From: owpurbo@nyquist.uwaterloo.ca
To: amcgee@netcom.com
Date: Tue, 20 Jul 93 14:14:23 -0400
AN ALTERNATIVE APPROACH TO BUILD LOW COST
TCP/IP-BASED WIDE AREA NETWORK IN INDONESIA
Onno W. Purbo
owpurbo@sunee.waterloo.edu
yc1dav@ve3.yc1dav.ampr.org
Department of Electrical and Computer Engineering
University of Waterloo
Waterloo, Ontario, CANADA N2L 3G1
ph: [519] 885-1211x2872 FAX: [519] 746-3077
on leave from:
Department of Electrical Engineering
Inter University Center on Microelectronics
Institute of Technology Bandung
Bandung 40132
INDONESIA
ABSTRACT
Based on a case study in the amateur radio in
Indonesia, an attempt to build a TCP/IP-based wide area
computer network is described. The network architecture
and its protocols as well as the low-cost hardware and
software designs are briefly reviewed. Experiments to
link the network into the international network are
reported. Unlike most Government's or private sector's
that adopts capital intensive high technology
information systems, ours rely heavily on the active
participation of the members. The use of a low-cost
PC-based equipments is proven to be significantly
reduced the overhead costs.
INTRODUCTION
The establishment of an infra-structure of information
systems plays an important role to encourage the socio-economics
and science-technology developments both at regional and national
levels. In view of the significant technological advances in
microelectronics, high performance computing equipments become
more affordable and widely use in most modern offices as well as
in daily household activities. Data communication networks have
become increasingly important to accommodate the need for
exchanging information among various Local Area Network (LAN) in
various organizations / institutions to participate in the socio-
economics as well as science-technology development of the
region.
In the case of Indonesia, to maintain an interconnection of
a small LAN (10-20 microcomputers) over our commercial X.25
packet switching network (SKDP) can easily take US$100-$200/month
not to mention the more advanced commercial data network such as
ISDN. Since net income of most civil servants is within the range
of US$50 to $100/month, to maintain such a LAN connection over
SKDP to form a Wide Area Network (WAN) is considered to be a
luxury. These situations have unfortunately impeded the
development of computer network in Indonesia, such as the
Indonesian Universities Network (UNINET) initiated by the Center
for Computer Science at University of Indonesia, Jakarta
(PUSILKOM-UI).
In this paper, an alternative approach to develop a low cost
WAN, a case study in the amateur radio in Indonesia, with
emphasis on the efforts to build prototypes as well as
experiments in packet radio network will be presented. Unlike
most government's and other private sectors' approach to adopt
highly centralized and capital intensive technology to build the
information system infra-structure, the amateur packet radio
network uses low-cost hardware and software equipments and is
decentralized in nature which relies heavily on the participation
of the members. In other words, each member may participate as a
router within the network to maintain the network integrity as
well as to push the overall overhead costs towards minimum. The
modem and radio transceiver may be obtained in the range of
US$200 to $500 with considerably lower operating costs than that
commercial X.25 PSN. Considering the advantages of such
technology in terms of overhead costs as well as
decentralization, it would be interesting to adopt such approach
to develop our very own low cost TCP/IP-based WAN in Indonesia
for private as well as informal sectors to elevate our socio-
economics as well as science-technology capacity based on a
cooperation among the members of the network.
This paper is organized as follows. In the second section,
the network architecture with emphasis in TCP/IP-based network
will be briefly reviewed. The packet radio network as an
alternative physical layer will be presented in section three.
Attempts to build hardware and software prototypes for packet
radio network at the Institute of Technology Bandung (ITB),
Indonesia will be reported in section four. In section five, some
results of our experiments in AX.25 and TCP/IP over amateur
packet radio network will be presented. Section six is a summary.
