Open Systems Interconnection (OSI) Model

UDP is a widely used #Transport Layer Protocol# (defined by #Open Systems Interconnection (OSI) Model for the #Internet Protocol Suite (TCP/IP). Unlike Transmission Control Protocol (TCP), it is an unreliable and connectionless protocol which is great for real time communication such as voice chat or video streaming. UDP doesn’t guarantee that the packets or datagram (its Protocol Data Units (PDU))# will reach their destination or arrive in order as there is no mean to acknowledge such state. It has a rather small segment headers, with only 8 bytes, and provides fine application control over data transmission, which allow application-specific error recovery at Application Layer# for reliability.

Transport Layer is the forth layer in #Open Systems Interconnection (OSI) Model. It has the same name under #Internet Protocol Suite (TCP/IP). Its main purpose is to transfer the chunk of data from Application Layer onto the network. Sometimes, it will cut down the sizes of the data and send them as several packets (its #Protocol Data Units (PDU)). Their header will identify the Well-Known Ports# or socket numbers of the sender and receiver.

TCP is a commonly used Protocol# in #Internet Protocol Suite (TCP/IP). It is a #Transport Layer protocol according to the classification of #Open Systems Interconnection (OSI) Model.

Session Layer is the fifth layer in the #Open Systems Interconnection (OSI) Model. It manages the connections between hosts. Sometimes, it will referred to as Application Layer with Presentation Layer and Application Layer.

Security Mechanism is a mechanism that detects, prevents or recovers from Security Attack#. Most mechanism utilises #cryptography. Based on whether it is general or specific to the Open Systems Interconnection (OSI) Model# layers, Security Mechanism could be categorised into the following two groups:

PDU is the basic data communication unit for layers in #Open Systems Interconnection (OSI) Model. It includes important data such as control information (in the form of headers and trailers) and user data. Each layer may name it differently. If the PDU is pass down (from higher layer to lower layer), the process is called Encapsulation# as more control information are added to it. Otherwise, it is Decapsulation#, where control information are strip over as it is passed up the stack.

Presentation Layer is the sixth layer in the #Open Systems Interconnection (OSI) Model. It mainly provides formatting services to the Application Layer such as file encryption and format conversion. Session Layer, Application Layer and itself are commonly known as Application Layer as a whole in Internet Protocol Suite (TCP/IP).

Physical layer is the first in #Open Systems Interconnection (OSI) Model. In #Internet Protocol Suite (TCP/IP), it is treated as Link Layer together with Data Link Layer. It is responsible to convert a frame into bits, which is its Protocol Data Units (PDU)#, to be transmitted over the networks. It has a mean to validate whether a data is corrupted.

Network layer is the third layer in #Open Systems Interconnection (OSI) Model, and it is commonly referred as Internet Layer in #Internet Protocol Suite (TCP/IP). This is where most of the communication protocols operate. It is responsible for addressing, packaging and routing functions. The header that it adds to the packet, which is its #Protocol Data Units (PDU) includes the source and destination IP Address# which are unique. Routing# is done in this layer.

Several network devices available in the market operates at different levels of layers#. The following sections are organised in a way that the network devices are group together regarding their corresponding layer.

It has the same advantages with Open Systems Interconnection (OSI) Model as they are both of layered model. However, unlike OSI, it doesn’t define which protocols to used when transmitting data over physical medium.

IP is the underlying protocol used by World Wide Web (WWW) to connect other computers over the network which is included in the #Internet Protocol Suite (TCP/IP). It is considered as #Network Layer protocol according to #Open Systems Interconnection (OSI) Model. Currently, it has two versions: IPv4# and IPv6#.

ISO is a Protocol Suite# follows the standard of Open Systems Interconnection (OSI) Model#.

Encapsulation is a process of adding control information as it passes down through the layered model such as Open Systems Interconnection (OSI) Model# and Internet Protocol Suite (TCP/IP)#. It is in direct contrast to Decapsulation.

Decapsulation is a process of removing control information as it passes down through the layered model such as Open Systems Interconnection (OSI) Model# and Internet Protocol Suite (TCP/IP)#. It is in direct contrast to Encapsulation.

Data Link layer is the second layer for #Open Systems Interconnection (OSI) Model. It is referred as Link Layer together with Physical Layer in #Internet Protocol Suite (TCP/IP). Its responsibility is to establish a communication session between two different devices at node level regardless of network types. It will encapsulate# the data with a header that includes the information about the protocol used and the source and destination Media Access Control Address (MAC)#. All Ethernet switching and bridging are done here. Its #Protocol Data Units (PDU)# is a frame.

Application Layer is the seventh layer in the #Open Systems Interconnection (OSI) Model. The main functionality for it is to provide networking services to user or application, for it to be ready to be sent down all the way down to Physical Layer. Networking engineers usually refer Session Layer, Presentation Layer and this layer as a single layer called Application Layer.