February 1st, 2001
There are a few ways two ways to approach this. The first is to roll our own infrastructure, the second, is to use the infrastructure that is being built around us. We'll address building our own infrastructure first, and the second approach will be discussed further into this document. 802.11 wireless ethernet devices have finally proliferated the market and are now in a price range within many people's grasp. Many support 1Mbit/sec and 2Mbit/sec data rates at a cost of under $100USD. Even 802.11b (11mbit/sec) NIC's can be purchased at prices under $150 US dollars. However this is changing every day and we are starting to see 802.11 Access Points that are under the 802.11 mark. One should not alienate non-802.11 wireless ethernet devices, as they can still be employed as point-to-point links, especially crossing a large distance, and Proxim ISA/PCI cards generally fit the bill. A very well written and maintained [Low-Cost Wireless How-to] describes how to modify Proxim cards to work over a greater distance inexpensively. Another non- 802.11 solution are the old wavelan 900Mhz and 2.4Ghz Wireless NIC (wNIC), which can be commonly purchased on ebay and other auction sites for around $80 US dollars. First some general descriptions of 802.11 hardware is in order. The major component is the Wireless STAtion (STA). These generally come in a PCMCIA (PCCARD) form factor however, I have heard of USB STA's entering the market. STA's are somewhat versatile in that they can be configured to operate in STA mode or Access Point(AP) mode. In STA mode the act as a client. In AP mode they act as a centeral server mode, allowing STAs to connect to them. Access Points can be a STA installed in a PC running specialized software, or can be a stand-alone unit with a wireless interface on one end, and an ethernet port on the other. STAs in the surrounding area connect to APs and APs connect to a backend Distribution Service(DS). The DS in Gnets case SHOULD be a wireless link as well. In traditional 802.11 networks the DS is the wired LAN. 802.11 can operate in two distinct modes. The first is Infrastructure mode, where there are STAs and APs, and STAs must communicate through an AP in order to participate in the network. The second is Ad Hoc mode, where STAs can talk to each other, and APs can act as relay points. Depending on the terrain and local situation Gnet may support either of these modes. We will mostly be using Infrastructure mode until custom software is written to handle automatic routing in dense areas. On to the generally network diagram. The basic 802.11 g.net installation of three nodes would be as follows:Cell 1 Cell 2 | | | directional directional | <- omni omni -> | | | | = | | = | V | <- omni V | |--------| / | \ |--------| | site 1 |--[ - - - - - - - | - - - - - - - -]-- | site 2 | |--------| \ | / |--------| = | | |---------| | <- omni | site 3 | | |---------| = | |-----| | | (^^--^-^) - ) ( Internet ) (_ - (_/----/ Key: omni = omni-directional vertical antenna directional = directional antenna (yagi, parabolic, etc.)Requisites: Requisites: All sites must be RADIO Line-of-Site(LoS). Optical LoS does not cut it alone. Read why this is the case [HERE]. Unfortunately, this generally requires participants to live on elevated geography or in top floor apartment buildings. The only time this is not the case, is when participants are less than 50m from each other. This is due to the fact that radio propagation in dense urban areas is difficult to predict. Multipath fading knife edge interference patters, and other propagation snares make it difficult to deploy reliable, long distance, low-power links. For this setup two wNIC's are required at each site. One handles the localized cell cloud, the other acts as a link to a multipoint site. The wNIC is used to provide cell coverage should be 802.11 based, as various vendor equipment conforming to the 802.11 standard can easily attach to the network. The point-to-point connections are not required to be 802.11. In many cases it may be better to use non-802.11 hardware lying around to prevent inadvertant interference and link degradation. [go into more depth about 802.11 - what 802.11b is, and that just because two cards are 802.11 compliant doesn't mean they can work together, as one can be DSSS and the other FHSS, also note that breezecom and wavelan don't play well together.] Description: A site is a PC running Linux and configured to use wNIC's. PCI/ISA wNIC's plug right into the motherboard I/O expansion bus. PCMCIA(PCcard) wNIC's will require a PCI<->PCMCIA board. These are relatively inexpensive and cost under $40USD. A site can also use an 802.11 Access Point(AP) as one of the wNIC's. The AP would be best employed by providing the cell cloud coverage, and not in Point-to-Multipoint links. However, these AP's can be very expensive, and can be difficult to manage as most management clients are written for Winblowz. Site 1,2,3 all support a cell through an omni antenna, set at a different freq. from what is used in the Point-to-Multipoint