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Course Overview
Syllabus/policy {handout}
Schedule {Web}
Comments on Term Project
Course Objectives
Book Comments
...
Opinions and Facts
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
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
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}