If you notice that report transmission is slower after upgrading to z/OS 1.6 or 1.7, it may be due to an IBM problem. Reports that took seconds to transmit, can now take minutes.
The IBM problem is:
PK12893: POOR TCP PERFORMANCE WHEN USING TCP SEGMENTATION OFFLOAD AND APPLICATIONS WITH SMALL DATA WRITES.
You may be able to use a TCPIP sniffer to determine if you have this problem. The apar text has other instructions to verify the problem scenario as well as a workaround and information about apars for z/OS 1.6 and 1.7.