IBM z/OS - Manual (Page 69)

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REXX Functions
z/OS 1.4 extends the REXX language on z/OS when used
in a UNIX System Services zSeries REXX environment.
It includes functions for standard REXX I/O and to easily
access some common fi le services and environments vari-
ables.
Communication Services
z/OS Version 1 Release 6 base elements
z/OS Communications Server (Multiprotocol/HPR Services, TCP/IP
Services, SNA/APPN Services)
OSA Support Facility
z/OS Version 1 Release 6 optional no charge features
z/OS Communications Server Security Level 3
The z/OS base includes z/OS Communication Server, which
enables: world class TCP/IP and SNA networking support,
including enterprise class dependability; performance and
scalability; highly secure connectivity; support for multiple
protocols; and effi cient use of networking assets.
z/OS can provide near continuous availability for TCP/IP
applications and their users with two key features in z/OS:
Sysplex Distributor and Dynamic VIPA.
Dynamic Virtual IP Address Takeover
VIPA represents an IP address that is not tied to a specifi c
hardware adapter address. The benefi t can be that if an
adapter fails, the IP protocol can fi nd an alternate path to
the same software, be it the TCP/IP services on a zSeries
server or an application.
In case of a failure of the primary IP stack, VIPA Takeover
introduced in OS/390 2.8 can support movement to a
backup IP stack on a different server in a Parallel Sysplex
cluster. Dynamic VIPA Takeover can enhance the initial 2.8
functions, providing VIPA takeback support. This can allow
the movement of workload back from the alternate to the
primary IP stack.
With Sysplex-Wide Security Associations (SWSA) in z/OS
1.4, IPSec protected workloads are expected to now
realize all the benefi ts derived from workload balancing,
such as optimal routing of new work to the target system
and server application based on QoS and WLM advice,
increased availability by routing around failed components
and increased fl exibility in adding additional workload in a
nondisruptive manner.
Sysplex Distributor
Introduced in OS/390 2.10, Sysplex Distributor is a soft-
ware-only means of distributing IP workload across a
Parallel Sysplex cluster. Client connections appear to be
connected to a single IP address, yet the connections are
routed to z/OS images on servers on different zSeries 800/
900 or S/390 servers. In addition to load balancing, Sys-
plex Distributor simplifi es the task of moving applications
within a Parallel Sysplex environment.
In z/OS we have taken the functions provided by the
Cisco MNLB Workload Agent and Systems Manager, and
integrated them into Enhanced Sysplex Distributor. This
can eliminate the need for separate Cisco LocalDirector
machines in the network and the need for MNLB work-
load agents to be run on the zSeries servers. It can also
improve performance, while allowing the Sysplex Distribu-
tor to decide, based on priority supplied by WLM, the
Service Policy Agent and the TCP/IP stack status, on the
application instance the packet is sent to.