General TCP/IP Problems

|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 Note: UDT is an alternative transport layer protocol designed for high latency with high-bandwidth connections. If you transfer files with a trading partner who is geographically distant and determine that the data congestion is caused by a high-latency, high-bandwidth connection, analyze your system and see if you would benefit from UDT. For additional information, see the *IBM® Sterling Connect:Direct® for z/OS® Release Notes*. - 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 Sterling Connect:Direct application only. - Whether the value set for PATHMTUDISCOVERY is an MTU size of 8992 (the default) In the Sterling 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.|