1-1 Internet Overview: roadmap 1.5 Protocol layers, service models 1.6 Internet for Wireless 1.7...
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Transcript of 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
1-9Lecture 3Image courtesy: Google
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
1-15Lecture 3Image courtesy: Google
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
1-16Lecture 3Image courtesy: Google
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
1-18Lecture 3Image courtesy: Google
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
1-19Lecture 3Image courtesy: Google
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
1-20Lecture 3Image courtesy: Google
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
1-21Lecture 3Image courtesy: Google
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
1-23Lecture 3Image courtesy: Google
Wireless Sensor Networks
• Particularly useful for sensing and Event detection
• Battlefield surveillance• Security surveillance
• Sensor Nodes• Low power, Small size
1-24Lecture 3Image courtesy: Google
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
1-25Lecture 3Image courtesy: Google
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