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Sub Code : 10IS841/10CS841 IA Marks : 25 Hrs/Week : 04 Exam Hours : 03 Total Hrs : 52 Exam Marks : 100
PART – A
UNIT 1 6 Hours Introduction: Ad hoc Networks: Introduction, Issues in Ad hoc wireless networks, Ad hoc wireless internet.
UNIT 2 7 Hours MAC – 1: MAC Protocols for Ad hoc wireless Networks: Introduction, Issues in designing a MAC protocol for Ad hoc wireless Networks, Design goals of a MAC protocol for Ad hoc wireless Networks, Classification of MAC protocols, Contention based protocols with reservation mechanisms.
UNIT 3 6 Hours MAC – 2: Contention-based MAC protocols with scheduling mechanism, MAC protocols that use directional antennas, Other MAC protocols.
UNIT 4 7 Hours Routing – 1: Routing protocols for Ad hoc wireless Networks: Introduction, Issues in designing a routing protocol for Ad hoc wireless Networks, Classification of routing protocols, Table drive routing protocol, On-demand routing protocol.
PART- B
UNIT 5 6 Hours Routing – 2: Hybrid routing protocol, Routing protocols with effective flooding mechanisms, Hierarchical routing protocols, Power aware routing protocols
UNIT 6 7 Hours Transport Layer: Transport layer protocols for Ad hoc wireless Networks: Introduction, Issues in designing a transport layer protocol for Ad hoc wireless Networks, Design goals of a transport layer protocol for Ad hoc wireless Networks, Classification of transport layer solutions, TCP over Ad hoc wireless Networks, Other transport layer protocols for Ad hoc wireless Networks.
UNIT 7 6 Hours Security : Security: Security in wireless Ad hoc wireless Networks, Network security requirements, Issues & challenges in security provisioning, Network security attacks, Key management, Secure routing in Ad hoc wireless Networks.
UNIT 8 7 Hours QoS: Quality of service in Ad hoc wireless Networks: Introduction, Issues and challenges in providing QoS in Ad hoc wireless Networks, Classification of QoS solutions, MAC layer solutions, network layer solutions.
Text Books:
- C. Siva Ram Murthy & B. S. Manoj: Ad hoc Wireless Networks, 2nd^ Edition, Pearson Education, 2005
TABLE OF CONTENTS
- UNIT 1: INTRODUCTION 1-
- UNIT 2: MAC– 1 16-
- UNIT 3: MAC– 2 31-
- UNIT 6: TRANSPORT LAYER 42-
- UNIT 7: SECURITY 53-
Adhoc wireless networks are defined as a category of wireless network. They utilize multi-hop radio replaying. They are capable of operating without the support of any fixed infrastructure. Absence of any central co-ordinator (or base station) makes the routing complex. Adhoc network topology for the cellular network is illustrated below (Fig 5.3). The path-setup for a call between 2 nodes, say, node C to E, is completed through the intermediate mobile node F.
Figure 5.3: An adhoc wireless network
Difference between Cellular Networks and Adhoc Wireless Networks
APPLICATIONS OF ADHOC WIRELESS NETWORKS
Military Application
- Adhoc networks can be used to establish communication among a group of soldiers for tactical operations.
- Setting up of a fixed infrastructure for communication among group of soldiers in enemy territories (or in inhospitable terrains) may not be possible. In such a case, adhoc networks can be used to provide required communication quickly.
- The military application enforces following requirements
- Reliability * Efficiency
- Secure communication * Support for multicast routing
Collaborative & Distributed Computing
- Adhoc network can be used to establish temporary communication infrastructure among a group of people in a conference.
- In distributed file sharing application, reliability is of high importance which would be provided by adhoc network.
- Other applications such as streaming of multimedia objects require support for soft real-time communication.
