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 System This 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 Interfaces Users

Network Definition "A network is a 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." 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- uClearly Defined Interfaces uSeparation of Functions uPeer to Peer Protocols uProvide Services Up, uRequest Services Down

PHYSICAL LINK NETWORK TRANSPORT Message Pkts Packets {Bits} {Signal} {Bits} Pkts Packets Message Layering

Packet Formats Framing Link Header Data Network Header Transport Header Session Header (?) Presentation “Header” Application “Header” Stream Packets

Protocols and Services This: or this... or this...?

Protocols and Services -a better model n+1 n-1 n 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 ICMP IP 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 Model

Example: OSI & the Internet Application Presentation Session Transport Network Data/Link Physical NFS XDR RPC UDP IP DIX Ethernet IEEE 802.3

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

Connectors for OSI {there can be multiple, separate entities at each layer} Repeater Bridge Router Gateway