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Showing posts with label COMPUTER NETWORKS - II. Show all posts
COMPUTER NETWORKS - II
* ZigBee is one of the newest
technologies enabling Wireless Personal Area Networks (WPAN).
* ZigBee is an established set of
specifications for wireless personal area networking (WPAN), i.e. digital radio
connections between computers and related devices.
* WPAN Low Rate or ZigBee
provides specifications for devices that have low data rates, consume very low
power and are thus characterized by long battery life. ZigBee makes possible
completely networked homes where all devices are able to communicate and be controlled
by a single unit.
* The IEEE 802.15.4 standard and
Zigbee wireless technology are designed to satisfy the market's need for a
low-cost, standard-based and flexible wireless network technology, which offers
low power consumption, reliability, interoperability and security for control and
monitoring applications with low to moderate data rates.
* The data which gets transmitted
includes temperature reading on or off state of a switch keystroke of a
keyboard etc.
* The Bluetooth technology which
is used in mobile phones, laptops, runs on zigbee. Zigbee is an IEEE 802.15.4
standard. Zigbee operates in a frequency range 900MHz- 2.5 GHz.
* The technology can be used for
transmitting the data within the range of 20mts.
* It can also be used for
transmission of data within a range greater than 20mts. This is possible
through the intermediate nodes.
COMPUTER NETWORKS - II
Inter cluster
routing [ICR]: It
is a destination initiated reactive routing algorithm. The destination is
called as local base station [LBS] it will start the route discovery by
creating interest signal and following them. ICR works in two phases, Route
discovery and data acquisition.
In Route
Discovery Phase, the
LBS initiates route discovery by sending an interest signal within the range
Ri,
1. All the nodes which are in the
range Ri will receive the interest signal.
2. Upon receiving the interest signal it will be
stored and flooding continues.
3. If an intermediate node
receive already processed interest signal it will be discarded
4. Before flooding the interest
signal the cost value will be updated. The format of the interest signal and
the formula for the cost is as given below.
Interest signal
|
Type
|
Period Source
|
Address
|
cost
|
The type field indicates message
format. The period indicates how often interest signal has to be sent. The
source address field is used for sorting address of the source node. The cost
field indicates number of hops required to reach the source. In formula for the
cost α and β are normalization factor based on environment.
Cost=αh+βΣ Bm/Bri
Where, h is hop count
Bm = It is the maximum battery
available in the node
Bri = it is the remaining battery in the node.
COMPUTER NETWORKS - II
Routing protocol
in sensor network: In
sensor network the routing of information can happen within a cluster or
between nodes of different clusters.
If the routing is happening
within a cluster. Then the protocol is called as intra cluster routing.
If the routing is happening
between the nodes of different clusters it is called as inter cluster routing.
Intracluster
routing
In intracluster routing, the
packets are transmitter with in a cluster It can be of two types.
1. Direct routing algorithm
2. Multihop routing algorithm
In direct routing, the cluster
head as the destination for all cluster nodes. The cluster nodes can
communicate directly with cluster nodes.
In multihop the destination is
reached through multiple hops. If there are many paths. Then only the path
which is energy efficient will be considered. In multihop routing, a node might
have to under go multiple hops before it reaches the destination. The sensor
node will be at different distances apart from other nodes. A packet from a
node is routed to a neighbor node that exhibits high energy. The number in the
node indicates the remaining energy in the node
COMPUTER NETWORKS - II
Decentralized
energy efficient propagation protocol [DEEP]: DEEP is used for
identifying a head and the
members. The algorithm works as follows
1. Initialize: when network is
created one of the node in the network will be made as cluster head. The
cluster head sends a signal known as cluster head declaration signal to all the
nodes which are in the range ’ . This is used for identifying the members of
the cluster. The cluster head sends cluster head exploration to all the nodes
which are in the range dr1 and dr2. This is done to identify a new cluster
head.
2. Repeat : even though many
nodes receive the cluster head exploration only one node fro which the equation
ERC1 < ER < ERC2 can become the candidate of the cluster head.
‘ER’ is the energy of cluster
head exploration and
‘ERC!’=Pout – ηwd 1
‘ERC2’=Pout–ηwd 2
η, w, n are dependent on environment factors.
