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Clarify mesh vs other topologies (#136)

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12
arednNetworkDesign/channel_planning.rst
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Channel Planning Channel Planning
================ ================
The previous section identified the different channels in each frequency band which are available for AREDN |trade| networking. Devices on each side of a radio link must use the same frequency band, channel, channel width, and SSID. Beyond that requirement, however, you have quite a bit of flexibility to select the radio channels that will ensure the highest signal quality and throughput for your network. In a basic AREDN |trade| network with several nodes spread across a limited geographical area, all of the nodes may use the same band, channel, and channel width. This allows them to establish the mesh network and route data to any of the sites as needed. The previous section identified the different channels in each frequency band which are available for AREDN |trade| networking. Devices on each side of a radio link must use the same frequency band, channel, channel width, and SSID. Beyond that requirement, however, you have quite a bit of flexibility to select the radio channels that will ensure the highest signal quality and throughput for your network. In a basic AREDN |trade| network with several nodes spread across a limited geographical area, all of the nodes may use the same band, channel, and channel width. This allows them to establish network routing to any of the sites as needed.
However, as more nodes join the network or when several nodes are :abbr:`collocated (same physical site)` and share the same channel, it is possible for overall network performance to degrade. In order for an AREDN |trade| network to scale up in size and complexity, frequency coordination and channel planning become increasingly important. To plan for future growth, mesh groups may need to partition network traffic by allocating channels for specific areas or types of links in order to ensure the network will be able to support the expected services. However, as more nodes join the network or when several nodes are :abbr:`collocated (same physical site)` and share the same channel, it is possible for overall network performance to degrade. In order for an AREDN |trade| network to scale up in size and complexity, frequency coordination and channel planning become increasingly important. To plan for future growth, local AREDN |trade| groups may need to partition use different network topologies and to allocate different channels for specific geographic areas or types of links in order to ensure the network will be able to support the expected services.
Wireless Network Operation Wireless Network Operation
-------------------------- --------------------------
A wireless network is a shared half-duplex medium on which only one station at a time should transmit. In that sense wireless operations are analogous to other types of radio transmissions. If two stations key up their transmitters at the same time, they will interfere with each other to the extent that neither of them will receive the other's message. That is why net control procedures are implemented to ensure controlled access to a radio channel during emergency communication. A wireless network is a shared half-duplex medium on which only one station at a time should transmit. In that sense wireless operations are analogous to other types of radio transmissions. If two stations key up their transmitters at the same time, they will interfere with each other to the extent that neither of them will receive the other's message. That is why net control procedures are implemented to ensure controlled access to a radio channel during emergency communication.
AREDN |trade| firmware automatically mediates station access to the wireless medium by implementing `IEEE 802.11a/b/g/n <https://en.wikipedia.org/wiki/IEEE_802.11n-2009>`_ standards and `Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA) <https://en.wikipedia.org/wiki/Carrier-sense_multiple_access>`_. This listen-before-talk technology helps nodes to determine whether a channel is busy. Each node performs a *Clear Channel Assessment (CCA)* as well as using `Request to Send / Clear to Send (RTS/CTS) <https://en.wikipedia.org/wiki/IEEE_802.11_RTS/CTS>`_ messages to negotiate access to a channel. A negligible amount of network traffic is also required for `OLSR (Optimized Link State Routing protocol) <https://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol>`_ to maintain routes for the mesh network as a whole, but this OLSR traffic is a very small fraction of the total. AREDN |trade| firmware automatically mediates station access to the wireless medium by implementing `IEEE 802.11a/b/g/n <https://en.wikipedia.org/wiki/IEEE_802.11n-2009>`_ standards and `Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA) <https://en.wikipedia.org/wiki/Carrier-sense_multiple_access>`_. This listen-before-talk technology helps nodes to determine whether a channel is busy. Each node performs a *Clear Channel Assessment (CCA)* as well as using `Request to Send / Clear to Send (RTS/CTS) <https://en.wikipedia.org/wiki/IEEE_802.11_RTS/CTS>`_ messages to negotiate access to a channel. A negligible amount of network traffic is also required for `OLSR (Optimized Link State Routing protocol) <https://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol>`_ to maintain routes for the network as a whole, but this OLSR traffic is a very small fraction of the total.
