1、SMPTE EGU30 95 H 8357401 OOOLBL3 375 H EG 30-1995 SMPTE ENGINEERING GUIDELINE Implementation of ESlan Standards 1 Scope This guideline defines the architecture, the compo- nent layers, and the relationships governing the ESlan-1 and ESlan-2 suite of control and data net- works to be used for audio a
2、nd television program production, post-production, and distribution equip- ment. It should be read in conjunction with SMPTE EG 29, which describes the basic control system; with SMPTE 275M, which defines the services and proto- cols contained within the lower layers of the network model for moderat
3、e-scale systems; and with other documents as listed in annex A. 2 Introduction The function of a remote control system is to establish connection between operational controlling and con- trolled devices. The ESlan specification is based on the concept of distributed intelligence. The use of distribu
4、ted intelligence within 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 node network; - the number of time-critical messages for transfe
5、r between nodes is minimized; - the control system is independent of the type of device connected to the node. Page 1 of 7 pages 3 OSIModel 3.1 OS1 and its relationship with the ESian control system In keeping with common networking practice, the interface for the ESlan remote-control system has bee
6、n defined so as to comply with the layered struc- ture of the open systems interconnection (OSI) model of the IS0 (see IS0 7498). 3.2 Principie of layering Layering divides the whole service offered by a com- munications system into logical layers (see figure 1). Each layer adds value to the service
7、 provided by the preceding layer. The additional value is established by an entity residing in that layer. Two entities operat- ing in the same layer, but in different parts of the network, are called peer entities. The objective is to permit communication between peer entities. This communication i
8、s governed by a protocol. The communication path between peers passes through lower layers, is connected over a physical medium, and is passed up again through the layers to the peer entity. Such communication is effected tran- sparently to the entity. The separation between any two layers is called
9、 an interface. The point where a communication path crosses an interface is called a service access point (SAP). The SAP that provides a physical connection is called a connection end point (CEP). Copyright O 1995 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartcdale Ave., White
10、 Plains, NY 10607 (914) 761-1100 Approved January 1,1995 - S e r V I C e - S e r V I C e - SYSTEM A SYSTEM B Service Access Point (SAP) -Interface -+-f 2 - Interface 1 7- I - Interface Point (CEP) - - Physical Link Connection End Figure 1 - System architecture terminology 3.3 OS1 model 3.3.1 The OS1
11、 model defines a seven-layer model providing the following functions: particular participant of those available in the session. It connects two presentation entities, providing housekeeping services (remapping, error recovery etc.). 3.3.1.1 Application layer 7 defines the users application tasks in
12、abstract terms. Each appli- cations entity serves a physical device, and is device specific, varying according to the charac- teristics of the device. 3.3.1.2 Presentation layer 6 gives a presentation of these abstract terms in coded and strictly formatted forms. 3.3.1.3 Session layer 5 is concerned
13、 only with a session involving more than one participant. It associates the coded and formatted data with a 3.3.1.4 Transport layer 4 provides for safe trans- port of data from end to end of a system. 3.3.1.5 Network layer 3 dismembers and re- assembles transported data into packages for sequential
14、transfer via a network system. 3.3.1.6 Data link layer 2 establishes a data link providing reliable error-free transmission in the presence of line disturbances. Where applicable, the association achieved in layer 5 is converted to an absolute system address. Layer 2 estab- lishes a communication be
15、tween physical units. Page 2 of 7 pages 3.3.1.7 Physical layer 1 defines the hardware properties needed to set up a physical link for the logically linked data. It should be emphasised that data passes physically only at layer 1. Higher layers are connected by a virtual (logical) connection. No laye
16、r provides confirmation of delivery by itself. An appropriate protocol is necessary if this capability is required. 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
17、 layers 7,6, and 5 are concerned with the specific application services and layers 4 to 1 relate to the general transport service. 3.3.2 The OS1 model applied to a television or audio equipment control system provides the following functions: 3.3.2.1 Application layer 7 provides an applica- tions pr
