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Lecture 9

Lecture 9. QOS, Power Management and Mobile IP. Objectives. Explain QOS and Power Management within 802.11 Describe the functions of mobile IP. QOS motivation. Transmitting on the WLAN: Quality of Service (QoS) and 802.11e. DCF does not work well for real-time, time-dependent traffic

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Lecture 9

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  1. Lecture 9 QOS, Power Management and Mobile IP

  2. Objectives • Explain QOS and Power Management within 802.11 • Describe the functions of mobile IP

  3. QOS motivation

  4. Transmitting on the WLAN: Quality of Service (QoS) and 802.11e • DCF does not work well for real-time, time-dependent traffic • Quality of Service (QoS): Capability to prioritize different types of frames • Wi-Fi Multimedia (WMM): Modeled after wired network QoS prioritization scheme • 802.11e draft: defines superset of features intended to provide QoS over WLANs • Proposes two new mode of operation for 802.11 MAC Layer

  5. Transmitting on the WLAN: Quality of Service and 802.11e (continued) Table 5-1: Wi-Fi Multimedia (WMM)

  6. Quality of Service (QoS) feature • Used for time critical traffic (voice, video) • Upstream will be supported with firmware upgrade. (802.11e QoS) • 802.11e includes: • Enhanced Distributed Coordination Function (eDCF), which is responsible for prioritization. • Transmission Opportunity (TXOP), which is responsible for transmission control.

  7. Enhanced Distributed Coordination Function • eDCF allows higher priority traffic first access to the WLAN media. • With QoS, instead of backing off for a random period of time, high priority packets will back off for reduced amount of time. • The higher priority traffic passes through the AP faster than packets with lower priority.

  8. Transmitting on the WLAN: Quality of Service and 802.11e (continued) • 802.11e draft (continued): • Enhanced Distributed Channel Access (EDCA): Contention-based but supports different types of traffic • Four access categories (AC) • Provides “relative” QoS but cannot guarantee service

  9. Transmission Opportunity • Transmission Opportunity (TXOP) is for environments that have a large amount of WLAN traffic. • High priority packets will only wait a few seconds to retransmit. • If the traffic volume is still high, the high priority packet will continue to resend again and again. • TXOP will always reserve a place in line for the high priority packets by reserving the first few seconds for high priority packets, guaranteeing priority packet handling. • If there is not a high priority packet in the queue, the AP processes the next packet in line.

  10. Association • If more than one AP replies, the client will associate based on the information returned.

  11. Re-association

  12. Remaining Connected to the WLAN: Reassociation • Reassociation: Device drops connection with one AP and establish connection with another • Several reason why reassociation may occur: • Roaming • Weakened signal • When device determines link to current AP is poor, begins scanning to find another AP • Can use information from previous scans

  13. Scalability • Scalability is the ability to locate more than one access point in the same area. This will increase the available bandwidth of that area for all users local to that access point. • Depending on the number and speed of the available channels, cells can achieve higher data rates. • With 802.11b, there are 3 separate, 11-Mbps channels, yielding up to a theoretical 33 Mbps per cell. User devices operate at a maximum theoretical value of 11Mbps, since they can only connect to one AP at any given time. • 802.11a has 8 54 Mbps channels, yielding a theoretical 432 Mbps.

  14. Remaining Connected to the WLAN: Power Management • When laptop is part of a WLAN, must remain “awake” in order to receive network transmissions • Original IEEE 802 standard assumes stations always ready to receive network messages • Power management: Allows mobile devices to conserve battery life without missing transmissions • Transparent to all protocols • Differs based on WLAN configuration • AP records which stations awake and sleeping • Buffering: If sleeping, AP temporarily stores frames

  15. Remaining Connected to the WLAN: Power Management (continued) • At set times AP send out beacon to all stations • Contains traffic indication map (TIM) • At same time, all sleeping stations switch into active listening mode • Power management in ad hoc mode: • Ad hoc traffic indication message (ATIM) window: Time at which all stations must be awake • Wireless device sends beacon to all other devices • Devices that previously attempted to send a frame to a sleeping device will send ATIM frame indicating that receiving device has data to receive and must remain awake

  16. Remaining Connected to the WLAN: Power Management (continued) Figure 5-19: Power management in infrastructure mode

  17. WLAN Network Layer Standards: WLAN IP Addressing • In standard networking, IP protocol responsible for moving frames between computers • Network layer protocol • TCP/IP works on principle that each network host has unique IP address • Used to locate path to specific host • Routers use IP address to forward packets • Prohibits mobile users from switching to another network and using same IP number • Users who want to roam need new IP address on every network

  18. WLAN Network Layer Standards: Mobile IP • Provides mechanism within TCP/IP protocol to support mobile computing • Computers given home address, • Static IP number on home network • Home agent: Forwarding mechanism that keeps track of where mobile computer located • When computer moves to foreign network, a foreign agent provides routing services • Assigns computer a care-of address • Computer registers care-of address with home agent

  19. WLAN Network Layer Standards: Mobile IP (continued) Figure 5-20: Mobile IP components

  20. WLAN Network Layer Standards: Mobile IP (continued) Figure 5-21: Computer relocated in Mobile IP

  21. WLAN Network Layer Standards: Mobile IP (continued) Figure 5-22: Encapsulated Mobile IP frame

  22. Proxy Mobile IP with CISCO • The wireless infrastructure contains the intelligence to allow user roaming. • Cisco’s Proxy Mobile IP is designed for use in complex network environments. As the wireless device leaves an area and enters the next, the new AP queries the device for its home agent. • After the home agent has been located, packet forwarding is established automatically between the new and old APs to ensure the device can transparently exchange data. • Does not require installation of client-side software; however both the router and the APs must be configured to support Proxy IP.

  23. Proxy Mobile IP

  24. Summary • The 802.11e draft defines a superset of features that is intended to provide QoS over WLANs

  25. Summary (continued) • Power management allows mobile devices to be off as much as possible to conserve battery life but not miss data transmissions • Mobile IP provides a mechanism within the TCP/IP protocol to support mobile computing

  26. Labs • 5-1 • 5-2 • 5-4

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