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1994-11-13
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Date: Wed, 13 Jul 94 04:30:04 PDT
From: Advanced Amateur Radio Networking Group <tcp-group@ucsd.edu>
Errors-To: TCP-Group-Errors@UCSD.Edu
Reply-To: TCP-Group@UCSD.Edu
Precedence: Bulk
Subject: TCP-Group Digest V94 #147
To: tcp-group-digest
TCP-Group Digest Wed, 13 Jul 94 Volume 94 : Issue 147
Today's Topics:
Bit Regeneration v. DAMA
KA9Q/Slip server
Managing MSS and Window (2 msgs)
Managing MSS and Window; IP encapsulation (2 msgs)
Speed and Bit regenerators
Send Replies or notes for publication to: <TCP-Group@UCSD.Edu>.
Subscription requests to <TCP-Group-REQUEST@UCSD.Edu>.
Problems you can't solve otherwise to brian@ucsd.edu.
Archives of past issues of the TCP-Group Digest are available
(by FTP only) from UCSD.Edu in directory "mailarchives".
We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
----------------------------------------------------------------------
Date: Tue, 12 Jul 1994 06:50:56 -0500 (CDT)
From: ssampson@sabea-oc.af.mil (Steve Sampson)
Subject: Bit Regeneration v. DAMA
To: tcp-group@UCSD.EDU
Barry Gm8SAU/Dc0HK writes:
> As there is an increase in the use of DAMA (csma/cd) Digi's inc latest
> flexnet 3.3a Is there any plans for inclusion to wampes the DAMA mode
> in the ax25 layer
Barry points out that bit regeneration and repeaters are a waste of resources.
DAMA would provide the same capability on a half-duplex channel with very
minor AX.25 protocol changes. I think the TNC coders (Kantronics, AEA) should
make the mode available (DAMA=ON), and probably NOS should run it also (DOS,
Linux). The argument that a router would be better than a repeater is off a
bit, as it assumes the user wants to route. Some may just want to chat, or
hook up with a (gulp) BBS... In this case the repeater attempts to solve the
hidden node problem, but so could DAMA, for a lot less.
--
Steve
------------------------------
Date: Tue, 12 Jul 94 13:35:44 CST
From: "Jan Dolejs" <jandol@mbox.fsv.cuni.cz>
Subject: KA9Q/Slip server
To: tcp-group@ucsd.edu
Hi,
Operations on a dial-slip line in one of distributions of KA9Q-NOS
(PA0GRI->N1BEE->CWRU->jandol)
1.Overview
The aim of usage of this dial-slip line(in connection with a modem) was to
realize running of networks(on Fig. 1). The aims we can divide into several
groups:
o the connection of an end-user to the faculty-network, possibly to the
Internet,
o the connection of sublocal Ethernet-network,e.g. Gymnazium for blind,
any separated department of faculty, home network,etc. to the faculty
network, possibly to the Internet.
The basic idea was a software realizing the user connection to a services
of faculty-network and Internet(e-mail,news,telnet,ftp,gopher,http....etc.)
was undependent on a type of used line.
+-----+ +-----+ +------+
| PC | .................. | PC | |Cisco |----> Internet
+--+--+ +--+--+ +---+--+
| | |
------+----------------------+-------+--------------+--------
Faculty | Ethernet
+---+--+ | +----+
| NOS | +-+ PC |
+---|--+ | +----+
M | .
+----+ ----|---- +------+ |Sublocal
| PC +-----M-------/ \----M----+ NOS +--+Ethernet
+----+ / \ +------+ | .
. / Telephone \ | +----+
. ! network ! |-+ PC |
+----+ \ / | +----+
| PC |-----M------\ /
+----+ \----|----/
End users M
|
+--+--+
| NOS |
+--+--+
|
--+-------+----------+--
| |
+-+-+ Sublocal +-+-+
|PC | ........... |PC |
+---+ Ethernet +---+
Fig.1. The connection of a telephone network to a faculty network.
2.Phase diagram
In the process of configuring,maintaining and terminating the dial-slip line,
the dial-slip line goes through several distinct phases:
Attach asy .. Start slipsv ..
| | Dialer ..
| | |
+-+-------+ +-+------+--+ +--------------+
|Dead | UP |Establish | OPENED |Authentication|
| +---->+ +--------------->| |
|---------| |-----------| |--------------|
| Closed | |Listen | |Opened |
+----+----+ +----+--+---+ +--+---+-------+
^ Fail/Stop | ^ DOWN Fail | |Success
+<--------------+ | +------+ |
| | | |
| +-------+---+ | +------+-------+
| Stop |Terminate | CLOSING | |Network |
+----------+ +<-----------+---+ |
|-----------| |--------------|
|Closing | |Open user/gate|
+-----------+ +--------------+
Fig.2. Phase diagram
This phase diagram is realized by several processes: slip server(slipsv)
and dialer, and in the phase Network bootp daemon too.
