LevelOne GEP-0950 User Manual

GEP-0950

8 GE PoE-Plus + 1 GE SFP

Web Smart Switch

User Manual

V1.0

Table of Contents

ELECTRONIC EMISSION NOTICES ....................................................................................... IV

WARNING: .......................................................................................................................... V

1. INTRODUCTION ....................................................................................................... 1

1-1. PRODUCT OVERVIEW ................................................................................................... 1

1-2. CHECKLIST .................................................................................................................. 1

1-3. FEATURES .................................................................................................................... 1

1-4. CONNECTORS AND LEDS ............................................................................................. 3

1-4-1. User Interfaces on the Front Panel (Button, LEDs and Plugs) .......................... 3

2. INSTALLATION ......................................................................................................... 4

2-1. INSTALLING THE SWITCH ............................................................................................. 4

2-1-1. Hardware and Cable Installation ....................................................................... 4

2-1-2. Cabling Requirements ........................................................................................ 6

2-1-3. Configuring the Management Agent of GEP-0950 ............................................. 9

2-1-4. IP Address Assignment ....................................................................................... 9

3. BASIC CONCEPT AND MANAGEMENT .............................................................14

3-1. WHAT’S THE ETHERNET ..............................................................................................14

3-2. LOGICAL LINK CONTROL (LLC) .................................................................................15

3-3. MEDIA ACCESS CONTROL (MAC) ..............................................................................17

3-4. FLOW CONTROL .........................................................................................................22

3-5. HOW DOES A SWITCH WORK? ......................................................................................25

3-6. VIRTUAL LAN ............................................................................................................26

3-7. LINK AGGREGATION ...................................................................................................32

4. OPERATION OF WEB-BASED MANAGEMENT ...................................................34

4-1. WEB MANAGEMENT HOME OVERVIEW ......................................................................35

4-2. CONFIGURATION .........................................................................................................36

4-2-1. System Information ............................................................................................36

4-2-2. System Time .......................................................................................................40

4-2-3. Port Configuration ............................................................................................41

4-2-4. VLAN Mode Configuration ................................................................................43

4-2-5. VLAN Group Configuration...............................................................................44

4-2-6. VLAN Port Isolation Configuration ...................................................................48

4-2-7. PoE ....................................................................................................................49

4-2-8. PoE Status .........................................................................................................51

4-2-9. PoE Auto Checking ............................................................................................53

4-2-10. PoE Scheduling ...............................................................................................54

4-2-11. Aggregation......................................................................................................56

4-2-12. IGMP Snooping ...............................................................................................57

4-2-13. Mirroring Configuration .................................................................................58

4-2-14. QoS(Quality of Service) Configuration ...........................................................59

4-2-15. Loop Detection ................................................................................................62

4-2-16. Broadcast Strom Protection .............................................................................64

4-2-17. SNMP...............................................................................................................66

4-3. MONITORING ..............................................................................................................68

4-3-1. Statistics Overview ............................................................................................68

4-3-2. Detailed Statistics ..............................................................................................69

4-3-3. IGMP Status ......................................................................................................72

4-3-4. Ping Status .........................................................................................................74

4-4. MAINTENANCE ...........................................................................................................76

4-4-1. Warm Restart .....................................................................................................77

4-4-2. Factory Default .................................................................................................78

IP Address

192.168.1.1

Username

admin

Password

admin

4-4-3. Software Upgrade ..............................................................................................79

4-4-4. Configuration File Transfer ...............................................................................80

Default Settings

Caution

EN55022(2003)/CISPR-2( 2002)

class A

IEC61000-4-2 (2001)

4K V CD, 8KV, AD

IEC61000-4-3( 2002)

3V/m

IEC61000-4-4(2001)

1KV – (power line), 0.5KV – (signal line)

Circuit devices are sensitive to static electricity, which can damage their delicate electronics. Dry weather conditions or walking across a carpeted floor may cause you to acquire a static electrical charge.

To protect your device, always:

 Touch the metal chassis of your computer to ground the static electrical charge

before you pick up the circuit device.

 Pick up the device by holding it on the left and right edges only.  If you need using outdoor device connect to this device with cable then you

need to addition an arrester on the cable between outdoor device and this device.

