99 lines
6.6 KiB
HTML
99 lines
6.6 KiB
HTML
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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-us">
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<title>APPN virtual controllers and communications performance</title>
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<body>
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<a id="Top_Of_Page" name="Top_Of_Page"></a><!-- Java sync-link -->
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<script language = "Javascript" src = "../rzahg/synch.js" type="text/javascript"></script>
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<a name="rzahjper-appnvrtctlcon"></a>
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<h3 id="rzahjper-appnvrtctlcon">APPN virtual controllers and communications performance</h3>
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<p>An <span class="bold">APPN virtual controller</span> is a controller description
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that Advanced Peer-to-Peer Networking® (APPN) can
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use, and that high-performance routing (HPR) support uses. It can be used
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to attach and manage advanced program-to-program communications (APPC) device
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descriptions. This type of controller does not represent a connection to a
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remote system. On iSeries™, local applications that need to establish LU 6.2
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sessions to other locations in the APPN network require an APPC device description
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that specifies APPN(*YES). For simplicity, these devices are referred to
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as APPN devices.</p>
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<p>The Allow APPN virtual support (ALWVRTAPPN) parameter is on the Change
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Network Attributes (CHGNETA) command. If the ALWVRTAPPN parameter is *YES,
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any existing APPN devices that are attached to the real APPN controller description
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will not be allowed to vary on. Message CPDB157 will be issued. If migrating
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to this new APPN object model, you may want to delete any existing APPN devices
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because they will no longer be used. You may also want to delete the devices
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if you have no intention of resetting the ALWVRTAPPN parameter to *NO.</p>
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<p>APPN virtual controllers provide the following:</p>
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<ul>
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<li>Virtual controllers can reduce the number of device descriptions
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<p><img src="delta.gif" alt="Start of change" />Prior to supporting APPN virtual controllers, multiple APPN device descriptions
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can be created and used simultaneously to communicate between the same local
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location and remote location pair. This situation was possible because alternate
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paths exist through the network. The first hop out of the local system (that
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is represented by a controller description) can be different for the two paths.
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After a session is established, the same APPN device description is used for
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the life of that session. With APPN virtual controller support, you can accomplish
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all communications between the same local location and remote location pair
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using a single device description. This single device description can be used,
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even if multiple paths to that remote location exist in the network.<img src="deltaend.gif" alt="End of change" /></p></li>
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<li>Virtual controllers bypass 254 device limit
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<p>iSeries allows a
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maximum of 254 devices to attach to a controller description. In some environments,
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there may be a requirement to access more than 254 different locations (that
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are each represented by devices) through a single system. For example, an iSeries may attach to a System/390®, connected to hundreds of systems
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that the local iSeries would like to communicate with (through System/390). Without
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APPN virtual controller support, this communication requires the definition
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of parallel transmission groups (multiple controller descriptions) between
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the local system and System/390. Using multiple real controller
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descriptions can be costly in regards to both the line costs and managing
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multiple connections. With APPN virtual controller support, you use one real
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controller description, but attach more than 254 devices that are spread across
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more than one virtual controller.</p></li>
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<li>Error recovery minimized
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<p>APPN virtual controller descriptions do not
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associate with any communication lines or adjacent system. Thus, there are
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no <span class="italic">communication failures</span> to associate with these
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controller descriptions. This situation highlights some key points regarding
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error recovery:</p>
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<p>When APPN virtual controller descriptions are not used,
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device descriptions attach to APPN controller descriptions that represent
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connections to adjacent systems. When communication failures occur, applications
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that are affected by the session outages must be notified. The system also
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performs error recovery on the controller description and all of the attached
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device descriptions. In some large environments, device error recovery can
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take a lot of time.</p>
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<p>When APPN virtual controller descriptions are used,
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the APPN controller descriptions that represent connections to adjacent systems
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do not have device descriptions attached. When communication fails (for example,
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a line failure), the applications affected by the session outages are notified.
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The system recovers errors on the controller description. No error recovery
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is required on the device descriptions if each of the following are true:</p>
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<ul>
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<li>The device descriptions are attached to the APPN virtual controller description.</li>
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<li>The APPN virtual controller descriptions are not marked as inoperative.</li></ul><p class="indatacontent">Eliminating error recovery at the device level can help decrease the
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amount of time iSeries requires to recover errors after some communication
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failures.</p></li></ul>
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<p>For more information about getting optimal performance from your network,
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see the page <a href="rzahjpernetdesinsts.htm#rzahjper-netdesinsts">Designing an APPN and HPR network</a>.</p>
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<a id="Bot_Of_Page" name="Bot_Of_Page"></a>
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</body>
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</html>
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