COMP 431 A Whirlwind Introduction to the Internet Internet Services - PowerPoint PPT Presentation

COMP 431 A Whirlwind Introduction to the Internet Internet Services & Protocols Overview Introduce the major nouns and verbs of A Whirlwind Introduction to the Internet ◆ What’s the Internet networking! ( “ Networking Nouns and V erbs ” ) mobile network ◆ Network core ◆ Network edge global ISP Jasleen Kaur ◆ Access nets, physical media ◆ Internet Structure & ISPs home January 14, 2019 network ◆ Performance: loss, delay regional ISP* ◆ Security ◆ Protocol layers, service models *Internet Service Provider Institutional network 2 3

Some Definitions Just What is the Internet? The “ nuts and bolts ” view Yes, there really are Internet toasters! mobile network ◆ Billions of connected computing Web-enabled toaster + global ISP devices: hosts, end-systems IP picture weather forecaster frame » PCs, laptops, servers home » Tablets, phones, e-readers, toasters running “ network applications ” network regional ISP ◆ Communication links » Different media (fiber, copper wire, radio, satellite) Slingbox: watch, Tweet-a-watt: » Different transmission rates – bits control cable TV remotely monitor energy use per second (bps) ❖ 10 3 (Kbps) to 10 6 (Mbps) to 10 9 (Gbps) Institutional network Internet ◆ Switches & Routers : refrigerator sensorized, router PC server » Forward “ packets ” of data though the bed network mattress smart Internet phones phone wireless links laptop 4 5

Just What is the Internet? Some Definitions The “ services ” view The “nuts and bolts” view mobile network mobile network ◆ Internet: “network of networks” ◆ Internet: A communication » Loosely hierarchical infrastructure enabling distributed global ISP global ISP applications » Public Internet versus private » WWW, email, games, e-commerce, intranet database, voting, … home home ◆ Protocols: network network regional ISP regional ISP » Control sending, receiving of ◆ Communication services provided: messages » Connectionless : ❖ No guarantees » e.g., TCP, IP, HTTP, SMTP, …. » Connection-oriented : ◆ Internet standards ❖ Guarantees order and completeness » RFC: Request for comments » IETF: Internet Engineering Task Institutional network Institutional network Force 6 7

Network Maps Just how big is the Internet…? 8 9

A Whirlwind Introduction to the Internet The Structure of the Internet Overview The physical makeup of the Internet mobile network mobile network ◆ What’s the Internet ◆ Network core: ◆ Network core » Routers global ISP global ISP » Network of networks ◆ Network edge ◆ Access nets, physical media home home ◆ Network edge: network network regional ISP regional ISP ◆ Internet Structure & ISPs » Applications running on hosts ❖ “ host ” = “ end system ” ◆ Performance: loss, delay ◆ Security ◆ In between: Access networks ◆ Protocol layers, service models » Physical media: communication links Institutional network Institutional network 10 11

Network Structure The Network Core The network core Circuit Switching ◆ Resources reserved end-to-end for mobile network mobile network the connection ( “ call ” ) ◆ A mesh of interconnected routers » Resources: global ISP global ISP ❖ Link bandwidth, switch processing capacity, memory buffers, etc . ◆ The fundamental architectural question: » Reservation: home home How is data forwarded through the network? network network ❖ Dedicated fraction of available regional ISP regional ISP » Circuit switching : “telephone model” bandwidth, buffers, etc . ❖ dedicated circuit (path) per call used by ◆ J : all data » Circuit-like (guaranteed) performance » Packet switching : “datagram model” ❖ data sent in discrete “ chunks ” (packets) ◆ L : ❖ each packet has a path chosen for it » Call setup required independently Institutional network Institutional network » Call rejection ( “ busy signal ” ) possible 12 13

