1. 1-1 Internet Overview: roadmap 1.5 Protocol layers, service models 1.6 Internet for Wireless 1.7 Internet under attack: security overview Lecture 3

2. 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…

3. 1-3 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers 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

4. 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

5. 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!)

6. 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

7. 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) 1-7 Lecture 3

8. 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 1-8 Lecture 3 Image courtesy: Google

9. 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 1-9 Lecture 3 Image courtesy: Google

10.  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 1-10 Lecture 3

11. 1-11 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch A complete view: Messages, Segments, Datagrams and Frames message M HtHt M HnHn frame Encapsulation Lecture 3 message

12. How about wireless connection?

13. 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 1-13 Lecture 3

14. Wireless Technology is everywhere  Driven by technology and vision  Wireless technologies  Device miniaturization  Mobile computing platforms Image courtesy: Google 1-14 Lecture 3

15. Today, Variety of Wireless-Capable Devices 1-15 Lecture 3 Image courtesy: Google

16. IEEE Wireless Standards IEEE 802.15 Bluetooth WAN MAN LAN PAN IEEE 802.11 Wi-Fi IEEE 802.16d WiMAX IEEE 802.20 IEEE 802.16e RAN IEEE 802.22 1-16 Lecture 3 Image courtesy: Google

17. 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 1-17 Lecture 3

18. 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 1-18 Lecture 3 Image courtesy: Google

19. WiMAX: worldwide interoperability of microwave access802.16-2004 Rural Urban DSL/T1 Replacement 802.16-2004 WiFi WiFi Rural Broadband 802.16-2004 WiFi WiFi WiFi WiFi WiFi 802.16e 1-19 Lecture 3 Image courtesy: Google

20. 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 1-20 Lecture 3 Image courtesy: Google

21. 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 1-21 Lecture 3 Image courtesy: Google

22. 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 1-22 Lecture 3

23. Ad-Hoc/Mesh Networks  Wireless Ad hoc networks 1.Mobile ad hoc networks 2.Wireless mesh networks 3.Wireless sensor networks Mobile ad hoc network Wireless mesh network 1-23 Lecture 3 Image courtesy: Google

24. Wireless Sensor Networks Particularly useful for sensing and Event detection Battlefield surveillance Security surveillance Sensor Nodes Low power, Small size 1-24 Lecture 3 Image courtesy: Google

25. 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 1-25 Lecture 3 Image courtesy: Google

26. Despite its popularity, Wireless has many Technical Challenges 1-26 Lecture 3

27. 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 1-27 Lecture 3

28.  Hidden terminal problem Challenge 2: “Open” Wireless Medium S1R1 S2 1-28 Lecture 3

29. 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 1-29 Lecture 3

30. 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 1-30 Lecture 3

31. 1-31 Internet Overview: roadmap 1.7 Internet under attack: security Lecture 3

32. 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

33. 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

34. 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 1-34 Lecture 3

35. 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

36. 1-36 Packet Sniffing Packet 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

37. The bad guys can use false source addresses  IP spoofing: send packet with false source address A B C src:B dest:A payload 1-37 Lecture 3  This was just an overview of challenges…

38. Summary We 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 1-38 Lecture 3