In a single-channel wireless network, any node that needs to transmit will automatically coordinate with the other nodes for a clear channel. This is by design, but as more devices try to gain access to the same channel there is an increased potential for each node to wait longer for its chance to transmit. This can result in increased latency and decreased network throughput as the number of network nodes increases. In a single-channel wireless network, any node that needs to transmit will automatically coordinate with the other nodes for a clear channel. This is by design, but as more devices try to gain access to the same channel there is an increased potential for each node to wait longer for its chance to transmit. This can result in increased latency and decreased network throughput as the number of network nodes increases.
Channel Contention Channel Contention
++++++++++++++++++ ++++++++++++++++++
The concept of *Overlapping Channel Interference* is illustrated on the right side of the following channel scan diagram. *Overlapping Channel Interference* is very serious, but it can be eliminated by selecting non-overlapping channels for all devices accessing your mesh network. A second issue related to how wireless networks operate is illustrated on the left side of the diagram. It is commonly called *Co-channel Interference* but is more accurately described as *Co-channel Contention* or *Co-channel Cooperation*. The concept of *Overlapping Channel Interference* is illustrated on the right side of the following channel scan diagram. *Overlapping Channel Interference* is very serious, but it can be eliminated by selecting non-overlapping channels for all of the devices accessing your network. A second issue related to how wireless networks operate is illustrated on the left side of the diagram. It is commonly called *Co-channel Interference* but is more accurately described as *Co-channel Contention* or *Co-channel Cooperation*.
.. image:: _images/cci-aci.png .. image:: _images/cci-aci.png
:alt: Co-Channel Contention :alt: Co-Channel Contention
@ -118,7 +118,7 @@ The AREDN |trade| web interface provides information that is helpful when aligni
Channel Planning Tips Channel Planning Tips
--------------------- ---------------------
.. sidebar:: Avoid Network Scalability Issues .. sidebar:: Network Scalability Tip
If there are two towers or cell coverage areas within range of each other, configure the nodes with different channels to avoid poor performance. If there are two towers or cell coverage areas within range of each other, configure the nodes with different channels to avoid poor performance.
@ -128,6 +128,6 @@ Based on the purpose for your network, try to create reliable paths to the locat
* Consider putting each local coverage area on its own channel to minimize the interaction between zones. Be sure to allow adequate RF separation between zones where channels are being reused. * Consider putting each local coverage area on its own channel to minimize the interaction between zones. Be sure to allow adequate RF separation between zones where channels are being reused.
* If you are installing long distance point-to-point links to connect mesh islands, be sure to use a separate band or channel for the backbone link. This type of link has a single purpose: to carry as much data as quickly as possible from one end to the other. Eliminate any type of channel contention so that these links can achieve high throughput. * If you are installing long distance point-to-point links to connect network islands, be sure to use a separate band or channel for the backbone link. This type of link has a single purpose: to carry as much data as quickly as possible from one end to the other. Eliminate any type of channel contention so that these links can achieve high throughput.
* Remember that a multi-hop path through the network must have good signal quality on each leg of the journey. You cannot expect adequate performance through a series of poor quality links. For example, if you traverse three links having :abbr:`LQ (Link Quality)` metrics of 65%, 45%, and 58%, your aggregate :abbr:`LQ (Link Quality)` will be 17% which is unusable. Ideally the aggregate :abbr:`LQ (Link Quality)` should be at least 80% to have a link that supports the applications and services you require. * Remember that a multi-hop path through the network must have good signal quality on each leg of the journey. You cannot expect adequate performance through a series of poor quality links. For example, if you traverse three links having :abbr:`LQ (Link Quality)` metrics of 65%, 45%, and 58%, your aggregate :abbr:`LQ (Link Quality)` will be 17% which is unusable. Ideally the aggregate :abbr:`LQ (Link Quality)` should be at least 80% to have a link that supports the applications and services you require.

