Data Communication Computer Network 简明教程
Network LAN Technologies
让我们简要了解一下各种局域网 (LAN) 技术：
Let us go through various LAN technologies in brief:
Ethernet
以太网是一种广泛部署的局域网技术，该技术由鲍勃·梅特卡夫和 D.R. 博格斯于 1970 年发明。它于 1980 年在 IEEE 802.3 中标准化。
Ethernet is a widely deployed LAN technology.This technology was invented by Bob Metcalfe and D.R. Boggs in the year 1970. It was standardized in IEEE 802.3 in 1980.
以太网共享介质。使用共享介质的网络数据很容易发生冲突。以太网使用载波侦听多路访问/冲突检测 (CSMA/CD) 技术来检测冲突。当在以太网中发生冲突时，所有主机都会回滚，等待一段时间，然后重新传输数据。
Ethernet shares media. Network which uses shared media has high probability of data collision. Ethernet uses Carrier Sense Multi Access/Collision Detection (CSMA/CD) technology to detect collisions. On the occurrence of collision in Ethernet, all its hosts roll back, wait for some random amount of time, and then re-transmit the data.
以太网连接器是具有 48 位 MAC 地址的网络接口卡。这有助于其他以太网设备识别以太网中的远程设备并与其通信。
Ethernet connector is,network interface card equipped with 48-bits MAC address. This helps other Ethernet devices to identify and communicate with remote devices in Ethernet.
传统的以太网使用 10BASE-T 规范。数字 10 表示 10Mbps 的速度，BASE 表示基带，而 T 表示粗以太网。10BASE-T 以太网提供高达 10Mbps 的传输速度，并使用同轴电缆或带有 RJ-45 连接器的 Cat-5 双绞线同轴电缆。以太网采用星形拓扑结构，线段长度最长为 100 米。所有设备都以星形方式连接到集线器/交换机。
Traditional Ethernet uses 10BASE-T specifications.The number 10 depicts 10MBPS speed, BASE stands for baseband, and T stands for Thick Ethernet. 10BASE-T Ethernet provides transmission speed up to 10MBPS and uses coaxial cable or Cat-5 twisted pair cable with RJ-45 connector. Ethernet follows star topology with segment length up to 100 meters. All devices are connected to a hub/switch in a star fashion.
Fast-Ethernet
为了满足快速发展的软件和硬件技术的需要，以太网扩展为快速以太网。它可以在 UTP、光纤和无线环境下运行。它可以提供高达 100 Mbps 的速度。此标准在 IEEE 803.2 中使用 Cat-5 双绞线电缆命名为 100BASE-T。对于有线介质，它使用 CSMA/CD 技术在以太网主机之间共享，而对于无线以太网局域网，它使用 CSMA/CA（CA 表示冲突避免）技术。
To encompass need of fast emerging software and hardware technologies, Ethernet extends itself as Fast-Ethernet. It can run on UTP, Optical Fiber, and wirelessly too. It can provide speed up to 100 MBPS. This standard is named as 100BASE-T in IEEE 803.2 using Cat-5 twisted pair cable. It uses CSMA/CD technique for wired media sharing among the Ethernet hosts and CSMA/CA (CA stands for Collision Avoidance) technique for wireless Ethernet LAN.
光纤上的快速以太网在 100BASE-FX 标准下定义，该标准提供高达 100 Mbps 的光纤速度。光纤上的以太网在半双工模式下可以扩展到 100 米，在多模光纤上的全双工模式下可以达到 2000 米。
Fast Ethernet on fiber is defined under 100BASE-FX standard which provides speed up to 100 MBPS on fiber. Ethernet over fiber can be extended up to 100 meters in half-duplex mode and can reach maximum of 2000 meters in full-duplex over multimode fibers.
Giga-Ethernet
快速以太网在 1995 年推出后，仅享受了 3 年的高速状态，直到千兆以太网的推出。千兆以太网提供高达 1000 兆位/秒的速度。IEEE802.3ab 使用 Cat-5、Cat-5e 和 Cat-6 电缆对千兆以太网进行了标准化。IEEE802.3ah 定义了光纤上的千兆以太网。
After being introduced in 1995, Fast-Ethernet could enjoy its high speed status only for 3 years till Giga-Ethernet introduced. Giga-Ethernet provides speed up to 1000 mbits/seconds. IEEE802.3ab standardize Giga-Ethernet over UTP using Cat-5, Cat-5e and Cat-6 cables. IEEE802.3ah defines Giga-Ethernet over Fiber.
Virtual LAN
局域网使用以太网，而以太网又使用共享介质。以太网中的共享介质会创建一个单一广播域和一个单一冲突域。将交换机引入以太网已经消除了单一冲突域问题，并且连接到交换机的每个设备都在其单独的冲突域中工作。但即使交换机也不能将网络划分为单独的广播域。
LAN uses Ethernet which in turn works on shared media. Shared media in Ethernet create one single Broadcast domain and one single Collision domain. Introduction of switches to Ethernet has removed single collision domain issue and each device connected to switch works in its separate collision domain. But even Switches cannot divide a network into separate Broadcast domains.
虚拟局域网 (VLAN) 是将单个广播域划分为多个广播域的解决方案。一个 VLAN 中的主机无法与另一个 VLAN 中的主机通信。默认情况下，所有主机都被置于同一 VLAN 中。
Virtual LAN is a solution to divide a single Broadcast domain into multiple Broadcast domains. Host in one VLAN cannot speak to a host in another. By default, all hosts are placed into the same VLAN.
在此图中，不同的 VLAN 以不同的颜色代码表示。同一 VLAN 中的主机即使连接到同一交换机上也无法看到或与不同 VLAN 中的其他主机通信。VLAN 是一项第 2 层技术，与以太网密切配合。要路由两个不同 VLAN 之间的包，需要使用第 3 层设备（如路由器）。
In this diagram, different VLANs are depicted in different color codes. Hosts in one VLAN, even if connected on the same Switch cannot see or speak to other hosts in different VLANs. VLAN is Layer-2 technology which works closely on Ethernet. To route packets between two different VLANs a Layer-3 device such as Router is required.