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TN3270 Server Implementation 2-5

Figure 2-2 Allocation PUs

The TN3270 Server can support conﬁgurations where a group of PUs have the same IP listening address, each

PU has its own separate listening address, or a combination of the two. Likewise, when deﬁning a PU, you can

deﬁne static LUs, dynamic LUs, or a combination of both.

Defining LUs

TN3270 clients need only an IP address and an optional LU name or type to connect to the TN3270 Server. The

server then maps requested sessions with actual LUs available on the hosts.

Each PU can have up to 255 LUs deﬁned. With historical SNA networks, an LU was a physical device attached

to a remote communications controller, such as an IBM 3274. Each port on these devices was a local address

known as a LOCADDR. When a LOCADDR was deﬁned, each LU within a PU was statically deﬁned to match

the static hardware. Today, with the virtual allocation of LOCADDRs, either static or dynamic LUs can be

established.

The TN3270 Server supports static and dynamic LUs.

• Static LUs are deﬁned individually within VTAM and are known by the client. Static LUs require a speciﬁc LU/

PU name to be supplied. Static LUs are typically printers or secure terminals.

• Dynamic LUs use the DDDLU feature of VTAM. These LUs are given to the TN3270 client without the client

knowing the PU or LU name of the session deﬁned in VTAM. If the PU allows dynamic LUs, any LOCADDR

not deﬁned as a static LU, within a PU deﬁnition, can be used as a dynamic LU.

When a standard TN3270 client establishes a connection, there is no mechanism for requesting an LU by name.

In this case, you must use dynamic LU pools or LU nailing. Because TN3270E supportsrequesting LUs by name,

a TN3270E client can use either dynamic or static LUs.

In most environments, it is more advantageous for TN3270 clients to specify a dynamic LU rather than a static

LU. For static LUs, the PU on the TN3270 Server allocates the required memory when the mainframe activates

the LU. For dynamic LUs, the memory is not allocated until the LU is requested. Therefore, memory on the

TN3270 Server is not allocated unnecessarily.

Activation of LUs

The LU activation process differs depending on whether the client is using a static or a dynamic LU.

172.26.56.1

172.26.56.17

IP Listening Point

CIP

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Cisco 11.0 BT Manual de usuario Pagina 5