Transcript Introduction - CS Course Webpages

CPSC 463
Networks and
Distributed
Processing
Mr. Willis F. Marti
http://www.cs.tamu.edu/faculty/willis
Class Admin
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Syllabus & Schedule
Opinions and Facts
Test taking
Attendance & Job Searches
• Sympathy
Course Objectives
• Science
• 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
• Engineering
• How networks are built
• Attitude
• 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?
Just insert a
network?
Mass
Storage
Computing
(CPU)
User
Interface
Distributed System (!)
Services
Servers (Storage, Compute)
Network
Users
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
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
LAN:
Data Transmission Time
Total Travel Time
Data Transmission Time
<= .01 to .05
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
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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
Layering
Message
Message
TRANSPORT
Packets
Pkts
Packets
Pkts
NETWORK
10010111001
{Bits}
LINK
PHYSICAL
{Signal}
10010111001
{Bits}
Packet Formats
Stream
Packets
Application “Header”
Data
Presentation “Header”
Data
Session Header (?)
Data
Transport Header
Network Header
Link Header
Framing
Data
Data
Data
Data
An Evolution of Layering
Application
Application
Application
Application
Application
Application
Physical
Data/Link
Transport
Transport
Presentation
Data/Link
Network
Session
Physical
Physical
Data/Link
Transport
Physical
Network
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
n-1
n-1
Which Architecture to Study?
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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
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.2 - Link Layer
.3 - CSMA/CD [Ethernet]
.4 - Token Bus
.5 - Token Ring
.11 – wireless Ethernet
(Partial) TCP/IP Stack
FTP
TELNET
DNS
TCP
UDP
IP
ARP
DIX Ethernet or ...
ICMP
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
NFS
Presentation
XDR
Session
RPC
Transport
UDP
Network
IP
Data/Link
Physical
DIX Ethernet
IEEE 802.3
OSI Reference Model
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Data/Link
Data/Link
Physical
Physical
{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}
Application
7
Presentation
6
Session
5
Transport
4
Network
3
Data/Link
2
Physical
1
OSI Model, cont
Application
Application
Presentation
Presentation
Session
Gateway
Transport
Session
Transport
Router
Network
Network
Bridge
Data/Link
Data/Link
Repeater
Physical
Physical
{there can be multiple, separate entities at each layer}
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
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
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Connection Oriented
Connectionless
Datagram
Primitives