INF570 Introduction dario.rossi INF570 Dario Rossi v08/2013 http://www.enst.fr/~drossi Agenda • Internet • At a glance • Internet history • Internet architecture • Applications • Terminology • Architectural models • P2P applications • A primer • Outlook on the course • References INF570 Internet dario.rossi Internet • Internet definition ? – Internet en 2001, http://www.caida.org/ Internet http://www.livinginternet.com/i/ia_myths_toast.htm Internet = components • Billions hots – PCs servers, phones, toasters – Equiped wtih communication capabilities • Communication links – Optical fiber, copper, air ,… carying bits and frames • IP routers – Interconnecting host, and routing data • TCP segments – Controlling data exchange and reception for all applications • Application messages – Exchanged among hosts to implement end-user services Internet http://www.livinginternet.com/i/ia_myths_toast.htm Internet = applications + users • Application list always growing – Remote access, file-transfer, e- mail, instant messaging, Web, video and audio streaming, gaming , cloud, social networking IP/TCP • User-base always growing – > 2 billion users (12/2011) ht tp://www.internetworldstats.com/stats.htm Internet Internet = standards • Internet Engineering Task Force (IETF) http://www.ietf.org • IETF Request For Comments (RFC ) – Technical reference documents on the TCP/IP world (HTTP, TCP, IP…) – Initially informal documents, today de facto standards – > 6000 RFCs (09/2012) http://www.ietf.org/download/rfc- index.txt http://javvin.com/map.html • Other application-specific fora – W3C pour WWW, BEP pour BitTorrent … • No documentation: – Proprietary protocols: KaZaa, Skype, etc. Internet Internet = architecture V. Cerf and R. Kahn, “A protocol for • Offering reliable application- packet network intercommunication“ independent end-to-end services IEEE Transactions on Communications , May 1974 • Over point-to-point unrealiable individual channels • Principles : – Minimalism, best-effort, stateless core, decentralized edge control • End-to-end – IP Routing, TCP transport, user application • Point-to-point – IP Forwading, MAC & PHY communication Internet Internet = complex ecosystem ISPs (telcos) content providers services (free/paying) users This viewpoint out of the scope of this course (but see readings) Internet History • 1960s : L. Kleinrock, (Internet size) P. Baran packet-switching • 1969: 1 node • 1970s : ALOHAnet , Ethernet • 1972: 15 nodes ARPAnet • 1983 : TCP/IP • 1979: 200 nodes • 1988 : Congestion control • 1980: 100K nodes • 1990s : Web • 1990: 1M nodes • 2000s : P2P • 2000: 1B nodes • 2010s : cloud, video (YouTube 2 nd search engine), social net (Facebook 4th country) Internet architecture Internet layers Data unit Layer Nb – Example protocol – HTTP, DNS, RIP, Message Application L7 BitTorrent, Skype,etc. Segment Transport L4 – TCP, UDP, SCTP, RTP, etc. Datagram Internet L3 – IP, ICMP, IGMP, OSPF, BGP, etc. Frame HostHost--toto--networknetworkL2 – PPP, HDLC , Ethernet, WiFi, etc. Internet operation mode Network taxonomy Internet Circuit switching Packet switching FDM TDM Virtual circuit Datagram Network IP Transport TCP UDP Circuit switching – Signaling: resource (frequences, temporal slots, etc.) allocated during connection set-up and released at tear-down by all intermediate devices – Switching : based on circuit ID, known to all intermediate equipment, fixed during all transmission – Transmission : data follow same path (i.e., the circuit), no delay – Example : Global System for Mobile (GSM), Public Switched Telephone Network (PSTN), ISDN, SONET/SDH application 6. Receive data application transport 5. Data flow begins transport network 4. Call connected 3. Accept call network data link 1. Initiate call 2. incoming call data link physical physical Packet switching – Datagram mode • Signaling: unnecessary, each packet carries control information • Switching : istantaneous for each packet; intermediate devices unaware of ongoing transmissions (scalability) • Transmission : no performance guarantee – Virtual circuit mode • Per-flow end-to-end signaling to emulate circuit-switching (TCP); just guarantee in-order delivery, no performance guarantees application application transport transport network network 1. Send data 2. Receive data data link data link physical physical Circuit vs packet switching • Circuit switching • Packet switching – Resources allocated to users – No allocation, ever – Signaling necessary for connection – Flexible use of all resources on set-up and teard down a first come, first serve basis – In network-state for all ongoing – Packets may be buffered to conversations wait for their service – No performance guarantees – Guaranteed performance (not even for virtual