LATNET: Wireless Internet Access
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`8 Jun 97 - 4 Apr 05
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`WIRELESS INTERNET ACCESS in Latvia
`
`Guntis Barzdins (main contact person)
`Institute of Mathematics and Computer Science, UL
`Rainis blvd.29, Riga LV1459, LATVIA
`Phone +371 9206943, Fax +371 7 820153,
`E-mail guntis@mii.lu.lv
`
`John Tully
`Acasia Research
`Aizkraukles 23-514, Riga LV1006, LATVIA
`Phone +371 9204836, Fax +371 7 820467,
`E-mail tully@mii.lu.lv
`
`Table of Content
`
`z 1. Introduction
`z 2. What Spread Spectrum Radio is?
`z 3. What You can buy off the shelf?
`z 4. Wireless IP Access in Latvia
`z 4.1 Using JNOS for building a PC based router
`z 4.2 ARLAN Network Setup
`
`z
`
`4.3 WaveLAN Network Setup
`Simple Case
`Advanced Case
`z 4.4 Antennas, cables, connectors, amplifiers
`z 5. Conclusion
`
`Abstract
`
`This paper describes the experiences accumulated by the Latvian Research Network (LATNET) where
`wireless solutions for connecting to the Internet, have been used routinely since 1993.
`
`The transmission technology used in LATNET is based on spread spectrum wireless LAN adapters
`adjusted for Internet interconnection - the original antennas are replaced with high gain antennas
`installed on tall buildings around the city and PC based IP routing software (JNOS) is used to provide
`efficient point-to-multipoint connections and error correction.
`
`Besides describing LATNET's experiences, this paper also contains
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`LATNET: Wireless Internet Access
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`z a brief introduction to the underlying wireless technology,
`z licensing terms in different countries,
`z overview of several wireless products.
`
`The paper should be of interest to networkers of developing countries where communications
`infrastructure is weak and wireless communications are not over-regulated. Wireless IP networking
`might be a cost effective solution also in industrial areas of the world.
`
`Introduction
`
`Sending data over the wireless links has been a dream for many networkers over the years, especially in
`the countries where appropriate communications infrastructure is not available. Until recent time
`wireless data links really were only a dream for most of us, because available radio transmission
`technology was:
`
`z very expensive (high speed microwave links cost well above 10,000 USD),
`z individual frequency licence required for operation,
`z required lot of knowledge to assemble a working link (modulators, transceivers, antennas, etc.)
`
`Only a few years ago a completely new wireless data link technology arrived which has made building
`private wireless data links as simple as plugging a radio adapter card into PC and connecting this card to
`an antenna. The new technology operates at LAN speeds (up to 2Mb/s) at distances up to 45km (with
`direct line of sight), and costs around 800 USD for the necessary PC card and high gain antenna. And
`what is most attractive about the new technology - in many countries (USA, most European countries) it
`is that it does not require a licence for operation at low power and short distances (5 -10 km). What is
`this miracle technology? It is called simply "spread spectrum radio".
`
`Since its introduction to the market in early 1990's, the popularity of spread spectrum wireless data
`transmission has growing dynamically. Today wireless LANs are used in many university campuses to
`interconnect distant buildings, in banks, hospitals, warehouses, shops etc. In these places it has become
`as common as cordless telephones.
`
`In this paper we will describe in detail the usage of wireless technology for providing Internet access.
`The description is based on the experience gained in LATNET while setting up a big wireless Internet
`access network in Riga, the capital city of Latvia. The network started in 1993 when five University of
`Latvia departments scattered all around the city were connected by wireless links to the Internet. Since
`then the network has evolved significantly: now it provides Internet connectivity at aggregate speed of
`2Mb/s to more than 30 buildings in Riga and its suburbs. Four backbone network antennas are installed
`on two high buildings in the central part of city, each antenna capable to serve more than 20 connections
`in the radius of 15km. The distinct property of the Riga network is that radio links are set up in the
`point-to-multipoint mode which significantly reduces the cost of individual connections. The remarkable
`feature of the network is that it has been built using only standard wireless LAN equipment operating at
`both 900MHz and 2.4GHz frequencies. This means that the solutions used in Riga can easily be repeated
`anywhere else.
