CPSC 463 Networks and

DistributedProcessing

Mr. Willis F. Martihttp://www.cs.tamu.edu/faculty/willis

Class Admin

• Syllabus & Schedule

• Opinions and Facts

• Test taking

• Attendance & Job Searches

• Sympathy

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

• 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...

Is this a Distributed System?

Computing(CPU)

MassStorage

UserInterface

Just insert a network?

Distributed System (!)

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."

Another Definition

• LAN vs WAN vs MAN vs CAN ...

Geography

Another Definition, cont.

• LAN - Local Area Network

• WAN - Wide Area Network

• MAN - Metropolitan Area Network

• CAN - A metal container

LAN vs MAN vs WAN

• Historical Def’n {geography}

• “Advance of Technology”

• Modern DefinitionsTotal Travel Time

Data Transmission Time

Total Travel Time

Data Transmission Time

<= .01 to .05

LAN:

LAN -- Key Points

• Historically, LANs meant fast speed.– Fast speeds meant short(er) distances.– Therefore LANs became defined by local

{short} distances

• the REAL key points– Travel time about 1 to 5% of total time– LANs ‘tend’ to use broadcast protocols;

WANs ‘tend’ to be point-to-point

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

An Evolution of Layering

Application

Application

Physical

Application

Transport

Session

Presentation

Data/Link

Network

Physical

Application

Transport

Data/Link

Network

Physical

Application

Transport

Data/Link

Physical

Application

Data/Link

Physical

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} CCITT {international PTT oriented} etc

Standards & Users {cost, flexibility}

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

IEEE 802

• .1 - Management– .1d - Bridge Spanning Tree

• .2 - Link Layer

• .3 - CSMA/CD [Ethernet]

• .4 - Token Bus

• .5 - Token Ring

• .11 – wireless Ethernet

(Partial) TCP/IP Stack

DIX Ethernet or ...

ARP

ICMPIP

TCP UDP

DNSTELNET

FTP

Why the OSI Reference Model?

• OSI model is not ISO protocol(s)

• Not tied to any specific protocol suite

• ‘Clean’ start

• Completeness

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}

The OSI Model

Application

Presentation

Session

Transport

Network

Data/Link

Physical 1

2

3

4

5

6

7{remember, enveloping at each layer}

OSI Model, cont

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

Physical Layer• Converts Bits -> Signals & sends signals across the media• Recovers Bits from incoming Signal

Key Aspects of Physical layer specifications:

• Signalling Method• Connectors• Media• Voltages/Power Levels

Media Considered -- Optical Fiber, Broadband Coax, baseband coax, UTP

Media not Considered -- Radio/Microwave/Satellite

Data/Link Layer

• Gets bits from A to B along a (logically) single physical link• Provides addressing and error detection.• OSI model talks about error recovery -- not usually implemented in LANs, and only in some point-to-point networks (X.25 best example)

• Why no error recovery? In the case of an error in the packet, where did itcome from and where was it really addressed to...

Network Layer

• End-to-end packets (each system on the network has a network address

BUT

each packet (is)(may be) treated separately

• This layer is supposed to hide all the messiness of differing link andphysical layer requirements from the upper layers

Transport Layer

• End-to-end messages

Usually provides reliable, sequenced byte stream to upper layers.Does error recovery.

• There are options for non-guaranteed transport

Session Layer

• Control layer

• Manages 'sessions'

Presentation Layer

• Provides information transform services

-> translation->encryption->compression

Application Layer

TCP/IP ISO

email SMTP X.400

file transfer FTP FTAM

remote terminal/access TELNET VTS

NOT all the applications in the world, but code to provide network services,And network specific apps.

Terminology

• Connection Oriented

• Connectionless

• Datagram

• Primitives