18、ocess which 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 inter- face to connect the entity to the lower network layers. The interface is device specific, and will vary according to th
19、e characteristics of the equipment being controlled. The application layer is not within the scope of ESlan (or ESbus) documentation. 3.3.2.2 Presentation layer 6 contains the virtual machine which responds to defined data -the control language - in a defined way, regardless of the characteristics o
20、f the physical machine used at the applications level. Each type of virtual machine utilizes a distinct dialect within the overall control language. Common and virtual machine (type-specific) messages are presentation layer constructs. 3.3.2.3 Session layer 5 connects two presenta- tion entities and
21、 controls communications between them. It provides services such as mapping logical addresses to physical addresses, error recovery, and identification of the dialect required for the type of machine used. System service control messages relating to linking and grouping are considered session layer
22、activities. 3.3.2.4 Transport layer 4 manages data to and from the session layer, isolating it from potential changes in hardware technology. To do this, the layer may break up messages into smaller packets, and provide a means for them to be received correctly at the other end. The layer provides f
23、or safe transport of system data. 3.3.2.5 Network layer 3 provides message block- ing (concatenation) and segmentation to allow more effective use of the message block. 3.3.2.6 Data link layer 2 establishes communica- tion between physical units connected to a net- work, and provides data synchroniz
24、ation, data transfer, and error recovery services. Local net- works include an access sublevei within the data link layer which apportions the use of the net- work between several connected entities. The access method to be used for ESlan-2 is yet to be defined; for ESlan-1 it is ANSVIEEE 802.3 (CSM
25、AKD) with the “length” field replaced with a 2-octet “type” field; and for ESbus, it is polling initiated by the bus controller. 3.3.2.7 Physical layer 1 consists of electrical and mechanical specifications which define the actual communications channel. 3.4 ESlan architecture ESlan is defined in te
26、rms of the six lower layers of the OS1 model (see table 1). Taken together, these six layers provide all the essential features of the remote- control system. (Proprietary machine commands are considered to be resident in the OS1 application layer and are, therefore, beyond the scope of the ESlan sp
27、ecification.) ESlan defines control-system elements in terms of an ideal “virtual” machine for each specific machine type - video tape recorder, audio tape recorder, telecine, router, etc. The virtual machine command structure is referred to as the control message architecture. Each specific machine
28、 type is allocated a set of messages - a dialect - which takes account of all Page 3 of 7 pages EG 30-1995 user-accessible control functions and machine responses. The lists of messages appropriate to each equipment type, and details of the corresponding bit representations, are provided as individu
29、al SMPTE Recommended Practices. Additionally, control messages common to all types of equipment are defined in SMPTE RP 172 and are termed common messages. 3.5 Relationship between ESlan and ESbus SMPTE 207M, SMPTE RP 11 3, SMPTE RP 138, and SMPTE RP 139 together define the ESbus standard, which can
30、 be employed for localized, small-scale, network operation. Devices communicate on the ESbus through communication handlers called tribu- taries. Using a polling protocol, a bus controller transfers messages between tributaries at a data rate of 38.4 kb/s. To attain higher performance, ESlan uses th
31、e higher data rates provided by CSMNCD networking technology. ESbus networks can coexist with ESlan on the same network through the use of gateways. It must be emphasised that thevirtual machine control messages are identical across all ES systems. 4 Network structure To accommodate the requirements
32、 of various sized facilities, ESlan has been implemented in a perform- ance hierarchy of compatible network architectures (see table 1 which includes ESbus for reference). ESlan-1 (as shown in table 1) is intended for applica- tion in small- to moderate-sized facilities requiring modest levels of pe
33、rformance. A study to determine limiting parameters on the size of ESlan-1 installa- tions is presently being undertaken by the SMPTE. ESlan-2 is intended for application in facilities which a) are of larger size than those anticipated by ESlan-I, or b) require a wider range of services than those a
34、nticipated by ESlan-1, or c) require a greater range of traffic types than that permitted by ESlan-I. Table 1 - Comparative structures of the ES architectures OS1 layer ESbus ESlan-1 Eslan-2 Application Presentation Session Transport Network Data link Physical Proprietary Virtual machine System serv
