The document discusses the 802.11 MAC protocol and mobility management in wireless networks. It describes the CSMA/CA protocol used in 802.11, including carrier sensing, random backoff, and acknowledgements. It also covers mobility management principles like home and foreign agents, care-of addresses, and indirect routing using tunneling between home and foreign agents. Triangle routing is identified as an issue when a mobile node visits a correspondent's network.

1. Information and Communication
Technologies(ICT)
Principles and Perspectives
Lecture : Distributed multimedia systems

2. The 802.11 MAC Protocol
• 3 classes of multiple access protocol
1. Channel partitioning
2. Random Access
3. Taking Turns
• Random access was chosen which is know as CSMA with collision avoidance
(CSMA/CA)
• CSMA : carrier sense multiple access

3. Ethernet Vs 802.11(aka Wifi)
• Ethernet collision detection
• An Ethernet station listens to the channel as it transmits. If, while transmitting, it
detects that another station is also transmitting, it aborts its transmission and tries to
transmit again after waiting a small, random amount of time
• 802.11 MAC doesn’t implement CD ( collision detection)
• For CD , ability to send and receive at same time is required which is costly in 802.11
adapter
• Even if it is build; due to hidden terminal all collisions will not be detected

4. 802.11 MAC
• once a station begins to transmit a frame, it transmits the frame in its entirety
• Link layer acknowledgment
• Receiver will send an ACK after a short period of time known as Short Inter-frame
Spacing (SIFS)
• If the transmitting station does not receive an acknowledgment within a given amount
of time, it assumes that an error has occurred and retransmits the frame
• If an ACK is not received after some fixed number of retransmissions, the transmitting
station gives up and discards the frame

6. 802.11 CSMA/CA protocol
1. If station sense channel idle; it will transmit after a short period of time
Distributed Inter-frame Space (DIFS)
2. Otherwise, the station chooses a random backoff value. Counts down this
values when channel is idle, if channel is busy value will remain frozen
3. When value counter is zero ( channel is idle) transmit entire frame and wait
for ACK
4. If ACK received , start process for second frame from step 2. If not
received station chooses a backoff value with larger interval

7. Why DIFS
• Why not immediate action when channel is idle
• Compare strategy with Ethernet Collision detection

8. Hidden Terminal Problem

9. Request to send /
Clear to send

10. Issues with RTS
• Collision can occur on RTS
• Delay will added in the system
• RTS should only be used for long data frames.
• In practice, each wireless station can set an RTS threshold such that the
RTS/CTS sequence is used only when the frame is longer than the threshold

11. Advance Features
• Rate adaptation
• Power management

12. Bluetooth
• to replace the cables used on mobile devices with radio frequency waves
• Each Bluetooth device comprises a 9x9 mm chip which enables it to
communicate with other
• Bluetooth uses the 2.45 GHz frequency band
• A Bluetooth piconet is a collection of devices connected via Bluetooth
technology in an ad hoc fashion

14. Wimax
• Reading assignment

15. Mobility management Principles

16. Mobility management Principles
• If a node can maintain its IP then mobility becomes invisible from the
application standpoint
• Example of an adult living at different places at different times

17. Terminologies
• the permanent home of a mobile node (such as a laptop or smartphone) is known
as the home network
• the entity within the home network that performs the mobility management
functions is known as the home agent
• The network in which the mobile node is currently residing is known as the foreign
(or visited) network
• the entity within the foreign network that helps the mobile node with the mobility
management functions discussed below is known as a foreign agent
• A correspondent is the entity wishing to communicate with the mobile node

19. Mobility management
• How network will know about mobile node’s current address
• COA ( care of address) will be created by foreign agent
• Foreign agent will inform home agent
• Sometimes mobile node acts as foreign agent (DHCP protocol)
• How data will be forwarded to mobile node from correspondent

21. Indirect Routing summary
• A mobile-node–to–foreign-agent protocol. The mobile node will register with the foreign agent when
attaching to the foreign network. Similarly, a mobile node will deregister with the foreign agent
when it leaves the foreign network.
• A foreign-agent–to–home-agent registration protocol. The foreign agent will register the mobile node’s
COA with the home agent. A foreign agent need not explicitly deregister a COA when a
mobile node leaves its network, because the subsequent registration of a new COA, when the
mobile node moves to a new network, will take care of this.
• A home-agent datagram encapsulation protocol. Encapsulation and forwarding of the
correspondent’s original datagram within a datagram addressed to the COA.
• A foreign-agent decapsulation protocol. Extraction of the correspondent’s original datagram from
the encapsulating datagram, and the forwarding of the original datagram to the mobile node.

22. Triangle routing problem
• Imagine a scenario where mobile node visiting correspondent network
• Direct routing is the solution
• Correspondent first learns about COA of mobile node from home agent

24. Mobile Routing
• Mobile user location protocol
• Mobile node move from one foreign network to other
• Anchor Foreign agent
• the foreign agent in that foreign network where the mobile node was first found