OSI Model: Open Systems Interconnection Reference Model

Lesson One: OSI Model: open Systems Interconnection Reference Model


7 Layers: All People Seem To need data processing
7. Applications

It sets up communication between Applications and lower layer network services.

The network needs to interpret application request and the application can interpret data to be sent to the network.

　

- In this Layer we see

-HTTP, FTP, DNS, POP3

-this is where all the applications work.

-separates data into PDUs (protocol data units) or discrete amounts of data.

　

　

　

6. Presentation

-Character encoding

-Application encryption and decryption

Often combined with Application layer

-Presentation layer accepts data from the application layer and formats so that I can be readable.

　

　

5. Session

-Communication management between devices


-Half-duplex, full-duplex (way of communication)
-Controls protocols, tunneling protocols

-Session is a connection of a data exchange between two parties.

-Another purpose is that it  establishes and keeps  communication alive between networks And it determines if a connection is cut-off or not.

An example, is an ISP and your computer negotiating a connection. If your physical connections is disconnected that is a fail session.

　

4. Transport

-The Post office layer

-Parcels and letters

-Transport takes info from the session layer and it make sure it reaches its end. If data is being transferred from point A to B it assures reliability and make sure its sent without erros.


TCP(Transmission Control Protocol) and UDP (User Datagram Protocol)

-TCP is connection oriented.

-UDP is not connection oriented. Basically Connectionless.
　

　

3. Network Layer
 The routing layer
 Internet Protocols are in this layer
 Network layer function is to translate network address into the devices and decide how they routed from the sender to the receiver.

IP Fragmentation Process
 -If bytes are too big they are broken and sent through IP header. Split into 3 separate frames. The fragments will always be in multiplea of 8.
　
2. Data Link
 Basic network "language"
 MAC (Media Accesss Control) address on Ethernet
 Every device has a MAC address
 You can find the MAC address by IP address
 Switch
 Data links purpose is to divide data they receive from the network layer into distinct frames so it can be sent to the physical layer.

Data link is divided into 2 sub layers
-Logical Link Control (which provides common setting, reliability and flow of control) (issues requests for the data errors)

-Media Access Control (Takes the MAC address and attaches to the frame)

　

　

1. Physical
 Signaling, cabling, connectors
 This layer isn't about protocols
 Protocols that detect signals

you have a physical layer problem

-Fix your cabling, punch-downs etc.

Fix Tutorial For Sound Icon Missing In Windowsn VISTA, Window 7 - -

Here is fix for Fix Tutorial the Speaker or Volume icon which disappear in Windows Vista or 7.

Implementing Universal Groups

Use Global Group to hold accounts as members. Avoid group nesting to the minimum to avoid confusion
Use Domain Local Groups to provide access to resources in specific domain then make domain local groups members of access control list for specific resources in the domain, such as share folders & printers
Use Universal Groups to provide extensive access to resources, particularly when Active Directory contains trees and forest, or to simplify access when there are multiple domains

Security Group Management

Types of groups and associated scopes:
Local: Stand-alone servers that are not part of any domain
Domain local: Used when there is a single domain or to manage resources in a particular domain so that global and universal groups can access those resources
Global: Used to manage group accounts from the same domain so that those accounts can access resources in the same and in other domains
Universal: Used to provide access to resources in any domain within the forest.
Security groups
Enable access to resources on a) a stand-alone server or b) in Active Directory
Distribution groups
Used for e-mail or telephone lists to provide a quick, mass distribution of information

User Account Management

There are 2 ways that we can create user accounts:


a) Accounts that are set up through a stand-alone server that does not have Active Directory installed

b) Accounts that are set up in a domain when Active Directory is installed

Transitive trust

• If A and B have a trust and B and C have a trust, A and C automatically have a trust as well
• Transitive and 2 ways trust relationship allow any new domain it the tree to have full access to any object in any child/parent domain
• Authentication to different object is enabled using Kerberos

Account Management

There are 2 ways that we can create user accounts:
1) Accounts that are set up through a stand-alone server that does not have Active Directory installed
Install Local Users and Groups MMC snap-in:
For standalone servers that do not use Active Directory



2) Accounts that are set up in a domain when Active Directory is installed.

Use Active Directory Users and Computers tool
From the Administrative Tools menu or as an MMC snap-in

Create each new account by entering account information and password controls
Domain users have access to domain any network resource in the domain (as long as they are authorized)