- Devices used can be → laptops with add-on wireless interface cards → enhanced PDA (Personal Digital Assistant) or → mobile devices with high processing power
Wireless Sensor Networks (WSN) These are used to provide a wireless communication infrastructure among the sensors deployed in a specific application domain. Sensor-nodes are tiny devices that have capability of → sensing physical parameters → processing the data gathered & → communicating to the monitoring system The issues that make sensor network a distinct category of adhoc network are the following
1. Node Mobility Mobility of nodes is not a mandatory requirement in sensor-networks. For example, → the nodes used for periodic monitoring of soil properties are not required to be mobile → the nodes fitted on the bodies of patients are designed to support partial mobility In general, sensor-networks need not in all cases be designed to support mobility of nodes. 2. Network Size The number of nodes in sensor network can be much larger than that in a typical adhoc network 3. Density of Deployment The density of nodes varies with the domain of application. For example, military applications require high availability of network, which makes redundancy a high priority. 4. Power Constraints The power constraints in sensor networks are much more severe than those in adhoc networks. This is mainly because the nodes are expected to operate in harsh environmental conditions, with minimum human supervision & maintenance. In certain case, the recharging of the energy source is impossible. Running such a network demands very efficient protocol at network, data link, and physical layer. The power sources can be classified into following 3 categories → Replenishable Power Source: The power source can be replaced when the existing source is fully drained. → Non-replenishable Power Source: The power source cannot be replenished once the network has been deployed. The replacement of node is the only solution. → Regenerative Power Source: Here, power source have the capability of regenerating power from the physical parameter under measurement. 5. Data/Information Fusion Data fusion refers to the aggregation of multiple packets into one before relaying it. Data fusion is used → to reduce bandwidth consumed by redundant headers of packets & → to reduce delay involved in transmitting multiple packets Information fusion is used → to process sensed data at intermediate nodes & → to relay the outcome to the monitoring system 6. Traffic Distribution The communication traffic pattern varies with the domain of application. For example, → Environmental sensing application generates short periodic packets indicating the status of environmental parameter. This kind of traffic requires low bandwidth → Military applications generally carry user traffic such as digitized & packetized voice stream This kind of traffic requires high bandwidth.
Hybrid Wireless Networks One of the major application areas of adhoc network is in the hybrid wireless architecture such as Multi-hop Cellular Network[MCN] & Integrated Cellular Adhoc Relay[iCAR]. The primary concept behind cellular networks is geographical channel-reuse. Several techniques like cell sectoring, cell resizing and multi tier cells increase the capacity of cellular networks. MCNs combine → reliability & support of fixed base-station of cellular network with → flexibility & multi-hop relaying adhoc networks Major advantages are as follows → Higher capacity than cellular networks due to the better channel reuse → Increased flexibility & reliability in routing → Better coverage & connectivity in holes of a cell can be provided by means of multiple hops through intermediate nodes in a cell
Routing
The responsibilities of a routing protocol include → exchanging the route information; → finding a feasible path to a destination. The major challenges that a routing protocol faces are as follows:
1. Mobility - The mobility of nodes results in * frequent path breaks * packet collisions * transient loops * stale routing information * difficulty in resource reservation 2. Bandwidth Constraint - Since the channel is shared by all nodes in the broadcast region, the bandwidth available per wireless link depends on the number of nodes & traffic they handle. 3. Error-prone & Shared Channel - The Bit Error Rate (BER) in a wireless channel is very high [10-5^ to 10-3] compared to that in its wired counterparts [10- (^12) to 10-9]. - Consideration of the state of the wireless link, signal-to-noise ratio, and path loss for routing in adhoc networks can improve the efficiency of the routing protocol. 4. Location Dependent Contention - The load on the wireless channel varies with the number of nodes present in a given geographical region. - When the number of nodes increases, the contention for the channel increases, which results in a high number of collisions & a subsequent wastage of bandwidth. 5. Other Resource Constraints - The constraints on following resources limit the capability of a routing protocol * computing power * battery power & * buffer storage The major requirements of a routing protocol in adhoc networks are the following. 1. Minimum Route Acquisition Delay
- The route acquisition delay for a node that does not have a route to a particular destination node should be as minimal as possible.
