1、SMPTE EG*29 93 8357401 O000125 823 = Remote Control of Television Eq u i pment EG 29-1993 1 Introduction This guideline provides a guide to the architecture of the SMPTEEBU ESbus digital control interface and related interfaces, which were developed for the purpose of standardizing the control of te
2、levision equip- ment. The digital control interface was developed jointiy by the SMPTE and the European Broadcasting Union (EBU). The referenced documents define the technical spec- ification and system characteristics required to allow the control of television production and distribution equipment
3、. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this guideline. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this guideline
4、are encouraged to investigate the possibliity of applying the most recent edition of the standards indicated below. ANSVSMPTE 207M-1992, Television - Digital Control Interface - Electrical and Mechanical Char- acteristics SMPTE RP 113-1 992, Supervisory Protocol for Digital Control Interface SMPTE R
5、P 138-1 992, Control Message Architec- ture SMPTE RP 139-1 992, Tributary Interconnection SMPTE RP 163-1 992, Television - System Service Messages Page 1 of 5 pages SMPTE RP 170-1993, Video Tape Recorder Type- Specific Messages for Digital Control Interface SMPTE RP 171 -1 993, Type-Specific Message
6、s for Digital Control Interface of Analog Audio Tape Recorders SMPTE RP 172-1 993, Common Messages for Digital Control Interface 3 Application 3.1 Introduction The ESbus and associated interfaces establish the system characteristics required for the remote control of television equipment, from any l
7、ocation, by the employment of an intelligent processor which should ideally be an integral part of the controlled equipment. This digital control interface is based on the ESbus developed and documented by the SMPTE and EBU and is, therefore, made available by a multitude of manufacturers. Both SMPT
8、E and EBU are continuing to develop specifications for additional applications. This guide- line will be updated to reference the appropriate documents as they are completed. 3.2 Overview Afunction of any remote control system is to establish a connection between operational controlling and controll
9、ed devices. The ESbus system is based on the concept of distributed intelligence whereby each device is attached to the system by means of an intelligent interface that will carry out the majority of local calculations and logical operations required by the device. The intelligent equipment will be
10、called a tributary of the remote control system. Copyright Q 1993 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartcdale Ave., White Plains, NY 10607 Approved July 1, 1993 (914) 761-1100 SMPTE EG*Z 73 E3 8357YOL OOOOLZb 7bT I EG 29-1993 The use of distributed intelligence within
11、the control system offers a number of advantages: -the ability to modify elements of the configuration without affecting other users; - high resilience, the majority of failures can be contained within a single tributary; -the number of time-critical messages needing to be transferred between tribut
12、aries is minimized; - the control system is independent of the type of device. The basic functional unit of the remote control system is the local network which comprises an interface bus, a bus controller, and a number of tributaries as required by the user. The number of tributaries on any one loc
13、al network may range from one to a practical maximum of up to 32, although typically the number will probably be in single figures. The configuration may be either multipoint in which one controller and more than one tributary share acommon interface bus or, alternatively, point-to-point in which mo
14、re than one interface bus radiates from the bus controller and only one tributary connects to each bus. Where larger systems are required, there is provision for local networks to be interconnected via a separate interconnection bus accessed through a gateway. This gateway may be integral with the b
15、us controller. 3.3 System architecture The system architecture conforms largely to the Inter- national Organization for Standardization (ISO) architecture. This is the logical model used by the IEEE 802 Committee in its recommendations on local area networks (IAN). Progress in communications over se
16、veral years has led to the development of a structured technique to describe communication systems. The systems are viewed as logically com- posed of layers. Layering divides the whole service offered by the system in such a way that each layer adds value to the service provided by the lower layers.
