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Multi-Access Services in Heterogeneous Wireless Networks
Kameswari Chebrolu, Ramesh R. Rao
Abstract
Multi-Access Services
BAG for Interactive Video Applications
Interfaces=3, Total Bandwidth=600kbps
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.
Internet
Client
Internet
Network
Proxy
Internet
Server
Wireless
Internet
interfaces
Base stations
Bandwidth Aggregation (BAG)
• If Ifa0=200kbps, Ifa1=100kbps, Ifa2=50kbps
Total Bandwidth = 350kbps
• Can improve quality of or support
demanding applications!
Mobility/Reliability Support
• Significant Reduction in Handoff delay
• Duplicated/Encoded packets sent on
multiple paths provide high reliability
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
WLAN
Introduction
Internet
WWAN
Interface
 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
BAG for TCP Applications
 Challenges: Fluctuating bandwidths; TCP’s adverse reaction to
packet reordering
 PET (Packet-Pair EDPF based scheduling for TCP) scheduling at
Network Proxy
Ad-hoc Network
 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
 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
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
Network Proxy
Interfaces = 2, Individual Bandwidth = 1000kbps
 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 basestations
Our Architecture
BAG for Streaming Video Applications
Base
stations
Internet
Client
Wireless
interfaces




Internet
Internet
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
Proxy
Server
 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
BAG
(Multiple
Interfaces)
Single
Interface
Lecture
Star Trek
<58,690> <69,1200>
(kbps)
(kbps)
Star Wars
<53,940>
(kbps)
Susi & Strolch
<79,1300>
(kbps)
2.3
3.1
2.9
4.6
7.9
8
8.3
8.6
Buffering Time (in sec) for continuous Playback
Conclusions
 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