EECS 228a Lecture 1 Overview: Networks Jean Walrand - PowerPoint PPT Presentation

EECS 228a – Lecture 1 Overview: Networks Jean Walrand www.eecs.berkeley.edu/~wlr Fall 2002

Course Information Instructor: Jean Walrand n Office Hours: M-Tu 1:00 - 2:00 Time/Place: MW 2:00-3:30 in 285 Cory Home Page: n http://www- inst.eecs.berkeley.edu/~ee228a EECS228a - Walrand 2

Topics Overview [1 week] Economics of Networks [4] Routing [4] Congestion Control [2.5] Traffic Models [2.5] Review [1] Theoretical background State of the art EECS228a - Walrand 3

Details Grading: n In class presentations: 50% n Project: 50% - Original research on selected topic Material: n Lecture Slides and Notes n Research Papers EECS228a - Walrand 4

Overview Network Examples Network Components Internetworking Internet Other Networks Packets Transport Web Browsing Telephone Call Resource Sharing – Multiplexing Protocols IETF EECS228a - Walrand 5

Network Examples Teleglobe Communications Corporation – Fiber + Satellite EECS228a - Walrand 6

Network Examples Global Crossing Corporation EECS228a - Walrand 7

Network Examples KPNQWEST EECS228a - Walrand 8

Network Examples Williams Communications EECS228a - Walrand 9

Network Examples Palo Alto Network EECS228a - Walrand 10

Network Components Link : carry bits from one place to another (or maybe to many other places) Switch/router : move bits between links, forming internetwork Host : communication endpoint (workstation, PDA, cell phone, toaster, tank) EECS228a - Walrand 11

Network Components Coaxial Cable Links Fibers Cat5 Unshielded Twisted Pairs Wireless EECS228a - Walrand 12

Network Components Ethernet Network Interface Card EECS228a - Walrand 13

Network Components Ethernet EECS228a - Walrand 14

Network Components Link: Ethernet Ethernet is a broadcast-capable, multi- access LAN EECS228a - Walrand 15

Network Components Telephone Switch Large Router EECS228a - Walrand 16

Network with Routers LANs interconnected by routers LAN2 LAN1 R1 R2 Internet R4 LAN3 R3 EECS228a - Walrand 17

Internetworking Provides message delivery between multiple networks: ISP 2 ISP 1 Subnet 2 Subnet 1 Example: Subnet 1 = network of LANs of previous slide ISP 1 = Sprint, ISP 2 = MCI Subnet 2 = UCB network EECS228a - Walrand 18

The Internet A global network of networks all using a common protocol (IP, the Internet Protocol) Focus of this class A challenge to understand: n large scale (10’s of millions of users, 10’s of thousands of networks) n heterogeneity, irregular topology, decentralized management EECS228a - Walrand 19

Scale of Internet • Data from www.nw.com EECS228a - Walrand 20

Other Networks The Telephone Network Processor Interconnection Networks ATM Networks Cable-TV Networks EECS228a - Walrand 21

Packets B A | B | ... 1 A | B | ... 2 A | B | ... 3 A B → port 2 EECS228a - Walrand 22

Packets: Main Ideas The switches have no memory of packets: scalability The network is independent of the applications: flexibility The packet formats and addresses are independent of the technology: extensibility EECS228a - Walrand 23

Transport Packets ACKs EECS228a - Walrand 24

Web Browsing Example Locating Resource: DNS Connection End-to-end Packets Bits Points to remember EECS228a - Walrand 25

Web: Example 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 EECS228a - Walrand 26

Web: Locating Resource 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 com www.google.com? IP = a.b.c.d www.google.com? host local EECS228a - Walrand 27 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 cnn.com Host connect OK get page page; close EECS228a - Walrand 28

Web: End-to-end www.google.com The byte stream flows from end to end across End-to-end pacing and many links and switches: flow control routing (+ addressing) That stream is regulated host and controlled by both ends: retransmission of erroneous or missing bytes; flow control Routing EECS228a - Walrand 29

Web: Packets www.google.com The network transports IP address: A bytes grouped into Host A | B | # , CKS | bytes packets IP address: B The packets are “self- contained” and routers handle them one by one The end hosts worry about errors and flow control: Destination C n Destination checks B C packet for errors (using error detection Next Hop code CKS) and sends ACKs with sequence number # n Source retransmits EECS228a - Walrand 30 k t th t t

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 01011...011...110 01011...011...110 Transmitter Physical Medium Receiver Optical Copper Wireless EECS228a - Walrand 31

Web: Points to remember Separation of tasks n send bits on a link: transmitter/receiver [clock, modulation,…] n send packet on each hop [framing, error detection,…] n send packet end to end [addressing, routing] n pace transmissions [detect congestion] n retransmit erroneous or missing packets [acks, timeout] n find destination address from name [DNS] Scalability n routers don’t know about connections n names and addresses are hierarchical EECS228a - Walrand 32

Telephone Call Telephone Network Dialing a Number Setting up a Circuit Phone Conversation Releasing the Circuit EECS228a - Walrand 33

Telephone Network 5ESS (Lucent) DMS100 (Nortel) EECS228a - Walrand 34

Telephone Network EECS228a - Walrand 35

Telephone Network Logic Diagram: EECS228a - Walrand 36

Dialing a Number S1 B A A Off-Hook S1 Listens A dials S1 Registers EECS228a - Walrand 37

Setting Up a Circuit 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. EECS228a - Walrand 38

Phone Conversation B A Voice signals use the reserved circuits EECS228a - Walrand 39

Release Circuits B A A or B goes Off-Hook Circuits get released EECS228a - Walrand 40

Resource Sharing - Multiplexing Networks are shared resources Sharing via multiplexing Fundamental Question: how to achieve controlled sharing EECS228a - Walrand 41

Multiplexing Methods for sharing a communication channel Tradeoff between utilization and predictability Common Approaches: n TDM (time-division multiplexing) n Statistical Multiplexing EECS228a - Walrand 42

Time Division Multiplexing (also called STDM --Synchronous Time Division Multiplexing) n links Multiplexer rate r bps 1 link, rate nr bps each Frame: Time “slots” are reserved bps = bits per second EECS228a - Walrand 43

Statistical Multiplexing n links Multiplexer any rate 1 link, any rate Trace Excerpt: Variable-sized “packets” of data are interleaved based on the statistics of the senders EECS228a - Walrand 44

Analysis of STDM/FDM 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 EECS228a - Walrand 45

Analysis of Statistical Mux’ing 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 packets are limited in size n prevents domination of single sender Resources are not guaranteed EECS228a - Walrand 46

Protocols Agreement dictating the form and function of data exchanged between two (or more) parties to effect a communication Two parts: syntax and semantics n syntax: where bits go n semantics: what they mean and what to do with them EECS228a - Walrand 47

Protocol Example Internet Protocol (IP) n if you can generate and understand IP, you can be on the Internet n media, OS, data rate independent TCP and HTTP n if you can do these, you are on the web EECS228a - Walrand 48

Protocol Standards 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 EECS228a - Walrand 49

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 EECS228a - Walrand 50