BRIEF REVIEW ON COMPUTER NETWORK ARCHITECTURE
Traditionally, the architecture of a computer network may be
represented by the famous 7 OSI protocol layers [1]. These
layers, in terms of its functionality from the lowest to the
highest level, are physical layer, link layer, network layer,
transport layer, session layer, presentation layer and
application layer. An end user does not have to understand how
these layers interacts to use the computer network. Various
application programs on the application layer of TCP/IP-based
network have been developed such as electronic mail (SMTP) [2],
remote login (TELNET) [3], file transfer (FTP) [4] and news
transfer (NNTP) [5]. Recently, more advanced protocols on the
application layer have been developed to maintain network
integrity as well as to monitor network performance such as
Simple Network Management Protocol (SNMP) [6] and Routing
Information Protocol (RIP) [7].
A simpler network architecture is used in the actual
implementation of TCP/IP-based computer network. Fig.1 shows the
major difference between TCP/IP architecture with respect to OSI
architecture in which the former has no session and presentation
layers. The computer's operating system such as UNIX used in most
TCP/IP platform will essentially perform the task of session and
presentation layer. The tasks of the other layer in TCP/IP
architecture are essentially the same as the corresponding layer
in OSI stack protocols.
An example of various protocols in network and transport
layer in TCP/IP family is shown in Fig. 2. Each of these
protocols has its own task to run the network properly. The major
protocols used in normal network operations are InterNet Protocol
(IP) [8] in the network layer and Transmission Control Protocol
(TCP) [9] in the transport layer. TCP is a connection-oriented
protocol that provide a reliable, full-duplex, byte stream for a
user process in layer 5 and above. IP is a connectionless-
oriented protocol that provides the packet delivery service for
the transport layer. IP uses Internet address known as IP
address. Address Resolution Protocol (ARP) [10] maps an Internet
address into hardware address used by the link layer protocol.
Reverse Address Resolution Protocol (RARP) [11] maps a hardware
address into an Internet address. Note that not all network
applications require the use of ARP and RARP. InterNet Control
Message Protocol (ICMP) [12] handles error and control
information between gateways and hosts. User Datagram Protocol
(UDP) [13], a connectionless protocol, is for user process in
layer 5 and above. However, unlike TCP, there is no guarantee
that UDP datagrams ever reach their intended destination.
The physical and link layer protocols used in a computer
network may vary depending on the form of the network. In most
high-speed LANs, 10Mbps Ethernet or Token Ring physical layer,
the IEEE 802 link layer protocol [14] is normally used. To form a
Wide Area Network, commercial packet switching network or even
ISDN may be used with various link layer protocol such as CCITT
X.25 [15]. The interconnection of various physical and link layer
protocols in various LAN / WAN to form a nation wide or even
worldwide computer network is transparent to the users by using
InterNet Protocol (IP) in TCP/IP-based WAN. The TCP/IP-based WAN
has currently emerged into worldwide computer network known as
InterNet which, to the best of our knowledge, includes Singapore
and Australia in the South East Asia region.
AMATEUR PACKET NETWORK AS AN ALTERNATIVE APPROACH
As mentioned in the previous section, the use of TCP/IP
protocols allows us to interconnect various computer network with
different data communication medium to form a WAN while keeping
the whole process transparent to the end users. Given the fact of
high overhead costs to use the current commercial data network in
Indonesia, packet radio network technology seems to give an ample
hope to build a low cost WAN in Indonesia while keeping a
reasonable performance. In this section, typical packet radio
equipments will be described.
As shown in Fig. 3, a typical packet radio station consists
of a microcomputer (most likely a PC clone) attached to a VHF/UHF
radio transceiver via a Terminal Node Controller (TNC). In more
advanced packet radio station especially for gateway or high-
speed trunk nodes, the layout of the station may be different to
accommodate the need of high speed operations. The physical layer
of the system consists of the radio transceiver and the modem
within the TNC.
A TNC is typically a dedicated 8 bit microprocessor system
with its own peripherals to perform AX.25 link layer protocol
tasks. It is connected to the microcomputer via a serial port and
to the radio transceiver via a modem, mostly Bell 202 AFSK modem
[16] (high speed operations may have different modulation
scheme). The AX.25 (Amateur X.25) protocol [17] is slightly
different than that of the CCITT X.25 used in most commercial
packet switching networks. The AX.25 protocol uses amateur radio
callsign in the address field and sub-station ID to allow several
stations using the same callsign. Furthermore, it has UI
(Unnumbered Information) frame for broadcast messages as well as
to carry messages using high level protocols, such as TCP/IP, in
more efficient manner.
