Outline for This Lecture

1
Outline for This Lecture

• Reality Check of Wireless Network Usage
• Overview of Wireless and Mobile Networking

2
Comparisons of 3G and 802.11

• Coverage
• 3G large coverage
• 802.11 small
• Throughput
• 802.11 up to 11/54 Mbps
• 3G up to 2 Mbps
• Cell size and density
• 802.11 several hundred feet
• 3G up to several kilometers
• Applications supported
• 802.11 mainly data, but may support VoIP
• 3G data plus voice in 1XEVDV

3
Measurements on 802.11 WLAN

• Mobile host is prevalent, but mobile flows are
  not
• Network usage is highly dependent on applications
• Highly nonstationary traffic pattern
• Days and evenings
• Workdays and weekends

4
Migration to 3G (Src Wireless Week Research)

• Carrier Network Technology
  Estimated Deployment
• ATT Wireless GSM/GPRS Overlay
  conclude year-end 2002
• upgrade to E-GPRS or EDGE
  mid-2002
• W-CDMA-based tech.
  Late 2002
• Cingular GPRS Overlay on GSM
  Year-end 2001
• Wireless EDGE Overlay on TDMA
  2002 2003
• EDGE overlay on GPRS/GSM
  2002 2003
• next step
  not determined
• Sprint PCS CDMA 1X (release 0)
  to early 2002
• CDMA 1X (release A)
  to early 2003
• CDMA 1XEV-DO
  early 2003
• CDMA 1XEV-DV
  20032005
• Verizon CDMA 1X
  year-end 2001
• Wireless CDMA 1XEV
  following 1X rollout
• next step
  not determined

5
Overview

• Fundamental issues and impact
• wireless
• mobility
• For each layer in the protocol stack
• A subset of design requirements
• Design challenges/constraints
• Possible design options

6
Wireless Channel Characteristics

• Radio propagation
• Multipath, fade, attenuation, interference
  capture
• Received power is inversely proportional to the
  distance distance-power gradient
• Free space factor 2
• Inbuilding corridors or large open indoor areas
  lt2
• Metal buildings factor 6
• Recommended simulation factors 23 for
  residential areas, offices and manufacturing
  floors 4 for urban radio communications

7
Wireless Channel

• Wireless transmission is error prone
• Wireless error and contention are location
  dependent
• Wireless channel capacity is also location
  dependent

8
Mobility

• Why mobility?
• 3040 of the US workforce is mobile (Yankee
  group)
• 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

9
Mobility

• Four types of activities for a typical office
  work during a workday
• Communication (fax, email)
• Data manipulation (word processing, directory
  services, document access retrieval)
• Information access (database access and update,
  internet access and search)
• Sharing of information (groupware, shared file
  space)
• Question how does mobility affect each of the
  above activities?

10
Mobility

• Possible scenarios of mobility
• Scenario 1 user logs out from computer 1, moves
  to computer 2 and logs in
• Should the user see the same workspace?
• Scenario 2 different devices for different
  network
• 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
• In stand-alone mode
• What kind of activities can the user do?
• What cannot be done?
• Can we provide an illusion of connectivity in
  this case?
• Can we automatically re-integrate the work (s)he
  has done while disconnected when (s)he finally
  reconnects to the network server?

11
Impact of Mobility

• 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
• Is the disconnection between network migration
  necessary?
• When can we make the disconnection transparent to
  users? When we cannot?
• What are the key issues to ensure seamless
  network migration?
• Is it really important or users do not care about
  the automatic process? For what applications?
  What to change for the applications?

12
Protocol Stack

• Draw the entire protocol stack
• For each component/layer
• Some requirements
• Issues to address
• Possible design options

13
Physical/MAC Layer

• Requirements
• Continuous access to the channel to transmit a
  frame without error
• Fair access to the channel how is fairness
  quantified?
• Low power consumption
• Increase channel throughput within the given
  frequency band
• Constraints
• Interference, fade, multi-path, and signal
  attenuation cause the channel to be error prone
• Channel contention and error are location
  dependent
• Channel capacity is fluctuating
• Transmission range is limited (but also enables
  channel reuse)
• Shared channel (hidden/exposed station problem)

14
Physical/MAC Layer

• Possible options
• Physical layer
• Narrow band vs wide band direct sequence,
  frequency hopping, OFDM
• Antenna technology smart antenna, directional
  antenna, MIMO
• Adaptive modulation
• MAC layer
• Multiple access protocols (CSMA/CA, MACAW, etc.)
• Frame reservation protocols (TDMA, DQRUMA, etc.)