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`The paper is organised as follows.
`
`z Section two briefly describes the spread spectrum radio transmission principle and explains why
`it usually does not interfere with other radio transmissions. The licensing terms for various
`countries are considered.
`z Section three lists popular spread spectrum wireless data communication products which can be
`purchased "off the shelf." For small installations these off-the-shelf products might be all that you
`need.
`z Section four gives a more complete example, based on LATNET's experience in the city of Riga,
`of how the wireless data communication products can be used to build an Internet access network
`in a city environment.
`
`Spread Spectrum Radio
`
`Spread spectrum technology was developed for use by U.S. military to overcome the problem of
`intentional interference by hostile jamming and eavesdropping (espionage). The term "spread
`spectrum" arose from the characteristic broad spectral shape of the transmitted signal.
`
`The spreading techniques normally used can be divided into two families:
`
`z Frequency Hopping Spread Spectrum (FHSS)
`z Direct Sequence Spread Spectrum (DSSS).
`
`The first approach resists interference by jumping rapidly from frequency to frequency in a
`pseudorandom way. The receiving system has the same pseudorandom algorithm as the sender, and
`jumps simultaneously. The second approach (most famous) resists interference by mixing the data signal
`with a Pseudo Random Noise Code (PN-code). A PN-code is a noise-like sequence of chips valued 0
`and 1. The number of chips within one code is called the period of code. In the most simple case a
`complete PN-code is multiplied with a single data bit (see Figure 1) and thus the resulting signal
`bandwidth becomes much larger. Receiving system applies to coded signal the same PN-code and
`retrieves the data signal.
`
`The total signal power doesn't change during spreading, the Power Spectral Density decreases. The
`result is a signal that is essentially "buried" in the noise floor of the radio band, is extremely hard to
`detect, does not interfere with other services (like conventional AM and FM radios), and still passes a
`great bandwidth of data (due to much higher than usual bandwidth occupancy). However the Gaussian
`Noise level is increasing.
`
`Figure 1. Direct Sequence Spread Spectrum signal components
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`The receiver examines the bandwidth of the spread signal, and correlates the data (despreads it). The
`process of correlation is symmetric to spreading and causes any other signals received to be spread as
`the wanted signal is de-spread (see Figure 2). This causes unwanted signals to be reduced to noise -
`allowing the same frequency to be reused many times within a given area. The possibility to multiplex
`users in the same frequency band by assigning them different spreading keys is called Code Division
`Multiple Access (CDMA).
`
`Figure 2. Interference reduction in Spread spectrum transmission
`
`The U.S. military de-classified spread spectrum technology in the mid-1980s. The FCC in 1985
`approved (47 Sec.15.257) three so called Industry, Medical & Science (ISM) bands for licence free use:
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`z 902-928MHz,
`z 2.400-2.4835GHz,
`z 5.725-5.850GHz.
`
`These bands are used by microwave ovens, garage door openers, and also spread spectrum radios.
`
`FCC allows maximum 1 Watt of radio power, with up to 6 dB antenna for spread spectrum devices
`operating at ISM bands. Higher gain antennas may be used, with a corresponding reduction in transmit
`power. With appropriate outdoor antennas, and line of sight conditions, 40 mile paths are possible, with
`some types of spread spectrum radios. As these devices do use radio signal the devices themselves must
`be approved by the US Federal Communications Commission.
`
`The present situation in most of Europe is that 2.4-2.4835GHz use needs no license with ETSI
`(European Telecommunications Standards Institute) certified equipment. According to ETSI standard
`ETS 300 328, the effective radiated power from the antenna must not exceed 100mW which is
`significantly lower than allowed by FCC in U.S. The 902-928MHz band generally is not permitted,
`because 890-915MHz band in Europe has been allocated for GSM mobile telephony.