Addition an arrester between outdoor device and this switch

 The switch supports the SFP Vendor includes: Manufacture, Agilent, Avago and

Finisa

Electronic Emission Notices

Federal Communications Commission (FCC) Statement

This equipment has been tested and found to comply with the limits for a class A computing device pursuant to Subpart J of part 15 of FCC Rules, which are designed to provide reasonable protection against such interference when operated in a commercial environment.

European Community (CE) Electromagnetic Compatibility Directive

This equipment has been tested and found to comply with the protection requirements of European Emission Standard EN55022/EN61000-3 and the Generic European Immunity Standard EN55024. EMC:

Warning:

 Self-demolition on Product is strictly prohibited. Damage caused by self-

demolition will be charged for repairing fees.

 Do not place product at outdoor or sandstorm.

 Before installation, please make sure input power supply and product

specifications are compatible to each other.

1. Introduction

 8 10/100/1000Mbps Auto-negotiation Gigabit Ethernet TP ports

 1 100/1000Mbps SFP Fiber port  512KB on-chip frame buffer

 Jumbo frame support 9KB

 Programmable classifier for QoS (Layer 2/Layer 3)

 8K MAC address and support VLAN ID (1~4094)

 IEEE802.1Q-in-Q nested VLAN support

 Full-duplex flow control (IEEE802.3x) and half-duplex backpressure

1-1. Product Overview

The LevelOne GEP-0950 is an intelligent Web Smart Switch, equipped with 8 x 10/100/1000Base-T PoE-Plus ports and 1 x 100/1000 Mbps dual speed SFP slot. It is IEEE802.3af/at compliant, provides power and data over a single Ethernet cable to any PoE device, with total power budget of 130W, up to 30W per port, and offers advanced PoE Manageability features which includes PoE Status, PoE Scheduling, PoE Power Delay and PoE Live Checking.

The switch is also contains several key network management features, designed to manage data traffic more effectively. Supports VLANs, Port Mirroring, IGMP v1/v2/v3, LAN security, IEEE 802.1p QoS with 8 priority queues, SNMP v2c and more. An ideal network solution for workgroups and edge deployments, or anyone looking for an affordable and efficient way to expand their network.

1-2. Checklist

Before you start installing the switch, verify that the package contains the following:

 GEP-0950

 Power Cord

 19” Rackmount Kit  Quick Installation Guide

 CD – User Manual

Please notify your sales representative immediately if any of the aforementioned items is missing or damaged.

1-3. Features

GEP-0950, a standalone off-the-shelf switch, provides the comprehensive features listed below for users to perform system network administration and efficiently and securely serve your network.

• Hardware

• Management

• Supports concisely the status of port and easily port configuration

• Supports per port traffic monitoring counters

• Supports 802.1Q VLAN

• Supports user management and limits one user to login

• Maximal packet length can be up to 9600 bytes for jumbo frame application

• Supports default configuration which can be restored to overwrite the current

configuration which is working on via Web UI and Reset button of the switch

• Supports on-line plug/unplug SFP modules

• Supports Quality of Service (QoS) for real time applications based on the

information taken from Layer 2 to Layer 3.

• Built-in web-based management instead of using CLI interface, providing a more convenient GUI for the user

1-4. Connectors and LEDs

LED

Color

Function

System LED

POWER

Green

Lit when +3.3V power is coming up

ALARM

Red

1. Lit when temperature over 70℃

2. Lit when loop detected when loop detection function is enabled

10/100/1000Ethernet Port 1 to 8 LED

LINK/ACT

Green

Lit when connection with remote device is good

Blinks when any traffic is present

SPD

Green/ Yellow/ Off

Lit Green when TP link on 1000Mbps speed

Lit Yellow when TP link on 10/100Mbps speed

Off when no link occur

1000SX/LX Gigabit Fiber Port 9 LED

LINK/ACT

Green

Lit when SFP connection with remote device is good

Blinks when any traffic is present

SPD

Green/ Yellow/ Off

Lit Green when SFP link on 1000Mbps speed

Lit Yellow when SFP link on 100Mbps speed

Off when no link occur

1-4-1. User Interfaces on the Front Panel (Button, LEDs and Plugs)

There are 8 Gigabit Ethernet PoE ports and 1 SFP fiber ports for optional removable modules on the front panel of the switch. LED display area, locating on the left side of the panel, contains a Power LED, which indicates the power status and 8 ports working status of the switch.

