TransferJet CNL Connection Layer

- details of TransferJet CNL connection layer: how it works to establish maintain and release connections and data links.

The TransferJet connection layer, CNL, is used to establish, maintain and release the data links.

The connection layer, CNL is an integral part of the overall TransferJet data stack, interfacing to the physical layer and to the higher layers within the stack.

TransferJet CNL basics

The OSI layer model defines a total of seven layers. The TransferJet Connection Layer, CNL, fulfils the actions of two layers, layers two and four. There is no layer three because TransferJet is a point to point, P2P only application.

TransferJet Connection Layer and OSI Layers
OSI Layer Layer Function TransferJet Layers
Layer 7 Provides human users and other programmes with services that use data communications User Applications
Layer 6 Converts data received from Layer 5 to a format that can be interpreted by the user or data sent from layer 7 to a suitable format for data communication User Applications
Layer 5 Establishes or releases a virtual path or connection for communication programmes to exchange data. Layer 5 PCL
Layer 4 Performs data compression, error correction, retransmission control, etc, to ensure secure and efficient data delivery to destination. TransferJet Connection Layer, CNL
Layer 3 Selects a communication path to deliver the data to the destination amd manages the addresses within the communication path. Not required within TransferJet as it is a point to point application only.
Layer 2 Secures a physical communication path to the destination and detects and corrects errors in the data flowing along the path. TransferJet Connection Layer, CNL
Layer 1 Responsible for the electrical conversion and other mechanical tasks needed to send data over the communication link. For wired connections, this may even include elements such as pin connections although for RF it includes the RF characteristics, etc. TransferJet physical layer

The data payload for the physical layer is assembled and disassembled within the Connection Layer. The payload is carried as a CPDU or Connection Layer Protocol Data Units. This contains headers, sub-headers, CRC bits and one or two payload packets of 4096 Bytes.

TransferJet CNL Connection Layer data structure
TransferJet CNL Connection Layer data structure

TransfetJet is a point to point system, i.e. there are two devices in any transfer. The device that transmits the initial connection request is known as the initiator and the device that responds is known as the responder.

The initiator sends out request signals to other devices - this may occur continuously, or at specific intervals as required.

The responder will respond to these initiation signals. However in its "search state" the responder can minimise its power consumption by operating intermittently. In this way, much of the circuitry can remain off for longer periods of time.

As with many wireless or other communication systems, provision has to be made for the possibility of a clash of signals. In the case of TransferJet, it is possible that more than one device may be trying to establish communications. In this case the Connection Layer, CNL will arbitrate the media access and select a single connection by applying a random back-off process.

One of the key elements of TransferJet is that it is a one to one, point to point data transfer system. No network connections exist. Therefore no network layer, layer 3 is required by the system. Accordingly the TransferJet Connection Layer, CNL communicates with both the Physical Layer in one direction, and the PCL which is effectively Layer 5.

By Ian Poole

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