1. EECS122 - Spring 2001 Communication Networks Prof. Jean Walrand Department of EECS University of California Berkeley

2. Course Objectives & Contents zExplain Internet and related networks zCompare solutions, identify trends zTechnology: yLinks: ADSL, Cable Modem, Optical yLANs: Ethernet yRouters, Switches zProtocols: yRouting, Transport, Applications

3. Organization zThree Lectures + 1 Discussion every week zGrading: HW: 20%, 2 Midterms: 30%, 1 Final: 30%, Projects: 20% zInstructors: yProf. Jean Walrand yTAs: zToday: Introduction to networks zFriday: Office hours, email addresses, TAs zWeb site: See Prof. Walrand’s home page

4. Introduction zWeb zVoice over IP

5. Web zExample zLocating Resource: DNS zConnection zEnd-to-end zPackets zBits zPoints to remember

6. zClick -> get page zpage from local or remote computer zlink: http://cnn.com specifies - protocol (http) - location (cnn.com) Web: Example

7. zClick -> get page zpage from local or remote computer zlink: http://cnn.com specifies - protocol (http) - location (cnn.com)

8. Web: Example zClick -> get page zpage from local or remote computer zlink: http://cnn.com specifies - protocol (http) - location (cnn.com)

9. Web: Locating Resource zcnn.com is the name of a computer (and, implicitly, of a file in that computer) zTo find the address, the application uses a hierarchical directory service called the Domain Name System

10. Web: Connection zThe protocol (http) sets up a connection between the host and cnn.com to transfer the page zThe connection transfers the page as a byte stream, without errors: pacing + error control

11. Web: End-to-end zThe byte stream flows from end to end across many links and switches: routing (+ addressing) zThat stream is regulated and controlled by both ends: retransmission of erroneous or missing bytes; pacing

12. Web: Packets zThe network transports bytes grouped into packets zThe packets are “self- contained” and routers handle them one by one zThe end hosts worry about errors and pacing: Destination sends ACKs Source checks losses

13. Web: Bits zEquipment in each node sends the packets as a string of bits zThat equipment is not aware of the meaning of the bits

14. Web: Points to remember zSeparation of tasks ysend bits on a link: transmitter/receiver [clock, modulation,…] ysend packet on each hop [framing, error detection,…] ysend packet end to end [addressing, routing] ypace transmissions [detect congestion] yretransmit erroneous or missing packets [acks, timeout] yfind destination address from name [DNS] zScalability yrouters don’t know about connections ynames and addresses are hierarchical

15. Voice Over IP: VoIP zGeneral Operations

16. VoIP: General Operations zGateways must reproduce the signaling and voice zSignaling: dialed digits, dial tone, ringing zVoice: Packetize and absorb delay jitter zNote: Routing problem