Outline for This Lecture <ul><li>Reality Check of Wireless Network Usage </li></ul><ul><li>Overview of Wireless and Mobile...
Comparisons of 3G and 802.11 <ul><li>Coverage </li></ul><ul><ul><li>3G: large coverage </li></ul></ul><ul><ul><li>802.11: ...
Measurements on 802.11 WLAN <ul><li>Mobile host is prevalent, but mobile flows are not </li></ul><ul><li>Network usage is ...
Migration to 3G (Src: Wireless Week Research) <ul><li>Carrier  Network Technology  Estimated Deployment </li></ul><ul><li>...
Overview <ul><li>Fundamental issues and impact </li></ul><ul><ul><li>wireless </li></ul></ul><ul><ul><li>mobility </li></u...
Wireless Channel Characteristics <ul><li>Radio propagation </li></ul><ul><ul><li>Multipath, fade, attenuation, interferenc...
Wireless Channel <ul><li>Wireless transmission is error prone </li></ul><ul><li>Wireless error and contention are location...
Mobility <ul><li>Why mobility? </li></ul><ul><ul><li>30~40% of the US workforce is mobile (Yankee group) </li></ul></ul><u...
Mobility <ul><li>Four types of activities for a typical office work during a workday: </li></ul><ul><ul><li>Communication ...
Mobility <ul><li>Possible scenarios of mobility </li></ul><ul><ul><li>Scenario 1: user logs out from computer 1, moves to ...
Impact of Mobility <ul><li>Scenario 4: a user has a notebook with a wireless connection, connects to a remote host via net...
Protocol Stack <ul><li>Draw the entire protocol stack </li></ul><ul><ul><li>For each component/layer </li></ul></ul><ul><u...
Physical/MAC Layer <ul><li>Requirements:  </li></ul><ul><ul><li>Continuous access to the channel to transmit a frame witho...
Physical/MAC Layer <ul><li>Possible options: </li></ul><ul><ul><li>Physical layer: </li></ul></ul><ul><ul><ul><li>Narrow b...
Link Layer <ul><li>Requirements: </li></ul><ul><ul><li>Error sensitive application </li></ul></ul><ul><ul><ul><li>A reliab...
Link Layer <ul><li>Possible options at the link layer </li></ul><ul><ul><li>Windowing to provide error and flow control </...
Network Layer <ul><li>Requirements: </li></ul><ul><ul><li>Maintain connectivity while user roams </li></ul></ul><ul><ul><l...
Network Layer <ul><li>Constraint: </li></ul><ul><ul><li>Unaware hosts running IP </li></ul></ul><ul><ul><li>Route manageme...
Network Layer <ul><li>Possible options: </li></ul><ul><ul><li>Mobile IP and its variants </li></ul></ul><ul><ul><ul><li>Tw...
Transport Layer <ul><li>Requirements: </li></ul><ul><ul><li>Congestion control and rate adaptation </li></ul></ul><ul><ul>...
Transport Layer <ul><li>Options: </li></ul><ul><ul><li>Provide indirection </li></ul></ul><ul><ul><li>Make transport layer...
Operating Systems <ul><li>Requirements: </li></ul><ul><ul><li>Provide the same environment to the user whether mobile (par...
File Systems <ul><li>Requirements: </li></ul><ul><ul><li>Access the same file as if connected </li></ul></ul><ul><ul><li>R...
File systems <ul><li>Four major aspects of disconnected or partially connected operations: </li></ul><ul><ul><li>Hoarding:...
Applications/Services <ul><li>A few questions for application designs: </li></ul><ul><ul><li>How much to know about mobili...