The new candidate sends cluster
head declaration for all the nodes in the range dr. if a node receives multiple
cluster head declaration which ever signal is having higher energy will be
chosen as cluster head. The other candidates will be eliminated.
3. Conclusion: if there are not
enough members in a cluster member exploration/search signal will be generated
atleast if a node does not receive any signal member exploration or search
signal will be generated.
COMPUTER NETWORKS - II
IEEE standards as 802.11a, b, and
g provide a wide range of data rates: 54,48,36,24,18,12,9 and 6 mb/s. this
range reflects the trade off between the transmission range and data rate intrinsic
in a wireless communication channel. An accurate energy model is crucial for
the development of energy efficient clustering and routing protocols. The
energy consumption, E for all components of the watts is summarized as
E=theta+ηwdn
Where Ѳ is the distance
independent term that accounts for the overhead of the radio electronics and
digital processing, and ηwd^n is the distance dependent term in which η represents
the amplifier inefficiency factor w is the free space path loss d is the
distance and n in the environmental factor. Based on an environmental
condition, n can be any number between 2 and 4 and η specifies the inefficiency
of the transmitter when generating maximum power wd^n at the antenna. Clearly
the distance dependent portal of total energy consumption depends on the
real-world Tranreceiver parameters, Ѳ, η and the path attenuation wd^n. if the
value of Ѳ overshadows ηwd^n, the reduction in the transmission distances
through the use of multihop communication is not effective.
COMPUTER NETWORKS - II
The sensor node consist of a
1. sensing unit
2. processing unit
3. memory unit
4. self power unit
5. wireless transreceiver
* Sensing unit: it
consists of a sensor and analog to digital converter [ADC]. the
analog signal produced by sensor
is converted to digital and is fed into processing
unit. The sensing unit is
responsible for collecting the data externally and interacts
with central processor
* Processing and memory unit: the
processing unit is responsible for performing
some computations it executes
some instructions which is responsible for setting up the connection with
another node. The memory unit is used for storing the data.
* Self power unit: it is
responsible for powering the node and keeping it alive. The
main task of the sensor node is
to identify events , to process data , and then to transmit the data. The power
of a node is consumed mainly in the transmitter and receiver unit. The sensor
node can be supplied by a self-power unit, self-power unit battery, or solar
cells.
COMPUTER NETWORKS - II
The protocol stack of sensor
network combines power efficiency and least cost path routing.
The architecture consist of
1. Physical layer
2. Data link layer
3. Network layer
4. Transport layer
5. Application layer
All these layers are backed by
management plane, mobility management plane and task management plane.
Physical layer is responsible for
transmitting and receiving signals.
* The data link layer consists of
medium access control [MAC] which is used to prevent packet collision.
* The network layer is
responsible for routing the packets
* The application layer is used
for creation of packets by making use of software.
* The power management plane monitors the sensor’s
power level among sensor node.
COMPUTER NETWORKS - II
WSNs, which can be
considered as a special case of ad hoc networks with reduced or no mobility,
are expected to find increasing deployment in coming years, as they enable
reliable monitoring and analysis of unknown and untested environments. These
networks are "data centric", i.e., unlike traditional ad hoc networks
where data is requested from a specific node, data is requested based on certain
attributes such as,"which area has temperature over 35°C or 95°F".
Therefore a large number of sensors need to be deployed to accurately reflect
the physical attribute in a given area. Routing protocol design for WSNs is
heavily influenced by many challenging factors, which must be overcome before
efficient communication can be achieved. These challenges can be summarized as follows:
Ad hoc
deployment -
Sensor nodes are randomly deployed which requires that the system be able to cope
up with the resultant distribution and form connections between the nodes. In
addition, the system should be adaptive to changes in network connectivity as a
result of node failure.
• Computational capabilities -
Sensor nodes have limited computing power and therefore may not be able to run
sophisticated network protocols leading to light weighted and simple versions
of routing protocols.
• Energy consumption without
losing accuracy - Sensor nodes can use up their limited energy supply
carrying out computations and transmitting information in a wireless
environment. As such, energyconserving forms of communication and computation
are crucial as the node lifetime shows a strong dependence on the battery
lifetime. In a multi-hop WSN, nodes play a dual role as data sender and data
router. Therefore, malfunctioning of some sensor nodes due to power failure can
cause significant topological changes and might require rerouting of packets
and reorganization of the network.
