A local Area Network
`
`:D'atnf Link Layer-
`and
`
`Physical Layer
`
`Specifications
`
`The Ethernet -.
`The Ethernet”
`
`AA—K'l'SQBr'TK.
`
`Eflfifllfill
`
`-
`
`XEROX
`
`Digital Eq‘ulpmenl Gomomion
`
`Magnum. MA
`
`-I'niel Cmporafioh
`
`Sir-III Gilli-a. 0h
`
`"xerox. Carpnmmn
`
`'Slamfo'rd,l.lcT
`
`Version 2.0
`
`Navanber,_ 1982
`
`Apple Exhibit 1039 Page 00001
`
`

`

`
`
`Page 00002
`
`Page 00002
`
`

`

`The Ethernet
`
`A Local Area Network
`
`Data Link Layer
`and
`Physical Layer
`Specifications
`
`Digital Equipment Corporation
`
`Maynard, MA
`
`Intel Corporation
`
`Santa Clara, CA
`
`Xerox Corporation
`
`Stamford, CT
`
`Version 2.0
`
`November, 1982
`AA-K759B-TK
`
`Page 00003
`
`

`

`
`-
`
`IMPORTANT INFORMATION AND DISCLAIMERS
`
`1. This specification includes subject matter relating to a patenth) of Xerox
`Corporation. No license under such patent(s) is granted by implication,
`estoppel or otherwise as a result of publication of this specification. Applicable
`licenses may be obtained from Xerox Corporation.
`
`This specification is furnished for informational purposes only. Digital, Intel,
`and Xerox do not warrant or represent that this specification or any products
`made in conformance with i t will work in the intended manner or be
`compatible with other products in a network system. Nor do they assume
`responsibility for any errors that the specification may contain, or have any
`liabilities or obligations for damages (including but not limited to special,
`indirect or consequential damages) arising out of or in connection with the use
`of this specification in any way. Digital, Intel and Xerox products may follow
`or deviate from the specification without notice a t any time.
`
`3. No representations or warranties are made that this specification or anything
`made from it is or will be free from infringements or patents of third persons.
`
`Page 00004
`
`

`

`ETHERNET SPECIFICATION:
`Preface
`
`Preface
`
`This document contains the specification of the Ethernet, a local area network
`developed jointly by Digital Equipment Corporation, Intel Corporation, and Xerox
`Corporation. The Ethernet specification is the result of an extensive collaborative
`effort of the three corporations, and several years of work at Xerox on an earlier
`prototype Ethernet.
`
`This specification is intended as a design reference document, rather than an
`introduction or tutorial. Readers seeking introductory material are directed to the
`reference list in Section 2, which cites several papers describing the intent, theory,
`and history of the Ethernet.
`
`This document contains 8 sections, falling into four main groups:
`
`Sections 1, 2, and 3 provide an overall description of the Ethernet, including its
`goals, and the scope of the specification.
`
`Sections 4 and 5 describe the architectural structure of the Ethernet in terms of
`a functional model consisting of two layers, the Data Link Layer and the
`Physical Layer.
`
`Sections 6 and 7 specify the two layers in detail, providing the primary technical
`specification of the Ethernet.
`
`Section 8 provides a description and specification for a configuration testing
`protocol for Network Management services. This protocol provides a minimum
`capability for testing any station's ability to communicate with other stations on
`the network.
`
`Readers wishing to obtain an initial grasp of the organization and content of the
`specification will be best served by reading Sections 1,3, and 4. Readers involved
`in actual implementation of the Ethernet will find Sections 5,6,7, and 8 to contain
`the central material of the specification. Section 2 provides references, and the
`appendices provide supplementary material.
`
`The approach taken in the specification of the Data Link Layer in Section 6 is a
`procedural one; in addition to describing the necessary algorithms in English and
`control flow charts, the specification presents these algorithms in the language
`Pascal. This approach makes clear the required behavior of the Data Link Layer,
`while leaving individual implementations free to exploit any appropriate
`technology.
`
`Because the procedural approach is not suitable for specifying the details of the
`Physical Layer, Section 7 uses carefully worded English prose and numerous
`figures and tables to specify the necessary parameters of this layer.
`
`Page 00005
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`