The data transaction procedures used by the AX.25 protocol
is similar to CCITT X.25 protocol [17]. The information to be
sent is sliced into packets and sent over the radio and, finally,
assembled into the original information at the receiver node.
Poll-Final bit as well as other link control procedures, such as
Unnumbered Acknowledged (UA), Receiver Not Ready (RNR), Receiver
Ready (RR), Disconnect (DISC), Disconnected Mode (DM) etc., are
used to control the data flow [15][17]. Note that the data
transaction procedures may be ignored when UI frame is used with
TCP/IP data on top.
Using the ID bits in the header of AX.25 protocol, one can
identity the type of information carried by the AX.25 frame. In
this fashion, the TCP/IP protocol is carried on top of the AX.25
protocols. The microcomputer attached to the TNC decodes the
TCP/IP protocols as well as performs the network tasks. The LAN
interconnection over the radio can be easily done by attaching
both LAN card, such as Ethernet or Token Ring, and the TNC with
radio transceiver on the same microcomputer. Routing of the IP
frame is performed by the software running on PC to decide which
port to be sent.
ATTEMPTS TO BUILD HARDWARE AND SOFTWARE PROTOTYPES
In this section, we report our attempts at the Institute of
Technology Bandung (ITB) in Indonesia to develop and to adopt
various hardware and software prototypes for use in packet radio
network. Several research groups have been involved in the
development of the necessary equipments for packet radio network
which include the group of Prof. Dr. Iskandar Alisyahbana (EE
Dept ITB) especially on high speed packet radio prototypes as
well as joint research with VITA (Volunteers In Technical
Assistance) a Washington D.C. based NGO to use the Packet Radio
Satellite (PACSAT); the group of Dr. S. Nasserie and Dr. Adang
Suwandi (EE Dept ITB) especially to develop high-performance low-
speed packet radio prototypes as well as to study the
possibilities in adopting such approach on the Indonesia's geo-
stationary satellite PALAPA; the group of Dr. Kusmayanto Kadiman
(PIKSI-ITB) is working especially in TCP/IP-based Campus Wide
Network with possible interconnection over the radio; the group
at IUC Microelectronics ITB especially in TCP/IP-based IC design
center and the ITB-Amateur Radio Club (ARC) especially on
hardware prototypes for low end users. In terms of the hardware,
the prototypes may be classified into:
1. Prototypes of 1200 bps AFSK modems.
2. Prototypes of PC add-on TNC with AFSK modems.
3. Prototypes of 56Kbps high-speed packet radio systems.
In terms of software, we are currently using and enhancing the
existing public domain packet radio software which may be freely
used in amateur radio and educational institutions.
To provide an end user with a reasonable hardware necessary
to become a part of the packet radio network, a simple 1200 bps
AFSK modem is developed. This modem relies on the assumption that
PC MS-DOS machines can be easily obtained and, thus, all the
necessary AX.25 protocols are written in the form of software
running on the PC to utilize the computing power of the PC as
well as to reduce the hardware costs. Typical layout of the
hardware prototype is shown in Fig. 4. The internal PC timer is
utilized as a reference to form and to decode the packet signal
over the serial or the parallel port. The digital signal is then
converted into audio signal by an AFSK modem connected to the
serial or parallel ports which then can be fed into VHF or UHF
transceivers. Three different AFSK modem designs are possible to
use which include single chip modem TI TCM3105 [18] (adopted by
the ITB-Amateur Radio Club), single chip modem AMD Am7910 [16]
and a combination of XR2207-XR2211 [19] (adopted by Dr. S.
Nasserie's group). Typical cost to built such modem is in the
range of US$20-$40. This approach has been successfully
implemented and tested by our colleague Suryono Adisoemarta N5SNN
to perform low cost (less than US$40) TCP/IP operation from his
microcomputer over radio. The major problem in this approach, the
PC's computing power is tied up to perform AX.25 link layer
protocol tasks and, thus, difficult to perform high speed (faster
than 2400 bps) TCP/IP operations.