Upcoming SlideShare
Loading in …5
×

October 8, 2003

293 views

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
293
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
2
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

October 8, 2003

  1. 1. Outline for This Lecture <ul><li>Reality Check of Wireless Network Usage </li></ul><ul><li>Overview of Wireless and Mobile Networking </li></ul>
  2. 2. Comparisons of 3G and 802.11 <ul><li>Coverage </li></ul><ul><ul><li>3G: large coverage </li></ul></ul><ul><ul><li>802.11: small </li></ul></ul><ul><li>Throughput </li></ul><ul><ul><li>802.11: up to 11/54 Mbps </li></ul></ul><ul><ul><li>3G: up to 2 Mbps </li></ul></ul><ul><li>Cell size and density </li></ul><ul><ul><li>802.11: several hundred feet </li></ul></ul><ul><ul><li>3G: up to several kilometers </li></ul></ul><ul><li>Applications supported: </li></ul><ul><ul><li>802.11: mainly data, but may support VoIP </li></ul></ul><ul><ul><li>3G: data plus voice in 1XEVDV </li></ul></ul>
  3. 3. Measurements on 802.11 WLAN <ul><li>Mobile host is prevalent, but mobile flows are not </li></ul><ul><li>Network usage is highly dependent on applications </li></ul><ul><li>Highly nonstationary traffic pattern </li></ul><ul><ul><li>Days and evenings </li></ul></ul><ul><ul><li>Workdays and weekends </li></ul></ul>
  4. 4. Migration to 3G (Src: Wireless Week Research) <ul><li>Carrier Network Technology Estimated Deployment </li></ul><ul><li>ATT Wireless GSM/GPRS Overlay conclude year-end 2002 </li></ul><ul><li>upgrade to E-GPRS or EDGE mid-2002 </li></ul><ul><li>W-CDMA-based tech. Late 2002 </li></ul><ul><li>Cingular GPRS Overlay on GSM Year-end 2001 </li></ul><ul><li>Wireless EDGE Overlay on TDMA 2002 & 2003 </li></ul><ul><li>EDGE overlay on GPRS/GSM 2002 & 2003 </li></ul><ul><li>next step not determined </li></ul><ul><li>Sprint PCS CDMA 1X (release 0) to early 2002 </li></ul><ul><li>CDMA 1X (release A) to early 2003 </li></ul><ul><li>CDMA 1XEV-DO early 2003 </li></ul><ul><li>CDMA 1XEV-DV 2003~2005 </li></ul><ul><li>Verizon CDMA 1X year-end 2001 </li></ul><ul><li>Wireless CDMA 1XEV following 1X rollout </li></ul><ul><li>next step not determined </li></ul>
  5. 5. Overview <ul><li>Fundamental issues and impact </li></ul><ul><ul><li>wireless </li></ul></ul><ul><ul><li>mobility </li></ul></ul><ul><li>For each layer in the protocol stack </li></ul><ul><ul><li>A subset of design requirements </li></ul></ul><ul><ul><li>Design challenges/constraints </li></ul></ul><ul><ul><li>Possible design options </li></ul></ul>
  6. 6. Wireless Channel Characteristics <ul><li>Radio propagation </li></ul><ul><ul><li>Multipath, fade, attenuation, interference & capture </li></ul></ul><ul><ul><li>Received power is inversely proportional to the distance: distance-power gradient </li></ul></ul><ul><ul><ul><li>Free space: factor 2 </li></ul></ul></ul><ul><ul><ul><li>Inbuilding corridors or large open indoor areas: <2 </li></ul></ul></ul><ul><ul><ul><li>Metal buildings: factor 6 </li></ul></ul></ul><ul><ul><ul><li>Recommended simulation factors: 2~3 for residential areas, offices and manufacturing floors; 4 for urban radio communications </li></ul></ul></ul>
  7. 7. Wireless Channel <ul><li>Wireless transmission is error prone </li></ul><ul><li>Wireless error and contention are location dependent </li></ul><ul><li>Wireless channel capacity is also location dependent </li></ul>
  8. 8. Mobility <ul><li>Why mobility? </li></ul><ul><ul><li>30~40% of the US workforce is mobile (Yankee group) </li></ul></ul><ul><ul><li>Hundreds of millions of users are already using portable computing devices and more than 60% of them are prepared to pay for wireless access to the backbone information </li></ul></ul>
  9. 9. Mobility <ul><li>Four types of activities for a typical office work during a workday: </li></ul><ul><ul><li>Communication (fax, email) </li></ul></ul><ul><ul><li>Data manipulation (word processing, directory services, document access & retrieval) </li></ul></ul><ul><ul><li>Information access (database access and update, internet access and search) </li></ul></ul><ul><ul><li>Sharing of information (groupware, shared file space) </li></ul></ul><ul><li>Question: how does mobility affect each of the above activities? </li></ul>
