BACKGROUND ART Originally cable networks were established to transmit television signals to homes and offices. Cable networks provided advantages over transmission television networks that included providing a clearer signal and a greater selection of channels. These networks were made up of co-axial cables routed in a tree and branch structure to customer sites and were intended simply to provide customers with analog television signals.

More recently, cable networks have been converted to transmit digital signals in a hybrid of fiber optic cable and co-axial cable structures. These converted networks accommodate not only traditional, analog television signals but also digital television signals, digital data signals and telephone signals. These cable networks have information (data) transferred over packet networks using packet switching techniques.

Digital television signals provide a crisper, more detailed picture along with enhanced sound. With the capability to transmit digital data signals, cable networks may now be coupled to the Internet thereby providing homes and offices access to the Internet. This Internet access is generally faster than access provided by other technologies. In addition, cable networks may now be used to transmit telephone voice signals in the form of packetized data. This involves a substantial savings in the amount of wiring around houses and offices because one co-axial cable can now carry analog, digital and voice signals.

To monitor the quality of the transmission of telephone signals in the form of packetized data, Perceptual Speech Quality Measurement (PSQM) according to the International

Telecommunication Union (ITU) P. 861 Standard may be used. Additional information about ITU and ITU Standards is available at http : //www. itu. ch. Determination of a PSQM score typically involves the following steps: a) sending of a PSQM file to from a home device to a remote device, b) receiving by the home device a returned PSQM file from the remote device, and c) calculating a PSQM score based on the PSQM and the returned PSQM The PSQM score is a number between one and six. The quality of signal transmissions is typically considered unacceptable when the PSQM score is above 4.

The quality of the transmission of telephone or voice signals in the form of packetized data is also measured by another criteria commonly known as the Quality of Services (QoS).

The QoS is a measurement of the amount of packet losses, jitter, delay, etc in the signal transmission. Both PSQM and the QoS are important criteria to determine the quality of signal transmissions in a packetized network.

It should be noted that the PSQM is more difficult to obtain than the QoS score as the PSQM score varies with time and location of the measurement. Therefore, it would be desirable to correlate the PSQM score with a corresponding QoS score by measuring the PSQM score and the QoS score for the same signal transmission. This would allow a user (or an administrator) of the packet network to use a QoS score to predict the corresponding PSQM score. When the predicted PSQM score rises above a maximum value indicative of network problems, the administrator will be informed to determine whether services to the network are needed to restore the signal transmission quality.

However, there are problems associated with the prior art systems which make the correlation of PSQM scores and QoS scores complicated and expensive. First, even for a small region, thousands of phone calls are being made at any given time which makes it very difficult to keep track of a particular test telephone call to allow the calculation of PSQM score and QoS score. Second, the PSQM scores vary from location to location and also from time to time for the same location because of variations in call patterns and the traffic conditions of the packet network.

Thus, there has long been a need for a more economical and simple monitoring method and system, which would monitor and calculate both PSQM and QoS scores for signal transmissions over a packet network and provide an accurate prediction of PSQM scores.

DISCLOSURE OF THE INVENTION The present invention provides a method and system for monitoring the quality of signal transmissions in a packet network.

The present invention further provides an economical and simple method and system for calculating both PSQM and QoS scores for signal transmissions over a packet network.

The present invention still further provides a method and system for providing a correlation between PSQM and QoS scores of a signal transmission over a packet network, thus allowing a user to use a QoS score to predict the corresponding PSQM score of a signal transmission.

The present invention provides a packet network having a cable modem termination system (CMTS); a voice band tester (VBT) coupled to the CMTS ; a cable modem tester coupled to the CMTS ; and a Voice over Internet Packet (VoIP) monitoring device coupled to the CMTS and the voice band tester. The voice band tester is located at a first location and the cable modem tester is located at a second location remote from the first location. The cable modem tester is adapted to generate a first communication signal to the voice band tester via the CMTS, monitor a first returned communication signal from voice band tester to the cable modem tester via the CMTS, and calculate a first Perceptual Speech Quality Measurement (PSQM) score based on the first communication signal and the first returned communication signal. The VoIP monitoring device is adapted to monitor the first communication signal and the first returned communication signal, and calculate a first Quality of Services (QoS) score based on the first communication signal and the first returned communication signal. The cable modem tester is further adapted to provide the first PSQM score to the VoIP monitoring device.

