Network Implementations are built on common network standards and models of networking that describe how devices and protocols interconnect. A network is two or more computer systems linked together by some form of the transmission medium that enables them to share information. It does not matter whether the network contains two or thousands of machines; the concept is essentially the same.
If you have different pieces of hardware and software, they all have to talk to each other and interact to be able to make your network. To help the interconnectivity work, they come up with something called the OSI 7-layer model.
When a message is sent from one node to another, it travels down the stack of layers (7 to 1) on the sending node, reaches the receiving node using the transmission media, and then passes up the stack (1 to 7) on that node. At each level (except the Physical layer), the sending node adds a header to the data payload, forming a "chunk" of data called a protocol data unit (PDU). This process is called encapsulation.
LAYER 1 (PHYSICAL)
The physical layer is right down to the hardware of the computer. This is
where the electrical pulses that make up data transfer over a network are sent
and received. It's the job of the physical layer to convert the binary data of
the transmission into signals and transmit them across the network, as well as
receive incoming signals and convert them back into binary data.
Devices that operate at the Physical Layer include:
- Transceivers: That part of a network interface that sends and receives signals over the network media.
- Repeaters: A device that amplifies an electronic signal to extend the maximum allowable distance for a media type.
- Hubs: A multiport repeater, deployed as the central point of connection for nodes.
- Media Converters: A device that converts one media signalling type to another.
- Modems: A device that converts between digital and analogue signal transmission.
LAYER 2 (DATA LINK)
The data link layer focuses on the physical addressing of the transmission.
It receives a packet from the network layer (that includes the IP address
for the remote computer) and adds the physical (MAC) address of the
receiving endpoint. Inside every network-enabled computer is a Network
Interface Card (NIC) which comes with a unique MAC (Media Access Control)
address to identify it. When information is sent across a network, it's
actually the physical address that is used to identify where exactly to send
the information. Additionally, it's also the job of the data link layer to
present the data in a format suitable for transmission.
In short, Layer 2 allows the upper network layers to access media and
controls how data is placed and received from media.
Connectivity devices found at the Data Link layer include:
- Network Adapters or Network Interface Cards (NIC): A NIC joins a host to network media (cabling or wireless) and enables it to communicate over the network by assembling and disassembling frames.
- Bridges: A bridge joins two network segments while minimizing the performance reduction of having more nodes on the same network. A bridge has multiple ports, each of which functions as a network interface.
- Switches: An advanced type of bridge with many ports. A switch creates links between large numbers of nodes more efficiently.
- Wireless access points (APs): An AP allows nodes with wireless network cards to communicate and creates a bridge between wireless networks and wired ones.
The Network Layer is responsible for moving data around a network of networks,
known as an internetwork or the Internet. While the Data Link layer is capable
of forwarding data by using hardware addresses within a single segment, the
Network layers move information around an internetwork by using logical
network and host IDs. The networks are often heterogeneous; that is, they use
a variety of Physical layer media and Data Link protocols.
The main appliance working at layer 3 is the router. Other devices include
layer 3 switches, which combine the function of switches and routers, and
basic firewalls.
LAYER 4 (TRANSPORT)
At the Transport layer, the content of the packets starts to become
significant. Any given host on a network will be communicating with many other
hosts using many different types of networking data. One of the critical
functions of the Transport layer is to identify each type of network
application by assigning it a port number. For example, data from the HTTPS
web browsing application can be identified as port 443, while data from an
email server can be identified as port 25.
It receives data from Layer 5 and segments it. Each segment, or data unit,
has a source and destination port number, as well as a sequence number. The
port number ensures that the segment reaches the correct application. The
sequence number ensures that the segments arrive in the correct order.
This layer also controls the amount of data transmitted. For example, your
laptop may be able to handle 100 Mbps, whereas your friend’s phone can only
process 10 Mbps. Layer 4 can dictate that the server slows down the data
transmission, so nothing is lost by the time your friend receives it. But
when your friend sends a message back, the server can increase the
transmission rate to improve performance.
Lastly, Layer 4 performs error-checking. If a segment of data is missing,
Layer 4 will re-transmit that segment.
TCP and UDP are both very well-known protocols, and they exist at Layer 4.
TCP favours data quality over speed, whereas UDP favours speed over data
quality.
LAYER 5 (SESSION) AND LAYER 6 (PRESENTATION)
The upper layers of the OSI model are less clearly associated with distinct
real-world protocols. These layers collect various functions that provide
useful interfaces between software applications and the Transport Layer.
LAYER 5
Most applications protocol requires the exchange of multiple messages between
the client and server. This exchange of such a sequence of messages is
called a session or dialog. This layer represents the dialog control functions
that administer the process of establishing the dialog, managing data
transfer, and then ending the session.
LAYER 6
The presentation layer receives data from the application layer. This data
tends to be in a format that the application understands, but it's not
necessarily in a standardized format that could be understood by the
application layer in the receiving computer. The presentation layer translates
the data into a standardized format, as well as handles any encryption,
compression, or other transformations to the data. With this complete, the
data is passed down to the session layer.
LAYER 7 (APPLICATION)
Application Layer protocols provide an interface for software programs on
network hosts that have established a communications channel through the
lower-level protocols to exchange data. For example, one of the most-used
services provided by the Application layer is file transfer.
TCP/IP Protocol Suite
The TCP/IP protocol suite maps to a four-layer conceptual model: Application,
Transport, Internet, and Link. This model is referred to as the
Internet Protocol Suite, the Department of Defense (DoD) model,
or the ARPA model. Each layer in the Internet Protocol
Suite corresponds to one or more layers of the OSI model.
The above figure demonstrates how the OSI model compares with the TCP/IP
protocol stack. Some of the OSI layers are performed by a single protocol,
some layers are performed by several protocols, and some protocols cover
several layers. This reflects the emphasis that consumes processing power and
bandwidth, as each header consists of a series of bytes that must be
transmitted and decoded in addition to the application data. Consequently,
actual protocol stacks tend to be simpler than the OSI model.
We hope this helps. If any suggestions or doubts you can add a comment and we
will reply as soon as possible.
%20Cover.jpg)
%20Cover.jpg)
No comments:
Post a Comment