CPSC 463 Networks and Distributed

Processing

Willis F. Marti

Intermission

Marketing Department

2 Drink Minimum!

Course Overview

Syllabus/policy {handout}

Schedule {Web}

Comments on Term Project

Course Objectives

Book Comments

...

Opinions and Facts

Class Admin

• Test taking

• Attendance & Job Searches

• Sympathy

Project

Purpose

Task Network Design

Approach {customer/boss/professor}

Teams {preferred size is 4 or 5}

Course Objectives

• Science

• Engineering

• Attitude

• Understand what a network is, especially in the context of distributed systems

• Learn a good model for investigating networks

• Learn some network programming

• Identify (some) real world components

• How networks are built

• Understand there’s more than one correct solution

• Understand “the map is not the territory”.

Why Study Networks• When computers were rare, we studied all the new facets of computers:

operating systems, languages, ... As computers became common, we added the fields that have become computer engineering. Now that computers are ubiquitous, we add the study of how best for them to communicate: networking.

• A network is part of a distributed system. Part of computer science (and computer engineering) is learning how to build all the components.

• What is a network? Surprisingly, few people will give you a definition that always fits.

• How will we study networks? There are several methods...

Distributed SystemThis represents our definition of a distributed system, focusing on

delivery of services to end users. We will explore this more after we

understand more about networks.

Network

Servers (Storage, Compute)

Services

User InterfacesUsers

Users

Network Definition

"A network is a collection of media, devices and protocols used to facilitate the exchange of informationbetween computing devices in a manner relativelytransparent to the end user."

Contrast:The Telephone Company (TELCO) & networks.:{network as a collection of media without regard to applications}

Still Defining a Network

• An ordered collection

• of media, devices and protocols

• used to facilitate the exchange of information

• between computing devices

• in a manner relatively transparent

• to the end user."

Studying Networking

• by protocols & programs ...

• by technology ...

• by components ...

• Layered Models of a System!

“The key to understanding networks is the idea

of layered architectures.”

Layered Architectures-Principles-

Clearly Defined Interfaces Separation of Functions Peer to Peer Protocols Provide Services Up, Request Services Down

PHYSICAL

LINK

NETWORK

TRANSPORT

Message

PktsPackets

10010111001 {Bits}

{Signal}

10010111001 {Bits}

PktsPackets

MessageLayering

Packet Formats

Framing

Link Header

Data

Data

Data

Data

Data

Data

Data

Network Header

Transport Header

Session Header (?)

Presentation “Header”

Application “Header”

Stream

Packets

Protocols and Services

<some function>This:or

this...or

this...?

Protocols and Services-a better model

n+1

n-1

n

n-1

n

n+1

Which Architecture to Study?

• TCP/IP {Internet suite}

• SNA

• Novell

• IEEE

• OSI Reference Model

Network Models

Standards & Committees ANSI IEEE {most important for LANs} EIA ISO {does more than just data standards} ITU-T {international PTT oriented. Formerly CCITT} etc

Standards & Users {cost, flexibility}

Purpose of the Open Systems Interconnection Model{remember, it's just a model}

Using Models for Understanding

Models are created by extracting key features, functions and information from a specific domain of interest so that the model contains essential attributes for understanding. Road maps are models. We extract positions of towns and cities and the roads that connect them. We ignore most terrain or reduce it to color. Road maps are good for planning trips by car but relatively useless for determining where to drill for oil. A key part of building a good model is ensuring that all features of interest are included, but only those. When using a model (network or otherwise), remember the limitation: "The map is not the

territory."

IEEE 802 Protocols

• .1 - Management

– .1d - Bridge Spanning Tree

• .2 - Link Layer

• .3 - CSMA/CD [Ethernet]

• .4 - Token Bus

• .5 - Token Ring

• .6 - DQDB

• .7 - MAN

• .11 - Wireless

(Partial) TCP/IP Stack

DIX Ethernet or ...

ARP

ICMPIP

TCP UDP

DNSTELNET

FTP

Author’s TCP/IP Model

Transport

Network

Data/Link

Physical

Application

Why the OSI Reference Model?

• OSI RM is not the ISO protocol(s)

• Not tied to any specific protocol suite

• ‘Clean’ start

• Completeness

The OSI Reference ModelApplication

Presentation

Session

Transport

Network

Data/Link

Physical 1

2

3

4

5

6

7

Example: OSI & the InternetApplication

Presentation

Session

Transport

Network

Data/Link

Physical

NFS

XDR

RPC

UDP

IP

DIX Ethernet

IEEE 802.3

OSI Reference ModelApplication

Presentation

Session

Transport

Network

Data/Link

Physical

Application

Presentation

Session

Transport

Network

Data/Link

Physical

{Each layer communicates with its peer by using the services of thelayer just below, and provides services to the layer above. Only thephysical layer has an actual connection}

Connectors for OSI

Application

Presentation

Session

Transport

Network

Data/Link

Physical

Application

Presentation

Session

Transport

Network

Data/Link

Physical

{there can be multiple, separate entities at each layer}

Repeater

Bridge

Router

Gateway