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

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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-

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EECS 228a – Lecture 1 Overview: Networks

Jean Walrand www.eecs.berkeley.edu/~wlr

Fall 2002

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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

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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

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Details

Grading:

n In class presentations: 50% n Project: 50% - Original research on

selected topic

Material:

n Lecture Slides and Notes n Research Papers

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Overview

Network Examples Network Components Internetworking Internet Other Networks Packets Transport Web Browsing Telephone Call Resource Sharing – Multiplexing Protocols IETF

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Network Examples

Teleglobe Communications Corporation – Fiber + Satellite

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Network Examples

Global Crossing Corporation

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Network Examples

KPNQWEST

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Network Examples

Williams Communications

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Network Examples

Palo Alto Network

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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)

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Network Components

Fibers Cat5 Unshielded Twisted Pairs Coaxial Cable

Links

Wireless

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Network Components

Ethernet Network Interface Card

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Network Components

Ethernet

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Network Components

Ethernet is a broadcast-capable, multi- access LAN

Link: Ethernet

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Network Components

Telephone Switch Large Router

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Network with Routers

LANs interconnected by routers

LAN1 LAN2 LAN3 Internet R1 R2 R3 R4

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Internetworking

Provides message delivery between multiple networks:

Subnet 1 Subnet 2 ISP 2 ISP 1

Example: Subnet 1 = network of LANs of previous slide ISP 1 = Sprint, ISP 2 = MCI Subnet 2 = UCB network

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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

  • f thousands of networks)

n heterogeneity, irregular topology,

decentralized management

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Scale of Internet

  • Data from www.nw.com
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Other Networks

The Telephone Network Processor Interconnection Networks ATM Networks Cable-TV Networks

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Packets

A B

A | B | ...

B → port 2 1 2 3

A | B | ... A | B | ...

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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

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Transport

Packets ACKs

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Web Browsing

Example Locating Resource: DNS Connection End-to-end Packets Bits Points to remember

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Click Link or URL get content from local

  • r remote computer

URL: http://www.google.com/string Specifies

  • Protocol: http
  • Computer: www.google.com
  • String

Computer (server) selects contents based on string

Web: Example

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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

local com host www.google.com? IP = a.b.c.d IP = a.b.c.d www.google.com?

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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

Host cnn.com connect OK get page page; close

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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; flow control

End-to-end pacing and flow control Routing www.google.com host

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Web: Packets

The network transports bytes grouped into packets The packets are “self- contained” and routers handle them one by one The end hosts worry about errors and flow control:

n Destination checks

packet for errors (using error detection code CKS) and sends ACKs with sequence number #

n Source retransmits

k t th t t

C

A | B | # , CKS | bytes

B C

www.google.com IP address: A Host IP address: B Destination Next Hop

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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 Transmitter Physical Medium Receiver 01011...011...110 Optical Copper Wireless

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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

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Telephone Call

Telephone Network Dialing a Number Setting up a Circuit Phone Conversation Releasing the Circuit

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Telephone Network

5ESS (Lucent) DMS100 (Nortel)

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Telephone Network

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Telephone Network

Logic Diagram:

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Dialing a Number

A Off-Hook S1 Listens A dials S1 Registers A B S1

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Setting Up a Circuit

A B ring 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.

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Phone Conversation

A B Voice signals use the reserved circuits

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Release Circuits

A B A or B goes Off-Hook Circuits get released

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Resource Sharing - Multiplexing

Networks are shared resources Sharing via multiplexing Fundamental Question: how to achieve controlled sharing

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Multiplexing

Methods for sharing a communication channel Tradeoff between utilization and predictability Common Approaches:

n TDM (time-division multiplexing) n Statistical Multiplexing

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Time Division Multiplexing

(also called STDM --Synchronous Time Division Multiplexing)

Multiplexer

n links rate r bps each 1 link, rate nr bps

Frame:

Time “slots” are reserved bps = bits per second

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Statistical Multiplexing

Multiplexer

n links any rate 1 link, any rate

Trace Excerpt:

Variable-sized “packets” of data are interleaved based on the statistics of the senders

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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

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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

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Protocols

Agreement dictating the form and function

  • f 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

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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

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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

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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