Computer Networks: Wireless Networks Ivan Marsic Rutgers University Chapter 6 – Wireless Networks
Wireless Networks Chapter 6
Topic: Mobile Ad-hoc Networks (MANETs) Ad-hoc Network Definition Routing Protocols Dynamic Source Routing (DSR) Ad Hoc On-Demand Distance- Vector (AODV)
Ad-hoc Networks Each mobile device (node) can act as a router Links form and break based on mobility and environmental factors Connectivity (e.g., high probability of instantaneous end-to-end paths existing) is assumed
Mobile Ad-hoc Networks (MANETs) Physical wireless links Network topology
Network Layer Notation vs. Link Layer Transmissions (1)
Network Layer Notation vs. Link Layer Transmissions (2)
Multihop Throughput Challenge: more hops, less throughput Links in route share radio spectrum Extra hops reduce throughput Throughput = 1 Throughput = 1/2 Throughput = 1/3
Ad-hoc Networks Goal: Nodes within the network can send data between themselves. Challenges: –No centralized coordinator to help routing –No “default route” for nodes within the network –Fast topology changes –Limited bandwidth – can’t have too much overhead S D
Ad-hoc Networks Nodes that want to route messages must: –Find out about the topology of the network –Use that topology to do something with the message Control Plane Data Plane S D
Routing Protocol Categories Proactive: –Nodes actively maintain and share topology information, regardless of if there is data to send –Generally timer- or event-based Reactive (On-demand): –“Lazy” approach: Don’t do more work then you have to –Only discover topology/routes when there is data to send Control Plane
Routing Protocol Categories Local next-hop forwarding: –Consult forwarding table for a next hop –Completely local decision Source routing: –Source node places complete path in packet header –Intermediate nodes don’t have to consult their forwarding tables Data Plane S S A A B B D D ABD
Reactive Protocols Names are useful hints at understanding the protocol properties: Ad-hoc On-demand Distance Vector (AODV) Dynamic Source Routing (DSR) Source Routing Next-hop Forwarding Distance Vector Reactive MANET
14 Dynamic Source Routing (DSR) When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery. Source node S floods the network with route request (RREQ) packets (also called query packets). Each node appends its own address in the packet header when forwarding RREQ.
Route Discovery in DSR (1)
Route Discovery in DSR (2) Broadcast RREQ[C] Represents a node that has received RREQ for H from C
Route Discovery in DSR (3)
Route Discovery in DSR (4)
Route Discovery in DSR (5) Unicast RREP[C, E, G, H]
Route Discovery in DSR
Route Discovery in AODV (1)
Route Discovery in AODV
Topic: IEEE n (MIMO Wi-Fi) Physical (PHY) Layer Enhancements MAC Layer Enhancements: Frame Aggregation Block Acknowledgement Reverse Direction (RD) Protocol Backward Compatibility
IEEE n - MIMO
802.11n Channel Bonding and 20/40 MHz Operation
802.11n PHY-layer Frame Format
IEEE Terminology
802.11n MAC-layer Frame Format
Packet Aggregation
802.11n Frame Aggregation E{b 0 }=16 slots
Frame Aggregation: A-MSDU and A-MPDU
Block Acknowledgement Session
Block Acknowledgement Frame
Block ACK Frame Subfields
Block ACK Example
Reverse Direction (RD) Protocol Unidirectional vs. Bidirectional RTS/CTS Access Scheme
802.11n Backwards Compatibility Modes: CTS-to-Self
Dual-CTS protection (CTS-to-self)
Example of L-SIG Duration Setting
802.11n Phased Coexistence Operation (PCO)
Topic: RFID: Radio-Frequency Identification Query Slot Protocol (ALOHA) for Tag Interrogation
RFID - Query Slot Protocol Visit for RFID Protocols Class-1 Generation-2http://
Classification of QoS Techniques in