CN_以太网规格和传输介质@双绞线@基带同轴电缆

文章目录

• 以太网规格和传输介质
• • 必备常识
  • • 常见传输介质规格
    • • 例
      • 10BASE5
      • 10BASE2
      • 双绞线命名
    • 屏蔽双绞线
  • 高速以太网
  • • (1)100BASE-T以太网
    • (2)吉比特以太网
    • (3)10吉比特以太网

以太网规格和传输介质

必备常识

常见传输介质规格

• 参数	10BASE5	10BASE2	10BASE-T	10BASE-FL
  传输媒体	基带同轴电缆(粗缆)	基带同轴电缆(细缆)	非屏蔽双绞线	光纤对 (850nm)
  编码	曼彻斯特编码	曼彻斯特编码	曼彻斯特编码	曼彻斯特编码
  拓扑结构	总线形	总线形	星形	点对点
  最大段长	500m	185m(200是理论设计长度) 实际只能185m	100m	2000m
  最多结点数目	100	30	2	2

  • 10BASE-T

    • 非屏蔽双绞线以太网拓扑结构为星形网，星形网中心为集线器，但使用集线器的以太网在逻辑上仍然是一个总线形网，属于一个冲突域

  • 从参数中可以看出:

    • BASE表示基带
    • 传输速率
    • 传输媒体、
    • 编码方式(全都是Manchester Coding )
    • 拓扑结构
    • …等信息的

例

• 10BASE-T
  • 10:速率为10 Mbit/s
    • 注意是Mbit而不是MByte
  • BASE:表示基带
  • T:表示双绞线
  • 如果结尾是F系列,那么是光纤(optical fiber)
• The common names for the standards derive from aspects of the physical media. The leading number (10 in 10BASE-T) refers to the transmission speed in Mbit/s.
• BASE denotes that baseband transmission is used.
• The T designates twisted-pair cable.
• Where there are several standards for the same transmission speed,
  • they are distinguished by a letter or digit following
    • the T, such as TX or T4, referring to the encoding method and number of lanes.
• Ethernet physical layer - Wikipedia

10BASE5

• 10BASE5 Name origination
• The name 10BASE5 is derived from several characteristics of the physical medium.
  • The 10 refers to its transmission speed of 10 Mbit/s.
  • The BASE is short for baseband signaling (as opposed to broadband[a]),
  • The 5 stands for the maximum segment length of 500 meters (1,600 ft).
• 10BASE5 (also known as thick Ethernet or thicknet) was the first commercially available variant of Ethernet. The technology was standardized in 1982[1] as IEEE 802.3.
• 10BASE5 uses a thick and stiff coaxial cable up to 500 meters (1,600 ft) in length. Up to 100 stations can be connected to the cable using vampire taps and share a single collision domain with 10 Mbit/s of bandwidth shared among them. The system is difficult to install and maintain.
• 10BASE5 was superseded by much cheaper and more convenient alternatives:
  • first by 10BASE2 based on a thinner coaxial cable,
  • and then, once Ethernet over twisted pair was developed, by 10BASE-T and its successors 100BASE-TX and 1000BASE-T.
  • In 2003, the IEEE 802.3 working group deprecated 10BASE5 for new installations

10BASE2

• The name 10BASE2 is derived from several characteristics of the physical medium.

• The 10 comes from the transmission speed of 10 Mbit/s.

• The BASE stands for baseband signaling, and the 2 for a maximum segment length approaching 200 m (the actual maximum length is 185 m).

• 10BASE2 (also known as cheapernet,[1] thin Ethernet, thinnet, and thinwire) is a variant of Ethernet that uses thin coaxial cable terminated with BNC connectors to build a local area network.

• During the mid to late 1980s this was the dominant 10 Mbit/s Ethernet standard, but due to the immense demand for high-speed networking, the low cost of Category 5 cable, and the popularity of 802.11 wireless networks, both 10BASE2 and 10BASE5 have become increasingly obsolete, though devices still exist in some locations.

