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4th Edition: Chapter 1

Introduction
Introduction

Computer Networking: A Top Down Approach

The Powerpoint slides are from Kurose and Ross’s book’s website.

7th edition
April 2016

Introduction
Chapter 1: introduction
get “feel” and terminology
more depth, detail later in course
use Internet as example

what’s the Internet?
what’s a protocol?
network edge; hosts, access net, physical media
network core: packet/circuit switching, Internet structure
performance: loss, delay, throughput
protocol layers, service models

Introduction

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
1.7 history

Introduction
What’s the Internet: “nuts and bolts” view
billions of connected computing devices:
hosts = end systems
running network apps
communication links
fiber, copper, radio, satellite
transmission rate: bandwidth
packet switches: forward packets (chunks of data)
routers and switches

smartphone

mobile network
global ISP
regional ISP
institutional

Introduction

“Fun” Internet-connected devices

IP picture frame
http://www.ceiva.com/
Web-enabled toaster +
weather forecaster

Internet phones

refrigerator

Slingbox: watch,
control cable TV remotely

Tweet-a-watt:
monitor energy use

sensorized,

Introduction
applications
Internet: “network of networks”
Interconnected ISPs
protocols control sending, receiving of messages
e.g., TCP, IP, HTTP, Skype, 802.11
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task Force
What’s the Internet: “nuts and bolts” view

mobile network
global ISP
regional ISP
institutional

What’s the Internet: a service view
infrastructure that provides services to applications:
Web, VoIP, email, games, e-commerce, social nets, …
provides programming interface to apps
hooks that allow sending and receiving app programs to “connect” to Internet
provides service options, analogous to postal service

Introduction

mobile network
global ISP
regional ISP
institutional

Introduction

What’s a protocol?
human protocols:
“what’s the time?”

human protocols:
… specific messages sent
… specific actions taken when messages received, or other events

Introduction

What’s a protocol?
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

TCP connection

Get http://www.awl.com/kurose-ross

TCP connection

Introduction

Introduction
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
global ISP
regional ISP
institutional

Introduction
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 (data rate) of access network?
bps (bits per second), Kbps, Mbps, Gbps
shared or dedicated?

Introduction

Access network: digital subscriber line (DSL)

central office

voice, data transmitted
at different frequencies over
dedicated line to central office

use existing telephone line to central office DSLAM
data over DSL phone line goes to Internet
voice over DSL phone line goes to telephone net
DSL has dedicated access to central office
< 2.5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstream transmission rate (typically < 10 Mbps) DSL access multiplexer Introduction data, TV transmitted at different frequencies over shared cable distribution network cable headend cable modem termination system HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router homes share access network to cable headend Access network: cable network Introduction Access network: cable network cable headend frequency division multiplexing: different channels transmitted in different frequency bands Introduction Access network: home network to/from headend or central office cable or DSL modem router, firewall, NAT wired Ethernet (1 Gbps) wireless access point (54 Mbps) often combined in single box Introduction Enterprise access networks (Ethernet) typically used in companies, universities, etc. 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet) Introduction Wireless access networks shared wireless access network connects end system to router via base station aka “access point” wireless LANs: within short range (100’s meters) 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, 5G to Internet to Internet Introduction Physical media signal: propagates between transmitter/receiver 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 twisted pair (TP) two insulated copper wires Category 5: 100 Mbps, 1 Gbps Ethernet Category 6: 10Gbps Introduction Physical media: coax, fiber coaxial cable: two concentric copper conductors bidirectional broadband: multiple channels on cable fiber optic cable: glass fiber carrying light pulses high-speed operation: high-speed point-to-point transmission (e.g., 10’s-100’s Gbps transmission rate) low error rate: repeaters spaced far apart immune to electromagnetic noise Introduction Physical media: radio 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) WiFi 6: 1.2Gbps wide-area (e.g., cellular) 4G: ~ 10 Mbps 5G: ~1Gbps Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude 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 bandwidth, aka link capacity R: link transmission rate two packets, L bits each transmission time needed to transmit L-bit packet into link R (bits/sec) Introduction Introduction 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 1.7 history Introduction mesh of interconnected routers packet-switching: hosts break application-layer messages into packets forward packets from one router to the next, across links on path from source to destination each packet transmitted at full link capacity The network core Introduction Packet-switching: store-and-forward takes L/R seconds 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 one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec more on delay shortly … destination per packet end-end delay = 2L/R (assuming zero propagation delay) Introduction Packet Switching: queueing delay, loss R = 100 Mb/s R = 1.5 Mb/s queue of packets waiting for output link queuing and loss: if arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up Two key network-core functions forwarding: move packets from router’s input to appropriate router output Introduction routing: determines source-destination route taken by packets routing algorithms routing algorithm local forwarding table header value output link destination address in arriving packet’s header Introduction Alternative core: circuit switching end-end resources allocated to, reserved for “call” between source & dest: in diagram, each link has four circuits. call gets 2nd circuit in top link and 1st circuit in right link. dedicated resources: no sharing circuit-like (guaranteed) performance circuit segment idle if not used by call (no sharing) commonly used in traditional telephone networks Introduction Circuit switching: FDM versus TDM Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136 Introduction Packet switching versus circuit switching 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: packet switching: with 35 users, probability > 10 active at same time is less than .0004

packet switching allows more users to use network!

1 Mbps link

Q: how did we get value 0.0004?
Q: what happens if > 35 users ?

Introduction
great for bursty data
resource sharing
simpler, no call setup
excessive congestion possible: packet delay and loss
protocols needed for reliable data transfer, congestion control
Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps
still an unsolved problem
is packet switching a “slam dunk winner?”

Packet switching versus circuit switching