15
Link Layer

• Requirements
• Error sensitive application
• A reliable link abstraction on top of error-prone
  physical channels
• Delay sensitive application
• A bounded delay link abstraction on top of
  error-prone channels
• Constraints
• Errors in the channel
• Spatial congestion
• Link capacity is changing due to modulation
  techniques

16
Link Layer

• Possible options at the link layer
• Windowing to provide error and flow control
• Combating error
• Proactive error correction via e.g. FEC
• Reactive error detectionretransmission, ARQ
• Channel-state predictionchannel swapping
• A few possible definitions of fairness long term
  vs short term, deterministic vs probabilistic,
  temporal vs throughput
• All users are treated equal
• Users in error prone or congested location suffer

17
Network Layer

• Requirements
• Maintain connectivity while user roams
• Allow IP to integrate transparently with roaming
  hosts
• Address translation to map location-independent
  addressing to location dependent addressing
• Packet forwarding
• Location directory
• Provide connection to packet flow as opposed to
  datagram (connection oriented networks)
• Support multicast, anycast
• Ability to switch interfaces on the fly to
  migrate between failure-prone networks
• Ability to provide quality of service what is
  QoS in this environment?

18
Network Layer

• Constraint
• Unaware hosts running IP
• Route management for mobile hosts needs to be
  dynamic
• A backbone may not exist (ad-hoc network)

19
Network Layer

• Possible options
• Mobile IP and its variants
• Two-tier addressing (location independent
  addressing lt-gt location dependent addressing)
• A smart forwarding agent which encapsulates
  packets from unware host to forward them to MH
• Location directory for managing location updates)
• Connection-oriented mobility support
• Multicast
• Finding the first branch point and rerouting
  packets
• Ad hoc routing
• Shortest path, source routing, multipath routing

20
Transport Layer

• Requirements
• Congestion control and rate adaptation
• Doing the right thing in the presence of
  different packet losses
• Handling different losses (mobility-induced
  disconnection, channel, reroute)
• Improve transient performance
• Constraints
• Typically unware of mobility, yet is affected by
  mobility
• Packet may be lost due to congestion, channel
  error, handoffs, change of interfaces, rerouting
  failures
• Link-layer and transport layer retransmit
  interactions

21
Transport Layer

• Options
• Provide indirection
• Make transport layer at the end hosts ware of
  mobility
• Provide smarts in intermediate nodes (e.g. BS) to
  make lower-layer transport aware
• Provide error-free link layers

22
Operating Systems

• Requirements
• 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
• Provide an abstraction of the environment for the
  aware application to adapt intelligently
• Constraints
• Scheduling limited CPU resources limited energy
• Limited disk, memory
• Partial connectivity

23
File Systems

• Requirements
• Access the same file as if connected
• Retain the same consistency semantics for shared
  files as if connected
• Availability and reliability as if connected
• ACID (atomic/recoverability, consistent,
  isolated/serializable, durable) properties for
  transactions
• Constraints
• Disconnection and/or partial connection
• Low bandwidth connection
• Variable bandwidth and latency connection,
• Connection cost

24
File systems

• Four major aspects of disconnected or partially
  connected operations
• Hoarding what to pre-fetch
• Consistency what to keep consistent when
  connectivity is partial
• Emulation how to operate when disconnected
• Conflict resolution how to resolve conflicts
• Many choices within each aspect

25
Applications/Services

• A few questions for application designs
• How much to know about mobility (dynamic state)?
• How much to control the activity of OS?
• How to structure the interaction btw. App and
  systems
• How to write location-aware applications?
• What kind of filtering, data retrieval, and
  control support to be provided at the backbone?