من يشرح لي الطبقات الـ 7 و بروتوكولاتها ؟

[بنتيوم 5]

السسسسسسسسسسسسلام عليكم




طلب صغنوووووووووووون !!!


ابغاك تفصل النت و تشرب كأسة شااااااي ........ وتحضر كاسة ثانية ......

وتبدأ تشرح اليرات السبع والبروتوكولات بتعتها وشوية تفاصيل



تبتغي الاجر من الله و في خوانك المسلمين :) في هذا الشهر الفضيل ......



شكراً وفي الانتظار ......


لا تستح من القليل فأن الحرمان اقل منه .......


بنتيوم 5

[بنتيوم 5]

لا اعرف من انت !! لكن شكراً لك على اية حال !! ( ناقل الموضوع )

[Cisco_Designer]

السلام عليكم

يوجد كتاب يشرح طبفات OSI بالعربي اذا احبتت ارسلته لك واذا كان هناك ايه سؤال فإذن الله نساعد في الإجابة.

بالنسبة ل بريدي الإلكتروني هوا نفسه Cisco_designer على الهوت ميل .

ودمتم

[nana17]

How OSI Works

by Jeff Tyson




Virtually all networks in use today are based in some
fashion on the Open Systems Interconnection (OSI)
standard. OSI was developed in 1984 by the
International Organization for Standardization (ISO),
a global federation of national standards
organizations representing approximately 130
countries.

The core of this standard is the OSI Reference Model,
a set of seven layers that define the different stages
that data must go through to travel from one device to
another over a network. In this article, you'll find
out all about the OSI standard.



The Layers
Think of the seven layers as the assembly line in the
computer. At each layer, certain things happen to the
data that prepare it for the next layer. The seven
layers, which separate into two sets, are:

Application Set

Layer 7: Application - This is the layer that actually
interacts with the operating system or application
whenever the user chooses to transfer files, read
messages or perform other network-related activities.

Layer 6: Presentation - Layer 6 takes the data
provided by the Application layer and converts it into
a standard format that the other layers can
understand.

Layer 5: Session - Layer 5 establishes, maintains and
ends communication with the receiving device.

Transport Set

Layer 4: Transport - This layer maintains flow control
of data and provides for error checking and recovery
of data between the devices. Flow control means that
the Transport layer looks to see if data is coming
from more than one application and integrates each
application's data into a single stream for the
physical network.

Layer 3: Network - The way that the data will be sent
to the recipient device is determined in this layer.
Logical protocols, routing and addressing are handled
here.

Layer 2: Data - In this layer, the appropriate
physical protocol is assigned to the data. Also, the
type of network and the packet sequencing is defined.

Layer 1: Physical - This is the level of the actual
hardware. It defines the physical characteristics of
the network such as connections, voltage levels and
timing.

The seven layers of the OSI Reference Model

The OSI Reference Model is really just a guideline.
Actual protocol stacks often combine one or more of
the OSI layers into a single layer.



Protocol Stacks
A protocol stack is a group of protocols that all work
together to allow software or hardware to perform a
function. The TCP/IP protocol stack is a good example.
It uses four layers that map to the OSI model as
follows:


Layer 1: Network Interface - This layer combines the
Physical and Data layers and routes the data between
devices on the same network. It also manages the
exchange of data between the network and other
devices.

Layer 2: Internet - This layer corresponds to the
Network layer. The Internet Protocol (IP) uses the IP
address, consisting of a Network Identifier and a Host
Identifier, to determine the address of the device it
is communicating with.

Layer 3: Transport - Corresponding to the OSI
Transport layer, this is the part of the protocol
stack where the Transport Control Protocol (TCP) can
be found. TCP works by asking another device on the
network if it is willing to accept information from
the local device.

