The document discusses MAC protocols for ad hoc networks. It begins by outlining problems MAC protocols must address, such as bandwidth efficiency, synchronization, and the hidden terminal problem. It then classifies MAC protocols into three categories: contention-based without reservation, contention-based with reservation, and contention-based with scheduling. Several example protocols are described for each category, including how they address issues like bandwidth utilization and collisions. The document also covers MAC protocols that use directional antennas and power control techniques.
The document discusses several MAC protocols for ad hoc networks including MACA, MACAW, and PAMAS. MACA uses RTS and CTS packets to avoid collisions but does not provide ACK. MACAW is a revision of MACA that includes ACK. It significantly increases throughput but does not fully solve hidden and exposed terminal problems. PAMAS uses a separate signaling channel for RTS-CTS and a data channel. It allows nodes to power down transceivers when not transmitting to save energy.
This document discusses computer networks and congestion control techniques. It provides information on routing algorithms, causes of congestion, effects of congestion, and open-loop and closed-loop congestion control methods. Specifically, it describes the leaky bucket algorithm and token bucket algorithm for traffic shaping, and how they regulate data flow rates to prevent network congestion.
This document discusses layer 2 switching fundamentals, including communication methods in LANs such as unicast, broadcast, and multicast. It describes how switches operate including forwarding frames based on the destination address and address table lookups. The document also covers collision domains, broadcast domains, and how switches help segment networks to reduce collisions and broadcast traffic.
This document discusses various MAC protocols for ad hoc wireless networks. It begins by outlining the key issues in designing such protocols, including bandwidth efficiency, quality of service support, and addressing hidden and exposed terminal problems. It then classifies MAC protocols into contention-based, contention-based with reservation, and contention-based with scheduling categories. Several examples of protocols are described for each category. The document provides an overview of the operation and key aspects of many MAC protocols proposed for ad hoc wireless networks.
Mobile IP allows mobile nodes to change their point of attachment between IP networks while maintaining ongoing connections. It defines entities like mobile nodes, home agents, and foreign agents to facilitate IP packet delivery to the mobile node's current location. The key operations in Mobile IP are agent discovery, registration of the mobile node's new location with its home agent, and tunneling of packets from the home agent to the foreign agent or mobile node's care-of address.
1) Medium Access Control (MAC) protocols regulate access to shared wireless channels and ensure performance requirements of applications are met. They assemble data into frames, append addressing and error detection, and disassemble received frames.
2) Common MAC protocols include Fixed Assignment (e.g. TDMA), Demand Assignment (e.g. polling), and Random Assignment (e.g. ALOHA, CSMA). Schedule-based MAC protocols avoid contention through resource scheduling while contention-based protocols (e.g. CSMA/CA) allocate resources on demand, risking collisions.
3) The document discusses various MAC protocols for wireless sensor networks and their objectives to minimize energy waste from idle listening, collisions,
Congestion occurs when routers receive packets faster than they can forward them, causing their queues to fill up. There are two ways routers deal with congestion - by preventing additional packets from entering the congested region until packets can be processed, or by discarding queued packets to make room for new ones. Congestion control techniques like warning bits, choke packets, and load shedding help detect and recover from congestion on a global scale across an entire subnet, while flow control operates on a point-to-point basis between individual senders and receivers.
The document discusses several MAC protocols for ad hoc networks including MACA, MACAW, and PAMAS. MACA uses RTS and CTS packets to avoid collisions but does not provide ACK. MACAW is a revision of MACA that includes ACK. It significantly increases throughput but does not fully solve hidden and exposed terminal problems. PAMAS uses a separate signaling channel for RTS-CTS and a data channel. It allows nodes to power down transceivers when not transmitting to save energy.
This document discusses computer networks and congestion control techniques. It provides information on routing algorithms, causes of congestion, effects of congestion, and open-loop and closed-loop congestion control methods. Specifically, it describes the leaky bucket algorithm and token bucket algorithm for traffic shaping, and how they regulate data flow rates to prevent network congestion.
This document discusses layer 2 switching fundamentals, including communication methods in LANs such as unicast, broadcast, and multicast. It describes how switches operate including forwarding frames based on the destination address and address table lookups. The document also covers collision domains, broadcast domains, and how switches help segment networks to reduce collisions and broadcast traffic.
This document discusses various MAC protocols for ad hoc wireless networks. It begins by outlining the key issues in designing such protocols, including bandwidth efficiency, quality of service support, and addressing hidden and exposed terminal problems. It then classifies MAC protocols into contention-based, contention-based with reservation, and contention-based with scheduling categories. Several examples of protocols are described for each category. The document provides an overview of the operation and key aspects of many MAC protocols proposed for ad hoc wireless networks.
Mobile IP allows mobile nodes to change their point of attachment between IP networks while maintaining ongoing connections. It defines entities like mobile nodes, home agents, and foreign agents to facilitate IP packet delivery to the mobile node's current location. The key operations in Mobile IP are agent discovery, registration of the mobile node's new location with its home agent, and tunneling of packets from the home agent to the foreign agent or mobile node's care-of address.
1) Medium Access Control (MAC) protocols regulate access to shared wireless channels and ensure performance requirements of applications are met. They assemble data into frames, append addressing and error detection, and disassemble received frames.
2) Common MAC protocols include Fixed Assignment (e.g. TDMA), Demand Assignment (e.g. polling), and Random Assignment (e.g. ALOHA, CSMA). Schedule-based MAC protocols avoid contention through resource scheduling while contention-based protocols (e.g. CSMA/CA) allocate resources on demand, risking collisions.
3) The document discusses various MAC protocols for wireless sensor networks and their objectives to minimize energy waste from idle listening, collisions,
Congestion occurs when routers receive packets faster than they can forward them, causing their queues to fill up. There are two ways routers deal with congestion - by preventing additional packets from entering the congested region until packets can be processed, or by discarding queued packets to make room for new ones. Congestion control techniques like warning bits, choke packets, and load shedding help detect and recover from congestion on a global scale across an entire subnet, while flow control operates on a point-to-point basis between individual senders and receivers.
This document discusses security issues and solutions related to Voice over IP (VoIP) systems. It begins with an introduction to VoIP and how it works, describing the protocols used including SIP, H.323, MGCP and RTP. It then outlines various security attacks on VoIP systems such as eavesdropping, denial of service attacks, and masquerading. Finally, it discusses approaches to enhancing VoIP security, including using encryption, firewalls, authentication, and secure protocols like SRTP.