- The delay may vary with the network-size and the network-load. 2. Quick Route Re-configuration
- The unpredictable changes in the network topology require that the routing protocol be able to quickly perform route re- configuration in order to handle path breaks and subsequent packet losses. 3. Loop-Free Routing
- This is a fundamental requirement to avoid unnecessary wastage of bandwidth.
- In adhoc networks, due to the random movement of nodes, transient loops may form in the route thus established.
- A routing protocol should detect such transient routing loops & take corrective actions. 4. Distributed Routing Approach
- An adhoc network is a fully distributed wireless network & the use of centralized routing approaches in such a network may consume a large amount of bandwidth. 5. Minimum Control Overhead
- The control packets exchanged for finding a new route, and maintaining existing routes should be kept as minimal as possible. 6. Scalability
- Scalability is the ability of the routing protocol to scale well in a network with a large number of nodes.
- This requires minimization of control overhead & adaptation of the routing protocol to the network size. 7. Provisioning of QoS
- The routing protocol should be able to provide a certain level of QoS as demanded by the nodes( or the category of calls).
- The QoS parameters can be bandwidth, delay, jitter, packet delivery ratio, & throughput. 8. Support for Time-sensitive Traffic
- Tactical communications & similar applications require support for time-sensitive traffic.
- The routing protocol should be able to support both hard real-time & soft real-time traffic. 9. Security & Privacy
- The routing protocol must be resilient to threats and vulnerabilities.
- It must have inbuilt capability to avoid attacks such as resource consumption, DOS, impersonation.
Multicasting
It plays important role in emergency search-&-rescue operations & in military communication. Use of single-link connectivity among the nodes in a multicast group results in a tree-shaped multicast routing topology. Such a tree-shaped topology provides high multicast efficiency, with low packet delivery-ratio due to the frequency tree breaks. The major issues in designing multicast routing protocols are as follows
1. Robustness - The multicast routing protocol must be able to recover-&-reconfigure quickly from potential link breaks thus making it suitable for use in high dynamic environments. 2. Efficiency •The protocol should make a minimum number of transmissions to deliver a data-packet to all the group- members. 3. Control Overhead - The scarce bandwidth availability demands minimal control-overhead for the multicast session. 4. QoS
- QoS support is essential in multicast-routing because, in most cases, the data transferred in a multicast session is time-sensitive. 5. Efficient Group Management
- Group management refers to the process of → accepting multicast session members & → maintaining the connectivity among them until the session expires. 6. Scalability
- The protocol should be able to scale for a network with a large number of nodes. 7. Security
- Authentication of session-members and prevention of non-members from gaining unauthorized information play a major role in military communications.
Transport Layer Protocol The main objectives of the transport layer protocols include:
- Setting-up & maintaining end-to-end connections
- Reliable end-to-end delivery of packets
- Flow control &
- Congestion control Examples of some transport layers protocols are a. UDP (User Datagram Protocol) → It is an unreliable connectionless transport layer protocol → It neither performs flow control & congestion control → It do not take into account the current network status such as congestion at the intermediate links, the rate of collision, or other similar factors affecting the network throughput b. TCP (Transmission Control Protocol) → It is a reliable connection-oriented transport layer protocol → It performs flow control & congestion control → Here, performance degradation arises due to frequent path breaks, presence of stale routing information, high channel error rate, and frequent network partitions
Pricing Scheme
- Assume that an optimal route from node A to node B passes through node C, & node C is not powered on.
- Then node A will have to set up a costlier & non-optimal route to B.
- The non-optimal path consumes more resources & affects the throughput of the system.
- As the intermediate nodes in a path that relay the data packets expend their resources such as battery-charge & computing- power, they should be properly compensated.
- Hence, pricing schemes that incorporate service compensation (or service reimbursement) are required.
Self-Organization
- One very important property that an adhoc network should exhibit is organizing & maintaining the network by itself.
- The major activities are → Neighbor discovery → Topology organization & → Topology reorganization (updating topology information)
Security
- Security is an important issue in adhoc network as the information can be hacked.
