Systems Issues in Wireless Networks

1
Systems Issues in Wireless Networks

• Henning Schulzrinne
• Columbia University
• NSF wireless workshop July 2003

2
Overview

• Applications
• Autoconfiguration
• Evolution
• Hybrid networks
• Non-data applications
• New wireless models?
• New types of networks?

3
What makes wireless networks different?

• Network probabilistic throughout
• wired generally hides this at lowest layer
• Node and link availability
• Identifier collisions
• Packet loss
• Link bandwidth availability

4
Applications

• Transition from general-purpose networks to niche
  networks
• Need honesty in scoping (cf. active networks)
• What are different types of networks good for
  (and what not)?
• Applications for ad-hoc and sensor networks
• Beyond the (dubious) emergency and military
  applications
• Clusters of vehicles
• Short-term ad-hoc networks
• Beer glasses waiting to be filled

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Autoconfiguration Discovery

• With open spectrum, how to find
• Available network services ? cant just scan 3
  GHz of bandwidth
• Might be hundreds of ad-hoc and infrastructure
  networks
• Available services that take my credentials
• That offer best/cheapest/ service
• Geographic service discovery
• Ad-hoc and disconnected network services
• How to automatically deploy networks
• In simulations, they just magically connect
• Not much usable development
• LDAP doesnt scale (administratively)
• SLP has severe functionality limitations (no
  hierarchy)
• UDDI, etc. too narrow
• Zero-conf too low level and not suitable for all
  networks

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Evolution

• Implicit assumption natural evolution
• from specialized to general
• from circuit to packets
• from ATM to IP
• from large to small cells
• from single network access to global AAA with
  roaming
• However, even IP networks can look rather crufty
• GPRS Russian-doll stack
• WAP 3G walled garden bias
• Longer lifetime of networks
• analog wireless may not disappear for a decade
• Specialization and large-enough eco system niches
• restricted applications simplify security (DOS),
  billing, lower cost
• Stuck with glueing together 30 years of wireless
  technology at the application layer?
• very little research on evolution, co-existence
  and gateway models
• economics, security and technical issues

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Non-data applications

• Almost exclusive research focus on data (and
  multimedia) applications
• higher bandwidth, general-purpose networks
• Other wireless applications
• location sensing (GPS, location beacons)
• awareness of other people and resources
• remote control (garage door opener)
• Layer on top of general-purpose networks or
  construct special-purpose networks?

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Hybrid networks

• Not just vertical hand-off
• Software-defined radios use diverse networks at
  (almost) the same time
• e.g., high-speed ad hoc network low bandwidth
  WWAN
• separate control and data channels?

9
New wireless models

• Have we explored the architecture space?
• infrastructure access
• ad-hoc as infrastructure funnel
• ad-hoc networks
• intermittent-connectivity networks
• Do things change with highly directional networks
  that are no longer broadcast?

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New types of networks

• Roughly now have tools for ubiquitous and
  high-bandwidth data delivery
• But still far too expensive for many applications
• BlueTooth USB 50 requires real processor
• only useful for very small groups, not clusters
  of O(100)
• New sets of applications for wide area, very low
  bandwidth, ultra low complexity devices
• many applications only need 1 bit/hour (light
  switch, thermostat)
• many sensor applications (toothbrush, scale,
  toaster, traffic light controlled by bus, )
• 802.15 status?
• Parasitic networks?

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Protocol design challenges

• Wireless starting to reach up the stack
  cross-layer design, but need to be precise
• Applications and transport have only limited
  repertoire of actions send packet, drop packet,
  delay packet, fragment packet
• Currently, usually dont even know
  outgoing/incoming interface for a socket (and its
  current bandwidth)
• Trade-off error rate vs. bit rate more explicit
  in wireless
• not just binary ? another example of
  probabilistic network behavior
• Examples
• packet loss ?
• wait (fade)
• reduce rate (congestion)
• retransmit (but probably better delegated down)
• Unequal error protection (UEP)
• Delivery of errored PDU to application
• application needs control
• may need stronger e2e checksum if done
  inadvertently