🚀 go-pugleaf

In article <1992Jul23.160241.23996@inesc.pt> prc@rabbit (Pedro Ramalho Carlos) writes:

>  1-Will I loose much performance by installing TCP/IP at all - even
>    with no sessions (due to daemons, etc.) ?

It's another set of started tasks, so it will lose you some
performance due to working set and real memory residence.
Fortunately, MVS does memory management and paging/swapping
management pretty well, so if your system is reasonably well
tuned to begin with, you shouldn't see a significant impact.

>  2-What is the relative load on the host of a tn3270 session compared
>    with a native 3270 session? 

About half again as much as a SNA-based user, as a rough
guideline. With an SNA user, the device controllers are handling
a significant amount of the I/O interrupts, which reduces the
interruptions to the access method and OS. Most of the MVS
implementations I've worked with of TCP essentially serve to
connect a TCP connection to a VTAM LU and then MVS manages it as
a SNA connected user. I have less of an estimate on non-terminal
functions such as FTP. 

The difference is very similar to driving a non-SNA terminal, but
not quite as resource hungry.

>  3-And what is the relative performance from the user standpoint?

Depends a lot on network load and CPU load. There is more host
processing involved in the TCP connection, but on a lightly
loaded network and moderatly loaded host, I wouldn't expect a
significant difference. It's comparable to a cross-domain VTAM
connection between two hosts connected by a real CTC.

>  4-Will I need to upgrade the mainframe with CPU or RAM?

Never hurts. 8-) More main storage might be useful if you're
heavily overcomitted on storage, but that's no different than any
other major application subsystem. The answer to this question
really depends on just how heavily loaded your current system is
and how much more load it can tolerate without some significant
(measured on your own scale) performance degradation. 

>  5-If I use IBM's own TCP/IP will I get the same kind of support from
>    them?

The IBM TCP/IP group is one of the most vocal and externally
visible groups of  IBM developers I know of. They listen, they
propose, and they're willing to fix things if the general
consensus of the net is that they're going the wrong direction.
IBM is still heavily committed to SNA, and they'll still be a lot
less confused if you stick to SNA, but TCP support is pretty
good. 

As a side note, most heavy MVS sites I'm aware of use IBM's TCPIP
software, but purchase the hardware interfaces from other
vendors, such as Bus-Tech, Interlink, or OpenConnect Systems.
Some use a device from McData that appears to the host as an
local SNA 3174, but accepts network connections instead of CUT
terminals. 

>--pedro ramalho carlos (prc@inesc.pt)


-- 
David Boyes
dboyes@rice.edu