Automatic modem identification system

• US 4,215,243 A
• Filed: 11/17/1978
• Issued: 07/29/1980
• Est. Priority Date: 11/17/1978
• Status: Expired due to Term

• Current Assignee: Racal-Datacom, Inc. (Thales SA)
• Original Assignee: Racal-Vadic, Inc.
• Inventors: Maxwell, Ronald K.
• Primary Examiner(s): Moffitt, James W.
• Assistant Examiner(s): Popek, Joseph A.
• Application Number:
  US05/961,849
• Time in Patent Office: 620 Days
• Field of Search: 179/2 DP, 179/2 AM, 179/15 BV, 364/200
• US Class Current: 379/93.34
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors

Abstract

Apparatus for communicating between a number of remote use terminals and a central computer. The apparatus initially answers an incoming call under concentrator control, and transmits an answer tone to the calling terminal. The terminal user places the modem at the terminal in data mode. The apparatus detects which modem type called, conditions the concentrator port interface and connects an answering modem of the same type into the circuit between the telephone line and the concentrator port. The port automatically detects speed and code, and conditions the computer adapter clock and software appropriately to be compatible. The user experiences no change in existing connection sequences and only one telephone number is necessary for servicing a number of different modem types having common access to the computer.

Claims

1. The method of identifying a particular modem type from a plurality of modem types having common access to a port over a telephone line, wherein said modem types include at least a first and a second modem type, comprising the steps of:

(a) answering all the incoming calls received over said telephone line with an answering modem of said first type by transmitting for a first time period an answer mark carrier of a frequency which is not only unique to an answering modem of said first type but is also compatible with any other of said modem types;

(b) monitoring said telephone line during said first time period to detect an originate mark carrier of a frequency unique to a calling modem of said first type;

(c) maintaining communication with said calling modem of said first type upon the condition that the originate mark carrier detected within said first time period is of a frequency unique to a calling modem of said first type;

(d) if no originate mark carrier is detected during said first time period, transmitting an answer mark of a frequency unique to an answering modem of said second type for a second time period;

(e) monitoring said telephone line during said second time period to detect an originate mark carrier of a frequency unique to a calling modem of said second type; and

(f) maintaining communication with said calling modem of said second type upon the condition that the originate mark carrier detected within said second time period is of a frequency unique to a calling modem of said second type.

2. The method set forth in claim 1 in which all steps are repeating until a connection is established.

3. The method set forth in claim 1, in which the plurality of modem types includes a third modem type, which includes the further steps of:

(g) if no originate mark carrier is detected during said second time period, transmitting an answer supervisory signal for a third time period;

5. The method set forth in claim 3 in which all steps are repeating until a connection is established.

7. The method of claim 5 in which the steps (c) and (e) are repeated until a connection is established.

8. The method of claim 5 which includes the further steps of:

(i) clocking a third time period subsequent to said second time period;

(j) changing said transmitting answer mark carrier to a frequency corresponding to the answer mark carrier of a modem of said third type during said third time period;

(k) monitoring said calling modem to detect a third originate mark carrier uniquely identifying a modem of said third type;

(l) establishing a connection between said third modem and said computer port upon the condition that said third mark carrier is detected within said third time period.

9. The method of claim 5 in which said answer mark carrier corresponding to said first modem type has a frequency of 2225 Hz.

10. The method of claim 8 in which said first originate mark carrier has a frequency of 1270 Hz.

11. The method of claim 8 in which said answer mark carrier corresponding to said second modem type has frequencies of 851 Hz and 1450 Hz.

12. The method of claim 10 in which said second originate mark carrier has frequencies of 1950 Hz and 2550 Hz.

4. (h) monitoring said telephone line during said third time period to detect one of a plurality of originate mark carriers of a frequency unique to one of a plurality of calling modems of a type other than said first and second type;

and

(i) maintaining communication with the detected calling modem upon the condition that the originate mark carrier detected within said third time period is of a frequency unique to a calling modem of said third type.

6. The method of automatically detecting a calling modem type from a plurality of different modem types having common access to common communication apparatus and of connecting an appropriate answering modem in circuit with said calling modem at a computer port, each calling modem being identifiable by a unique originate mark carrier generated by said modem, said method comprising the steps of:

(a) connecting a modem of a first type in circuit with incoming calls to answer all incoming calls by transmitting a data transmit ready signal detectable by each of the plurality of different modem types;

(b) clocking a first time period subsequent to said ready signal and a second time period subsequent in time to said first time period;

(c) transmitting during said first time period an answer mark carrier of a frequency which not only corresponds to the answer mark carrier of said first type modem but which is also compatible with any other of said modem types;

(d) monitoring said calling modem during said first time period to detect a first originate mark carrier uniquely idenifying a modem of said first type;

(e) changing said transmitting answer mark carrier to a frequency corresponding to the answer mark carrier of a modem of said second type during said second time period;

(f) monitoring said calling modem to detect a second originate mark carrier uniquely identifying a modem of said second type;

(g) establishing a connection between said first modem and said computer portion upon the condition that said first originate mark carrier is detected within said first time period; and

(h) establishing a connection between said second modem and said computer port upon the condition that said second mark carrier is detected within said second time period.