IEEEStd802.3™-2008(RevisionofIEEEStd802.3-2005)Section3资源-CSDN文库

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### IEEE Std 802.3™-2008 Section 3：1000Mb/s Operation and Physical Layer Specifications #### 概述 IEEE Std 802.3™-2008 标准的第三部分涵盖了从第34条到第43条以及附录36A至附录43C的内容。这一部分主要介绍了千兆以太网（Gigabit Ethernet）的操作原理、物理层规范以及与ISO/IEC 8802-3标准之间的关系。该章节对于理解千兆以太网如何实现高速数据传输至关重要。 #### 34.1 1000Mb/s 基带网络介绍 **34.1 Overview** 千兆以太网将一个扩展版本的ISO/IEC 8802-3 (CSMA/CD MAC)协议与一系列1000Mbps物理层相结合。如图34-1所示，千兆以太网与扩展的ISO/IEC 8802-3 (CSMA/CD MAC)以及ISO/IEC开放式系统互连(OSI)参考模型之间存在着密切的关系。千兆以太网使用了扩展的ISO/IEC 8802-3 MAC层接口，并通过Gigabit Media Independent Interface (GMII)连接到了诸如1000BASE-LX、1000BASE-SX、1000BASE-CX和1000BASE-T等物理层实体(PHY子层)。 **34.1.1 Reconciliation Sublayer (RS) 和 Gigabit Media Independent Interface (GMII)** GMII（第35条）提供了一个连接媒体访问控制(MAC)子层与物理层实体(PHY)以及PHY层与站管理(STA)实体之间的接口。GMII支持1000Mbps操作，通过其八位宽(字节宽)的发送和接收路径实现。Reconciliation子层为GMII提供的信号与MAC/PL服务定义之间提供了映射。 #### 物理层规范 **1000BASE-LX:** 使用单模光纤进行长距离传输的标准，支持高达10公里的距离。 **1000BASE-SX:** 使用多模光纤进行短距离传输的标准，通常用于建筑物内部。 **1000BASE-CX:** 使用屏蔽双绞线进行短距离传输的标准，主要用于数据中心内的服务器集群。 **1000BASE-T:** 使用未屏蔽或屏蔽的双绞线进行传输的标准，是目前最常用的千兆以太网技术之一。 #### CSMA/CD 和全双工模式在半双工模式下，千兆以太网仍然采用CSMA/CD机制来避免碰撞并处理数据包的冲突。然而，在全双工模式下，这种机制被取消，因为全双工模式允许同时进行发送和接收数据，从而消除了碰撞的可能性。在全双工模式下，最小的数据包传输时间相比半双工模式减少了一个数量级。而在半双工模式下，最小的数据包传输时间虽然也有所减少，但没有达到全双工模式下的程度。 #### 电缆延迟预算和拓扑结构千兆以太网的电缆延迟预算与100BASE-T类似，这意味着它能够支持类似的拓扑结构。无论是全双工还是半双工模式下，可实现的拓扑结构都与100BASE-T相似。这表明即使是在更高的数据传输速率下，千兆以太网依然保持了良好的兼容性和灵活性。 #### 结论 IEEE Std 802.3™-2008 第三部分为读者提供了关于千兆以太网操作原理和技术细节的深入理解。通过这一章节的学习，可以了解到千兆以太网是如何利用扩展的CSMA/CD MAC协议和不同的物理层技术来实现高速数据传输的。此外，本章节还介绍了千兆以太网在不同操作模式下的特点以及与100BASE-T相比的优势。这对于网络工程师和IT专业人员来说是非常宝贵的信息资源。

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IEEE Standard for Information technology—

Telecommunications and information exchange between systems—

Local and metropolitan area networks—

Specific requirements

Part 3: Carrier Sense Multiple Access with

Collision Detection (CSMA/CD) access method

and Physical Layer specifications

SECTION THREE: This section includes Clause 34 through Clause 43 and Annex 36A through

Annex 43C.

34. Introduction to 1000 Mb/s baseband network

34.1 Overview

Gigabit Ethernet couples an extended version of the ISO/IEC 8802-3 (CSMA/CD MAC) to a family of

1000 Mb/s Physical Layers. The relationships among Gigabit Ethernet, the extended ISO/IEC 8802-3 (CSMA/

CD MAC), and the ISO/IEC Open System Interconnection (OSI) reference model are shown in Figure 34–1

Gigabit Ethernet uses the extended ISO/IEC 8802-3 MAC layer interface, connected through a Gigabit

Media Independent Interface layer to Physical Layer entities (PHY sublayers) such as 1000BASE-LX,

1000BASE-SX, and 1000BASE-CX, and 1000BASE-T.

Gigabit Ethernet extends the ISO/IEC 8802-3 MAC beyond 100 Mb/s to 1000 Mb/s. The bit rate is faster,

and the bit times are shorter—both in proportion to the change in bandwidth. In full duplex mode, the mini-

mum packet transmission time has been reduced by a factor of ten. Achievable topologies for 1000 Mb/s full

duplex operation are comparable to those found in 100BASE-T full duplex mode. In half duplex mode, the

minimum packet transmission time has been reduced, but not by a factor of ten. Cable delay budgets are

similar to those in 100BASE-T. The resulting achievable topologies for the half duplex 1000 Mb/s CSMA/

CD MAC are similar to those found in half duplex 100BASE-T.

