 Structure of EIA553 Since we claim that every protocol can be designed by defining a suitable logi- cal network structure, a discrimination and a message handling model, we will do just that as a reverse engineering effort on EIA553. First, apply a logical network structure and identify the discrimination functions that are supported by EIA553 message formats, SO that individual protocol networks can be identified. For the latter part, we will focus on the process control system. As a result of investigating EIA553 in that respect, the logical node/protocol element model for the MS, depicted in Fig. 5.33, emerged. EIA553 MS physical node Terminal Process Controller InService CallControl In-service messages control Service access McsMessTrain control Broadcast messages data handling OvhMessTrain messages Integrator MessTrain messages Audio (RECC) (FOCC) Processing Transport Access interface control (MS-network) (FVC, (FOCC, RECC) Transport protocol RF transport node FOCC,RECC,FVC,RVC Fig. 5.33 The logical node model for an EIA553 MS The model shows only the units that terminate the EIA553 protocol. How these units cooperate inside the MS is not shown, since we only intend to describe the messages. A short description of the structure follows: The functionality of the MS is separated into three logical nodes and corre- sponding logical networks: the terminal process controller (part of the process control system), the RF transport node (part of the resource system for connec- 5.5 The EIA553 Case Study tion handling), the audio processing unit (part of the resource system for tele- service handling). 2. The RF transport node handles four types of unidirectional 30-kHz radio chan- nels: FOCC, RECC, FVC and RVC. There is often only one FOCC (network to MS) and RECC (MS to network) in each cell, used for control signalling between MSs and the network, before an MS has entered in connection with its remote counterpart (in data communication called "the data phase"). After that, audio signals (voice or data) over the ra