CMPE 80N - Introduction to Networks and the Internet 1 CMPE 80N Winter 2004 Lecture 10 Introduction to Networks and the Internet

CMPE 80N - Introduction to Networks and the Internet 2 Announcements Quiz 2 on Monday, Quiz 1 statistics: –Maximum score: 70/70. –Minimum: 13/70. –Average: 50.8/70 (~70%). HTML tutorial: Friday, –In class. –By Debasree.

CMPE 80N - Introduction to Networks and the Internet 3 Announcements Studying for the quiz: –Office hours. –Discussion sessions. Always one before quiz. Next one is Friday, from 4:45-6pm in BE 354l. Newsgroup project: –Deadline for subscription to the newsgroup is this Friday, by midnight.

CMPE 80N - Introduction to Networks and the Internet 4 Wireless Networks Wireless LANs. Cellular networks. Ad hoc networks.

CMPE 80N - Introduction to Networks and the Internet 5 Cellular Architecture cell BS mobile

CMPE 80N - Introduction to Networks and the Internet 6 Frequency Reuse A B C D E F G G E F

CMPE 80N - Introduction to Networks and the Internet 7 MANETs Mobile, (wireless), multi-hop ad-hoc networks. Formed by wireless hosts which may be mobile. Without (necessarily) using a pre-existing infrastructure. Routes between nodes may potentially contain multiple hops. Mobility cause routes to change.

CMPE 80N - Introduction to Networks and the Internet 8 Multi-hop May need to traverse multiple hops to reach destination.

CMPE 80N - Introduction to Networks and the Internet 9 Why MANETs ? Ease of deployment. Speed of deployment. Decreased dependence on infrastructure.

CMPE 80N - Introduction to Networks and the Internet 10 Many Applications Personal area networking. –Cell phone, laptop, ear phone, wrist watch. Military environments. –Soldiers, tanks, planes. Civilian environments. –“Smart” environments. Emergency operations –Search-and-rescue –Policing and fire fighting –Monitoring and surveillance.

CMPE 80N - Introduction to Networks and the Internet 11 Data Link Layer PHYSICAL DATA LINK NETWORK TRANSPORT SESSION PRESENTATION APPLICATION

CMPE 80N - Introduction to Networks and the Internet 12 Data Link Layer Data link layer: responsible for error-free (reliable) communication between adjacent nodes. Functions: framing, error control, flow control, addressing, and medium access (in shared networks).

CMPE 80N - Introduction to Networks and the Internet 13 Framing Take data coming from the upper layers and add layer 2 control (header) information. –E.g., addressing, error control information. On the receiving end: –Take bit stream received from physical layer. –Recognize frames. Frames start and end with special characters (flags). Check if frames arrived correctly: error control. De-encapsulation.

CMPE 80N - Introduction to Networks and the Internet 14 Error Control Error-free hop-by-hop communication. Node 1 Node 2 Node 3 Hop 1 Hop 2

CMPE 80N - Introduction to Networks and the Internet 15 Error Recovery Error detection versus error correction. –Additional information to detect an error occurred versus additional information to be able to detect and correct the error.

CMPE 80N - Introduction to Networks and the Internet 16 Parity Example of error detection technique. Parity bit appended to data. –Even parity: append “1” if number of “1”’s is odd. –In odd parity… How many bits in error can the parity bit detect?