`

`ETHERNET SPECIFICATION:
`Preface
`
`Some aspects of the Ethernet are necessarily discussed in more than one place in
`this specification. Whenever any doubt arises concerning the official definition in
`such a case, the reader should utilize the Pascal procedural specification of the
`Data Link Layer in Section 6.5, and the detailed prose specification of the Physical
`Layer in Sections 7.2 through 7.9.
`
`One aspect of an overall network architecture which is addressed by this
`specification is network management. The network management facility
`performs operation, maintenance, and planning functions for the network:
`- Operation functions include parameter setting, such as address selection.
`- Maintenance functions provide for fault detection, isolation, and repair.
`
`- Planning functions include collection of statistical and usage information,
`necessary for planned network growth.
`
`While network management itself is properly performed outside the Ethernet
`Data Link and Physical Layers, it requires appropriate additional interfaces to
`those layers. A functional description of the network management interfaces is
`given in Section 4.5, while detailed procedural models are given in Sections 5 and
`6. Configuration control and overall network management for Ethernets which
`may
`interconnect machines from different manufacturers,
`implementing
`different, perhaps incompatible communication software a t the client layer of
`Ethernet, will require a minimum, common communication capability for network
`management purposes. The specification for the configuration testing protocol
`appears in Section 8.
`
`Version 2.0 of the Ethernet specification reflects the experience of the three
`corporations in designing equipment to the Version 1.0 specification. Version 2.0
`includes network management functions and better defines the details of the
`physical channel signalling. Version 2.0 is upward compatible with Version 1.0.
`Equipment designed to the two specifications is interoperable.
`
`Section 7.6.4 on Repeaters is incomplete. Further study of the repeater design is
`desirable, with the goal to relax some of the configuration restrictions in Section
`7.1.5.
`
`Version 2.0 of the Ethernet specification is substantially compatible with
`standards for CSMAJCD local area networks being developed by IEEE and ECMA.
`The three corporations have been active participants in these standard efforts and
`have now endorsed their documents. Version 2.0 of the Ethernet specification is
`an interim document. We expect that future work will take place in these
`standards bodies.
`
`Page 00006
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`

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`ETHERNET SPECIFICATION: Contents
`
`T a b l e of Contents
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`. 1 INTRODUCTION
`1
`2 . REFERENCES
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`3
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`4 . FUNCTIONAL MODELOFTHE ETHERNET ARCHITECTURE
`7
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`Layering
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`Data Link Layer
`4.2
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`Physical Layer
`4.3
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`Network Management
`4.4
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`15
`Ethernet Operation and the Functional Model
`4.5
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`4.5.1 Transmission Without Contention
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`4.5.2 Reception Without Contention
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`4.5.3 Collisions: Handling of Contention
`Functional Description of Network Management Interface . 17
`4.5.4
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`5 . INTER-LAYER INTERFACES
`19
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`Client Layer to Data Link Layer
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`5.1
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`Data Link Layer to Physical Layer
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`5.2
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`DataLink to Network Management Interface
`23
`5.3
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`6 . ETHERNET DATA LINK LAYER SPECIFICATION
`26
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`6.1
`Data Link Layer Overview and Model
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`6.2
`Frame Format
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`6.2.1 Address Fields
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`6.2.1.1 Destination Address Field
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`Frame Transmission
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`6.3.1 Transmit Data Encapsulation
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`6.3.1.1
`Frame Assembly
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`6.3.1.2
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`6.3
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`ETHERNET SPECIFICATION: Contents
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`31
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`6.3.2 Transmit Link Management .
`31
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`6.3.2.1 Carrier Deference .
`31
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`6.3.2.2
`Interframe Spacing
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`6.3.2.3
`Collision Handling.
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`6.3.2.3. 1 Collision Detection and Enforcement
`6.3.2.3.2 Collision Backoffand Retransmission . 32
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`6.4.1 Receive Data Decapsulation .
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`6.4.1.1 Framing .
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`6.4.1.1.1 Maximum Frame Size.
`6.4. 1. 1. 2 Integral Number of Octets1n Frame
`6.4.1.2 Address Recognition .
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`Frame Check Sequence Validation .
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`6.4.2 Receive Link Management
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`The Data Link Layer Procedural Model.
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`6.5.1 Overview of the Procedural Model
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`6.5.1.1 Ground Rules for the Procedural Model
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`Frame Transmission.
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`Fralne Reception
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`6.5.2.4 Network Management Interface Procedures .
`6. 5. 2. 4. 1 State Variable Initialization
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`7. ETHERNET PHYSICAL LAYER SPECIFICATION
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`Implementation of the Channel.
`7.1.4.1 General Overview of Channel Hardware .
`7.1.4.2 Compatibility Interfaces .
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`ETHERNET SPECIFICATION: Contents
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`7.1.6 Channel Interfaces
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`7.3.1 Coaxialcable Component Specifications
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`ETHERNET SPECIFICATION: Contents
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`8.2
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`Page 00010
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`

