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-Chapter 1. Introducing SNA Telecommunication Networks 1-:37
Tandem Configurations
Network A
Figure 1-10 presents a configuration of networks in tandem. The ACF/VTAM in PROC2 serves with NCPl as the gateway between networks A and B, and with NCP2 as the gateway between networks Band C. Note that the
ACF /VTAMs in PROCI and PROC3 do not have to be upgraded.
Figure 1-11 presents a configuration in which two networks are separated by a network without a gateway ACF /VT AM, that is, they are nonadjacent. In this illustration, networks A and C have more configuration isolation than if they were adjacent, since most of the information that must be exchanged when connecting networks only pertains to adjacent networks.
Tandem configurations can be used with networks that are geographical neighbors. For example, a series of networks for hospital associations in the northeastern, mid-Atlantic, and southeastern regions might use tandem interconnection. On the other hand, a nationwide network with the address constraints described earlier might be sectioned into a tandem configuration of eastern, midwestern, and western networks.
A tandem configuration requires more gateways than the configuration shown in Figure 12. Network maintenance and problem determination is less centralized and requires more coordination. Performance is not as good and tends to degrade further as the number of networks increases.
Network B Network C
Processor PROC1 Processor PROC2 Processor PROC3
NCP1 (Gateway ACF/NCP)
NLDM
Figure 1-10. An Example of Tandem Interconnected Networks (Adjacent)
NCP2 (Gateway ACF/NCP)
NLDM NCCF ACF/VTAM
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Network A
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Network B
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Figure 1 .. 11. An Example of Tandem Interconnected Networks (Nonadjacent)
Chapter 1. Introducing SNA Telecommunication Networks 1-39
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Chapter 1. Introducing SNA Telecommunication Networks 1-41
Chapter 2. Network Program Product Functions
This chapter is primarily for users migrating to ACF /VTAM Version 2 Release 2 and the equivalent releases of ACF/NCP, ACF/SSP, NCCF, andNLDM. New customers can also use it for more details on functions mentioned in Chapter 1.
The program products are described in the following order;
• ACF/VTAM and ACF/NCP together ACF/SSP
• NCCF NLDM ACF /VTAM and ACF /NCP Functions
This section contains general descriptions of A CF /VT AM and then ACF /NCP, followed by a description of the enhancements made to these program products since VTAM Level 2 and NCP LevelS.
Introduction to ACF/VTAM Functions
ACF /VTAM provides the interface between application programs in the host processor and other resources in the network. In order to do this, ACF /VTAM:
• Activates and deactivates resources in its domain, including application programs, ACF /NCPs and the devices they control, and devices to which A CF /VT AM is attached directly
Establishes, monitors, and terminates sessions between application programs and devices or other application programs, forwarding the session data to and from each session partner
• Keeps records on the configuration in its domain, sessions under its control, and network conditions
Receives commands from the ACF/VTAM operator to perform network services and keeps the operator informed about these services, as well as network conditions, with operator messages.
Basic functions relating to A CF /VT AM are described below under the categories:
Network structure Network flow control Network operation Network performance
Problem determination and network maintenance
Chapter 2. Network Program Product Functions 2-1
Network Structure
Session Flow
Network Operation
Network Performance
• Network recovery
• Network security
• Application programs.
ACF /VT AM controls resources directly (through direct attachment) or indirectly (through an ACF /NCP). It owns resources that it has activated and you have defined it to own. It sends and receives session data over defined paths related to the lines and ACF /NCPs of the network configuration.
A CF /VT AM uses pacing to control the flow of data. It specifies the number of path information units (PIUs) that can be sent before a response from the receiver must be returned. A CF /VT AM also uses virtual route pacing, which limits the amount of data that can be sent over a route at anyone time.
The ACF /VTAM operator controls ACF /VT AM through specific commands:
• Start and halt commands for starting and stopping ACF /VTAM
• DISPLAY commands for obtaining the status of network resources
• V AR Y commands for activating and deactivating resources
MODIFY commands for changing the status of operations such as traces and the performance of utility functions.
The programmed operator interface (POI) enables application programs to perform ACF /VTAM operator functions. NCCF is an IBM program product that uses this interface.
ACF /VT AM buffers can he specified according to the needs of your installation.
You can also specify the maximum size of path information units (PIUs) that are sent and received. You can specify ways for ACF /VTAM to save processor cycles.
Problem Determination and Network Maintenance
Network Recovery
ACF /VT AM provides the following functions:
• A dump of ACF /NCP contents
• Traces of ACF/VTAM buffer use, line use, and I/O events
• Error recordings provided by the system.
ACF /VTAM can notify its operator of failing resources and sessions and can reactivate them. In response to operator commands it can take over an
ACF /NCP and its resources from a failing host. It can also reload and reactivate
Network Security
Application Programs
an ACF /NCP and reactivate its resources. The ACF /NCP's configuration can be reactivated to its status just before the failure or to its status when the ACF /NCP was originally activated.
The way you define an application program to ACF /VT AM can limit access to other application programs. Access can also be controlled through the
ACF /VTAM authorization exit routine or session management exit routine.
You can also use the Encrypt/Decrypt Feature of ACF /VT AM with either the Programmed Cryptographic Facility program product or the Cryptographic Unit Support program product to encipher and decipher data sent between application programs and devices and to prevent data from appearing in traces or dumps.
An application program obtains telecommunication services from A CF /VT AM by using ACF /VTAM macro instructions. It receives notification from
ACF/VTAM of events such as logon requests, completion of I/O requests, etc., either directly or through exits for which routines can be written.
Application programs can be coded to acquire logical units (LUs) as session partners and to pass them on to other application programs. You can also define LUs to be logged on by ACF /VTAM to an application program automatically when both have been activated.