`
`In the developing world the situation will go country by country. Our experience has been that one way
`is to obtain a secondary license for use of the spectrum you desire to use (2.4GHz will be the easiest),
`with a stipulation that you will not interfere with the primary license holders transmissions. An example
`of this situation is in Latvia, where LATNET has a secondary licence for 902-928MHz band, while
`primary licence for 890-915MHz band belongs to GSM operator. Practice shows that low power spread
`spectrum wireless LAN adapters at 902-928MHz band do not interfere with GSM.
`
`Those who would like to learn more about spread spectrum radio, can check Spread spectrum home
`page on
`http://www.tapr.org/ss/other.html
`
`.
`
`What You can buy off the shelf?
`
`The wireless industry now offers a wide range of spread spectrum devices operating in the licence free
`ISM bands. Currently data rates from 1200 baud through 2Mb/s are available. Many hardware interfaces
`are available, including V.35, RS-530, Ethernet, T1, and RS-232. Here we will list the most popular
`series of these devices.
`
`z CYLINK Corporation is one of the pioneers in the ISM band spread spectrum device
`manufacturing and still is considered to be the best in this area. CYLINK manufactures the Airlink
`series of wireless modems for 902-928MHz (L-band) and 2.450-2.485GHz (S-band). The S-band
`modems have also ETSI certificate for licence free operation in most of Europe. The distances up
`to 45km (with direct line of sight and appropriate antennas) can be reached. The modems typically
`have synchronous V.35 interface and operate at speeds up to 512kb/s. The list price for different
`models is in the range 3000-5000USD.
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`For more information, check
`
`http://www.wolfe.net/~nts/cylink/cytop.html.
`
`z Free Wave Technologies, Inc. manufactures asynchronous 115.2kb/s modems with ordinary
`serial RS-232 interface operating in 902-928MHz band. The distances up to 30km (with direct
`line of sight and appropriate antennas) can be reached. The list price of the modem is around
`1300USD.
`
`For more information, check
`
`http://www.wolfe.net/~nts/freewave/freetop.html.
`
`z AT&T manufactures WaveLAN series of wireless LAN equipment: ISA, MCA, and PCMCIA
`adapters for PC, Access points for interconnecting wired and wireless LANs, wireless LAN
`bridges. WaveLAN is probably the most popular wireless LAN equipment today. Available are
`models for 902-928MHz and 2.4-2.4835GHz bands. The 2.4GHz model has ETSI certificate for
`licence free operation in most of Europe. The speed is 2Mb/s and distances up to 6km (with direct
`line of sight and appropriate antennas) can be reached reliably. Security in WaveLAN network is
`provided by network-id selection (16 thousand combinations) and optional DES chip. The list
`price for ISA adapter is around 600USD, Access Point around 1800USD, Wireless LAN bridge
`around 2500USD.
`
`For more information, check
`
`http://www.ncr.com:80/product/wavelan/.
`
`z Aironet Communications, Inc. manufactures ARLAN series of wireless LAN equipment: ISA
`and PCMCIA adapters for PC, Access points for interconnecting wired and wireless LANs,
`multipoint wireless LAN bridges. Available are models for 902-928MHz and 2.4-2.4835GHz
`bands. The 2.4GHz model has ETSI certificate for licence free operation in most of Europe.
`Modifications for licence free operation in other countries are available. The speeds up to 1Mb/s
`and distances up to 10km (with direct line of sight and appropriate antennas) can be reached
`reliably. The distinct feature of ARLAN is that already in hardware it incorporates special link
`level protocol for error correction, wireless inter-repeater routing, and roaming functionality. This
`protocol ensures that ARLAN network is as reliable as ordinary wired network and does not
`introduce any packet loss even at max. distances. Access point can be managed remotely via telnet
`protocol. Security in ARLAN network is provided by MAC address based access lists and
`network-id selection (16 million combinations). The list price for ISA adapter is around 900USD,
`Access Point around 1900USD, Wireless LAN bridge around 2600USD.
