General TCP/IP Problems

There are many causes of general TCP/IP problems.

This table lists TCP/IP problems and factors to consider:

Problem	Factors to Consider
Host Issues	Inadequate memory Slow disk speed/contention Slow channel speed/contention Excessive workload Inadequate processors/slow processor speed Inefficient performance groups and dispatch priorities Resource competition among applications on same system Resource competition among LPARs
Network issues	At the link level, look for: Link errors Hardware or interface errors Latency problems Collisions At the IP layer, look for: Discarded packets Reassembly failures Whether the DoNotFragment Bit is set TOS (TCP/IP Type of Service) such as Telnet with low delay (interactive priorities overriding batch transmissions) Small MTU/MSS (Maximum Transmission Unit/Maximum Segment Size) Note: If the MTU is too small, inefficiency results whereas if it is too large, datagram fragmentation may result.
Network issues (cont'd)	At the TCP layer, look for: Segments retransmitted Connections reset Frequency of ACKs Window size too small In the TCP/IP stack, look for: The maintenance level of the two TCP stacks involved The use of PORT and 1364 TCP CDSTC NODELAYACKS which may delay ACKS The values of TCPSENDBFRSIZE and TCPRCVBFRSIZE in the TCP/IP PROFILE data set Note: These values affect all applications using the TCP/IP protocol whereas the V2.BUFSIZE initialization parameter (see below) affects the operation of the IBM® Connect:Direct® application only. Whether the value set for PATHMTUDISCOVERY is an MTU size of 8992 (the default) In the IBM Connect:Direct global initialization parameters file, look at: V2.BUFSIZE = (maximum transmission buffer size, TCP/IP send/receive buffer size)–The default is V2.BUFSIZE=(32K,128K). Adjust if needed based on the bandwidth and speed of your communications lines. DEBUG–Make sure this setting is 00000000 so that internal traces are turned off. TCP.API.TIMER = 00:00:00 \| hh:mm:ss–To reduce the number of hung sessions, specify this keyword. Set this value to at least 20 minutes and specify TIMEOUT=YES on IUI signon panels for individual users. Session waits before timing out and exiting.

Problem

Factors to Consider

Host Issues

Inadequate memory
Slow disk speed/contention
Slow channel speed/contention
Excessive workload
Inadequate processors/slow processor speed
Inefficient performance groups and dispatch priorities
Resource competition among applications on same system
Resource competition among LPARs

Network issues

At the link level, look for:

Link errors
Hardware or interface errors
Latency problems
Collisions

At the IP layer, look for:

Discarded packets
Reassembly failures
Whether the DoNotFragment Bit is set
TOS (TCP/IP Type of Service) such as Telnet with low delay (interactive priorities overriding batch transmissions)
Small MTU/MSS (Maximum Transmission Unit/Maximum Segment Size)
Note: If the MTU is too small, inefficiency results whereas if it is too large, datagram fragmentation may result.

Network issues (cont'd)

At the TCP layer, look for:

Segments retransmitted
Connections reset
Frequency of ACKs
Window size too small

In the TCP/IP stack, look for:

The maintenance level of the two TCP stacks involved
The use of PORT and 1364 TCP CDSTC NODELAYACKS which may delay ACKS
The values of TCPSENDBFRSIZE and TCPRCVBFRSIZE in the TCP/IP PROFILE data set
Note: These values affect all applications using the TCP/IP protocol whereas the V2.BUFSIZE initialization parameter (see below) affects the operation of the IBM® Connect:Direct® application only.
Whether the value set for PATHMTUDISCOVERY is an MTU size of 8992 (the default)

In the IBM Connect:Direct global initialization parameters file, look at:

V2.BUFSIZE = (maximum transmission buffer size, TCP/IP send/receive buffer size)–The default is V2.BUFSIZE=(32K,128K). Adjust if needed based on the bandwidth and speed of your communications lines.
DEBUG–Make sure this setting is 00000000 so that internal traces are turned off.
TCP.API.TIMER = 00:00:00 | hh:mm:ss–To reduce the number of hung sessions, specify this keyword. Set this value to at least 20 minutes and specify TIMEOUT=YES on IUI signon panels for individual users. Session waits before timing out and exiting.