How to be an ISP:
Build your own hot spot
Build your own hot spot
By Jason Luther and Allen Fear
(March 6, 2003)
Free, ubiquitous Internet access may be just around the corner--literally. One of the most exciting aspects of wireless LAN technology lies in its potential for broadband sharing. Universities have been leading the way by providing wireless networks to students. Cities have begun to offer free Internet access zones in parks and shopping areas. Businesses are beginning to recognize that a free or subscription-based hot spot can be a very affordable, or even profitable, added service that they can offer to their customers. And private individuals have discovered that a hot spot is a great way to share resources with the neighborhood or the community. A loose patchwork of coverage for those with wireless-networking cards is taking shape across the world. The coverage is a long way from being seamless, but the number of hot spots is growing exponentially, and you too can add to the expanding patchwork of public Internet access by setting up your own hot spot.
(March 6, 2003)
What's a hot spot?
In general, a hot spot provides users unfettered access to the Internet via one or more wireless access points. In more technical terms, a hot spot serves one IP subnet and uses a single 802.11 extended service set (ESS). The cost for using a public or private hot spot can vary. For example, grassroots, community-run networks such as San Francisco's SF Wireless or New York's NYCwireless typically offer free Internet access, while co-ops and other organizations may charge membership fees to cover the cost of bandwidth and equipment.
In this article, we'll tell you how to set up your own hot spot, from determining your coverage area to installing and controlling access to your hot spot. But before we begin, make sure your ISP lets you share your Internet connection. To find out, check your ISP's acceptable-usage policy or give them a call. The Electronic Frontier Foundation also provides a list of wireless-friendly ISPs on its Web site.
Who you want to connect Where you want them to connect What your ISP's connection-sharing policy is for your service Which network resources on your network require protection from hot-spot users Required attention span: 1 hour or more (depending on the complexity of your setup)
Follow these five steps.
Step 1 |
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Determine hot-spot coverage:
The goal of a hot spot is to cover a public area with an 802.11 signal. Most of the decisions about how and where to mount your access point and what antenna to use will depend on your desired coverage area. For small areas close to the physical location of your access point, a standard off-the-shelf device such as the 3Com OfficeConnect wireless cable/DSL gateway or the more versatile dual-band D-Link AirPro DI-764 may fill your range requirements. If, however, you want to provide coverage to a municipal park a mile away, you will probably need to attach a more sensitive antenna and establish a line-of-site connection between your access point and the hot-spot location.
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| 802.11 | Operates at 2.4GHz; the lowest common denominator of the IEEE wireless LAN standards; provides bandwidth of only 1Mbps; equipment based on this older standard may be hard to find. | |||||
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| 802.11b | Operates at 2.4GHz; backward compatible with the older 802.11 standard; delivers bandwidth of up to 11Mbps; has the largest user base; a good choice for those interested in offering broad public access. | |||||
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| 802.11a | Operates at 5GHz; delivers bandwidth of up to 54Mbps; is not compatible with 2.4GHz systems; range is generally poorer than that of 802.11b; user base is still relatively small. | |||||
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| 802.11g | Operates at 2.4GHz; currently a draft standard awaiting ratification by the IEEE; delivers bandwidth of up to 54Mbps; backward compatible with 802.11b; we expect this standard to overtake 802.11b as the standard of choice. | |||||
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| Bluetooth | Operates at 2.4GHz; is a short-range, low-bandwidth solution designed to connect peripheral devices without the use of cables; is not compatible with any of the above standards; is not well suited for hot-spot deployment. | |||||
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Step 2 |
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 Click to enlarge Panel antenna.  Click to enlarge Yagi antenna. |
Choose an antenna type:
Antennae transmit signals in different ways. For example, if you want to share Internet access with your immediate neighbors, install an omni-directional antenna on your roof. If, however, you want to cover a specific location, such as the park across the street, a directional antenna works best. For faraway areas, you will need a high-gain antenna capable of bridging the gap.
High-gain antennas concentrate radiation in a certain direction, in much the same way that flashlights focus beams of light. A low-gain, omni-directional antenna spreads the signal in a 360-degree circular pattern, whereas a high-gain antenna focuses the signal in a particular direction, reducing the coverage from 360 degrees to 180 degrees or less. But because a high-gain antenna delivers a more-concentrated radiation pattern, it's capable of spanning a greater distance. For example, a 24dB-gain antenna may reduce your coverage to a 10-degree swath of space but will dramatically increase the sensitivity and range of your access point in one direction. Some of the more popular types of high-gain antennae include yagi, sector, and panel models. You can also make your own high-gain antenna out of a Pringles container or a soup can. |
Step 3 |
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 click to enlarge Assorted pigtails.  click to enlarge PC Card with antenna connector. |
Connect the antenna:
Once you've determined the appropriate antenna based on your desired coverage area, you'll need to attach it to your access point. While most antennas feature N or SMA connectors, access points can vary. Check the access point's documentation or the company's Web site for information on connector types. The NoCat Project also provides a list of the more common connector types.
To attach an external antenna to your access point, you generally need a pigtail, a short length of cable with connectors on each end. However, because a pigtail can introduce a significant amount of signal loss, make sure you keep it as short as possible. In fact, we recommend you mount your access point on the roof next to your antenna. For tips on how to weatherproof your access point, see Step 4. You can purchase antennae and pigtails from several Internet sources. Some Web sites sell FCC-certified setups, which means the antenna and the access point have been tested and certified to work together. We recommend purchasing an FCC-certified setup, especially for large-scale installations. |
Step 4 |
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Mount the antenna:
If your entire setup sits inside, mounting the antenna should prove fairly easy. But if your rig sits outside, you will need to put your access point into a weatherproof case. Just how weatherproof you need to make the enclosure depends on the local climate. There are both commercial and home-brew options available, ranging from simple to elaborate.
