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.
Protocol Data Units (PDU)
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User Datagram Protocol (UDP)
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.
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Transport Layer
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.
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Transmission Control Protocol (TCP)
It breaks messages into segments (its Protocol Data Units (PDU)#) and reassemble at the destination. If there is a failure on sending such messages, TCP will resend it. It also provides virtual circuits between application. At the end, the connection will be torn down if there is no need for it.
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Physical Layer
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.
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Open Systems Interconnection (OSI) Model
Information are passed in Protocol Data Units (PDU)#.
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Network Layer
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.
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Data Link Layer
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.