`
`For more information, check
`
`http://www.wolfe.net/~nts/aironet/airotop.html.
`
`All above mentioned hardware manufacturers provide also necessary software and manuals for
`installation and operation of the devices, as well as they sell separately high gain antennas and RF
`cables. Meanwhile many other companies provide better accessories - less expensive (but good)
`antennas and custom made cables. There are a number of companies which sell also their own LAN
`bridging software+hardware based on WaveLAN adapters: Persoft, C-SPEC, Solectek, KarlNet. For
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`CYLINK Airlink modems the LAN bridges are sold by CYLINK, while specialised IP routers are made
`by TAL Inc. Bilateral amplifiers for 915MHz and 2.4GHz bands sell Hyperamp Inc.
`
`For simple installations with point-to-point or few point-to-multipoint connections there is nothing
`easier than selecting one of the above mentioned "off the shelf" LAN bridging products (they come
`complete with antennas, cables, software, and hardware.) A very good overview of LAN bridging
`products by "Network Computing" can be found at
`http://192.216.191.71/techweb/nc/613/613f2.html.
`
`The above mentioned products are not specifically aimed for providing Internet connectivity - they are
`general purpose data links or wireless LAN bridges (although C-SPEC, KarlNet and TAL products
`provide also IP routing functionality). If wireless links are used solely for providing IP connectivity
`between the distant sites, then there is less expensive and more flexible solution available, described in
`the Wireless IP Access in Latvia.
`
`Finally it has to be mentioned that in near future we can expect new products entering the wireless
`market, as the technologies like IEEE 802.11 standard and ETSI HIPERLAN standard for wireless LAN
`will be finalised. These standards will permit development of competitive wireless LAN market,
`currently dominated by the proprietary products and protocols (this is why none of the above mentioned
`products will interoperate with others).
`
`Wireless IP Access in Latvia
`
`The goal of wireless Internet access network set up in capital of Latvia, Riga by LATNET is to provide
`Internet connectivity to various University of Latvia departments and other establishments scattered
`around the one million inhabitant city with a diameter of approximately 25km. Riga is on a plain without
`hills with several high (25 store) buildings in the central part (hotels, office buildings). Since
`international Internet connection for LATNET is over single 128kb/s line, then 64kb/s to individual sites
`is considered sufficient.
`
`From various spread spectrum hardware options (listed in Section 3) we chose to use wireless LAN,
`because:
`
`z Wireless LAN adapters inherently deliver high speed (around 1Mb/s),
`z In case of wireless LAN, one central node can "talk" to numerous "client" nodes simultaneously,
`thus requiring only one wireless adapter per connected client site (see Figure 3),
`z Distances up to 10km (from the centre of the city to perimeter) can be covered using available
`wireless LAN adapters with high gain omni-directional antennas in the centre and directional
`antennas at client sites,
`z Using wireless bridges it is not possible to provide sufficient isolation between the LANs of
`connected organisations; most of them will want an IP router on the border of their network. The
`least expensive IP router "on the market" is PC running some IP routing software. With LAN
`adapters such a router can deliver up to 2Mb/s throughput and simultaneously act as a gateway
`between wired and wireless network.
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`Figure 3. Point-to-multipoint wireless IP access network
`
`The wireless network for Internet access in Riga has been in operation three years now, since starting in
`1993. Actually two independent radio networks have been built (for comparison purposes) based on
`different hardware: WaveLAN at 915MHz and ARLAN at 2.4GHz.
`
`The WaveLAN 915MHz installation historically was the first. We have found it necessary to add link
`level error correction (LAP-B) in router software for WaveLAN installation, because in case of marginal
`radio signal quality at long distances, multipoint configuration, and heavy traffic load, a significant
`packet loss (>30%) is encountered. The random 30% packet loss deteriorates TCP/IP performance
`catastrophically. Meanwhile, after adding link level error correction the 30% packet loss causes only
`some speed reduction.
