Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1: Base Functions, Connectivity, and Routing

2 Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1 - Base Functions, Connectivity, and Routing

1.1 Overview

CS for z/OS IP provides the industry-standard TCP/IP protocol suite, allowing z/OS

environments to share data and computing resources with other TCP/IP computing

environments, when authorized. CS for z/OS IP enables anyone in a non-z/OS TCP/IP

environment to access resources in the z/OS environment and perform tasks and functions

provided by the TCP/IP protocol suite. It provides the computer platform with the freedom

desired by organizations to distribute workload to environments best suited to their needs. CS

for z/OS IP, therefore, adds the z/OS environment to the list of environments in which an

organization may share data and computer processing resources in a TCP/IP network.

CS for z/OS IP supports two environments:

򐂰 It provides a native MVS (z/OS) environment in which users may exploit the TCP/IP

protocols in the z/OS applications environment. This includes batch jobs, started tasks,

TSO, CICS® applications, and IMS™ applications.

򐂰 It also provides native TCP/IP support in the UNIX® Systems Services environment in

which users may create and use applications that conform to the POSIX or XPG4

standard (a UNIX specification). The UNIX environment and services may also be

exploited from the z/OS environment and vice versa.

1.1.1 Basic concepts

The TCP/IP address space is where the TCP/IP protocol suite is implemented for CS for z/OS

IP. The TCP/IP address space is commonly referred to as a

stack. In earlier versions Open

Edition (OE) TCP/IP could run either as a stand-alone or in parallel with the TCP/IP for MVS.

This was often necessary since the OE stack did not support all the functions and network

connections available with TCP/IP for MVS. CS for z/OS IP now has a highly efficient direct

communication between the UNIX System Services address space (OMVS) and a TCP/IP

stack that was integrated in UNIX System Services. This communication path includes the

UNIX System Services Physical File System (PFS) component for AF_INET and AF_INET6

(Addressing Family-Internet) sockets communication. The z/OS Communications Server has

the following features:

򐂰 A process model that provides a full multiprocessing capability. It includes full duplex data

paths of reduced lengths.

򐂰 An I/O process model that allows VTAM to provide the I/O device drivers. MultiPath

Channel (MPC) Data Link Control (DLC) is shared between VTAM and TCP/IP. It

executes multiple dispatchable units of work and is tightly integrated with the common

storage management support.

򐂰 A storage management model handles expansion and contraction of storage resources as

well as requests of varying sizes and types of buffers. Common Storage Management

(CSM) manages communication between the Sockets PFS through the transport provider

and network protocols to the network interface layer of CS for z/OS IP stack. The data that

is placed in the buffers can be accessed by any function all the way down to the protocol

stack.

In contrast to earlier versions of the product, CS for z/OS IP is integrated with OE and exploits

UNIX Systems Services. CS for z/OS IP requires some UNIX Systems Services

configuration. CS for z/OS IP runs as a single stack that serves both the traditional MVS

(z/OS) environment and the z/OS UNIX (UNIX Systems Services) environment.

CS for z/OS IP offers two variants of the UNIX shell environment:

򐂰 The OMVS shell, which is much like a native UNIX environment