Tcp/ip explanation (version 2) notes / 3 link layer / 3.2 Ethernet and IEEE 802 lan/man standards

Catalog

---

3.2 Ethernet and IEEE 802 LAN/MAN standard

Ethernet （Ethernet） The term usually refers to a set of Standards
This standard applies to 1980 First released in 2004 , And in 1982 Year by year Digital Equipment company 、 Intel （Intel） Company and Xerox （Xerox） Company revision
The first common form of Ethernet is sometimes called “10Mb/s Ethernet ” or “ Shared Ethernet ”, By IEEE use （ Only minor changes have been made ）, The standard number is 802.3
Such a network usually follows the diagram 3-1 The network arrangement shown

chart 3-1
A basic shared Ethernet network consists of one or more devices connected to a shared cable segment station（ Such as ： The workstation 、 supercomputer ） form
When the media is determined to be free , Link layer PDU（ frame ） From a station Send to one or more other station
If more than one station Send data at the same time （ It may be caused by signal propagation delay ） There will be conflicts
Conflicts can be detected , Sending data station Will therefore wait for a random period of time , Then try again
This common pattern is called Carrier sense , Multiple access / Collision detection （carrier sense, multiple access with collision detection (CSMA/CD)）

Due to the multiple station Share the same network , Therefore, the standard includes a distributed algorithm implemented in each Ethernet network interface
Controlled by this algorithm station When to start sending data
This particular method is called Carrier sense , Multiple access / Collision detection （carrier sense, multiple access with collision detection (CSMA/CD)）
It can be used without any other special protocol or synchronization , Mediate which computers can access the shared media （ cable ） The problem of
This relatively simple approach reduces the cost of Ethernet Technology , It promotes the popularization of Ethernet technology

Use CSMA/CD when , One station（ Such as ： Computer ） First, find the signal currently being sent on the network , And send your own frames when the network is idle
This step is in the agreement Carrier sense （carrier sense） part
If some other station Happened to send data at the same time , The generated overlapping electrical signals will be detected as conflicts
under these circumstances , Every station Will try again after waiting a random time
The length of waiting time is extracted from a uniform probability distribution , This probability distribution doubles in length each time a subsequent conflict is detected
Final , Every station After a certain number of attempts , Either the data is successfully sent or the maximum number of retries is exceeded （ Traditional Ethernet can retry at most 16 Time ）
Use CSMA/CD when , Only one frame is transmitted on the network at any time
image CSMA/CD The more formal name of such an access method is ： Media access control （Media Access Control (MAC)） agreement , There are many different types of MAC agreement
Some of them are based on making each station Try to use the network independently （ image CSMA/CD Such a competition based agreement ）
Others are based on pre arranged coordination （ Such as ： For each station Allocate time slots to send data ）

since 10Mb/s Since the birth of Ethernet , Faster computers and infrastructure drive LAN The increase in the speed of
Given the popularity of Ethernet , Major innovations and efforts have successfully moved its speed from 10Mb/s Up to 100Mb/s, Until then 1000Mb/s, Until then 10Gb/s, Now even higher
10Gb/s The form of is becoming more and more popular in large data centers and large enterprises , And it has been proved that 100Gb/s The speed of
first （ To study ） Ethernet has only 3Mb/s The speed of
DIX（Digital、 Intel （Intel）、 Xerox （Xerox）） Standards are achieved by using shared physical cables or a set of cable segments interconnected by electrical repeaters , Reached 10Mb/s The speed of
To 1990 s , The shared cable is largely twisted pair （ Like a telephone line , Usually called “ 10BASE-T ”） replaced
With 100Mb/s Network development （ Also known as “ Fast Ethernet ”, Its most popular version is called “ 100BASE-TX ”）, Based on competition MAC Agreements have become less popular
In its place , Every LAN station Cabling between is usually not shared , Instead, dedicated circuits are provided in the star topology
This can be done via Ethernet Switch （switches） To achieve , Pictured 3-2 Shown

chart 3-2
Switched Ethernet consists of one or more station form , Every station Both use dedicated cabling paths to connect to switch ports
When using switched Ethernet , In most cases, the network operates in full duplex mode , And there's no need for CSMA/CD The algorithm
adopt “ Interconnect switch ports ”（ Sometimes called “ Uplink （uplink）” port ）, Switches can be cascaded together to form larger Ethernet LAN

Nowadays, the use of switches is very common
Switches can be used for each Ethernet station Provide the ability to send and receive data at the same time （ be called “ Full duplex Ethernet ”）
although 1000Mb/s Ethernet （1000BASE-T） Half duplex is still supported （ One time, one direction ） operation , But compared with full duplex Ethernet, it is rarely used
We will discuss in more detail later how the switch handles PDU Of

One of the most popular technologies for accessing the Internet today is the wireless network
For wireless LAN （wireless local area networks (WLANs)） Come on
The most common technique is one called Wireless fidelity （Wireless Fidelity） or Wi-Fi Of IEEE standard
Sometimes called “ Wireless Ethernet ” or 802.11
Although this standard is different from 802 Wired Ethernet standard , But its frame format and general interface are largely borrowed from 802.3, And are IEEE 802 LAN Part of the standard set
therefore ,TCP/IP Most of the functions used for Ethernet in also apply to Wi-Fi The Internet
Each of these technologies will be discussed in more detail later , But before that , Let's first look at all the tools used to set up home and business networks IEEE 802 The big picture of relevant standards is very useful
Management is also cited in this chapter MAN Standard ones IEEE standard
Include IEEE 802.16（WiMAX） Medium independent handoff standards in cellular networks （IEEE 802.21）

---

Catalog