`

`ETHERNET SPECIFICATION: Contents
`
`8.4.2.1 Restrictions on Forward Data Messages
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`8.5
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`8.6
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`Operation of the Protocol
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`8.6.1 Local Control Test Example
`8.6.2 Remote Control Test Example
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`Appendices
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`APPEXDIX B: ASSIGNMENT OF ADDRESS AND TYPE VALUES
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`APPENDIX C: CRC IMPLEMENTATION
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`Figures and Tables
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`Figure 4-1: Ethernet Architecture and Typical Implementation
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`Figure 4-2: Architectural Layering
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`Figure 4-4: Physical Layer Functions
`Figure 4-5: Architecture Including Network Management Interface .
`Figure 6-1: Data Link Layer Frame Format .
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`Figure 6-2: Structure of the Data Link Procedural Model .
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`Figure 6-4: Control Flow Sumrnary .. Data Link Layer Processes .
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`Figure 7-1: Physical Channel Configurations
`Table 7-1: Physical Channel Propagation Delay Budget .
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`Figure 7-2: Maximum Transceiver Cable Transfer Impedance
`Figure7-3:TypicalTransceiverCableWaveform .
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`Page 00011
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`

`

`ETHERNET SPECIFICATION: Contents
`
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`Figure 7-7: Preamble Encoding
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`Figure 7-9: Functional Logic of carriersense Signal
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`Figure 8-1: A Loopback Frame Encapsulated in an Ethernet Packet
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`Figure 8-2: A Reply Message Encapsulated in a Forward Data Message
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`Figure C-1: CRC Implementation
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`Figure D-1: Typical Transceiver Cable Driver
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`Figure D-2: Typical Transceiver Cable Receiver
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`Figure D-3: Shows Relationship Between Figure D-1 and Figure D-2
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`Figure D-4: Typical Transceiver Block Diagram
`
`Page 00012
`
`

