Submission for mod-protocols
al...@columbia.edu.uucp
From: al...@columbia.UUCP (Alan Crosswell)
Newsgroups: mod.protocols,mod.computers.vax
Subject: Need help with LAN Bridges
Message-ID: <43...@columbia.UUCP>
Date: 23 Feb 87 22:42:25 GMT
Reply-To: al...@columbia.edu (Alan Crosswell)
Organization: Columbia University CS Department
Lines: 34
We have several LAN Bridges interconnecting departmental ethernets
to our campus "backbone." We have recently noticed that a lot of
traffic that should be filtered by the LAN Bridge is not being filtered;
packets between a host on the backbone and another department are showing
up on a second department's network. These are not broadcasts, they
are things like tcp/telnet and tcp/ftp.
Unfortunately, we do not have a VMS system or RBMS so I can't dump
out the LAN Bridge's tables to see if that will provide any clueas
to what it going on. My understanding was that the factory default
would be to do all the right filtering so we wouldn't need RBMS for
day-to-day stuff -- only for unusual situations.....
I have also noticed the LAN Bridge for our department is transmitting
a "LAN Bridge protocol" packet about once a second onto the departmental
network.
The LAN Bridge installation manual (the only documentation of the thing
I have) says that the Bridges talk to each other when they boot so that
they can see if there are any loops. Are they saying anything else to
each other and can they possibly get confused if, for instance, some of
them have the "A" port plugged into the backbone while others are plugged
in with the "B" port?
Any help and/or explanations of how LAN Bridges work or what might be
wrong would be greatly appreciated! One of our departmental networks
that just got connected to the backbone may have to disconnect -- the
extra noise is wiping out their diskless SUN performance.
Alan Crosswell
Columbia University
al...@columbia.edu
(212) 280-3754
la...@pdn.uucp.uucp
From: la...@pdn.UUCP (Larry Swift)
Newsgroups: mod.protocols
Subject: Re: OSI references & flow control
Message-ID: <6...@pdn.UUCP>
Date: 2 Mar 87 16:50:14 GMT
Organization: Paradyne Corporation, Largo, Florida
Lines: 30
(In response to an email request for OSI reference material)
There's a good collection of articles and original work by Stallings,
"Computer Communications: Architectures, Protocols, and Standards", IEEE
Computer Society Press, 1985. (He's from MIT also, I believe.) The OSI
Ref. Model (ISO is 7498) itself is available from the American National
Standards Institute. A good seminar (and the material that goes with it,
if one can find it without taking the seminar) is available from Omnicom,
Inc, Vienna, Va. Omnicom's executive director, Hal Folts, has also
published "A Tutorial on the OSI Reference Model", 1982, which is probably
available from Omnicom. Other compendiums are readily available in works
such as Auerbach and Datapro's Data Communications. (I have no affiliation
with any of these people or organizations.) As I said, there are many others.
In locating these references for you, I discover that I may be somewhat out
of date in citing OSI's Layer five (Session Control) as that "where the data
path is finally narrowed to a single user", although I suppose it may still
be arguable. If sessions and transport connections are indeed tied
together in one-for-one relationships, then it would seem that Layer 4
is the upper limit of flow control mechanisms. (This seems to me to be in
conflict with the transport layer's responsiblity for cost-effective
conections.)
--------------------------------
Larry Swift
UUCP: {ihnp4,gatech,cbosgd}!akgua!usfvax2!pdn!larry
Snail mail: LF-207, Paradyne Corp., 8550 Ulmerton Road, Largo, FL, 33541
Phone: (813) 530-8605
news@seismo.CSS.GOV@hafro.uucp
From: gun...@hafro.UUCP (Gunnar Stefansson)
Newsgroups: mod.protocols
Subject: X.25 software for Unix ?
Message-ID: <3...@hafro.UUCP>
Date: 2 Mar 87 21:38:55 GMT
Reply-To: gun...@hafro.UUCP (Gunnar Stefansson)
Distribution: world
Organization: Marine Research Institute, Reykjavik
Lines: 17
Does anyone know of software for handling the X.25 protocol on Unix
machines ?
In particular, we do not want to have to connect our machines to a
PAD with n serial ports, which will then force us to use up n serial
ports on the computer. Rather, the ports should be implemented in
software as is done on several other systems, with just one physical
connection going out of the machine, but several logical ones.
We would be most interested in specific solutions for the HP 9000
series, but general information on solutions under Unix will also be
appreciated.
Thanks,
Gunnar
la...@pdn.uucp.uucp
From: la...@pdn.UUCP (Larry Swift)
Newsgroups: mod.protocols
Keywords: OSI flow control
Message-ID: <6...@pdn.UUCP>
Date: 4 Mar 87 14:51:45 GMT
Organization: Paradyne Corporation, Largo, Florida
(In reply to an email discussion)
>specific references to how to do FLOW CONTROL in the OSI model.
Peer-to-peer flow control, as you have indicated, is much discussed in
OSI circles. I don't know of any references addressing flow control
at the service interface, however (see below). If I find any, I'll
let you know.
>I suspect whoever defined the standard do not know how well their stuff works
>in the real network.
You might have a good point, there!
> In OSI model, each layer determines its own flow control parameter
> values. Now assume transport layer sends lots of data (it has a large
> window size), but the net can't send that fast. Where are data buffered?
> What problems does this cause? (in reality, not in definition. These
> real problems are seen everyday.)
You are referring to a resource problem in the service interface(s), which,
I agree, the Model hasn't addressed at all, as of yet. One of the reasons,
I'm sure, is that the problem is usually internal to the node rather
than the network (ie, the given two layers are operating in the same
program environment). I know from experience that this takes a rather
sophisticated, communications-oriented operating system to resolve in a
common manner, and therefore is subject to all sorts of non-networking
requirements being imposed. Unix, for example, is a long way from being
able to address the problems.
I suspect the OSI Model won't be upgraded to address the problems for a
long time either, since I don't believe the upper layers are yet locatable
in separate program environments (ie, machines).
neu...@mcvax.uucp.uucp
support within the unix kernel ... interfaced via sockets. It also includes
PAD support as a client within user process (there is a call out/in daemon).
The software requires a DMF-32 on a Vax (there is also a DUP-11 driver). It
also runs on a Sun.