Layer 4: Application - Layer 4 combines the Session,
Presentation and Application layers of the OSI model.
Protocols for specific functions such as e-mail
(Simple Mail Transfer Protocol, SMTP) and file
transfer (File Transfer Protocol, FTP) reside at this
level.
As you can see, it is not necessary to develop a
separate layer for each and every function outlined in
the OSI Reference Model. But developers are able to
ensure that a certain level of compatibility is
maintained by following the general guidelines
provided by the model


================================================== ==============================\
============================


The 7 Layers of the OSI Model

The OSI, or Open System Interconnection, model defines
a networking framework for implementing protocols in
seven layers. Control is passed from one layer to the
next, starting at the application layer in one
station, proceeding to the bottom layer, over the
channel to the next station and back up the hierarchy.

Application
(Layer 7) This layer supports application and end-user
processes. Communication partners are identified,
quality of service is identified, user authentication
and privacy are considered, and any constraints on
data syntax are identified. Everything at this layer
is application-specific. This layer provides
application services for file transfers, e-mail, and
other network software services. Telnet and FTP are
applications that exist entirely in the application
level. Tiered application architectures are part of
this layer.
Presentation
(Layer 6) This layer provides independence from
differences in data representation (e.g., encryption)
by translating from application to network format, and
vice versa. The presentation layer works to transform
data into the form that the application layer can
accept. This layer formats and encrypts data to be
sent across a network, providing freedom from
compatibility problems. It is sometimes called the
syntax layer.
Session
(Layer 5) This layer establishes, manages and
terminates connections between applications. The
session layer sets up, coordinates, and terminates
conversations, exchanges, and dialogues between the
applications at each end. It deals with session and
connection coordination.
Transport
(Layer 4) This layer provides transparent transfer of
data between end systems, or hosts, and is responsible
for end-to-end error recovery and flow control. It
ensures complete data transfer.
Network
(Layer 3) This layer provides switching and routing
technologies, creating logical paths, known as virtual
circuits, for transmitting data from node to node.
Routing and forwarding are functions of this layer, as
well as addressing, internetworking, error handling,
congestion control and packet sequencing.
Data Link
(Layer 2) At this layer, data packets are encoded and
decoded into bits. It furnishes transmission protocol
knowledge and management and handles errors in the
physical layer, flow control and frame
synchronization. The data link layer is divided into
two sublayers: The Media Access Control (MAC) layer
and the Logical Link Control (LLC) layer. The MAC
sublayer controls how a computer on the network gains
access to the data and permission to transmit it. The
LLC layer controls frame synchronization, flow control
and error checking.
Physical
(Layer 1) This layer conveys the bit stream -
electrical impulse, light or radio signal -- through
the network at the electrical and mechanical level. It
provides the hardware means of sending and receiving
data on a carrier, including defining cables, cards
and physical aspects. Fast Ethernet, RS232, and ATM
are protocols with physical layer components.




================================================== ==============================\
============================


some useful links:


https://www.geocities.com/SiliconValley/Monitor/3131/ne/osimodel.html#Session


https://www.geocities.com/SiliconValley/Monitor/3131/ne/netoc.html

فى الخدمة.... دعواتكم

[nana17]

OSI Seven-Layer Model
In the 1980s, the European-dominated International Standards Organization (ISO), began to develop its Open Systems Interconnection (OSI) networking suite. OSI has two major components: an abstract model of networking (the Basic Reference Model, or seven-layer model), and a set of concrete protocols. The standard documents that describe OSI are for sale and not currently available online.

Parts of OSI have influenced Internet protocol development, but none more than the abstract model itself, documented in OSI 7498 and its various addenda. In this model, a networking system is divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacts directly only with the layer immediately beneath it, and provides facilities for use by the layer above it. Protocols enable an entity in one host to interact with a corresponding entity at the same layer in a remote host.



The seven layers of the OSI Basic Reference Model are (from bottom to top):


The Physical Layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. Ex: this layer defines the size of Ethernet coaxial cable, the type of BNC connector used, and the termination method.