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arednNetworkDesign/network_topology.rst
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Network Topologies Network Topologies
================== ==================
Every AREDN |trade| node is capable of automatically joining an AREDN |trade| mesh network which is operating with the same SSID, channel, and bandwidth. New nodes will each explore their surroundings by broadcasting their identity and listening for their neighbors' responses. Once nodes identify others within radio range, they share this information so that each node has a picture of the network topology. Periodic updates adjust the network routes based on changes in signal quality or loss of a link, allowing the network to adapt to changing conditions. Since there can be several possible routes between nodes, and since network disruptions typically effect only part of the network, this type of topology can provide redundancy for network links. Every AREDN |trade| node is capable of automatically joining an *ad hoc* mesh network which is operating with the same SSID, channel, and bandwidth. New nodes will each explore their surroundings by broadcasting their identity and listening for their neighbors' responses. Once nodes identify others within radio range, they share this information so that each node has a picture of the network topology. Periodic updates adjust the network routes based on changes in signal quality or loss of a link, allowing the network to adapt to changing conditions. Since there can be several possible routes between nodes, and since network disruptions typically effect only part of the network, a mesh topology can provide redundancy for network links.
.. image:: _images/mesh-topology.png .. image:: _images/mesh-topology.png
:alt: Mesh Topology :alt: Mesh Topology
:align: right :align: right
Every AREDN |trade| node within radio range of other nodes will be able to participate in the network to extend its reach, provide route redundancy, or host services needed on the network at large. This simple network topology may serve its purpose perfectly for a short-term network deployed in support of a local event, or even for more permanent communication between nodes which are always within radio range. However, as mentioned in the previous chapter, the most important consideration for you network design is *"What is the purpose for this particular network?"* The specific requirements of your mission should drive the design of your data network. Every AREDN |trade| node within radio range of other nodes will be able to participate in the network to extend its reach, provide route redundancy, or host services needed on the network at large. This simple mesh topology may serve its purpose perfectly for a short-term network deployed in support of a local event, or even for more permanent communication between nodes which are always within radio range. However, as mentioned in the previous chapter, the most important consideration for you network design is *"What is the purpose for this particular network?"* The specific requirements of your mission should drive the design of your data network.
Types of Topologies Types of Topologies
------------------- -------------------
Although AREDN |trade| nodes are capable of forming a simple mesh network topology, it is more common for operators to use other designs in order to accomplish their data communication goals. Typical network designs include Point-to-Point, Hub-and-Spoke, Tree or hybrid topologies. Although AREDN |trade| nodes are capable of forming a simple mesh network, it is more common for operators to use different topologies in order to accomplish their data communication goals in growing networks. Typical network designs include Point-to-Point, Hub-and-Spoke, Tree or hybrid topologies.
Point-to-Point Topology Point-to-Point Topology
Point-to-Point topologies are best suited for moving data between the far endpoints, potentially using one or more intermediate nodes in order to traverse different types of terrain or overcome obstacles in the network path. Point-to-Point topologies are best suited for moving data between the far endpoints, potentially using one or more intermediate nodes in order to traverse different types of terrain or to overcome obstacles in the network path.
