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Chapter 1: Introduction

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1 Chapter 1: Introduction
Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay protocol layers, service models network modeling Introduction

2 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

3 What’s the Internet: “nuts and bolts” view
PC server wireless laptop cellular handheld millions of connected computing devices: hosts = end systems running network apps Home network Institutional network Mobile network Global ISP Regional ISP communication links fiber, copper, radio, satellite transmission rate = bandwidth wired links access points routers: forward packets (chunks of data) router Introduction

4 “Cool” internet appliances
Internet gaming, chatting Web-enabled toaster + weather forecaster Radio Frequency Identification (RFID) Internet phones Introduction

5 What’s the Internet: “nuts and bolts” view
protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Ethernet Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Home network Institutional network Mobile network Global ISP Regional ISP Introduction

6 What’s the Internet: a service view
communication infrastructure enables distributed applications: Web, VoIP, , games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery Provide a comment playground for everyone Introduction

7 What’s a protocol? human protocols: “what’s the time?”
“I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction

8 What’s a protocol? a human protocol and a computer network protocol:
Hi TCP connection request Hi TCP connection response Got the time? Get 2:00 <file> time Introduction

9 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

10 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

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

12 Network edge: connection-oriented service (TCP)
Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service TCP service [RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested Introduction

13 Network edge: connectionless service (UDP)
Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: connectionless unreliable data transfer no flow control no congestion control No need to setup App’s using TCP: HTTP (Web), FTP (file transfer), Telnet/ssh (remote login), SMTP ( ) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony Introduction

14 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

15 Residential access: point to point access
Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” DSL: digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) Why asymmetric ? Why not 0 bps for upstream? FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone Introduction

16 Residential access: cable modems
HFC: hybrid fiber coaxial cable asymmetric: up to 30Mbps downstream, 2 Mbps upstream deployment: available via cable TV companies homes in neighborhood share access to router Cable modem compared to DSL: Pro: Higher bandwidth (30 vs. 8; 2 vs. 1) Con: Shared medium with neighbors Introduction

17 Residential access: cable modems
Diagram: Introduction

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

19 Cable Network Architecture: Overview
server(s) cable headend home cable distribution network Introduction

20 Cable Network Architecture: Overview
cable headend home cable distribution network (simplified) Introduction

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

22 Company access: local area networks
company/univ local area network (LAN) connects end system to edge router Ethernet: 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet modern configuration: end systems connect into Ethernet switch LANs: chapter 5 Introduction

23 Wireless access networks
shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access provided by telco operator WAP in Europe, i-mode in Japan 3G ~ 384 kbps -- Will it happen?? next up (?): WiMAX (31mile, 70Mbps) over wide area mesh network? router base station mobile hosts Introduction

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

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

26 Physical Media: coax, fiber
Fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: 10’s-100’s Gps low error rate: immune to electromagnetic noise Why lights not go out? Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFC Introduction

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

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