Modem resistant to cellular dropouts

• US 5,673,268 A
• Filed: 08/11/1994
• Issued: 09/30/1997
• Est. Priority Date: 01/08/1993
• Status: Expired due to Fees

• Current Assignee: Multi-Tech Systems Incorporated
• Original Assignee: Multi-Tech Systems Incorporated
• Inventors: Davis, Jeffrey P., Li, Ping, Young, Steve, Sharma, Raghu, Gunn, Timothy D., Maitra, Sidhartha, Thanawala, Ashish
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Nguyen, Chau T.
• Application Number:
  US08/289,296
• Time in Patent Office: 1,146 Days
• Field of Search: 370/94.1, 370/60, 370/32.1, 370/94.2, 370/110.1, 370/13, 370/14, 370/15, 370/16, 455/33.1, 379/59, 379/63, 379/93, 371/32, 371/33, 375/222
• US Class Current: 370/522
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: H04L 12/6418 Hybrid transport
• CPC Class Codes: H04L 2012/6424 Access arrangements
• CPC Class Codes: H04L 2012/6427 Subscriber Access Module; Concentrator; Group equipment
• CPC Class Codes: H04L 2012/6459 Multiplexing, e.g. TDMA, CDMA
• CPC Class Codes: H04L 2012/6475 N-ISDN, Public Switched Telephone Network [PSTN]
• CPC Class Codes: H04L 2012/6481 Speech, voice
• CPC Class Codes: H04L 2012/6491 Echo cancellation
• CPC Class Codes: H04L 2012/6494 Silence suppression
• CPC Class Codes: H04L 27/3416 in which the information is carried by both the individual signal points and the subset to which the individual points belong, e.g. using coset coding, lattice coding, or related schemes
• CPC Class Codes: H04L 65/1069 Session establishment or de-establishment
• CPC Class Codes: H04L 65/1101 Session protocols
• CPC Class Codes: H04L 65/762 at the source reformatting of additional data in video distribution servers H04N21/2355
• CPC Class Codes: H04L 65/80 Responding to QoS
• CPC Class Codes: H04L 69/04 Protocols for data compression, e.g. ROHC
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04M 1/247 Telephone sets including user guidance or feature selection means facilitating their use user interfaces specially adapted for cordless or mobile telephones H04M1/724
• CPC Class Codes: H04M 1/2473 Telephone terminals interfacing a personal computer, e.g. using an API (Application Programming Interface) details of API H04M7/0021
• CPC Class Codes: H04M 1/2477 for selecting a function from a menu display H04M1/2474 takes precedence
• CPC Class Codes: H04M 1/253 Telephone sets using digital voice transmission
• CPC Class Codes: H04M 1/57 : Arrangements for indicating or recording the number of the calling subscriber at the called subscriber's set at the operator set in a manual exchange H04M5/20
• CPC Class Codes: H04M 1/6033 : for providing handsfree use or a loudspeaker mode in telephone sets arrangements for preventing acoustic echo H04M9/08
• CPC Class Codes: H04M 1/6505 : storing speech in digital form
• CPC Class Codes: H04M 1/663 : Preventing unauthorised calls to a telephone set
• CPC Class Codes: H04M 11/06 : Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
• CPC Class Codes: H04M 11/064 : Data transmission during pauses in telephone conversation
• CPC Class Codes: H04M 11/068 : using time division multiplex techniques; integrated services digital networks H04Q11/0428
• CPC Class Codes: H04M 2203/4509 : Unified messaging with single point of access to voicemail and other mail or messaging systems unified messaging in packet switching networks H04L51/56
• CPC Class Codes: H04M 3/002 : Applications of echo suppressors or cancellers in telephonic connections in two-way loud-speaking telephone systems H04M9/08, echo suppressors or cancellers per se H04B3/20
• CPC Class Codes: H04M 3/42 : Systems providing special services or facilities to subscribers specially adapted for wireless communication networks H04W4/00
• CPC Class Codes: H04M 3/436 : Arrangements for screening incoming calls , i.e. evaluating the characteristics of a call before deciding whether to answer it based on the calling party profile H04M3/42059; based on location H04M3/42348; based on presence H04M3/42365; diversion H04M3/54
• CPC Class Codes: H04M 3/5307 : for recording messages comprising any combination of audio and non-audio components
• CPC Class Codes: H04M 3/533 : Voice mail systems
• CPC Class Codes: H04M 3/567 : Multimedia conference systems
• CPC Class Codes: H04M 7/0027 : Collaboration services where a computer is used for data transfer and the telephone is used for telephonic communication
• CPC Class Codes: H04M 7/0057 : Services where the data services network provides a telephone service in addition or as an alternative, e.g. for backup purposes, to the telephone service provided by the telephone services network
• CPC Class Codes: H04M 7/006 : Networks other than PSTN/ISDN providing telephone service, e.g. Voice over Internet Protocol (VoIP) , including next generation networks with a packet-switched transport layer H04L65/00 takes precedence; aspects not specific to the type of network H04M3/00; special services in those networks H04M3/42
• CPC Class Codes: H04M 7/1295 : Details of dual tone multiple frequency signalling
• CPC Class Codes: H04N 1/00204 : with a digital computer or a digital computer system, e.g. an internet server programmed control between transmitter and receiver or between image input and image output device H04N1/32561
• CPC Class Codes: H04N 1/00206 : Transmitting or receiving computer data via an image communication device, e.g. a facsimile transceiver H04N1/00236 takes precedence
• CPC Class Codes: Y10S 379/908 : Multimedia