17、 The layers and service referred to are logical in nature as distinct from a physical entity or software implementation. The logical functions are carried out in software resid- ing in hardware, but the implementation is carried forth using these logical entities to represent the software elements o
18、f the final program. This added value contributed by each layer is established by the char- acteristics of an entity residing in the layer. Two entities operating in the same layer but in different parts of the network are called peer entities. The aim is to permit communication between peer entitie
19、s; this communication is governed by a protocol. The route between peer entities using a protocol is only a virtual one; in reality, the communication path passes through lower layers and is completed over a physical medium, such communication being effected trans- parently. In software terms, the i
20、nterface is the logical line separating two layers. It is not necessarily a physical reality. The point where a communication path crosses an interface is called a service access point (SAP). The point within a SAP that provides a real connection is called a connection end point (CEP). 3.4 Internati
21、onal Organization for Standardiza- tion (ISO) Model OS1 The IS0 has established a model consisting of seven layers and specified the function of each. This is called open system interconnection (OSI) architec- ture. The OS1 reference model defines the following seven layers: Layer 7 serves the user
22、directly by defining his appli- cation tasks in abstract terms. An application pro- cess performs a function such as playing a tape. Each applications entity serves a physical device and is device-specific, varying according to the character- istics of the device. Layer 6 gives a presentation of tho
23、se abstract terms in coded and strictly formatted forms. The presenta- tion layer contains the virtual machine which re- sponds to defined data, the control language in a defined manner using a distinct dialect within the control language. Layer 5 is concerned only with session involving more than o
24、ne participant. It associates the coded and formatted data with a particular participant of those available in the session. It connects two pre- sentation entities providing housekeeping services . ,* O Page 2 of 5 pages - -_- SMPTE EG*2 93 8357YOL OOOOL27 bTb EG 29-1993 (remapping, dialect identifi
25、cation, error recovery, etc.). Layer 4 provides facilities for safe transport of data from end to end of a system. Layer 3 dismembers and reassembles transported data into packages for sequential transfer via a net- work system. Layer 2 establishes a data link providing reliable error-free transmiss
26、ion in the presence of line disturb- ances. Where applicable, the association achieved in layer 5 is converted to an absolute system address. Layer 2 establishes a communication between phys- ical units and is defined for the ESbus in SMPTE RP 113. Layer 1 defines the hardware properties needed to s
27、et up a physical link for the logically linked data and is defined for the ESbus in ANSI/SMPTE 207M. The above description shows: - how data generated by each layer is handed on from layer to layer; and - how the quality of service increases from bottom to top. It should be noted that layers 7, 6, a
28、nd 5 are con- cerned with the specific application service; layers 4 to 1 relate to a general transport service. The logical tributary encompasses layers 1 to 5 inclusive. 3.5 OS1 model applied to a television control system It is very helpful to define a remote control system for television equipme
29、nt using a layered technique. Because of the protection properties within the super- visory protocol SMPTE RP 113, (2), there is little need for additional end-to-end control facilities normally incorporated in entity (4). The remaining layers 7, 6, 5, 3, 2, and 1 are of particular importance for ES
30、bus digital control inter- face application. The applications layer (7) -An applications process performs a specified system function such as playing a video tape. Each applications entity consists of a physical device and the necessary hardware and software interface to connect the entity to lower
31、net- work layers. The interface is device specific and will vary according to the characteristics of the equipment being controlled. The applications layer is not within the scope of the ESbus documentation. The presentation layer (6) contains the virtual machine, which responds to defined data - th
32、e control language in a defined manner regardless of the characteristics of the physical machine used at the applications level. Each type of virtual machine uti- lizes a distinct dialect within the overall control lan- guage. Common and virtual machine (type specific) messages are presentation laye
33、r con- structs. The session layer (5) connects two presentation en- tities and controls communications between them. It provides such services as mapping logical addresses to physical addresses, identification of the dialect required for the type of machine used, error recovery, etc. System service
34、control messages relating to linkage and grouping are considered session layer activities. The transport layer (4) normally manages data to and from the session layer, isolating it from potential changes in hardware technology. To do this, this layer may break up messages into smaller packets, and p
35、rovide the means for them to be received correctly at the other end. It provides for safe transport of system data. There are arguably no true transport layer functions required by the ESbus structure; thus, it is considered that this layer?s function is encom- passed by the system service control s
36、tructure. The network layer (3) provides message blocking (concatenation) and segmentation such as to allow more effective use of the message block. System service control messages relating to blocking and segmentation are considered network layer activities. The data link layer (2) establishes comm
37、unication between physical units connected to the network and provides data synchronization, data transfer, and error recovery services. Local networks include an access sublevel within the data link which appor- tions use of the network between several connected entities. The access method used in
38、this guideline is polling initiated by the bus controller. SMPTE RP 11 3 supervisory protocol provides datalink layer functions. Page 3 of 5 pages SMPTE EG*29 93 8357401 0000128 532 0 EG 29-1993 The physical layer (1) consists of the electrical and mechanical specifications which define the actual c
39、ommunication channel. ANSVSMPTE 207M pro- vides these specifications. Figure 1 illustrates the functional distribution of ESbus functions within the OS1 model layers. Application Presentation Session Virtual Machine -a TP W mf3309Cs System % their effect, however, difers as between tributaries and t
40、he bus controller. Some system service messages address the bus controller only. These originate in a tributary and cause the bus controller to set up a new internal condition, or to originate further messages. Other system service messages are sent by the bus controller to accomplish linkage tasks
41、in tributaries. The content of the system service messages is de- scribed in SMPTE RP 163. 4.7 Common messages Common messages are used to perform certain func- tions common to all equipment types within a general- purpose communications channel of an interface system. The content of the common mess
42、ages is described in SMPTE RP 172. 4.8 Type-specific machine messages The documents listed in this section define the type- specific virtual machine messages which are applica- ble to specific types of machines. Type-specific messages applicable to various categories of equip- ment shall be as follows: - Audio tape recorders: - Video tape recorders: SMPTE RP 171 ; SMPTE RP 170. Page 5 of 5 pages
