Editing Econet (section)

== Network and transport layers ==
Econet used a [[connectionless]] transmission model, similar to [[User Datagram Protocol|UDP]], with no checksumming or error correction at this layer. Each [[Network packet|packet]] had a four byte header consisting of:
# The destination station number
# The destination network number
# The source station number
# The source network number

A single data transmission consisted of four frames, each with a header as above:
# The sending station sends a ''scout'' packet with a port number and a [[flag byte]]
# The addressed receiving station returns a ''scout acknowledge'' to the sender
# The sending station sends the ''data''
# The receiving station finishes with a ''final acknowledge'', identical to the ''scout acknowledge''

Each device on a network segment is identified by a "station ID" number which serves a similar purpose to a [[MAC address]]. The address is not set at time of manufacture but is set manually and a network administrator must ensure addresses do not collide when new machines are installed. In the BBC Micro the station ID is set using [[Jumper (computing)|jumper]] pins on the motherboard. Conventionally a [[file server]] would be assigned station ID 254 but there is no specific requirement for this to be the case.

There was provision for ''[[Broadcasting (networking)|broadcast]] transmissions'', a single frame sent with its destination station and network numbers set to 255.  There was also provision for [[promiscuous mode]] reception, termed ''wild receive''
in the PRM, requested by listening for station and network numbers both being zero.

Technical details of packets and frames, the Econet API, and worked examples in ARM assembler and [[BBC BASIC]]
are given in the RISC&nbsp;OS Programmer's Reference Manual.<ref>{{cite book
|title=RISC OS 3 Programmer's Reference Manual
|publisher=Acorn Computers Ltd
|volume=2
|chapter=Chapter 47 - Econet
|pages=2–609 et seq
|isbn=1-85250-110-3
|date=1992}}</ref>