Scalability - The number of
sensor nodes deployed in the sensing area may be in the order of hundreds,
thousands, or more. Any routing scheme must be scalable enough to respond to
events and capable of operating with such large number of sensor nodes. Most of
the sensors can remain in the sleep state until an event occurs, with data from
only a few remaining sensors providing a coarse quality.
• Communication range -
The bandwidth of the wireless links connecting sensor nodes is often limited,
hence constraining inter sensor communication. Moreover, limitations on energy
forces sensor nodes to have short transmission ranges. Therefore, it is likely
that a path from a source to a destination consists of multiple wireless hops
Fault tolerance - Some sensor
nodes may fail or be blocked due to lack of power, physical damage, or
environmental interference. If many nodes fail, MAC and routing protocols must
accommodate formation of new links and routes to the data collection BSs. This
may require actively adjusting transmit powers and signaling rates on the
existing links to reduce energy consumption, or rerouting packets through
regions of the network where more energy is available. Therefore, multiple
levels of redundancy may be needed in a fault tolerant WSN.
• Connectivity - High node
density in sensor networks precludes them from being completely isolated from
each other. Therefore, sensor nodes are expected to be highly connected. This,
however, may not prevent the network topology from varying and the network size
from shrinking due to sensor nodes failures. In addition, connectivity depends
on the, possibly random, distribution of nodes.
Transmission
media -
In a multi-hop sensor network, communicating nodes are linked by a wireless medium.
Therefore, the traditional problems associated with a wireless channel (e.g.,
fading, high error rate) also affect the operation of the sensor network. In
general, bandwidth requirements of sensor applications will be low, in the
order of 1-100 kb/s. As we have seen in Chapters 4 and 5 and in the previous
section, the design of the MAC protocol is also critical in terms of conserving
energy in WSNs.
• QoS - In some
applications (e.g., some military applications), the data should be delivered
within a certain period of time from the moment it is sensed, otherwise the
data will be useless. Therefore, bounded latency for data delivery is another
condition for time constrained applications.
• Control Overhead - When
the number of retransmissions in wireless medium increases due to collisions,
the latency and energy consumption also increases. Hence, control packet
overhead increases linearly with the node density. As a result, tradeoffs
between energy conservation, selfconfiguration, and latency may exist.
• Security - Security is
an important issue which does not mean physical security, but it implies that both
authentication and encryption should be feasible. But, with limited resources,
implementation of any complex algorithm needs to be avoided. Thus, a tradeoff
exists between the security level and energy consumption in a WSN.
COMPUTER NETWORKS - II
The attack in adhoc network can
be prevented by using a securing routing protocol. It should have following
properties
1. Authenticity: when a
routing table is updated, it must verify whether updates were provided by
authenticated node.
2. Integrity of information : when
a routing table is updated the information must be verified whether it is
modified or not
3. In order updates: sequence
numbers or some mechanism must be used to maintain updates in order.
4. Maximum update time: updates
in routing table must be done as quickly as possible.
5. Authorization: only
authorized nodes must be able to send update packets.
COMPUTER NETWORKS - II
The attack can be classified into
2 types
1. Passive 2. Active
In passive
attack, the
normal operation of routing protocol is not interrupted. The attacker just
tries to gather the information
In active
attack, the
attacker can insert some arbitrary packets and therefore might affect the normal
operation of network
Attack can also be one of the
following types
1. Pin attack : with the
pin attack, an unauthorized node pretends to have shortest path to the
destination
The attacker can listen to path
setup phase and become the part of network.
2. Location disclosure attack
: by knowing the locations of intermediate nodes, the attacker can find out
the location of target node
3. Routing table overflow : the
attacker can create some routes whose destination do not exist. It will have
major impact on proactive based routing
4. Energy exhaustion attack :
the attacker tries to forward unwanted packets or send unwanted requests which
can conserve the battery of the nodes
COMPUTER NETWORKS - II
The following are the security
threat in adhoc network.
