Efficient Internet Traffic Delivery over Wireless Networks

1
Efficient Internet Traffic Delivery over Wireless
Networks

• Sandhya Sumathy

2
Introduction

• High Demand for Wireless Internet Connectivity
• Internet applications usually generate elastic
  traffic. e.g. Web, FTP, email.
• Main objective for elastic traffic is
  minimization of the total file transmission time.
• Randomness is the basic characteristics of
  wireless communications

3
Overview of Internet Stack Architecture
4
Link Layer Optimizations for Elastic Traffic

• Packet Transmission Scheduling-increase
  throughput by exploiting the temporal
  fluctuations in Channel qualities.
• At any one time some users will enjoy better
  channel conditions.
• In order to increase users channel qualities
  packets are separated into buffers thus allowing
  a Scheduler to select an optimal user to transmit
  at any time.
• A scheduler will decide on the next queue to be
  serviced based on Signal to noise ratio, Mean
  channel rate, Priority, Queue size.

5
Packet Transmission Scheduling continued..

• Scheduling can be made optimal if buffers has
  packets queued and awaiting transmission.
• Emptying a users packet at the base station leads
  to suboptimal scheduling.
• TCP flow control mechanism should not cause a
  buffer to drain and hold packets at the source.

6
Link Layer Rate Adaptation

• Incremental Redundancy (IR) Techniques vary the
  code rate on a transmission , tracking
  fluctuations in the channel quality.
• Link Adaptations (LA) Techniques measure the
  average channel quality and choose an appropriate
  modulation or coding scheme.
• The net effect Time series of successful packet
  transmission time ,as perceived by TCP flow
  control scheme is random and non stationary.

7
Transport Layer Objectives and adverse effects

• TCP is a window-based flow control algorithm.
• Its window size is minimum of congestion window
  (CWND) which is set by sender and the advertised
  window (AWND) set by receiver.
• Two dominant algorithms Slow start and
  Congestion avoidance.
• In a wireless network the link rate is a random
  quantity which varies on distinct timescales.

8
Transport Layer Objectives and adverse effects
continued

• In order to keep the link buffer needs to be very
  large.
• TCPs congestion control algorithm will attempt
  to fill this buffer.
• If the link rate drops suddenly excessively large
  latencies result.
• Small buffer will cause the link to be frequently
  starve for packets.
• This problem has been observed in recent studies
  of TCPs performance over UMTS.

9
Proposed TCP Enhancements

• Recent proposals
• Sender-side modifications changes to
• Internet Hosts.
• Performance enhancing proxies affects
• IP layer security, scalability
• Receiver-side modifications only require
• changes to wireless hosts.
• Explicit Window Adaptation control TCP sender
  from receiving host by controlling the AWND
  feature. This is referred as receiver-side
  explicit window adaptation

10
Proposed TCP Enhancements continued..

• An Algorithm CLAMP is recently proposed for
  receiver-side explicit window adaptation.
• This algorithm calculates a new AWND value taking
  into account the proximity factor, current rate
  of transfer etc.
• This algorithm tries to reduce the time that the
  link is left idle because of TCP holding packets
  at source.

11
Conclusion

• A flow control algorithm over wireless links
  should allow control over the trade-off between
  latency and utilization.
• Receiver-side flow control can be used to control
  existing TCP sources to reach desired objectives
  and increase the performance of wireless access
  to Internet.
• An algorithm such as CLAMP supplements TCPs flow
  control mechanism .This can be
• used to ensure that lower-layer scheduling
  mechanisms can perform as intended.

12

• Questions??

13

• Thank You.