• LED Indicators

2. Installation

2-1. Installing the Switch

This section will give users a quick start for:

- Hardware and Cable Installation

- Management Station Installation

- Software booting and configuration

2-1-1. Hardware and Cable Installation

At the beginning, please do first:

 Wear a grounding device to avoid the damage from electrostatic discharge

 Be sure that power switch is OFF before you insert the power cord to power

source

• Installing Optional SFP Fiber Transceivers to the Switch

Note: If you have no modules, please skip this section.

• Connecting the SFP Module to the Chassis:

The optional SFP modules are hot swappable, so you can plug or unplug it before or after powering on.

1. Verify that the SFP module is the right model and conforms to the chassis

2. Slide the module along the slot. Also be sure that the module is properly

seated against the slot socket/connector

3. Install the media cable for network connection

4. Repeat the above steps, as needed, for each module to be installed into

slot(s)

5. Have the power ON after the above procedures are done

• TP Port and Cable Installation

 In the switch, TP port supports MDI/MDI-X auto-crossover, so both types of

cable, straight-through (Cable pin-outs for RJ-45 jack 1, 2, 3, 6 to 1, 2, 3, 6 in 10/100M TP; 1, 2, 3, 4, 5, 6, 7, 8 to 1, 2, 3, 4, 5, 6, 7, 8 in Gigabit TP) and crossed-over (Cable pin-outs for RJ-45 jack 1, 2, 3, 6 to 3, 6, 1, 2) can be used. It means you do not have to tell from them, just plug it.

 Use Cat. 5 grade RJ-45 TP cable to connect to a TP port of the switch and the

other end is connected to a network-aware device such as a workstation or a server.

 Repeat the above steps, as needed, for each RJ-45 port to be connected to a

Gigabit 10/100/1000 TP device.

Now, you can start having the switch in operation.

• Power On

The switch supports 100-240 VAC power supply. The power supply will automatically convert the local AC power source to DC power. It does not matter whether any connection plugged into the switch or not when power on, even modules as well. After the power is on, all LED indicators will light up and then all off except the power LED still keeps on. This represents a reset of the system.

• Firmware Loading

After resetting, the bootloader will load the firmware into the memory. It will take about 30 seconds, after that, the switch will flash all the LED once and automatically performs self-test and is in ready state.

2-1-2. Cabling Requirements

To help ensure a successful installation and keep the network performance good, please take a care on the cabling requirement. Cables with worse specification will render the LAN to work poorly.

2-1-2-1. Cabling Requirements for TP Ports

 For Fast Ethernet TP network connection

 The grade of the cable must be Cat. 5 or Cat. 5e with a maximum length of

100 meters.

 Gigabit Ethernet TP network connection

 The grade of the cable must be Cat. 5 or Cat. 5e with a maximum length of

100 meters. Cat. 5e is recommended.

2-1-2-2. Switch Cascading in Topology

• Typical Network Topology in Deployment

A hierarchical network with minimum levels of switch may reduce the timing delay between server and client station. Basically, with this approach, it will minimize the number of switches in any one path; will lower the possibility of network loop and will improve network efficiency. If more than two switches are connected in the same network, select one switch as Level 1 switch and connect all other switches to it at Level 2. Server/Host is recommended to connect to the Level 1 switch. This is general if no VLAN or other special requirements are applied.

Case1: All switch ports are in the same local area network. Every port can access

each other

If VLAN is enabled and configured, each node in the network that can communicate each other directly is bounded in the same VLAN area.

Here VLAN area is defined by what VLAN you are using. The switch supports both port-based VLAN and tag-based VLAN. They are different in practical deployment, especially in physical location. The following diagram shows how it works and what the difference they are.

Case2a: Port-based VLAN

Port-based VLAN Diagram

1. The same VLAN members could not be in different switches.

2. Every VLAN members could not access VLAN members each other.

3. The switch manager has to assign different names for each VLAN groups at one switch.

Case 2b: Port-based VLAN

1. VLAN1 members could not access VLAN2, VLAN3 and VLAN4 members.

2. VLAN2 members could not access VLAN1 and VLAN3 members, but they could access VLAN4 members.

3. VLAN3 members could not access VLAN1, VLAN2 and VLAN4.

4. VLAN4 members could not access VLAN1 and VLAN3 members, but they could access VLAN2 members.

Case3a: The same VLAN members can be at different switches with the same VID.

Default IP Setting: IP = 192.168.1.1 Subnet Mask = 255.255.255.0 Default Gateway = 192.168.1.254

2-1-3. Configuring the Management Agent of GEP-0950

In the way of web, user is allowed to startup the switch management function.

