ISDN wide area bridging of local area networks for small offices

Chris Avram

Department of Computer Technology;
Monash University, Caulfield.
Chris.avram@monash.edu.au

Abstract

This document describes an experiment in which two ISIS ISDN PC Adapter cards from Network Designers are used with NOS by KA9Q to route TCP/IP traffic between two Ethernet segments over a dial up Telecom basic rate ISDN service.

The following network fragment (figure 1) was created for test purposes.

Figure 1 An ISDN router between two ethernet segments

           Campus      Remote
           segment     segment
  abc.def.ghk.x _       _ abc.def.mnp.x
                |       |
                |       |
     Thinwire   o    /\ |
     x=mnp      |\  /  \|
                | \/    o   Longwire
                |  ISDN |   x=ghk
        Jpole   o       |
        x=133   |       |
                |       o   Yagi
                |       |   x=158
CISCO gateway   o       |
x=254           |       o   Silver
                |       |   x=160
                -       -

Background to the research

ISDN has been proposed as a low cost high data transfer rate means of providing wide area access to local area networks.

In order to connect two widely separated local area networks, expensive (> A$7,000) routers have been used with links over leased lines or ISDN dial up services. The cost of leased lines (> A$20,000 per year) adds a high operating cost to a quite high initial cost. For small offices, these costs can be prohibitive.

Low cost partial solutions involve the use of high speed modems and plain old telephone lines (POTS). Even with the latest modems working at 14,400 bits per second with compression to 28,800 bits per second some local area network protocols fail due to long latencies. Particular problems exist with X Windows and Network File Services.

It is the aim of the experiment described here to demonstrate that low cost high data rate router services can be established over ISDN lines.

In the following sections of this document there is a summary of the results followed by a detailed description of the hardware and software configuration used.

Related documents to follow will detail the results of the 108 different file transfer tests performed, an analysis of the results to determine if the location of bottle-necks, the nature of the network file system tests and X windows tests, the features of the ISIS ISDN Adapter card and the features of three other cards available in Australia, and finally an analysis of the desirability of the features.

A. Summary Conclusions

1. The Capacity
Using the FTP protocol and NOS KA9Q FTP clients and servers, the router can carry data at either about 7,300 bytes per second over one ISDN channel or at 14,400 bytes per second over two ISDN channels with channel aggregation.

The maximum data rate, with no protocol headers, over 64,000 bps lines is 8,000 bytes per second and 16,000 bytes per second for one and two channel services respectively. This is reduced to approximately 7,466 and 14,932 with TCP/IP and ethernet overheads. Thus the results obtained represent a line utilisation of approximately 97.9%.

2. The Cost
The total cost of one router, hardware, software, and ISDN adapter card is about A$3,500. If the remote site consists of only one computer (rather than a small network) then that computer can be attached directly to the ISDN network reducing the cost to about A$2,000. The annual cost is A$1,000 plus call charges from $1 per hour.

3. The Capability
Network file services (over ISDN routers) are very usable. Subjective tests using windows for Workgroups and Kodak Imaging software were used to determine the suitability of this configuration for remote access to document imaging systems data for legal applications.

X Windows services (over ISDN routers) are very usable. Tests using a remotely located Sony News Workstation X server connected to a distantly located client were successful. This particular client was known to cause timeout problems with remotely located servers under slower modem and phone line routers.

4. The Limitations
In this experiment, neither LAN bridging nor IPX routing were tested.

5. The Conclusions
Subject to the limitations, it is possible to construct routers which will allow wide area connections to a local area networks at high speeds. These connections will be relatively low cost and suitable for connecting small offices.

B. Installation

The steps to installation are:- install the ISDN lines; purchase the ISDN adapter cards; configure the computers and operating software for the routers; configure the ISDN cards and ISDN call control functions. These four steps are now described.

1. Telecom Microlink services were ordered. Delays in installation were experienced. Microlink provides a device, at each service location, called an NT1 to which the ISDN PC Adapter card may attach. Installation is about $380 per site.

A Microlink or basic rate service provides two ISDN B channels, each able to carry 64,000 Bits per second and one common signalling channel, a D channel. This whole service is delivered over the normal twisted pair telephone lines on one pair.

The service charges are rental, about $980 per year, and usage charges, see table 1 below. Even local calls are charged on a time basis.

Table 1 Telecom ISDN approximate call charges 31/12/1993

One channel Data Calls (have access to full 64,000 bps) Day Night Economy NDD1 Local $ 2.56 $ 0.72 $ 0.72 NDD2 25-50km $ 9.30 $ 6.24 $ 3.97 NDD5 >745km $33.60 $23.14 $11.91

2. Two ISIS ISDN Workstation kits (available from Network Designers) were purchased. The cost of these is high so it may be wise to borrow, evaluate then consider alternatives before purchase. Like all these cards in Australia, start planning around $2,000 per card with driver software.

Philips cards from Telecom were considered but it was decided to run the trial with the ISIS cards because of such features as demand dialling, channel aggregation FTP packet driver support and a little serendipity.

