CEA-600.41-1998.pdf
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1、 CEA Standard Description of the Data Link Layer ANSI/CEA-600.41 February 1998 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 20:34:58 MDTNo reproduction or networking permitted without
2、 license from IHS -,-,- 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 improvement of products, and assisting the purchaser in s
3、electing 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 selling products not conforming to such Standards, Bull
4、etins 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 internationally. Standards, Bulletins and other technic
5、al 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 adopting the Standard, Bulletin or other technical public
6、ation. 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 claim or of any patent rights in connection therewith.
7、 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 publisher. This CEA Standard is considered to have Intern
8、ational 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 address all safety problems associated with its use or
9、 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 3516, formulated under the cognizance of the CEA R7 Ho
10、me Networks Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2002 Technology (b) all retransmissions have been sent without success; or (c) a maximum time limit has been reached. Obviously, acknowledged connectionless service may provide a greater degree of reliability than unacknowledged s
11、ervice. The drawback, of course, is the extra traffic generated on the channel and an increase in the average channel access delay. When the Data Link Layer of a destination node correctly receives a frame requiring acknowledgment, it must transmit the acknowledgment, disassemble the frame, and pass
12、 a data indication to the receiving Network Layer. This indication contains the NPDU and control information obtained from the frame disassembly. Because acknowledged service may deliver multiple copies of the same frame, the receiving Data Link Layer must identify and discard any duplicate frames.
13、Note that the IACK and retransmission mechanisms are totally contained in the Data Link Layer and are transparent to the Network Layer. The Network Layer simply subscribes to the higher grade of service offered by the Data Link Layer. For acknowledged service the service primitives LL_ACK_DATA.reque
14、st, LL_ACK_DATA.confirm, and LL_ACK_DATA.indication define the interface between the Network Layer and the Data Link Layer. These service primitives are also described briefly in Section 4 of this document and are properly named and specified in the document Node Logical Link Control Sublayer. 2.1.2
15、. Specification of the Network Layer. Specification of the CEBus Network Layer is contained in the document Node Network Layer. A prose description of Network Layer functionality is contained in the document Description of the Node Network Layer. 2.2. The Physical Layer and Media. 2.2.1. Overview an
16、d Functional Divisions. The Physical Layer is the lowest layer in the network hierarchy and bridges the gap between the Data Link Layer and the physical medium. Its function is to perform the actual transmission and reception of the symbols which make up a Data Link Layer frame. To accomplish this t
17、ask, the transmitting Data Link Layer passes the symbols down sequentially to the Physical Layer for encoding into electrical signals appropriate for a particular medium (power line, twisted pair, etc.). The Physical Layer establishes a channel in the physical medium which interconnects the network
18、nodes and generates electrical signals onto the channel, representing the data symbols. The Physical Layer of the receiving node picks up the electrical signals from the channel, decodes the received symbols, and passes the symbols up Revision: 11-15-91 4 Copyright Consumer Electronics Association P
19、rovided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 20:34:58 MDTNo reproduction or networking permitted without license from IHS -,-,- CEA 600.41 DESCRIPTION OF THE DATA LINK LAYER to the Data Link Layer. In performing these services,
20、 the Physical Layer supports the data rate that is expected by the Data Link Layer. The Physical Layer may be functionally divided into two pieces: the Symbol Encoding (SE) Sublayer and the (Medium Dependent Physical (MDP) Sublayer as shown in Figure 2-1. The MDP Sublayer and Physical Medium are cov
21、ered in EIA 600.3x. The SE Sublayer of the Physical Layer provides the encoding and decoding of symbols during transmission and reception and for some media provides error detection. The MDP Sublayer of the Physical Layer is subordinate to the SE Sublayer. The MDP Sublayer encompasses the transmissi
22、on and reception of electrical signals and the hardware interface to the physical medium. Data Link Layer of the Physical Layer SE Sublayer of the Physical Layer MDP Sublayer Physical Medium Figure 2-1. Functional Division of the Physical Layertc “Figure 2-1. Functional Division of the Physical Laye
23、r“ f f 2.2.2. The Medium. The physical medium is the entity which transports signals between physically separate nodes. All media must have the ability to represent two distinct physical states: SUPERIOR and INFERIOR, such that a SUPERIOR state emanating from one node will override INFERIOR states e
24、manating from any number of other nodes on the network. This ability is essential to the Data Link Layers channel access mechanism, which is explained in Section 3 of this document. 2.2.3. The MDP Sublayer of the Physical Layer. The MDP Sublayer of the Physical Layer (for each medium) includes elect
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