3.Link Dead
This phase begins with the command Attach asy .....(with parameters).Note
that argv[8] must be "d".From this moment circuits(8250,16450,16550) and
interrupt handlers(in,out processes and buffer) are initialised and the
input process for SLIP line is suspend.The output process is saved in
memory and new output process discards output data.The process responding
on change of modem(RLSD) signal is not started too.
4.Link establishment phase
The precondition for establishing of line is -so called- pasive open line
(LISTEN).Process Slip server(start slipsv ifacename) realizes this
function. From this moment, dial-slip line is ready for all changes,done
by opening of line. That could be: change of modem signal(RLSD) or an
activity of administrator or operator(starting of process dialer..).The
process slip server carries out its immer initialization and waits for
RLSD change(to state moved_up).The process dialer...(with parameters)
carries out its synchronization with the process slip server and it does
an usual service for modem and its translation to data mode. This process
holds the line active(option automatical redial) without data discarding.
5.Authentication phase
This phase is necessary.It's choosen a simple format for communication between
both ends of line(like in communication with modem in command mode is always
necessary return[\r] on the end of line.This simple communication protocol
starts in moment, when both modems are already in data mode.The slip server
requires the communication after the following scheme(Fig.3).
server client
| RLSD in moved_up |
|<--------------- |
| |
| Verification |
+----------------> |
| |
| Username: |
+----------------> |
| |
| uuuuuuu\r |
| <------------------+
| Password: |
+----------------> |
| xxxxxxx\r |
| <------------------+
| |
| slip-server> or |
| Access denied |
+----------------> |
| SLIP\r |
| <-----------------+
| |
| MTU= |
+----------------> |
| |
| |
| |
Fig.3. Authentication protocol
The authentication of line runs by data in file slipuser. The format of line
in this file is similar to format in popusers.
Format:
ifacename:Username:Password:Ustype:filterup:filterdn:Uslimit:
where:
ifacename ..............name of asy interface
Username ...............user
Password ...............password of user
Ustype ...............type of user("b" user used bootp,
"a" user not used bootp,
"g" slip-gate)
filterup,filterdn.......files with commands for configuration of IP-filter,
filterup is done by opening of line and filterdn by
termination of line,
Uslimit ...............time limit for user.
Tab.1. The usage of individual data in the file slipuser, in dependence on
user type and type of getting of IP address.
+--------------------+------+-----+-----+--------+---------+-------+
| User type |iface |User |Pass |filterup|filterdn |Uslimit|
|--------------------|------|-----|-----|--------|---------|-------|
|b |Open user |bootp| x | x | x | x | x | x |
|---| |-----|------|-----|-----|--------|---------|-------|
|a | |adm | x | x | x | x | x | x |
|---|----------|-----|------|-----|-----|--------|---------|-------|
| g |Open gate |adm | x | x | x | - | - | - |
+---+----------+-----+------+-----+-----+--------+---------+-------+
x .... used
- .... not used
6.Network layer protocol phase
If authentication is OK,the line passes to state Network.The usage of IP
protocol is assumed.In this moment we can distinguish following cases:
o The end user opened the line and it uses BOOTP protocol for assignment
of IP address,
o The end user opened the line and it does not use BOOTP protocol for
assignment of IP address,
o The dial-slip gateway opened the line.
In the first case, the BOOTP server assigns IP address by interface name of
serial line(name asy interface).The slip server fills in(automatically)
routing and arp tables and it uses filters(executes bootp daemon).
In the second case, the network administrator answers the purpose for
assignment of IP addresss.He must fill in manually data in routing and
arp tables. The slip server executes the usage of filter.
In the third case, the network administrator answers the purpose for setting
of routing and arp tables in both dial-slip gateways.
7.Link termination phase
The dial-slip line can be terminated in any moment, by falling down of line
or by operator.Both ends of line find termination, based on change of modem
signal(RLSD to moved_down). The proper termination of line should be carried
out by that end of line,which opened the line(i.e. in case slip-gate:the
process dialer or in case end user:software phone,umslip etc.).In case
user type "g" are the same systems in both ends(NOS, which work contemporarily
as server and client).It makes no difference, what system starts opening of
line(proces dialer).The NOS system, opening line must hold the line(automatical
redial) and must do the proper termination of line.
Note:Further information and the distribution(binary) of this software is
available for anonymous by FTP on:
mbox.fsv.cuni.cz(192.108.140.149) /pub/nos
jan.fsv.cuni.cz(192.108.140.148) /pub/nos
------
Jan Dolejs,Charles University,Prague,Czech Republic
e-mail:jandol@mbox.fsv.cuni.cz
jandol@jan.fsv.cuni.cz
------------------------------
Date: Tue, 12 Jul 1994 21:22:20 -0500 (CDT)
From: ssampson@sabea-oc.af.mil (Steve Sampson)
Subject: Managing MSS and Window
To: tcp-group@UCSD.EDU
In discussing MTU/MSS I put together this list. Maybe others will want
to comment on it. The only thing I left out is NOS Segmentation (which
won't work over Net/Rom) and the fact that MSS should be 40 less than the
*Maximum* MTU. In this case I was tuning it for radio.
