Connectivity Providers Database

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, September 1981. [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. [15] CCITT Recommendation X.25, Interface between Data Terminal Equipment (DTE) and Data-Circuit Terminating Equipment (DCE) for Terminals Operating in the Packet Mode on Public Data Networks. [16] Advanced Micro Devices, Modem Technical Manual: modem Am79101, Am7910, Am7911, 1988. [17] Terry L. Fox, WB4JFI, AX.25 Amateur Packet-Radio Link-Layer Protocol version 2.0, American Radio Relay League, 1984. [18] Texas Instrument, Telecommunications Circuits: Transmission, Switching, Subscriber, and Transient Suppresors, Linear Products Data Book, 1991. [19] Raytheon, Linear Integrated Circuits, 1989. [20] M. Davidoff, K2UBC, The satellite experimenter's handbook, 2nd edition, American Radio Relay League, 1990. [21] H.E. Price, NK6K and J. Ward, G0/K8KA, "PACSAT Protocol Suite - an overview," 9th ARRL Computer Networking Conference, pp. 203-206, 1990.