Lecture 7 8 ad hoc wireless media access protocolsChandra Meena
1) The document discusses issues with media access control (MAC) protocols in ad hoc wireless networks, including problems like hidden terminals and exposed nodes.
2) It classifies MAC protocols as synchronous, asynchronous, receiver-initiated, or sender-initiated. The RTS-CTS handshake is presented as a solution to the hidden terminal problem.
3) However, the RTS-CTS approach has shortcomings like collisions when RTS and CTS messages are sent by different nodes or when multiple CTS messages are granted. Solutions to the exposed node problem are also discussed.
The GSM radio interface uses FDMA to divide the frequency band into channels and TDMA to divide each frequency channel into time slots to allow multiple users, with each user assigned a single time slot. The normal GSM burst carries digitized voice data or other information in a 57-bit data field, and includes guard periods and training sequences to help with timing synchronization and equalization between the mobile station and base transceiver station. GSM networks operate at different frequencies around the world, with GSM-900 being most common in Europe and other parts of the world.
The document discusses the installation and configuration of an STM-16 synchronous digital hierarchy (SDH) transmission link between Ramna and SBN sites. Key steps included installing single-mode fiber, optical multiplexer equipment, electrical interfaces and cross-connects. Testing validated the optical power levels, fiber continuity and service commissioning over the 2.5 Gbps link. Minor issues were addressed during installation and the STM-16 SDH connection was completed successfully.
Una red conecta ordenadores mediante cable o medios inalámbricos para compartir recursos como archivos e impresoras. Las redes se clasifican según su alcance geográfico en PAN, LAN, MAN y WAN. Una LAN típica conecta ordenadores en una oficina usando cable, mientras que una WAN global como Internet usa líneas telefónicas. Los componentes clave de una red son las tarjetas de red, cableado, dispositivos de distribución como switches, y sistemas operativos de red.
ATM is a packet-oriented transfer mode. It allows multiple logical connections to be multiplexed over a single physical interface. The information flow on each logical connection is organized into fixed-size packets, called cells. As with frame relay, there is no link-by-link error control or flow control.
Computer Networks Unit 2 UNIT II DATA-LINK LAYER & MEDIA ACCESSDr. SELVAGANESAN S
The document discusses data link layer framing and protocols. It describes:
1) Two main approaches to framing - byte-oriented (using sentinel characters) and bit-oriented (using bit stuffing). Protocols discussed include BISYNC, DDCMP, and HDLC.
2) Features of PPP framing including negotiated field sizes and use of LCP control messages.
3) Functions of data link layer including framing, flow control, error control, and media access control. The relationship between the logical link control and media access control sublayers is also covered.
This presentation provides an overview of Mobile IPv6. It introduces Mobile IPv6 and explains that it enables IPv6 nodes to move between IP subnets. It describes the key entities in a Mobile IPv6 implementation including home agents and foreign agents. It also covers features of IPv6 like address autoconfiguration, neighbor discovery, and extension headers. The presentation compares IPv4 and IPv6, explains why IPv5 was not adopted, and discusses advantages and applications of IPv6 as well as Mobile IPv6.
This document discusses network management for wireless sensor networks. It begins with an introduction to traditional network management models and then discusses key design issues for network management in WSNs including power efficiency, scalability, and simplicity. It provides MANNA as an example management architecture for WSNs and discusses other related issues like naming, localization, and fault tolerance. The document also outlines applications of WSNs such as habitat monitoring, structural monitoring, and smart roads.
PDH and SDH are digital multiplexing techniques. PDH uses asynchronous multiplexing and operates over asynchronous networks, applying positive justification. It allows tributary clocks to differ slightly. SDH uses synchronous multiplexing and operates over synchronous networks, applying zero justification. Tributary clocks must be synchronized to a master clock. SDH was developed to simplify interconnection between network operators and expand compatibility by establishing a international standard to replace the different PDH standards.
The document discusses wireless WAN technologies including cellular telephone networks and satellite networks. It covers the evolution of cellular networks from first to third generation, describing technologies like AMPS, D-AMPS, GSM, and IS-95. It also discusses different types of satellite systems including GEO, MEO, and LEO satellites, as well as examples of satellite systems like Iridium and Teledesic that provide global voice and data communication services.
Mobile computing unit2,SDMA,FDMA,CDMA,TDMA Space Division Multi Access,Frequ...Pallepati Vasavi
This document discusses various terminology related to the MAC sublayer, including:
1. The station model consisting of independent stations that generate frames for transmission.
2. The single channel assumption where a single channel is available for all communication.
3. The collision assumption where if two frames are transmitted simultaneously they will overlap and be garbled.
It then covers concepts such as carrier sensing, hidden and exposed terminals, and near and far terminals that create challenges for wireless networks. Finally, it introduces various multiple access methods including SDMA, FDMA, TDMA, and CDMA.
What is Quality of Service?
-Basic mechanisms
-Leaky and token buckets
-Integrated Services (IntServ)
-Differentiated Services (DiffServ)
-Economics and Social factors facing QoS
-QoS Vs. Over Provisioning
The document discusses MAC layer protocols, specifically CSMA/CD and CSMA/CA.
CSMA/CD is used for wired networks and works by having nodes listen to check if the medium is free before transmitting. If a collision is detected, transmission stops and resumes after a backoff time.
CSMA/CA is used for wireless networks and aims to avoid collisions through the use of request to send, clear to send, and acknowledgement frames exchanged between nodes, rather than detecting collisions.
Both protocols reduce collisions compared to simple CSMA, but CSMA/CA is less efficient and cannot completely solve collisions in wireless networks due to issues like hidden terminals.
ATM is a cell relay protocol designed to optimize fiber optic networks. It breaks data into fixed-size cells for uniform transmission. ATM aims to maximize bandwidth, interface existing systems, be inexpensive, support telecom hierarchies, ensure reliable delivery, and minimize software functions. Connections between endpoints are established through virtual paths and circuits identified by header fields. Cells contain a 5-byte header and 48-byte payload. Connections can be permanent or switched. ATM defines layers for applications, cell processing, and physical transmission. It supports various quality of service levels through parameters like cell error and loss rates.
The document discusses different types of transmission media used to transmit signals from sender to receiver. It describes guided media like twisted-pair cable, coaxial cable and fiber-optic cable. It provides details on their characteristics, applications, advantages and disadvantages. Twisted-pair cable is commonly used for telephone lines and low-speed LANs. Coaxial cable has higher bandwidth but is more expensive over long distances. Fiber-optic cable has the highest bandwidth and data rates but requires more skilled installation and maintenance.