1. Limited computational
capabilities : the nodes in the mobile adhoc network are modular,
independent and will have limited computational capability. It becomes a source
of vulnerability when they handle public key cryptography.
2. Limited power supply : since
nodes have limited power supply attacker can exhaust batteries by giving
excessive computations to be carried out.
3. Challenging key management
: the key management becomes extremely difficult as the mobile devices will
be under movement.
COMPUTER NETWORKS - II
It is also a source initiated
routing algorithm, creates multiple routes for any source/ destination pair.
The advantage of multiple routes is that route discovery is not required for every
alteration in the network topology.
TORA consists of three phases,
1. Route Creation/discovery
2. Route maintenance
3. Route erasure
TORA uses three types of packets:
Query Packets for route creation, Update Packets for both creation and
maintenance
The route will be discovered from
the source to destination only when a request is made for the transmission. In
this algorithm the source will generate a query packet which will be broadcasted
in the network this continues as long as a node that is directly connected to
the destination is identified.
When the destination is
identified an update packet will be generated and sent back to the source. The
update packet will have the path information if there are more than one update
packet received by the source, it means there are multiple paths to the
destination, the source has to choose best path available.
COMPUTER NETWORKS - II
It is a source initiated routing
protocol in mobile adhoc networks.
The algorithm consist of 2 phases
1. Route discovery phase
2. Route maintenance phase
In route discovery phase the path
from source to destination is identified by broadcasting route request packet
[RREQ]. When the intermediate node receive RREQ they will create a backward
pointer and continue the broadcast when the route request packet reaches the destination
a route reply would be generated [RREP]. The route reply will have information about
the path that can be chosen for the packet transmission.
The route request packet can have
following information.
1. Source id
2. Destination id
3. Sequence number
4. Backward pointer information
5. CRC and
6. Time to live[TTL]
In the above network the RREQ
will be broadcasted by the source node 1 to its neighbor and neighbors will
check whether RREQ is already processed. If it is already processed the packet
will be discarded.
If it is not processed a backward
pointer is created and the broad cast continues.
When the packet is reached at
destination a route reply is created [RREP] in the above network the first RREP
is sent to the source can have the path information as 1-2-4-6-8.
When the source receives this
information it will be stored in the routing table. Mean while the destination
can create one more RREP which can have the information as 1-3-7-8 the
destination will send this RREP to the source and will also ask the source to
discard old path as the new path is having minimum number of hops.
Route
maintainence phase
The nodes in the network
periodically exchange hello messages to inform that they
are still a part of network and
the path is valid. Whenever there is a link failure detected. A route error
packet [RERR] will be sent to the source indicating the path is no more valid.
COMPUTER NETWORKS - II
Associated based
routing [ABR]:
ABR is an efficient on-demand or source initiated routing protocol. In ABR, the
destination node decides the best route, using node associativity. ABR is
suitable for small networks, as it provides fast route discovery and creates
shortest paths through associativity. Each node keeps track of associativity
information by sending messages periodically.
If the associativity value is
more means nodes mobility is less.
If the associativity value is
less means nodes mobility is
In ABR the source which wants to
send the packet to the destination will create a query packet and broadcast in
the network. Query packet generation is required for discovering the route.
The broadcast continues as long
as destination is reached once the destination is reached it creates the reply
packet and sends back to the source.
The query packet will have the
following information.
1. Source id
2. Destination id
3. All intermediate node id
4. Sequence number
5. CRC and
6. Time to live [TTL]
A node sends an update packet to
the neighbors and waits for the reply if update is received back, then
associative tick will be incremented high then it means mobile device is still
a part of the network otherwise it might not be.
COMPUTER NETWORKS - II
* Dynamic source routing
[DSR]: DSR is a source initiated or on demand routing
protocol in which source finds
unexpired route to the destination to send the packet. It is used in the
network where mobile nodes move with moderate speed.
* Overhead is significantly
reduced, since nodes do not exchange routing table information it has 2 phases.
1. Route discovery
2. Route maintenance
The source which wants to send
the information to the destination will create a route request
message by adding its own
identification number and broadcasts them in the network. The intermediate
nodes will continue the broadcast but adding their own identification number.
When the destination is reached a
route reply message is generated which will be sent back to the source.