`
`The ARLAN 2.4GHz network installation was started in early 1995 because of two reasons: ARLAN
`2.4GHz is ETSI compliant and therefore will not cause licensing problems in long term, and ARLAN
`has built-in link level error correction, thus avoiding the need for error correction done by routers.
`ARLAN also has more sophisticated management and security features.
`
`As PC routing software was chosen JNOS - freeware software developed by ham packet radio
`community and freely available on the Internet. JNOS has originated from the famous KA9Q package
`developed by Phil Karn in 1990-1991. Actually there are many IP routing software options available for
`PC: any UNIX running on PC, Windows NT, Novell server, KA9Q, PCroute, etc. The main reasons for
`selecting JNOS were:
`
`z JNOS is freeware for non-commercial applications, source code is available on the Internet,
`z JNOS executable is very small and runs under DOS: no hard disk needed in router, 320kb
`bootable floppy and 640K RAM is sufficient,
`z JNOS supports IP subnetting,
`z JNOS supports link level LAP-B error correction (called "ax25 virtual circuit"),
`z JNOS has many useful additional features: ping, traceroute, telnet, ftp, IP tunnelling, IP filtering
`(for firewall installation), etc.
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`z JNOS can be configured remotely (through ftp and rebooting),
`z JNOS supports an integrated web server, SMTP and POP mail, BBS application.
`
`But these options consume much of the limited PC DOS resources when configured on the same PC as
`the router. Therefore in this paper we will consider only JNOS as a PC based router software.
`
`Finally we will give also short overview about cables, connectors, antennas, and amplifiers used with
`900MHz and 2.4GHz spread spectrum radio systems. The typical working distances for different setups
`are given.
`
`Using JNOS for building a PC based router
`
`JNOS (Johan Reinalda's Network Operating System) is one of the descendants of the famous KA9Q
`software developed by Phil Karn primarily for ham packet radio use, but afterwards widely used also for
`IP routing in other circumstances. Ham packet radio networks were initially low-speed (1.2kb/s) and
`very congested and unreliable. This lead to the reliable link AX.25 protocol (a derivative of X.25) for
`the encapsulated support of IP in wireless links (we will use this feature in advanced setup of WaveLAN
`network). Compared to original KA9Q software, JNOS has many more features and also is more
`reliable. You can download the latest version of JNOS from
`ftp://ftp.ucsd.edu/hamradio/packet/tcpip/jnos
`
`.
`
`You must download three files (version numbers may change):
`
`z jnos110k.exe - JNOS executable for 8086 processor (JNOS is a single .exe file!),
`z jnos110k.zip - JNOS source code (You will need a supported compiler, e.g. Borland C 3.1, to use
`this code. Alternatively you can make your own CONFIG.H file and ask someone on the mailing
`list to compile it for you, for example, for 486 processor),
`z docs110.zip - full JNOS documentation with lot of examples.
`
`With JNOS being very well documented, there is no need to repeat it in this paper. Moreover, you can
`subscribe to JNOS mailing list at
`http://hydra.carleton.ca/cgi-bin/lwgate/NOS-BBS/
`
`We will only mention that JNOS has incredibly lot of features, including
`
`z ping,
`z traceroute (called 'hop check'),
`z telnet,
`z ftp,
`z SLIP,
`z PPP,
`z SMTP,
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`z POP,
`z NNTP,
`z RIP,
`z IP tunneling,
`z IP filtering,
`z remote configuration and rebooting,
`z lot of amateur packet radio specific stuff, etc.
`
`Meanwhile you can recompile JNOS only with the features which you really need, and get a small and
`efficient executable file. Here, to sense the flavour of JNOS, we will show only tiny example of how to
`configure JNOS as IP router between multiple packet driver interfaces (for example, wired Ethernet
`LAN adapter and wireless LAN adapter). To start an IP routing process on the PC, it is necessary to:
`
`1. Load the FTP Specification compliant packet drivers for both LAN interface cards. These drivers
`usually are supplied with LAN adapters on the diskette. Assume that the drivers are loaded at
`interrupts 0x60 and 0x62.
