EECS122 Spring 2001 Communication Networks Prof Jean Walrand Department of EECS University of California Berkeley Course Objectives Contents Explain Internet and related networks Compare solutions identify trends Technology Links ADSL Cable Modem Optical LANs Ethernet Routers Switches Protocols Routing Transport Applications Organization Three Lectures 1 Discussion every week Grading HW 20 2 Midterms 30 1 Final 30 Projects 20 Instructors Prof Jean Walrand TAs Today Introduction to networks Friday Office hours email addresses TAs Web site See Prof Walrand s home page Introduction Web Voice over IP Web Example Locating Resource DNS Connection End to end Packets Bits Points to remember Web Example Click get page page from local or remote computer link http cnn com specifies protocol http location cnn com Web Example Click get page page from local or remote computer link http cnn com specifies protocol http location cnn com Web Example Click get page page from local or remote computer link http cnn com specifies protocol http location cnn com Web Locating Resource cnn com is the name of a computer and implicitly of a file in that computer To find the address the application uses a hierarchical directory service called the Domain Name System com c n n c o m c n n c o m host lo c a l IP a b c d IP a b c d Web Connection The protocol http sets up a connection between the host and cnn com to transfer the page The connection transfers the page as a byte stream without errors pacing error control H ost c n n c o m Web End to end The byte stream flows from end to end across many links and switches routing addressing That stream is regulated and controlled by both ends retransmission of erroneous or missing bytes pacing e n d to e n d p a c in g a n d e rro r c o n tro l r o u t in g HO ST C N N C O M Web Packets The network transports bytes grouped into packets The packets are selfcontained and routers handle them one by one The end hosts worry about errors and pacing Destination sends ACKs Source checks losses A B C R C b y te s C N N C O M A HO ST B C B to C Web Bits Equipment in each node sends the packets as a string of bits That equipment is not aware of the meaning of the bits 0 1 0 1 1 0 1 1 1 1 0 0 1 0 1 1 0 1 1 1 1 0 T r a n s m it t e r P h y s ic a l M e d iu m O p tic a l C opper W ir e le s s R e c e iv e r Web Points to remember Separation of tasks send bits on a link transmitter receiver clock modulation send packet on each hop framing error detection send packet end to end addressing routing pace transmissions detect congestion retransmit erroneous or missing packets acks timeout find destination address from name DNS Scalability routers don t know about connections names and addresses are hierarchical Voice Over IP VoIP General Operations VoIP General Operations Gateways must reproduce the signaling and voice Signaling dialed digits dial tone ringing Voice Packetize and absorb delay jitter Note Routing problem PSTN s ig n a lin g v o ic e s ig n a l In te rn e t PSTN
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