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Transcript
Networking Basics: A Review Carey Williamson iCORE Chair and Professor Department of Computer Science University of Calgary Communications Networks • Historically, there have been two different philosophies guiding the design, operation, and evolution of communication networks – the “telco” view (i.e., telecommunications networks to support voice telephony and other emerging services, such as fax, data, location, etc.) – the “data networking” view (i.e., the Internet) • While the two approaches share some similar goals and challenges (e.g., scale, geography, heterogeneity), they often have quite different underlying assumptions CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 2 Telco Networks (1 of 2) • • • • About 100 years old Circuit-switched network Designed for transmission of human voice Twisted pair copper wire for residential access – “cheap”, adequate bandwidth, easy to handle... • Aggregation of multiple calls at toll office for multiplexing/demultiplexing using TDM • Low bandwidth required per call (e.g., 64 Kbps) • Fixed bandwidth required per call CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 3 Telco Networks (2 of 2) • Call routing and circuit allocation decided once per call at time of call arrival • End to end path allocation, with dedicated circuit (reserved bandwidth) per active call • All bits travel same path; stay in same order • Call state information crucial in network switches • Busy signal if no path possible (blocking <= 2%) • Billing model based on time used (in minutes) • Single class of service; high reliability (99.99%) • New services: faxes, modems, mobility, ... CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 4 The Internet (1 of 2) • • • • • • • • • About 30 years old Packet-switched network Variable size packets permitted Designed for transmission of data Wide range of access technologies Wide range of user and application behaviour Bursty, variable bandwidth required per call Aggregation of traffic at routers/switches Transmission links shared on stat mux basis CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 5 The Internet (2 of 2) • • • • • • • • Connection-less network layer protocol (IP) “Best effort” datagram delivery model Packet routing decided on a per packet basis No end to end path allocation; no reserved bandwidth per active call Packets can travel any path; packets can be delayed, lost, duplicated, re-ordered Minimal state info in network switches Single class of service Billing model? (hours? pkts? bytes? bandwidth?) CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 6 Asynchronous Transfer Mode (1of2) • • • • • • • • • About 20 years old Packet-switched network Small fixed-size packets (53 bytes) Designed for integrated services (voice, video, data, imaging, interactivity,…) High speed network technologies (optical) Wide range of user and application behaviour Bursty, variable bandwidth required per call Aggregation of traffic at switches Transmission links shared on a stat mux basis CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 7 ATM (2 of 2) • Connection-oriented • Allocates a virtual channel (VC) per active call • End to end path allocation determined at time of call arrival; reserved bandwidth per active call • All packets travel same path (order preserved) • Crucial state info in ATM switches • Multiple classes of service (priority levels) • Offers end to end QOS guarantees (SLAs) • Billing model? (cells? bandwidth? time?) CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 8 Internet Protocol Stack • Application: supporting network applications and end-user services – FTP, SMTP, HTTP, DNS, NTP • Transport: end to end data transfer Application Transport – TCP, UDP • Network: routing of datagrams from source to destination – IPv4, IPv6, BGP, RIP, routing protocols • Data Link: hop by hop frames, channel access, flow/error control – PPP, Ethernet, IEEE 802.11b Network Data Link Physical 001101011... • Physical: raw transmission of bits CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 9 Internet Protocol Stack Application Application Transport Transport Network Network Data Link Data Link Physical Core Network CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science Physical 10 Internet Protocol Stack Application Application Application Transport Transport Transport Network Network Network Data Link Data Link Data Link Physical Physical Physical Router CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 11 Internet Protocol Stack Application Application Application Transport Switch Transport Transport Network Network Network Data Link Data Link Data Link Physical Physical Physical CPSC 641 Winter 2011 Copyright © 2005 Department of Computer Science 12