`

`ETHERNET SPECIFICATION:
`Introduction
`
`1.
`
`INTRODUCTION
`
`The Ethernet local area network provides a communication facility for high-speed
`data exchange among computers and other digital devices located within a
`moderate-sized geographic area. Its primary characteristics include:
`
`Physical Layer:
`
`Data rate: 10 Million bitsjsec
`
`Maximum station separation: 2.8 Kilometers
`
`Maximum number of stations: 1024
`
`Medium: Shielded coaxial cable, base band signalling
`
`Topology: Branching non-rooted tree
`
`Data Link Layer:
`
`Link control procedure: Fully distributed peer protocol, with statistical
`contention resolution (CSMNCD)
`
`Message protocol: Variable size frames, "best-effort'' delivery
`
`The Ethernet, like other local area networks, falls in a middle ground between
`long-distance, low-speed networks that carry data for hundreds or thousands of
`kilometers, and specialized, very high speed interconnections that are generally
`limited to tens of meters. The Ethernet is intended primarily for use in such areas
`as office automation, distributed data processing, terminal access, and other
`situations requiring economical connection to a local communication medium
`carrying bursty traffk at high-peak data rates. Situations demanding resistance
`to hostile environments, real-time response guarantees, and so on, while not
`specifically excluded, do not constitute the primary environment for which the
`Ethernet is designed.
`
`The precursor to the Ethernet specified in this document was the "Experimental
`Ethernet,?* designed and implemented by Xerox in 1975, and used continually
`since that time by thousands of stations. The Ethernet defined here builds on that
`experience, and on the larger base of the combined experience of Digital, Intel, and
`Xerox in many forms of networking and computer interconnection.
`
`In specifying the Ethernet, this document provides precise detailed definitions of
`the lowest two layers of an overall network architecture. It thus defines what is
`generally referred to as a link-level facility. It does not specify the higher level
`protocols needed to provide a complete network architecture. Such higher level
`protocols would generally include such functions as internetwork communication,
`error recovery, flow control, security measures (e.g., encryption), and other higher
`
`Page 00013
`
`

`

`ETHERNET SPECIFICATION:
`Introduction
`
`level functions that increase the power of the communication facility and/or tailor
`it to specific applications. In particular, it should be noted that all error recovery
`functions have been relegated to higher level protocols, in keeping with the low
`error rates that characterize local area networks.
`
`One of the main objectives of this specification is compatibility. As stated in
`Section 3, it is intended that every implementation of the Ethernet be able to
`exchange data with every other implementation. It should be noted that higher level
`protocols raise their own issues of compatibility over and above those addressed by
`the Ethernet and other link-level facilities. This does not eliminate the
`importance of link-level compatibility, however. While the compatibility provided
`by the Ethernet does not guarantee solutions to higher level compatibility
`problems, it does provide a context within which such problems can be addressed,
`by avoiding low-level incompatibilities that would make direct communication
`impossible.
`
`Page 00014
`
`

`

`ETHERNET SPECIFICATION: References
`
`2. REFERENCES
`
`The following three papers describe the Experimental Ethernet, and are reprinted
`in: 'The Ethernet Local Network: Three Reports," Xerox Pa10 Alto Research
`Center Technical Report CSL-80-2 (February 1980).
`
`[I] Metcalfe, R. M. and Boggs, D. R., "Ethernet: Distributed Packet Switching for
`Local Computer Networks," Communications of the ACM 19 7 (July 1976).
`
`] Crane, R. C. and Taft, E. A. "Practical Considerations in Ethernet Local
`Network Design," Presented a t Hawaii International Conference on System
`Sciences (January 1980).
`
`1 Shoch, J. F. and Hupp? J. A. 'tMeasured Performance of an Ethernet Local
`Network," Presented at Local Area Communications Network Symposium
`Boston (May 1979).
`
`The following references describe the I S 0 Open Systems Model:
`
`[4] Zimmermann, H., "OSI Reference Model-The IS0 Model of Architecture for
`Open Systems Interconnection,"
`IEEE Transactions on Communication
`COM-28 4 (April 1980).
`
`[5] International Organization for Standardization (ISO), "Reference Model of
`Open Systems Interconnection,'' Document no. ISO/TC97/SCl6 N227 (June
`1979).
`
`The following references describe the Pascal language (used i n the Data Link Layer
`procedural model) and its derivative Concurrent Pascal:
`
`[6] Jensen, K. and Wirth, N., Pascal User Manual and Report, 2nd Edition.
`Springer-Verlag (1974).
`
`[7] Brinch Hansen, P., Concurrent Pascal Report. Technical Report CIT-IS-TR
`17, California Institute of Technology (1975).
`
`The following references discuss the CRC code used for the frame check sequence:
`
`[8] Hammond, J. L., Brown, J. E. and Liu, S. S.? "Development of a Transmission
`Error Model and an Error Control Model," Technical Report RADC-TR-75-
`138, Rome Air Development Center (1975).
`
`[91 Bittel, R.? t'On Frame Check Sequence (FCS) Generation and Checking,"
`ANSI working paper X3-S34-77-43? (1977).
`
`Page 00015
`
`