links. Site 3 can act as a multipoint link for other participants not at the greatest elevations. This can help people connect to others that are not LoS to each other. At least one of the sites must interconnect to the internet. A wired connection can be used to interconnect multipoint cells that do not enjoy radio LoS. This interconnection should be encrypted. This very generalized radio network model can be scaled out to a considerable size. Antenna: The configuration called for an omni-directional antenna and some type of directional antenna. Both can be obtained or constructed relatively inexpensively. [Plans for the construction of a high-wattage overkill 2.4GHz omni-directional antenna] (our design) [Plans for the construction of a lower-cost equal gain omni-directional antenna at 2.4GHz.] (our design) [Plans for the construction of a low-cost directional 2.4ghz antenna] (our design) [Sources to buy antenna's here] [Sources for coax here (LMR400, LMR200) How to get started: The first thing you should do is sweep your area for existing, open 802.11 networks. There is a nationwide 802.11 DSSS g.net frequency. The channel is 11. Always check this channel first for activity. If this frequency is not active in your area, establish at least one interface on this channel. Next, you should look for other networks in your area. The easiest way to do this is to use the [wlandump] utility, that works with a host of wireless NIC's based on the Harris/Symbol/Intersil original Prism chipset. The reason for this is two-fold. First, one must examine the RF landscape in your area so you can better choose an unused frequency. The second is to possibly use AP's and Ad-hoc networks that are configured to accept any STA associations. In the event that your searching reveals networks, you will need to determine what services the AP's are providing. Such as DHCP, or acting as a NAT proxy to the internet, or perhaps providing a proxy type connectivity, for example, via an http proxy. Some sites restrict association except from known MAC addresses. We do not advocate MAC spoofing in order to gain access to an unknown access point. If they have an access control list and you do not belong to that list, it will require you to masquerade as someone you are not. The idea here is to use existing open wavelan AP's as repeaters for gnet services. [Need to experiment here. Have to see how AP's treat non-dhcp'ed addresses. If it just re-broadcasts any traffic it hears like a hub, we are all set. I think this is the case.] Therefore, we can assign any STA to act as a gateway into the GNET network by setting it up as a router and allowing that machine to route between different 802.11 channels. +--------------------------+ | | | unknown AP | +---------------------------+ | | | | | AP1 +--------------------------+ | | | | G.Net AP | | | unknown AP to | | | | G.Net AP GW | AP3 | +-------------------| | | | AP2 | | | |--------------------+ | | +--------------------------+ Here AP2 will act as a gateway for the gnet STA's in AP1 to get to AP3. The STA's associated to AP1 use the machine in AP2 as the gateway. AP2 is setup to route packets out to AP3 for those in AP1. [need more examples of configurations in here] If you are the only person working in your local area, you will become the the primary contact for that state. When you contact the g.net coordinator, he will supply you with other people's email addresses that have inquired in a certain area. It is then up to you to coordinate with them to setup a wireless network. Start a mailing list and keep communication lines going. Nothing kills a project faster than a lack of communication. Recruit. Talk with people at Special Interest Groups (SIG's) (like a local Linux Users Group or computer society.) This network can be as open as we want as every participant is responsible for protecting thier content over gnet and out into the wired network. Go to Amateur Radio club meetings, you will be bound to find a few people interested in the concept. If they are interested in an AX.25 or a TCP/IP connection, perhaps something can be worked out in exchange for co-location at some repeater sites. Share resources. The network is only as good as it's coverage. If you are a bit less-strapped for cash, purchase some equipment and help dole it out to nodes to get it started. Un-manned locations work well for this type of roll-out. Once you start making connections and people setup some equipment you will soon find that others will be willing to join. It just takes a bit to get the proverbial ball rolling. Many people only have the capacity to buy a turn-key system, configure it once, and walk away. It takes a bit of work to get the system to this point, but I'm sure it is not an unreachable goal. And finally, let us know how your network is going, and share any information learned. For more information on individual components and configurations, please consult: [Station setup] (describe bare-bones site requirements, radio-linux) [Network Architecture] (describe routing and address assigning)