(Read Why Structured Mesh Networks out perform other mesh architectures)
A mature and well
understood technique for building scalable wired networks is to split up
a wired network into smaller and more manageable sub-networks, each of which
operate independently. Switches discover and maintain information related to how
packets from devices (shown as triangles) need to be routed to reach their
destination.
When connected together switches form a network switch
stack. Each switch is responsible for its sub network, and the system is
both scalable and stable. Additionally, as compared to conventional wireless
mesh technology, there is no significant degradation with
each hop.
Wired Network
Switch Stacks preserves bandwidth - over multiple hops.
Conventional mesh cannot preserve bandwidth: Radio is a shared
medium - only one person can be "talking" at a time. As networks grow,
performance degrades rapidly as more clients join an Access Point (AP). The
AP's Basic Service Set (BSS) becomes unmanageable. Splitting up a large network
into smaller sub-groups is essential to maintain network performance. This is
not possible with single radio mesh nodes: the mesh nodes must share the same
channel to be able to communicate with each other!
The problem is
exacerbated in multi-hop topologies using one radio systems. In one radio units
everyone is on the same channel. Which means that every data packet received and
re-transmitted ("hopping") uses up twice the time than a single transmission.
Bandwidth is reduced to half with each hop in the network. Also, since radio is
a shared medium, near by radios have to stay silent when a re-transmission from
one hop to another hop (within the same BSS) occurs.
Conventional mesh networks do not scale well beyond 2-3
hops
Figure 2: Multiple channels "splits" up the network into
manageable sections (click to enlarge)
Structured Mesh Preserves Bandwidth In figure the backhaul
radios (blue) communicate on different channels, depicted by the different
colors of the dashed lines. Note also that the service radios (pink) are also
on different channels and in a different band (802.11b/g vs. 802.11a) as the
backhauls. Thus, backhaul paths do not interfere or contend with any of the
service radios and there are sufficient available channels (in 802.11a) to
ensure that the backhaul radios do not interference with each other.
The
two backhauls operate independently and their channels are allocated
automatically to minimize interference between service sets. Bandwidth
degradation effects endemic to single radios are eliminated - since each service
set operates independently and simultaneous send/receives are now
possible.
Structured
MeshTM uses separate backhaul radios to avoid bandwidth loss through
contention
Structured Mesh is a scalable
architecture: Structured Mesh is closer to a network switch stack
configuration than a conventional mesh. It splits up the wireless network into
smaller groups or Basic Service Sets (BSS), each of which is operating on a
non-interfering channel with other groups.
The tree-like structure that
forms for the Structured Mesh begins to resemble that of wired switch
stacks which provide stable, scalable network connectivity within the
Enterprise. Our Structured Mesh approach makes wireless systems look and behave
like a wired switch stack. There is no significant performance degradation with
multiple hops. Also, dynamic pipe thickness changes and channel allocation to
minimize external interferences are not possible with single radio
mesh.
Simultaneous "conversations" are now possible. Providing
bridging across sub networks, requires at least two radios operating on
non-interfering channels - it cannot be done with single radio mesh. With
multiple channels, the network can be split up into non-interfering sections
just like switch stacks work in wired networks. Switch stacks are a proven
approach for scalable network connectivity.
Structured MeshTM emulates the scalability of network
switch stacks.
Structured Mesh enables faster
routing: Enterprise class wired network
switches use an efficient tree structure for routing. In contrast, Ad hoc
Mesh manages a large routing table - generally O(n2) - both
system overhead and reaction time are higher. The Structured Mesh Tree structure
engenders a faster routing mechanism than ad hoc mesh.
Structured MeshTM Tree
Structure engenders mobility and fast routing.
Value Proposition for WISPs
Competing mesh technologies lack the ability to distribute bandwidth
over wide areas requiring multiple hops of the mesh backhaul. As a result, they
need to be "re-charged" every few hops - through an Ethernet link. Costs of
additional Ethernet links must be added to compare the overall deployment cost,
especially for large Hotspots and city-wide HotZones requiring many nodes (see
grids below).
In dense areas with many simultaneous accessing users per node, conventional
mesh cannot deliver better than "dialup" bandwidth beyond 3 hops. A city wide
wireless network therefore requires additional Ethernet links if each mesh is
limited to 2-3 hops.
Each Point to Point Ethernet link to the mesh adds
increased capital equipment expenses. Also, each Ethernet feed service adds to
the running cost of the network. For wide area, city wide deployments,
Structured Mesh is thus by far the most cost effective means of providing VOIP
and data coverage.
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