10.2 DETAILS

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10.2.1 Physical Alternatives (Layer 1 OSI Model),

Networks,

Broadband

- 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

Carrierband

- less expensive

- uses smaller cables

- rate of 5 to 10 Megabits second (single channel)

Other Equipment,

Bridge

- allows connections between different network types (such as a connection between Broadband and Carrierband)

10.2.2 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.

10.2.3 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