3. Install two dedicated machines to act as routers.

Since these machines will be running NOS by KA9Q, one could make use of the bootp server, anonymous FTP server, SMTP and NNTP services in KA9Q. In my case thinwire at times acts as a SLIP router over the plain old telephone service as well as an ISDN router.

It is simpler if the exposition continues assuming the routers thinwire and longwire (see figure 1) are dedicated to the routing task. This assumption will be made.

The configurations of these two machines are described in the following file listings. For each machine is shown its initialisation files CONFIG.SYS and AUTOEXEC.BAT. These are used by the operating system, MS DOS. Also shown is AUTOEXEC.NET, this file is used by NOS KA9Q as an initialisation script.

The next 6 figures figure 2 to figure 7 display the files.

First the configuration of thinwire is described.

The hardware for thinwire is a reasonably powerful ISA bus computer. Its a 486DX33 with four megabytes of memory, a 200 megabyte hard disk, SMC Ethernet card, VGA video and the usual serial and parallel ports. The specialised ISDN hardware is a single full length PC bus (8 bit) adapter card with an ISDN S bus interface. This card is plugged directly into the NT1 provided by the ISDN Basic rate service provider.

Figure 2 CONFIG.SYS from thinwire

Stacks=9,256
Files=40
Buffers=30,0
Fcbs=4,0
Dos=HIGH,UMB
Lastdrive=E
DEVICE=C:\DOS\HIMEM.SYS
Rem eXclude a section of memory for the ram buffer used
Rem by the ISIS ISDN card and the SMC Ethernet card
DEVICE=C:\DOS\EMM386.EXE NOEMS X=c800-c9ff X=d000-d3ff
DEVICEHIGH =C:\WINDOWS\protman.dos /i:C:\WINDOWS
DEVICEHIGH=C:\WINDOWS\dis_pkt.dos
DEVICEHIGH=C:\WINDOWS\KNXISIS.DOS
DEVICEHIGH=C:\WINDOWS\smcmac.dos
DEVICEHIGH /L:2,7280 =C:\WINDOWS\WORKGRP.SYS
DOS was installed on thinwire. DOS 6.2 was used. The ISDN card and the ethernet card must have packet drivers installed in order that NOS by KA9Q be able to be used as a TCP/IP router. Windows for workgroups was choosen, this detected the SMC ethernet card and installed the NDIS driver stack. Figure 2 is a configuration file roughly as provided by windows after installing MS DOS 6.2 then MS Windows for Workgroups and then using the Windows for Workgroups network configuration tool in the control panel to install the NDIS drivers provided with the ISDN card. Finally the instructions that come with the network card were followed to add the packet driver shim dis_pkt.dos.

Figure 3 AUTOEXEC.BAT from thinwire

@Echo off
Path c:\windows;c:\dos;c:\isdnws\bin
Set is-dir=c:\isdnws
Set temp=c:\windows\temp
Rem the batch file iws is provided by the ISDN 
Rem adapter card supplier
Call iws
Rem the following line initialises the NDIS 
Rem protocol stack (performs a netbind)
c:\windows\net start
Lh /l:0;2,43920 /s c:\windows\smartdrv.exe
:loop
c:
cd \nos
wd8003e -n -d -w 0x79 2 0x240 0xD000
net -d c:\nos
termin 0x79
if exist c:\stop goto endit
goto :loop
:endit
c:
cd \
The AUTOEXEC.BAT file does some common operations; executes the ISDN card start up script (Call iws) and then performs a netbind. When thinwire boots and whenever the router NET.EXE the Network Operating System (NOS) by KA9Q exits, this start up script will re-start the router.

Using the remote exit command and protocol built into NOS, one can remotely download new start up and configuration files (via FTP) then remotely either exit NOS or remotely reboot the computer. The AUTOEXEC.BAT above thus allows remote router configuration and management.

The files wd8003e and termin load and unload the packet driver interface software to the ethernet card. These are available at many sites on the internet as is net.exe.

The files IWS.BAT, DIS_PKT.DOS and KNXISIS.DOS are provided with the ISDN card in the Workstation kit.

Strictly speaking, windows for workgroups is not needed, any other product that uses NDIS may be used instead. It was not possible to perform the netbind with the software provided by the ISDN card supplier. All the rest of the NDIS software was provided.

Figure 4 AUTOEXEC.NET from thinwire

hostname thinwire.your.domain.edu.au
ip address abc.def.ghk.mnp
ip address

#ISIS ISDN packet driver shim on NDIS
attach packet 0x7A pk0 5 1500
#WD8003 packet driver
attach packet 0x79 pk1 5 1500

log c:\nos\spool\net.log

#pk0 is the ISDN card pk1 is the ethernet card
route add [abc.def.mnp.0/24] pk0 [abc.def.mnp.ghk] 1
route addprivate [abc.def.ghk.0/24] pk1
route add default pk1 [abc.def.ghk.254] 2


arp add [abc.def.ghk.255] ether ff:ff:ff:ff:ff:ff
rip add [abc.def.ghk.255] 30 1
rip merge on

domain addserver abc.def.32.98
domain suffix your.domain.edu.au.

ip ttl 64
tcp mss 1460
tcp window 11680

remote -s password
start smtp
start ftp
start echo
start discard
start finger
start rip
start remote
start telnet
The file called AUTOEXEC.NET initialises NET.EXE. Once initialised, NET.EXE will route all appropriate TCP/IP packets from the abc.def.ghk subnet to the abc.def.mnp subnet via the ISDN card and route packets it receives from the ISDN card to either the abc.def.ghk subnet or to the rest of the world via the abc.def.ghk.254 router.