- Attacks against network are of 2 types: I. Passive attack → Made by malicious node to obtain information transacted in the network without disrupting the operation II. Active attack → They disrupt the operation of network Further active attacks are of 2 types: External attack: The active attacks that are executed by nodes outside the network Internal attack: The active attacks that are performed by nodes belonging to same network
- The major security threats that exist in adhoc networks are as follows DoS (Denial of Service) – The attack affected by making the network resource unavailable for service to other nodes, either → by consuming the bandwidth or → by overloading the system Resource Consumption – The scarce availability of resources in adhoc network makes it an easy target for internal attacks, particularly aiming at consuming resources available in the network. The major types of resource consumption attacks are, I. Energy Depletion
- Highly constrained by the energy source
- Aimed at depleting the battery power of critical nodes II. Buffer Overflow
- Carried out either by filling the routing table with unwanted routing entries or by consuming the data packet buffer space with unwanted data
- Lead to a large number of data packets being dropped, leading to the loss of critical information Host Impersonation – A compromised internal node can act as another node and respond with appropriate control packets to create wrong route entries, and can terminate the traffic meant for the intended destination node Information Disclosure – A compromised node can act as an informer by deliberate disclosure of confidential information to unauthorized nodes Interference – A common attack in defense applications to jam the wireless communication by creating a wide spectrum noise
Energy Management
- Energy management is defined as the process of managing the sources & consumers of energy in a node (or in the network) for enhancing the lifetime of a network.
- Features of energy management are →Shaping the energy discharge pattern of a node’s battery to enhance battery life →Finding routes that consumes minimum energy →Using distributed scheduling schemes to improve battery life →Handling the processor & interface devices to minimize power consumption
- Energy management can be classified into the following categories a. Transmission Power Management The power consumed by the Radio Frequency (RF) module of a mobile-node is determined by several factors such as * State of operation * Transmission power & * Technology used for the RF circuitry The state of operation refers to transmit, receive, and sleep modes of the operation. The transmission power is determined by → Reachability requirement of the network → Routing protocol & → MAC protocol employed b. Battery Energy Management The battery management is aimed at extending the battery-life of a node → by taking advantage of its chemical properties, discharge patterns and → by selection of a battery from a set of batteries that is available c. Processor Power Management The clock-speed and the number of instructions executed per unit time are some of the processor parameters that affect power consumption. The CPU can be put into different power saving modes during low processing load conditions. The CPU power can be completely turned off if the machine is idle for a long time. In such a case, interrupts can be used to turn on the CPU upon detection of user interaction. d. Devices Power Management Intelligent device management can reduce power consumption of a mobile node significantly. This can be done by the OS(operating system) → by selectively powering down interface devices that are not used or → by putting devices into different power saving modes, depending on their usage
AD HOC WIRELESS INTERNET
Adhoc wireless internet extends the services of the internet to the end-users over an adhoc network (Fig 5.7). Some of the applications are
- Wireless mesh network
- Provisioning of temporary internet services to major conference venues
- Sports venues
- Temporary military settlements
- Battlefields &
- Broadband internet services in rural regions
Figure 5.7 Schematic diagram of adhoc wireless internet
The major issues to be considered for a successful adhoc wireless internet are the following:
1. Gateway They are the entry points to the wired-internet. Generally, they are owned & operated by a service-provider. They perform following tasks * Bandwidth management * Load balancing * Traffic shaping * Packet filtering & * Address, service & location discovery 2. Address Mobility This problem is worse here as the nodes operate over multiple hops. Solution such as Mobile IP can provide temporary alternative. 3. Routing It is a major problem due to * dynamic topological changes * presence of gateways * multi-hop relaying & * hybrid character of network Possible solution is to: use separate routing protocol for the wireless part of adhoc wireless internet. 4. Transport Layer Protocol Several factors are to be considered here, the major one being the state-maintenance-overhead at the gateway-nodes.
