1、SMPTE STANDARD ANSVSMPTE 275M-1995 for Television and Audio Equipment - o c 3 o,- n r r ESlan-1 Remote Control System 1 Scope This standard defines the services and protocols contained within the physical, data link, network, transport, and session layers of ESlan-1, a control and data network for u
2、se in television and audio program production, post-production, and distri- bution equipment. ESlan-1 is intended for applica- tion in small- to moderate- sized facilities requiring modest levels of performance. A study to deter- mine limiting parameters on the size of ESlan-1 installations is curre
3、ntly being undertaken by the SMPTE. Page 1 of 12 pages SMPTE Standards EG 30-1995, Implementation of ESlan RFC 768, User Datagram Protocol (UDP)* RFC 791 updated by RFC 1349, Internet Protocol (V* RFC 826, Ethernet Address Resolution Protocol (ARP)* RFC 1349, Type of Service in the Internet Protocol
4、 Suite (IPS) This standard isto be read in conjunction with SMPTE *For nfOmatOn On obtaining RFC documents, Contact EG 29, SMPTE EG 30, and with other documents listed in clause 2 and annex C. the 3 Introduction Engineering Department. 2 Normative references The following standards contain provision
5、s which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most r
6、ecent edition of the standards indicated below. ANSVIEEE 802.3-1 993, Information Technology - Lo- cal and Metropolitan Area Networks - Part 3: Car- rier Sense Multiple Access with Collision Detection (CSMAICD) Access Method and Physical Layer Specifications SMPTE EG 29-1993, Remote Control of Telev
7、ision Equipment In order to simplify as much as possible the interface between audio and television equipment and computer systems used to establish medium- to large-scale remote-control networks, ESlan-1 employs, wherever possible, standard or industry- standard networking services and protocols. I
8、ts archi- tecture complies with the model for open systems interconnection (OSI) defined by the International Organization for Standardization (ISO). (See IS0 7498.) The section ordering of this standard follows that described in the model for open systems inter- connection of the ISO, starting at t
9、he physical and rising to the session layer. The content of the presen- tation layer, the virtual machine, is contained within other SMPTE documents (see annex C). The content of the application layer, which is proprietary to users, is outside the scope of the ES hierarchy of network standards. CAUT
10、ION NOTICE This Standard may be revised or withdrawn at any time The procedures of the Standard Developer require that action be taken to reaffirm, revise. or withdraw this standard no later than five years from the date of publication. Purchasers of standards may recelve current information on all
11、standards by calling or writing the Standard Developer Printed in USA Copyrighi 0 1995 by THE SOCIETY OF American National Standard MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave, White Plains, NY 10607 (914) 761-1100 Approved June 6,1995 SMPTE 27511 95 = 8357403 0003985 442 ANSVSMPTE
12、2751111-1995 4 Structure of the ESlan-I addressing scheme 4.1 ESlan-1 provides for layered addressing from individual machines to the full wide-area network. 4.2 Each individual node on the network has a specific CSMA/CD address. The CSMA/CD (6- octet, 8-bit byte) destination and (6-octet) source ad
13、dresses are transmitted first within a message packet. 4.3 The Internet (IP) (4-octet) source address and (4-octet) destination address contained within the IP header follow the CSMA/CD ad- dresses. 4.4 Each individual item of equipment on the network is allocated one of the 8064 (2-octet) device ad
14、dresses fully compliant with existing ESbus systems. 4.5 A device group addressing scheme is pro- vided. This operates in conjunction with the delegation bitmap (see 8.4). 4.6 The data structure of the ESlan-1 message packet is shown in figure 1. 5 Physical and data link layers and access control 5.