  10. 10. Mobility <ul><li>Possible scenarios of mobility </li></ul><ul><ul><li>Scenario 1: user logs out from computer 1, moves to computer 2 and logs in </li></ul></ul><ul><ul><ul><li>Should the user see the same workspace? </li></ul></ul></ul><ul><ul><li>Scenario 2: different devices for different network </li></ul></ul><ul><ul><li>Scenario 3: user docks a laptop, works in a networked mode for a while, then disconnects and works in the standalone mode for a while, and then docks back </li></ul></ul><ul><ul><ul><li>In stand-alone mode </li></ul></ul></ul><ul><ul><ul><ul><li>What kind of activities can the user do? </li></ul></ul></ul></ul><ul><ul><ul><ul><li>What cannot be done? </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Can we provide an illusion of connectivity in this case? </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Can we automatically re-integrate the work (s)he has done while disconnected when (s)he finally reconnects to the network server? </li></ul></ul></ul></ul>
  11. 11. Impact of Mobility <ul><li>Scenario 4: a user has a notebook with a wireless connection, connects to a remote host via network 1, shuts down connections, connects to the remote host via network 2, continues to work </li></ul><ul><ul><li>Is the disconnection between network migration necessary? </li></ul></ul><ul><ul><li>When can we make the disconnection transparent to users? When we cannot? </li></ul></ul><ul><ul><li>What are the key issues to ensure seamless network migration? </li></ul></ul><ul><ul><li>Is it really important or users do not care about the automatic process? For what applications? What to change for the applications? </li></ul></ul>
  12. 12. Protocol Stack <ul><li>Draw the entire protocol stack </li></ul><ul><ul><li>For each component/layer </li></ul></ul><ul><ul><ul><li>Some requirements </li></ul></ul></ul><ul><ul><ul><li>Issues to address </li></ul></ul></ul><ul><ul><ul><li>Possible design options </li></ul></ul></ul>
  13. 13. Physical/MAC Layer <ul><li>Requirements: </li></ul><ul><ul><li>Continuous access to the channel to transmit a frame without error </li></ul></ul><ul><ul><li>Fair access to the channel: how is fairness quantified? </li></ul></ul><ul><ul><li>Low power consumption </li></ul></ul><ul><ul><li>Increase channel throughput within the given frequency band </li></ul></ul><ul><li>Constraints: </li></ul><ul><ul><li>Interference, fade, multi-path, and signal attenuation cause the channel to be error prone </li></ul></ul><ul><ul><li>Channel contention and error are location dependent </li></ul></ul><ul><ul><li>Channel capacity is fluctuating </li></ul></ul><ul><ul><li>Transmission range is limited (but also enables channel reuse) </li></ul></ul><ul><ul><li>Shared channel (hidden/exposed station problem) </li></ul></ul>
  14. 14. Physical/MAC Layer <ul><li>Possible options: </li></ul><ul><ul><li>Physical layer: </li></ul></ul><ul><ul><ul><li>Narrow band vs wide band: direct sequence, frequency hopping, OFDM </li></ul></ul></ul><ul><ul><ul><li>Antenna technology: smart antenna, directional antenna, MIMO </li></ul></ul></ul><ul><ul><ul><li>Adaptive modulation </li></ul></ul></ul><ul><ul><li>MAC layer </li></ul></ul><ul><ul><ul><li>Multiple access protocols (CSMA/CA, MACAW, etc.) </li></ul></ul></ul><ul><ul><ul><li>Frame reservation protocols (TDMA, DQRUMA, etc.) </li></ul></ul></ul>
  15. 15. Link Layer <ul><li>Requirements: </li></ul><ul><ul><li>Error sensitive application </li></ul></ul><ul><ul><ul><li>A reliable link abstraction on top of error-prone physical channels </li></ul></ul></ul><ul><ul><li>Delay sensitive application </li></ul></ul><ul><ul><ul><li>A bounded delay link abstraction on top of error-prone channels </li></ul></ul></ul><ul><li>Constraints: </li></ul><ul><ul><li>Errors in the channel </li></ul></ul><ul><ul><li>Spatial congestion </li></ul></ul><ul><ul><li>Link capacity is changing due to modulation techniques </li></ul></ul>
  16. 16. Link Layer <ul><li>Possible options at the link layer </li></ul><ul><ul><li>Windowing to provide error and flow control </li></ul></ul><ul><ul><li>Combating error: </li></ul></ul><ul><ul><ul><li>Proactive: error correction via e.g. FEC </li></ul></ul></ul><ul><ul><ul><li>Reactive: error detection+retransmission, ARQ </li></ul></ul></ul><ul><ul><ul><li>Channel-state prediction+channel swapping </li></ul></ul></ul><ul><ul><li>A few possible definitions of fairness: long term vs short term, deterministic vs probabilistic, temporal vs throughput </li></ul></ul><ul><ul><ul><li>All users are treated equal </li></ul></ul></ul><ul><ul><ul><li>Users in error prone or congested location suffer </li></ul></ul></ul>
  17. 17. Network Layer <ul><li>Requirements: </li></ul><ul><ul><li>Maintain connectivity while user roams </li></ul></ul><ul><ul><li>Allow IP to integrate transparently with roaming hosts </li></ul></ul><ul><ul><ul><li>Address translation to map location-independent addressing to location dependent addressing </li></ul></ul></ul><ul><ul><ul><li>Packet forwarding </li></ul></ul></ul><ul><ul><ul><li>Location directory </li></ul></ul></ul><ul><ul><li>Provide connection to packet flow as opposed to datagram (connection oriented networks) </li></ul></ul><ul><ul><li>Support multicast, anycast </li></ul></ul><ul><ul><li>Ability to switch interfaces on the fly to migrate between failure-prone networks </li></ul></ul><ul><ul><li>Ability to provide quality of service: what is QoS in this environment? </li></ul></ul>
