[pyr.syseng.comm] Packet size & number of windows in UUCP

csg@pyramid.pyramid.com (Carl S. Gutekunst) (01/24/88)

In article <567@acornrc.UUCP> bob@acornrc.UUCP (Bob Weissman) writes:
>Can someone tell me the effect of tweaking the "packet size" and
>"number of windows" parameters in UUCP?

Sure. You'll break it. :-)

>E.g., are there settings which are appropriate for different transmission
>speeds?  Will responding hosts understand different (presumably larger)
>packet sizes?  What's a "window" anyway?

The uucico 'g' protocol is characterized as "packetized, sequenced, windowed"
meaning that:

- The data to be transferred is fragmented into packets;
- Each packet has a sequence number and the packets must arrive in sequence;
- A number of packets can be sent back-to-back without acknowledgement. The
  space into which these packets fit is called the "window," and the maximum
  number of unacknowledged packets is called the "window size." The advantage
  is parallelism: new packets can still be arriving while old acks are being
  calculated and sent.

In uucico pk.h, the usual window size is 3, and the packet size is 64.

You *can* increase the window size up to 7, and the two sites will negotiate
the actual window size (based on who has the highest maximum). This has very
little effect when using normal modems; it is a big win when the 'g' protocol
is used on dialup public data networks (for example, PC Pursuit). It also
helps with packetized modems, including MNP modems.

You *cannot* increase the packet size beyond its current limit of 64. Although
the protocol supports packets up to 4096, no UUCP version in use to date has
buffers to handle anything bigger than 64. So if you increase the packet size
and buffer sizes on your end, you will core dump the uucico on the other end.