.. image:: _images/point-to-point.png .. image:: _images/point-to-point.png
:alt: Point-to-Point Topology :alt: Point-to-Point Topology
@ -51,9 +51,9 @@ Backbone Links
As the name implies, these links form the backbone or superhighway along which large amounts of data can travel for long distances at relatively high speed. Typically backbone or "backhaul" links are permanent installations on mountain peaks, tall buildings, or high towers. They are usually point-to-point links with large high-gain antenna systems running on reliable power sources. In some cases these links are designed with redundant radios which help ensure path protection. Backbone links can operate over distances between 10 to 30+ miles. As the name implies, these links form the backbone or superhighway along which large amounts of data can travel for long distances at relatively high speed. Typically backbone or "backhaul" links are permanent installations on mountain peaks, tall buildings, or high towers. They are usually point-to-point links with large high-gain antenna systems running on reliable power sources. In some cases these links are designed with redundant radios which help ensure path protection. Backbone links can operate over distances between 10 to 30+ miles.
Relay Links Relay Links
Relay links bridge the gaps between endpoint nodes. Their primary purpose is to pass network data, but there may be cases where they also serve as mesh access nodes for users. Sometimes these links are called "mid-mile", "distribution", or "intermediate" nodes. They are usually installed on medium-height towers or buildings in order to achieve high signal quality with good line of sight to other relay nodes. Depending on conditions, intermediate links may operate over distances between 3 to 10+ miles. Relay links bridge the gaps between endpoint nodes. Their primary purpose is to pass data efficiently, but there may be cases where they also serve as network access points for users. Sometimes these links are called "mid-mile", "distribution", or "intermediate" nodes. They are usually installed on medium-height towers or buildings in order to achieve high signal quality with good line of sight to other relay or backbone nodes. Depending on conditions, intermediate links may operate over distances between 3 to 10+ miles.
Endpoint Links Endpoint Links
Endpoint links are used to connect destination nodes to the mesh network. Sometimes these links are called "last mile", "tactical", or "terminal" nodes. Usually these nodes serve either as the originator or the final destination for network traffic. Depending on local conditions, endpoint links typically operate over distances of 3 miles or less. Endpoint links are used to connect destination nodes to the network. Sometimes these links are called "last mile", "tactical", or "terminal" links. Usually the nodes at the far end will serve either as the originators or the final destinations for network traffic. Depending on local conditions, endpoint links typically operate over distances of 3 miles or less.
Different types of radio links may be needed to connect all of the nodes that are required in order to fulfill the purposes for your network. The ultimate goal of your network topology is to have a reliable data network that accomplishes its purpose for providing services to the intended destinations and users. Different types of radio links may be needed to connect all of the nodes that are required in order to fulfill the purposes for your network. The ultimate goal of your network topology is to have a reliable data network that accomplishes its purpose for providing services to the intended destinations and users.

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arednNetworkDesign/networking_overview.rst
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@ -7,9 +7,9 @@ This **Network Design Guide** will discuss some of the useful principles for cre
There are a variety of ways to interconnect AREDN |trade| nodes, but the most important question that should be answered is *"What is the purpose for this particular network?"* The specific requirements of your situation will drive the design of your data network. For example, consider the following issues. There are a variety of ways to interconnect AREDN |trade| nodes, but the most important question that should be answered is *"What is the purpose for this particular network?"* The specific requirements of your situation will drive the design of your data network. For example, consider the following issues.
Temporary or Permanent Temporary or Permanent
Is your network being deployed as a short-term communication mechanism, possibly to meet the needs of a day-long event or a training exercise? If so, then several amateur radio operators with portable nodes can quickly establish an *ad hoc* network with a specific set of services to meet the communication needs for that situation. Those nodes and computers can probably operate from portable batteries, without any external power dependencies for such a limited-time deployment. Is your network being deployed as a short-term communication mechanism, possibly to meet the needs of a day-long event or a training exercise? If so, then several amateur radio operators with portable nodes can quickly establish an *ad hoc* mesh network with a specific set of services to meet the communication needs for that situation. Those nodes and computers can probably operate from portable batteries, without any external power dependencies for such a limited-time deployment.