5. Load Balancing It is essential to distribute the load so as to avoid the situation where the gateway-nodes become bottleneck-nodes. 6. Pricing/Billing Since internet-bandwidth is expensive, it is very important to introduce pricing/billing strategies for the adhoc network. 7. Provisioning of Security Security is a prime concern, since the end-users can utilize the adhoc network to make e-commerce transaction. 8. QoS Support Provisioning of QoS-support is a very important issue because of * widespread use of voice over IP(VOIP) & * growing multimedia applications over the internet 9. Service, Address & Location Discovery Service discovery refers to the activity of identifying the party which provides the service( or resource). Address discovery refers to the services such as those provided by ARP or DNS operating within the wireless domain. Location discovery refers to different activities such as * detecting location of a particular mobile-node in network or * detecting geographical location of nodes
Distributed Nature
- There is no central point of coordination due to the mobility of the nodes.
- Nodes must be scheduled in a distributed fashion for gaining access to the channel. Mobility of Nodes
- Nodes are mobile most of the time
- The protocol design must take this mobility factor into consideration so that the performance of the system is not affected due to node mobility.
DESIGN GOALS OF A MAC PROTOCOL FOR AD HOC WIRELESS NETWORKS
- The available bandwidth must be utilized efficiently.
- Control overhead must be kept as low as possible.
- The operation of a protocol should be distributed.
- The access delay must be kept low. (Access delay refers to the average delay experienced by any packet to get transmitted).
- The protocol should provide QoS support for real-time traffic.
- The protocol should minimize the effects of hidden and exposed terminal problems.
- The protocol should provide time synchronization among nodes.
- The protocol should ensure fair allocation of bandwidth to nodes.
- The protocol must be scalable to large networks.
- The protocol should have power control mechanisms in order to efficiently manage energy consumption of the nodes.
- The protocol should have mechanisms for adaptive data-rate control.
- The protocol should try to use directional antennas which can provide advantages such as → reduced interference → increased spectrum reuse & → reduced power consumption
CLASSIFICATION OF MAC PROTOCOLS
Ad hoc network MAC protocols can be classified into three basic types: i. Contention-based protocols ii. Contention-based protocols with reservation mechanisms iii. Contention-based protocols with scheduling mechanisms iv. Other MAC protocols [protocols which do not fall under above 3 categories]
Contention-Based Protocols
- Here, the channel access policy is based on competition.
- Whenever a node needs to send a packet, it tries to get access to the channel.
- These protocols cannot provide QoS, since access to the network cannot be guaranteed beforehand.
- It can be further subdivided into: → Sender-initiated protocols: Packet transmissions are initiated by the sender node. * Single-channel sender-initiated protocols: A node that wins the contention to the channel can make use of the entire bandwidth. * Multichannel sender-initiated protocols: The available bandwidth is divided into multiple channels. Many nodes can simultaneously perform data transmission using multiple channels. → Receiver-initiated protocols: The receiver node initiates the contention resolution protocol. Contention-Based Protocols with Reservation Mechanisms
- These protocols provide bandwidth reservation ahead; therefore, they can provide QoS support.
- These can be further subdivided into: → Synchronous protocols : There is time synchronization among all nodes in the network; the nodes in the neighborhood are informed of the reservations; → Asynchronous protocols: no global synchronization is needed. Relative time is used for the reservations. Contention-Based Protocols with Scheduling Mechanisms
- There can be -packet scheduling at the nodes or -node scheduling for access to the channel
- Node scheduling should not treat the nodes unfairly.
- Some of these protocols consider battery power in their node scheduling. Other protocols are those MAC protocols that do not strictly fall under the above categories.
MACA
- When a node wants to transmit a data packet, it first transmits a RTS (Request To Send) frame.
- The receiver node, on receiving the RTS packet, if it is ready to receive the data packet, transmits a CTS (Clear to Send) packet.
- Once the sender receives the CTS packet without any error, it starts transmitting the data packet.
- If a packet transmitted by a node is lost, the node uses the binary exponential back-off (BEB) algorithm to back off a random interval of time before retrying.
- The binary exponential back-off mechanism used in MACA might starve flows sometimes. The problem is solved by MACAW.