The demand dialling and call control functions are performed by the ISDN adapter card as described later in this document.

The computer called longwire in figure 1 is described along with its configuration files.

Two different computers have acted as longwire. One version was an XT class machine with no hard disc, screen or keyboard and only a single 3.25 inch High Density floppy disk. Another version was a 386DX computer with 16 megabytes of memory other hardware similar to thinwire. For the bulk of the performance tests, this later version of longwire was used.

It is the configuration of XT version I describe here.

Figure 5 CONFIG.SYS from longwire

Files= 40
Buffers=30
STACKS=9,256
device=A:\protman.dos /i:A:\
device=A:\KNXISIS.DOS
rem device=A:\workgrp.sys
device=A:\dis_pkt.dos
Lastdrive=p:
This computer (longwire) boots under MS DOS 6.2 and loads network software similar to that in thinwire. Since disk space is very scarce on longwire, only the minimum required files are on the disk.

Figure 6 AUTOEXEC.BAT from longwire

@Echo off
Prompt $p$g
call a:\isdnws\bin\iws
net start
wd8003e -n -d -w 0x79 2 0x240 0xca00
:loop
a:
cd \nos
net -d a:\nos
if exist a:\stop goto stopit
goto loop
:stopit
See the comments that follow figure 3 for a commentary on the function of AUTOEXEC.NET. Since longwire has no screen or keyboard, remote management is the only easy way to re-configure this computer.

Figure 7 AUTOEXEC.NET from thinwire

hostname longwire.your.domain.edu.au
ip address [abc.def.mnp.ghk]
ip address

#ISIS ISDN
attach packet 0x7A pk0 5 1500
#WD8003
attach packet 0x79 pk1 5 1500

route add [abc.def.mnp.0/24] pk1
route add default pk0 [abc.def.ghk.mnp] 1
route add [abc.def.ghk.mnp] pk0

arp add [abc.def.mnp.255] ether ff:ff:ff:ff:ff:ff
rip merge on

domain addserver abc.def.32.98
domain addserver abc.def.1.99
domain suffix your.domain.edu.au

ip ttl 64
tcp mss 1460
tcp window 11680

remote -s password
start ftp
start echo
start discard
start rip
start remote
start telnet
The initialisation script listed in figure 7, will configure the program NET.EXE, the network operating system (NOS) written by KA9Q, as a TCP/IP router. NET.EXE will route packets, for any node other than those for the abc.def.mnp subnet, via the ISDN card to abc.def.ghk.mnp for further disposition.

4. Configure the ISDN cards

Step 3, installation, above was a long detailed discussion of the installation of the computers and operating system for the router function. That software works with a variety of hardware as a router. NET.EXE has no special code in it which would allow ISDN call control. Research has been unable to determine any standards for ISDN call control in the PC environment.

In this section of the installation instructions, a brief description of the call control functions in the ISIS ISDN Adapter Card from Network Designers is given.

This card has a V50 processor on it. The card has software and a configuration data base down loaded by the IWS.BAT batch file (see figure 3 and 6). Incidentally, the card interface software then only occupies a very small portion of PC memory.

The data base includes security features such as the telephone numbers from which calls may be accepted (assuming calling line identification data is available). The station names of stations from which calls may be accepted. The passwords of stations from which calls may be accepted.

The data base also includes out going call data such as the telephone number to call when a packet for a particular IP address needs to be sent. The number of channels (1 or 2) to be used for the call. Weather ISDN card based compression should be used on the call. Weather the call should be shut down and at what level of data flow that should occur.

The automatic call establishment and shut-down over ISDN is very quick. Telecom claims a new call can be placed in under 300 milliseconds.

There are problems with automatic call establishment, for example mail sent to a non existent node, in the present case say abc.def.mnp.33, will cause continuous calls to made for say three days before the mailer decides the mail can not be delivered. For this reason some card manufacturers have chosen to keep call control and data delivery functions separated.

The ISIS ISDN card call management data base can be configured on a computer other than the router then sent to the router via FTP. The configuration management software is menu driven.

This ends the detailed description of the steps required to install the network described in figure 1.

C. Performance of the router

In this document there has been a summary of the results followed by a detailed description of the hardware and software configuration used.

Related documents to follow will detail the results of the 108 different file transfer tests performed, an analysis of the results to determine if the location of bottle-necks, the nature of the network file system tests and X windows tests, the features of the ISIS ISDN Adapter card and the features of three other cards available in Australia, and finally an analysis of the desirability of the features.

Please contact the author if you wish to be placed on the mailing list for the complete technical report contiaining these results.