? Computer the IMT2431 - Data Communication and Network Security January 7, 2008
? Teachers are Lasse Øverlier and http://www.hig.no/~erikh Lectures and Lab in A126/A115 Course webpage http://www.hig.no/imt/in/emnesider/imt2431 Course mailinglist IMT2431@list.hig.no IMT2431-subscribe@list.hig.no to join Lasse s office A124C (and lasse@hig.no) and Erik s office A132
? 10 credits 15 hrs per week Evaluation based on: Mid-term exam Project Final exam Grading based on 100 point scale
: Nuts and Bolts view?
: Nuts and Bolts view? millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets
: Nuts and Bolts view? s control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, ARP : network of networks loosely hierarchical public versus private intranet standards IETF: Engineering Task Force RFC: Request for comments http://www.rfc-editor.org/
: Service view? communication infrastructure enables distributed applications: Web, email, games, e-commerce, file sharing communication services provided to apps: Connectionless unreliable Connection-oriented reliable
s? all communication activity in governed by protocols: protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
Network Structure? Network edge applications and hosts Network core routers/switches network of networks networks, physical media communication links
? End systems with distributed applications Client/Server model server listens, clients make initial request e.g. www, email, dns Peer-peer (P2P) model end systems are both clients and servers minimal (or no) use of dedicated servers e.g. Gnutella, Kazaa, Bittorrent
: Two Services? Distributed applications use one of two services for data transfer between end systems Connectionless UDP - User Datagram protocol (RFC768) unreliable, no state information or handshake no flow control no congestion control but possibly fast! Connection-oriented TCP - Transmission Control (RFC793) reliable, in-order bytestream flow control congestion control
? Mesh of interconnected routers How is data transferred through networks? circuit switching packet switching
? : Circuit Switching Dedicated resources: no sharing Circuit-like (guaranteed) performance Call setup required Resource piece idle if not used by owning call (no sharing) Frequency division and time division multiplexing
: Packet Switching? Each end-end data stream divided into packets Users packets share network resources Each packet uses full link bandwidth Resources used as needed Is an example of statistical multiplexing
Packet-switched Networks: Forwarding? Move packets through routers from source to destination (Chp 4) Datagram network destination address in packet determines next hop routes may change during session Virtual circuit network each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup time, remains fixed thru call routers maintain per-call state
Networks How to connect end systems to edge router??
Networks? Residential access networks Dialup via modem ISDN xdsl Cable (HFC) Institutional access networks Ethernet Mobile access networks (Note: Prof. Tan s course IMT4751 Wireless Communication Security) wireless LANs: 802.11 wider-area wireless access: GSM data, GPRS, 3G
? Bit: propagates between transmitter/rcvr pairs link: what lies between transmitter and receiver guided media: signals propagate in solid media copper fiber coax unguided media: signals propagate freely radio
? Tier 1 are backbone networks POP (Points of Presence) are the ISP s routers where customers (possibly other ) connect interconnect through private peering points or NAPs/IXPs (Network Points/ Exchange Points) http://www.nix.no
Types of Delay? Processing Queuing Transmission Propagation Total nodal delay: d nodal = d proc + d queue + d trans + d prop
Queuing Packet? R = link bandwidth (bps) L = packet length (bits) a = average packet arrival rate traffic intensity = La R Packet loss queue (aka buffer) has finite capacity when packet arrives to full queue, packet is dropped lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all
Traceroute? Prints the route packets take to network host Provides three delay measurements > traceroute rtfm.mit.edu traceroute to PENGUIN-LUST.mit.edu (18.181.0.29), 30 hops max, 38 byte packets 1 128.39.243.1 (128.39.243.1) 0.442 ms 0.241 ms 0.208 ms 2 gjovik-gw.uninett.no (128.39.3.61) 0.648 ms 1.045 ms 0.449 ms 3 oslo-gw1.uninett.no (128.39.46.85) 2.168 ms 2.175 ms 1.905 ms 4 no-gw.nordu.net (193.10.68.101) 2.087 ms 2.105 ms 2.072 ms 5 se-kth.nordu.net (193.10.68.29) 9.484 ms 9.624 ms 9.667 ms 6 nordunet.se1.se.geant.net (62.40.103.117) 9.944 ms 9.849 ms 9.792 ms 7 se.uk1.uk.geant.net (62.40.96.126) 44.710 ms 44.792 ms 45.433 ms 8 uk.ny1.ny.geant.net (62.40.96.169) 113.529 ms 113.534 ms 113.319 ms 9 198.32.11.61 (198.32.11.61) 114.368 ms 113.523 ms 113.795 ms 10 nox230gw1-po-9-1-nox-nox.nox.org (192.5.89.9) 119.108 ms 118.733 ms 122.500 ms 11 nox230gw1-peer-nox-mit-192-5-89-90.nox.org (192.5.89.90) 119.368 ms 119.019 ms 118.655 ms 12 NW12-RTR-2-BACKBONE.MIT.EDU (18.168.0.21) 119.345 ms 118.940 ms 119.357 ms 13 PENGUIN-LUST.MIT.EDU (18.181.0.29) 120.185 ms 119.113 ms 119.687 ms >
Networks are Complex!? Is there any hope of organizing structure of network? Or at least our discussion of networks?
Example?
Networks under Attack? Malware (D)DoS Packet sniffing Masquarading/spoofing Modifying messages (MITM)
Very Brief? 1961-1972: Early packet-switching principles 1972-1980: working, new and proprietary nets 1980-1990: The as we know it 1990-: commercialization, the Web, new apps
? Spend much time reading and doing theory exercises Join the mailing list and visit the course webpage