UCB Lecture 2 TOC Applications Design Web Browsing Telephone Call Multiplexing Protocols IETF EECS122 Lecture 2 Department of Electrical Engineering and Computer Sciences University of California Berkeley EECS 122 UCB Web Example Applications Web Browsing Example Locating Resource DNS Connection End to end Packets Bits Points to remember Click Link or URL get content from local or remote computer URL http www google com string Specifies Protocol http Computer www google com String Computer server selects contents based on string EECS 122 UCB 3 Web Locating Resource EECS 122 UCB 4 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 www google com is the name of a computer Network uses IP addresses To find the IP address the application uses a hierarchical directory service called the Domain Name System cnn com Host com www google com 2 connect IP a b c d OK www google com get page host local page close EECS 122 UCB EECS 122 IP a b c d 5 EECS 122 UCB 6 UCB Lecture 2 Web End to end Web Packets www google com 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 flow control www google com End to end pacing and flow control host Routing EECS 122 UCB 7 Web Bits IP address A The network transports Host bytes grouped into packets A B CKS bytes IP address B The packets are selfcontained and routers handle them one by one The end hosts worry about errors and flow control n Destination checks Destination packet for errors using C error detection code CKS and sends ACKs B C with sequence number n Source retransmits Next Hop packets that were not ACKed and adjusts rate of transmissions EECS 122 UCB Web Points to remember Separation of tasks Equipment in each node sends the packets as a string of bits That equipment is not aware of the meaning of the bits n n n n 01011 011 110 01011 011 110 n n Transmitter Physical Medium EECS 122 UCB n n 9 Applications Telephone routers don t know about connections names and addresses are hierarchical EECS 122 UCB 10 Telephone Telephone Network Telephone Network Dialing a Number Setting up a Circuit Phone Conversation Releasing the Circuit EECS 122 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 Receiver Optical Copper Wireless EECS 122 UCB 8 Switches Network Logic Diagram 11 EECS 122 UCB 12 UCB Lecture 2 Telephone Network Network Telephone Network Switches 5ESS Lucent DMS100 Nortel EECS 122 UCB 13 EECS 122 UCB 14 Telephone Dialing a Number Telephone Network Logic Diagram S1 B A A Off Hook S1 Listens A dials S1 Registers EECS 122 UCB 15 Telephone Setting Up a Circuit EECS 122 UCB Telephone Phone Conversation ring B A Circuit capacity to carry one phone call shown by thin lines Circuit is allocated to the call between A and B Circuits are not shared they are dedicated EECS 122 UCB 17 EECS 122 16 B A Voice signals use the reserved circuits EECS 122 UCB 18 UCB Lecture 2 Design Multiplexing Telephone Release Circuits B A Overview Operations TDM FDM Statistical Multiplexing Analysis of TDM FDM Analysis of Statistical Multiplexing A or B goes Off Hook Circuits get released EECS 122 UCB 19 Multiplexing Overview EECS 122 UCB Multiplexing Operations Networks are shared resources Sharing via multiplexing Fundamental Question how to achieve controlled sharing Methods for sharing a communication channel Tradeoff between utilization and predictability Common Approaches n n EECS 122 UCB 21 MPX Time Division Multiplexing n links rate r bps each Multiplexer EECS 122 UCB 1 link rate nr bps n links any rate 22 Multiplexer 1 link any rate Trace Excerpt Variable sized packets of data are interleaved based on the statistics of the senders Time slots are reserved bps bits per second EECS 122 TDM time division multiplexing Statistical Multiplexing MPX Statistical Multiplexing Frame EECS 122 UCB 20 23 EECS 122 UCB 24 UCB Lecture 2 MPX Analysis of TDM FDM MPX Analysis of SM TDM FDM frequency division multiplexing and WDM wavelength may under utilize channel with idle senders Applicable only to fixed numbers of flows Requires precise timer or oscillator and guard bands for FDM Resources are guaranteed EECS 122 UCB Traffic is sent on demand so channel is fully utilized if there is traffic to send Any number of flows Need to control sharing n n Resources are not guaranteed 25 Design Protocols EECS 122 UCB Agreement dictating the form and function of data exchanged between two or more parties to effect a communication Two parts syntax and semantics n n 27 Protocols Examples n if you can generate and understand IP you can be on the Internet media OS data rate independent TCP and HTTP n EECS 122 UCB EECS 122 syntax where bits go semantics what they mean and what to do with them EECS 122 UCB 28 Protocols Standards Internet Protocol IP n 26 Protocols Definition Definition Examples Standards EECS 122 UCB packets are limited in size prevents domination of single sender if you can do these you are on the web 29 New functions require new protocols Thus there are many e g IP TCP UDP HTTP RIP OSPF IS IS SMTP SNMP Telnet FTP DNS NNTP NTP BGP PIM DVMRP ARP NFS ICMP IGMP Specifications do not change frequently Organizations IETF IEEE ITU EECS 122 UCB 30 UCB Lecture 2 Design The IETF Specifies Internet related protocols Produces RFCs www rfc editor org Quotation from IETF T shirt We reject kings presidents and voting We believe in rough consensus and running code David Clark EECS 122 UCB EECS 122 31
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