Circuit Switching The Network Core Allocating fractions of bandwidth — Multiplexing Packet Switching ◆ Each sender divides its messages ◆ But now we have resource Transmission ◆ Network bandwidth divided into “ packets ” (sequence of bits) contention! Frequency 4 KHz into transmission “ slots ” » Aggregate resource demand can » Each packet uses full link capacity until exceed amount available Call 1 » Slots allocated to calls transmission completed Link Call 2 » Congestion: packets queue, » Slots are unused ( “ idle ” ) if not FDM » Senders ’ packets share (compete for) capacity wait for link availability used by owning call Call 3 network resources Call 4 » No sharing of slots! ◆ Also introduces Store-and- » Resources allocated & used as needed Forward delays: Time ◆ How to divide link Call data » packets move one hop at a time bandwidth into slots? ❖ Routers receive complete TDM 1 2 3 4 1 2 3 4 1 2 3 4 packet over incoming link » Frequency division multiplexing (FDM) ◆ Bandwidth division into slots ❖ Then transmit over Slot Frame outgoing link » Time division multiplexing ◆ Dedicated allocation (TDM) ◆ Resource reservation frames / sec X bits / slot = TDM per-call transmission rate 14 15

Packet Switching The Network Core Statistical multiplexing Packet switching v . Circuit switching 10 Mbps 1 Mbps link statistical multiplexing C A Ethernet N users 1.5 Mbps Packet switching B allows more users queue of packets 45 Mbps to use the network! waiting for output link ◆ Assume that on a 1 Mbps link: » Each user consumes 100Kbps when “ active ” D E » Each user active 10% of time ◆ Circuit-switching can support 10 users ◆ Packet-switching versus circuit switching: ◆ Packet switching can support 35 users » Restaurant seating analogy » With 35 users the probability of more than 10 users active simultaneously is less than 0.0004 » Other familiar analogies? 16 17

Packet Switching (Store and Forward) Packet Switching vs. Circuit Switching Why switch packets instead of entire messages? Is packet switching a “ no brainer ” ? ◆ J : 1.5 Mbps » Great for bursty data J ❖ Resource sharing » No call setup 5 seconds 5 seconds 5 seconds » Light-weight fault recovery 7.5 Mb 15 second end-to-end delay ◆ Excessive congestion: packet delay and loss L Message » Protocols needed for reliable data transfer, congestion control ◆ “Message switching” example ◆ How to provide circuit-like behavior? » Transmit a 7.5 Mb message over a network with 1.5 Mbps » Bandwidth guarantees needed for audio/video applications? links » Still an unsolved problem (go to grad school!) » What is the total elapsed transmission time? 18 19

Packet Switching (Store and Forward) Packet Switching mobile network Why switch packets instead of entire messages? Forwarding global ISP 1.5 Mbps ◆ Forwarding: home Time network » The process of moving packets among regional ISP 1 0.000 routers from source to destination 7.5 Mb 2 1 0.001 Message 3 2 1 0.002 ◆ Datagram network: 4 3 2 1 0.003 5 4 3 2 » Each packet carries a destination address 0.004 5,000 Packets ... ... ... ... ... » Destination address used to look up next hop » Route (next hop) may change at any time Still took 4999 4998 4997 4996 4.998 full 5 secs 5000 4999 4998 4997 4.999 5000 4999 4998 to xmit msg! 5.000 Institutional network 5000 4999 5.001 ◆ Virtual circuit (path) network: ~ 5 second 5000 5.002 end-to-end delay » Packets carry a “ tag ” (virtual circuit ID) that determines the next hop ◆ Packet-switching: store and forward behavior » Path determined at call setup time & remains fixed throughout call Animation » Routers maintain per-call path state » 1,500 bit packets, 1 packet forwarded every 1 ms https://wps.pearsoned.com/ecs_kurose_compnetw_6/216/55463/14198702.cw/index.html 20 21

Forwarding in Packet Switched Networks Forwarding in Packet Switched Networks Virtual circuit forwarding Datagram forwarding / / / / a b a b / / / / / / / / c c Network Next / / / / ID Hop / / / / xxx.yyy. b / / / / uuu.vvv. b Inbound VC Outbound New VC sss.ttt. c Interface Number Interface Number ... ... a 127 b 19 ◆ Routers maintain per- a 32 b 8 ◆ Packets contain complete destination address connection state b 84 c 63 » And perform set-up/tear- ... ... ... ... » Address specifies both a network and a host down operations ◆ Each router examines the destination address ◆ A (static) route is computed before » And forwards packet to the next router closest to the destination network any data is sent (Why not choose a single VC identifier for the entire path and ❖ Routers maintain a table of “ next hops ” to all destination networks ◆ Packets contain a VC identifier avoid replacing it at each hop?) ◆ Routers maintain no per-connection state » Identifier replaced at every hop 22 23