Packet Exchange Protocol (PXP) Configuration

The Packet Exchange Protocol (PXP) Configuration screen (#93) in Figure 4-5 “Packet Exchange Protocol (PXP) Configuration Screen” is displayed when you press the [Go To PXP] function key at the General Protocol Configuration screen (Figure 4-4 “General Protocol Configuration Screen”). It is also displayed when you type the path name:

@NETXPORT.GPROT.PXP

in the command window of any screen and press the [Enter] key.

Figure 4-5 Packet Exchange Protocol (PXP) Configuration Screen

This screen contains the information necessary to configure packet exchange protocol (PXP) for the node. The information configured falls into two categories:

Reliability (checksum field).
Performance parameters (retransmission fields).

Press the [Save Data] function key to transfer the data displayed on the screen to the configuration file you are creating or modifying. Verify that the data record has been created by checking that the Data flag is set to Y.

Fields

Checksum enabled (Y/N)

Checksumming is a method of error checking. Enter a Y (yes) to enable checksumming for all sockets for this protocol. Enter an N (no) to allow individual sockets to choose checksumming for themselves.

PXP checksumming causes significant overhead, and is not normally needed for this protocol. Also, error checking is provided for at the link level. For these reasons, HP recommends the default value (N) for this field unless communication to a non-HP machine is desired.

Default value: N

Retransmission interval (secs)

The time in seconds to wait for a reply from a remote node before retransmitting a request. In general, the value to configure should reflect the load on the local system, the remote system, and the networks through which the request and the reply must travel. If the value is set too low, needless retransmissions may occur, or IPCLOOKUP calls may fail. If the value is set too high, an unnecessarily long delay will occur when a packet is lost, and a retransmission will be necessary. Frequent log messages indicating that retransmissions are taking place or that requests are failing indicate that the value needs to be increased.

Default value: 10

Range: 1-600

Maximum retransmissions per request

This is the number of times that PXP will retransmit a request when a reply has not been received within the retransmission interval (explained above).

As in the discussion of retransmission interval above, this field is a tuning parameter. The two values work together to determine the maximum time that a PXP user will wait for a reply. This maximum reply time is calculated as follows:

RTXinterval + (RTXinterval * MAXRTX)

where RTXinterval is the configured retransmission interval and MAXRTX is the configured maximum retransmissions per packet. Note that excessive values would cause unacceptably long delays before IPCLookup would fail under normal conditions such as the remote node failing.

Default value: 4

Range: 1-100

Packet Exchange Protocol (PXP) Configuration

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