The document summarizes contention-based MAC protocols for wireless sensor networks. It discusses the PAMAS protocol, which provides detailed overhearing avoidance and uses two channels - a data channel and control channel. Signaling packets like RTS, CTS, and busy tones are transmitted on the control channel. It also covers concepts like low duty cycles, wake up mechanisms, and protocols like S-MAC that coordinate node schedules to reduce idle listening. Quizzes are included to test understanding of discussed concepts.
This document discusses various MAC protocols for ad hoc wireless networks. It begins by outlining key issues in designing MAC protocols for these networks, such as bandwidth efficiency, quality of service support, and the hidden and exposed terminal problems. It then covers classifications of MAC protocols including contention-based, contention-based with reservation mechanisms, and contention-based with scheduling mechanisms. Specific protocols are discussed within each category.
The document discusses MAC protocols for ad hoc networks. It begins by outlining problems MAC protocols must address, such as bandwidth efficiency, hidden/exposed terminals, and mobility. It then classifies MAC protocols into contention-based without reservation, contention-based with reservation, and contention-based with scheduling. Examples are provided for each category, including MACA, BTMA, D-PRMA, and DPS. The document also covers MAC protocols that use directional antennas to improve throughput and reuse.
This document discusses security issues and solutions related to Voice over IP (VoIP) systems. It begins with an introduction to VoIP and how it works, describing the protocols used including SIP, H.323, MGCP and RTP. It then outlines various security attacks on VoIP systems such as eavesdropping, denial of service attacks, and masquerading. Finally, it discusses approaches to enhancing VoIP security, including using encryption, firewalls, authentication, and secure protocols like SRTP.
Lecture 7 8 ad hoc wireless media access protocolsChandra Meena
1) The document discusses issues with media access control (MAC) protocols in ad hoc wireless networks, including problems like hidden terminals and exposed nodes.
2) It classifies MAC protocols as synchronous, asynchronous, receiver-initiated, or sender-initiated. The RTS-CTS handshake is presented as a solution to the hidden terminal problem.
3) However, the RTS-CTS approach has shortcomings like collisions when RTS and CTS messages are sent by different nodes or when multiple CTS messages are granted. Solutions to the exposed node problem are also discussed.
The GSM radio interface uses FDMA to divide the frequency band into channels and TDMA to divide each frequency channel into time slots to allow multiple users, with each user assigned a single time slot. The normal GSM burst carries digitized voice data or other information in a 57-bit data field, and includes guard periods and training sequences to help with timing synchronization and equalization between the mobile station and base transceiver station. GSM networks operate at different frequencies around the world, with GSM-900 being most common in Europe and other parts of the world.
The document discusses the installation and configuration of an STM-16 synchronous digital hierarchy (SDH) transmission link between Ramna and SBN sites. Key steps included installing single-mode fiber, optical multiplexer equipment, electrical interfaces and cross-connects. Testing validated the optical power levels, fiber continuity and service commissioning over the 2.5 Gbps link. Minor issues were addressed during installation and the STM-16 SDH connection was completed successfully.
Una red conecta ordenadores mediante cable o medios inalámbricos para compartir recursos como archivos e impresoras. Las redes se clasifican según su alcance geográfico en PAN, LAN, MAN y WAN. Una LAN típica conecta ordenadores en una oficina usando cable, mientras que una WAN global como Internet usa líneas telefónicas. Los componentes clave de una red son las tarjetas de red, cableado, dispositivos de distribución como switches, y sistemas operativos de red.
ATM is a packet-oriented transfer mode. It allows multiple logical connections to be multiplexed over a single physical interface. The information flow on each logical connection is organized into fixed-size packets, called cells. As with frame relay, there is no link-by-link error control or flow control.
Computer Networks Unit 2 UNIT II DATA-LINK LAYER & MEDIA ACCESSDr. SELVAGANESAN S
The document discusses data link layer framing and protocols. It describes:
1) Two main approaches to framing - byte-oriented (using sentinel characters) and bit-oriented (using bit stuffing). Protocols discussed include BISYNC, DDCMP, and HDLC.
2) Features of PPP framing including negotiated field sizes and use of LCP control messages.
3) Functions of data link layer including framing, flow control, error control, and media access control. The relationship between the logical link control and media access control sublayers is also covered.
This presentation provides an overview of Mobile IPv6. It introduces Mobile IPv6 and explains that it enables IPv6 nodes to move between IP subnets. It describes the key entities in a Mobile IPv6 implementation including home agents and foreign agents. It also covers features of IPv6 like address autoconfiguration, neighbor discovery, and extension headers. The presentation compares IPv4 and IPv6, explains why IPv5 was not adopted, and discusses advantages and applications of IPv6 as well as Mobile IPv6.
This document discusses network management for wireless sensor networks. It begins with an introduction to traditional network management models and then discusses key design issues for network management in WSNs including power efficiency, scalability, and simplicity. It provides MANNA as an example management architecture for WSNs and discusses other related issues like naming, localization, and fault tolerance. The document also outlines applications of WSNs such as habitat monitoring, structural monitoring, and smart roads.
PDH and SDH are digital multiplexing techniques. PDH uses asynchronous multiplexing and operates over asynchronous networks, applying positive justification. It allows tributary clocks to differ slightly. SDH uses synchronous multiplexing and operates over synchronous networks, applying zero justification. Tributary clocks must be synchronized to a master clock. SDH was developed to simplify interconnection between network operators and expand compatibility by establishing a international standard to replace the different PDH standards.
The document discusses wireless WAN technologies including cellular telephone networks and satellite networks. It covers the evolution of cellular networks from first to third generation, describing technologies like AMPS, D-AMPS, GSM, and IS-95. It also discusses different types of satellite systems including GEO, MEO, and LEO satellites, as well as examples of satellite systems like Iridium and Teledesic that provide global voice and data communication services.
Mobile computing unit2,SDMA,FDMA,CDMA,TDMA Space Division Multi Access,Frequ...Pallepati Vasavi
This document discusses various terminology related to the MAC sublayer, including:
1. The station model consisting of independent stations that generate frames for transmission.
2. The single channel assumption where a single channel is available for all communication.
3. The collision assumption where if two frames are transmitted simultaneously they will overlap and be garbled.
It then covers concepts such as carrier sensing, hidden and exposed terminals, and near and far terminals that create challenges for wireless networks. Finally, it introduces various multiple access methods including SDMA, FDMA, TDMA, and CDMA.
What is Quality of Service?
-Basic mechanisms
-Leaky and token buckets
-Integrated Services (IntServ)
-Differentiated Services (DiffServ)
-Economics and Social factors facing QoS
-QoS Vs. Over Provisioning
The document discusses MAC layer protocols, specifically CSMA/CD and CSMA/CA.
