1.2 DETAILS

 

1.2.1 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)

 

 

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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