The data layer, or layer 2, is the second layer of the seven-layer OSI model of
computer networking. This layer is the protocol layer that transfers data
between adjacent network nodes in a wide area network (WAN) or between nodes on
the same local area network (LAN) segment
The data link layer has three main functions:
MiMo Antenna Explained
MiMo is an acronym for "multi in multi out". Most wireless broadband modems sold these days contain MiMo technology. MiMo technology enables the device to dynamically set up many signal paths to optimise transmission and reception to the tower. When a 4G modem is used in a 4G coverage area and, if the 4G signal is strong enough, the modem will switch to MiMo mode usually resulting in higher data speed.
MIMO can be sub-divided into three main categories:
Precoding is multi-stream beamforming, in the narrowest definition. In more
general terms, it is considered to be all spatial processing that occurs at
the transmitter. In (single-stream) beamforming, the same signal is emitted
from each of the transmit antennas with appropriate phase and gain weighting
such that the signal power is maximized at the receiver input. The benefits
of beamforming are to increase the received signal gain – by making signals
emitted from different antennas add up constructively – and to reduce the
multipath fading effect. In line-of-sight propagation, beamforming results
in a well-defined directional pattern. However, conventional beams are not
a good analogy in cellular networks, which are mainly characterized by
multipath propagation. When the receiver has multiple antennas, the transmit
beamforming cannot simultaneously maximize the signal level at all of the
receive antennas, and precoding with multiple streams is often beneficial.
Note that precoding requires knowledge of channel state information (CSI) at
the transmitter and the receiver.
Spatial Multiplexing requires MIMO antenna configuration. In spatial multiplexing, a high-rate signal is split into multiple lower-rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures and the receiver has accurate CSI, it can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser of the number of antennas at the transmitter or receiver. Spatial multiplexing can be used without CSI at the transmitter, but can be combined with precoding if CSI is available. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access or multi-user MIMO, in which case CSI is required at the transmitter. The scheduling of receivers with different spatial signatures allows good separability.
Diversity Coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain from diversity coding. Diversity coding can be combined with spatial multiplexing when some channel knowledge is available at the transmitter.
It is imperative that all Ubiquiti™ devices mounted externally
on a pole/tower use a mechanism to ground the device
For added protection, it is recommend to install two GigE PoE surge protectors. Install the first surge protector within one meter of the M900 data port, and install the second surge protector at the ingress point of the location housing the wired network equipment.
Ethernet Surge Protector PoE+100M RJ-45 Model: ETH-SP $18.84 inc GST ea
Notes to the Order:
The length of Mt Cotton data cable has been estimates as half the height of the tower, assumed to be 34 meter(100 ft), plus 3 meters from tower to the earthed bulkhead of the radio shed. Measurements must be confirmed on site.
The length of the hosts site cabling is assumed to be 20 meters. Measurements must be confirmed on site.
The M900 comes with a AC mains to 24 volt power injector, I have specified an additional DC 9 to 36 volt power injector so the link can remain active during maions power outages. This will have to be supplied with 12 volts DC. I consider it good policy to rely upon the DC power source over mains.
I have specified factory manufactured data cables. This will eliminate the possability of faulty conectors, the requirement to source the correct crimp tool, and the waistage of purchasing 305 meter roll of cable. This will also ensure warranty conditions are met.
I have included a spare 30 meter data cable as backup in case of accidential damage to the cable at rigging time or in case the 20 meter cable proves too short.
A saving of $433 can be achieved by removing the antennas fron the UBWH order. The antennas can be purchase form Amazons Australia for $315.50 including delivery, or Mwave for $283.48 including Delivery (to be confirmed by telephone)
The earth bulkhead plate in the shed will have to provide for a data cable penetration and the affixing of a ETH-SP-G2 surge protection device.
Quote from Freenet Warehouse Pty Ltd
(Trading as UBWH Australia and UBIQUITI WAREHOUSE)
2 x Rocket M900 $731.12 4 x 1m Grounded, External CAT5e $94.00 2 x 20m Grounded, External CAT5e $89.10 4 x Ethernet Surge Protector $75.36 1 x 900 MHz 16 dBi MIMO Yagi *Pair* $319.31 1 x POE 9-36 DC to 24V DC $50.39 2 x Universal Arm Bracket $24.12 1 x 30m Grounded, External CAT5e $56.69 1 x 10m Grounded, External CAT5e $32.41 Sub-Total: $1,472.50 TNT (Road Express 5-12 Day by Road) $161.43 Loss/Damage Cover: $22.20 Included GST 10.0%: $150.56 Total: $1,656.13
2 x Rocket M900 $731.12 (with custom firmware that is compatible with the Australian Frequency and Power (EIRP) standards) 4 x 1m Grounded, External CAT5e $94.00 2 x 20m Grounded, External CAT5e $89.10 4 x Ethernet Surge Protector $75.36 1 x POE 9-36 DC to 24V DC $50.39 2 x Universal Arm Bracket $24.12 1 x 30m Grounded, External CAT5e $56.69 1 x 10m Grounded, External CAT5e $32.41 Sub-Total: $1,153.19 Aust Post (Regular with trracking) $52.67 Loss/Damage Cover: $17.40 Included GST 10.0%: $111.21 Total: $1,223.26
Trees (and any obstacle within the Fresnel Zone) affect RF in two ways:
The higher your frequency, the more opaque obstacles become; at "light"
frequencies obstacles are fully opaque. For maximum throughput, you must assure
you have a clear Fresnel Zone. If you do not have a clear Fresnel Zone,
then throughput will suffer.
5 GHz can actually get through a tree or two if signal levels are high enough. However, not with 100 Mbps throughput. For that, you need a 100% clear Fresnel Zone. 2 GHz can actually get through a grove of trees if signal levels are high enough. However, not with 100 Mbps throughput. For that, you need 100% clear Fresnel Zone.
900 MHz can actually get through a quarter mile of trees if you can get the radios high enough to assure the Fresnel Zone does not intersect the ground, even so you won't get 100 Mpbs throughput. For that, you need 100% clear Fresnel Zone.
How much loss is incurred impossible to precalculate due to the complex nature of RF ray analysis. If there is an incursion to the Fresnel Zone there is no authoritative way to predict how much of an impact it will have on throughput (and latency) or overall performance. Experimentation is the only solution.