Users can use any one of them to monitor and configure the switch.

2-1-3-1. Configuring Management Agent of GEP-0950 through Ethernet Port

There are two ways to configure and monitor the switch through the switch’s Ethernet port. They are Web browser and SNMP manager. The user interface for the last one is Management software dependent and does not cover here. We just introduce the first type of management interface. Web-based UI for the switch is an interface in a highly friendly way.

• Managing GEP-0950 through Ethernet Port

Before you communicate with the switch, you have to finish first the configuration of the IP address or to know the IP address of the switch. Then follow the procedures listed below.

1. Set up a physical path between the configured the switch and a PC by a qualified UTP Cat. 5 cable with RJ-45 connector.

Note: If PC directly connects to the switch, you have to setup the

2. Run web browser and follow the menu. Please refer to Chapter 4.

2-1-4. IP Address Assignment

For IP address configuration, there are three parameters needed to be filled

in. They are IP address, Subnet Mask, Default Gateway and DNS.

IP address:

The address of the network device in the network is used for internetworking communication. It is “classful” because it is split into predefined address classes or categories.

Each class has its own network range between the network identifier and host identifier in the 32 bits address. Each IP address comprises two parts: network

same subnet mask between them. But, subnet mask may be different for the PC in the remote site.

identifier (address) and host identifier (address). The former indicates the network

Network identifier

Host identifier

110

Bit # 0 1 7 8 31

Network address Host address

Bit # 01 2 15 16 31

Network address Host address

Bit # 0 1 2 3 23 24 31

Network address Host address

where the addressed host resides, and the latter indicates the individual host in the network which the address of host refers to. And the host identifier must be unique in the same LAN. Here the term of IP address we used is version 4, known as IPv4.

With the classful addressing, it divides IP address into three classes, class A, class B and class C. The rest of IP addresses are for multicast and broadcast. The bit length of the network prefix is the same as that of the subnet mask and is denoted as IP address/X, for example, 192.168.1.0/10. Each class has its address range described below.

Class A:

Address is less than 126.255.255.255. There are a total of 126 networks can be defined because the address 0.0.0.0 is reserved for default route and

127.0.0.0/8 is reserved for loopback function.

Class B:

IP address range between 128.0.0.0 and 191.255.255.255. Each class B network has a 16-bit network prefix followed 16-bit host address. There are 16,384 (2^14)/16 networks able to be defined with a maximum of 65534 (2^16 –2) hosts per network.

Class C:

IP address range between 192.0.0.0 and 223.255.255.255. Each class C network has a 24-bit network prefix followed 8-bit host address. There are 2,097,152 (2^21)/24 networks able to be defined with a maximum of 254 (2^8 –2) hosts per network.

Class D and E:

Class D is a class with first 4 MSB (Most significance bit) set to 1-1-1-0 and

Class A

10.0.0.0 --- 10.255.255.255

Class B

172.16.0.0 --- 172.31.255.255

Class C

192.168.0.0 --- 192.168.255.255

10000000.00000001.00000010.1 0000000

25 bits

1 0000000 1 1111111

All 0s = 128.1.2.128

All 1s= 128.1.2.255 Subnet

Network

is used for IP Multicast. See also RFC 1112. Class E is a class with first 4 MSB set to 1-1-1-1 and is used for IP broadcast.

According to IANA (Internet Assigned Numbers Authority), there are three specific IP address blocks reserved and able to be used for extending internal network. We call it Private IP address and list below:

Subnet mask:

It means the sub-division of a class-based network or a CIDR block. The subnet is used to determine how to split an IP address to the network prefix and the host address in bitwise basis. It is designed to utilize IP address more efficiently and ease to manage IP network.

For a class B network, 128.1.2.3, it may have a subnet mask 255.255.0.0 in default, in which the first two bytes is with all 1s. This means more than 60

thousands of nodes in flat IP address will be at the same network. It’s too large to

manage practically. Now if we divide it into smaller network by extending network

prefix from 16 bits to, say 24 bits, that’s using its third byte to subnet this class B

network. Now it has a subnet mask 255.255.255.0, in which each bit of the first three bytes is 1. It’s now clear that the first two bytes is used to identify the class B network, the third byte is used to identify the subnet within this class B network and, of course, the last byte is the host number.

