Method and apparatus for establishing protocol spoofing from a modem

• US 5,309,562 A
• Filed: 08/19/1991
• Issued: 05/03/1994
• Est. Priority Date: 08/19/1991
• Status: Expired due to Term

• Current Assignee: Multi-Tech Systems Incorporated
• Original Assignee: Multi-Tech Systems Incorporated
• Inventors: Li, Ping
• Primary Examiner(s): Harrell, Robert B.
• Assistant Examiner(s): Philipp, Timothy L.
• Application Number:
  US07/746,875
• Time in Patent Office: 988 Days
• Field of Search: 370/94.1, 395/325, 395/500, 395/200, 375/8
• US Class Current: 709/237
• CPC Class Codes: H04L 67/06 specially adapted for file transfer, e.g. file transfer protocol [FTP]
• CPC Class Codes: H04L 69/24 Negotiation of communication capabilities
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A method for establishing a spoofing service for a high-level file transfer protocol from a modem. A modem spoofing initiation protocol (MSIP) word containing modem limitations is appended to the initial negotiation frame sent by the host to the receiver. If the receiving modem detects the MSIP word at the end of the negotiation frame, it compares its own limits with the received limits, takes the lower limit as the agreement, then appends the agreement word to the frame sent to acknowledge the negotiation frame. If the sending modem detects the agreement word, both modems use the agreed limits to examine the maximum block size and window size in the negotiation frame of the high-level file transfer protocol. If the block size and window size are within the agreed values, the spoofing service begins.

Claims

1. In a modem for transmitting data between a host computer and a receiving computer over a communication line, the host computer and receiving computer communicating through a high level data transfer protocol wherein data is sent in portions and the host computer waits for an acknowledgement from the receiving computer after each portion is sent before sending another portion, the high level protocol further including the host computer and receiving computer engaging in a negotiation prior to a data transfer operation, the negotiation including the transfer of an initial negotiation frame to the receiving computer, the receiving computer responding to the initial negotiation frame with an initial acknowledgement frame, and the host and receiving computers thereafter exchanging one or more frames of information regarding respective data transfer capabilities, the modem having a spoofing service wherein the spoofing service provides that when the modem receives a portion of data from a host computer over the communication line to be supplied to a receiving computer, the modem automatically provides a high level protocol acknowledgement to the host computer even though the receiving computer has not actually received all of the portion of data yet from the modem, the spoofing service also suppressing the high level protocol acknowledgement sent by the receiving computer to prevent the host computer from receiving two acknowledgements for the same data portion, a spoofing service initiation system, comprising:

first means for detecting an initial negotiation frame received by the modem from a host computer to be applied to the communication line, and in response to the detection of the initial negotiation frame;

(a) appending a modem spoofing initiation protocol (MSIP) word to the initial negotiation frame, the MSIP word signalling that the modem can support the spoofing service and containing information on data transfer modes supported by the modem for the spoofing service; and

(b) detecting an initial acknowledgement frame received from a communication line to be supplied to a host computer, and monitoring the detected initial acknowledgement frame for an agreement word, and, if the word is present

(i) determining a mutually supported data transfer mode from the agreement word, and

(ii) monitoring subsequent high level protocol negotiation data exchanged by the receiving computer and the host computer, the high level negotiation data specifying a high level data transfer protocol, and if the high level data transfer protocol is compatible with the mutually supported data transfer mode, establishing the spoofing service;

second means for detecting an initial negotiation frame received from the communication line to be supplied to a receiving computer, and monitoring a detected initial negotiation frame for the presence of an appended MSIP word, the second means including means responsive to the presence of an appended MSIP word and the detection of an initial acknowledgement frame sent by the receiving computer connected to the modem for

(a) appending an agreement word to the initial acknowledgement frame, the agreement word signalling that the modem can support the spoofing service and specifying a data transfer mode for the modem compatible with a data transfer mode specified in the MSIP word, to establish the mutually supported data transfer mode, and

(b) monitoring subsequent high level protocol negotiation data exchanged by the receiving computer and the host computer, the high level negotiation data specifying a high level data transfer protocol, and if the high level data transfer protocol is compatible with the mutually supported data transfer mode, establishing the spoofing service.

2. Apparatus according to claim 1 wherein the data transfer mode specified in the MSIP word specifies a window size and a block size for a data transfer operation.

3. Apparatus according to claim 2 wherein the high level data transfer protocol specifies a window size and a block size for a data transfer operation.

