Ch02-S-13x

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23 Οκτ 2013 (πριν από 3 χρόνια και 10 μήνες)

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1

Protocol Interaction (ISO’s Open Systems
Interconnection (OSI model))


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The OSI Reference Model

Not UPS, but
APS transport network data physically
.

The OSI Reference Model


Created by the International Organization for
standardization in the 70’s


Accepted world wide as standard for data
network communications


An example of layered approach


This allow changes at one layer not affect
functions at other layers


encapsulation of
implementation details

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3 + 4 division


The top three layers know nothing about the
network


The bottom four layers handles about
network communications.

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The Top Three


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The Bottom Four

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Data Encapsulation

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The Application Layer


Includes the following protocols:


File Transfer Protocol (FTP)


Hypertext Transfer Protocol (HTTP)


Simple Mail Transfer Protocol (SMTP)


Post Office Protocol, Version 3 (POP3)


Internet Mail Access Protocol (IMAP)


Simple Network Management Protocol (SNMP)


Domain Name System (DNS)


Dynamic Host Configuration Protocol (DHCP)


The Application Layer


IE, an application, interacts with this layer to
carry out FTP related operations


I can write an app using C#, IIS and Visual
Studio 2012 that sends emials using SMTP
library. If the SMTP service is available, the
app can actually send the emails.

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The Presentation Layer



The presentation layer uses the following
translation process:




1.

The sender translates its abstract syntax to



transfer syntax.



2.

The sender transmits data to the receiver.



3.

The receiver translates transfer syntax to it in



abstract syntax.

Example, PC and Apple data formats conversion

Other examples are Unicode, compression,
encryption/decryption, and multimedia data

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The Session Layer


The two most important functions at this
layer are


Dialog control


Two way alternate TWA


Two way simultaneous TWS (IM)


Dialog separation



For example, you have two browser sessions
connected to your bank account, this layer
makes sure messages in this two sessions are
not mixed up

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The Transport Layer


Includes the following protocols:


Transmission Control Protocol (TCP)


User Datagram Protocol (UDP)


IPX


NetWare Core Protocol (NCP)


Sequenced Packet Exchange (SPX)



Performs the following functions:


Packet acknowledgment


Data segmentation


different from Fragmenting


Flow control


Error detection


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Connection
-
Oriented and
Connectionless Protocols

Connection
-
Oriented (CO)
Protocols


Connectionless (CL)
Protocols


Require a handshake


Do not require a handshake


Have larger headers and more
overhead


Have smaller headers and less
overhead


Provide packet acknowledgments,
data segmentation, flow control,
and error detection and correction


Do not provide additional
services


Acknowledge transmitted packets,
so they are considered reliable


Do not acknowledge
transmitted packets, so they
are considered unreliable


Example: TCP

Example: UDP

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The Network Layer


Includes the following protocols:



Internet Protocol (IP and IP v6)


Internetwork Packet Exchange (IPX)


NetBIOS Extended User Interface (NetBEUI)


AppleTalk


Performs the following functions:


IP level Addressing


Fragmenting (message size)


Routing


Protocol identification


Routing


Two types of packets: data and route
-
update


It uses the routing table to determine where to
send


One protocol per routing table (IP and IP v6 use
different tables)


It drops the packet if it cannot determine where to
send


It does not forward broadcast messages , which
can be used to build up the routing table

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Routing Example

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The Data
-
Link Layer


Includes the following protocols:


Ethernet (10Base2, 10Base5, 10BaseT, 100BaseT, etc)


Token Ring


Fiber Distributed Data Interface (FDDI)


Serial Line Internet Protocol (SLIP)


Point
-
to
-
Point Protocol (PPP)



The selection of data
-
link layer protocols defines
NIC and driver, cable, and hubs/switch


Mostly LAN level communications or between
routers

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The Data
-
Link Layer (Cont.)



Includes the following protocol components:


Frame format


Media Access Control (MAC) mechanism


Physical layer specifications

(Coaxial cable or UTP)


Performs the following functions:


Hardware addressing (MAC address, 48 bits)


Error detection


Protocol identification


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The Physical Layer


Defines the hardware elements of the network,
including


The network medium


How the network is installed


The type of signaling



Includes the following elements:


Cables (UTP


EIA/TIA 568A
(Electronics/Telecommunications Industry Association))


Network interface adapters (also called network
interface cards, or NICs)


Hubs


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Summary: The OSI Reference Model


OSI Model
Layer

Function

Physical

Defines the hardware elements and structure of the network
installation

Data
-
link

Provides addressing, data encapsulation, and media access
control

Network

Provides end
-
to
-
end routing and addressing

Transport

Provides packet acknowledgment, flow control, and error
detection

Session

Provides dialog control and dialog separation

Presentation

Translates syntaxes between different systems

Application

Provides an interface to applications running on the computer