Not all IP address is available in the sub-netted network. Two special addresses are reserved. They are the addresses with all zero’s and all one’s host number. For example, an IP address 128.1.2.128, what IP address reserved will be looked like? All 0s mean the network itself, and all 1s mean IP broadcast.

In this diagram, you can see the subnet mask with 25-bit long,

255.255.255.128, contains 126 members in the sub-netted network. Another is that the length of network prefix equals the number of the bit with 1s in that subnet mask. With this, you can easily count the number of IP addresses matched. The following table shows the result.

Prefix Length

No. of IP matched

No. of Addressable IP

/32

/31

/30

/29

/28

/27

/26

/25

128

126

/24

256

254

/23

512

510

/22

1024

1022

/21

2048

2046

/20

4096

4094

/19

8192

8190

/18

16384

16382

/17

32768

32766

/16

65536

65534

According to the scheme above, a subnet mask 255.255.255.0 will partition a network with the class C. It means there will have a maximum of 254 effective nodes existed in this sub-netted network and is considered a physical network in an autonomous network. So it owns a network IP address which may looks like

168.1.2.0.

With the subnet mask, a bigger network can be cut into small pieces of network. If we want to have more than two independent networks in a worknet, a partition to the network must be performed. In this case, subnet mask must be applied.

For different network applications, the subnet mask may look like

255.255.255.240. This means it is a small network accommodating a maximum of 15 nodes in the network.

Default gateway:

For the routed packet, if the destination is not in the routing table, all the traffic is put into the device with the designated IP address, known as default router. Basically, it is a routing policy.

For assigning an IP address to the switch, you just have to check what the IP address of the network will be connected with the switch. Use the same network address and append your host address to it.

First, IP Address: as shown in the figure above, enter “192.168.1.1”, for

instance. For sure, an IP address such as 192.168.1.x must be set on your PC.

Second, Subnet Mask: as shown in the figure above, enter “255.255.255.0”. Any subnet mask such as 255.255.255.x is allowable in this case.

3. Basic Concept and Management

This chapter will tell you the basic concept of features to manage this switch

and how they work.

3-1. What’s the Ethernet

Ethernet originated and was implemented at Xerox in Palo Alto, CA in 1973 and was successfully commercialized by Digital Equipment Corporation (DEC), Intel and Xerox (DIX) in 1980. In 1992, Grand Junction Networks unveiled a new high speed Ethernet with the same characteristic of the original Ethernet but operated at 100Mbps, called Fast Ethernet now. This means Fast Ethernet inherits the same frame format, CSMA/CD, software interface. In 1998, Gigabit Ethernet was rolled out and provided 1000Mbps. Now 10G/s Ethernet is under approving. Although these Ethernet have different speed, they still use the same basic functions. So they are compatible in software and can connect each other almost without limitation. The transmission media may be the only problem.

In the figure above, we can see that Ethernet locates at the Data Link layer and Physical layer and comprises three portions, including logical link control (LLC), media access control (MAC), and physical layer. The first two comprises Data link layer, which performs splitting data into frame for transmitting, receiving acknowledge frame, error checking and re-transmitting when not received correctly as well as provides an error-free channel upward to network layer.

Coaxial/STP/UTP

IEEE 802.2 LLC

IEEE802.3 CSMA/CD MAC

IEEE 802.3 PLS

ANSI X3T9.5 PMD

IEEE 802.3

MAU

Physical

Layer

Data Link

Layer

MII

Fiber

This above diagram shows the Ethernet architecture, LLC sub-layer and MAC sub-layer, which are responded to the Data Link layer, and transceivers, which are responded to the Physical layer in OSI model. In this section, we are mainly describing the MAC sub-layer.

3-2. Logical Link Control (LLC)

Data link layer is composed of both the sub-layers of MAC and MAC-client.

Here MAC client may be logical link control or bridge relay entity.

Logical link control supports the interface between the Ethernet MAC and upper layers in the protocol stack, usually Network layer, which is nothing to do with the nature of the LAN. So it can operate over other different LAN technology such as Token Ring, FDDI and so on. Likewise, for the interface to the MAC layer, LLC defines the services with the interface independent of the medium access technology and with some of the nature of the medium itself.

The table above is the format of LLC PDU. It comprises four fields, DSAP,

SSAP, Control and Information. The DSAP address field identifies the one or more

0xAAAA

SNAP

0xE0E0

Novell IPX

0xF0F0

NetBios

0xFEFE

IOS network layer PDU

0xFFFF

Novell IPX 802.3 RAW packet

0x4242

STP BPDU

0x0606

0x9898

ARP

service access points, in which the I/G bit indicates it is individual or group address.