The Data Link Layer describes the logical organization of data bits transmitted on a particular medium. Ex: this layer defines the framing, addressing and checksumming of Ethernet packets.

The Network Layer describes how a series of exchanges over various data links can deliver data between any two nodes in a network. Ex: this layer defines the addressing and routing structure of the Internet.

The Transport Layer describes the quality and nature of the data delivery. Ex: this layer defines if and how retransmissions will be used to ensure data delivery.

The Session Layer describes the organization of data sequences larger than the packets handled by lower layers. Ex: this layer describes how request and reply packets are paired in a remote procedure call.

The Presentation Layer describes the syntax of data being transferred. Ex: this layer describes how floating point numbers can be exchanged between hosts with different math formats.

The Application Layer describes how real work actually gets done. Ex: this layer would implement file system operations.
The original Internet protocol specifications defined a four-level model, and protocols designed around it (like TCP) have difficulty fitting neatly into the seven-layer model. Most newer designs use the seven-layer model.



--------------------------------------------------------------------------------
دعواتكمممممم

[nana17]

What do the layers do?
As data passes from an application and moves down the stack, each layer adds a header according to the protocol that exists at that layer. This is known as encapsulation. The only exception is the data link layer, a header and a trailer is added. After the data has been transmitted across whatever media is in use, the process of deencapsulation begins. Each layer of the stack, at the destination, removes the header (or header and trailer in the case of the data link layer) that was placed by its corresponding source layer. The physical and data link layers exist in hardware, all other layers are software driven.


Layer 7 - Application
This layer has protocols that support user applications, but it does not include the applications themselves. There is an opinion that the network operating system should be included in this layer, but this is open to disagreement. Strictly speaking, this layer deals with file access and management and includes the OSI X.400 and X.500 email protocols. X.400 allows interoperability between different email software and X.500 synchronises email across different systems.


Layer 6 - Presentation
The presentation layer protocols deal with data syntax during transfer between two application processes. If the client and server are using different file formats, this layer has conversion protocols. Therefore, computers using different file formats can still communicate with each other. Data encryption and decryption protocols also exist at the presentation layer.


Layer 5 - Session
Protocols at this layer are necessary for establishing, maintaining and ending sessions between user applications. Such protocols are designed to make the differences, across various platforms, transparent to the user.


Layer 4 - Transport
Transport layer protocols are responsible for the reliability of end to end connections. These protocols assemble multiple network layer packets into a coherent message. This layer also provides flow-control and error recovery.


Layer 3 - Network
The network layer protocols establish, maintain and terminate end to end (network) links. These protocols route messages across the network(s) between two computers. Different network operating systems often have their own network layer protocols, but can also use other protocols. This flexibiltity is essential when communicating accross multiple client/server platforms.


Layer 2 - Data Link
Data link protocols provide logical link control and medium access control. These protocols provide reliability to the physical layer transmission by ordering the data into frames and adding error checking and addressing information. The network interface card assembles the data link layer frames.


Layer 1 - Physical
Protocols at the physical layer are responsible for establishing, maintaining and ending physical connections (point to point) between computers. These protocols are manifested in the media across which transmission occurs. These protocols do not specify the various cables and connectors, these specifications are sometimes said to belong to layer 0.




لو فى اى اسئلة اتفضل اسأل

[nana17]

Layer
Function Protocols Network Components
Application
User Interface
used for applications specifically written to run over the network
allows access to network services that support applications;
directly represents the services that directly support user applications
handles network access, flow control and error recovery
Example apps are file transfer,e-mail, NetBIOS-based applications
DNS; FTP; TFTP; BOOTP; SNMP;RLOGIN; SMTP; MIME; NFS; FINGER; TELNET; NCP; APPC; AFP; SMB Gateway
Presentation
Translation
Translates from application to network format and vice-versa
all different formats from all sources are made into a common uniform format that the rest of the OSI model can understand
responsible for protocol conversion, character conversion,data encryption / decryption, expanding graphics commands, data compression
sets standards for different systems to provide seamless communication from multiple protocol stacks
not always implemented in a network protocol
Gateway
Redirector

