Hardware considerations for NJE

BSC lines, channel-to-channel (CTC) adapters, SNA or TCP/IP network lines connect JES2 systems participating in an NJE environment.

BSC lines attached to IBM® 3704, 3705, or 3725 Communication Controllers operate in emulation mode. Generate NJE 3704s and 3705s to emulate a 2701 communication controller (see both IBM 3704 and 3705 Communications Controllers and IBM 3725 Model 1 Communications Controller).

During system installation, use hardware configuration definition (HCD) to define the attached NJE lines as follows:

On the ‘Primary Task Selection’ panel, select ‘1. Define, modify, or view configuration’. On the resulting panel, select ‘5. I/O devices’
On the ‘Add Device’ panel, specify the device type as BSC1.
On the ‘Define Parameter / Feature’ panel, specify the TCU parameter as 2701

See z/OS HCD User's Guide for a complete list of the steps involved in defining a device.

Channel-to-channel adapters supported as high-speed communication lines for NJE must be on block multiplexers because they can “lock up” selector channels. Use the LINE(nnnn) JES2 initialization statement to define these adapters. (See z/OS JES2 Initialization and Tuning Reference for details concerning the LINE(nnnn) parameters.) If you do not code these specifications and I/O errors occur when establishing the network, you might find it very difficult to analyze those errors. Connections using internal or external CTC devices only operate in 360 compatibility mode.

Use the following steps to add the control units and CTC:

Add the control units:
- Follow the steps as described in z/OS HCD User's Guide.
- On the ‘Add Control Unit’ panel (accessed from the ‘Select Processor / Control Unit’ panel), specify the ‘I/O concurrency level’ as 2. (This corresponds to SHARED=NO in I/O Configuration Program (IOCP) ).
Add the CTC:
- Use HCD and follow the steps as described in z/OS HCD User's Guide.
  On the ‘Define Parameter / Feature’ panel, specify Yes or No, as applicable, for the LOCANY, DYNAMIC and OFFLINE keywords.
- Add UNIT=unit-addr to the JES2 LINE(nnnn) initialization statement.

Note that multiple systems through multiple CTCs on the same channel path could cause a deadlock condition.

You can also use CTC adapters to support an SNA NJE environment; however, ACF/VTAM controls these CTC adapters. Consult z/OS Communications Server: SNA Resource Definition Reference for VTAM-CTC requirements.

Channel-to-channel (CTC) connections are identical to BSC communications except CTC connections do not use EP or PEP. CTC connections are best suited for connections to nodes within the same computer facility. NJE protocols support an ESCON* Basic Mode CTC (defined to the hardware configuration dialog as BCTC) and a 3088 CTC, but do not support an ESCON® CTC (defined to the hardware configuration dialog as SCTC).

TCP/IP NJE sessions take advantage of TCP/IP's hardware independent layered stack to establish connections over a number of existing hardware protocols such as Ethernet and token ring. To use TCP/IP sessions, z/OS® Communications Server TCP/IP requires z/OS UNIX System Services and ACF/VTAM to be configured and active. If there is support on the node connected, TCP/IP NJE sessions support IPv6 and TLS/SSL.

SNA NJE application-to-application sessions using SDLC lines require that the Advanced Communication Function (ACF) for the Network Control Program/VS (NCP/VS) or the partitioned emulator program (PEP) resides in the IBM 3705. Also, the processors participating in these sessions must have ACF for VTAM® and the Multi-System Networking Facility VTAM installed.

Many parameters affect the performance of BSC NJE traffic on a channel-to-channel adapter. At times, increasing or decreasing buffer sizes can result in a decrease of performance because of varying channel loads, hardware limitations, and the speed of the CTC adapter itself. Experienced system programmers (with their system engineers) should tune JES2 parameters. While adjusting the parameters, carefully consider the effects of the following on performance:

Teleprocessing (TP) buffer sizes
The number of buffers per spool page
The loads on the channel
Other demands on the BSC processes (such as RJE devices).