1.2.1 Physical Alternatives (Layer 1 OSI Model),
- many simultaneous communications on same wire at same time, using varied frequencies for transmit channels and receive channels.
- uses a head end remodulator to retransmit the signal
- each station needs MAP hardware
- for very large factories
- uses a 1 inch (2.5 cm) thick cable
- maximum 10 Megabits/sec. per channel
- less expensive
- uses smaller cables
- rate of 5 to 10 Megabits second (single channel)
• Other Equipment,
- allows connections between different network types (such as a connection between Broadband and Carrierband)
1.2.2 Data Link Layer (Layer 2 OSI Model),
• Real time response was required, so token passing is used.
• Token passing allows a ‘token’ to be passed between computers, whichever computer has the token is given control of the network.
• The token is continually passed to each machine on a network.
• If a token passing ring is broken, the computers will wait, and eventually each half of the broken ring will have tokens being passed.
• Extensive algorithms have been developed for control of token passing, and resolution of conflicts.
• Preferred Standards.
• Preferred LAN is IEEE 802.4 token-passing bus.
• Uses standard ISO network, transport, session, and presentation layers.
1.2.3 Application Layer:
• Some specifics,
- FTAM (File Transfer Access Method) for file transfer
- MMS (Manufacturing Message System) for content of messages bound for robotic equipment
- ACSE (association Control for Service Elements) for program to program communication.
- Set of protocols should make communication between heterogeneous devices, not only in moving data around, but also in communication the meaning of that data.
- MAP has been delayed because of changes to the standard between 2.1 (1985) and 3.0 (1988)
- A version of MAP, EPA (Enhanced Performance Architecture) has been developed, and is supported by the process control industry, and CNMA (Communication Networks for Manufacturing Applications)
- CNMA has lobbied for the inclusion of Ethernet (IEE 802.3) as an alternative for the standard.
• MAP Layers Compared with the ISO/OSI Reference Model
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