USE OF THE FICON ESTABLISH LOGICAL PATH FUNCTION TO INITIALIZE OPERATING FICON PARAMETERS
Original Publication Date: 2002-Mar-21
Included in the Prior Art Database: 2003-Jun-19
This disclosure describes a method for a FICON (FC-SB-2) channel to discover the operating parameters which a control unit supports, and to set the mode of operation to use those parameters for all communication between the channel and that control unit. A method of discovering operating parameters is needed because initial releases of FICON used a default set of operating parameters. As enhanced modes of operation developed and were supported by control units and channels, a channel needed the ability to discover the set of parameters supported by a given control unit so that it could use the enhanced parameters when communicating with that control unit. Without this capability, there would be no mechanism to accommodate newly developed functions into the FICON definition without causing incompatibilities with existing products or forcing design changes. In order to discover the set of operating parameters, this scheme expands the usage of the FC-SB-2 Establish Logical Path (ELP) function to (a) discover the set of enhanced operating parameters common to a channel and a control unit, and (b) set the mode of operation to use those features. To accomplish this, a "supported optional feature vector" is included in the ELP request. Each bit of this vector corresponds to an optional feature. The bit for the optional feature is set to one if the optional feature is supported; otherwise the bit is set to zero. Examples of optional features which may be supported are: increased IU size (8K vs.16K vs. 32K), variable link timeout values (500 microseconds vs. 1 millisec vs. 3 millisec), etc. When a control unit receives the ELP request, it compares those optional features to its own set of supported optional features. Those optional features which both the control unit and the channel support represent the common set of optional features to be used for all future communication between that channel and that control unit. The control unit then returns the Logical Path Established (LPE) response containing an optional feature vector. The bit corresponding to an optional feature is set to a one if both the channel and the control unit support that feature; otherwise the bit is set to zero. This vector represents the set of optional features to be used in all future communication between that channel and that control unit until a reinitialization takes place. In order to allow a channel to maintain only one set of optional features for each control unit with which it communicates, the channel always indicates the same set of supported optional features in all ELP requests which it sends to a particular control unit. Likewise, if a control unit recognizes that the channel has attempted to change the set of operational features used between the channel and the control unit, the control unit returns a Logical Path Not Established response and does not establish the logical path.