1-1 internet overview: roadmap 1.5 protocol layers, service models 1.6 internet for wireless 1.7...

1-1

Internet Overview: roadmap

1.5 Protocol layers, service models1.6 Internet for Wireless1.7 Internet under attack: security overview

Lecture 3

1-2

Protocol “Layers”Networks are complex!

Millions of components: hosts routers Access networks

Question: How to organize such

complex structure?

Lecture 3

Millions of operations and conflicts among them:

1. What if multiple computers transmit at the same time?

2. What if packets get lost?3. How to retransmit packets?4. Retransmission: How many times?5. What about the other packets?6. How to find routes in the Internet?7. What if I am browsing web or I am

watching live broadcasting?8. How to distinguish among

computers (addressing)?

Just a few mentioned here…

1-3

ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departureairport

arrivalairport

intermediate air-trafficcontrol centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

An analogy: Organization of airline functionality

a series of steps Layers: each layer implements a service

via its own internal-layer actions relying on services provided by layer above/below

Another example: Postal Service!

Lecture 3

1-4

What are the adv. of layering?

Reduce the design complexity Ease of updating the system

change of implementation of layer’s service transparent to rest of system

e.g., Postal service (overnight flight or overnight ground)

Network is a huge complex system Why not take help of layering architecture?

Lecture 3

1-5

Internet protocol stack

application

transport

network

link

physical

Lecture 3

application support host/network applications Email, FTP, HTTP (HTML)

transport process-process data transfer TCP, UDP

network routing of datagrams from src. to destn. IP address, routing protocols

link data transfer between neighboring network

elements Ethernet, PPP

physical bits “on the wire” (Compare with the Postal

System!)

1-6

ISO/OSI reference model(Open Systems Interconnection model) presentation: allow applications

to interpret meaning of data, e.g., encryption, compression, machine-specific conventions

session: synchronization, checkpointing, recovery of data exchange

The 5-layer protocol stack is more famous

application

presentation

session

transport

network

link

physical

Lecture 3

Protocol Stack View

While hosts (computers) view it as 5-layer protocol stack, it is slightly different for routers/data forwarders… Data forwarders view it as 1-layer, 2-layer or 3-layer protocol

stack depending on the functionality!

Data forwarder classifications (based on complexity) Hub (simplest) Switch (medium complexity) Router (most complex)

1-7Lecture 3

Hubs Hubs: unsophisticated devices for connecting multiple

devices together, low cost Example: Ethernet Hub

Hubs work at the physical layer (1-layer protocol stack view only)

Any packet received in any port is broadcast out in all other ports

If multiple computers connected to a hub transmit packet at the same time, packets will collide with each other Hub detects this collisions and signal the computers to transmit

again

1-8Lecture 3Image courtesy: Google

Switch Switch: sophisticated devices for connecting multiple devices

together, medium cost Example: Ethernet Switch

Nearly identical to hubs but contain more intelligence Switches may work at multiple layers (typically 2 layer view) Switches have multiple buffers for incoming packets in

multiple ports Avoid packet collision


Router: most sophisticated device, expensive

Routers work at multiple layers (typically 3 layer view)

Routers have multiple network interfaces and are more intelligent than switches Decide routes for packets

based on destination IP addresses, network load, delay etc.

Router

1-10Lecture 3

1-11

source

application

transportnetwork

linkphysical

HtHn M

segment Ht

datagram

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

A complete view: Messages, Segments, Datagrams and Frames

message M

Ht M

Hn

frame

Encapsulation

Lecture 3

message

How about wireless connection?

Why Wireless?

Advantages Mobility (on the go)

Flexibility (any place, any time, temporary, permanent)

No problems with wiring (e.g. historical buildings, fire protection, esthetics), also cost reducing

Robust against disasters like earthquake, fire; in emergency situations

It has really been a wireless revolution decade…with more to come

Wireless is no longer a luxury but a necessity

1-13Lecture 3

Wireless Technology is everywhere

Driven by technology and visionWireless technologiesDevice miniaturizationMobile computing platforms

Image courtesy: Google1-14Lecture 3

Today, Variety of Wireless-Capable Devices


IEEE Wireless Standards

IEEE 802.15 Bluetooth

WAN

MAN

LAN

PAN

IEEE 802.11 Wi-Fi

IEEE 802.16d WiMAX

IEEE 802.20IEEE 802.16e

RANIEEE 802.22


Wireless LANs: WiFi/802.11 Based on the IEEE 802.11a/b/g/n family of standards

Designed to provide in-building or campus broadband coverage. IEEE 802.11b peak physical layer data rate of 11 Mbps IEEE 802.11a/g peak physical layer data rate of 54 Mbps and

indoor coverage over a distance of 100 feet.

