Entire Net-Work channel-to-channel line drivers provide high speed, high volume data transfer capabilities using:

• channel-to-channel adapters (CTCAs);

• IBM 3088 Multisystem Channel Communication Units;

• suitably configured ESCON or FICON channels; or

• compatible products from other vendors.

The devices (or device address exposures) used by Entire Net-Work are dedicated and cannot be shared with other users, such as VTAM, JES, or GRS. However, any such CTCA or FCTC (described later) users can run in parallel with Entire Net-Work as long as each is using separate device addresses. It is also possible to use a CTCA with different products at different times.

In practice, the number of channel-to-channel links that Entire Net-Work can establish is limited only by storage constraints or by the capacity of z/OS systems to attach peripheral devices.

The Entire Net-Work CTCA line driver observes its own proprietary channel programming protocol that is not compatible with other software using CTCAs. It is compatible with earlier supported versions of the Entire Net-Work channel-to-channel line driver. As of version 6.3 SP1, FCTC channels are not compatible with previous versions.

In the CTCA line driver, channel-to-channel adapters are driven by attention interrupts. Entire Net-Work's CTCA line driver includes a line driver module and an attention routine module. Both modules are unloaded from the installation media into your Entire Net-Work load library.

The Entire Net-Work fast channel-to-channel line driver (FCTC) is a newer version of the CTCA line driver. In the FCTC line driver, changes have been made in the channel program logic flow to improve performance. Once connection is established, the channel designated as the READ channel will issue READ CCWs in anticipation of WRITEs from the other side. This reduces disconnect time on the WRITE side of the channel, and greatly reduces the number of interrupts, thus improving performance. When installing and using the FCTC line driver, you must pay attention to differences in the parameters and parameter settings used by the CTCA line driver.

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FCTC LINKS Operating in Impaired Mode

FCTC LINKs can function even if only one unit is active; this is referred to as operating in impaired mode. In this case, the active unit reverts to bidirectional communication similar to a CTCA link.

• If one unit is unavailable when the link is connected, the connection will succeed and the link will function in impaired mode. Note however that both the UNITREAD and UNITWRT parameters must always be specified on the FCTC LINK statement.

• If a unit fails while the link is active, for example due to a hardware error, the other unit reverts to bidirectional communication, allowing the link to continue to function in impaired mode. Normally this happens seamlessly, and the message NETC126W is issued. However, in rare cases, depending on the state of the channels and the messages that were in progress at the time of the failure, the link must be disconnected and reconnected in order to properly clean up. The reconnect can be done by operator command or automatically via the RESTART parameter. The link will then function impaired until the problem can be resolved.

If a link is active in impaired mode, after the failed unit is repaired, the link must be disconnected and reconnected in order for both units to become active again. Note that if the unit was previously offline, the connect may need to be initiated on the side that was offline, in order for the unit to be properly allocated.