Exploring Computer Networks: Protocols, Layers, and Internet Architecture, Slides of Computer Networks

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Introduction

Why study computer networks?

 They are engineering marvels!

 Scalability, layered protocols, lots of

subtleties- worthy of study

 They are all around us!

 Understanding the nuts and bolts behind a

technology you use every day is exciting

 They are changing the world!

 Profound societal changes taking place in our

lifetime

Goals of this class

 Understand both basic computer

networking concepts and their instantiation

in the current Internet

 Question why the current Internet is the

way it is

 Appreciate good

 Understand limitations and consider solutions

 Gain practical skills (network analysis,

network programming)

Network Trace Analysis?

 Network Trace Analysis - what happens on

our local network when use a network

application?

Example: Web browsing

 Trace a common network operation like web browsing

 URL like http://www.google.com specifies

• protocol (http)
• location (www.google.com)

 What network traffic results?  Request page  Send page  What else? Lots….

DNS traffic

 www.google.com is the

name of a computer

(and, implicitly, of a

file in that computer)

 To find the address,

the application uses a

hierarchical directory

service called the

Domain Name System to translate human readable names to IP addresses

local

com

host

www.google..com?

www.google.com? (^) IP = a.b.c.d

IP = a.b.c.d

TCP Connection Establishment

 The protocol (http) sets up a connection (another

protocol, tcp) between the host and

www.google.com to transfer the page

 SYN, SYNACK, ACK

Host www.google.com

connect

OK get page page; close

HTTP request/response

 GET /foo.html HTTP/1.

 Server responds sending page

2: Application Layer 13

QUICK LOOK AHEAD: TCP vs UDP

TCP service:

 connection-oriented: setup

required between client, server

 reliable transport between

sending and receiving process

 flow control: sender won’t

overwhelm receiver

 congestion control: throttle

sender when nework overloaded

 does not providing: timing,

minimum bandwidth guarantees

UDP service:

 unreliable data transfer between sending and receiving process  does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee

IP Datagrams

 Datagrams labeled with where they are

going and where they are from – no

directions

 Source IP address

 Destination IP address

Path through the Internet

 Network trace analysis very useful but it gave us

very little hint that between our machine and the

remote machine there are many hops

Traceroute/tracert

How are paths established?

 Packets flows from end to end across many links

 Routers receive packet and try to forward one step closer to destination ( routing )

 The packets contain all information necessary to indicate destination (addressing) and are handled individually  Example: Caravan of cars on a road trip

 Packets may take different paths

C

HOST: B

GOOGLE. COM: A A | B | # , CRC | bytes

B: to C

Internet Topology?

 Traceroute gave us one slice through the Internet

 What does that tell us about the routes in the

entire Internet? The full Internet map?