Mapping SNA session flow control to TCP flow control
AssigneeCisco Technology, Inc.
InventorsBarry K. Chan, Michael Boe
Life of this patent
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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.
Claims8
A computer communications system comprising:
- A) an SNA link
- B) an SNA node, coupled to the SNA link, for transmitting information and SNA pacing requests into an SNA connection that the SNA node maintains over the SNA link;
- C) a TCP/IP link
- D) a TCP/IP node for receiving information from, and transmitting messages that acknowledge transmitted bytes and specify a TCP window size into, a TCP/IP connection that the TCP/IP connection maintains over the TCP/IP link;
- and
- E) a communications gateway including circuitry for maintaining the SNA and TCP/IP connections with the SNA and TCP/IP nodes, respectively, and:
- i) receiving from the SNA connection the information transmitted by the SNA node;
- ii) forwarding to the TCP/IP node through the TCP/IP connection at least some of the information thereby received;
- iii) monitoring the TCP connection for acknowledgement messages transmitted by the TCP/IP node;
- iv) monitoring the SNA connection for the pacing requests;
- and
- v) transmitting a pacing response to the SNA node in response to a pacing request therefrom only if forwarding the previously received information not yet forwarded would not result in a number of unacknowledged bytes transmitted into the TCP connection that exceeds the specified window size.
A communications method comprising:
- A) transmitting information and SNA pacing requests from an SNA node into an SNA connection maintained by the SNA node;
- B) receiving the information and SNA pacing requests by way of the SNA connection at a communications gateway,
- C) forwarding at least some of the received information by employing the communications gateway to transmit bytes over a TCP connection maintained by the communications gateway;
- D) receiving the forwarded information at a TCP/IP node that maintains the TCP connection with the communications gateway
- E) employing the TCP/IP node to transmit to the communications gateway over the TCP connection acknowledgement messages that acknowledge transmitted bytes and specify a TCP window size;
- F) employing the communications gateway to monitor the TCP connection for the acknowledgement messages;
- G) employing the communications gateway to monitor the SNA connection for request messages that include pacing requests;
- and
- H) employing the communications gateway to transmit a pacing response over the SNA connection in response to reception of a pacing request from the SNA connection 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.
Dependencies are inferred from the claim text.