If all bit of DSAP is 1s, it’s a global address. The SSAP address field identifies the

specific services indicated by C/R bit (command or response). The DSAP and SSAP pair with some reserved values indicates some well-known services listed in the table below.

LLC type 1 connectionless service, LLC type 2 connection-oriented service and LLC type 3 acknowledge connectionless service are three types of LLC frame for all classes of service. In the figure above, it shows the format of Service Access Point

(SAP). Please refer to IEEE802.2 for more details.

3-3 SAP Format

3-3. Media Access Control (MAC)

1st byte

2nd byte

3rd byte

4th byte

5th byte

6th byte

OUI code

Serial number

3-3-1. MAC Addressing

Because LAN is composed of many nodes, for the data exchanged among these nodes, each node must have its own unique address to identify who should send the data or should receive the data. In OSI model, each layer provides its own mean to identify the unique address in some form, for example, IP address in network layer.

The MAC is belonged to Data Link Layer (Layer 2), the address is defined to be a 48-bit long and locally unique address. Since this type of address is applied only to the Ethernet LAN media access control (MAC), they are referred to as MAC addresses.

The first three bytes are Organizational Unique Identifier (OUI) code assigned by IEEE. The last three bytes are the serial number assigned by the vendor of the network device. All these six bytes are stored in a non-volatile memory in the device. Their format is as the following table and normally written in the form as aa-bb-cc-dd-ee-ff, a 12 hexadecimal digits separated by hyphens, in which the aa-bb-cc is the OUI code and the dd-ee-ff is the serial number assigned by manufacturer.

Bit 47 bit 0

The first bit of the first byte in the Destination address (DA) determines the address to be a Unicast (0) or Multicast frame (1), known as I/G bit indicating individual (0) or group (1). So the 48-bit address space is divided into two portions, Unicast and Multicast. The second bit is for global-unique (0) or locally-unique address. The former is assigned by the device manufacturer, and the later is usually assigned by the administrator. In practice, global-unique addresses are always applied.

A unicast address is identified with a single network interface. With this nature of MAC address, a frame transmitted can exactly be received by the target an interface the destination MAC points to.

A multicast address is identified with a group of network devices or network interfaces. In Ethernet, a many-to-many connectivity in the LANs is provided. It provides a mean to send a frame to many network devices at a time. When all bit of DA is 1s, it is a broadcast, which means all network device except the sender itself can receive the frame and response.

3-3-2. Ethernet Frame Format

There are two major forms of Ethernet frame, type encapsulation and length encapsulation, both of which are categorized as four frame formats 802.3/802.2 SNAP, 802.3/802.2, Ethernet II and Netware 802.3 RAW. We will introduce the basic Ethernet frame format defined by the IEEE 802.3 standard required for all MAC implementations. It contains seven fields explained below.

PRE

SFD

Type/Length

Data

Pad bit if any

FCS

7 7 6 6 2

46-1500

0x0800

IP datagram

0x0806

ARP

0x0835

RARP

0x8137

IPX datagram

0x86DD

IPv6

- Preamble (PRE) —The PRE is 7-byte long with alternating pattern of ones and zeros used to tell the receiving node that a frame is coming, and to synchronize the physical receiver with the incoming bit stream. The preamble pattern is:

10101010 10101010 10101010 10101010 10101010 10101010 10101010

- Start-of-frame delimiter (SFD) — The SFD is one-byte long with

alternating pattern of ones and zeros, ending with two consecutive 1-bits. It immediately follows the preamble and uses the last two consecutive 1s bit to indicate that the next bit is the start of the data packet and the left-most bit in the left-most byte of the destination address. The SFD pattern is 10101011.

- Destination address (DA) — The DA field is used to identify which

network device(s) should receive the packet. It is a unique address. Please see the section of MAC addressing.

- Source addresses (SA) — The SA field indicates the source node. The SA

is always an individual address and the left-most bit in the SA field is always

- Length/Type — This field indicates either the number of the data bytes

contained in the data field of the frame, or the Ethernet type of data. If the value of first two bytes is less than or equal to 1500 in decimal, the number of bytes in the data field is equal to the Length/Type value, i.e. this field acts as Length indicator at this moment. When this field acts as Length, the frame has optional fields for 802.3/802.2 SNAP encapsulation, 802.3/802.2 encapsulation and Netware 802.3 RAW encapsulation. Each of them has different fields following the Length field.

