64145819-06-Ethernet-Principle-20090724-A

www.huawei.com

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Ethernet Principle

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page2

Objectives

Upon completion of this course, you will be able to:

Know the technical background of the Ethernet and its basic

concepts

Describe the common Ethernet equipment and their working

principle

Understand the function of VLAN


Contents

1. Ethernet Concept

2. Ethernet Port Technology

3. VLAN Basis


Do you know why IP address is

not fixed as MAC?

00000001 10111011 00111010 10111010 10111110 10101000

It means this is a multicast address.

Ethernet MAC Address

00.e0.fc.39.80.34

MAC address includes 48 bits and it is shown as 12 dotted

hexadecimal notations

MAC address is exclusive globally which is allotted and managed by

IEEE. Every MAC address is composed of two parts. The first 24 bits

part is the vendor code and the other 24 bits part is serial number

If 48 bits are all “1”, it means the address is used for broadcast

If the 8th bit is “1”, it means the address is used for multicast


Ethernet_II

DMAC SMAC Length/T DATA/PAD FCS

Length/Type Mean

Length/T > 1500

Length/T <= 1500

Type of the frame

Length of the frame 802.3

46---1500 bytes

64---1518 bytes

Ethernet Frame Structure


Ethernet Principle---CSMA/CD

CS: carrier sense

Sense before sending data to ensure the cable is idle and reduce

collision.

MA: multiple access

The data from every station can be received by other multiple stations.

CD: collision detection

Detect collision while sending data and stop it when the station find

collision then continue to send after waiting for a random time.


1 2 3 4 5

IN

OUT OUT OUT OUT

HUB only changes the physical topology of Ethernet,

It is half duplex.

Working Principle of HUB


HUB

LAN

LAN

LAN

LAN

LAN

HUB only repeats all the signals coming from connected LAN and

all the physical equipment construct a collision domain.

Collision Domain


Defects of Traditional Ethernet

The transmission efficiency is low in case of many hosts

connected

A lot of collisions

Broadcast storm

No security

Use HUBs to construct the LAN as a sharing Ethernet


Physical

layer

Data link

layer

(BRIDGE/Ethernet switch/L2) equipment work

mode

L2 Work Mode

Application layer

Presentation layer

Conversation layer

Transport layer

Network layer

Data link layer

Physical layer Physical

layer

L2 switch

Data link

layer

Application layer

Presentation layer

Conversation layer

Transport layer

Network layer

Data link layer

Physical layer


L2 Work Principle

Learning based on source

Segment 1 Segment 2

A

B

C

PORT

1

PORT

2 D

typical use of the switch

switch

MAC ADD. port

MAC A 1

MAC B 1

MAC C 2

MAC D 2


L2 Work Principle (Cont.)

Forwarding based on destination address

Port 1

Port 2

L2 Switch

MACD MACA ………

MACA MACD ………

MAC ADD. port

MAC A 1

MAC B 1

MAC C 2

MAC D 2


L2 Switch Principle

Receive all the data frames from the network segment

Save the source MAC addresses of the received frames to establish MAC

address table( self-learning based on source address) and maintain the

address table by aging mechanism

Check the MAC address table to find out the port corresponding to the

destination address. If it is the receiving port, it will take the frame; if it is

not the receiving port, the data will be broadcasted to all the other ports

(except the source port)

Forward broadcast and multicast frames to all other ports (except the

source port)


Three Switch Modes

Cut-Through：

Switch forward the frame immediately after it receive destination address

Short time delay

Switch don’t check the error

Store-and-Forward：

Switch forward the frame after it receive the whole frame

Long time delay

Switch check the error so no error frame will be forwarded

Fragment-free：

Switch forward the frame after it receive 64 bytes( the shortest frame length)

Integrate the advantage of the cut-through and store-and-forward mode


L2 will forward the received frames according to the MAC

address so collision domain is limited to one port. But it can not

limit the broadcast domain.

Broadcast Domain

SWITCH

LAN

LAN

LAN

LAN

LAN

Broadcast domain

collision domain

collision domain collision domain

collision domain collision domain


Contents

1. Ethernet Concept


3. VLAN Basis


Ethernet Connection Requirements

Ethernet connection must ensure the performance of the

network

Bandwidth

Delay

Two methods to increase bandwidth for users:

Increase the overall network bandwidth

Build switching Ethernet, and use bandwidth exclusively.

Increase link rate: 10M--100M--1000M

Decrease the number of equipment attached to the same shared

medium


Technical

Standard Types of Cable

Transmission

Distance

100BaseTX 2 pairs EIA/TIA Type 5 (UTP) Unshielded Twisted Pair 100m

100BaseT4 4 pairs EIA/TIA Type 3, 4 and 5 (UTP) Unshielded Twisted Pair 100m

100BaseFX Multi-Mode Fiber (MMF) cable 550m-2km

1000BaseCX Copper shielded twisted-pair 25m

1000BaseT Copper EIA/TIA Category 5 (UTP) Unshielded twisted-pair, 4 pair 100m

1000BaseSX Multi-mode fiber, 50/62.5um fiber, use 850nm laser 550m/275m

EIA: Electronics Industries Association

TIA: Telecommunications Industries Association

Transmission Distance of Fast Ethernet


If there is no auto-negotiation mechanism, the following

problems will arise:

Cannot realize the auto dual-rate configuration function of the

port (such as 10Mbit/s and 100Mbit/s)

Cannot confirm the operation mode of duplex

Cannot confirm whether it's in need of the flow-control function

or not

If both of the equipment provide auto-negotiation then, it is

the best choice.