`

`ETHERNET SPECIFICATION: References
`
`The following references are cited as support information for
`standards to which the specifications given in Section 7 comply.
`
`the electrical
`
`IEC Recommendation,
`[lo] International Electrotechnical Commission,
`Publication 435, Safety of Data Processing Equipment, First Edition, 1973.
`
`[ I l l Underwriters Laboratories, UL 478 Standard for Electronic Data-Processing
`Units and Systems, Fourth Edition, April 1980.
`
`[I21 National Fire Protection Association, National Electrical Code.
`
`Page 00016
`
`

`

`ETHERNET SPECIFICATION:
`Physical Layer
`
`7.
`
`ETHERNET PHYSICAL LAYER SPECIFICATION: Baseband Coaxial
`System
`
`7.1
`
`Physical Channel Overview and Model
`
`The Ethernet physical channel (henceforth referred to as the channel) provides the
`lowest layer in the Ethernet architecture. It performs all the functions needed to
`transmit and receive data a t the physical level, while supporting the Data Link
`Layer to Physical Layer Interface described in 5.2.
`
`This section describes the requirements for interface and compatibility with a
`baseband coaxial implementation of the channel.
`
`7.1.1 Channel Goals and Non-goals
`
`This section states the objectives underlying the design of the channel.
`
`7.1.1.1 Goals
`
`The following are the goals of the channel:
`
`Provide a means for communication between Ethernet data link entities.
`
`Define physical interfaces so that hardware manufacturers' implementations
`are compatible.
`
`Provide all clocks, synchronization, and timing required for both the channel
`and the Ethernet data link.
`
`Provide high bandwidth and low bit error rates.
`
`Provide for ease of installation and service.
`
`Provide for high network availability.
`
`Support the Ethernet Data Link Layer to Physical Layer Interface.
`
`Low cost.
`
`7.1.1.2 Non-Goals
`
`The following are not goals of the baseband coaxial channel design:
`
`Operation a t data rates other than 10 Mbps per second.
`
`Operation with media other than the specified coaxial cable.
`
`Simultaneous use of the channel by transmitters using signals not specified in
`
`Page 00017
`
`

`

`ETHERNET SPECIFICATION:
`Physical Layer
`
`this document.
`
`a Protection against a malicious user or a malfunctioning data link entity is not
`provided by the channel as specified. However, higher layers (above the data
`link) and/or physical security means may be employed to achieve this.
`
`7.1.2 Characteristics of the Channel
`
`The channel provides (and the data link assumes) the following characteristics:
`
`The ability to send and receive information (non-simultaneously) between any
`two or more data link entities on the same network.
`
`The ability to detect the presence of another station's transmission while not
`transmitting (carrier sense).
`
`a The ability to detect the presence of another station's transmission while
`transmitting (collision detect).
`
`A total worst-case round trip signal propagation delay (including actual
`propagation time, synchronization time for all intervening electronics, and
`signal rise time degradation) of less than 464 bit times (equal to 46.4 ps for this
`10 Mbps channel).
`
`7.1.3
`
`Functions Provided by the Channel
`
`The channel hardware provides the following functions in the performance of its
`role:
`
`Means for transmitting and receiving serial bit streams between the data link
`layer and the media.
`
`a Generation of clock for synchronization and timing.
`
`a Means for detecting carrier (non-idle channel).
`
`Means for detecting collisions (simultaneous transmission attempts by
`multiple stations).
`
`Coding and decoding of the data link bit stream into a self-synchronizable
`sequence of electrical signals suitable for transmission on the media provided
`by the channel.
`
`(a
`information
`a Generation and removal of coding-specific preamble
`synchronizing header sequence inserted before the first bit of the frame) to
`ensure that all channel electronics are brought to a known steady-state before
`the data link frame is transmitted.
`
`Page 00018
`
`