• As of 2011, IEEE 802.3 has deprecated this standard for new installations

双绞线命名

• Naming conventions@ref:Ethernet over twisted pair - Wikipedia

Generally, layers are named by their specifications:

• 10, 100, 1000, 10G, … – the nominal, usable speed at the top of the physical layer (no suffix = megabit/s, G = gigabit/s), excluding line codes but including other physical layer overhead (preamble, SFD, IPG); some WAN PHYs (W) run at slightly reduced bitrates for compatibility reasons; encoded PHY sublayers usually run at higher bitrates

• BASE, BROAD, PASS – indicates baseband, broadband, or passband signaling respectively

• -T, -T1, -S, -L, -E, -Z, -C, -K, -H … – medium (PMD):

  • T = twisted pair,
  • -T1 = single-pair twisted pair,
  • S = 850 nm short wavelength (multi-mode fiber),
  • L = 1300 nm long wavelength (mostly single-mode fiber),
  • E or Z = 1500 nm extra long wavelength (single-mode),
  • B = bidirectional fiber (mostly single-mode) using WDM,
  • P = passive optical (PON),
  • C = copper/twinax,
  • K = backplane, 2 or 5 or 36 = coax with 185/500/3600 m reach (obsolete),
  • F = fiber, various wavelengths,
  • H = plastic optical fiber

• X, R – PCS encoding method (varying with the generation):

  • X for 8b/10b block encoding (4B5B for Fast Ethernet),
  • R for large block encoding (64b/66b)

• 1, 2, 4, 10 – for LAN PHYs indicates number of lanes used per link;

  • for WAN PHYs indicates reach in kilometers

• For 10 Mbit/s, no encoding is indicated as all variants use Manchester code.

• Most twisted pair layers use unique encoding, so most often just -T is used.

• The reach, especially for optical connections, is defined as the maximum achievable link length that is guaranteed to work when all channel parameters are met (modal bandwidth, attenuation, insertion losses etc.).

• With better channel parameters, often a longer, stable link length can be achieved.

  • Vice versa, a link with worse channel parameters can also work but only over a shorter distance.
  • Reach and maximum distance have the same meaning.

屏蔽双绞线

• UTP 非屏蔽双绞线(Unshielded Twisted pair)

高速以太网

• 速率达到或超过100M/s的以太网称为高速以太网。

(1)100BASE-T以太网

• 100BASE-T以太网是在双绞线上传送100Mb/s基带信号的星形拓扑结构以太网，它使用CSMA/CD协议。
  • 这种以太网既支持全双工方式，又支持半双工方式
    • 可在全双工方式下工作而无冲突发生。
      • 因此，在全双工方式下不使用CSMA/CD协议。
• MAC帧格式仍然是802.3标准规定的。
  • 保持最短帧长不变，但将一个网段的最大电缆长度减小到100m。
  • 帧间时间间隔从原来的9.6μs改为现在的0.96μs.

(2)吉比特以太网

• 吉比特以太网又称千兆以太网，允许在1G/s速率下用全双工和半双工两种方式工作。
  • 使用802.3协议规定的帧格式。
  • 在半双工方式下使用CSMA/CD协议
  • 全双工方式不需要使用CSMA/CD协议
• 与10BASE-T和100BASE-T技术向后兼容

(3)10吉比特以太网

• 10吉比特以太网与10Mb/s、100Mb/s和1Gb/s以太网的帧格式完全相同。
• 10吉比特以太网还保留了802.3标准规定的以太网最小和最大帧长，便于升级。
• 10吉比特以太网不再使用铜线而只使用光纤作为传输媒体。
• 10吉比特以太网只工作在全双工方式，因此没有争用问题，也不使用CSMA/CD协议。
• 以太网从IOMb/s到10Gb/s的演进证明了以太网是
  • 可扩展的(从10Mb/s到10Gb/s)、
  • 灵活的(多种传输媒体、全/半双工、共享交换)，
  • 易于安装，稳健性好。