34.1.1 Reconciliation Sublayer (RS) and Gigabit Media Independent Interface (GMII)

The Gigabit Media Independent Interface (Clause 35) provides an interconnection between the Media

Access Control (MAC) sublayer and Physical Layer entities (PHY) and between PHY Layer and Station

Management (STA) entities. This GMII supports 1000 Mb/s operation through its eight bit wide (octet wide)

transmit and receive paths. The Reconciliation sublayer provides a mapping between the signals provided at

the GMII and the MAC/PLS service definition.

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IEEE

Std 802.3-2008 REVISION OF IEEE Std 802.3:

34.1.2 Physical Layer signaling systems

This standard specifies a family of Physical Layer implementations. The generic term 1000 Mb/s MAC

refers to any use of the 1000 Mb/s IEEE 802.3 MAC (the Gigabit Ethernet MAC) coupled with any Physical

Layer implementation.

The following portion of this standard specifies a family of Physical Layer implementations. 1000BASE-T

(Clause 40) uses four pairs of balanced copper cabling. 1000BASE-SX (Clause 36, Clause 37, and

Clause 38) uses two multimode fibers. There are a number of other PHY types and their associated media.

34.1.3 Repeater

A repeater set (Clause 41) is an integral part of any Gigabit Ethernet network with more than two DTEs in a

collision domain. A repeater set extends the physical system topology by coupling two or more segments.

Only one repeater is permitted within a single collision domain.

34.1.4 Auto-Negotiation, type 1000BASE-X

Auto-Negotiation (Clause 37) provides a 1000BASE-X device with the capability to detect the abilities

(modes of operation) supported by the device at the other end of a link segment, determine common abili-

ties, and configure for joint operation. Auto-Negotiation is performed upon link startup through the use of a

special sequence of reserved link codewords. Clause 37 adopts the basic architecture and algorithms from

Clause 28, but not the use of fast link pulses. Auto-Negotiation for 1000BASE-KX is defined in Clause 73.

GMII

PRESENTATION

APPLICATION

SESSION

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

OSI

REFERENCE

MODEL

LAYERS

LAN

CSMA/CD

LAYERS

LLC (LOGICAL LINK CONTROL) OR

MAC—MEDIA ACCESS CONTROL

PMA

HIGHER LAYERS

MDI = MEDIUM DEPENDENT INTERFACE

GMII = GIGABIT MEDIA INDEPENDENT INTERFACE

PCS = PHYSICAL CODING SUBLAYER

PMA = PHYSICAL MEDIUM ATTACHMENT

PHY

PHY = PHYSICAL LAYER DEVICE

GMII

MDI

PCS

PMD

PMD = PHYSICAL MEDIUM DEPENDENT

RECONCILIATION

PMD

PHY

MDI

PMA

PCS

1000 Mb/s

Repeater

Baseband

PMD

PHY

MDI

PMA

1000 Mb/s link segment

MEDIUM

1000 Mb/s link segment

MEDIUM

1000 Mb/s

Baseband

Repeater

Unit

Figure 34–1—Architectural positioning of Gigabit Ethernet (1000 Mb/s operation)

Set

PCS

MAC CONTROL (OPTIONAL)

OTHER MAC CLIENT

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IEEE

CSMA/CD Std 802.3-2008

34.1.5 Auto-Negotiation, type 1000BASE-T

Auto-Negotiation (Clause 28) is used by 1000BASE-T devices to detect the abilities (modes of operation)

supported by the device at the other end of a link segment, determine common abilities, and configure for

joint operation. Auto-Negotiation is performed upon link startup through the use of a special sequence of

fast link pulses.

34.1.6 Management

Managed objects, attributes, and actions are defined for all Gigabit Ethernet components (Clause 30). That

clause consolidates all IEEE 802.3 management specifications so that agents can be managed by existing

network management stations with little or no modification to the agent code.

34.2 State diagrams

State diagrams take precedence over text.

The conventions of 1.2 are adopted, along with the extensions listed in 21.5.

34.3 Protocol implementation conformance statement (PICS) proforma

The supplier of a protocol implementation that is claimed to conform to any part of IEEE 802.3, Clause 35

through Clause 41, shall complete a protocol implementation conformance statement (PICS) proforma.

A completed PICS proforma is the PICS for the implementation in question. The PICS is a statement of

which capabilities and options of the protocol have been implemented. A PICS is included at the end of each

clause as appropriate. Each of the Gigabit Ethernet PICS conforms to the same notation and conventions

used in 100BASE-T (see 21.6).

34.4 Relation of Gigabit Ethernet to other standards

Supported applications for 10 Gigabit Ethernet can be found in ISO/IEC 11801:2002, Annex F.

Suitable entries for Table G1 of ISO/IEC 11801:1995, Annex G, would be as follows:

a) Within the section Optical Link:

CSMA/CD 1000BASE-SX ISO/IEC 8802-3/ PDAM 26

b) Within the section Optical Link:

CSMA/CD 1000BASE-LX ISO/IEC 8802-3/PDAM 26

c) Within the section Balanced Cabling Link Class D (defined up to 100 MHz):

CSMA/CD 1000BASE-T* ISO/IEC 8802-3/DAD 1995

*To support 1000BASE-T applications, Class D links shall meet the requirements for return loss, ELFEXT

and MDELFEXT specified in 40.7.

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