CSMA/CD is used for wired networks and works by having nodes listen to check if the medium is free before transmitting. If a collision is detected, transmission stops and resumes after a backoff time.
CSMA/CA is used for wireless networks and aims to avoid collisions through the use of request to send, clear to send, and acknowledgement frames exchanged between nodes, rather than detecting collisions.
Both protocols reduce collisions compared to simple CSMA, but CSMA/CA is less efficient and cannot completely solve collisions in wireless networks due to issues like hidden terminals.
ATM is a cell relay protocol designed to optimize fiber optic networks. It breaks data into fixed-size cells for uniform transmission. ATM aims to maximize bandwidth, interface existing systems, be inexpensive, support telecom hierarchies, ensure reliable delivery, and minimize software functions. Connections between endpoints are established through virtual paths and circuits identified by header fields. Cells contain a 5-byte header and 48-byte payload. Connections can be permanent or switched. ATM defines layers for applications, cell processing, and physical transmission. It supports various quality of service levels through parameters like cell error and loss rates.
The document discusses different types of transmission media used to transmit signals from sender to receiver. It describes guided media like twisted-pair cable, coaxial cable and fiber-optic cable. It provides details on their characteristics, applications, advantages and disadvantages. Twisted-pair cable is commonly used for telephone lines and low-speed LANs. Coaxial cable has higher bandwidth but is more expensive over long distances. Fiber-optic cable has the highest bandwidth and data rates but requires more skilled installation and maintenance.
The document summarizes contention-based MAC protocols for wireless sensor networks. It discusses the PAMAS protocol, which provides detailed overhearing avoidance and uses two channels - a data channel and control channel. Signaling packets like RTS, CTS, and busy tones are transmitted on the control channel. It also covers concepts like low duty cycles, wake up mechanisms, and protocols like S-MAC that coordinate node schedules to reduce idle listening. Quizzes are included to test understanding of discussed concepts.
This document discusses various MAC protocols for ad hoc wireless networks. It begins by outlining key issues in designing MAC protocols for these networks, such as bandwidth efficiency, quality of service support, and the hidden and exposed terminal problems. It then covers classifications of MAC protocols including contention-based, contention-based with reservation mechanisms, and contention-based with scheduling mechanisms. Specific protocols are discussed within each category.
The document discusses MAC protocols for ad hoc networks. It begins by outlining problems MAC protocols must address, such as bandwidth efficiency, hidden/exposed terminals, and mobility. It then classifies MAC protocols into contention-based without reservation, contention-based with reservation, and contention-based with scheduling. Examples are provided for each category, including MACA, BTMA, D-PRMA, and DPS. The document also covers MAC protocols that use directional antennas to improve throughput and reuse.
This document discusses various MAC protocols for ad hoc wireless networks. It begins by outlining key issues in designing MAC protocols for these networks, such as bandwidth efficiency, quality of service support, and the hidden and exposed terminal problems. It then covers classifications of MAC protocols including contention-based, contention-based with reservation mechanisms, and contention-based with scheduling mechanisms. Specific protocols are discussed within each category.
The document summarizes the Cluster Based Routing Protocol (CBRP) for mobile ad hoc networks. CBRP divides the network into clusters with cluster heads that maintain routing information and perform routing functions. Key aspects of CBRP include periodic hello messages to track neighbors, identifier-based clustering, on-demand route discovery using cluster heads, source routing with loose and strict routes, local route repair instead of re-routing, and advantages like lower overhead and higher delivery rates compared to other protocols. CBRP is well-suited for situations requiring mobile network connectivity like disaster recovery or military operations.
Mobile ad-hoc networks have frequent host and topology changes with no cellular infrastructure and require multi-hop wireless links for data transmission between nodes. Routing protocols must discover routes between nodes that may not be directly connected. Table-driven protocols like Destination Sequenced Distance Vector (DSDV) and Wireless Routing Protocol (WRP) maintain up-to-date routing tables through periodic broadcasts but generate significant control overhead. DSDV uses sequence numbers to distinguish stale routes and avoid loops while WRP maintains four tables for routing information.
The document discusses on-demand driven reactive routing protocols. It provides an overview of table-driven vs on-demand routing protocols and describes two popular on-demand protocols - Dynamic Source Routing (DSR) and Ad Hoc On-Demand Distance Vector Routing (AODV) in detail. DSR uses source routing by adding the complete route to packet headers. AODV maintains routing tables at nodes and relies on dynamically establishing next hop information for routes.
The document summarizes several routing protocols used in wireless networks. It discusses both table-driven protocols like DSDV and on-demand protocols like AODV. It provides details on how each protocol performs routing and maintains routes. It also outlines some advantages and disadvantages of protocols like DSDV, AODV, DSR, and TORA.
The document discusses several IEEE 802 standards for local and metropolitan area networks. It describes the purpose of IEEE 802 standards to define physical network interfaces and the lowest three layers of the network architecture. It provides details on some famous IEEE 802 standards including 802.2 (LLC), 802.3 (Ethernet), 802.4 (Token Bus), 802.5 (Token Ring), 802.6 (DQDB), and 802.11 (Wireless LAN). It then focuses on explaining the Ethernet, Token Bus and Token Ring standards in more depth including their frame formats and other specifications.
Lecture 1 mobile and adhoc network- introductionChandra Meena
This document provides an overview of a course on mobile and ad hoc networks. It lists two textbooks that will be used and states that the goal is to cover fundamental design issues and solutions for network architecture and protocols. It also lists some related websites and outlines the objectives of chapters that will introduce wireless communication technologies, network standards, and multiple access techniques for ad hoc networks.
The document discusses ad hoc networks and wireless sensor networks. It defines an ad hoc network as a temporary network composed of mobile nodes without preexisting infrastructure that is self-organizing. Wireless sensor networks are introduced as a collection of sensor nodes densely deployed to monitor conditions and cooperatively pass data back to central nodes. The document outlines key characteristics of both networks including their temporary and adaptive nature, multi-hop routing, and challenges of mobility, power constraints, and dynamic topology changes.
The document discusses ad-hoc networks and their key characteristics. It describes several challenges in ad-hoc networks including limited battery power, dynamic network topology, and scalability issues. It also summarizes several ad-hoc network routing protocols (e.g. DSDV, AODV, DSR), addressing both table-driven and on-demand approaches. Additionally, it outlines some ad-hoc MAC protocols like MACA and PAMAS that aim to manage shared wireless medium access.