35、ice O (SMPTE RP 163) System service O (SMPTE RP 163) Supervisory protocol Supervisory protocol Electrical/mechanical Proprietary Virtual machine System service (SMPTE EG 30) RFC 768 RFC 791 RFC 826 Proprietary Virtual machine System service 2 (To be developed) To be decided RFC 791 RFC 826 ANSI/IEEE
36、 802.3 One or more interconnected standard networks providing an aggregate data rate much greater than that of CSMA/CD, to be spec- ified in ESlan-2 documentation. Physical interfaces Page 4 of 7 pages 5 Comparative ESlan layer structure (ESbus is included for reference) 5.1 Application layer 5.1.1
37、ESlan-1 The application layer employs proprietary manufac- turer-specific commands outside the scope of the specification. 5.1.2 ESlan-2 The application layer employs proprietary manufac- turer-specific commands outside the scope of the specification. 5.1.3 ESbus The application layer employs propri
38、etary manufac- turer-specific commands outside the scope of the specification. characteristics of the physical machine attached at the application level. Each type-specific virtual machine utilizes a distinct dialect. 5.3 Session layer 5.3.1 ESlan-1 A system service level (defined within SMPTE 275M)
39、 provides all necessary services of the session layer. These include mapping logical addresses to physical addresses, identification of the dialect required for each type of machine used, message segmentation and assembly, message blocking, and error recovery. 5.3.2 ESlan-2 A further system service
40、level (yet to be determined) will expand upon the range of services contained within ESlan-1, to provide additional facilities such as name serving and priority definition. 5.3.3 ESbus 5.2 Presentation layer 5.2.1 ESlan-1 The presentation layer is referred to as the virtual machine level. It contain
41、s the virtual machine, a logi- cal entity that responds to defined data (the control messages) in a defined manner, regardless of the characteristics of the physical machine attached at the application level. Each type-specific virtual machine utilizes a distinct dialect. The system service level (S
42、MPTE RP 163) provides all necessary services of the session layer. 5.4 Transport layer 5.4.1 ESlan-1 Services within this layer are provided by UDP (see RFC 768). 5.4.2 ESlan-2 5.2.2 ESlan-2 The presentation layer is referred to as the virtual machine level. It contains the virtual machine, a logi-
43、cal entity that responds to defined data (the control messages) in a defined manner, regardless of the characteristics of the physical machine attached at the application level. Each type-specific virtual machine utilizes a distinct dialect. 5.2.3 ESbus The presentation layer is referred to as the v
44、irtual machine level. It contains the virtual machine, a logi- cal entity that responds to defined data (the control messages) in a defined manner, regardless of the EG 30-1995 A protocol for the transport layer within ESlan-2 is under current consideration by the SMPTE. No recommendation can be mad
45、e at the present time. 5.4.3 ESbus The system service level provides all necessary serv- ices of the transport layer (see SMPTE RP 163). 5.5 Network layer 5.5.1 ESlan-1 Services within this layer are provided by RFC 791 (W Page 5 of 7 pages SMPTE EG*30 75 8357403 000383B 757 I EG ml995 Additionally,
46、 RFC 826 (ARP) is employed in order to relate IP addresses to CSMNCD addresses. (It should be noted that ARP requests are sent as “broad- casts” and all receiving devices must be capable of responding to ARP requests.) access sublevel within the data link layer, which apportions the use of the netwo
47、rk among several connected entities. The access method used by ES- bus is polling, initiated by the bus controller. 5.7 Physical layer 5.5.2 ESlan-2 5.7.1 ESlan-1 As with ESlan-1, services within this layer are pro- vided by the IP and by ARP. 5.5.3 ESbus The supervisory level provides all necessary
48、 services of the network layer (see SMPTE RP 113). It estab- lishes communication between physical units connected to the network, and provides data synchro- nization, data transfer and error-recovery services. 5.6 Data link layer 5.6.1 ESlan-1 ANSVIEEE 802.3 (CSMNCD) is selected to provide the nece
49、ssary services of the data link layer. As in the data link layer, ANSVIEEE 802.3 (CSMAKD) has been selected, operating at 1 O Mb/s. The physical medium and its access mechanism shall be in accordance with accepted CSMNCD practice. These may include AUI, 1 OBase2, 1 OBaseT, etc. 5.7.2 ESlan-2 The network configuration will include one or more interconnected standard networks providing an aggregate data rate much greater than that of CSMNCD, to be specified in ESlan-2 documenta- tion. Equipment bearing ESlan-l (or ESbus) inter- faces will remain connectable via protocol
