ad hoc networks
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Ad-Hoc Wireless Network
Sandeep NagarI-Mtech
Computer Science(08559)
Road Map
• Introduction Cellular & Ad Hoc Wireless Network
Application Of Ad Hoc Wireless Network
• Issues In Ad Hoc Wireless Network Medium Access Scheme
Routing
Multicasting
Security
• Classification Of MAC Protocol Contention-Based Protocols
Contention-Based Protocols with R Reservation Mechanism
Contention-Based Protocols with R Schedule Mechanism
Introduction
• The 1st innovative communication system was devised in 500 BC by the king of Persia for sending the messages(from his capital to remote provinces of his empire). This system was 25 times faster then the available at that time.
• In 1994 Swedish communication equipment maker Ericsson proposed to develop a short range, low power, low complexity & inexpensive radio interface & that device called BLUETOOTH.
• The principal behind the Ad Hoc n/w is multi hop relaying.
• Introduction Cellular & Ad Hoc Wireless Network
Cellular & Ad Hoc Wireless Network
• Cellular Wireless Network
• In Cellular wireless n/w the p presence of base stations I msimplifies routing & resource mmanagement.
• Routing direction are made in a a centralized manner with m o more information about the d destination.
Cellular & Ad Hoc Wireless Network…
• Ad Hoc Wireless Network
• In Ad Hoc wireless n/w routing & resource management are done in a distributed manner.
• This require each node to be more intelligent, so that it can function both as n/w host for transmitting & receiving data.
Cellular Vs Ad Hoc Wireless Network
Cellular Wireless Network• Fixed Infrastructure-Based• Single-Hop Wireless links• Centralized routing• Seamless connectivity(low call
drops during handoffs)• Reuse of frequency spectrum
through Geographical channel reuse.
• High cost of network maintenance( backup, power sour, staffing & etc…)
Ad Hoc Wireless Network• Infrastructure-less• Multi-Hop Wireless links• Distributed routing• Frequent path breaks due to
mobility• Dynamic frequency reuse
based on carrier sense mechanism
• Self-organization and maintenance properties are built into the network.
Cellular & Ad Hoc Wireless Network…
Cellular Wireless Network
Ad-Hoc Wireless Network
Wireless Mesh
Network
Wireless Sensor
Network
Hybrid wireless network
• Introduction Cellular & Ad Hoc Wireless Network
Application Of Ad Hoc Wireless Network
Hybrid Wireless Network
Wireless Mesh Network Wireless Sensor Network
Application Of Ad Hoc Wireless Network
Hybrid Wireless Network• It is the combination of CELLULAR network & Ad-Hoc network .• It support Multi-Hop Cellular Network.• Primary concept behind cellular network is geographical channel reuse.
MAIN ADVANTAGES o Higher Capacityo Increased Flexibility & Reliable Routingo Better Coverage & Connectivity in Holes
Application Of Ad Hoc Wireless Network
Wireless Mesh Network• Mesh networking is a way to route data, voice and instructions between nodes• Mesh networks are self-healing: the network can still operate even when a node breaks down or a connection goes bad.
Application Of Ad Hoc Wireless Network
Wireless Sensor Network • A wireless sensor network (WSN) is a wireless network consisting of spatially distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations.• The development of wireless sensor networks was originally motivated by military applications such as battlefield surveillance.
• Introduction Cellular & Ad Hoc Wireless Network
Application Of Ad Hoc Wireless Network
• Issues In Ad Hoc Wireless Network Medium Access Scheme
Routing
Multicasting
Issues In Ad Hoc Wireless Network
Medium Access Scheme• The primary responsibility of MAC(Medium Access Control)
Protocol in ad-hoc network is distributed arbitration for the shared channel for transmission of packet.
• Major issues in MAC Protocol are:– Distributed Operating System :-> Ad-Hoc wireless n/w needs to operate in
environment where no centralized co-ordination is possible.– Synchronization :-> MAC protocol design should take into account the
requirement of time synchronization. It is mandatory for TDMA based system for management of transmission & reception slots.
– Capability for Power Control :-> The transmission power control reduce the energy consumption at the node, causes a decrease in interface at neighboring nodes & increase frequency reuse.
Issues In Ad Hoc Wireless Network
Routing The responsibility of routing protocol are
Exchange the route information, finding the feasible path from source to destination(such as Hop-length)
Minimum power required & it save wireless link life time(till the network is there).
The major challenges that a routing protocol faces are Quick route reconfiguration:- The unpredictable changes in the topology of
the network require that the routing protocol be able to quickly perform route reconfiguration.
Loop-Free Routing :- This is the fundamental requirement of any routing protocol to avoid unnecessary wastage of nodes.
Issues In Ad Hoc Wireless Network
Multicasting• It plays an important role in typical network application of ad-hoc
network. • For example: Emergency search & rescue operation, Military
communication & etc… In such environment certain tasks that require are:o Point to multipoint(voice & data communication)o Multipoint to multipoint(voice & data communication)
• The arbitrary movement of nodes changes the topology dynamically in unpredictable manner.