The present invention further provides a method for monitoring quality of signal transmissions within a packet network. The packet network has a Cable Modem Termination System (CMTS), and a Voice over Internet Packet (VoIP) monitoring device. The method includes the steps of : (a) generating a first communication signal from a cable modem tester located at a first location to a voice band tester (VBT) located at a second location remote from the first location via the CMTS ; (b) identifying the first communication signal and begins monitoring signal transmissions from the VBT to the cable modem tester via the CMTS ; (c) identifying and receiving a first returned communication signal from the VBT to the cable modem tester via the CMTS ; (d) calculating a first Perceptual Speech Quality Measurement

(PSQM) score based on the first communication signal and the first returned communication signal; (e) calculating a first Quality of Services (QoS) score based on the first communication signal and the first returned communication signal; and (f) providing the first PSQM score to the VoIP monitoring device.

The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a packet network organization constructed in accordance with the present invention; and FIGS. 2A and 2B are flowcharts which illustrate a method for determining the PSQM scores and QoS scores of test telephone calls using the packet network organization 100 as shown in FIG. 1 in accordance with the present invention ; FIGS. 3A shows a graph of the forward PSQM score as a function of the QoS; and FIGS. 3B shows a graph of the reverse PSQM score as a function ofthe QoS.

BEST MODES FOR CARRYING OUT THE INVENTION Referring now to FIG. 1, therein is shown a block diagram of a communications network <BR> <BR> (e. g. , a packet network) organization 100 constructed in accordance with the present invention.

The network organization 100 includes a plurality of Broadband Termination Interfaces (BTIs) 102a and 102b, a Cable Modem Termination System (CMTS) 104, an Internet Service Provider (ISP) 106, a Cable Modem (CM) Tester 108, a Voice Over Internet Packet (VoIP) monitoring device 110, a gateway 112, a telephone switch 114, and a Voice Band Tester (VBT) 116. The CMTS 104 is coupled to the BTIs 102a and 102b via co-axial cables 118a and 118b, respectively. For simplicity of illustration, only two BTIs (102a and 102b) are shown. It should be understood that the CMTS 104 may be connected to a large number of BTIs.

The CMTS 104 is coupled to the Cable Modem Tester 108 via a co-axial cable 120, and to the ISP 106 via a conventional backbone line 122. The CMTS 104 is also coupled to the gateway 112 via a co-axial cable 124. The BTI 102a is coupled to a television 126a, a personal

computer (PC) 128a, and a telephone 130a. Similarly, BTI 102b is coupled to a television 126b, a PC 128b, and a telephone 130b.

The VoIP monitoring device 110 is coupled to an endpoint 132 of the c-axial cable 124 so that it can monitor the communication between the CMTS 104 and VBT 116 through the gateway 112. The gateway 112 is coupled to the telephone switch 114 via a c-axial cable 128.

The telephone switch 114 is coupled to the VBT 116 via a telephone wire 134.

The BTIs 102a and 102b are typically located at customer sites. The CMTS 104, the VoIP monitoring device 110, the telephone switch 114, the VBT 116 and the VoIP monitoring device 110 are typically located in a central office. The Cable Modem Tester 108 is typically located at a customer site and may be used in place of a BTI at a customer site. Alternatively, the Cable Modem Tester 108 may be integrated with a BTI (102a or 102b) at a customer site.

Each of the BTIs 102a and 102b converts broadband signals from the CMTS 104 to television, packetized data, and video/voice signals for use by each of the televisions 126a and 126b, PC 128a and 128b, and telephone 130a and 130b. Each of the BTIs 102a and 102b also converts packetized data, and video/voice signals from each of the PC 128a and 128b, and telephone 130a and 130b to broadband signals and provide the broadband signals to the CMTS 104.

The CMTS 104 functions as a router which is an internetworking device that expedites message delivery by determining the optimal path along which network traffic (or signals) should be forwarded. The CMTS 104 may optionally include a computer and a memory (not shown) for data storage.

The Cable Modem Tester 108 performs Perceptual Speech Quality Measurement (PSQM) and determines the PSQM scores for telephone calls between the Cable Modem Tester 108 and the VBT 116. The PSQM scores are used as a measure of the quality of the transmission of voice signals according to the ITU Standard P. 861.

The ISP 106 is a conventional Internet service provider that provides Internet service to a user of the network organization 100.