The source can receive multiple route replies indicating the presence of multiple
paths.
The source will pick up one of
the path and will use for transmission. If there is a link failure one of the
node will detect and will create a route error message which will be
sent back to the source in this case the path has to be re-established for
further transmission.
COMPUTER NETWORKS - II
WRP is also based on table driven
approach this protocol makes use of 4 tables
1. Distance table :- Which
contains information like destination, next hop, distance
2. Routing table: - Which
contains routing information.
3. Link cost table:- Which contains
cost information to each neighbor
4. Message retransmission list
table: - this table provides sequence number of the message, a retransmission
counter, acknowledgements and list of updates sent in update message.
Whenever there is a change in the
network an update will be made which will be broadcasted to other nodes.
Other nodes upon receiving the
updated information will make an update in their table. If there is no update
in the network a hello message should be sent.
COMPUTER NETWORKS - II
CGSR is also a table driven
routing protocol. In this algorithm the mobile devices will be grouped to form
a cluster the grouping is based on the range and each cluster is controlled by cluster
head. All the mobile devices will maintain 2 tables cluster member table and
routing table.
The cluster member table will
have the information about the cluster head for each
destination the routing table
will have routing information. In this protocol the packet cannot be directly
sent to the destination instead cluster heads are used for routing.
CGSR routing involves cluster
routing, where a node finds the best route over cluster heads from the cluster
member table.
COMPUTER NETWORKS - II
* Destination sequenced
distance vector [DSDV]: The DSDV is table driven based routing algorithm.
DSDV is improved version of Bellman Ford routing algorithm.
* Each DSDV node maintain two
routing tables: - table for forwarding packets, and table for advertising
incremental updates. The nodes will maintain a routing table that consists of a
sequence number. The routing table periodically exchanged so that every node
will have latest information.
* DSDV is suitable for small
networks.
The algorithm
works as follows
* A node or a mobile device will
make an update in its routing table and send the information to its neighbor
upon receiving the updated information and make an update in its own routing
table.
* The update is made by comparing
the sequence number received is greater than present sequence number than the
new one will be used.
* If there is a link failure in
one of the node will change the metric value to infinity and broadcast the
message.
COMPUTER NETWORKS - II
Ad-hoc Routing protocols can be
categorized as table-driven or source initiated. Table-driven or proactive
,routing protocols finds routes to all possible destinations ahead of time. The
routes are recorded in the nodes’ routing tables and are updated within the predefined
intervals. Proactive routing protocols are faster in decision making ,but cause
problems if the topology of the network continually changes. These protocols
require every node to maintain one or more tables to store updated
routing information from every
node to all other nodes.
Source-initiated routing
protocols:
Source-initiated, or reactive,
routing protocols are on-demand procedures and create routes only when
requested to do so by source nodes. A route request initiates a route-discover process
in the network and is completed once a route is discovered. If it exists, at
the time of request, a route is maintained by a route-maintenance procedure
until either the destination node becomes irrelevant to the source or the route
is no longer needed. Control overhead of packets is smaller than of proactive
protocols.
COMPUTER NETWORKS - II
Collaborative Work
-
For some business scenarios, the need for collaborative computing might be more
important outside office environments than inside a building. After all, it is
often the case where people do need to have outside meetings to cooperate and
exchange information on a given project;
• Crisis-management
Applications - These arise, for example, as a result of natural disasters
where the entire communications infrastructure is in disarray (for example,
Tsunamis, hurricanes, etc.). Restoring communications quickly is essential. By
using ad hoc networks, an infrastructure could be set up in hours instead of
days/weeks required for wire-line communications;
Personal Area
Networking -
A personal area network (PAN) is a short-range, localized network where nodes
are usually associated with a given person. These nodes could be attached to
someone's cell phone, pulse watch, belt, and so on. In these scenarios,
mobilityis only a major consideration when interaction among several PANs is
necessary, illustrating the case where, for instance, people meet in real life.
Bluetooth [Haarstenl998] is an example of a technology aimed at, among other things,
supporting PANs by eliminating the need of wires between devices such as
printers, cell phones, PDAs, laptop computers, headsets, and so on, and is
discussed later in this book. Other standards under the IEEE 802.15 working
group for wireless PANs are also described.
