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1、 CEA Standard Control Network Protocol Specification CEA-709.1-B January 2002 NOTICE CEA Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and imp
2、rovement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any member or nonmember of CEA from manufacturing or s
3、elling products not conforming to such Standards, Bulletins or other technical publications, nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the standard is to be used either domestically or i
4、nternationally. Standards, Bulletins and other technical publications are adopted by CEA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, CEA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties ado
5、pting the Standard, Bulletin or other technical publication. Note: The users attention is called to the possibility that compliance with this standard may require use of an invention covered by patent rights. By publication of this standard, no position is taken with respect to the validity of this
6、claim or of any patent rights in connection therewith. The patent holder has, however, filed a statement of willingness to grant a license under these rights on reasonable and nondiscriminatory terms and conditions to applicants desiring to obtain such a license. Details may be obtained from the pub
7、lisher. This CEA Standard is considered to have International Standardization implication, but the International Electrotechnical Commission activity has not progressed to the point where a valid comparison between the CEA Standard and the IEC document can be made. This Standard does not purport to
8、address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (From Project Number
9、4183, formulated under the cognizance of the CEA R7.1 HCS-1 Subcommittee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2002 Technology Phone 800-854-7179; Fax 303-397-2740; Internet http:/; Email 3 Related Documents For complementary specifications, see references listed in the bibliography at th
10、e end of this document. 4 Definitions and Symbols 4.1 Use of Terms The following section introduces the basic terminology employed throughout this document. Most of it is commonly used and the terms have the same meaning in both the general and the EIA-709 context. However, for some terms, there are
11、 subtle differences. For example, in gen- eral, bridges do selective forwarding based on the layer 2 destination address. There are no layer CEA-709.1-B 2 2 addresses in the EIA-709 protocol, so bridges forward all packets, as long as the domain ad- dress in the packet matches a domain of which the
12、bridge is a member. Routers, in general, per- form network address modification so that two protocols with the same transport layer but dif- ferent network layers can be connected to form a single logical network. EIA-709 routers may perform network address modification, but typically they only exam
13、ine the network address fields and selectively forward packets based on the network layer address fields. 4.2 Definitions Channel: A physical unit of bandwidth linking one or more communication nodes. Refer to Annex E for further explanation of the relationship between an EIA-709 channel and a sub-
14、net. Physical Repeater: Device that reconditions the incoming physical layer signal on one chan- nel and retransmits it on to another channel. Store-and-Forward Repeater: Device that stores and then reproduces data packets on to a sec- ond channel. Bridge: Device that connects two channels (x and y)
15、; forwards all packets from x to y and vice versa, as long as the packets originate on one of the domain(s) that the bridge belongs to. Configuration: The non-volatile information used by the device to customize its operation. There is configuration data for the correct operation of the protocol in
16、each device, and op- tionally, for application operation. The network configuration data stored in each device has a checksum associated with the data. Examples of network configuration data are node ad- dresses, communication media parameters such as priority settings, etc. Application configu- rat
17、ion information is application specific. Domain: A virtual network that is the network unit of management and administration. Group and subnet (see below) addresses are assigned by the administrator responsible for the do- main, and they have meaning only in the context of that domain. Flexible Doma
18、in: Used in conjunction with Unique_Node_ID and broadcast addressing. A node responds to a Unique_Node_ID-addressed message if the address matches, regardless of the domain on which the message was sent. To respond so that the sender receives it, the re- sponse must be sent on the domain in which it
19、 was received. Furthermore, this domain must be remembered for the duration of the transaction so that duplicate detection of any retries is possible. This transitory domain entry at a node is called the flexible domain. How many flexible domain entries a node supports is up to the implementation. H
20、owever, a minimum of 1 is required. Subnet: A set of nodes accessible through the same link layer protocol; a routing abstraction for a channel; EIA-709 subnets are limited to a maximum of 127 nodes. Node: An abstraction for a physical node that represents the highest degree of address resolv- abili
21、ty on a network. A node is identified (addressed) within a subnet by its (logical) node identifier. A physical node may belong to more than one subnet; when it does, it is assigned CEA-709.1-B 3 one (logical) node number for each subnet to which it belongs. A physical node may belong to at most two
22、subnets; these subnets must be in different domains. A node may also be iden- tified (absolutely) within a network by its Unique_Node_ID. Group: A uniquely identifiable set of nodes within a domain. Within this set, individual members are identified by their member number. Groups facilitate one-to-m
23、any communica- tion and are intended to support functional addressing. Router: Device that routes data packets to their respective destinations by selectively for- warding from subnet to subnet; a router always connects two (sets of) subnets; routers may modify network layer address fields. Routers
24、may be set to one of four modes: repeater mode, bridge mode, learning mode, and configured mode. In repeater mode, packets are for- warded if they are received with no errors. In bridge mode, packets are forwarded if they are received with no errors and match a domain that the router is a member of.
