PCI Express is a layered protocol, consisting of a transaction layer , a data link layer , and a physical layer .

All this additional information, plus the original service data unit from the higher layer, constitutes the protocol data unit at this layer.

CSMA CA is a protocol that operates in the Data Link Layer (Layer 2) of the OSI model.

In a layered system, a unit of data which is specified in a protocol of a given layer and which consists of protocol control information and possibly user data of that layer.

Protocol operation EAPOL operates at the network layer on top of the data link layer, and in Ethernet II framing protocol has an EtherType value of 0x888E.

In the Internet Protocol Suite, TLS and SSL encrypt the data of network connections in the application layer.

The Datagram Congestion Control Protocol (DCCP) is a message oriented transport layer protocol.

In Open Systems Interconnection (OSI) terminology, a service data unit (SDU) is a unit of data that has been passed down from an OSI layer to a lower layer and that has not yet been encapsulated into a protocol data unit (PDU) by the lower layer.

The protocol is based on pairs of request response PDUs (protocol data units, or packets) exchanged over OSI layer 4 (TCP session or X.25 SVC3) connections.

Internetwork Packet Exchange (IPX) is the network layer protocol in the IPX SPX protocol suite.

In order to do this, the protocol layer will add to the SDU certain data it needs to perform its function.

UDP provides no guarantees to the upper layer protocol for message delivery and the UDP protocol layer retains no state of UDP messages once sent.

SSL is the Secure Sockets Layer protocol, a security protocol that provides communications privacy over the Internet.

Examples of application layer protocols include the Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), the Simple Mail Transfer Protocol (SMTP), and the Dynamic Host Configuration Protocol (DHCP).

AS Interface (Actuator Sensor Interface, AS i) is an industrial networking solution (physical layer, data access method and protocol) used in PLC, DCS and PC based automation systems.

On the ARPANET, the protocols in the Physical Layer, the Data Link Layer, and the Network Layer used within the network were implemented on separate Interface Message Processors (IMPs).

Since lower protocol layers were provided by the IMP host interface, NCP essentially provided a Transport Layer consisting of the ARPANET Host to Host Protocol (AHHP) and the Initial Connection Protocol (ICP).

SPARQL is a protocol and query language for semantic web data sources.

Packet switched data networks In the context of packet switched data networks, a protocol data unit (PDU) is best understood in relation to a service data unit (SDU).

Unless we have already arrived at the lowest (physical) layer, the PDU is passed to the peer using services of the next lower layer in the protocol stack .

ST uses the same IP address structure and the same link layer protocol number (ethertype 0x800) as IP.

In computer networking, Point to Point Protocol (PPP) is a data link protocol used to establish a direct connection between two nodes.

As an example of network layer over network layer, Generic Routing Encapsulation (GRE), a protocol running over IP (IP Protocol Number 47), often serves to carry IP packets, with RFC 1918 private addresses, over the Internet using delivery packets with public IP addresses.

Internet Relay Chat (IRC) is an application layer protocol that facilitates transfer of messages in the form of text.

The transmission of streaming data itself is not a task of the RTSP protocol.

In computer networking, Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support virtual private networks (VPNs) or as part of the delivery of services by ISPs.

This layer provides independence from data representation (e.g., encryption) by translating between application and network formats.

The SDU at any given layer, layer 'n', is the PDU of the layer above, layer 'n 1'.

Data carried by the ADSL are typically routed over the telephone company's data network and eventually reach a conventional Internet Protocol network.

When the PDU passes over the interface from the layer that constructed it to the layer that merely delivers it (and therefore does not understand its internal structure), it becomes a service data unit to that layer.

In OSI model equivalences, TLS SSL is initialized at layer 5 (session layer) and works at layer 6 (the presentation layer).

In iOS, there are four abstraction layers the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer.

In both models, TLS and SSL work on behalf of the underlying transport layer, whose segments carry encrypted data.

The Reverse Address Resolution Protocol (RARP) is an obsolete computer networking protocol used by a client computer to request its Internet Protocol (IPv4) address from a computer network, when all it has available is its Link Layer or hardware address, such as a MAC address.

See Sodium layer.