Multiplex communications – Diagnostic testing – Fault detection
Reexamination Certificate
1999-12-27
2003-11-25
Vu, Huy D. (Department: 2665)
Multiplex communications
Diagnostic testing
Fault detection
C370S401000, C370S465000, C370S467000, C375S222000, C702S183000
Reexamination Certificate
active
06654348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to detecting problems arising from the use of a modem device that is positioned in a remote location (field modem debugging) and particularly to increasing the speed of such modem debugging. Additionally, the present invention can be used to support a service for offering remote wholesale modems through a voice-over-Internet Protocol (VoIP) carrier from the end-user to the wholesale modem banks.
2. Description of the Prior Art
In modern communication systems, information is transmitted from a point of origin to a destination point often through packet networks such as an Internet Protocol (IP), frame relay or Asynchronous Transfer Mode (ATM) networks. The point of origin and the destination point each may be any number of devices such as a Plain Old Telephone System (POTS), a fax machine, modem attached to a personal computer (PC) and the like. The information emanating from any one of such devices may be initiated in one country and received at another.
As an example, when a phone call is initiated from a telephone unit in Germany, in order for it to be transmitted over an IP network, which would either be the Internet or any other propriety IP network, it is forwarded to a local public switching telephone network (PSTN) in Germany. The telephone call is forwarded from the PSTN to a local network access server (NAS) in the form of compressed digital signals. Inside of the NAS, a Digital Signal Processor (DSP) device receives the voice calls from the PSTN in the form of digitized voice signals or pulse code modulation (PCM) samples, as defined by an industry standard, the ITU-T G.711.
Inside of the NAS, the voice signals are packetized (voice samples) into Real-time Transport Protocol (RTP) packets and sent over the IP network. RTP provides end-to-end network transport functions for applications that transmit real-time data, such as audio and video. The information in the form of RTP packets is transmitted from the IP network to a local NAS in the U.S. wherein the packets are reassembled into voice signals. The DSP inside of the NAS in the U.S. then transmits the voice signals to a local PSTN. Finally, the latter forwards the voice calls to the destination phone unit in the U.S.
To the end users at the point of origin and the destination point, the above mode of transmitting phone calls, also known as the IP phone or VoIP, is indistinguishable from a regular phone call, which is transmitted over the PSTN network. The call is tunneled through the IP network in order to connect the two PSTNs. Accordingly, using the IP phone to establish connection between 2 communication devices is alternatively called tunneling.
There are two distinct ways in which tunneling can be accomplished between two people, one who is located in Germany and the other who is located in the U.S., when the originating and destination (or terminating) devices are modem devices. The first mode is referred to as “pass-through”. In the pass-through mode of tunneling, the NAS in Germany recognizes an incoming modem signal from the local PSTN by detecting a modem tone. The NAS subsequently sends a message to the IP network alerting the latter that high priority information is about to be transmitted so that the IP network can provide quality of service. The voice signals are bundled together as RTP packets in the NAS and transmitted over the IP network to a local NAS in the U.S. The receiving NAS reassembles the RTP packets as voice signals and sends them over to a local PSTN, which in turn forwards them to their destination modem device.
In pass-through, the transmitting NAS sends the voice calls in the form of PCM samples in both directions simultaneously. In other words, the NAS establishes a full-duplex communication channel. The data rate of a PCM voice call is 64 kbits/sec when data is sent in one direction (half-duplex) and 128 kbits/sec when voice signals are sent in both directions at all times. In the latter case, data is constantly being transmitted over the IP network for every single application. This is a considerable amount of bandwidth for one application alone, which makes pass-through an expensive method of tunneling.
Alternatively, tunneling can be accomplished using a method known as demodulation/remodulation, or relay. In relay, the NAS in Germany converts the PCM bytes into a word representing the linear digital equivalent of the analog signal received by the modem. Thereafter, the converted digital signal is demodulated into data bits. The demodulated bits are then forwarded across the IP network to the destination NAS in the U.S. The latter remodulates the bits into voice samples, which are then transmitted to the destination point by sending them through the local PSTN. In relay, data is transmitted when the latter is available with a lower rate transmission than in pass-through because in relay only modem data is transmitted without the sampled modulated signals. In addition relay transmits data in the direction that data is available. The transmission of data is half or full duplex depending on whether the data is transmitted in one or both directions. In pass-through, however, modem signal data is transmitted in both directions at all times and at a maximum rate of 64 kbps regardless of whether there is any modem data to be transmitted or not because the modem signals must be continuously transmitted to keep the modems at both ends operational and synchronous.
The pass-through mode of tunneling is more time-sensitive to delays than relay since in the former case, raw data rather than demodulated bits is being transmitted. Additionally, in pass-through, the likelihood of data being adversely affected by packet loss, packet corruption and packet delay jitter is less than it is in relay mode. As an example, in IP phone, using pass-through transmission, the connection has to be such that voice samples are not delayed or lost during transmission. Accordingly, the demand for bandwidth during voice transmission is high. On the other hand, faxes are transmitted using relay in the form of modulated bits where it is more tolerable to wait for modulated bits to arrive as a fax page, which makes relay less sensitive to networks impairments such as time delays and packet loss than the pass-through mode of tunneling. This is the method of voice data transport.
There are several reasons for the failure of a modem to establish communication. The most common ones are related to firmware problems. Most common problems with modems, such as the modem
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, have been known to relate to the modem's software (or firmware) and, in particular, to the incompatibility of the software with the modem hardware in which the software is being employed. For instance, the version of the software in the server modem may be incompatible with the specific client modem in which it is used or it may be that the software is incompatible with or not robust enough for the environment in which the modem is located.
At the present time, problems with the server modem, at the point of origination, (commonly referred to as the customer's server modem) are investigated by dispatching diagnostic equipment to the site of the customer's NAS. The diagnostic equipment must be inserted in the data path within the customer's NAS in order to analyze the server modem's behavior and to particularly monitor negotiations between the user's client modem and the server modem located within the NAS at the destination point. The analyzing device samples data on the transmission lines which couple the PSTN on the originating side of the communication path with the customer's NAS. Generally such transmission lines are of either T1 or E1 type.
Twenty-four channels of voice or modem channels are included in a T1 transmission line and
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channels of voice or modem channels are included in an E1 transmission line.
However, there are limitations associated with dispatching equipment to the field. For example, if there are a
Doty, II Jerry Dwight
Viriato Luis Alexandre
Cisco Technology Inc.
Ho Duc
Law Offices of Imam
Vu Huy D.
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