Mobile ad hoc networks (MANETs) are formed spontaneously by wireless devices without any preexisting infrastructure. Nodes in a MANET are free to move and dynamically change the network topology. MANETs have applications in military operations, emergency response, education, and home/office use. Key challenges include dynamic topology, limited resources, and lack of centralized management. Media access control protocols address issues like hidden and exposed terminals. Routing protocols can be proactive (table-based) or reactive (on-demand) to find routes between nodes in the changing network.
This document discusses different medium access control protocols. It covers random access protocols like ALOHA and slotted ALOHA, carrier sensing protocols like CSMA and CSMA/CD, and scheduling protocols like polling and token passing. It provides analysis of the throughput and efficiency of these different MAC protocols. It also compares the approaches and discusses factors in selecting a MAC protocol.
The document discusses ad hoc networks. It defines an ad hoc network as a temporary network connection between devices without fixed infrastructure. Key characteristics of ad hoc networks include dynamic topology, nodes that can freely join and leave, multi-hop routing, and limited bandwidth. The document compares ad hoc networks to wired and managed wireless networks. It also discusses different types of ad hoc networks and routing protocols like DSR and AODV. Applications of ad hoc networks include military operations, conferences, and emergency response situations.
The document discusses MAC protocols for wireless sensor networks. It begins by outlining issues in designing MAC protocols for ad-hoc wireless networks, such as bandwidth efficiency, quality of service support, synchronization, and the error-prone shared wireless medium. It then describes the design goals of MAC protocols. The document classifies MAC protocols into three categories: contention-based protocols, contention-based protocols with reservation mechanisms, and contention-based protocols with scheduling mechanisms. Several examples are provided for each category, including MACA, FAMA, and RTMAC protocols.
MAC PROTOCOLS FOR AD HOC WIRELESS NETWORKS
Issues in designing a MAC Protocol- Classification of MAC Protocols- Contention based protocols- Contention based protocols with Reservation Mechanisms- Contention based protocols with Scheduling Mechanisms – Multi channel MAC-IEEE 802.11
A New MultiChannel MAC Protocol With On-Demand Channel Assignment For Multi-H...Wendy Hager
The document presents a multi-channel MAC protocol called SM that uses static channel assignment. Each mobile host is assigned a single channel and uses that channel for all transmissions following the IEEE 802.11 standard. However, several issues are identified when directly applying a single-channel protocol to a multi-channel system, including missing control packets, exposed terminals, and channel deadlocks. To address these issues, the document proposes a new dynamic multi-channel MAC protocol called DCA that flexibly assigns channels based on demand and requires only two transceivers per host.
This document discusses MAC protocols for ad hoc wireless networks. It begins by outlining key issues in designing MAC protocols, such as bandwidth efficiency, quality of service support, and addressing hidden and exposed terminal problems. It then classifies MAC protocols into contention-based, contention-based with reservation mechanisms, and contention-based with scheduling mechanisms. Several example protocols are described for each category, including how they address the issues outlined earlier in the document.
This document discusses MAC protocols for ad-hoc wireless networks. It begins by outlining key issues in designing these protocols, such as bandwidth efficiency, quality of service support, and the hidden/exposed terminal problems. It then describes the classifications of MAC protocols, including contention-based, contention-based with reservation, and contention-based with scheduling mechanisms. Several example protocols are discussed for each classification, including how they address the issues and provide distributed channel access in ad-hoc networks.
The document summarizes MAC protocols for wireless mesh networks. It begins with an introduction to wireless mesh network architectures and important definitions. It then discusses single channel MAC protocols like S-MAC, T-MAC, and a new TDMA-based protocol. It also covers multi-channel MAC protocols classifications and examples like CC-MMAC and SSCH MAC. The document provides detailed explanations of the mechanisms and concepts behind various single and multi-channel MAC protocols.
This document summarizes research on medium access control (MAC) layer protocols for ad-hoc networks. It begins with an introduction to ad-hoc networks and their key properties. It then discusses important issues at the MAC layer for these dynamic networks, including limited bandwidth, errors, and changing topologies. Several MAC protocol classifications and examples are provided, such as power-aware, multiple channel, and quality of service protocols. The document concludes by discussing future research directions for addressing open problems at the MAC layer in ad-hoc networks.
Simulation based Evaluation of a Simple Channel Distribution Scheme for MANETsIOSR Journals
This document presents a proposed multi-channel distribution scheme for mobile ad hoc networks (MANETs) and evaluates it through simulation. The proposed scheme assigns channels to nodes based on their node IDs to avoid control overhead from time synchronization. While neighboring nodes on the same channel is possible, the probability is low given random node distribution. The proposed scheme is compared to a single-channel scheme in ns-2 simulations. Results show the proposed technique has better performance.
The document discusses challenges with using TCP in mobile ad hoc networks (MANETs) and evaluates potential solutions. Specifically, it finds that:
1) TCP performs poorly in MANETs due to high packet loss from route failures and wireless errors, which TCP misinterprets as congestion.
2) TCP variants like Westwood and Jersey that more accurately estimate bandwidth perform better but are not sufficient.
3) A new transport protocol like ATP that is rate-based rather than window-based and leverages intermediate nodes may better address MANET issues.
A preamble-based approach for Providing QOS support in Wireless Sensor Networkdiala wedyan
The document discusses various MAC protocols for wireless sensor networks, including TDMA, Low Power Listening, XMAC, and BMAC protocols. It then describes a proposed Back off Preamble-based MAC protocol that uses different preamble lengths to prioritize medium access. The protocol is evaluated through simulation in OPNET Modeler, comparing its performance under different quality of service strategies for handling high and low priority traffic flows. The proposed protocol aims to provide reliable delivery and satisfy quality of service requirements for wireless sensor networks.
1) Wireless networks developed in the 1990s with incompatible products until standardization by the IEEE 802 committee.
2) The IEEE 802 standards include 802.11 for wireless LANs which supports both infrastructure with access points and ad hoc networks without access points.
3) The 802.11 standard defines the physical and MAC layers including addressing problems like the hidden and exposed terminal problems through the use of CSMA/CA and RTS/CTS messaging.
Medium Access Control (MAC) protocols provide reliable communication between nodes sharing the same physical medium. For wireless networks, MAC protocols must address power efficiency and scalability challenges. Common MAC approaches include random access protocols like CSMA/CA, scheduled access using TDMA, and hybrid approaches. Duty-cycling techniques like low power listening in B-MAC aim to minimize idle listening to reduce energy use.