For advanced packet radio applications such as TCP/IP
operations, the PC computing power should be freed to perform
high-level networking tasks. This can be done by leaving lower
level protocol operations to a dedicated hardware. Prof. Iskandar
Alisyahbana and Dr. S.Nasserie group are adopting the High-Level
Data link Controller chip (HDLC) Intel 8273 to help performing
AX.25 link layer protocol function. Typical layout of the system
is shown in Fig. 5, the Intel 8273 is imbedded into an add-on
card on PC with an AFSK modem attached to it. Since the AX.25
protocol uses similar transaction procedures as the HDLC chip,
this is simplify the making of hardware and software for AX.25
operation. Furthermore, TCP/IP operation becomes easier with more
computing power on the PC may be dedicated to high-level
networking tasks.
As the network grows to interlink various high-speed LANs
into WAN, it is most likely the long-distance packet switching
backbone nodes will experiencing a heavy traffic which might
create network congestion. To accommodate the need for inter-city
high-speed packet radio trunk, Prof. Iskandar Alisyahbana's group
is currently working on 56Kbps high-speed packet radio system on
900MHz and 1.2GHz. In Fig. 6 is shown the typical diagram of the
system. It utilized special I/O card on PC to allow high-speed
data transfer from the modem directly to the PC-memory (RAM)
through DMA operations. An 56Kbps MSK RF modem operate at 29MHz
is adopted. A transverter from 29MHz to 900MHz or 1.2GHz is used
to translate the frequency into the actual operating frequency.
EXPERIMENTS ON AX.25 AND TCP/IP-BASED PACKET RADIO NETWORK
In this section, we report on our experiment on packet radio
network, an experiment which has been performed by the author
using his amateur radio station, licensed in Waterloo, Canada.
The equipment consists of a microcomputer connected to a Terminal
Node Controller in KISS (Keep It Simple Stupid) mode for AX.25
and TCP/IP operations on 144MHz VHF band.
In the amateur radio, the major Metropolitan Area Network
(MAN) frequencies are normally located in simplex band in 144MHz
and 435MHz running at 1200-2400bps. Intercity high-speed trunk
are normally running at 4800-9600bps and in some areas in the US
and Canada are running at 56Kbps or higher. For intercontinental
back bone, a slow 300-1200bps HF packet radio links are usually
used. However, more recently, as the Amateur Packet Radio
Satellites (PACSAT) becomes available some long distance traffics
are carried on-board the satellites.
In the case of the amateur packet radio network in
Indonesia, most MAN are concentrated in 435MHz UHF band and in
some areas in 144MHz VHF band. Most areas are served by a network
of Packet Radio Bulletin Board Systems (PBBS). 7 MHz and 14 MHz
band are normally used as the national and the international
backbone, respectively. Recently, a PACSAT gateway in Jakarta has
been established to perform long distance message forwarding over
the PACSAT. Unlike in most western nations, TCP/IP operations in
Indonesia are still very sporadic in terms of the stations and
operation time. Work is currently underway at ITB-ARC to link the
TCP/IP operation on the radio to the existing LAN. We hope the
establishment of LAN connection over the radio will give more
incentives to operate such high performance TCP/IP protocols over
the radio.
Experiments to deliver messages between North America and
Indonesia via amateur packet radio network have been performed by
the author in cooperation with several amateurs in Indonesia,
especially Robby Soebiakto YB1BG in Jakarta. In Indonesia, the
method to exchange long distance messages is still restricted to
PBBS only messages. Along the way to reach Indonesia, we have
exercised various methods to deliver the messages from Canada to
Indonesia which include direct delivery to the nearest PBBS;
piggy-backing over the InterNet and use TCP/IP network in amateur
radio to reach the PBBSes in Australia and Hawaii from which
messages are then carried over HF link to Indonesia.
Store-and-forward method is used to deliver messages in PBBS
network. In other words, messages are stored in a PBBS prior
forward it to the next PBBS and the process continue until it
reaches the destination. The PBBS program can perform as both
User Agent (UA) and Mail Transfer Agent (MTA) at the same time.
The author is currently in a regular e-mail contact via PBBS
network with Indonesia. The typical turn around time for
exchanging messages between Indonesia and Canada is about 2-4
days depending on the path and the condition of the network.
