1. Computer Networks: Wireless Networks
Ivan Marsic
Rutgers University
Chapter 6 – Wireless Networks

2. Wireless Networks
Chapter 6

3. Topic: Mobile Ad-hoc Networks (MANETs)
 Ad-hoc Network Definition
Routing Protocols
Dynamic Source Routing (DSR)
Ad Hoc On-Demand Distance-Vector (AODV)

4. 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

5. Mobile Ad-hoc Networks (MANETs)
Physical wireless links
Network topology

6. Network Layer Notation vs. Link Layer Transmissions (1)

7. Network Layer Notation vs. Link Layer Transmissions (2)

8. 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

9. Ad-hoc Networks S D
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

10. 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

11. Routing Protocol Categories
Control Plane
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

12. Routing Protocol Categories
Data Plane
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 S A B D A B D

13. Reactive Protocols
Names are useful hints at understanding the protocol properties:
Dynamic Source Routing (DSR)
MANET
Source Routing
Ad-hoc On-demand Distance Vector (AODV)
Reactive
Next-hop Forwarding
MANET
Distance Vector

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. 14 14

15. Route Discovery in DSR (1)

16. Route Discovery in DSR (2)
Broadcast RREQ[C]
Represents a node that has received RREQ for H from C

17. Route Discovery in DSR (3)

18. Route Discovery in DSR (4)

19. Route Discovery in DSR (5)
Unicast RREP[C, E, G, H]

20. Route Discovery in DSR

21. Route Discovery in AODV (1)

22. Route Discovery in AODV

23. Topic: IEEE 802.11n (MIMO Wi-Fi)
 Physical (PHY) Layer Enhancements
MAC Layer Enhancements:
Frame Aggregation
Block Acknowledgement
Reverse Direction (RD) Protocol
 Backward Compatibility 23

24. IEEE n - MIMO

25. 802.11n Channel Bonding and 20/40 MHz Operation

26. 802.11n PHY-layer Frame Format

27. IEEE Terminology

28. 802.11n MAC-layer Frame Format

29. Packet Aggregation

30. 802.11n Frame Aggregation
E{b0}=16 slots

31. Frame Aggregation: A-MSDU and A-MPDU

32. Block Acknowledgement Session

33. Block Acknowledgement Frame

34. Block ACK Frame Subfields

35. Block ACK Example

36. Reverse Direction (RD) Protocol
Unidirectional vs. Bidirectional RTS/CTS Access Scheme

37. 802.11n Backwards Compatibility Modes: CTS-to-Self

38. Dual-CTS protection (CTS-to-self)

39. Example of L-SIG Duration Setting

40. 802.11n Phased Coexistence Operation (PCO)

41. Topic: RFID: Radio-Frequency Identification
 Query Slot Protocol (ALOHA) for Tag Interrogation 41

42. RFID - Query Slot Protocol
Visit for RFID Protocols Class-1 Generation-2

44. Classification of QoS Techniques in 802.11