway endpoints. A packet sent from the originating gateway is sent to the destination gateway and then automatically looped back to the originating gateway. The roundtrip delay from the originating gateway to the destination gateway and back to the originating gateway is then calculated.
A distributed packet switched network includes different subsystems or subnetworks connected together through different network processing nodes such as routers, switches, etc. Any one or more of these subnetworks or processing nodes could be the primary contributor to the end to end delay. End to end delay measurements do not identify where these delays occur in the packet switched network. The subsystems or processing nodes that cause the delay problems, therefore, cannot be located.
Existing loopback systems also do not test QoS for voice traffic sent over a packet switched network. During any given telephone conversation, the voice packets may be routed through different paths depending on network congestion and other similar considerations. Also, the voice path for incoming voice packets may be different than the voice path for outgoing voice packets. Existing loopback systems, e.g., ping, can only generate one packet about every second. Thus, these loopback systems do not simulate the traffic conditions that are created with an actual audio packet stream. Additionally, ping is based on ICMP, which may receive different treatment by routers than regular traffic.
Accordingly, a need remains for a system that can identify and locate causes of audio QoS problems in a distributed packet switched network.
SUMMARY OF THE INVENTION
Loopback interfaces are put into routers throughout a packet switched network. When an end to end path in the network is not providing satisfactory Quality of Service (QoS), the delay and jitter characteristics of an audio signal are measured for individual network subsystems between the end to end path. The audio signal is converted into a stream of audio packets and sent hop by hop to the different routers in the network with the loopback interfaces. The QoS for the subsystems are determined by measuring the audio packet stream looped-back from the different routers.
Subsystems with QoS problems can be identified by comparing the results of adjacent hop by hop loopbacks. If a loopback from a first router has minimal delay and the loopback from a next router has excessive delay, the QoS problem exists in the subsystem between the two routers. The capacity of the network can then be adjusted as necessary according to the measured transmission delay. For example, telephone calls may be rerouted around the problem subsystem through a different network path or additional equipment may be added to the problem subsystem to increase capacity.
Existing network utilities such as trace route can be used to automatically calculate routes in the packet switched network between a source gateway and a destination gateway. Loopback calls are then automatically sent to routers with loopback interfaces. The loopback delays are then calculated for each of the loopback calls to determine the QoS for the different network subsystems.
Hop by hop loopback is especially useful to Internet Service Providers (ISPs) that buy network services for different backbone carriers. The QoS can be separately measured for both the ISP network and the backbone carrier networks to determine whether the backbone carrier is meeting agreed upon QoS.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.
REFERENCES:
patent: 4506358 (1985-03-01), Montgomery
patent: 5933490 (1999-08-01), White et al.
patent: 6011790 (2000-01-01), Fisher
patent: 6154448 (2000-11-01), Petersen et al.
patent: 6259677 (2001-07-01), Jain
patent: 6292479 (2001-09-01), Bartholomew et al.
Cisco Technology Inc.
Hsu Alpus H.
Marger Johnson & McCollom PC
Stevens Roberta
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