> I have a question in regards to how the HP3000 communicates
> with a DTC device.  I am having problems with the HP3000's
> losing it's communication session with some of the DTC
> devices and they must be rebooted before discovering the HP3000 again.
> What does HP use to communicate between the HP3000 and the
> DTC.  They must have some type of proprietary protocol or
> keepalive like a hello update to maintain that session.
> Someone told me that HP's protocol is called Ivesta but I
> can't find any information on it, including RFC 1700 which
> lists all assigned port numbers.  Any help would be extremely
> useful.  Thanks,  --Mike

The DTC-to-3000 link uses the Avesta Flow Control Protocol, "AFCP". It (and
its brother ALCP) is a low-overhead non-routable protocol sitting directly
on the LLC layer.

Here's a June 1998 posting (by me) on the subject:

-----------
According to our friends at Cisco, “The Avesta Flow Control Protocol (AFCP)
is HP's LAT. The HP terminal controllers (DTCs) use AFCP to talk to HP3000s
for remote sessions. AFCP is written on top of 802.3, so it has no
addressing and must be bridged.”

And at http://www.cisco.com/warp/public/99/2.html they mention that

“Q: What is the type code (or LSAP) for AFCP, and how can you set up a Cisco
to bridge only AFCP?

A: You can't. All HP packets from a DTC (including HP Probe VNA, HP
Probe-Proxy, and AFCP) use the LSAP FCFC. HP then uses the "HP Extended
SAP," which incorporates the first 4 bytes of the data portion to determine
the exact packet type. So, unless you want to stop all HP traffic, you
cannot use an LSAP list.”
-----------

FWIW, I think the Cisco item has a typo (or simple error): I'm pretty sure
that AFCP talks to the 802.2 LLC rather than the 802.3 MAC. In any case,
it's "below" IP or any other routable layer, so it must be bridged in a
routed network. Another good reason to dump internal routers in favor of
boundary routers and internal switches.

When a DTC powers up, it broadcasts a request for a server. Whichever 3000
answers up and provides the configuration download becomes the "owner" of
that DTC; it can't be redirected to a different box without a power-cycle or
reset.

If you're consistently losing the link, I'd look at a hardware problem
either with the DTC or the link; people have DTCs that run, literally, for
years without problems.



Steve Dirickson   WestWin Consulting
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