Transport Layer (7Eh) and (7Dh)

Isotropic Sensor Network Specifications, Transport Layer

OSI: Transport Layer

Keywords: Connection/-less network, flow control, reliable transport service, low communication overhead, sensors, internet of things, embedded systems, sensor networks

Document: ISN-Transport-1.x released on September 15, 2018 by Isotel, (c) All Rights Reserved

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Isotropic Network Specifications: Transport Layer 1.x by Isotel is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.
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Note: Any adaptations to this specifications made by groups, individuals or companies are according to the license not allowed for general publication, but we strongly encourage you to send your modifications back to us for further consideration for the next releases.


The scope of this project is to define the Isotropic Sensor Network Transport layer for broadcast and peer to peer connection in distributed sensor area network, wired or wireless, low and high data rate devices, battery powered devices, short-range devices with short operational space, low-cost devices to support trivial sensors, besides the fully featured devices.


The purpose of this specifications is to provide a standard for low complexity, low cost, and low power (aware) consumption devices (sensors) to provide a connection-less and reliable connection-oriented network in combination with a Sensor Frame layer.

Key features

  • Adds Logical Ports and Sequence Counters
  • Basic Hand-Shaking
  • Low-Cost and Compact Implementation

Definitions, Acronyms and Abbreviations

An entity containing this protocol implementation. Also referred as sensor device or just sensor or device.
The format of aggregated bits that are transmitted together in time.
The format of aggregated bits that are transmitted together in time across the physical medium.
least significant byte/bit
most significant byte/bit

Packet Formats

Protocol defines short and long frame formats:

  • short frame format supports connection-less network, with up to 64 logic ports and 2 pending transactions
  • long frame format supports connection-oriented network, with up to 256 logic ports, 8 pending transactions, and flow-control acknowledge bits

Both protocol can be nested to address larger space and more complex structures.

Short Frame Format (16-bits)

Fields Protocol ID Port Counter Payload
Bits 8 6 2 N
Value 0x7E 0-63 0-3 user
Protocol ID:
defines the unique protocol identification number
logical port 0..31
packet counter 0..3
User Payload:
of arbitrary length, typically defined by upper or nested Frame Layer (80h+)

Long Frame Format (24-bits)

Extends the Short Frame format and adds optional hand-shaking with two acknowledge bits.

Fields Protocol ID Port Counter Ack Payload
Bits 8 8 14 2 N
Value 0x7D 0-255 0-16383
Protocol ID:
defines the unique protocol identification number
logical port 0..255
packet counter 0..16383
User Payload:
of arbitrary length, typically defined by upper or nested Frame Layer

Opening and Closing Port

Opening a port starts with a first message from or to selected port and non-empty message.

Any side may close the port by sending an empty message, a message which does not contain any user payload.

Packet Counter

In general counter is incremented after every transmission of a packet,

Acknowledge Bits

To be revised.

Document Changes

Date Release Changes
January 17, 2015
Initial specifications.
February 21, 2016 1.0 Public version of Renewed Sensor Transport Layer
September 15, 2018 1.x Reviewing in progress



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