25、 Routers in learn- ing mode learn the topology by examining packet traffic, while routers that are set to config- ured mode have the network topology stored in their memory and make their routing deci- sions solely upon the contents of their configured tables. (Application) Gateway: Interconnects ne
26、tworks at their highest protocol layers (often two different protocols). Two domains can also be connected through an application gateway. Beta1: Period immediately following the end of a packet cycle. A node attempting to trans- mit monitors the state of the channel, and if it detects no transmissi
27、on during the Beta1 pe- riod, it determines the channel to be idle. Beta2: Randomizing slot. A node wishing to transmit generates a random delay T. This delay is an integer number of randomizing slots of duration Beta2. Network Variable: A variable in an application program whose value is automatica
28、lly propa- gated over the network whenever a new value is assigned to it. Standard Network Variable Types (SNVTs): Variables with agreed-upon semantics. These variables are interpreted by all applications in the same way, and are the basis for interopera- bility. Definition of specific SNVTs is beyo
29、nd the scope of this document. Manual service request Message: A network management message containing a nodes Unique_Node_ID. Used by a network management device that receives this message to in- stall and configure the node. May be generated by application or system code. May be trig- gered by ext
30、ernal hardware event, e.g., driving a “manual service request” input low. Transaction: A sequence of messages that are correlated together. For example, a request and the responses to the request are all part of a single transaction. A transaction succeeds when all the expected messages from every n
31、ode involved in the transaction are received at least once. A transaction fails in EIA 709 if any of the expected messages within the transaction are not received. Retries of messages within a transaction are used to increase the probability of success of a transaction in the presence of transient e
32、rrors. CEA-709.1-B 4 4.3 Symbols and Graphical Representations Figure 1 shows the basic topology of networks based on this protocol and the symbolic repre- sentations used in this document. Bridge Store and Forward Repeater Channel Subnet Subnet A, A Subnet B, B Router Nodes Domain ADomain B Gateway
33、 Figure 1 Network Topology routers with config- ured tables may operate on topologies with physical loops, as long as the communication paths are logically tree-like. In this topology, a packet may never appear more than once at the router on the side on which the packet originated. The unicast rout
34、ing algorithm uses learning for minimal overhead and no additional routing traffic. Use of configured routing tables is sup- ported for both unicast and group addresses, although in many applications a simple flooding of group addressed messages is sufficient. The heart of the protocol hierarchy is
35、the Transport and Session layers. A common Transaction Control Sublayer handles transaction ordering and duplicate detection for both. The Transport layer is connection-less and provides reliable message delivery to both single and multiple des- tinations. Authentication of the message senders ident
36、ity is included as a transport layer ser- vice, for use when the security of sender authentication is required. The authentication server requires only the Transaction Control Sublayer to accomplish its function. Thus Transport and CEA-709.1-B 7 Session layer messages may be authenticated using all
37、of the addressing modes other than broadcast. The session layer provides a simple Request-Response mechanism for access to remote servers. This mechanism provides a platform upon which application specific remote procedure calls can be built. The EIA-709 network management protocol, for example, dep
38、ends upon the Request- Response mechanism in the Session layer. A transport layer acknowledged message expects indication of message delivery from remote destination(s). A session layer Request message expects indication that application-specific re- mote task(s) have been completed. A given message
39、 uses only one or the other type of service, but not both. This specification includes the Presentation Layer and the lowest level of the Application Layer. These layers provide services for sending and receiving application messages including network variables, and other types of messages such as n
40、etwork management and diagnostic messages and foreign frames (see 11). For a network variable update, the APDU header pro- vides information on how to interpret the APDU. This application-independent interpretation of the data allows data to be shared among nodes without prior arrangement. 6 MAC Sub
41、layer There are two MAC sublayers allowed within this standard. The first is descibed immediately below. The other alternative is to use EIA/CEA-852 and follow the instructions for the imple- mentation of EIA 709.1. An implementation must support at least one of these two alternatives. EIA/CEA-852 d
42、escribes a means for tunneling control network packets such as those defined in this standard across an IP network. When using an IP network as, in effect, the physical layer of EIA 709.1, the p-persistent CSMA defined in this standard is not used. Instead, the media access provided by the underlyin
43、g IP network is used for packet transmission. 6.1 Service Provided The EIA-709 Media Access Control (MAC) sublayer facilitates media access with optional pri- ority and optional collision detection/collision resolution. It uses a protocol called Predictive p- persistent CSMA (Carrier Sense, Multiple
44、 Access), that has some resemblance to the p- persistent CSMA protocol family. Predictive p-persistent CSMA is a collision avoidance technique that randomizes channel access using knowledge of the expected channel load. A node wishing to transmit always accesses the channel with a random delay in th
45、e range (0w). To avoid throughput degradation under high load, the size of the randomizing window, w, is a function of estimated channel backlog BL: w = (BL*Wbase) 1), where Wbase is the base window size. Wbase is measured in time. Its duration, derived from Beta2 (see 6.7), equals 16 Beta2 slots. -
46、,-,- CEA-709.1-B 8 6.2 Interface to the Link Layer The MAC sublayer is closely coupled to the Link layer, described in 6. With the MAC sublayer being responsible for media access, the Link layer deals with all other layer 2 issues, including framing and error detection. For explanatory purposes, the
47、 interface between the two layers is described in the form shown in Figure 4. Figure 4 Interface between the MAC and Link Layers Although the service interface primitives are defined using a syntax similar to programming language procedure calls, no implementation technique is implied. Frame recepti
48、on is handled entirely by the Link layer, that notifies the MAC sublayer about the backlog increment via the Frame_OK() primitive. The following service interface primitives facilitate the interface between the Link and the MAC layers: M_Data_Request (Priority, delta_BL, ALT_Path, LPDU) This primiti
49、ve is used by the Link layer to pass an outbound LPDU/MPDU to the MAC sublayer. Priority defines the priority with which the frame is to be transmitted; delta_BL is the backlog increment expected as a result of delivering this MPDU. ALT_Path is a bi- nary flag indicating whether the LPDU is to be transmitted on the primary or alternate channel, baud rate, etc. See 6.4 for how ALT_Path is set. Frame_OK (delta_BL) On receiving a frame and verifying that its CRC is correct, the Link layer invokes this primitive to no