HW2 Grade. CS585: Applications. Traditional Applications SMTP SMTP HTTP 11/10/2009

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1 HW2 Grade CS585: Applications CS585\CS485\ECE440 Fall 2009 Traditional Applications SMTP Simple Mail Transfer Protocol HTTP HyperText Transport Protocol DNS Domain Name System Protocol Overlay Networks SMTP Standard protocol for transmission across IP networks SMTP is running over TCP Used by mail servers to send and receive, and used by clients to send message Clients use either POP or IMAP to receive CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall SMTP Mail Server HTTP Running over TCP Text-oriented protocol Message form Start line Message Header Message body CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall

2 DNS: Domain Name System Internet hosts, routers: IP address (32 bit) - used for addressing datagrams name, e.g., - used by humans Need mapping between IP addresses and name. Domain Name System: Distributed database implemented in hierarchy of many name servers Why Not Centralized DNS? Single point failures Traffic Volume Doesn t Scale! CS585\CS485\ECE440 Fall Distributed, Hierarchical Database Root DNS Servers com org edu yahoo.com amazon.com pbs.org poly.edu umass.edu Client wants IP for Client queries a root server to find com DNS server Client queries com DNS server to get amazon.com DNS server Client queries amazon.com DNS server to get IP address for CS585\CS485\ECE440 Fall Local Name Server Does not strictly belong to hierarchy Each ISP (residential ISP, company, university) has one. Also called default name server Example Host xyz.cs.unm.edu wants IP address for local DNS server in cs.unm.edu 2 8 root DNS server 3 TLD DNS server When a host makes a DNS query, query is sent to its local DNS server Acts as a proxy, forwards query into hierarchy. requesting host xyz.cs.unm.edu authoritative DNS server google.com CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall DNS: caching and updating records Overlay Networks Once (any) name server learns mapping, it caches mapping cache entries timeout (disappear) after some time TLD servers typically cached in local name servers Thus root name servers not often visited Overlay Network Physical Network Overlay nodes are connected by tunnels. CS585\CS485\ECE440 Fall 2009 CS585\CS485\ECE440 Fall

3 Fundamental difference Take advantage of resources at the edges of the network N N 2 N3 Quickly grown in popularity Hundreds of file sharing applications Large population of users Audio/Video transfer now dominates traffic on the Internet Key= title Value=MP3 data Publisher N 4 Internet N5? N 6 Client Lookup( title ) CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall Common Primitives: Join: how do I begin participating? Publish: how do I advertise my file? Search: how to I find a file? Fetch: how to I retrieve a file? Gnutella: Overview Query Flooding: Join: on startup, client contacts a few other nodes; these become its neighbors Publish: no need Search: ask neighbors, who as their neighbors, and so on... when/if found, reply to sender. Fetch: get the file directly from peer CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall Gnutella: Search I have file A. I have file A. Aside: All Peers Equal? Reply 0Mbps LAN Query Where is file A? CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall

4 KaZaA: Overview Smart Query Flooding: Join: on startup, client contacts a supernode... may at some point become one itself Publish: send list of files to supernode Search: send query to supernode, supernodes flood query amongst themselves. Fetch: get the file directly from peer(s); can fetch simultaneously from multiple peers KaZaA: Network Design Super Nodes CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall KaZaA: File Insert insert(x, )... Publish I have X! KaZaA: File Search Where is file A? search(a) --> Query Replies search(a) --> CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall BitTorrent: Overview Swarming: Join: contact centralized tracker server, get a list of peers. Publish: Run a tracker server. Search: Find a tracker for the file you want. Fetch: Download chunks of the file from your peers. Upload chunks you have to them. BitTorrent: Publish/Join Tracker CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall

5 BitTorrent: Fetch P2P: Summary Lessons learned: Single points of failure are very bad Flooding messages to everyone is bad Underlying network topology is important Not all nodes are equal Need incentives to discourage freeloading CS585\CS485\ECE440 Fall CS585\CS485\ECE440 Fall No office hour today! Don t forget Midterm graduate project demo on Nov. 7 HW3 due on Nov. 24 CS585\CS485\ECE440 Fall