Data transmission with improved message format

• US 4,885,749 A
• Filed: 12/28/1987
• Issued: 12/05/1989
• Est. Priority Date: 12/28/1987
• Status: Expired due to Fees

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.), AT&T Information Systems Inc. (AT&T, Inc.)
• Original Assignee: American Telephone & Telegraph Company (AT&T, Inc.), AT&T Information Systems Inc. (AT&T, Inc.)
• Inventors: Golden, Glenn D.
• Primary Examiner(s): ATKINSON, CHARLES
• Application Number:
  US07/137,996
• Time in Patent Office: 708 Days
• Field of Search: 371/32, 371/33, 371/37, 371/47, 370/85, 370/91, 370/94, 370/99, 370/100
• US Class Current: 714/748
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

In a voiceband data multipoint network, each tributary modem transmits, in a trailer which follows the user data, a tributary modem identification, a sequence number which advances for each start-up and a checksum. The observation at the receiver of a gap in the series of sequence numbers in messages determined to have originated from a particular tributary modem is used to accurately compute a missed message rate for that modem.

Claims

1. A data transmission system comprising:

a first modem including means for generating a line signal which represents a stream of user data followed by a predetermined delimiting signal followed by a trailer which contains information-bearing data generated from within said first modem, and

a second modem for receiving said line signal, said second modem including;

a received data lead,

means for providing an indication of the presence of valid received user data on said received data lead, and

means for terminating said indication in response to the receipt of said delimiting signal,

whereby terminal equipment associated with said second modem is enabled to initiate the transmission of data at a point in time at which the portion of said line signal containing said trailer is still being received by said second modem.

2. The invention of claim 1 wherein said information-bearing data includes data identifying said first modem.

3. The invention of claim 2 wherein said information-bearing data further includes a sequence number that is advanced for every N messages transmitted by said tributary modem, N being a predetermined number.

4. The invention of claim 1 wherein said information-bearing data includes an error-checking code word.

5. The invention of claim 4 wherein said error-checking code word is a checksum.

6. The invention of claim 4 wherein said error-checking code word is a function of both said user data and at least a predetermined porton of the data in said trailer.

7. A first modem comprising:

means for creating messages to be communicated to a second modem, each said message including user data supplied to said first modem and further including a trailer which follows said user data and which contains information-bearing data generated from within said first modem, and

means for communicating said messages to said second modem wherein said communicating means communicates said user data and said trailer using predetermined points from a predetermined signal space and wherein said communicating means communicates a synchronization signal between said user data and said trailer, said synchronization signal including at least a first point in said signal space which is other than one of said predetermined points.

8. A method for use in a data transmission system, said method comprising the steps of:

generating in a first modem in line signal which represents a stream of user data followed by a predetermined delimiting signal followed by a trailer which contains information-bearing data generated from within said first modem,

receiving said line signal in a second modem, said second modem being of the type which includes a received data lead and means for providing an indication of the presence of valid received user data on said received data lead, and

terminating said indication in response to the receipt of said delimiting signal, whereby terminal equipment associated with said second modem is enabled to initiate the transmission of data at a point in time at which the portion of said line signal containing said trailer is still being received by said second modem.

9. The invention of claim 8 wherein said information-bearing data includes data identifying said first modem.

10. The invention of claim 9 wherein said information-bearing data further includes a sequence number that is advanced for every N messages transmitted by said tributary modem, N being a predetermined number.

11. The invention of claim 8 wherein said information-bearing data includes an error-checking code word.

12. The invention of claim 11 wherein said error-checking code word is a checksum.

13. The invention of claim 11 wherein said error-checking code word is a function of both said user data and at least a predetermined portion of the data in said trailer.

14. A method for use in a first modem, said method comprising the steps of:

creating messages to be communicated to a second modem, each said message including user data supplied to said first modem and further including a trailer which follows said user data and which contains information-bearing data generated from within said first modem, and

communicating said messages to said second modem wherein said communicating means communicates said user data and said trailer using predetermined points from a predetermined signal space and wherein said communicating means communicates a synchronization signal between said user data and said trailer, said synchronization signal including at least a first point in said signal space which is other than one of said predetermined points.

15. A method for use in a first modem adapted to communicate with a second modem over a voiceband telephone line, said method comprising the steps of:

transmitting over said telephone line a line signal which includes a stream of symbols representing at least a first message, said message including, in the order named, user data, a synchronization symbol and a trailer which includes modem-to-modem data generated by said first modem and which identifies at least a first characteristic of said message,

receiving said line signal in a second modem, said second modem being of the type which includes a received data lead and means for providing an indication of the presence of valid received user data on said received data lead, and

terminating said indication in response to the receipt of said synchronization symbol, whereby terminal equipment associated with said second modem is enabled to initiate the transmission of data at a point in time at which the portion of said line signal containing said trailer is still being received by said modem.

16. The invention of claim 15 wherein said modem-to-modem data includes data identifying said first modem.

17. The invention of claim 17 wherein said modem-to-modem data further includes a sequence number that is advanced for every N messages transmitted by said first modem, N being a predetermined number.

18. The invention of claim 17 wherein said modem-to-modem data includes an error-checking code word.

19. The invention of claim 19 wherein said error-checking code word is a checksum.

20. The invention of claim 19 wherein said error-checking code word is a function of both said user data and at least a predetermined portion of the data in said trailer.