The VoIP monitoring device 110 manages network quality, including monitoring and assessing Quality of Services (QoS) for each connection in a network. A QoS result typically includes the computation of packet loss, latency and jitter that are the most common problems that affect real time applications such as voice. Packet loss often increases with traffic and

congestion. Buffering requirements causes latency. Jitter results from unequal queuing and routing of network nodes. A discussion of the QoS can be found in Request for Comment (RFC) <BR> <BR> 1889 document which is available under http ://www. pasteur. fr/infosci/RFC. RFCs are the official publications of the Internet and have been used since 1969 to describe and obtain comments about protocol, procedures, and programs applicable to the Internet. The RFC 1889 document defines a real-time transport protocol, consisting of two closely-linked parts. The first part contains the data carrying the real-time properties (RTP). The RTP provides end-to-end delivery services for data with real-time characteristics, such as interactive audio and video. The second part is the RTP control protocol (RTCP) which is used to monitor the quality of services and to convey information about the participants in an on-going session.

The VoIP monitoring device 110 is adapted to provide per call QoS results. The QoS results provide the detail needed to diagnose a network and its effect on live applications. The VoIP monitoring device 110 provides real time monitoring and identification of packet irregularities which may lead to significant cost savings in resolving network problems.

An example of such VoIP monitoring device is the VoIP Explorer Protocol and QoS analyzer, available from Sunrise Telecom of San Jose, California.

The VoIP monitoring device 110 monitors the communications between the CMTS 104 and the gateway 112. The VoIP monitoring device 110 determines the QoS of calls between the Cable Modem Tester 108 (via the CMTS 104) and the VBT 116 and correlates the QoS score with its corresponding PSQM score for any particular test telephone call.

The VoIP monitoring device 110 may track telephone calls using either a detection of content-based information, such as RTP packet that is based on the G. 711 Standard, or a detection of signaling-based information, such as by adding a code"X"commands used in the Packet Cable Network Base Call Signal (NCS) Protocol. The NCS Protocol permits a user to create special command if it's preceded with an"X". In one embodiment, the code"XTST" means"test".

In one embodiment, the telephone switch 114 is a conventional 5ESS switch commonly used in offices and homes.

Referring now to FIG. 2A and 2B, therein are shown flowcharts of a method for determining the PSQM and QoS score of test phone calls using the packet network organization 100 as shown in FIG. 1 in accordance with the present invention.

In one embodiment, the method begins in step 200 with Cable Modem Tester 108 generating a first test telephone call with a signal having a unique pattern that is formatted in accordance with the Packet Network Base Call Signal (NCS) protocol. The signal includes a first PSQM file. The Cable Modem Tester 108 sends the first PSQM file via CMTS 104 to the VBT 116, which is located at the central office. In this embodiment, the Cable Modem Tester 108 is located at a customer site and replaces a broadband termination interface that is used at the customer site. Alternatively, the Cable Modem Tester 108 may be integrated with a broadband termination interface at the customer site. In one embodiment, the signal further includes a special code which has, for example, an"X"preceding a command. For example, the term "XTST"means"test".

In a step 202, the VoIP monitoring device 110 recognizes the test telephone call based on its unique pattern of the signal, such as the presence of a special code which includes an"X" preceding a command. The special code may also include an identifier which identifies the Cable Modem Tester 108. The VoIP monitoring device 110 starts tracking signal transmissions, that is, returned calls from the VBT 116 to the CMTS 104.

In a step 204, the VoIP monitoring device 110 identifies and receives a first returned signal transmission which contains a first returned PSQM file from the VBT 116. The first returned signal transmission is provided by the VBT 116 in response to the first PSQM file sent by the Cable Modem Tester 108.

In a step 206, the cable modem 108 received the first returned PSQM file from the VBT 116 via CMTS 104. The Cable Modem Tester 108 calculates a first PSQM score (or a forward PSQM score as will later be described) based on the first returned PSQM file.

In a step 208, the Cable Modem Tester 108 provides the first PSQM score to the VoIP monitoring device 110.

In a step 210 which is performed simultaneously or in parallel with step 206, the VoIP monitoring device 110 performs a first QoS measurement on the first returned PSQM file and calculates a first QoS score.

In a step 212, the VoIP monitoring device 110 records the time of the first test telephone call, the first PSQM score and the first QoS score. In one embodiment, the VoIP monitoring device 110 provides the time of the first test telephone call, the first PSQM score and the first QoS score to the CMTS 104 for storage.

In a step 214, the VBT 116 generates a second test telephone call with a signal having a unique pattern that is formatted in accordance with the Packet Network Base Call Signal (NCS) protocol via the CMTS 104 to the Cable Modem Tester 108 located at the customer site. The signal includes a second PSQM file. In one embodiment, the signal further includes a special code which includes, for example, an"X"preceding a command.

