Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Manual do Utilizador descarregar pdf (Página 18)

Chapter 1

Publication

17706.5.16 - October 1996

Network Layers

Your network is made up of several layers, including:

Physical layer transmits bits between communication devices.

Datalink layer runs protocol to guard against errors, detects errors, and corrects

errors. Packages data and puts it onto the physical cable. Manages the flow of the

data bit stream into and out of each network node.

Network

layer establishes connections for communication between network nodes.

Transport layer performs segmentation and reassembly of messages.

Provides recovery from transmission errors.

Session

layer establishes and terminates network communications between

applications.

Presentation

layer manages data formats for the applications.

Application layer serves as the window through which applications access

communication services, including file transfers, virtual terminal functions, and email.

Nodes send data through the layers.

In this chapter, we discuss the physical, data-link, and application

layers. (We refer to the data-link and application layers as the

software layers.) This chapter contains these sections:

Section Page

Physical Layer 1-2

Software Layers 1-7

Message Packet Structure

1-9

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 250 251

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Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Manual do Utilizador Página 18