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Transcript
4122102 :
Computer Network
& Distributed
Computer Network and Distributed
Rachphat Sriprom
Rajabhat Institute Chandrakasem
1
Computer Network
• A network is a set of devices (nodes)
connected by media links
• A node can be a computer, printer,
etc.
• The links are called communication
channels
2
Simplified Network Model
3
LAN : Local Area Network
4
WAN : Wide Area Network
5
WAN : Dial On Demand-PSTN
6
WAN : Leased line - PSTN
7
WAN : PSDN
8
WAN : ISDN
9
Enterprise Network
10
Network Criteria
11
Performance
The performance of a network depends on a
number of factors ;
•
•
•
•
Number of users
Type of transmission medium
Hardware
Software
12
Reliability
• Frequency of failure
• Recovery time of a network after
failure
• Catastrophe
13
Security
• Unauthorized access
– For a network to be useful, sensitive
data must be protected from
unauthorized access. Protection can
be accomplished at a number of levels
• Viruses
– A good network is protected from
viruses by hardware and software
designed specifically for that purpose.
14
Computer Networks &
Computer Communications
• Computer Networks: two or more
computer interconnected via a
communication network
• Computer Communications: the
exchange of information between two
computers for purpose of cooperative
action
15
Communications Tasks
• Transmission
system utilization
• Interfacing
• Signal generation
• Synchronization
• Exchange
Management
• Error detection and
correction
• Flow control
•
•
•
•
Addressing
Routing
Recovery
Message
formatting
• Security
• Network
management
16
Protocols
• Protocol - a set of rules governing
the exchange of data between two
entities in a system
• Must speak the same language
• Entities
• Systems
– User applications
-Computer
-Terminal
– e-mail facilities
-Remote sensor
– terminals
17
Key Elements of a Protocol
• Syntax
– Data formats
– Signal levels
• Semantics
– Control information
– Error handling
• Timing
– Speed matching
– Sequencing
18
Protocol Data Unit (PDU)
19
Protocol Data Unit (PDU)
• The sending application generates
a block of data and passes this to
the transport layer
• Each of these blocks the transport
layer appends a transport header,
containing protocol information
• The combination of data from the
next higher layer and control
information is known as a protocol
data unit (PDU)
20
Encapsulation in PDU
• Addition of control information to data
– Address information
– Error-detecting code
– Protocol control
21
Protocol Data Unit (PDU)
22
Standard or Nonstandard
23
OSI Model
• The Open Systems Interconnection
model is a layered framework for the
design of network systems that allows
for communication across all types of
computer systems
• It consists of seven separate but
related layers
• An ISO standard
ISO is the organization. OSI is the model.
24
OSI seven layers
•
•
•
•
•
•
•
Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data Link layer
Physical layer
25
OSI layers
26
The OSI Environment
Headers are added to the data at layers 6, 5, 4, 3, and 2. Trailers are usually added only at layer 2.
27
Functions Of The Layers
• Physical Layer
– Physical interface between devices
• Information Transmission
• Medium & Signal
• Mechanical (Connector)
28
Data Link Layer
• Control the information transfer over
Physical link
• Physical addressing
• Framing
• Flow control
• Error control
• Synchronization
• Access control
29
Data Link Layer
Figure shows Framing
30
Data Link Layer Example
31
Network Layer
• The network layer is responsible for the
source-to-destination delivery of a
packet possibly across multiple
networks (links)
• Switching & Routing
• Logical Addressing
• Higher layers do not need to know
about underlying technology
• Not needed on direct links
32
Network Layer Example
33
Network Layer Example
34
Transport Layer
• Control for information transfer
between end user system
• Segmentation & Reassembly
• In sequence
• Connection control
• Flow control
• Error control
• Quality of service (QoS)
35
Transport Layer
36
Transport Layer Example
37
Session Layer
• Control of dialogues between
applications in end systems
• Dialogue discipline (full duplex or
half duplex)
• Grouping
• Recovery
38
Presentation Layer
• The presentation layer is
concerned with the syntax and
semantics of the information
exchanged between two systems
– Data formats and Encoding
– Data compression
– Encryption (senders transforms the
original information to another from
and sends it out over the network)
39
Presentation Layer
40
Application Layer
• The application layer provides user
interface and support for services such as
electronic mail, remote file access and
transfer, shared database management, etc.
– Network virtual terminal (allows a user to log on
to a remote host)
– File transfer, access, and management (FTAM)
– Mail services
– Directory services
41
Application Layer
42
Summary of Layer Functions
43