This document discusses various contention-based MAC protocols for ad-hoc and sensor networks. It describes the protocols MACA, MACAW, MACA-BI, BTMA, DBTMA, and RI-BTMA. These protocols differ in how they handle issues like hidden and exposed terminals and whether they are sender-initiated or receiver-initiated. A table compares the protocols based on how well they solve hidden/exposed terminal problems, their throughput, fairness, the signals they use, whether they use a single or multiple channel, and whether they are sender-initiated or receiver-initiated.
The document discusses wireless and mobile computing, specifically focusing on MAC (media access control) layer protocols for wireless networks. It provides an overview of MAC layer issues for wireless networks, classifications of MAC protocols (including contention-based, reservation-based, and scheduling-based), and design goals of MAC protocols such as distributed operation, quality of service support, bandwidth efficiency, and minimizing hidden and exposed terminal problems.
The document summarizes and compares several MAC layer synchronization protocols for wireless sensor networks, including IEEE 802.11, IEEE 802.15.4, S-MAC, T-MAC, and OB-MAC. It describes the operation and key features of each protocol, such as sleep schedules, synchronization techniques, and handling of channel contention. Simulation results using the NS2 simulator show that OB-MAC has the lowest energy consumption compared to the other protocols. The document concludes that all WSN MAC protocols are designed for energy efficiency and proposes further analyzing OB-MAC and collision handling through a hardware testbed implementation.
The document discusses various medium access control (MAC) protocols for wireless sensor networks. It begins with an introduction to wireless sensor networks, including their components, goals, communication patterns, and applications. It then discusses the major challenges of power consumption in wireless sensor networks and the sources of wasteful power usage. The document outlines several conventional MAC protocols including CSMA, CSMA/CA, and IEEE 802.11 and their disadvantages for wireless sensor networks. It distinguishes scheduled and unscheduled MAC protocols for wireless sensor networks and provides examples of some prominent protocols for each category like S-MAC and B-MAC.
This document summarizes several medium access control (MAC) protocols for wireless networks, focusing on those suitable for mobile and energy-efficient operation. It discusses both contention-based protocols like MACA, S-MAC, and B-MAC, which use carrier sensing and random access, as well as schedule-based protocols like LEACH, SMACS, and TRAMA, which establish schedules to avoid collisions. It also covers the IEEE 802.15.4 standard for low-power wireless personal area networks.
The document summarizes key points from an 8th lecture on wireless sensor networks. It discusses various medium access control (MAC) protocols that control when nodes can access a shared wireless medium. These include contention-based protocols like MACA that use RTS/CTS handshaking and schedule-based protocols with fixed or dynamic scheduling. It also describes energy-efficient MAC protocols for low data rate sensor networks like S-MAC, T-MAC, and preamble sampling that increase sleep time to reduce energy use through synchronized sleep schedules or long preambles.
This document proposes a time division beacon scheduling mechanism for building synchronized multi-hop cluster-tree wireless sensor networks using the IEEE 802.15.4/Zigbee protocol stack. It analyzes challenges with beacon frame collisions in cluster-tree networks and reviews approaches proposed by others. The key contributions are a beacon frame scheduling mechanism based on time division to avoid collisions, a duty cycle management methodology, and an experimental demonstration of feasibility using a test bed. The goal is to overcome limitations in the standards for constructing synchronized multi-hop networks.
The document is a technical report from the Center for Satellite and Hybrid Communication Networks (CSHCN) at the University of Maryland that proposes a new single channel TDMA-based broadcast scheduling protocol called the Five-Phase Reservation Protocol (FPRP) for mobile ad hoc networks. The FPRP allows nodes to efficiently make nearly conflict-free reservations for TDMA broadcast slots in a distributed manner without relying on centralized coordination or prior network information. It employs a five-phase contention process localized to each node's two-hop neighborhood to minimize collision probability during reservation.
The document discusses medium access control (MAC) protocols for wireless ad-hoc networks. It describes several MAC protocols including the Five Phase Reservation Protocol (FPRP) and Distributed Wireless Ordering Protocol (DWOP). FPRP uses a five phase process for distributed reservation of time slots. DWOP aims to provide fair channel access that approximates a first-in-first-out scheduling order by sharing packet arrival times between nodes. The document evaluates these protocols and discusses their advantages in providing quality of service guarantees and fair scheduling in wireless ad-hoc networks.
The document discusses MAC layer protocols for wireless networks. It begins by explaining that MAC (Media Access Control) controls access to the shared transmission medium on a local area network. It aims to prevent nodes from interfering with each other's transmissions. Common MAC protocols discussed include CSMA/CD used in Ethernet, and early wireless MAC protocols like MACA which introduced RTS/CTS to avoid the hidden terminal problem. A key part of wireless MAC is the IEEE 802.11 distributed coordination function, which uses carrier sensing, backoff mechanisms and RTS/CTS/DATA/ACK to allow multiple nodes fair access to the shared wireless channel.
This document summarizes a research paper on a CDMA-based MAC protocol for wireless ad hoc networks. The protocol, called CA-CDMA, addresses the near-far problem in CDMA systems by incorporating distributed power control and interference feedback between nodes. Simulation results show that CA-CDMA can increase throughput by up to 280% compared to 802.11 by allowing simultaneous transmissions through power control. Future work may involve combining CA-CDMA with other capacity enhancement techniques like directional antennas or multi-rate support.
This document proposes a new contention-based forwarding (CBF) mechanism for position-based routing in mobile ad hoc networks. CBF selects the next hop through a distributed contention process using biased timers, without requiring periodic beacon messages. It aims to use more accurate position information than existing beacon-based approaches and eliminate routing overhead from beacons. CBF works in three steps: broadcast of the packet, contention between neighbors to become the next hop using biased timers, and suppression of duplicate packets from losing neighbors. The document analyzes CBF's properties and compares its performance to beacon-based greedy forwarding through simulation.
The document describes an opportunistic packet scheduling and media access control (OSMA) protocol for wireless LANs and multi-hop ad hoc networks. The OSMA protocol aims to alleviate the head-of-line blocking problem and exploit multiuser diversity by allowing a node to schedule transmissions to receivers with good channel conditions. The key mechanisms of OSMA are multicast RTS frames containing a list of candidate receivers, and priority-based CTS frames where the receiver with the best channel and highest priority replies first to avoid collisions. Simulation results show the OSMA protocol can significantly improve network throughput while maintaining fairness between links.
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OUTLINE:
• Problems for MAC to deal with;
• Design goals;
• Classification of MAC protocols
• Contention-based protocols
• Contention-based with reservation mechanism
• Contention-based with scheduling mechanism
• MAC protocols for directional antennas
• Power control MAC protocols
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1. Problems for MAC to deal with
Aim of MAC: provide fair access to shared broadcast radio channel.
