The present invention relates generally to communication networks, and more specifically to the monitoring and management of quality of signal transmissions in a communications network.
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 use packet switching techniques to transfer information (data) 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.
Another signal transmission technology that offers significant improvement in data transfer is the Digital Subscriber Line (DSL) technology. DSL technology provides increased communications bandwidth while using existing twisted-pair copper lines that are prevalent throughout much of the world. DSL delivers a basic data transfer rate of 128 kbps. High speed DSL, or HDSL, can deliver a data transfer rate of 1.544 megabits per second (Mbps) in North America, and 2.048 Mbps elsewhere. Asymmetric DSL, or ADSL, can deliver data rates ranging from 1.5 to 9.0 Mbps on a downstream or receiving path, and 16 to 800 kbps on an upstream or sending path. Taken together, varying DSL technologies are referred to as xDSL.
A conventional xDSL communication network includes a Main Distribution Frame (MDF), an access matrix, a DSL Access Multiplexer (DSLAM), and a test unit. The MDF is coupled to the access matrix, which itself is coupled to the DSLAM and the test unit. The MDF, the access matrix, the test unit, and the DSLAM each reside at an xDSL service provider site (or Central Office). At a customer site, a set of Customer Premises Equipment (CPE) units is connected to the MDF. Each CPE unit includes an xDSL modem.
To monitor the quality of the transmission of telephone or voice signals in the form of packetized data, various transmission impairment tests (TIT) are used. One common type of transmission impairment test is the Perceptual Speech Quality Measurement (PSQM) according to the International Telecommunication Union (ITU) P.861 Standard. Information about ITU and ITU Standard P.861 is available at http://www.itu.ch. Determination of a PSQM score typically involves sending of a PSQM file from a home device to a remote device, and calculating a PSQM score by the remote device based on the PSQM file received at the remote device. A PSQM file is a file including digital signals representative of voice signals of various people (e.g., men, women, children, etc.) speaking different languages. Alternatively, a PSQM score can be determined by sending a PSQM file from a remote device to a home device, and calculating the PSQM score by the home device based on the PSQM file received at the home device. The PSQM score is a number between one and seven where a higher number represents higher quality.
Another type of TIT is the Perceptual Evaluation of Speech Quality (PESQ) according to the ITU P.862 Standard. Information about ITU P.862 is available at http://www.itu.ch. PESQ has been found to be more accurate than PSQM at predicting quality in a very wide range of networks, including the speed transmission quality of packet-oriented networks. The PESQ score is a number between one and seven where a higher number represents higher quality.
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. Transmission impairment tests (e.g., PSQM and PESQ), and QoS are important criteria to determine the quality of signal transmissions in a packetized network.
It should be noted that the TIT scores is more difficult to obtain than the QoS score as the TIT score, such as the PSQM score, varies with time and location of the measurement. Therefore, it would be desirable to correlate the TIT scores with a corresponding QoS score by measuring the TIT scores 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 TIT scores. When the predicted TIT score drops below a minimum 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 that make the correlation of TIT 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 TIT score and QoS score. Second, the TIT 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 TIT scores, such as PSQM scores and PESQ scores, and QoS scores for signal transmissions over a packet network; and then use QoS scores to provide an accurate prediction of the corresponding TIT scores.
The present invention provides a method and system for monitoring the quality of signal transmissions in a communications network.
The present invention further provides an economical and simple method and system for calculating both Transmission Impairment Test (TIT) scores and QoS scores for signal transmissions over a communications network.
The present invention still further provides a method and system for providing a correlation between TIT scores and QoS scores of signal transmissions over a communications network, thus allowing a user of the communications network to use a QoS score to predict the corresponding TIT score. When the TIT score falls below a minimum TIT score, the user may be informed and will have an opportunity to determine if service to the communications network is required to restore signal transmission quality.
The present invention provides a communications 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 VBT. The VBT 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 provide a first communication signal to the voice band tester via the CMTS. The VoIP monitoring device is adapted to monitor the first communication signal and calculate a first Quality of Services (QoS) score based on traffic density between the CMTS and the VBT. The VBT is further adapted to calculate a first Transmission Impairment Test (TIT) score based on the first communication signal and a first received communication signal received by the VBT from the cable modem tester and provide the first TIT score to the VoIP monitoring device. The first TIT score could be a score such as a Perceptual Speech Quality Measurement (PSQM) score, or a Perceptual Evaluation of Speech Quality (PESQ) score.
The present invention further provides a method for monitoring quality of signal transmissions within a communications network. The method includes the steps of: (a) providing 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 a Cable Modem Termination System (CMTS); (b) identifying the first communication signal and begins monitoring signal transmissions from the cable modem tester to the VBT via the CMTS; (c) calculating a first Transmission Impairment Test (TIT) score based on the first communication signal and a first received communication signal received by the VBT from the cable modem tester; (d) providing the first TIT score to a Voice over Internet Packet (VoIP) monitoring device; and (e) calculating a first Quality of Services (QoS) score based on traffic density between the CMTS and the VBT.
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.