Ethernet Technology---Auto-

Negotiation


Fast link pulse includes a series of clock/digital

sequence comprised of link integration test pulse.

The basic mechanism of the auto-negotiation function is to

encapsulate the negotiation message into the link

integration test pulse.

16ms

Every pulse includes 16 digital sequence

……

Fast link pulse

Ethernet Technology---Auto-

Negotiation (Cont.)


Auto-Negotiation

If one device can not support auto-negotiation, the other device

that can support auto-negotiation will work at the default work

method.

Half-Duplex Full-Duplex

10M Support Support

100M Support Support

1000M - Support

10G - Support


Auto-Negotiation on Optical Fiber

For the optical fiber Ethernet, the conclusion is:

The operation modes at two ends of the link must be manually

configured (speed, duplex modes, flow-control and etc.)

The auto-negotiation of Gigabit Ethernet has been realized


Flow Control

The function of flow control is to prevent frames from being

lost in case of congestion

Under half duplex mode, the flow control is achieved by

backpressure technology

Under full duplex mode, the flow control generally abides by

standard IEEE 802.3x


Half Duplex Flow Control

backpressure

Pretend that there is

collision, then you will not

constantly transfer!


PAUSE Frame

DATA Frame

Full Duplex Flow Control

IEEE802.3x standard defines a new method named PAUSE

frame, to realize the flow control in the full duplex

environment.

PAUSE frame uses a reserved multicast address which

wouldn't be repeated by bridge or switch

Stop Congestion


Contents

1. Ethernet Concept


3. VLAN Basis


Broadcast flooding is the main disadvantage of L2

switch

Disadvantage of Full Duplex and L2

Switch

Full duplex and L2 make Ethernet progress, resolve the

conflict problem and improve the Ethernet performance.

Furthermore the security is enhanced to some extent. But

the following disadvantages are still in the Ethernet:

Broadcast flooding

Security can’t be guaranteed completely


……

Cause of VLAN Generation---

Broadcast Storm

broadcast


Broadcast domain1

VLAN 10 Broadcast domain2

VLAN 20

Broadcast domain3

VLAN 30

Engineering Department

Financial Department Marketing Department

Prevent Broadcast Storm via

VLAN

Prevent Broadcast Storm


MAC VLAN

MAC A 5

MAC B 10

MAC C 5

MAC D 10

MAC A MAC B MAC C MAC D

Switch

Port VLAN

Port 1 5

Port 3 10

Port 7 5

Port 10 10

PC A PC B PC C PC D

Switch

Port 1

Port 3 Port 7

Port 10

VLAN Based on MAC or Port


Protocol VLAN

IPX 5

UDP 10

IP 2

………. 11

IPX IP UDP IP

Switch

IP VLAN

1.1.1.1/24 5

1.1.2.1/24 10

1.1.3.1/24 2

………. 11

1.1.1.1/24 1.1.2.1/24 1.1.3.1/24 2.1.1.1/24

Switch

VLAN Based on Protocol or Subnet


Frame Format of VLAN

DA SA Type Data CRC

Standard Ethernet Frame

DA SA Type Data CRC tag

TPID Priority CFI VLAN ID

TCI

Ethernet Frame with IEEE802.IQ Flag


VLAN 2 VLAN 1

VLAN 1 VLAN 2

Ethernet frame

with VLAN tag 1

Ethernet frame

with VLAN tag 2

Ethernet frame

without VLAN flag

Frame Changes in Network

Communication


Ethernet Card Port Tag Mode Packets

Port Tag flag Untag flag

Tag aware (In) Transmit transparently Drop

Tag aware (Out) Transmit transparently －

Access (In) Drop Attach a Tag flag (default VLAN

ID)

Access (Out) Remove the Tag flag (default

VLAN ID) －

Hybrid (In) Transmit transparently Attach a Tag flag (default VLAN

ID)

Hybrid (Out)

If VLAN ID is the same, remove

the Tag flag, otherwise transmit

transparently

－


Advantage and Disadvantage of VLAN

VLAN technology resolves the broadcast problem and

enhances the communication security.

Disadvantage of VLAN:

Improve the bandwidth utilization rate by dividing a physically

interconnected network into several small logic networks. But

what should we do if different VLANs need to communicate

with each other?


Questions

Please describe the working mechanism of L2 Switch?

What is the advantage of VLAN?


Summary

Ethernet Concept

Ethernet Port Technology

VLAN Basis

Thank you www.huawei.com

Documents

64145819-06-Ethernet-Principle-20090724-A