Announcements TAs office hours: Mohamed Grissa: grissam@oregonstate.edu Tuesday: 4-5 Friday: 11-12 Mohamed Alkalbani: alkalbmo@oregonstate.edu Wednesday: 11-12 Thursday: 11-12 Lecture slides: Will be posted today in the course website. Introduction 1-1
Chapter 1: introduction our goal: get feel and terminology more depth, detail later in course use Internet as the example Introduction 1-2
Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 end-to-end throughput analysis Introduction 1-3
What s the Internet: a service view Communication infrastructure enables distributed applications Web, VoIP, email, games, e- commerce, social nets, Communication services provides programming interface to apps hooks that allow sending and receiving app programs to connect to Internet provides service options, analogous to postal service mobile network home network institutional network global ISP regional ISP Introduction 1-4
What s the Internet: nuts and bolts view PC server wireless laptop smartphone wireless links wired links hosts or end systems: billions of connected computing devices running network apps communication links: fiber, copper, radio, satellite transmission rate: bandwidth mobile network home network global ISP regional ISP router routers & switches: forward packets (chunks of data) institutional network Introduction 1-5
What s the Internet: nuts and bolts view Internet: network of networks Interconnected ISPs Internet standards IETF: Internet Engineering Task Force RFC: Request for comments IEEE for links/hardware Ethernet, 802.11, protocols control sending, receiving of messages e.g., TCP, IP, HTTP, Skype, 802.11 mobile network home network institutional network global ISP regional ISP Introduction 1-6
What s a protocol? a human protocol and a computer network protocol: Hi Hi Got the time? 2:00 time TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> Introduction 1-7
What s a protocol? human protocols: what s the time? I have a question introductions specific messages sent specific actions taken when messages received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt Introduction 1-8
Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 end-to-end throughput analysis Introduction 1-9
A closer look at network structure: network edge: hosts: clients and servers servers often in data centers access networks, physical media: wired, wireless communication links network core: interconnected routers network of networks mobile network home network institutional network global ISP regional ISP Introduction 1-10
Access networks Q: How to connect end systems to edge router? residential access nets enterprise/institutional access networks school, company, mobile/wireless access networks Introduction 1-11
Residential access networks wireless devices often combined in single box to/from headend or central office cable or DSL modem wireless access point (54 Mbps) router, firewall, NAT wired Ethernet (1 Gbps) Introduction 1-12
Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch institutional mail, web servers typically used in companies, universities, etc. 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch Introduction 1-13
Mobile/wireless access networks shared wireless access network connects end system to router via base station aka access point wireless LANs: within building (100 ft.) 802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate wide-area wireless access provided by telco (cellular) operator, 10 s km between 1 and 10 Mbps 3G, 4G: LTE to Internet to Internet Introduction 1-14
Host: sends packets of data host sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth 2 host 1 two packets, L bits each R: link transmission rate packet transmission delay time needed to transmit L-bit packet into link = = L (bits) R (bits/sec) Introduction 1-15
Physical media bit: propagates between transmitter/receiver pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper (twisted pair), fiber, coax unguided media: signals propagate freely, e.g., wireless Twisted pair cable Coaxial cable fiber optic cable Introduction 1-16
Unguided media signal carried in electromagnetic spectrum no physical wire bidirectional propagation environment effects: reflection obstruction by objects interference radio link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., WiFi) 54 Mbps wide-area (e.g., cellular) 4G cellular: ~ 10 Mbps satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay Introduction 1-17
Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 end-to-end throughput analysis Introduction 1-18
The network core The fundamental question: how is data transferred through net? circuit-switching: dedicated circuit per call: telephone nets packet-switching: data sent thru net in discrete chunks Introduction 1-19
Network core: packet-switching A 100 Mb/s Ethernet C B 1.5 Mb/s Packet-switching: Source breaks application-layer message into packets Forward from one router to the next until reaching destination Introduction 1-20
Network core: packet-switching A 100 Mb/s Ethernet C B 1.5 Mb/s Packet-switching: no dedication/reservation: all streams share resources no setup is required resources used as needed each packet uses full link bandwidth aggregate resource demand can exceed capacity no guarantee Introduction 1-21
Packet Switching: statistical multiplexing A R = 100 Mb/s statistical multiplexing C B queue of packets waiting for output link R = 1.5 Mb/s D E Sequence of A & B packets does not have fixed pattern, shared on demand statistical multiplexing Introduction 1-22
Packet-switching: store-and-forward L bits per packet source 3 2 1 R bps R bps destination takes L/R sec to transmit (push out) L-bit packet into link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link end-end delay = 2L/R (assuming zero propagation delay) one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec more on delay shortly Introduction 1-23
Packet Switching: queueing delay, loss A R = 100 Mb/s C B queue of packets waiting for output link R = 1.5 Mb/s D E queuing and loss: if arrival rate (in bits) to link exceeds transmission rate of link for a period of time, then there will be consequences: delay: packets will queue, wait to be transmitted on link loss: packets can be dropped if memory (buffer) fills up Introduction 1-24
Two key network-core functions routing: determines sourcedestination route taken by packets routing algorithms forwarding: move packets from router s input to appropriate router output routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 3 2 1 destination address in arriving packet s header Introduction 1-25
Alternative core: circuit switching reserved resources: resources divided into pieces end-end resources are reserved for each call in diagram, each link has four circuits call gets 2 nd circuit in top link and 1 st circuit in right link. no sharing: dedicated resources: guarantees: circuit-like performance Introduction 1-26
Alternative core: circuit switching wasted if not used: circuit segment idle if not used by call (no sharing) overhead: call setup is required admission control same path for all chunks commonly used in traditional telephone networks Introduction 1-27
Circuit switching: FDM versus TDM Two ways of dividing bandwidth into pieces frequency division time division Introduction 1-28
Circuit switching: FDM versus TDM Freq. Division Multiplexing (FDM) Example: 4 users frequency Time Division Multiplexing (TDM) time frequency time Introduction 1-29
Packet switching versus circuit switching A B B: has no packets to send Circuit switching 2 Mb/s Utilization = 50% only = 1 Mb/s 2 circuits (use TDM) A reserves 1 circuit B reserves 1 circuit A B Packet switching 2 Mb/s Utilization = 100% = 2 Mb/s statistical multiplex. B uses full link since A is not using it Introduction 1-30
Numerical example How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? The link s transmission rate = 0.64 Mbps Each link uses TDM with 10 slots/sec 0.5 sec to establish end-to-end circuit Let s work it out! You have few minutes! Solution: Bandwidth of circuit (in kbps)=.64x1000/10 = 64 kbps Time to send: 640 kbits/64 kbps + 0.5s = 10.5s Introduction 1-31