Background PeertoPeer File Sharing Network Constantly changing network

Background Peer-to-Peer File Sharing Network Constantly changing network, no central server. Gnutella, Napster, Swarmcast ~50, 000 users/day and increasing Clip 2. Gnutella http: //www. clip 2. com/gnutella. html

Problems - Scenario A Ticcy’s trying to download a song on 56 K modem and $15 speaker Have to download the whole file before you can listen to the whole song. Host can drop off, leaving the song incomplete. Can’t control the quality/size of the song. She’d rather have the whole song with lower quality than an incomplete song

Problems – Scenario B Doddie’s on ADSL, trying to download a movie 10 hits, only one free, but slow. Can’t switch to faster peer when it becomes available.

Solutions Progressive Audio Quality increases as file size grow Allows preview Control Quality Good for users with slow connection Parallel download from multiple peers Faster download Don’t miss out on good connections Good for broadband users

Related work on Progressive Audio streaming Requires copies of the same file at different quality Can’t build on downloaded file to increase quality Progressive JPEG Next slide…

Progressive JPEG Sequential Progressive Buffer • Stores all DTC coefficients of image. • Group DCT coefficients into serveral spectral bands. • Typically, low-frequency bands are sent first, and then highfrequency bands. Similar approach may be taken for progressive audio, except that sound has a more complicated model of perception. It also requires that the file is encoded & decoded as progressive JPEG. B. Furht, Y. Weng, and J. Celi, "Interactive Progressive Encoding System for Transmission of Complex Images", Proc. of SPIE Symposium on Multimedia Storage and Archiving Systems, Boston, Nov 1998. Figs from http: //wwwicg. informatik. uni-rostock. de/Projekte/Mo. Vi/jpeg/pexamples. html

MPEG Overview "A tutorial on MPEG/Audio Compression" by Davis Pan. Motorola Inc, 96

MPEG Overview cont. . Psychoacoustic model works out the signal energy to masking threshold ratio for each frequency subband How sensitive human ear is to that frequency Neighboring frequencies make it more/less audible The bit allocation block uses the signal-to-mask ratios to decide how many code bits to allocate for quantization of that subband. Allocates more code bits to subband with low mask-to-moise ratio. "A tutorial on MPEG/Audio Compression" by Davis Pan. Motorola Inc, 96 http: //www. cs. sfu. ca/undergrad/Course. Materials/CMPT 365/material/ notes/Chap 4. 3/Chap 4. 3. html

Progressive Constraints Transfer any mp 3 file progressively end file should be identical to original file Real time Technique Decode the mp 3 file -> 32 quantized subbands/packet Rate the importance of subbands (signal-to-mask ratios) Running the signal through psychoacoustic model again Or Look at the number of code bits allocated to that subband! Send each subband in the order of importance. Maximum 32 passes, but normally a few subband dominates. Minimum 1 pass (all the sound appears in one subband, unlikely) Fast

Peer-to-Peer Connection Manager Search Resource Manager Transport

Searching in P 2 P Files are found by forwarding queries to one’s neighbors until the target is found. Broadcast search is costly on bandwidth and not scalable. Search utilizing high degree nodes Each client keep lists of files stored by their first and second degree neighbors. passed when a new node joins the network. Update periodically. Pass queries along the highest degree nodes. IP of the nodes already queried are appended to the query, and avoided. Simulation shows 50% of files can be found in 8 steps or less. “Search in Power-Law Networks” A Adamic et al, Stanford University, March 2001

Parallel Download Take advantage of the replication of data in P 2 P and download from multiple peers simultaneously. Task allocation to peers Qo. S (available bandwidth, latency) Divide file up accordingly and assign to peers Adapt to network changes (drop out, degraded Qo. S) Submit new request for resource from reliable peer Terminate or update request for a smaller file from bad Qo. S peers. "Resource Management in Networked Multimedia Systems" K. Nahrstedt, Distributed System Lab, UPenn, R. Steinmetz, IBM European Networking Center "The Dynamic MAnagement of Guaranteed Performance Connections in Packet Switched Integrated Service Networks" C Parris et al, Berkeley, 94.

Transport Protocol 70% of people don’t share their files because uploading their files slows their downloads. Our modems have separate channels for upload and download so why would upload affect download? Problem in TCP use acks for congestion control. i. e. if sender receives few acks it slows down transmission and vice-versa. when uploading, acks are queued behind data packets => the slow download. Solution Reduce frequence of acks (red marking) Handle infrequent acks Implement own congestion control using UDP TCP friendly – user control “How to get good TCP performance over asymmetric networks” H. Balakrishnan, MIT Nov 99 “Free Riding on Gnutella” Eytan Adar and Bernardo A. Huberman. Xerox Palo Alto

File Hashing – MD 5 Same file can have different filename, different file can have same filename. The original file needs an unique key to ensure file integrity for parallel download and file resume (for progressive) Solution - MD 5 A message-digest algorithm provides a output a 128 -bit "fingerprint" of a file of arbitrary length. Simple to implement (source available). Fast to compute. R. Rivest, "MD 5 Digest Algorithm. " RFC 1321, MIT and RSA Data Security, Inc. , April 1992.

System Overview Reuse of existing software LAME encoder http: //www. mp 3 dev. org MPG 123 decoder http: //mpg. 123. org/ MD 5 http: //www. fourmilab. ch/md 5/

Plan of Action

Thank you

Appendix - MD 5 Step 1. Append Padding Bits The message is "padded" (extended) so that its length (in bits) is congruent to 448, modulo 512 Step 2. Append Length A 64 -bit representation of b (the length of the message before the padding bits were added) is appended to the result of the previous step. Step 3. Initialize MD Buffer word A: 01 23 45 67 word B: 89 ab cd ef word C: fe dc ba 98 word D: 76 54 32 10 Step 4. Process Message in 16 -Word Blocks Too long. . Step 5. Output R. Rivest, "MD 5 Digest Algorithm. " RFC 1321, MIT and RSA Data Security, Inc. , April 1992.

Appendix – Fourier analysis Any wave may be represented as a sum of sine waves. Fourier analysis help us determine which sine waves must be used. Fig taken from http: //www. bores. com/courses/intro/freq/3_dist. htm Computer Graphics – Foley, 97