Point-to-point links typically provide an Internet connection where such access isn't otherwise available. One side of a point-to-point link will have an Internet connection, while the other uses the link to reach the Internet. If the main building has an unobstructed view of the remote site, a point-to-point connection can be used to link the two together. This can augment or even replace existing dial-up links. With proper antennas and clear line of sight, reliable point-to-point links in excess of thirty kilometers are possible.
Of course, once a single point-to-point connection has been made, more can be used to extend the network even further. If the remote building in our example is at the top of a tall hill, it may be able to see other important locations that can't be seen directly from the central campus. By installing another point-to-point link at the remote site, another node can join the network and make use of the central Internet connection.
Point-to-point links don't necessarily have to involve Internet access. Suppose you have to physically drive to a remote weather monitoring station, high in the hills, in order to collect the data which it records over time. You could connect the site with a point-to-point link, allowing data collection and monitoring to happen in realtime, without the need to actually travel to the site. Wireless networks can provide enough bandwidth to carry large amounts of data (including audio and video) between any two points that have a connection to each other, even if there is no direct connection to the Internet.
The next most commonly encountered network layout is point-tomultipoint. Whenever several nodes are talking to a central point of access, this is a point-to-multipoint application. The typical example of a point-to-multipoint layout is the use of a wireless access point that provides a connection to several laptops. The laptops do not communicate with each other directly, but must be in range of the access point in order to use the network.
Point-to-multipoint networking can also apply to an example at a university. Suppose the remote building on top of the hill is connected to the central campus with a point-to-point link. Rather than setting up several point-to-point links to distribute the Internet connection, a single antenna could be used that is visible from several remote buildings. This is a classic example of a wide area point (remote site on the hill) to multipoint (many buildings in the valley below) connection.
Using Repeaters - for long range connectivity
The most critical component to building long distance network links is line of sight (often abbreviated as LOS). Terrestrial microwave systems simply cannot tolerate large hills, trees, or other obstacles in the path of a long distance link. You must have a clear idea of the lay of the land between two points before you can determine if a link is even possible But even if there is a mountain between two points, remember that obstacles can sometimes be turned into assets. Mountains may block your signal, but assuming power can be provided they also make very good repeater sites. Repeaters are nodes that are configured to rebroadcast traffic that is not destined for the node itself. In a mesh network, every node is a repeater. In a traditional infrastructure network, nodes must be configured to pass along traffic to other nodes.
A repeater can use one or more wireless devices. When using a single radio (called a one-arm repeater), overall efficiency is slightly less than half of the available bandwidth, since the radio can either send or receive data, but never both at once. These devices are cheaper, simpler, and have lower power requirements. A repeater with two (or more) radio cards can operate all radios at full capacity, as long as they are each configured to use nonoverlapping channels. Of course, repeaters can also supply an Ethernet connection to provide local connectivity.
Typically, repeaters are used to overcome obstacles in the path of a long distance link. For example, there may be buildings in your path, but those buildings
contain people. Arrangements can often be worked out with building owners to provide bandwidth in exchange for roof rights and electricity. If the building owner isn't interested, tenants on high floors may be able to be persuaded to install equipment in a window.
If you can't go over or through an obstacle, you can often go around it. Rather than using a direct link, try a multi-hop approach to avoid the obstacle.