`

`ETHERNET SPECIFICATION:
`Physical Layer
`
`7.1.4
`
`Implementation of the Channel
`
`The physical channel specification is implementation dependent; most of the
`channel hardware is fully specified, and little leeway is given to the individual
`designer. This is done in the interest of compatibility; any system which allows
`different implementers to use different channel cables, connectors, clock speeds,
`and the like will not be compatible across manufacturer boundaries. Only the
`design of channel components which are not critical to system compatibility is left
`to the implementer.
`
`7.1.4.1 General Overview of Channel Hardware
`
`The channel minimally consists of the following functional blocks:
`
`Passive broadcast medium (coaxial cable).
`
`Transceiver (transmitter-receiver for the coaxial cable).
`
`Means for connecting transceivers to a coaxial cable segment and for
`connecting coaxial cable segments together.
`
`Channelclock.
`
`Channel data encoder and decoder.
`
`Preamble generator and remover.
`
`Carrier and collision detect circuits.
`
`The coaxial medium is the only element common to the entire network. A
`transceiver is required for connection to the medium, and must be located adjacent
`to the coaxial cable. The last four components are generally located within, and
`tightly coupled to, the station hardware implementing the data link function.
`
`It may be desirable to physically separate the transceiver from the rest of the
`channel hardware. This permits topological flexibility, packaging advantages,
`and improved system availability, and allows for independent manufacture of
`station hardware and transceivers. To ensure that compatibility is maintained, a
`physical interface (known as the transceiver cable) is identified and specified to
`connect the transceiver to the station.
`
`Finally, it is necessary to add repeaters to the system to reach the maximum
`allowable distance between stations, and to provide additional topological
`flexibility. Repeaters are implemented using standard transceivers, plus a finite
`state machine.
`
`7.1.4.2 Compatibility Interfaces
`
`Page 00019
`
`

`

`ETHERNET SPECIFICATION:
`Physical Layer
`
`There are a number of possibilities for implementing systems or subsystems
`compatible in whole or in part with this specification. It is important that all
`implementations be compatible at some point, so that heterogeneous systems from
`different manufacturers' implementations can be interconnected on the same
`medium. It is not necessary in every case to implement all of the components
`described here; e.g., it is possible to design an integrated stationltransceiver
`(without requiring the transceiver cable). The implementer must make the
`required
`tradeoffs between
`topological
`flexibility,
`system availability,
`configurability, user needs, and cost, when designing the system.
`
`For a device to be considered compatible, it must meet the applicable requirements
`at either the transceiver cable or the coaxial cable interface, as appropriate, in
`addition to the Data Link compatibility required for all stations connected to the
`network.
`
`All Ethernet implementations must be compatible a t the coaxial cable.
`
`If a transceiver cable is used, it should be the one specified in this document. This
`allows device manufacturers to build hardware compatible with the Ethernet a t
`the transceiver cable level, without concerning themselves with the details of
`transceiver
`implementation.
`Devices
`implementing
`transceiver
`cable
`compatibility should be capable of using transceivers designed and built by
`another manufacturer, on the specified coaxial cable.
`
`Equipment designed for connection to the specified coaxial cable either without a
`physically separate transceiver or with a non-standard transceiver cable interface
`will be capable of communication. However, a sacrifice may have been made with
`respect to interchangeability with other stations.
`
`This scheme of multiple compatibility interfaces allows individual designers some
`flexibility in making system tradeoffs, yet allows cable manufacturers, transceiver
`manufacturers, and systems manufacturers to use standard commodity parts to
`produce a compatible communications system.
`
`7.1.5
`
`Channel Configuration Model
`
`Certain physical limits have been placed on the physical channel. These revolve
`mostly around maximum cable lengths (or maximum propagation times), as these
`affect the slot time as defined in the data link. While the precise specification (in
`later sections) states these maxima in terms of propagation times, they were
`der