Is your network intended as a long-term or permanent infrastructure to serve the on-going communication needs of a local area or region? If so, then a more sophisticated network topology must be designed and constructed to meet those long-term requirements. More robust or ruggedized radio equipment may be necessary, and more reliable AC power or off-grid renewable energy resources will be required to ensure consistent operations. Is your network intended as a long-term or permanent infrastructure to serve the on-going communication needs of a local region? If so, then a more sophisticated network topology must be designed and constructed to meet those long-term requirements. More robust or ruggedized radio equipment may be necessary, and more reliable AC power or off-grid renewable energy resources will be required to ensure consistent operations.
Geography and Terrain Geography and Terrain
Where is data communication needed? Are there specific locations where network nodes are required? What level of :abbr:`RF (Radio Frequency)` coverage will be needed in order to reach those locations? The places that the network must reach will determine the number and position of AREDN |trade| nodes. Where is data communication needed? Are there specific locations where network nodes are required? What level of :abbr:`RF (Radio Frequency)` coverage will be needed in order to reach those locations? The places that the network must reach will determine the number and position of AREDN |trade| nodes.
@ -17,11 +17,11 @@ Geography and Terrain
What are the geographical characteristics of the area across which your data network will operate? Different types of terrain may require specific types of network connections in order to adequately cover the region over which data communications are needed. More demanding terrain may require a larger number of intermediate nodes or possibly larger higher-gain antenna systems and mounting structures. What are the geographical characteristics of the area across which your data network will operate? Different types of terrain may require specific types of network connections in order to adequately cover the region over which data communications are needed. More demanding terrain may require a larger number of intermediate nodes or possibly larger higher-gain antenna systems and mounting structures.
Expansion and Growth Expansion and Growth
Will your network need to expand or adapt to changing conditions over time? Mesh networks are ideally suited for *ad hoc* growth and least cost routing based on the availability of nodes. As more devices are added to the network, however, the topology becomes more complicated and data traffic may be routed through multiple "hops" in order to reach its intended destination. This could result in increased latency on the network, with some network segments becoming almost unusable if application response time thresholds cannot met. Will your network need to expand or adapt to changing conditions over time? Mesh networks are ideally suited for *ad hoc* growth and least cost routing based on the availability of nodes. As more devices are added to the network, however, a simple *ad hoc* mesh topology will not properly scale in size. It could result in increased latency on the network, with some network segments becoming almost unusable if application response time thresholds are exceeded. A growing network will probably require a different well-designed topology that routes data traffic efficiently in order to reach its intended destination.
Applications and Throughput Applications and Throughput
What network programs, applications, or services should be provided in order to fulfill the purpose for this network? Each application will generate a certain amount of data traffic, and some programs or services are more data-intensive than others. The network needs to be designed to adequately pass the traffic for the required applications. What network programs, applications, or services should be provided in order to fulfill the purpose for this network? Each application will generate a certain amount of data traffic, and some programs or services are more data-intensive than others. The network needs to be designed to adequately pass the traffic for the required applications.
How many simultaneous users will be generating network traffic at different times? As the number of users increases, the amount of data traversing the network will also increase. In addition, with an increasing number of nodes on the network there will be a corresponding increase in the amount of `OLSR (Optimized Link State Routing protocol) <https://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol>`_ traffic that is necessary to maintain the mesh network. An AREDN |trade| network should be designed to handle the expected workload. How many simultaneous users will be generating network traffic at different times? As the number of users increases, the amount of data traversing the network will also increase. In addition, with an increasing number of nodes on the network there will be a corresponding increase in the amount of `OLSR (Optimized Link State Routing protocol) <https://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol>`_ traffic that is necessary to maintain the network. An AREDN |trade| network should be designed to handle the expected workload.
With these issues in mind, it is always best to keep your network as simple as possible and to include only those services which are required. Be sure to design your network so that it accomplishes its mission and suits its intended purpose. With these issues in mind, it is always best to keep your network as simple as possible and to include only those services which are required. Be sure to design your network so that it accomplishes its mission and suits its intended purpose.