Cisco 11.0 BT Instrukcja Użytkownika Pobierz pdf (Strona 6)

2-6 TN3270 Design and Implementation Guide

For static LUs, the ﬁrst phase is LU activation. The LU requested must be deﬁned at the host under the PU. The

activation process is as follows:

1. The LU is activated by the host.

2. The client issues a connect with server request. If the device is listedin the table of LU names and is not being

used, then the router sends a positive response. If the device is being used, then the router sends an “in use”

response.

3. If the client connection is successful, the router sends a NOTIFY(ENABLED) request to the host.

Network Management Vector Transports (NMVTs) are also sent to any running network management

application, which allows the host to track the IP address of any device connecting to each LU.

For dynamic LUs, the ﬁrst phase is session negotiation. This phase includes steps necessary to initiate the

client-to-CIP/CPA connection and to select the LU:

1. TheTN3270 client requestsa pooledLU session.The client’s request includesthe terminaltype. The TN3270

client must be conﬁgured with a destination IP address, TCP port, and terminal type for a pooled LU session

to occur.

2. The TN3270 Server forms an EBCDIC string based on the model typeand number requested by the TN3270

client.The server usesthis stringas a ﬁeldin theREPLYproduct-set identiﬁcation (PSID)NMVT ﬁeldit sends

to the host.

3. The TN3270 Server allocates a LOCADDR from the next available LU in the LU pool for the chosen IP

address. Subject to conﬁguration control, all LUs that the host does not immediately activate are

automatically placed in the pools. The LOCADDR is sent in the REPLY-PSID(power-on) NMVT. When

VTAM receives the NMVT, it uses the EBCDIC model type and number string to look up an LU template

under the LUGROUP. An activate logical unit (ACTLU) is sent and a terminal session is established.

The second phase is session bind and data transfer. This phase includes the steps of the TN3270 host-to-client

SNA session bind and data transfer:

1. After the ACTLU is provided by the host, the information is transferred between the system services control

point (SSCP) and the LU. The CIP manages the necessary protocol conversions. At this stage, the type of

TN3270 clientis important. If youare using a TN3270 client, SSCP mustbe conﬁgured to communicatewith

the LUusing the TN3270 data stream (using hostparameters USSTAB and SSCPFM).If TN3270E clients are

usedand theyrequestthe BIND-IMAGEfunction (normally LU1 andLU3 printers),they mustcommunicate

withSSCP usingtheSNA characterstring (SCS).In somecases,the clientLU bypassesSSCP completely(using

the host variable LOGAPPL) and connects directly to a host application.

2. When the LU data is received by the SSCP, it requests a bind with the LU, which is locally acknowledged by

the CIP/CPA.

3. The LU-to-LU data is transferred.

The third phase is session termination. Sessions are terminated in the following conditions:

• The client logs off the LU-to-LU session, causing the server to send an UNBIND message followed by a

NOTIFY (UNAVAIL) message to the host.

• The client disconnects at the TCP layer and the LU is conﬁgured to disconnect on UNBIND. The TCP session

is disconnected and the host is sent a NOTIFY (UNAVAIL) message.

• The client is idle too long or will not respond to a DO TIMING MARK message. The server sends UNBIND

message to the host and then sends a NOTIFY (UNAVAIL) message.

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Cisco 11.0 BT Instrukcja Użytkownika Strona 6