Transcript Wireless MESH Networks

Wireless MESH
Networks
By: Tapu Ahmed
Marshall Grillos
Current Cellular Topology
Basic Layout
Problems with Current Design
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Single point of failure
Solution
When you have a single node failure in MESH topology, the other nodes can simply
“go around” to get to their neighbors.
Advantages to MESH
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Incredible amount of flexibility in session setup.
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All that is needed is a radio
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Radio acts as both transmitter and receiver
MESH networks can be extremely advantageous to small business owners.
Problems with MESH
Distance is the primary disadvantage of MESH
networks
Coverage area becomes a problem as well
Problems continued
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Routing Complexity
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You must dynamically locate your neighbors.
Battery-Life
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Mobiles must remain “on” for a wireless MESH
network to be useful.
Why not MESH Now?
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Shannon’s Law (Spectrum Capacity)
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Amount of throughput that can be achieved
depends on the level of interference.
If interference goes up, throughput goes down.
Mesh Protocols
802.11 Standard
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Most MESH operate on this standard since the
802.11 standard is by far the most widely
deployed in wireless LAN.
Thus it will contain: physical, MAC, and link
layer.
802.11 Basic design
Source
Destination
RTS
Data
CTS
Questions to consider:
•When to initiate a route request
•When and how to buffer packets during route discovery
•When to update the lifetime of an active route
ACK
AODV
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Ad-hoc On Demand Distance Vector
AODV is a reactive routing protocol.
 Routes to other nodes are determined only when
needed.
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Source
Node1
Node2
Destination
Hello
Route Request
Route Reply
Data
X
Route Error
AODV
Advantages:
Since the nodes can change in and out of the
network quickly, you will not run into dead ends
 Uses little memory
 Good for small applications
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Disadvantages
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Inefficient when there is a large number of routes
needed and for applications that cannot tolerate the
delay of route discovery.
TBRPF
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Topology Broadcast based on Reverse-Path
Forwarding
TBRPF is a proactive routing protocol.
 Each node is provided with the state of each link in
the network.
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Broadcast trees are updated automatically
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Creates a link-state design that has minimal
overhead.
TBRPF
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Advantages:
Improved efficiency
 Alternate paths immediately available. Helps the
quality of service.
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Disadvantages
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Better suited for larger applications
Extensions
Redundancy
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The meaning of “redundancy” in general network architecture is
a matter of degree and must be carefully specified.
To reach higher levels of redundancy, you may add an additional
line of fiber next to an existing one.
In a mesh network, the degree of redundancy is essentially a
function of node density.
A network can be deliberately over-designed for reliability simply
by adding extra nodes, so each device has two or more paths for
sending data.
It can additionally be achieved by increasing the number of
simultaneous connections a node may have.
Example, Simple vs. Complex Mesh
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A simple mesh network is one that requires
relationships between the nodes or devices on the
LAN.
Devices need not all directly connected for a simple
mesh
Complex Mesh (Pure Mesh or
Logical Mesh)
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In a complex mesh, all nodes
must be connected to all other
nodes.
The number of relationships in a
network can be represented by
the formula N(N-1) where N is
the number of devices in the
network.
A complex mesh is vastly more
redundant than a simple mesh.
This is often at the cost of
higher network overhead.
Mesh Networks
Security Issues
Another Mesh Example
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Dynamically configured and modified.
What implications on security?
Each node acts as a router and an end user.
Security Implications
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Security in data transmission (much more than
typical WLAN due to multiple hops over
wireless).
Actually sending packets over the air.
 Ensuring who’s receiving the packets is the intended
target.
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Security of Network Access
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Ensuring everyone on the network should be on the
network (user authentication).
User Authentication and Partial
Mesh
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Mesh exists outside
of WLAN
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Relies on WLAN
RADIUS servers
for Authentication
(much like WLINE
networks today)
What about pure Mesh
authentication?
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Each node must have all authentication data or
connectivity to an authentication agent.
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Generally multiple authentication agents must
exist for redundancy and efficiency (number of
hops).
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ASIC security can be implemented to have pure
hardware authentication of a device.
MeshDynamics suggests ASIC
Security and “Smart Cards”
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ASIC - Application-Specific Integrated Circuit: a very
large scale integrated circuit (a VLSI chip) designed for
a specific customer and function (often on the basis of
a Programmable Gate Array).
Security chip devised for one way authentication.
Used by Satellite TV Providers (DishNetworks,
DirecTV).
Used by American Express (American Express Blue).
ASIC Continued
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Security chip contains application specific
modifiable software for key decryption.
Card must be ‘activated’ in authentication server
to receive proper decryption keys.
Cards are easily changeable/upgradeable by
companies.
Removes the need for ‘login’ procedure.
Cards can be read by wireless units (PDA,
Laptop, etc).
Secure Data Transmission - WPA
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Wi-Fi Protected Access
WPA is the Wi-Fi Alliance’s new security standard that
supersedes WEP (wired equivalent privacy). WPA is based on an
early version of the IEEE 802.11i standard.
WPA upgrades WEP encryption with a stronger cipher,
Temporal Key Integrity Protocol (TKIP) – timed keys, that fixes
known vulnerabilities in the WEP encryption algorithm.
WPA also introduces stronger authentication using RADIUS as
well as port-based access control based on IEEE 802.1x.
WPA contributes to network access control and secure data
transmission.
Modern Day
Applications of Mesh
MeshDynamics Offers Three-Radio
Mesh Network Solution
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From neighborhoods up to citywide coverage
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Services Include:
Mobile Data, VoIP, and Public Safety Networks
U.S. Military
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The Pentagon, about a decade ago, set out to design a
wireless communications network that could survive a
war.
One design that has emerged, in portable military
communications gear that has been used in Afghanistan
and could be used in the Iraqi theater, is called "mobile
ad-hoc" or mesh networking.
This provides instant up to date troop and unit
movements (all units are connected to the wireless
mesh network).
Surveillance and tracking opposition
Industry
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Mesh based diagnostic networks
Efficiency and stability monitoring
Real Time Diagnostics
Industry Diagnostics
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Mesh Networks can provide a low-cost diagnostic channel
outside of normal control loops.
This enables significant productivity improvements where
manual measurements may have previously been required.
By regularly capturing diagnostic data, plants can use predictive
maintenance for cost savings.
Questions
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Q1: What problems do centralized designs
present and how does a MESH network go
about addressing those problems?
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Q2: Would you use a proactive or reactive
protocol in a large MESH environment. Why?
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Q3: How do you increase redundancy in a Mesh
network?
Answers
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Answer1: MESH networks avoid a single point of
failure which can be detrimental to centralized systems.
MESH topology eliminates routers, controllers, etc.
Answer2: You should use a proactive (TBRPF)
protocol since large applications cannot tolerate the
delay of route discovery.
Answer3: In a mesh network, the degree of
redundancy is essentially a function of node density.
You can increase the number of nodes (to increase the
density). Additionally, it can be achieved by increasing
the number of simultaneous connections a node may
have.
References
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http://dailywireless.org/modules.php?name=Ne
ws&file=article&sid=2010
http://www.iapplianceweb.com/story/oeg20040
117s0019.htm
http://home.pacific.net.au/~djames.hub/mesh/
routing_faq.html
http://www.oreillynet.com/pub/a/wireless/200
4/01/22/wirelessmesh.html
References Cont.
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http://www.meshdynamics.com/
http://wi-fi.org/
http://www.sensorsmag.com/articles/0203/38/
main.shtml