In a step 216, the VoIP monitoring device 110 recognizes the test telephone call based on its unique pattern of the signal, which may include a special code. The special code may use an "X"preceding a command. The special code may also include an identifier which identifies the VBT 116. The VoIP monitoring device 110 starts tracking signal transmissions, that is, returned calls from the Cable Modem Tester 108 to the VBT 116.

In a step 218, the VoIP monitoring device 110 identifies and receives a second returned signal transmission which contains a second returned PSQM file from the Cable Modem Tester 108. The second returned signal transmission is provided by the Cable Modem Tester 108 in response to the second PSQM file sent by VBT 116.

In a step 220, the VBT 116 received the second returned PSQM file from the Cable Modem Tester 108 via CMTS 104. The VBT 116 calculates a second PSQM score (or a reverse PSQM score as will later be described) based on the second returned PSQM file.

In a step 222, the VBT 116 provides the second PSQM score to the VoIP monitoring device 110.

In a step 224 which is performed simultaneously with a step 220, the VoIP monitoring device 110 performs a second QoS measurement on the second returned PSQM file and calculates a second QoS score.

In a step 226, the VoIP monitoring device 110 records the time of the second test telephone call, the second PSQM score and the second QoS score. hi one embodiment, the VoIP monitoring device 110 provides the time of the second test telephone call, the second PSQM score and the second QoS score to the CMTS 104 for storage.

In a step 228, the Cable Modem Tester 108 determines if it is time to generate a third test telephone call. If so, the method returns to the step 200. Otherwise, the method ends.

In a second embodiment, only the cable modem tester is used to generate test telephone calls. In this case, the method will go through the steps 200 to 212, and then to the step 228.

Referring now to FIG. 3A, therein is shown a graph 300 of the forward PSQM score as a function of the corresponding QoS score. As used herein, forward PSQM scores refer to PSQM scores of PSQM files that are: generated by the Cable Modem Tester 108, sent to the VBT 116 by the Cable Modem Tester 108, and returned by to the Cable Modem Tester 108 by the VBT 116. For example, the first PSQM score described in FIG. 2A and 2B is a forward PSQM score.

As the QoS score decreases, the forward PSQM score increases. The graph 300 can be prepared by generating a number of test telephone calls from the Cable Modem Tester 108 to the VBT 116 at different times and obtaining the forward PSQM scores and the corresponding QoS scores using the method in accordance with the present invention as described in FIG. 2A and 2B.

P1 is the maximum forward PSQM score allowable for an acceptable signal transmission in a packetized network. Q1 is the QoS value that corresponds to P1. Therefore, a graph 300 allows a user to monitor the signal transmissions in a packetized network by keeping track of the QoS scores which can be used to predict the corresponding PSQM scores. When QoS score drops to Q1 or below, it means that the predicted forward PSQM score is not acceptable which indicates network problems. A message may be sent to the user to inform the user that services to the network organization 100 may be needed to restore signal transmission quality.

Referring now to FIG. 3B, therein is shown a graph 302 of reversed PSQM score as a function of the corresponding QoS score. As used herein, reverse PSQM scores refer to PSQM scores of PSQM files that are : generated by the VBT 116, sent to the Cable Modem Tester 108 by the VBT 116, and returned to the VBT 116 by the Cable Modem Tester 108. For example, the second PSQM score described in FIG. 2A and 2B is a reverse PSQM score. As the QoS decreases, the reverse PSQM score increases. The graph 302 can be prepared by generating a number of test telephone calls from the VBT 116 to the Cable Modem Tester 108 at different times and obtaining the reverse PSQM scores and the corresponding QoS scores using the method in accordance with the present invention as described in FIG. 2A and 2B.

P2 is the maximum reverse PSQM score allowable for an acceptable signal transmission in a packetized network. Q2 is the QoS value that corresponds to P2. Therefore, a graph 302 allows a user to monitor the signal transmission in a packetized network by keeping track of the QoS. When QoS drops to Q2 or below, it means that the reverse PSQM score is not acceptable which indicates network problems. A message may be sent to the user to inform the user that services to the network organization 100 may be needed to restore signal transmission quality.

Therefore, the present invention provides a. method and system for monitoring the transmission quality of a packetized network. Specifically, QoS can be used to predict the corresponding forward or reversed PSQM scores and allow a user to keep track of quality of signal transmissions in a packetized network.

While the invention has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the included claims. All matters set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense.