Multi-Access Services in Heterogeneous Wireless Networks

1
Multi-Access Services in Heterogeneous Wireless
Networks Kameswari Chebrolu, Ramesh R. Rao
Abstract
Multi-Access Services
BAG for Interactive Video Applications
Interfaces3, Total Bandwidth600kbps
Today's wireless world is characterized by
heterogeneity. A variety of wireless interfaces
are available to the mobile user to access
Internet content. Examples include 802.11,
Bluetooth, GPRS, CDMA2000, UMTS etc. When
coverage areas of these different technologies
overlap, a terminal equipped with multiple
interfaces can use them simultaneously to improve
the performance of its applications. We term the
services enabled by such simultaneous use of
multiple interfaces as Multi-Access Services.
In this work, we develop a network layer
architecture that supports multiple communication
paths. We also implement most of the functional
components that make up our architecture as proof
of concept for the different services. We
experiment with different application scenarios -
Streaming video, Interactive video, TCP
applications and propose necessary scheduling,
buffer management algorithms and protocols to
improve their performance. Our experiments
carried on the test-bed and through simulations
show that considerable improvement in performance
can be achieved through use of multiple
interfaces over single interface use.

• Challenges Strict delay (QoS) requirements,
  packet reordering
• Earliest Delivery Path First (EDPF) scheduling
  algorithm at Proxy
• Considers overall path characteristics between
  proxy and client
• Schedules packet on the path which delivers the
  packet the earliest at the client
• Simulation carried using video frame and delay
  traces
• Video Server generates packets based on video
  frame size traces
• Internet paths simulated using delay traces
  collected on various Internet Paths
• Base-Stations serve packets on a first-come-first
  basis, no cross traffic (channel considered
  dedicated)
• Client begins video display after a fixed delay
  (Maximum Delay Bound).
• Client displays frames consecutively every t sec
  (frame period) after that. Arrival after playback
  deadline results in frame loss

• Bandwidth Aggregation (BAG)
• If Ifa0200kbps, Ifa1100kbps, Ifa250kbps Total
  Bandwidth 350kbps
• Can improve quality of or support demanding
  applications!

Network Proxy
Internet
Client
Internet
Internet
Server

• Mobility/Reliability Support
• Significant Reduction in Handoff delay
• Duplicated/Encoded packets sent on multiple
  paths provide high reliability

Wireless interfaces
Internet
Base stations
WWAN

• Resource Sharing
• Nodes form ad-hoc network using WLAN interface
• The WWAN resources of a subset of nodes is
  shared among all nodes to access external
  Internet

WLAN
BAG for TCP Applications
WLAN
Interfaces 2, Individual Bandwidth 1000kbps

• Challenges Fluctuating bandwidths TCPs adverse
  reaction to packet reordering
• PET (Packet-Pair EDPF based scheduling for TCP)
  scheduling at Network Proxy
• Based on EDPF, packets sent in pairs for
  bandwidth estimation
• Client implements Buffer Management Policy (BMP)
• BMP buffers packets and send them in order to TCP
• Thus, BMP hides residual reordering from TCP
• NS-2 based simulation
• Server initiates a large file transfer (FTP)
• Base-Stations introduce random cross-traffic
• Mix of FTP and Web flows
• Losses introduced via wireless errors and
  congestion at base-stations

Introduction

• Recent mobile Internet growth spurred deployment
  of different wireless technologies
• GPRS, CDMA2000, HDR, 802.11, Bluetooth etc
• End-Users have flexibility regarding Interface
  choice
• Can choose any number of interfaces to best fit
  application needs
• Simultaneous use of multiple interfaces opens
  interesting possibilities
• Bandwidth Aggregation, Mobility/Reliability
  Support, Resource Sharing, Data-Control Plane
  Separation

• Data-Control Plane Separation
• WWAN is used for out of band control
  communication
• WLAN interface is used for mostly data
  communication
• Helps distributed protocols such as routing

Our Architecture
BAG for Streaming Video Applications
Base stations
Conclusions

• Test-bed implementation
• Interfaces used - two 1xRTT cards
• Video Server generates packets based on video
  frame size trace file
• Network Proxy performs Weighted Round Robin (WRR)
  scheduling onto the multiple interfaces
• Client measures time needed to Buffer packets to
  enable continuous playback.

Internet

• Network-layer architecture to enable multi-access
  services
• Prototype Implementation of the architecture
• Streaming Video Applications
• Use of multiple interfaces shows good improvement
  in performance over using just a single interface
• Interactive Video Applications
• EDPF Scheduling Algorithm
• Reduces reordering
• Utilized bandwidth effectively
• EDPF mimics ASL closely, outperforms WRR based
  approaches
• TCP Applications
• PET Scheduling algorithm
• BMP buffering
• Good bandwidth aggregation
• BAG BMP follow MTCP closely, outperforms WRR
  scheduling
• Future work Explore other multi-access services
  (Resource Sharing, Data-Control Plane Separation
  ) in depth

Internet
Internet
Server
Network Proxy
Client
Internet
Wireless interfaces

• High level Overview
• Based at the Network layer
• Achieves application transparency
• Minimum changes to Infrastructure
• Proxy provides multi-access services to the
  Client
• Functional Components
• Implemented as Linux loadable kernel modules
• Profile Manager/Server
• Profile Manager generates profile to handle
  different applications
• Profile specifies interfaces to use, type of
  scheduling etc

• Access Selection/ Access Discovery
• Bring up necessary interfaces based on profile
• Mobility Manager/Server
• Mobility Manager Registers acquired care-of IP
  addresses at Server
• Traffic Manager
• Performs necessary processing and scheduling of
  traffic
• Performance Monitoring Unit
• Monitor characteristics (available bandwidth,
  delay, loss rate etc ) of the path between Proxy
  and Client

Alg / Video Lecture lt58,690gt (kbps) Star Trek lt69,1200gt (kbps) Star Wars lt53,940gt (kbps) Susi Strolch lt79,1300gt (kbps)
BAG (Multiple Interfaces) 2.3 3.1 2.9 4.6
Single Interface 7.9 8 8.3 8.6
Buffering Time (in sec) for continuous Playback