15、1 The physical connection and data link services shall be provided by a 10 Mb/s data communication highway operating under ANSIA E EE 802.3. The physical medium and its access shall be in ac- cordance with accepted CSMNCD practice. It may include AU, 1 OBase2, 1 OBaseT, etc. Any limitation in segmen
16、t length for a particular medium can be over- come by the use of bridges and repeaters. However, the latency of such devices and multipaths to a CSMA/CD Destination Address (6 octets) (TRANSLLPITED FIRST) CSMA/CD Source address (6 octets) Type pieid (2 octets) 1p Header as described in RFC 791 UDP H
17、eader as described in RFC 768 ESan-1 Version number (1 octet) Destination Device address (2 octets) Source Device addreee (2 octets) ESan-1 Packet sequence number (1 octet) I ESlan-1 Delegation Bitmap (4 octets) I ESlsn-1 Byte Count (i octet) Eslan-1 message (1 to 256 octeta) i/m DP/ARP n-1 Figure 1
18、 - Data structure of message packet (excluding preamble and postamble) Page 2 of 12 pages SMPTE 27511 95 U 8357401 000198b 389 - receiver within large networks must be considered within any network design. In networks extended by the use of such devices, it may prove necessary to use a protocol capa
19、ble of higher granularity in order to avoid timing errors in the receipt of messages. 5.2 The data packet shall be a CSMAICD packet, except that the “length” field (as defined in ANSIIIEEE 802.3) shall be replaced by a 2-octet “type” field whose value shall be set to 0800h, defining it as an Interne
20、t packet. 6 Network layer 6.1 The network layer of ESlan-1 shall employ the RFC 791 Internet protocol (IP), as updated by RFC 1349. 6.2 RFC 826 address resolution protocol (ARP) shall be used to determine the CSMAICD address of a device for which only the IP address is known. 7 Transport layer The t
21、ransport layer of ESlan-1 shall employ RFC 768 user datagram protocol (UDP). 8 Session layer 8.1 Version number Asingle octet field within each message block is used to determine the ESlan-1 version number in order to allow for future developments. The version described by this standard is version z
22、ero (O). 8.2 ESlan-1 addressing 8.2.1 Association directory By the use of IP/UDP and ARP, it is possible to communicate with any ESlan-1 device by the use of sockets or streams. The addressing mechanisms provided by the IP and UDP protocols enable peer-to-peer communication sessions between devices.
23、 A device specifies the IP address and the port required when seeking connec- tion. For ESlan-1, the UDP port field shall be set to 420 (1A4h). ANSVSMPTE 2751111-1 995 The IP address identifies the particular node con- nected to the ANSIIIEEE 802.3 network; the unique UDP pori fiel XXXX (bound to a
24、specific socket) identifies this as ESlan-1 traffic, and the device address identifies the specific machine within the local area network. To establish a link with an ESlan-1 device, an asso- ciation between the IP address and the device ad- dress is required. Each network device shall establish and
25、 maintain an association directory, in order to map device addresses to IP addresses. The mapping of device addresses to IP addresses shall be aged. The aging mechanism used in ARP shall be followed. Address mappings older than those specified by the aging period shall be deleted. System service com
26、mands (see clause 9) are pro- vided which enable the association directory to be constructed and modified, and for the association status to be determined. 8.2.2 Individual machine selection An ESlan-1 device requiring communication with another ESlan-1 device shall first look for an IP address asso
27、ciation in its association directory. If no association information exists, then the device shall issue the system service command ASSOCIATION R EQU EST. This command shall be transmitted as a network broad- cast, since the IP address is generally unknown. The UDP ESlan-1 socket shall be specified,
28、and the network destination address set to broadcast format (all bits set to 1). The ESlan-1 destination address shall be used to specify the ESlan-1 device for which the association is required. Alternatively, the command may be directed to a specific network address to obtain the ESlan-1 device ad
29、dress connected to a known IP address. In this case. the ESlan-1 address field shall be set to zero. A network device that receives the ASSOCIATION REQUESTcommand at its ESlan-1 UDP portconnec- tion shall check the ESlan-1 destination address field. Page 3 of 12 pages SMPTE 275N 95 8357403 0003987 2
30、35 ANSVCMPTE 275M-1995 If the specified ESlan-1 address is not a controlled device at that network connection, no response shall be given. If the specified ESlan-1 address is a device controlled at that network connection or the ESlan-1 address is O, then an ASSOCIATION STATUS response shall be retu
31、rned. Note that the network design requires that the ASSO- CIATION REQUEST shall reach all nodes. 8.2.3 Group machine selection This mechanism enables a number of ESlan-1 devices to respond to a single group address. Potentially, any network device may make a group assignment. Group assignment shall
32、 operate in conjunction with the delegation bitmap in order to avoid conflict between different devices each attempting to assign group addresses. Therefore: - Network devices capable of group assignment shall be given unique bitmap values (.e., no bit- setting shall be repeated on another device th