Session
"syncs and sessions"
establishes, maintains and ends sessions across the network
responsible for name recognition (identification) so only the designated parties can participate in the session
provides synchronization services by planning check points in the data stream => if session fails, only data after the most recent checkpoint need be transmitted
manages who can transmit data at a certain time and for how long
Examples are interactive login and file transfer connections, the session would connect and re-connect if there was an interruption; recognize names in sessions and register names in history
NetBIOS
Names Pipes

Mail Slots

RPC
Gateway
Transport

packets; flow control & error-handling
additional connection below the session layer
manages the flow control of data between parties across the network
divides streams of data into chunks or packets; the transport layer of the receiving computer reassembles the message from packets
"train" is a good analogy => the data is divided into identical units
provides error-checking to guarantee error-free data delivery, with on losses or duplications
provides acknowledgment of successful transmissions; requests retransmission if some packets don’t arrive error-free
provides flow control and error-handling
TCP, ARP, RARP;
SPX

NWLink

NetBIOS / NetBEUI

ATP
Gateway
Advanced Cable Tester

Brouter

Network

addressing; routing
translates logical network address and names to their physical address (e.g. computername ==> MAC address)
responsible for
addressing
determining routes for sending
managing network problems such as packet switching, data congestion and routing
if router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into smaller units. At the receiving end, the network layer reassembles the data
think of this layer stamping the addresses on each train car
IP; ARP; RARP, ICMP; RIP; OSFP;
IGMP;

IPX

NWLink

NetBEUI

OSI

DDP

DECnet
Brouter
Router

Frame Relay Device

ATM Switch

Advanced Cable Tester

Data Link

data frames to bits
turns packets into raw bits 100101 and at the receiving end turns bits into packets.
handles data frames between the Network and Physical layers
the receiving end packages raw data from the Physical layer into data frames for delivery to the Network layer
responsible for error-free transfer of frames to other computer via the Physical Layer
this layer defines the methods used to transmit and receive data on the network. It consists of the wiring, the devices use to connect the NIC to the wiring, the signaling involved to transmit / receive data and the ability to detect signaling errors on the network media
Logical Link Control
error correction and flow control
manages link control and defines SAPs
802.1 OSI Model

802.2 Logical Link Control
Bridge
Switch

ISDN Router

Intelligent Hub

NIC

Advanced Cable Tester

Media Access Control
communicates with the adapter card
controls the type of media being used:
802.3 CSMA/CD (Ethernet)

802.4 Token Bus (ARCnet)

802.5 Token Ring

802.12 Demand Priority

Physical

hardware; raw bit stream
transmits raw bit stream over physical cable
defines cables, cards, and physical aspects
defines NIC attachments to hardware, how cable is attached to NIC
defines techniques to transfer bit stream to cable
IEEE 802
IEEE 802.2

ISO 2110

ISDN
Repeater
Multiplexer

Hubs

Passive
Active
TDR

Oscilloscope

Amplifier

[بنتيوم 5]

السلام عليكم


بدر ... .. ما تقصر اخوي ووصلتك رسالة ع بريدك .وجزاك الله خير ... والي يريد الكتاب يرد في نفس الموضوع ....


nana17 شاكر لك ... والله يجزاك خير ..... المصدر هو اليوزفل لينك ؟؟




تبدأ الجلسة الان ...... واي اسئلة ان شاء الله راح تكون هنا :)


تحياتي للجميع ....

عمر ... بنتيوم 5

[Cisco_Designer]

السلام عليكم

بارك الله فيك أخي عمر والكتاب فعلاً قد تم إرساله وأرجو أن ينال استحسانك ،،،، وإذا وُجد أي استفسار فبإذن الله نحن في الخدمة.....

ودمتم