Transcript 01-Computer Networks

Computer Networks
A History Lesson of Networking
1969 – ARPANET, first packet switched
network consist of UCLA, Stanford, UC Santa
Barbara and Utah University
• 1971 – first email program
• 1974 – TCP/IP
• 1980’s – Local Area Networks (LANs)
• 1984 – OSI Layer
• 1990’s – WWW / Internetworking
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Why Networking?
Efficiency and Productivity
 Reliability
 Distributed Systems
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What Applications?
Client/Server Business Applications
 Electronic Messaging
 Information Retrieval
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Network Classification by Area
Wide Area Network
 Metropolitan Area Network
 Local Area Network
 Personal Area Network
 Ad Hoc Network
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Protocols
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Driving Force: need for different proprietary
networking system to communicate
Protocol: set of rules for acceptable behaviour (how
communication should take place in)
Specifically:
 the
set of rules used by communicating parties for that
communication to be successful
 Suite of protocols cover all required behaviour
 Mostly implemented in Software
 Complexity demands that protocols are ‘layered’
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Advantages of Layering Protocols
Dividing complex network operation into more
manageable layers
 Defining the standard interface for the “plugand-play” multi-vendor integration
 Facilitate Modular Engineering
 Simplifies Teaching and Learning
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ISO/OSI Reference Model
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ISO in 1984
 Open
Systems Interconnect (OSI)
 A design guideline for network layering
 Abstract layers provide different services
 Defines 7 layers of service
 Each layer provides service to adjacent layers
 Each layer communicates with same layer in
remote machine…
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OSI Reference Model
Application Layer
Application Layer
Presentation Layer
Presentation Layer
Session Layer
Session Layer
Transport Layer
Transport Layer
Network Layer
Network Layer
Link Layer
Link Layer
Physical Layer
Physical Layer
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Layer 1 - Physical
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Physical Layer:
 Move
bits between devices
 Specifies voltage, wire speed, and pin out cables
 Passes data up to data link layer (and receives
from data link layer)
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Layer 2 – Data Link
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Data Link Layer:
 Performs
framing of bits, flow and error control but
not correction
 Responsible for transmission of frames across the
physical link
 Provide access to media using MAC address
 Passes data between physical and network layers
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The Institute of Electrical and Electronics Engineers (IEEE)
has subdivided the data link layer into two sublayers: Logical
Link Control (LLC) and Media Access Control (MAC).
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The Logical Link Control (LLC) 802.2 sublayer is responsible
for identifying Network Layer protocols and then
encapsulating them. An LLC header tell the Data Link Layer
what to do with the packet if a frame is coming. Also provide
flow control and sequencing of control bits
The Media Access Control (MAC) sublayer of the data link
layer manages protocol access (logical topologies) to the
physical network medium. The IEEE MAC specification
defines MAC addresses, which enable multiple devices to
uniquely identify one another at the data link layer. IEEE
802.3 dan 802.5
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Layer 3 - Network
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Network Layer:
 Passes
data between data link and transport
layers
 Responsible for routing data across a network,
from source to destination using network-wide
addressing
 Pass data between (separate) subnetworks
 Hides network topology from higher layers
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Layer 4 - Transport
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Transport Layer:
 Passes
data between network and session layers
 Provides reliable end-to-end delivery of data,
including flow and error control of packets
 Fragmentation of large messages
 Quality of Service (QoS), usually with layer 3
 Last of the pure network layers
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Layer 5 - Session
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Session Layer:
 Passes
data between presentation and transport
layers
 Responsible for managing network sessions
(series of related data streams)
 Provides synchronization and scheduling
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Layer 6 - Presentation
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Presentation Layer:
 Passes
data between application and session
layers
 Provides translation services for data to ensure
applications are using compatible formats
 E.g. converting from ASCII to EBCDIC text
representations
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Layer 7 - Application
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Application Layer:
 Passes
data to presentation layer (and receives
from presentation layer)
 … to and from the user!
 Communicates with remote applications
 Determines the user capability within the network
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Data Encapsulation
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Data Encapsulation
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OSI Layer vs. TCP/IP Layer
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5-7
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FTP – File Transfer Protocol
HTTP – Hypertext Transfer Protocol
WAP – Wireless Application Protocol
SMTP – Simple Mail Transfer Protocol
TCP
UDP
IP
e.g. IEEE 802.x
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Some Protocols in TCP/IP Suite
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Quiz
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Protocols
 What
are they?
 Why do we layer protocols?
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ISO/OSI – 7 layer reference model
 How
does the OSI abstract services?
 How does data pass between layers
(local/remote)?
 How does Internet stack relate to OSI?
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