Other method to send long distance messages is via the
Amateur Packet Radio Satellite (PACSAT). PACSATs are tiny
satellites with polar orbit hovering at about 900km above the
earth. It is built and operated by the Amateur Satellite (AMSAT)
[20]. The on-board microcomputer has about 4 MB RAM disk for
store-and-forward services. A PACSAT ground station may access
PACSAT about four or five times a day with about 14 minutes
access window. At 9600bps with only 56 minutes access time per
day can move nearly 5.7 million bytes of data [21]. PACSAT
broadcast protocol on top the AX.25 link layer protocol is used
which enables PACSAT users to catch files being requested by
other users so as to increase the satellite's efficiency [21].
Figure 7. shows the path used by the author to send messages to
Indonesia via PACSAT. WA0PTV in Western New York area and YB0QC
in Jakarta act as PACSAT gateway nodes. To send the messages,
YC1DAV (author's machine) connects and delivers messages directly
to WA0PTV via the existing AX.25 as well as using the network
layer protocol. Subsequently, messages will be uploaded into
satellite by WA0PTV and in less than 12 hours will be retrieved
by YB0QC in Jakarta. The major problem faced by the PACSAT
gateways is no standard to perform third party message deliveries
and, thus, some processes have to be manually done by the
operators.
Especially in North America, Europe, Australia and Japan,
the TCP/IP-based network in amateur radio is quite active and
known as AMPRNet under the ampr.org domain in InterNet.
Experiments have been performed to operate a world-wide AMPRNet
TCP/IP network with Internet access via a AMPRNet - InterNet
gateway installed by the University of Waterloo Amateur Radio
Club VE3UOW. Similar approach has been installed and operated by
various university-based Amateur Radio Club as shown in Table 1.
The network topology is shown in Fig. 8. at.ve3uow.ampr.org
(also known as at.ve3uow.watstar.waterloo.edu in Internet) acts
as the packet radio - Internet gateway. at.ve3uow.ampr.org is
attached to a 10Mbps Token Ring LAN at University of Waterloo,
from which one may reach wider networks, such as Internet, and to
radio via its serial port connected to the local amateur packet
radio network. This approach has been used as a test-bed to
explore the possibility in interconnecting a low-speed network,
such as packet radio network, with a high-speed network, such as
Token Ring LAN as well as to enhance the software used by the
gateways and the AMPRNet nodes. The AMPRNet Domain Name Server in
InterNet has assisted other machines in InterNet to reach AMPRNet
hosts. This has enabled us in AMPRNet to communicate with
Internet hosts utilizing our AMPRNet-InterNet gateway as our MX
(mail exchanger) host. Furthermore, the existence of AMPRNet-
InterNet gateways allow AMPRNet hosts to reach distance AMPRNet
hosts by piggy-backing its IP frames over Internet and, thus,
long distance networking tasks may be done. TCP/IP protocols have
proven to be robust and reliable in low-speed and congested
packet radio network.
Table 1. Lists of AMPRNet-InterNet gateway
(as of 16 December 1991)
gateway location
at.ve3uow.ampr.org Waterloo, Canada
ve3ocr.ampr.org Ottawa, Canada
minnie.vk1xwt.ampr.org Canberra, Australia
vk3rum.ampr.org Melbourne, Australia
gw.af2j.ampr.org Pennsylvania, US
gw.n3eua.ampr.org Colorado, US
wa4ong.ampr.org Virginia, US
uhm.ampr.org Honolulu, Hawaii, US
hb9zz.ampr.org Switzerland
hamgate.wb5bbw.ampr.org Texas, US
ke9yq.ampr.org Chicago, Illinois, US
k9iu.ampr.org Indiana, US
wb9uus.ampr.org Illinois, US
Having experience of different environments of both high-
speed and low-speed TCP/IP-based network, in terms of robustness,
no significant differences is shown. Furthermore, in terms of
hardware and software technology, although most packet radio
equipments use late '80 microelectronics, it is proven to be a
reliable and workable solution to expose remote areas such as
"Indonesia" into world wide computer information society.
