ZETRON 2000 Series Especificaciones descargar pdf (Pagina 135)

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TNPP Details

The other network configuration is duplex, which allows a bi-directional exchange of data

between terminals. A terminal is directly connected to one or more terminals using duplex

links, one link for each node to which it connects. One terminal does not need to be

directly connected to another terminal node in order to exchange data. What does matter is

that there is a chain of nodes that connect the two terminals. In duplex mode, TNPP nodes

pass data packets in a bucket brigade fashion. Each node in turn passes the packet along to

a node nearer the destination of the packet.

Figure 31: A Simple Duplex System

Even when traffic in a system is always in one direction, duplex mode is preferable. In

duplex mode, each received packet will cause a response code to be sent back to the node

that sent the packet. The response codes are used to indicate in what condition the packet

was received.

In addition, during periods of inactivity the nodes will send link test messages to each

other. This bi-directional handshaking allows each terminal to monitor the state of the

inter-node links, and report any failures.

Each node is assigned its own address, the node address or node ID, that is unique within

the particular network the node is part of and which is often referred to as the primary

node ID. This node address may be used to identify what node is the origin of a packet,

and to direct a packet to a particular node.

With some implementations of TNPP, including Zetron's, a node may have several

secondary node addresses. A secondary address may be used simply as an alias for a

given node to separate classes of pages for some reason. A secondary address may also be

shared by several terminals in what is called page and pass. This allows the assigning of a

single secondary node address to some wide area function. As an example, a group of

terminals might use the address “5555” with all “wide area P5” pages.

Acknowledge (ACK) the packet was received correctly

Negative Acknowledge (NACK) a transmission error was detected

Resend temporarily there was not room to hold the packet

Cancel there was something unacceptable about the packet

Page

MODEL 2200

PAGING TERMINAL

MODEL 2200

PAGING TERMINAL

ACK

PagePage

ACK

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ZETRON 2000 Series Especificaciones Pagina 135