Introduction Chapter 1: roadmap 1.1 What is the Internet? 1.2 - PDF document

Introduction

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge � end systems, access networks, links 1.3 Network core � circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-2

A closer look at network structure: � network edge: applications and hosts � access networks, physical media: wired, wireless communication links � network core: � interconnected routers � network of networks Introduction 1-3

The network edge: � end systems (hosts): � run application programs � e.g. Web, email peer-peer � at “edge of network” � client/server model � client host requests, receives service from always-on server client/server � e.g. Web browser/server; email client/server � peer-peer model: � minimal (or no) use of dedicated servers � e.g. Skype, BitTorrent Introduction 1-4

Access networks and physical media Q: How to connect end systems to edge router? � residential access nets � institutional access networks (school, company) ‏ � mobile access networks Keep in mind: � bandwidth (bits per second) of access network? � shared or dedicated? Introduction 1-5

Dial-up Modem central office telephone network Internet home ISP home dial-up modem PC modem (e.g., AOL) ‏ � Uses existing telephony infrastructure � Home is connected to central office � up to 56Kbps direct access to router (often less) ‏ � Can’t surf and phone at same time: not “always on”

Digital Subscriber Line (DSL) ‏ Existing phone line: Internet 0-4KHz phone; 4-50KHz home upstream data; 50KHz-1MHz phone downstream data DSLAM telephone network splitter DSL central modem office home PC � Also uses existing telephone infrastruture � up to 1 Mbps upstream (today typically < 256 kbps) ‏ � up to 8 Mbps downstream (today typically < 1 Mbps) ‏ � dedicated physical line to telephone central office

Residential access: cable modems � Does not use telephone infrastructure � Instead uses cable TV infrastructure � HFC: hybrid fiber coax � asymmetric: up to 30Mbps downstream, 2 Mbps upstream � network of cable and fiber attaches homes to ISP router � homes share access to router � unlike DSL, which has dedicated access Introduction 1-8

Residential access: cable modems Introduction Diagram: http://www.cabledatacomnews.com/cmic/diagram.html 1-9

Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) ‏ Introduction 1-10

Cable Network Architecture: Overview server(s) ‏ cable headend home cable distribution network Introduction 1-11

Cable Network Architecture: Overview cable headend home cable distribution network (simplified) ‏ Introduction 1-12

Cable Network Architecture: Overview FDM (more shortly): C O N V V V V V V D D T I I I I I I A A R D D D D D D T T O E E E E E E A A L O O O O O O 5 6 7 8 9 1 2 3 4 Channels cable headend home cable distribution network Introduction 1-13

Fiber to the Home ONT optical Internet fibers ONT optical fiber OLT optical splitter central office ONT � Optical links from central office to the home � Two competing optical technologies: � Passive Optical network (PON) � Active Optical Network (PAN) ‏ � Much higher Internet rates; fiber also carries television and phone services

Ethernet Internet access 100 Mbps Institutional router To Institution’s Ethernet ISP switch 100 Mbps 1 Gbps 100 Mbps server � Typically used in companies, universities, etc � 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet � Today, end systems typically connect into Ethernet switch

Wireless access networks � shared wireless access network connects end system to router router � via base station aka “access point” base � wireless LANs: station � 802.11b/g (WiFi): 11 or 54 Mbps � wider-area wireless access � provided by telco operator � ~1Mbps over cellular system mobile (EVDO, HSDPA) ‏ hosts � next up (?): WiMAX (10’s Mbps) over wide area Introduction 1-16

Home networks Typical home network components: � DSL or cable modem � router/firewall/NAT � Ethernet � wireless access point wireless laptops to/from cable router/ cable modem firewall headend wireless access Ethernet point Introduction 1-17

S ummary: Network edge � End systems � various kinds of networks � hosts are clients, servers, peers � distributed applications involve both client and server processes � Access networks � connection from an end system to an IS P's "edge router" � most depend on PS TN infrastructure • Dial-up, DS L (ADS L!), T1/ T3 lines Introduction

S ummary: End/ edge connections � some access-network technology is also part of the end system � Ethernet varieties connect LANs to institutional (and home!) routers � Ethernet protocols increasingly applied beyond the end systems � WiFi • wireless access points (WAPs) often combined w/ routers to form "wireless routers" � WiMAX – long-distance form of wireless network, intended for use in access networks Introduction

Physical Media Twisted Pair (TP) ‏ � Bit: propagates between � two insulated copper transmitter/rcvr pairs wires � physical link: what lies � Category 3: traditional between transmitter & phone wires, 10 Mbps receiver Ethernet � Category 5: � guided media: 100Mbps Ethernet � signals propagate in solid media: copper, fiber, coax � unguided media: � signals propagate freely, e.g., radio Introduction 1-20

Physical Media: coax, fiber Fiber optic cable: Coaxial cable: � glass fiber carrying light � two concentric copper pulses, each pulse a bit conductors � high-speed operation: � bidirectional � baseband: � high-speed point-to-point transmission (e.g., 10’s- � single channel on cable 100’s Gps) ‏ � legacy Ethernet � low error rate: repeaters � broadband: spaced far apart ; immune � multiple channels on to electromagnetic noise cable � HFC Introduction 1-21

Physical media: radio Radio link types: � signal carried in electromagnetic � terrestrial microwave spectrum � e.g. up to 45 Mbps channels � no physical “wire” � LAN (e.g., Wifi) ‏ � bidirectional � 11Mbps, 54 Mbps � wide-area (e.g., cellular) ‏ � propagation environment effects: � 3G cellular: ~ 1 Mbps � satellite � reflection � obstruction by objects � Kbps to 45Mbps channel (or multiple smaller channels) ‏ � interference � 270 msec end-end delay � geosynchronous versus low altitude Introduction 1-22

S ummary: Physical media � Coaxial cable – "coax" � thinnet, thicknet � carry (digital) data encoded as analog signals � Twisted-pair � digital signals (telephone wire: analog-only) � UTP Cat5, 5e, 6 are current standards; S TP less common � Fiber optics � multi-gigabit capacity – OC-192 gives 9.953 Gbps � long distances between repeaters � Terrestrial, satellite radio � environment, latency issues Introduction