SUMMARY
In this paper, we have reported the efforts to build the
hardware and software prototypes to support the development of
packet radio network in Indonesia as well as experiments to
explore the possibility in expanding the capability of our
current computer network without having to be dependent on any
single data communication service. It has been experimentally
proven that the packet radio technology is a reliable and
workable solution to built a low cost TCP/IP-based wide area
computer network to support the socio-economics as well as
science-technology development in Indonesia.
The microelectronics technology used in the packet radio is
not the state-of-the art technology such as FDDI and ISDN rather
a late '80 technology and, thus, easier to adopt and replicate
the hardware and software prototypes to provide a self-support in
the development of TCP/IP-based WAN. Furthermore, unlike other
capital intensive information technology such as ISDN, packet
radio technology is more low-profile and decentralized in nature
which relies heavily on the participatory actions of the member.
This enables us to develop a low-cost TCP/IP-based WAN in
Indonesia without having to depend entirely on the services
provided by any commercial data network. Since the total cost to
operate as well as to build packet radio network is much less
than that of maintaining connections via commercial data network,
we are convinced that this approach is favourable in support of
the development of TCP/IP-based WAN in Indonesia. We wish to see
Indonesia as part of the Internet in the next decades.
ACKNOWLEDGEMENTS
We wish to thank Robby Soebiakto YB1BG and Dwi YB0QC to
enable us in performing experiments on long distance message
deliveries as well as for exposing to the Amateur Packet Radio
Satellite (PACSAT). We wish to thank the University of Waterloo -
Amateur Radio Club VE3UOW to allow the author to perform
experiments in TCP/IP-based packet radio network. Furthermore,
thanks to Armein Langi VE4ARM, Suryono YG1QN/N5SNN, Tony AH6BW,
Marsudi YC3MR, Roger VE3RKS, Ralph VE3EUK, Peter VK3AVE, Ron
YC0DZA, Wirjono YC2BIE, Prof. Chapman (University of Wisconsin -
Madison), Prof. Iskandar Alisyahbana (ITB), Dr. Kusmayanto
Kadiman (PIKSI-ITB), Dr. S. Nasserie (ITB), Dr. Adang Suwandi
(ITB), the members of ITB-ARC and the members at PAU-Mikronet
(pau-mikro@eeserv.ee.umanitoba.ca) for their valuable comments
and encouragements during the course of the work.
The financial supports from the Indonesian Government as
well as the Canadian International Development Agency (CIDA)
through Canadian Bureau of International Education (CBIE) are
greatfully acknowledged.
REFERENCES
[1] W.R. Stevens, UNIX network programming, Prentice Hall, 1990.
[2] J. Postel, "Simple mail transfer protocol," RFC 821, August
1982.
[3] J. Postel and J. Reynolds, "Telnet protocol specification,"
RFC 854, May 1983.
[4] J. Postel and J. Reynolds, "File transfer protocol (FTP),"
RFC 959, October 1985.
[5] B. Kantor and P. Lapsley, "Network news transfer protocol,"
RFC 977, February 1986.
[6] J.D. Case, M. Fedor, M.L. Schoffstall, and C. Davin, "Simple
Network Management Protocol (SNMP)," RFC 1157, May 1990.
[7] C.L. Hedrick, "Routing Information Protocol," RFC 1058, June
1988.
[8] J. Postel ed., "Internet protocol," RFC 791, September 1981.
[9] J. Postel ed.,"Transmission control protocol," RFC 793,
September 1981.
[10] D.C. Plummer, "An ethernet address resolution protocol," RFC
826, November 1982.
[11] R. Finlayson, T. Mann, J. Mogul, and M. Theimer, "A reverse
address resolution protocol," RFC 903, June 1984.
[12] J. Postel, "Internet control message protocol," RFC 792,
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[13] J. Postel, "User datagram protocol," RFC 768, August 1980.
[14] W. Stallings, Handbook of computer communications standards:
local network standards, vol. 2, MacMillan Book, 1987.
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[19] Raytheon, Linear Integrated Circuits, 1989.
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[21] H.E. Price, NK6K and J. Ward, G0/K8KA, "PACSAT Protocol
Suite - an overview," 9th ARRL Computer Networking
Conference, pp. 203-206, 1990.