`2. Create the JNOS configuration file autoexec.net. In the configuration file must be configured
`interfaces (e1, e2 - name of interface, 8 - output buffer size in packets, 1500 - MTU of interface)
`and IP routing table:
`attach packet 0x60 e1 8 1500
`ifconfig e1 ipaddress 10.5.5.1
`ifconfig e1 netmask 0xffffff00
`attach packet 0x62 e2 8 1500
`ifconfig e2 ipaddress 10.5.6.1
`ifconfig e2 netmask 0xffffff00
`route add 10.5.8.0/24 e2 10.5.6.3
`route add default e1 10.5.5.2
`
`3. Start JNOS with this configuration file:
`jnos110k.exe autoexec.net
`
`This is all - now JNOS is routing the IP packets between the two interfaces. After starting JNOS, your
`PC screen gets into the monitor mode from where you can issue numerous JNOS commands to monitor
`the network (type "?" for the list of commands). Later you can always return to the monitor mode by
`pressing F10.
`
`There are a few things to remember about JNOS: the PC on which you run JNOS preferably must be
`dedicated for that, you may remove keyboard and screen from this PC when it is configured. No hard
`disk required in this PC - DOS, JNOS and configuration file will fit on floppy disk. JNOS will work on
`any PC, including 8086 with 640K of memory, while at least 386SX 40MHz is needed for full speed.
`JNOS can be configured with a maximum of 3 packet driver interfaces.
`
`ARLAN Network Setup
`
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`Setting up IP router network using ARLAN wireless LAN is very simple: ARLAN completely hides the
`radio "visibility/invisibility" and packet loss problems from the user, therefore regardless of the actual
`topology of radio links, the whole wireless network to the user appears as one long Ethernet cable. This
`property is achieved by employing already in the ARLAN hardware the link level cell routing between
`repeaters, and cell acknowledging and retransmission. The only price for this simplicity of use is higher
`cost of ARLAN (compared to WaveLAN) and lower (but guaranteed!) throughput.
`
`To set up the ARLAN network, you must use ARLAN 630 Access Point for the central site (Access
`Point is a "transparent" device that connects two medias: wireless LAN and wired Ethernet),and
`ARLAN 655 ISA adapters mounted in PC routers for the client sites (see Figure 4). ARLAN 655 ISA
`adaters normally do not communicate directly, but all communication between ISA adaters goes through
`the central ARLAN 630 Access Point. The distinct property of ARLAN is that several Access Points can
`be used to cover larger area; the Access Points themself can be interconnected through wired Ethernet
`interfaces, or over radio, if one Access Point can "see" another Access Point. In this way it is possible to
`use an Access Point as a radio repeater to extend the range of wireless communication.
`
`Figure 4. ARLAN 630 Access Point and ARLAN 655 ISA adapter
`
`All ARLAN devices come complete with good manuals and utilities for set-up and testing of radio
`connectivity. To set up ARLAN devices, in the simplest case you have to configure only three
`parameters: bitrate, frequency, and network-id. ARLAN 630 Access Point can be configured locally
`through terminal, or remotely over telnet. ARLAN 655 ISA cards are configured through pkt.ini file
`used by packet driver. Once radio connectivity between the devices has been established, you can forget
`about ARLAN being a wireless network. In the PC router containing ARLAN 655 ISA and ordinary
`wired Ethernet adapter, load the packet drivers for both adapters and run the JNOS with a similar setup
`as shown in the previous section. Adjust the IP routing as necessary.
`
`There is one thing to be careful about ARLAN - there are ARLAN modifications for Europe, USA,
`Japan etc., which have slightly different frequency sets - modifications for different regions generally
`will not interoperate!
