1. Multi-Access Services in Heterogeneous Wireless Networks Kameswari Chebrolu, Ramesh R. Rao Abstract 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. Introduction Multi-Access Services Our Architecture Our Architecture 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 WWAN WLAN Network Proxy WWAN Interface Internet Ad-hoc Network 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 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 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 Client Wireless interfaces Internet Network Proxy Internet Server Base stations Client Wireless interfaces Internet Server Internet Network Proxy 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 BAG for Streaming Video Applications 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. Alg / VideoLecture (kbps) Star Trek (kbps) Star Wars (kbps) Susi & Strolch (kbps) BAG (Multiple Interfaces) 2.33.12.94.6 Single Interface 7.988.38.6 Buffering Time (in sec) for continuous Playback BAG for Interactive Video Applications 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: 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 BAG for TCP Applications 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 Conclusions Interfaces=3, Total Bandwidth=600kbps Interfaces = 2, Individual Bandwidth = 1000kbps