If you have an Ethernet, I guess that the MTU would be 1500, and MSS will then
be 1460, and thus when talking through an AX.25 to another system with both
radio and Ethernet the two will agree on a 1460 MSS?? Problem there...
Sorry if this was beat to death in a previous thread.
-------------------------------------------------------------------------------
This assumes a dependable RF circuit
Paclen 256 Not used in datagram mode.
Example 1200 baud DG or VC:
MTU 256
TCP MSS 216 MTU - 40 40 for IP header
TCP Window 864 MSS * 4
Example 1200 baud over Net/Rom VC:
MTU 236 PACLEN - 20 20 for Net/Rom header
TCP MSS 196 MTU - 40 40 for IP header
TCP Window 392 MSS * 2 (memory may be problem on Net/Rom)
9600 baud DG or VC over AX.25:
MTU 512
TCP MSS 472 MTU - 40
TCP Window 1888 MSS * 4
--
Steve, N5OWK
------------------------------
Date: Tue, 12 Jul 1994 21:32:25 -0500 (CDT)
From: ssampson@sabea-oc.af.mil (Steve Sampson)
Subject: Managing MSS and Window
To: tcp-group@UCSD.EDU
In discussing MTU/MSS I put together this list. Maybe others will want
to comment on it. The only thing I left out is NOS Segmentation (which
won't work over Net/Rom) and the fact that MSS should be 40 less than the
*Maximum* MTU. In this case I was tuning it for radio.
If you have an Ethernet, I guess that the MTU would be 1500, and MSS will then
be 1460, and thus when talking through an AX.25 to another system with both
radio and Ethernet the two will agree on a 1460 MSS?? Problem there...
Sorry if this was beat to death in a previous thread.
-------------------------------------------------------------------------------
This assumes a dependable RF circuit
Paclen 256 Not used in datagram mode.
Example 1200 baud DG or VC:
MTU 256
TCP MSS 216 MTU - 40 40 for IP header
TCP Window 864 MSS * 4
Example 1200 baud over Net/Rom VC:
MTU 236 PACLEN - 20 20 for Net/Rom header
TCP MSS 196 MTU - 40 40 for IP header
TCP Window 392 MSS * 2 (memory may be problem on Net/Rom)
9600 baud DG or VC over AX.25:
MTU 512
TCP MSS 472 MTU - 40
TCP Window 1888 MSS * 4
--
Steve, N5OWK
------------------------------
Date: Wed, 13 Jul 1994 01:14:57 -0700
From: Phil Karn <karn@qualcomm.com>
Subject: Managing MSS and Window; IP encapsulation
To: ssampson@sabea-oc.af.mil
FYI, I'm probably going to implement Path MTU Discovery in my TCP
fairly soon.
By the way, I'd like to survey the NOS variants out there that people
are using to build their wormholes. When I originally wrote that code,
I used IP protocol number 94 to mean "IP on top of IP". I later
discovered that that protocol number normally implies something a
little different, and the preferred protocol number for IP directly on
top of IP is 4. It's used for multicast backbone tunneling, among
other things.
Some time ago I redid the receive routine so that NOS would accept
incoming tunneled packets with either PID (4 or 94). The idea was to
get that disseminated so that I could eventually switch the
encapsulating side over to PID 4 without invoking a flag day. Can
people tell me whether the receive-side change has made it yet to the
NOS variants that people are using as wormhole gateways? Or do I need
to keep 94 on the transmit end a little longer to avoid compatibility
problems?
Phil
------------------------------
Date: Wed, 13 Jul 1994 10:39:38 +0200 (BST)
From: A.Cox@swansea.ac.uk (Alan Cox)
Subject: Managing MSS and Window; IP encapsulation
To: karn@qualcomm.com (Phil Karn)
> FYI, I'm probably going to implement Path MTU Discovery in my TCP
> fairly soon.
In the light of SIPP/TUBA and the IPng stuff is this actually worth doing,
especially given the number of places it breaks and the number of sites
behind gateways that just do not cope with MTU discovery ?
Alan
------------------------------
Date: Tue, 12 Jul 1994 08:16:43 -0500
From: rush@dns.sprintcorp.com
Subject: Speed and Bit regenerators
To: "Milton D. Miller II" <miltonm@bga.com>
Milton:
I got another reply from my comments about the bit regen, which pointed out
the hidden transmitter bugaboo. I was familiar with that problem, but I
hadn't considered how the bit regen would have an advantage in such a case.
But I would still prefer a cross-frequency solution... but that's obviously
more expensive :-(
Thanks for the note.
David, rush@erg.sri.com, david@n0oxh.ampr.org
------------------------------
End of TCP-Group Digest V94 #147
******************************