Issues to deal with:
• Bandwidth efficiency:
– must be maximized.
• Real-time traffic support:
– should be provided.
• Synchronization:
– sometimes needed, e.g. TDMA.
• Shared broadcast medium:
– collisions must be avoided/minimized.
• Lack of central coordination:
– fully distributed MAC design.
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• Hidden terminal problem:
– collisions → inefficient bandwidth utilization.
receiver senderhidden terminal
collisionpackets packets
Figure 1: Illustration of the hidden terminal problems.
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• Exposed terminal problem:
– inability to transmit → inefficient bandwidth utilization.
sender receiverexposed terminal
packets
receiver
packets
Figure 2: Illustration of the exposed terminal problem.
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• Mobility of nodes:
– loss of connectivity;
– network partitioning;
– bit errors.
t
t+Delta(t)
Figure 3: Network partitioning is one of the biggest problem to deal with at MAC sublayer.
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2. Design goals
What we want from MAC protocol:
• operation of the protocol should be distributed;
• should support real-time traffic;
• the access delay must be minimized;
• available bandwidth must be utilized efficiently;
• fair bandwidth allocation to competing nodes;
• control overhead must be minimized;
• the effects of hidden/exposed terminals must be minimized;
• must be scalable;
• should minimize power consumption;
• should provide synchronization between nodes.
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3. Classification of MAC protocols
MAC protocol for ad-hoc networks must be classified into:
• Contention-based protocols without reservation/scheduling:
– no reservation of the bandwidth is made;
– guarantees are not possible.
• Contention-based protocols with reservation mechanisms:
– bandwidth for transmission is reserved in advance.
– guarantees are possible.
• Contention-based protocols with scheduling mechanisms:
– distributed scheduling between nodes is used.
– guarantees are possible.
• Protocols that do not fall to any of these categories:
– implement several features of different protocol groups or
– use completely different approach
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4. Contention based protocols w/o reservation/scheduling
The basic idea: do your best to not cause a collision.
4.1. MACA protocol
MACA is based on CSMA/CA that operates as follows:
• the sender sense the channel for the carrier signal;
• if the carrier is present it retries to sense the channel after some time (exp. back-off);
• if not, the sender transmits a packet.
The following shortcomings are inherent to CSMA/CA:
• −: hidden terminal problem leading to frequent collisions;
• −: exposed terminal problem leading to worse bandwidth utilization.
To avoid it:
• virtual carrier sensing;
• RTS-CTS handshake before transmission.
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Neighbor Sender Receiver Neighbor
RTS
CTS CTS
Data
RTS
Data
ACK ACK
Figure 4: Packet transmission in MACA.
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BACK-OFF RTS
CTS
DATA
ACK
BACK-OFF
NAV FROM RTS
NAV FROM CTS
NAV FROM DATA
SENDER
REVEIVER
NEIGHBOR
NEIGHBOR
Figure 5: Usage of virtual carrier sensing.
NAV: network allocation vector – implementation of virtual carrier sensing.
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If the transmission fails:
• contention window: CW×2 (multiplicative increase, immediate decrease);
• retransmission.
31
63
127
255
511
1023 slots
initial
1st
2nd
5th
3rd
4th
Figure 6: Evolution of the contention window with increasing of transmission attempts.
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Problem 1 of MACA: starvation of flows:
• both S1 and S2 have the high volume of traffic, S1 seizes the channel first;
• packets transmitted by S2 get collided and it doubles CW (CW = 2CW);
• the probability that the node S2 seizes the channel is decreasing.
S1 S2R
Figure 7: Starvation of the flow from S2.
Solution:
• the packet header contains the field set to the current back-off value of the transmitting node;
• a node receiving this packet copies this value to its back-off counter (fairness);
• CW = CWmin after every successful transmission.
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Problem 2 of MACA: fast adjustment of CW:
• when a node successfully transmits a packet;
• when a collisions is detected by a node.
RTS CTS DATA ACK
RECEIVER
S2
CW=511
S1
S1 S2R
BACKOFF
CW=511
BACKOFF
CW=CWmin
BACKOFF
Figure 8: Rapid adjustments of the CW.
Solution: multiplicative increase when collision, linear decrease when success.
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Problem 3 of MACA: an exposed node is free to transmit.
• ongoing transmission S1-R1;
• node S2 hears RTS but not CTS (exposed node);
• S2 initiates transfer to R2;
• DATA from S1 and CTS from R2 may collide, CW unnecessary increases at S2.
S1 S2 R2R1
CTS
RTSDATA RTS
DATA
RTS
CTS
Figure 9: Problems with exposed node.
Solution: use of small data sending packet (DS) to update information.
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4.2. Busy tone multiple access protocol (BTMA)
Multichannel protocol where the channel is separated into:
• control channel: used for data transmission;
• data channel: used for busy tone transmission.
BTMA works as follows:
• a node senses the control channel to check whether the busy tone is active;
• if not, it turns on the busy tone signal and starts data transmission;
• if yes, a node waits for a random period of time and repeats the procedure;
• any node that senses the carrier on the incoming data channel also transmits a busy tone.
There are following advantages are shortcoming of the BTMA:
• +: simple enough;
• +: probability of collision is extremely low;
• −: bandwidth utilization is low (nodes are blocked in two-hop neighborhood).
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4.3. MACA by invitation (MACA-BI)
Receiver-initiated MAC protocol providing the following extension to MACA:
• MACA: RTS-CTS-DATA-ACK;
• MACA-BI eliminates the need for CTS using the receiver’s ready-to-receive (RTR) packet.
Sender Receiver Neighbor
RTR RTR
DATA
Figure 10: Transmission in MACA-BI.
• needs information about the traffic at neighboring nodes;
• this information is included into DATA packets.
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4.4. Media access with reduced handshake (MARCH)
RTS packet is used only for the first DATA packet of the stream:
• nodes know about packet arrival at neighboring node listening to CTS signals;
• to relay packet, it sends a CTS packet to the concerned node.
node 1 node 2 node 3
RTS
node 4
CTS CTS
DATA
CTS
DATA
CTS
CTS
DATA
Chain relaying
Figure 11: Relaying using the MARCH.
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The CTS packet in MARCH carries the following information:
• the MAC address of the sender and the receiver node;
• route identification number Rid to distinguish between routes.
A B C D E
X
Y
Route 1: A-B-C-D-E
Route 2: X-C-Y
MARCH is characterized by the following advantages and shortcomings:
• +: very high throughput;
• +: very low control overhead;
• −: access to routing information is required → cross-layering!