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`WaveLAN Network Setup
`(Simple Case)
`
`Setting up WaveLAN based wireless network is quite different from that described for ARLAN. The
`basic difference is that WaveLAN has no link level protocol, except CSMA/CA (Carrier Sense Multiple
`Access with Collision Avoidance, similar to CSMA/CD used by wired Ethernet) to avoid too many
`collisions and packet losses due to simultaneous transmissions. WaveLAN has no packet forwarding, or
`acknowledging/retransmission functionality. This means that the WaveLAN based wireless network
`behaves as one long Ethernet cable on which some stations "see" each other, but others don't (depending
`on the radio "visibility" between the stations); significant packet loss can occur in case of weak signal,
`radio interference, or network congestion.
`
`In WaveLAN based network, WaveLAN ISA adapter(see Figure 5) equipped stations communicate
`peer-to-peer. Although there is available also WaveLAN Access Point which connects transparently
`wired network to wireless network, it passes packets only from wired network to wireless network and
`vice versa. WaveLAN Access Point never passes packets from one wireless station to another wireless
`station (if there is such need, the packets must be routed by the JNOS software). This also means that
`WaveLAN Access Point cannot be used as radio repeater to increase the range of wireless
`communication (as it was in case of ARLAN). In most cases WaveLAN Access Point has no use for
`providing wireless IP connectivity.
`
`Figure 5. WaveLAN ISA wireless LAN adapter
`
`Despite all of the above mentioned limitations, the WaveLAN still is a highly useful device for
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`providing IP connectivity, if used properly. Besides other things, WaveLAN is twice less expensive than
`ARLAN and at short distances delivers higher speeds (2Mb/s).
`
`Setting up IP routing in WaveLAN wireless network is similar to ARLAN case, except that there is no
`central Access Point - all WaveLAN nodes communicate peer-to-peer. First, using utilities supplied with
`WaveLAN ISA adapter, you must make sure that radio connectivity between the necessary sites has
`been established (for WaveLAN there is only one parameter to configure - network-id). One should use
`the test utility supplied with WaveLAN, which provides a realtime graphic display of signal level,
`packet loss, and link reliability. After performing these end to end tests, in each PC router containing
`WaveLAN ISA adapter and wired Ethernet adapter, load the packet drivers for both and run the JNOS as
`described previously.
`
`If you have a portable PC, the PCMCIA WaveLAN adapter is a very valuable tool for surveying
`proposed sites and troubleshooting links and software configurations. Unfortunately, you cannot connect
`an external antenna to this adapter.
`
`There are several things to remember while setting up WaveLAN wireless IP network:
`
`z Since in a WaveLAN wireless network all nodes are "equal" and communicate peer-to-peer, you
`must make sure that between nodes where you configure IP packet forwarding, there is actual
`radio connectivity (in WaveLAN network the facts that A can communicate to B, and B can
`communicate to C, does not imply that A can communicate to C).
`z Use only static IP routing with WaveLAN (do not use RIP). Due to peer-to-peer communication
`nature of WaveLAN, RIP may select the communication paths with low pure radio connectivity.
`Static routing also increases the security of the wireless network.
`z WaveLAN adapters come without a packet driver - only ODI and NDIS drivers are supplied on
`the accompanying diskette. You must use an ODI-to-Packet or NDIS-to-Packet driver shims
`(freely available on the Internet) to convert to packet driver interface for WaveLAN ISA adapter.
`Although there exist self-made packet drivers for WaveLAN, our experience is that an ODI-to-
`Packet shim is more reliable at heavy loads.
`z In a multipoint WaveLAN configuration, at a heavy network load, significant packet loss may be
`encountered (>30%). Such situation must be avoided in IP networks, because although TCP
`protocol is supposed to cope with packet loss, in case of this high random packet loss the
`performance of most applications drops catastrophically.
`
`WaveLAN Network Setup
`(Advanced Case)
`
`Advanced WaveLAN setup deals with two problems (which in case of ARLAN are solved already in the
`ARLAN hardware):
`
`z Packet delivery acknowledgement and retransmission. This allows to deal with high packet loss
`encountered in heavy loaded multipoint WaveLAN networks.
`z Configuring a WaveLAN PC router to act similar to ARLAN Access Point: one node on the
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`wireless network can act as the central gateway through which other nodes communicate between
`each other.