Abstract

A personal communications system is described which includes components of software and hardware operating in conjunction with a personal computer. The user interface control software operates on a personal computer, preferably within the Microsoft Windows® environment. The software control system communicates with hardware components linked to the software through the personal computer serial communications port. The hardware components include telephone communication equipment, digital signal processors, and hardware to enable voice, fax and data communication with a remote site connected through a standard telephone line. The functions of the hardware components are controlled by control software operating within the hardware component and from the software components operating within the personal computer. The major functions of the system are a telephone function, a voice mail function, a fax manager function, a multi-media mail function, a show and tell function, a terminal function and an address book function. The telephone function allows the present system to operate, from the users perspective, as a conventional telephone using either hands-free, headset or handset operation. The telephone function is more sophisticated than a standard telephone in hat the present system converts the voice into a digital signal which can be processed with echo cancellation, compressed, stored as digital data for later retrieval and transmitted as digital voice data concurrent with the transfer of digital information data.

Claims

1. A method of maintaining a modem connection over a telephone line connection which includes a cellular telephone link connection, comprising the steps of:

calling a remote modem from a local modem over a telephone line connection, line a portion of which includes a cellular telephone link connection;

establishing a modem connection between the local modem and the remote modem;

transmitting data packets over the telephone line connection from the local modem of a local computer at a local site to the remote modem of a remote computer at a remote site;

periodically transmitting from the local modem a supervisory packet over the telephone line connection;

ignoring the carrier detect of the remote modem during carrier dropouts;

continuing to periodically send the cellular supervisory packet and continuing to maintain the modem connection over the telephone line if the remote site had acknowledged receipt of the cellular supervisory packet within a predetermined period of time; and

disconnecting the modem connection over the telephone line if the remote site fails to acknowledge the receipt of the cellular supervisory packet within the predetermined period of time.

2. The method according to claim 1 wherein the step of continuing to periodically send the cellular supervisory packet and continuing to maintain the modem connection includes the substeps of receiving the supervisory packet and decoding an acknowledgment field within the supervisory packet.

3. The method according to claim 2 wherein the step of continuing to periodically send the cellular supervisory packet and continuing to maintain the modem connection further includes the substeps of restarting a timer upon receipt of the supervisory packet to begin timing the first predetermined time and wherein the step of disconnecting the modem connection further includes the step of disconnecting the telephone line if the predetermined period of time has lapsed.

4. A method of maintaining a modem connection over a cellular telephone connection even during the temporary dropout of the connection, comprising the steps of:

calling a remote modem from a local modem over a cellular telephone connection;

ignoring the carrier detect of the remote modem during carrier dropouts;

sending a cellular supervisory packet from the local modem to the remote modem and starting a timer;

receiving the cellular supervisory packet at the remote modem;

storing an acknowledgment signal in the cellular supervisory packet at the remote modem;

sending the cellular supervisory packet from the remote modem to the local modem;

receiving the cellular supervisory packet at the local modem;

restarting the timer in the local modem; and

continuing to send the cellular supervisory packet as long as the timer in the local modem does not time out; and

disconnecting the telephone connection if the timer in the local modem times out.