4. In a modem for transmitting data between a host computer and a receiving computer over a communication line, the host computer and receiving computer communicating through a high level data transfer protocol wherein data is sent in portions and the host computer waits for an acknowledgement from the receiving computer after each portion is sent before sending another portion, the high level protocol further including the host computer and receiving computer engaging in a two-way communication prior to a data transfer operation to determine the high level data transfer protocol to be used, the two-way communication including the transfer of one or more data frames between the host and the receiving computers, the modem having a spoofing service wherein the spoofing service provides that when the modem receives a portion of data from a host computer over the communication line to be supplied to a receiving computer, the modem automatically provides a high level protocol acknowledgement to the host computer even though the receiving computer has not actually received all of the portion of the data yet from the modem, the spoofing service also suppressing the high level protocol acknowledgement sent by the receiving computer to prevent the host computer from receiving two acknowledgements for the same data portion, a spoofing service initiation system, comprising:

first means for detecting one or more data frames received by the modem from a host computer to be applied to the communication line, and in response to the detection of the one or more data frames,

(a) appending a modem spoofing word to one or more of the data frames, the one or more data frames comprising part of a two-way communication in a high level protocol between the host computer and a receiving computer prior to a data transfer operation, the modem spoofing word signalling that the modem can support the spoofing service, and

(b) monitoring one or more of the data frames sent by a receiving computer back to the host computer during the two-way communication, the data frames monitored for the presence of an agreement word, and if the word is present establishing the spoofing service; and

second means for detecting one or more of the data frames received from the communication line to be supplied to a receiving computer during the two-way communication, and in response to the detection of the one or more data frames monitoring the one or more data frames for the presence of an appended modem spoofing word, and if the word is present appending an agreement word to one or more subsequent data frames sent by the receiving computer back to the host computer during the two-way communication, and establishing spoofing service, the agreement word signalling that the modem can support the spoofing service.

5. Apparatus according to claim 4 wherein the modem spoofing word further specifies data transfer capabilities of the modem.

6. Apparatus according to claim 5 further wherein the data transfer capabilities are specified as a window size and a block size for a data transfer operation.

7. Apparatus according to claim 6 wherein the high level data transfer protocol specifies a window size and a block size for a data transfer operation, and further including means for monitoring the exchange of data frames during the negotiation to determine the compatibility of the modem spoofing service with the high level protocol.

8. Apparatus according to claim 4 further including means for monitoring data exchanged by the host and receiving computers during the negotiation to determine if the spoofing service can be initiated.

9. In a modem for transmitting data between a host computer and a receiving computer over a communication line, the host computer and receiving computer communicating through a high level data transfer protocol wherein data is sent in portion and the host computer waits for an acknowledgement from the receiving computer after each portion is sent before sending another portion, the high level protocol further including the host computer and receiving computer engaging in a two-way communication prior to a data transfer operation to determine the high level data transfer protocol to be used, the two-way communication including the transfer of one or more data frames between the host and the receiving computers, the modem having a spoofing service wherein the spoofing service provides that when the modem receives a portion of data from a host computer over the communication line to be supplied to a receiving computer, the modem automatically provides a high level protocol acknowledgement to the host computer even though the receiving computer has not actually received all of the portion of data yet from the modem, the spoofing service also suppressing the high level protocol acknowledgement sent by the receiving computer to prevent the host computer from receiving two acknowledgements for the same data portion, a spoofing service initiation method, comprising the steps of:

the modem detecting one or more data frames received by the modem from a host computer to be applied to the communication line, and in response to the detection of the one or more data frames,

(a) appending a modem spoofing word to one or more of the data frames, the one or more data frames comprising part of a two-way communication in a high level protocol between the host computer and a receiving computer prior to a data transfer operation, the modem spoofing word signalling that the modem can support the spoofing service; and

(b) monitoring one or more of the data frames sent by a receiving computer back to the host computer during the two-way communication, the data frames monitored for the presence of an agreement word, and if the word is present establishing the spoofing service; and

the modem detecting one or more of the data frames received from the communication line to be supplied to a receiving computer during the two-way communication, and in response to the detection of the one or more data frames monitoring the one or more data frames for the presence of an appended modem spoofing word, and if the word is present appending an agreement word to one or more subsequent data frames sent by the receiving computer back to the host computer during the two-way communication, and establishing spoofing service, the agreement word signalling that the modem can support the spoofing service.

10. A method according to claim 9 wherein the modem spoofing word further specifies data transfer capabilities of the modem.

11. A method according to claim 10 further wherein the data transfer capabilities are specified as a window size and a block size for a data transfer operation.

12. A method according to claim 10 wherein the high level data transfer protocol specifies a window size and a block size for a data transfer operation, and further including means for monitoring the exchange of data frames during the negotiation to determine the compatibility of the modem spoofing service with the high level protocol.

13. A method according to claim 12 further including the step of monitoring data exchanged by the host and receiving computers during the negotiation to determine if the spoofing service can be initiated.