MD4250 Application in Video Surveillance and Perimeter Security 
MD4250 Two RadioMD4350 Three RadioMD4452 Four Radio Two DownlinksMD4454 Four Radio Four DownlinksMD4488 Four Radio Two AP radiosMD4355 Mobile Mesh NodeMD4455 Four Radio with Mobility ScannerUbiquiti Bullet, Mesh Enabled
Mesh Network applications often require a string-of-pearls formation where the end-to-end path is non line-of-site (NLOS). Additionally, there may be points along the path where sensor data needs to be collected. One typical such application is perimeter surveillance using remote video cameras mounted at regular intervals along the perimeter being surveyed 
Figure 1: Camera input may be wired in directly into Meshdynamics Ethernet Port IXP1 (right) 
A perimeter-surveillance deployment does not require the use of 2.4GHz AP radios for client access. The MD4250-AAxx is therefore the most suitable mesh node. IP cameras may be wired into the right-hand Ethernet port on the node, and directional antennas can be used on the uplink and downlink radios for more range between nodes.

If a 2.4GHz wireless IP camera is used in the deployment, the MD4350-AAIx will be needed in the line of mesh nodes to provide the AP to which the camera can associate. Otherwise the MD4250 is sufficient for wired camera input.

Figure 2: Dual Backhaul Root node converges data traffic from two branches 

Figure 2 depicts two string-of-pearls mesh chains “snakes” around the perimeter of an airport. The large blue box is  MD4452 "root" node with two backhaul downlinks to cover both directions - the  two string of pearls chains. Traffic from both chains converges via the Ethernet port connected to the root node. A MD4454 can support up to 4 such forks. 
The two radio, basic backhaul configuration comes in two flavors. MD4250-AAxx uses radios configured to operate in the 5GHz spectrum. MD4220-IIxx uses radios configured to operate in the 2.4 GHz spectrum.

When deciding whether to use 2.4GHz based products (4220) vs the 5.8GHz (4250) product, RF pollution must be considered. Wi-Fi 802.11b/g clients are 2.4GHz and will interfere with a 2.4GHz node-to-node (backhaul) link.

In addition, 802.11b clients - if attached to the 2.4GHz backhaul downlink will slow the performance of of the node-to-node link.

4220 mesh nodes thus should be limited in servicing few child nodes. On the positive side, 2.4 GHZ has about twice the range at 5GHz, so 4220 are preferable where range supersedes backhaul capacity.  4220 are also used when the nodes are edge based - that is no child nodes connected to them. [Image]

See Also:

1. Perimeter Security For Department of Homeland Security (DHS) Web Page
2. Tutorial on choosing Frame Rate etc for video camera, based on backhaul capacity  Video and Slides
3. Calculations of range based on radio settings and node placement examples. Mesh Network Layout Design
4. Backhaul Range   Access Point Range  and  Antenna Alignment. Range Calculations Related.