Operates over a bandwidth of 20 MHz

Disadvantages WiFi users share “air” medium - inefficient for large numbers

of users Wi-Fi systems are not designed to support high-speed mobility

1-17Lecture 3

WPAN (Wireless Personal Area Network)

Cable replacement RF technology (low cost)

Short range {10m (1mW), 100m (100 mW)} Lower power than WiFi

Widely supported by telecommunications, PC, and consumer electronics companies. Hands free phone (ear set) for cars,

internet chat/VoIP Intra-car networking announced by

some car manufacturers in Europe

IEEE 802.15 includes seven task groups… Numbered from 1 – 7 with each of

them having own responsibility


WiMAX: worldwide interoperability of microwave access

802.16-2004

802.16-2004

Rural

Rural

Rural

UrbanDSL/T1 Replacement

802.16-2004802.16-2004

WiFiWiFi

WiFiWiFi

RuralBroadband

802.16-200

4802.1

6-2004

WiFiWiFi

WiFiWiFi

WiFiWiFi

WiFiWiFi

WiFiWiFi

802.16e

802.16e


WiMAX Fixed and Mobile WiMAX Fixed

802.16d or 802.16-2004 Usage: Backhaul, Wireless

DSL Devices: outdoor and indoor

installed CPE Frequencies: 2.5GHz, 3.5GHz

and 5.8GHz (Licensed and LE) Description: wireless

connections to homes, businesses, and other WiMAX or cellular network towers

WiMAX Mobile 802.16e Usage: Long-distance mobile

wireless broadband Devices: PC Cards, Notebooks

and future handsets Frequencies: 2.5GHz Description: Wireless

connections to laptops, PDAs and handsets when outside of Wi-Fi hotspot coverage


Wide Area: Satellite Systems

Cover very large areas Different orbit heights

Low Earth Orbit (LEO): ~1000 miles Mid Earth Orbit (MEO): ~6000 miles Geosynchronous Orbit (GEO): ~22,300 miles

Optimized for one-way transmission

location positioning, GPS systems, Satellite Radio

Most two-way systems struggling or bankrupt


Ad hoc Networks All the wireless networks mentioned so far are known as

infrastructure network Require initial setup Radios mostly follow master/slave concept Base stations act as master while user devices are controlled by

BS Infrastructure networks are not appropriate in

emergency situations like natural disasters or military conflicts or in areas where access is difficult

Ad hoc networks are particularly suitable in such scenarios Decentralized Peer-to-peer Does not depend on a central entity Minimal configuration and quick deployment

1-22Lecture 3

Ad-Hoc/Mesh Networks

Wireless Ad hoc networks1. Mobile ad hoc networks2. Wireless mesh networks3. Wireless sensor networks

Mobile ad hoc network

Wireless mesh network


Wireless Sensor Networks

• Particularly useful for sensing and Event detection

• Battlefield surveillance• Security surveillance

• Sensor Nodes• Low power, Small size


Wireless Sensor Network Classification

Infrastructure-less•No human intervention• Not replaceable• One time deployment• Finite energy available with sensor nodes

Infrastructured•In buildings• Secured places


Despite its popularity, Wireless has many

Technical Challenges

1-26Lecture 3

Challenge 1: Unreliable and Unpredictable Wireless Coverage

Wireless channel “feels” very different from a wired channel. Wireless links are not reliable: they may vary over time and space Noise adds on to the signal Signal strength falls off rapidly with distance Signal strength may weaken due to obstacles Medium “air” shared among many users

Results: Variable capacity Unreliable channel: errors, outages Variable delays

1-27Lecture 3

Hidden terminal problem

Challenge 2: “Open” Wireless Medium

S1 R1 S2

1-28Lecture 3

Challenge 3: Mobility

Mobility causes poor-quality wireless links

Mobility causes intermittent connection under intermittent connected networks,

traditional routing, TCP, applications all break

Mobility changes context, e.g., location

1-29Lecture 3

Challenge 4: Portability: Energy-Constrained Nodes

Limited battery power

Limited processing, display and storage

Transmission energy minimized to maximize life Introduces a delay versus energy tradeoff for each

bit

1-30Lecture 3

1-31

Internet Overview: roadmap

1.7 Internet under attack: security

Lecture 3

1-32

Network Security The field of network security is about:

how bad guys can attack computer networks

how we can defend networks against attacks

Internet not originally designed with (much) security in mind original vision: “a group of mutually trusting

users attached to a transparent network” Internet protocol designers playing “catch-

up”Lecture 3

1-33

Bad guys can put malware into hosts via Internet Malware

virus Worm trojan horse

Spyware malware can record keystrokes, web sites visited, upload info to collection site.

Infected host can be enrolled in a botnet, used for spam and DDoS attacks.

Malware is often self-replicating: from an infected host, seeks entry into other hosts

Lecture 3

Quick Malware Overview

Trojan horse Hidden part of some

otherwise useful software

Today often on a Web page (Active-X, plugin)

Virus infection by receiving

object (e.g., e-mail attachment), actively executing

self-replicating: propagate itself to other hosts, users

Worm: infection by passively

receiving object that gets itself executed

self- replicating: propagates to other hosts, users

1-34Lecture 3

Lecture 3 1-35

Bad guys can attack servers and network infrastructure

Denial of service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic

1. select target

2. break into hosts around the network (see botnet)

3. send packets toward target from compromised hosts

target

1-36

Packet SniffingPacket sniffing:

broadcast media (shared Ethernet, wireless) promiscuous network interface reads/records all packets

(e.g., including passwords!) passing by

A

B

C

src:B dest:A payload

Lecture 3

The bad guys can use false source addresses IP spoofing: send packet with false source

addressA

B

C

src:B dest:A payload

1-37Lecture 3

This was just an overview of challenges…

SummaryWe now covered Internet overview what’s a protocol? network edge, core,

access network packet-switching

versus circuit-switching

Internet structure performance: loss,

delay, throughput layering, service models Wireless Security

Next Up: Application layer

protocols

1-38Lecture 3

1-1 internet overview: roadmap 1.5 protocol layers, service models 1.6 internet for wireless 1.7...

Documents