Computer Networks and the Internet

Transcription

1 ? Computer the IMT Data Communication and Network Security January 7, 2008

2 ? Teachers are Lasse Øverlier and Lectures and Lab in A126/A115 Course webpage Course mailinglist to join Lasse s office A124C (and [email protected]) and Erik s office A132

3 ? 10 credits 15 hrs per week Evaluation based on: Mid-term exam Project Final exam Grading based on 100 point scale

4 : Nuts and Bolts view?

5 : 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

6 : 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

7 : Service view? communication infrastructure enables distributed applications: Web, , games, e-commerce, file sharing communication services provided to apps: Connectionless unreliable Connection-oriented reliable

8 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

9 Network Structure? Network edge applications and hosts Network core routers/switches network of networks networks, physical media communication links

10 ? End systems with distributed applications Client/Server model server listens, clients make initial request e.g. www, , dns Peer-peer (P2P) model end systems are both clients and servers minimal (or no) use of dedicated servers e.g. Gnutella, Kazaa, Bittorrent

11 : 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

12 ? Mesh of interconnected routers How is data transferred through networks? circuit switching packet switching

13 ? : 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

14 : 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

15 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

16 Networks How to connect end systems to edge router??

17 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: wider-area wireless access: GSM data, GPRS, 3G

18 ? 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

19 ? 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)

20 Types of Delay? Processing Queuing Transmission Propagation Total nodal delay: d nodal = d proc + d queue + d trans + d prop

21 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

22 Traceroute? Prints the route packets take to network host Provides three delay measurements > traceroute rtfm.mit.edu traceroute to PENGUIN-LUST.mit.edu ( ), 30 hops max, 38 byte packets ( ) ms ms ms 2 gjovik-gw.uninett.no ( ) ms ms ms 3 oslo-gw1.uninett.no ( ) ms ms ms 4 no-gw.nordu.net ( ) ms ms ms 5 se-kth.nordu.net ( ) ms ms ms 6 nordunet.se1.se.geant.net ( ) ms ms ms 7 se.uk1.uk.geant.net ( ) ms ms ms 8 uk.ny1.ny.geant.net ( ) ms ms ms ( ) ms ms ms 10 nox230gw1-po-9-1-nox-nox.nox.org ( ) ms ms ms 11 nox230gw1-peer-nox-mit nox.org ( ) ms ms ms 12 NW12-RTR-2-BACKBONE.MIT.EDU ( ) ms ms ms 13 PENGUIN-LUST.MIT.EDU ( ) ms ms ms >

23 Networks are Complex!? Is there any hope of organizing structure of network? Or at least our discussion of networks?

24 Example?

25 Networks under Attack? Malware (D)DoS Packet sniffing Masquarading/spoofing Modifying messages (MITM)

26 Very Brief? : Early packet-switching principles : working, new and proprietary nets : The as we know it 1990-: commercialization, the Web, new apps

27 ? Spend much time reading and doing theory exercises Join the mailing list and visit the course webpage