For PU type 1: |
.-MAXDATA--=--261-------------.
>>-+-----------------------------+-----------------------------><
'-MAXDATA--=--number_of_bytes-'
|
statements: |
GROUP, PU |
dependency: |
see notes |
range: |
20-65535 |
For PU type 2: |
.-MAXDATA--=--265-------------.
>>-+-----------------------------+-----------------------------><
'-MAXDATA--=--number_of_bytes-'
|
statements: |
PU |
dependency: |
see notes |
range: |
20-65535 |
Specifies the maximum number of bytes that the physical
unit can receive in one PIU or PIU segment, including the transmission
header (TH) and the request or response header (RH). To determine
the maximum PIU (or PIU segment) size that the physical unit can receive,
consult the component publications for the specific type of SDLC station
represented by this PU definition statement.
The maximum amount of user data that VTAM® sends to the physical unit in one PIU is:
- MAXDATA minus 2 bytes (for a PU type 1)
- MAXDATA minus 6 bytes (for a PU type 2)
Note: The RU part of the PIU contains the user data. When VTAM segments the PIU, the middle
and last PIUs will contain three more bytes of user data in the RU
because there is no RH field. The value for the PIU varies with the
device; for example, the 3276 requires MAXDATA=262.
You must specify a MAXDATA value for a type 4 or 5 physical
unit; there is no default for these physical units.
Note: - In a local area network, the value for the MAXDATA operand on
the PU definition statement must be less than or equal to the value
for the MAXDATA operand on the PORT definition statement for the LAN
major node to which the switched physical unit is connected.
- NCP V4R3 changed the MAXDATA calculation for a type 1 physical
unit. See NCP, SSP, and EP Resource Definition Reference for
information about calculating a MAXDATA value for physical units on
non-switched links.
- MAXDATA is ignored for type 2.1 nodes attached through an NCP,
an IBM® 3172 Nways Interconnect Controller,
or through an IP network for Enterprise Extender. The type 2.1 node
supplies the actual value used when the connection is established.