CPSC 463 Networks and Distributed Processing Mr. Willis F. Marti

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) Mass Storage User Interface Just insert a network?

Distributed System (!) 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."

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 Definitions Total 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- 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

An Evolution of Layering 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 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} CCITT {international PTT oriented} etc Standards & Users {cost, flexibility} Purpose of the Open Systems Interconnection Model {remember, it's just a model}

IEEE 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 ICMP IP 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 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}

The OSI Model {remember, enveloping at each layer}

OSI Model, cont {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 it come 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 and physical 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 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