Reddy Mainampati Udit Parikh Alex Kardomateas

Introduction How does application behavior impact wireless performance? What can be done to improve performance? A3: Application-Aware Acceleration for Wireless Data Networks Application-aware but application transparent Changes required by entities at each end

Evaluation Applications FTP – file transfer protocol CIFS – printer and file sharing SMTP – email communication HTTP – web pages Traffic IxChariot – software to generate traffic

Environment Wireless Networks WLAN – wireless local area WWAN – wireless wide area SAT – satellite area Transport Protocols TCP-ELN – NewReno + explicit loss notification WTCP – Wide area wireless TCP STP – Satellite transport protocol Table of Parameters Avg RTT Avg Loss Avg BW WLAN 5 ms 1 % 5 Mbps WWAN 200 ms 8 % 0.1 Mbps SAT 1000 ms 3 % 1 Mbps

Analysis of Transport Protocols FTP CIFS

Analysis of Transport Protocols SMTP HTTP

Impact of Application Behavior Thin session control messages When thin message loss occurs, it takes one RTT to recover from the loss When there is no packet following a lost thin message, loss may only be detected by RTO expiration Batched data fetches When requested data is smaller than BDP, there is underutilization of the network Inflation of transaction time causes lower performance

Impact of Application Behavior Flow control bottlenecked operations If application reads slowly or freezes, receiver buffer can fill up causing communication to halt Other reasons Non-prioritization of data Example: web browsing on a PDA Non-use of data reduction techniques Reducing content transferred between SMTP servers

A3 Design Why not change the applications to address these problems? Rewrite applications or implement A3 A3 is an optimization module that is application-aware but application transparent Transaction Prediction Redundant and Aggressive Retransmission Prioritized Fetching Infinite Buffering Application-aware Encoding

Transaction Prediction Transaction Prediction (TP) An approach to deterministically predict future application data requests to the server and issue them ahead of time As the application requests new blocks, TP requests future blocks as well instead of waiting for the application Blocks are cached by TP and sent when the application requests them TP will aid in conditions where BDP is larger than the application batch fetch size and where RTT is large For CIFS, TP requests the entire file at once instead of pieces Benefits CIFS and HTTP

Redundant and Aggressive Retransmissions Redundant and Aggressive Retransmissions (RAR) An approach to protect thin messages from losses RAR recognizes thin messages and uses a combination of packet level redundancy and aggressive retransmission to protect them When A3 receives a message from the application, it checks to see if it is a thin message If the message is a thin message, redundant copies are created, information about current time is stored, and retransmission timer is started When a response arrives, the timestamp is checked and RTT is estimated from timestamp and message is forwarded to application If retransmission timer expires for a thin message, the message is copied and retransmitted A3 uses a timeout value of RTTavg + α Benefits CIFS, SMTP, and HTTP

Prioritized Fetching Prioritized Fetching An approach to prioritize data and transfer high priority data faster Uses a separate module called application state monitor (ASM) which gets information from application ASM classifies objects as high or low priority ASM informs A3 about which objects are high priority and which are low priority Data that is more important uses TCP-like congestion control for high priority information Low priority congestion control (Ex. TCP-LP) for low priority data Benefits HTTP and SMTP

Infinite Buffering Infinite Buffering (IB) An approach to fix the flow control bottleneck by removing the limit on the receiver buffer Uses secondary storage such as hard disk for buffer IB keeps track of ACKs received by active TCP connection If advertised window is less than maximum possible window size, IB changes the window size to max If receivers buffer is full, IB stores data packets to disk cache and sends a proxy ACK back to the server Once buffer has space, packets are sent from Disk cache to the buffer When applications generates ACK for data that was already ACKed by IB, IB suppresses it Benefits CIFS, SMTP, HTTP

Application-Aware Encoding Application-Aware Encoding (AE) An approach that uses application specific information to encode or compress data Data compressed messages are marked so that the end user recognizes and de-compress data Example: Table of words commonly used in emails used to compress data when transmitting emails In A3 application vocabulary table are created on a user pair-wise basis (Ex. A-B vocabulary table created based on all past transmissions from A to B) Benefits SMTP and HTTP

A3 Point Solution – A3● A3 is an end-to-end approach A3● is a point solution and doesn’t require changes at both ends AE cannot be used in A3● because compression and encoding requires an end-to-end approach TP functions by generating more data requests and is effective as long as the server supports multiple simultaneous requests RAR generates redundant transmissions and functions properly as long as the server can filter duplicate messages If not, the redundant transmissions must be done in the transport layer, since TCP filters redundant messages

Performance Evaluation CIFS SMTP HTTP Integrated results for performance in WWAN

Related Work Odyssey Project System support for collaboration between operating system and individual applications by letting them be aware of wireless environment Coda file system Designed to support disconnect operations for mobile hosts Caches files at the client for disconnect periods

Critique In performance evaluation, the integrated results were only tested in the WWAN environment For the integrated results, A3 was modified for each protocol to support only three features instead of having A3 with every feature for each protocol which is more realistic There were no performance evaluations done for A3●

Questions?