circuit) – No buffering – Variable delay – Easy planning for simple services – More efficient for varying traffic – Potential resource waste demand (statistical multiplexing) – Scalability problems – Simple, scalable core Internet delay Delay source at each IP hop: – Processing (< µs) - Transmission = P/C ( µs – ms) – Buffering ( µs – s) - Propagation = D/V (1 ms – 0.5s) Variable components Fixed components (for different packets of the same flow) (for all packets of the same flow) Processing Transmission P=packet size C=link capacity D=distance V=transmission speed Buffering Propagation (“Bufferbloat” if very large; see later on) Internet in this course application application application transport transport transport network network network data link data link data link physical physical physical Application : taxonomy today (P2P apps later on) Transport: quick recap on TCP (similar problems later on) Network: quick recap on IP routing (routing at overlay later on) Internet in this course applicationapplication application transport transport transport application network network network transport data link data link data link network physical physical physical data link physical Application: data producer and consumer Transport: when and how much data to send Network: where to send data (short + long timescales) Transport: TCP & UDP • UDP TCP TCP – Datagram, unrealiable, connectionless service SYN – Bitrate and message-size Round flexibility (≤ MTU) Trip -way Time SYN+ACK • TCP (RTT) Three Three handshake handshake – Virtual circuit, connection-oriented ACK + GET with inorder and reliable delivery – Imposed tx speed (next slide) and RTT segment size (preferably =MTU) Data + FIN data User – Initial delay due to connection setup FINACK time Connection tear-down Transport: TCP & UDP TCP • TCP data transfer TCPTCP – A t any tme, the tx speed is w = min(cwnd,rwnd) RTT – Rwnd = receiver window, flow control (avoid tx more than rx can handle) RTT – Cwnd = congestion window, congestion control (avoid tx more than the network RTT can sustain) transfer transfer Data Data • Cwnd dynamic Time – Algorithms: slow-start, congestion avoidance, fast-recovery, fast-retransmit, timeout,etc. cwnd Congestion Packet – Flavors: NewReno, Cubic, Compound avoidance losses – Slow-start (cwnd<sstrhesh): exponential growth, start at 1 segment par RTT, then cwnd++ at each ACK reception Fast-recovery – Congestion avoidance (cwnd>sstrhesh): Slow start linear growth , cwnd+=1/cwnd at each ACK Timeout 1 2 3 … Time (RTT) Network: IP forwarding • At each data packet – Decide the next hop, based on the destination address • Short timescale: istantaneous switching function – At low level implemented as a Forwarding Information Base (FIB) lookup • Longest prefix matching • Ternary Content Addressable Memory (TCAM) Network: IP routing • Periodically – Exchange topological information between IP routers, to build FIB used in fowarding – Taxonomy: • Link state: local information to all nodes (OSPF) • Distance vector: global information to neighbors (RIP, BGP) – Internet: inter-AS + intra-AS routing Link state Distance vector Internet structure • Three-tiered architecure – Tier-3 (local ISPs) Tier-3 – Tier-2 (regional/national Tier-2 ISPs) – Tier -1 ( international ISPs ) Tier -1 • Full mesh between Tier-1 • Interco business model – Network access point – Customer-provider – Peering Internet structure On their end-to-end trip, IP packets traverse (i) multiple AS, and (ii) multiple routers per AS Virtual Tier 3 local ISP local local ISP ISP ISP ISP Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Internet references • Organisations – http://www.isoc.org • Internet Society – http://www.ietf.org • IETF (Internet Engineering Task Force) – http://www.w3c.org • World Wide Web Consortium – http://www.ieee.org • IEEE (Institute of Electrical and Electronics Engineers) – http://www.acm.org • ACM (Association for Computing Machinery) • Optional reading – « A brief history of the Internet », by those who made the history http://www.isoc.org/internet/history/brief.shtml « The Internet Ecosystem », http://www.isoc.org/pubpolpillar/docs/internetmodel.pdf INF570 Internet dario.rossi Applications Agenda • Terminology • Applications & Protocols • Application-centric vs network-centric architectures • Application: Client-server, Content distribution networks, Peer-to-peer • Network: IP Multicast, Content centric networking • Application vs transport layer • Interactions • Interface (socket) • Applications performance • Data vs multimedia (voice, video) • Quality of Service (QoS) vs Quality of Experience (QoE) • Implication on lower-layer choices • References Internet applications User • Ultimate reason why Internet exists application