33、at may assign group addresses); -An ESlan-1 device given a new bitmap setting shall clear any previous group address assign- men t(s) . 8.2.4 Group mode communication Acommand to be actioned by a group of devices shall be sent as a network broadcast, and with the ESlan-1 destination address field se
34、t to the previously as- signed group address. No acknowledge or error messages shall be returned by any device in response to a group mode or broad- cast message, with the exception of ASSOCIATION REQUEST. 8.3 Packet sequence number In order to confirm the correct sequence of packets in an ordered s
35、equence of commands, each packet shall contain a sequence number field. Transmitting devices shall increment the packet sequence number by 1 modulo 256 for each packet transmitted in the stream to each destination address. A receiving device shall compare the sequence number of each newly received,
36、correctly addressed packet from the same ESlan-1 source address with that of the previously addressed packet using modulo 256 arithmetic. If an out-of-sequence packet is received, other than NOOP, it shall be discarded and a system service error message with exec code returned. 8.4 Delegation bitmap
37、 It is possible that a command may be sent to a destination by a source not authorized to control that destination; for example, an edit command to the wrong VTR. To minimize the possibility of responding to an unauthorized command, a delegation bitmap (32-bit) field is provided. A bitmap field valu
38、e shall be assigned to each opera- tional device within an operational session, and this value shall be attached to each message from that device. When a destination device receives a source message, it shall perform a logical AND on the source delegation bitmap field and its own internai delegation
39、 bitmap field. Initial session values shall be set such that if the result is NON-ZERO, the message shall be accepted and if the result is ZERO, the message shall be ignored and the session management error mes- sage , with exec code , returned. (A detailed description of this mechanism is given in
40、annex A.) 8.5 Bytecount The byte count field shall contain a byte count of the message to follow. Byte count is an unsigned 8-bit value. 8.6 Message block field This field shall contain any ESlan-1 message, such as a system service, common, or dialect type-specific message. Page 4 of 12 pages SMPTE
41、27511 95 8357403 0003988 351 ANSUSMPTE 275M-1995 9 System service commands and responses 9.1 Keywords SYSTEMSERVICENOOPEFL“ (SNOP) System service no-operation. Format: Reserved for BEGIN (RBGN) Reserved for END (REND) In Eslan-1 operations, these two keywords shall be used for two purposes: firstly
42、as BEGIN and END delimiters Format: and secondly for flow control. If a device, receiving many messages from another device, is unable to receive more data for a short period, it shall issue the keyword. This shall cause the sending device to stop sending until the receiving device issues the keywor
43、d reenabling transmission. On receipt of the keyword, a device shall either continue with its interrupted transmission or, if its transmission has been completed, shall send a keyword (coot-,). A device employing this flow control shall incorporate a timer. On receipt of the keyword, the timer shall
44、 be started. If the keyword is not received before the timer expires, the keyword shall be deemed to have been lost, and transmission shall be resumed. The duration of the timer is not specified. It is left to the system designer to determine the optimum duration for each system. The receipt of mult
45、iple or keywords shall be treated as if a single command only had been received. SYSTEM SERVICE RESET (SRST) Resets all system service level functions to the power-up default state. Format: INITIAL SEGMENT (ISGT) Directs the session (system service) layer to commence message segment assembly. Page 5
46、 of 12 pages SMPTE 2751 95 8357401 0001989 098 ANSVCMPTE 275M-1995 Format: 8-bit binary unsigned number; count zero shall be the final segment. NOTE - The final octet of a data segment shall be the final octet of the block. cO5p SUBSEQUENT SEGMENT (SSGT) Directs the session (system service) layer to
47、 continue segment assembly. Format: BLOCK (BLCK) Format: 8-bit binary unsigned number; count zero shall be the final segment. Directs the session (system service) layer to disassemble virtual machine messages which have been concatenated within a single supervisory level frame. The BLOCK command sha
48、ll be employed to delimit messages on every occasion where message concatenation is employed. 8-bit binary unsigned number, specifies the length of the individual blocked message, in octets, not including the byte count. SYSTEM SERVICE ERROR (SERR) Advises that the system service command in the last
49、 frame received had not been understood, or could not be performed. Following receipt of a SYSTEM SERVICE ERROR, no further processing shall take place on the frame, although any virtual machine messages encountered up to that point shall be forwarded. Format: 8-bit: O0 - parse error O1 - unrecognized command 02 - insufficiently equipped 03 - buffer overflow 04 - invalid keyword argument 05 - destination device unavailable 06 - out-of-sequence packet number 8 bits, not including the byte count. Page 6 of 12 pages SMPTE 27511 95 8357403 OOOL990 BOT M ASSOCIATION REQUEST (ASRQ)