Providing power to an outdoor access point can be difficult. Some enterprise-level access points such as the AirPointPro deliver power over the unused wires in an Ethernet cable. To provide full power over Ethernet, you must use a power injector or a switch. You can also build a simple version for short runs with a few dollars' worth of parts.
Providing power to an outdoor access point can be difficult. Some enterprise-level access points such as the AirPointPro deliver power over the unused wires in an Ethernet cable. To provide full power over Ethernet, you must use a power injector or a switch. You can also build a simple version for short runs with a few dollars' worth of parts.
Step 5 |
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Lock down your network: The layout of your network will determine your ability to secure local computers. To understand the options available, consider the following diagram:
The wireless network (red) will most likely be a subnet in the RFC1918 space (addresses allocated for private interests, such as 192.168.1.0/24), so the gateway must perform NAT for wireless clients to reach the Internet.
The private network (green) is protected by a firewall and is accessible by only wired devices. The firewall lets you use the Internet while protecting your private network from malicious users. You don't need to worry about what passwords or data travel over this network (you can allow Windows file sharing, or you might telnet from one local machine to another) because only trusted people have physical access to the network. Depending on the type of firewall and the way your ISP assigns IP addresses, this network may or may not use NAT, and it may or may not be a part of the same IP network as the Internet network described below.
The Internet network (blue) is accessible from anywhere on the Internet, which means it uses globally routable IP addresses. You don't want to place any computers without strong host security or built-in firewalls onto this network.
Most home-network configurations can be described as a variation (and simplification) of this layout. Depending on the availability of public IP addresses and the equipment you have on hand, your network may be more or less complicated. For example, if you are using a power injector, you can combine the access point and the gateway into one box.
Alternatively, many home access points act as NAT routers instead of bridges. In this scenario, you would plug the access point directly into the Internet network (blue). You can also use a captive portal such as NoCatAuth to collect information and communicate whatever usage rules you would like to enforce as well as require a user login.
There are many combinations, but if you understand your own network layout, you will be able to build a secure hot-spot network in no time.
Once you have lit up your hot spot, you can let people know about it by listing it in a public hot-spot database. If you are offering your hot spot as a paid service in conjunction with a billing partner such as Boingo or Footloose Networks, you can list it with them. Those more inclined to hi-tech philanthropy that plan to offer their hot spots as free comunity services can list them in a hot-spot database and with your local community hot-spot group. A list of community networks is available at freenetworks.org.
Creating a hot spot is easy. In the simplest scenario, it requires nothing more than plugging in an access point, but be aware of the security risks. If your hot spot is connected to your home network, consider placing a firewall between them. And if you add antennae to your system, make sure that you are operating in accordance with FCC guidelines. Using an amplifier or the wrong antenna can wreak havoc with other networks and hot spots in the area, defeating your philanthropic goal of network sharing, so think before you hack.
click for larger view of diagram
The wireless network (red) will most likely be a subnet in the RFC1918 space (addresses allocated for private interests, such as 192.168.1.0/24), so the gateway must perform NAT for wireless clients to reach the Internet.
The private network (green) is protected by a firewall and is accessible by only wired devices. The firewall lets you use the Internet while protecting your private network from malicious users. You don't need to worry about what passwords or data travel over this network (you can allow Windows file sharing, or you might telnet from one local machine to another) because only trusted people have physical access to the network. Depending on the type of firewall and the way your ISP assigns IP addresses, this network may or may not use NAT, and it may or may not be a part of the same IP network as the Internet network described below.
The Internet network (blue) is accessible from anywhere on the Internet, which means it uses globally routable IP addresses. You don't want to place any computers without strong host security or built-in firewalls onto this network.
Most home-network configurations can be described as a variation (and simplification) of this layout. Depending on the availability of public IP addresses and the equipment you have on hand, your network may be more or less complicated. For example, if you are using a power injector, you can combine the access point and the gateway into one box.
Alternatively, many home access points act as NAT routers instead of bridges. In this scenario, you would plug the access point directly into the Internet network (blue). You can also use a captive portal such as NoCatAuth to collect information and communicate whatever usage rules you would like to enforce as well as require a user login.
There are many combinations, but if you understand your own network layout, you will be able to build a secure hot-spot network in no time.
Once you have lit up your hot spot, you can let people know about it by listing it in a public hot-spot database. If you are offering your hot spot as a paid service in conjunction with a billing partner such as Boingo or Footloose Networks, you can list it with them. Those more inclined to hi-tech philanthropy that plan to offer their hot spots as free comunity services can list them in a hot-spot database and with your local community hot-spot group. A list of community networks is available at freenetworks.org.
Creating a hot spot is easy. In the simplest scenario, it requires nothing more than plugging in an access point, but be aware of the security risks. If your hot spot is connected to your home network, consider placing a firewall between them. And if you add antennae to your system, make sure that you are operating in accordance with FCC guidelines. Using an amplifier or the wrong antenna can wreak havoc with other networks and hot spots in the area, defeating your philanthropic goal of network sharing, so think before you hack.
Jason Luther works as a project manager for AirWave Wireless and is cofounder of SF Wireless. He also operates a public hot spot in San Francisco's Inner Sunset neighborhood.
Allen Fear is R&D project manager for CNET Labs in San Francisco.
