Mapping SNA session flow control to TCP flow control

• US 6,049,833 A
• Filed: 08/29/1997
• Issued: 04/11/2000
• Est. Priority Date: 08/29/1997
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Boe, Michael, Chan, Barry K.
• Primary Examiner(s): Dinh, Dung C.
• Assistant Examiner(s): SALAD, ABDULLAHI ELMI
• Application Number:
  US08/920,392
• Time in Patent Office: 956 Days
• Field of Search: 709/246, 709/236, 709/237, 709/200, 709/202, 709/230, 709/231, 709/233, 395/200.3
• US Class Current: 709/237
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/19 at layers above the network layer network arrangements for networked applications for scheduling or organising the servicing of application requests H04L67/60
• CPC Class Codes: H04L 47/193 at the transport layer, e.g. TCP related
• CPC Class Codes: H04L 47/27 Evaluation or update of window size, e.g. using information derived from acknowledged [ACK] packets

Abstract

A TN3270 server (26) that forwards a 3270 data stream from a Systems Network Architecture ("SNA") connection (28) to a Transmission Control Protocol ("TCP") connection (24) monitors the TCP connection for segments that acknowledge thereby-transmitted bytes. It also keeps track of the unacknowledged-byte window sizes specified by received TCP-connection segments. It responds with a pacing response to a pacing-request-containing SNA message only when forwarding of previously received information from the SNA can be completed without resulting in a number of unacknowledged bytes that exceeds the specified window size.

Claims

1. For transferring information between a Transmission Control Protocol connection and a Systems Network Architecture connection, a method comprising the steps of:

A) from the SNA connection, receiving information to be forwarded over the TCP connection;

B) forwarding at least some of the received information by transmitting bytes over the TCP connection;

C) monitoring the TCP connection for acknowledgment messages that acknowledge transmitted bytes and specify a TCP window size;

D) monitoring the SNA connection for request messages that include pacing requests; and

E) in response to reception of a pacing request from the SNA connection, transmitting over the SNA connection a pacing response only if forwarding the previously received information would not result in a number of unacknowledged bytes transmitted into the TCP connection that exceeds the specified window size.

2. For transferring information between a Transmission Control Protocol connection and a Systems Network Architecture connection, a communications gateway comprising circuitry for:

A) from the SNA connection, receiving information to be forwarded over the TCP connection;

B) forwarding at least some of the received information by transmitting bytes over the TCP connection;

C) monitoring the TCP connection for acknowledgment messages that acknowledge transmitted bytes and specify a TCP window size;

D) monitoring the SNA connection for request messages that include pacing requests; and

E) in response to reception of a pacing request from the SNA connection, transmitting over the SNA connection a pacing response only if forwarding the previously received information would not result in a number of unacknowledged bytes transmitted into the TCP connection that exceeds the specified window size.

3. For transferring information between a Transmission Control Protocol connection and a Systems Network Architecture connection, a communications gateway comprising:

A) means for receiving from the SNA connection, information to be forwarded over the TCP connection;

B) means for forwarding at least some of the received information by transmitting bytes over the TCP connection;

C) means for monitoring the TCP connection for acknowledgement messages that acknowledge transmitted bytes and specify a TCP window size;

D) means for monitoring the SNA connection for request messages that include pacing requests; and

E) means for transmitting over the SNA connection in response to reception of a pacing request from the SNA connection, a pacing response only if forwarding the previously received information would not result in a number of unacknowledged bytes transmitted into the TCP connection that exceeds the specific window size.