- If the Length/Type value is greater than 1500, it means the Length/Type

acts as Type. Different type value means the frames with different protocols running over Ethernet being sent or received.

For example,

- Data — Less than or equal to 1500 bytes and greater or equal to 46 bytes.

If data is less than 46 bytes, the MAC will automatically extend the padding bits and have the payload be equal to 46 bytes. The length of data field must equal the value of the Length field when the Length/Type acts as Length.

- Frame check sequence (FCS) — This field contains a 32-bit cyclic

redundancy check (CRC) value, and is a check sum computed with DA, SA, through the end of the data field with the following polynomial.

- It is created by the sending MAC and recalculated by the receiving MAC to

check if the packet is damaged or not.

How does a MAC work?

The MAC sub-layer has two primary jobs to do:

1. Receiving and transmitting data. When receiving data, it parses frame to detect error; when transmitting data, it performs frame assembly.

2. Performing Media access control. It prepares the initiation jobs for a frame transmission and makes recovery from transmission failure.

Frame transmission

As Ethernet adopted Carrier Sense Multiple Access with Collision Detect (CSMA/CD), it detects if there is any carrier signal from another network device running over the physical medium when a frame is ready for transmission. This is referred to as sensing carrier, also “Listen”. If there is signal on the medium, the MAC defers the traffic to avoid a transmission collision and waits for a random period of time, called backoff time, then sends the traffic again.

After the frame is assembled, when transmitting the frame, the preamble (PRE) bytes are inserted and sent first, then the next, Start of frame Delimiter (SFD), DA, SA and through the data field and FCS field in turn. The followings summarize what a MAC does before transmitting a frame.

1. MAC will assemble the frame. First, the preamble and Start-of-Frame delimiter will be put in the fields of PRE and SFD, followed DA, SA, tag ID if tagged VLAN is applied, Ethertype or the value of the data length, and payload data field, and finally put the FCS data in order into the responded fields.

2. Listen if there is any traffic running over the medium. If yes, wait.

3. If the medium is quiet, and no longer senses any carrier, the MAC waits for a period of time, i.e. inter-frame gap time to have the MAC ready with enough time and then start transmitting the frame.

4. During the transmission, MAC keeps monitoring the status of the medium. If no collision happens until the end of the frame, it transmits successfully. If there is a collision happened, the MAC will send the patterned jamming bit to guarantee the collision event propagated to all involved network devices, then wait for a random period of time, i.e. back off time. When backoff time expires, the MAC goes back to the beginning state and attempts to transmit again. After a collision happens, MAC increases the transmission attempts. If the count of the

transmission attempt reaches 16 times, the frame in MAC’s queue will

be discarded.

Ethernet MAC transmits frames in half-duplex and full-duplex ways. In half-

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duplex operation mode, the MAC can either transmit or receive frame at a moment, but cannot do both jobs at the same time.

As the transmission of a MAC frame with the half-duplex operation exists only in the same collision domain, the carrier signal needs to spend time to travel to reach the targeted device. For two most-distant devices in the same collision domain, when one sends the frame first, and the second sends the frame, in worstcase, just before the frame from the first device arrives. The collision happens and will be detected by the second device immediately. Because of the medium delay, this corrupted signal needs to spend some time to propagate back to the first device. The maximum time to detect a collision is approximately twice the signal propagation time between the two most-distant devices. This maximum time is traded-off by the collision recovery time and the diameter of the LAN.

In the original 802.3 specification, Ethernet operates in half duplex only.

Under this condition, when in 10Mbps LAN, it’s 2500 meters, in 100Mbps LAN, it’s

approximately 200 meters and in 1000Mbps, 200 meters. According to the theory, it

should be 20 meters. But it’s not practical, so the LAN diameter is kept by using to

increase the minimum frame size with a variable-length non-data extension bit field which is removed at the receiving MAC. The following tables are the frame format suitable for 10M, 100M and 1000M Ethernet, and some parameter values that shall be applied to all of these three types of Ethernet.

Actually, the practice Gigabit Ethernet chips do not feature this so far. They all have their chips supported full-duplex mode only, as well as all network vendors’ devices. So this criterion should not exist at the present time and in the future. The switch’s Gigabit module supports only full-duplex mode.

Gigabit Ethernet Frame

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