So for such type of network MESH-SHAPED structure is very beneficial because it work in high mobility environment.
• Introduction Cellular & Ad Hoc Wireless Network
Application Of Ad Hoc Wireless Network
• Issues In Ad Hoc Wireless Network Medium Access Scheme
Routing
Multicasting
Security
• Classification Of MAC Protocol Contention-Based Protocols
Contention-Based Protocols with R Reservation Mechanism
Contention-Based Protocols with R Schedule Mechanism
Contention-Based Protocols
• In this protocol, node does not make any resource reservation priori. But whenever it receives a packet to be transmitted it compete with its neighbor nodes for access to the share channel.
• This protocol cannot provide QoS(Quality of Service)In this Protocol we discuss MACAW(Medium Access Protocol for Wireless LAN) mechanism.
• MACAW in this we use Back-off mechanism.
Contention-Based Protocols cont….
BACK-OFF MECHANISM Back-Off mechanism is a method for reducing the collision.
Start
Set Back-off to zero
Send the frame
Collision?
Success
Send jam
signal
Increment back-off
Back-off limit
abort
Wait back-off time
No
yes
yes
no
Contention-Based Protocols cont….
• Back-off continue… The Station wait time= 2N x maximum_propagation_time N is the no. of attempted transmissions. maximum_propagation_time is the time needed for a bit
r reach the end of network.
Contention-Based Protocols cont….
• In MACAW use control packets RTSCTSDSDATAACK RTS-Request to send CTS-Clear to send DS-Data sending(30 bytes) ACK-Acknowledgement
Sender Receiver
RTS
CTSDS
DATA
ACK
Contention-Based Protocols with Reservation Mechanism
• Ad-Hoc wireless n/w sometime need to support real-time traffic, which require QoS(Quality Of Service) guarantees to be provided.
• In content-based protocol nodes are not provide QoS. So for support real-time traffic we need to reserving bandwidth.
Contention-Based Protocols with Reservation Mechanism cont…
• D-PRMA(Distributed Packet Reservation Multiple Access Protocol)– Basically PRMA (Packet Reservation Multiple Access) was proposed for
voice support in wireless LAN with base station.
– But now PRMA use with distributed system that’s why it is called D-PRMA.
– D-PRMA is based on TDMA(Time Division Multiple Access). In this the channels are divided into fixed & equal-sized frames along with time access.
Contention-Based Protocols with Reservation Mechanism cont…
• Frame Structure In D-PRMA
– Each frames is composed of slots ‘s’ & each slots consist of mini slots ‘m’
– Each mini slots can be further divided into two control field• RTS/BI(Request to Send/Busy Indication)• CTS/BI(Clear to Send/Busy Indication)• The control fields RTS & CTS are used for slots reservation and overcoming the
hidden terminal problem.
Slot 1 Slot 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slot s
Mini Slot 1 Mini Slot 2 . . . . . . . . . . . . . . . . . Mini Slot m
RTS/BI CTS/BI
Frame Length
Contention-Based Protocols with Reservation Mechanism cont…
• Hidden Terminal Problem:
• In this situation Receiver can receive packets from two or many nodes which cannot here each other.
• Receiver may be bombard by both the sender, resulting Collision & Reducing Throughput.
• SOLUTION for this problem is :• When all nodes having packets ready for transmission are compete for the first
minislot of each slot. The remaining (m-1) minislot are granted to the node that wins the competition.
RS1
S2
Contention-Based MAC Protocols with Scheduling Mechanism
• This protocol focus on packet scheduling at nodes & also scheduling nodes to access to channel.
• This Protocol proposed two mechanism- for providing quality of service(QoS) support for connection in ad-hoc wireless n/w.– DPS(Distributed Priority Scheduling)– Multi-Hop Co-ordination
• DPS(Distributed Priority Scheduling)– It is based on 802.11 IEEE distributed co-ordinate function.– DPS use same basic RTS->CTS->DATA->ACK packet exchange mechanism.– The RTS packet transmitted by a ready node then it carries the priority tag.
Contention-Based MAC Protocols with Scheduling Mechanism cont…
• DPS Continue…• It build the schedule table(ST) in which 3 columns are
RTS CTS ACKDATA
RTS CTS ACKDATA
NAV
Source(node 1)
Destination(node 2)
Neighbor Node(node 4)
Scheduling Table Update at neighbor Node 4S - Source ID, D - Destination ID, P - Priority Index
Contention-Based MAC Protocols with Scheduling Mechanism cont…
• Multi-Hop Co-ordination
– It Just extend the DPS Scheme. It scheduling over the multi-hop paths.
– In this case each node calculate the priority index of DATA packet in the recursive fashion, based on the received value of the priority index.
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