  18. 18. Network Layer <ul><li>Constraint: </li></ul><ul><ul><li>Unaware hosts running IP </li></ul></ul><ul><ul><li>Route management for mobile hosts needs to be dynamic </li></ul></ul><ul><ul><li>A backbone may not exist (ad-hoc network) </li></ul></ul>
  19. 19. Network Layer <ul><li>Possible options: </li></ul><ul><ul><li>Mobile IP and its variants </li></ul></ul><ul><ul><ul><li>Two-tier addressing (location independent addressing <-> location dependent addressing) </li></ul></ul></ul><ul><ul><ul><li>A smart forwarding agent which encapsulates packets from unware host to forward them to MH </li></ul></ul></ul><ul><ul><ul><li>Location directory for managing location updates) </li></ul></ul></ul><ul><ul><li>Connection-oriented mobility support </li></ul></ul><ul><ul><ul><li>Multicast </li></ul></ul></ul><ul><ul><ul><li>Finding the first branch point and rerouting packets </li></ul></ul></ul><ul><ul><li>Ad hoc routing </li></ul></ul><ul><ul><ul><li>Shortest path, source routing, multipath routing </li></ul></ul></ul>
  20. 20. Transport Layer <ul><li>Requirements: </li></ul><ul><ul><li>Congestion control and rate adaptation </li></ul></ul><ul><ul><ul><li>Doing the right thing in the presence of different packet losses </li></ul></ul></ul><ul><ul><li>Handling different losses (mobility-induced disconnection, channel, reroute) </li></ul></ul><ul><ul><li>Improve transient performance </li></ul></ul><ul><li>Constraints: </li></ul><ul><ul><li>Typically unware of mobility, yet is affected by mobility </li></ul></ul><ul><ul><li>Packet may be lost due to congestion, channel error, handoffs, change of interfaces, rerouting failures </li></ul></ul><ul><ul><li>Link-layer and transport layer retransmit interactions </li></ul></ul>
  21. 21. Transport Layer <ul><li>Options: </li></ul><ul><ul><li>Provide indirection </li></ul></ul><ul><ul><li>Make transport layer at the end hosts ware of mobility </li></ul></ul><ul><ul><li>Provide smarts in intermediate nodes (e.g. BS) to make lower-layer transport aware </li></ul></ul><ul><ul><li>Provide error-free link layers </li></ul></ul>
  22. 22. Operating Systems <ul><li>Requirements: </li></ul><ul><ul><li>Provide the same environment to the user whether mobile (partially connected) or on the backbone network: same files, same context, ability to run same programs, access the same databases, servers & services, retain the same ID </li></ul></ul><ul><ul><li>Provide an abstraction of the environment for the aware application to adapt intelligently </li></ul></ul><ul><li>Constraints: </li></ul><ul><ul><li>Scheduling limited CPU resources & limited energy </li></ul></ul><ul><ul><li>Limited disk, memory </li></ul></ul><ul><ul><li>Partial connectivity </li></ul></ul>
  23. 23. File Systems <ul><li>Requirements: </li></ul><ul><ul><li>Access the same file as if connected </li></ul></ul><ul><ul><li>Retain the same consistency semantics for shared files as if connected </li></ul></ul><ul><ul><li>Availability and reliability as if connected </li></ul></ul><ul><ul><li>ACID (atomic/recoverability, consistent, isolated/serializable, durable) properties for transactions </li></ul></ul><ul><li>Constraints: </li></ul><ul><ul><li>Disconnection and/or partial connection </li></ul></ul><ul><ul><li>Low bandwidth connection </li></ul></ul><ul><ul><li>Variable bandwidth and latency connection, </li></ul></ul><ul><ul><li>Connection cost </li></ul></ul>
  24. 24. File systems <ul><li>Four major aspects of disconnected or partially connected operations: </li></ul><ul><ul><li>Hoarding: what to pre-fetch </li></ul></ul><ul><ul><li>Consistency: what to keep consistent when connectivity is partial </li></ul></ul><ul><ul><li>Emulation: how to operate when disconnected </li></ul></ul><ul><ul><li>Conflict resolution: how to resolve conflicts </li></ul></ul><ul><li>Many choices within each aspect </li></ul>
  25. 25. Applications/Services <ul><li>A few questions for application designs: </li></ul><ul><ul><li>How much to know about mobility (dynamic state)? </li></ul></ul><ul><ul><li>How much to control the activity of OS? </li></ul></ul><ul><ul><li>How to structure the interaction btw. App and systems </li></ul></ul><ul><ul><li>How to write location-aware applications? </li></ul></ul><ul><ul><li>What kind of filtering, data retrieval, and control support to be provided at the backbone? </li></ul></ul>

×