Problem

--RFC1323 compatibility with CFT and Interpel on z/os / TCP networks with large bandwidth and high latency

Resolution

Since z/os V1R11, Communications Server has been improved to deliver better performance for inbound streaming TCP connections over networks with large bandwidth and high latency.
Interpel and Transfert CFT for z/os does not prevent the use of that enhancement.
It doesn’t mean the product cannot be enhanced in the future to perhaps make a better use of the large network bandwidth when it is available.

High latency with large bandwith network works as expected with CFT and Interpel as long as the pre-requisites are respected.
TCPRCVBUFRSIZE is not set by IPEL and must be higher than 64K so DRS can take effect for the application (same for CFT even though some versions make use of the SO_RCVBUF socket option, but always to higher value than 64K)
IPEL does not use the SO_RCVBUF socket option
Special care must be given to the protocol parameters choice. (especially in regards of the checkpoints mechanism).

A 'netstat all' report shows the DRS-adjusted receive buffer size. The report shows the current window size in the RcvWnd field and the fact that DRS is in effect for the connection is indicated with the x40 bit in the TcpPrf byte.

TCP's Dynamic Right Sizing is then transparent to both CFT and Interpel