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5. Contention-based protocols with reservations
Use bandwidth reservation techniques:
• contention occurs here only at resource reservation phase;
• once bandwidth is reserved a node gets an exclusive access to the media.
5.1. Distributed packet reservation multiple access protocol (D-PRMA)
D-PRMA is a TDMA based scheme where the channel is divided into frames.
Minislot 2
Slot 1 Slot 2 Slot n...
Minislot 1 Minislot m
RTS/BI CTS/BI
Frame length
DATA
Figure 12: Frame structure in D-PRMA.
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Slot reservation and overcoming the hidden terminal problem:
• Request to send / busy indication (RTS/BI) and clear to send / busy indication (CTS/BI).
The protocol operates as follows:
• nodes having a packet for transmission contend in the first minislot of each slot;
• the remaining (m − 1) minislots in the slot are granted to the node that wins the contention;
• the same slot in subsequent frames is reserved for the this terminal, until it ends transmission;
• if no node wins the first minislot, the remaining minislots subsequently used for contention;
• within a reserved slot communication is performed using TDD or FDD.
Slot reservation mechanism performs as follows:
• a certain period in the beginning of each minislot is reserved for carrier-sensing;
• if a nodes detects a channel to be idle, it sends a RTS packet to destination using RTS/BI;
• receiver answers with CTS packets in the CTS/BI field of the same minislot;
• the sender upon receiving CTS, gets a reservation for current slot (all minislots).
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To prioritize the voice traffic:
• Rule 1:
– voice nodes traffic are allowed to start contention from minislot 1 with probability 1.
– data nodes start contention from minislot 1 with probability < 1;
– for the remaining (m − 1) minislots all nodes contend with probability 1.
• Rule 2:
– if the node winning the contention is the data node, only the current slot is reserved;
– if the node winning the contention is the voice node, subsequent slots are also reserved.
To make it real the following requirements must be satisfied:
Requirements for nodes other than a winning one:
• hidden and exposed terminals should be avoided;
• no contention:
– no contention in remaining minislots;
– no contention in the subsequent slots.
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Requirement 1: (no contention in other minislots)
Hidden terminal problem:
• RTS packet do not suffer a collision due to carrier sensing (winning node transmits);
• a node hearing the CTS is not allowed to transmit in the remaining period of the slot.
Exposed terminal problem:
• A node hearing the RTS but not CTS is allowed to transmit.
Requirement 2: (no contention in other slots)
• the receiver and sender transmit a BI signal in minislot 1 of the reserved slot;
• when any node hears BI signal it does not contend in this slot;
• when the transmission is completed both sides stops transmission of BI signal.
Advantages and shortcomings:
• +: D-PRMA is best suited for voice applications;
• −: requires synchronization (TDMA).
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6. Contention-based protocols with scheduling mechanisms
Aim is on transmission scheduling at nodes considering metrics:
• delay targets of packets;
• traffic load at nodes;
• remaining battery power at nodes, etc.
6.1. Distributed priority scheduling (DPS)
This protocols is primarily based on IEEE 802.11 DCF using RTS-CTS-DATA-ACK mechanism.
The communication is as follows:
• RTS packet transmitted by a node carries priority index of the packet (delay, etc.);
• the receiver responds with CTS containing the priority tag and source ID copied from RTS;
• neighbors retrieve this information from RTS and CTS and make entry in scheduling tables;
• source sends DATA and receiver responds with ACK;
• after DATA and ACK is transmitted neighbor updates their scheduling tables.
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RTS
RTS CTS
CTS DATA
DATA ACK
ACK
Node 1
Node 2
Node 3 (neighbor to node 1)
Node 4 (neighbor to node 2)
S D P
6 7 2
RTS
S D P
6 7 2
1 2 7
DATA
S D P
6 7 2
S D P
5 6 5
S D P
5 6 5
1 2 7
CTS ACK
S D P
5 6 5
Figure 13: Packet exchange and scheduling tables update in DPS.
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7. MAC protocols for directional antennas
The following advantages can be achieved using the directional antennas:
• reduced signal interference;
• increase in system throughput;
• improved channel reuse.
7.1. MACA for directional antennas
For this protocol the following assumptions are used:
• each node has only one radio transceiver;
• transceiver is equipped with M directional antennas;
• each antenna covers angle 2π/M;
• transmissions by adjacent antennas never overlap;
• MAC layer is able to switch antennas individually or all antennas together.
Packet transmission is made using RTS-CTS-DATA-ACK.
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CTSRTS
DATA
Figure 14: Packet transmission using directional antennas.
The main problem is to determine the direction of each other:
• idle node listens on all antennas;
• the sender transmits RTS using omnidirectional transmission;
• the receiver responses with CTS using omnidirectional transmission;
• both determines the antennas with the highest quality of the signal and switch them up.
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7.2. Directional busy tone based MAC protocol
The major features of this protocol are as follows:
• it uses directional antenna consisting of N elements;
• for broadcast all elements are used;
• for unicast only one element is used;
• when a node is idle all elements sensing the channel;
• while receiving only one element receives the signal.
It operates as follows:
• a node senses the channel for presence of receiver busy tone (BTr);
• if BTt is not active, it sends RTS on all antennas elements;
• the receiver receives RTS and makes sure that BTt is not present;
• then, the receiver transmits CTS directionally to the sender and turn on the BTr;
• the sender turns on the BTt and sends the DATA packet.
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8. Power control MAC protocol
This protocol allows to vary a transmission range of nodes on a per-packet basis.
There are two modes of operation:
• BASIC protocol;
• PCM protocol.
The BASIC protocol operates as follows:
• RTS and CTS packets are transmitted using the maximum power pmax;
• RTS-CTS packets are used to decide necessary transmission power for DATA and ACK packets:
– Method 1: The receiver send CTS with estimated transmitted level pd < pmax;
– Method 2: CTS is sent back using pmax and the source calculates pd based on pmax:
pd =
pmax
pr
Rxthc, (1)
where
∗ Rxth is the minimum required power and c is a constant
∗ pr is the received signal strength.
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BA CTSRTS
DATA
ACK
C
D
RTS
sensing CTS
sensing
Node C sense carrier of RTS but not CTS;
Node D sense carrier of CTS but not RTS;
Both waits for extended IFS:
- C packet may collide with ACK;
- D packet may collide with DATA.
Solution: increase power to pmax
during
DATA packet transmission:
pmax
pd
DATA packet
Figure 15: The major problem associated with BASIC protocol.
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