Ethernet. Standards and Implementation. Part I

Содержание

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Ethernet Standards and Implementation

Ethernet

Standards and Implementation

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Standards and Implementation The most common LAN technology. Different media (copper

Standards and Implementation

The most common LAN technology.
Different media (copper cable, optical fibre)
Different bandwidths (10, 100Mbps Gigabit,

10Gigabit)
Same addressing scheme
Same basic frame format
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Standards and Implementation History: First LAN was Ethernet, designed at Xerox.

Standards and Implementation

History:
First LAN was Ethernet, designed at Xerox.
1980: First Ethernet

standard published by DIX (Digital, Intel, Xerox).
1985: IEEE modified the Ethernet standard and published as 802.3.
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Standards and Implementation 802.3 OSI Model Compatibility: Needs of Layer 1.

Standards and Implementation

802.3 OSI Model Compatibility:
Needs of Layer 1.
The lower portion

of Layer 2 of the OSI model.
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Standards and Implementation Layer 2 divided into two distinct areas of

Standards and Implementation

Layer 2 divided into two distinct areas of functionality

or sub-layers.
Logical Link Control (LLC) – 802.2:
To communicate with the Network Layer.
Media Access Control (MAC) – 802.3:
To handle MAC addressing, framing and communication with the Physical Layer.
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Standards and Implementation Layer 1 limitations were addressed at Layer 2.

Standards and Implementation

Layer 1 limitations were addressed at Layer 2.

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Standards and Implementation Logical Link Control (LLC) – 802.2: Communicates with

Standards and Implementation

Logical Link Control (LLC) – 802.2:
Communicates with the upper

layers independent of the type of physical media.
Media Access Control (MAC) – 802.3:
Controls access to the media.
Not the only standard that performs the same function.
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Standards and Implementation Ethernet 802.3

Standards and Implementation

Ethernet 802.3

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Standards and Implementation Logical Link Control (LLC) – 802.2: Prepares the

Standards and Implementation

Logical Link Control (LLC) – 802.2:
Prepares the data for

the upper layers.
Allows running multiple network protocols on the same machine. Each protocol is assigned a specific ID.
Implemented mainly in software.
Media Access Control (MAC) - 802.3:
Creates the frame and addresses the frame with the source and destination MAC address.
Checks for any errors using the FCS field.
Controls the assignment of frames on the media.
Controls the recovery of the media due to collisions.
Implemented mainly in hardware.
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Physical Implementations Most of the traffic on the Internet originates and

Physical Implementations

Most of the traffic on the Internet originates and ends

with Ethernet connections.
When optical fiber media was introduced, Ethernet adapted to this new technology.
The success of Ethernet is due to the following factors:
Simplicity and ease of maintenance
Ability to incorporate new technologies
Reliability
Low cost of installation and upgrade
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Ethernet Communication Through the LAN

Ethernet

Communication Through the LAN

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Historical Ethernet CSMA/CD

Historical Ethernet

CSMA/CD

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Early Media

Early Media

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Legacy Ethernet Hub Switch

Legacy Ethernet

Hub

Switch

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Legacy Ethernet Hub Half Duplex: One way traffic. Necessary on a

Legacy Ethernet

Hub

Half Duplex:
One way traffic.
Necessary on a shared media.
Only one device

can transmit at a time.
Collisions occur.
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Switch Legacy Ethernet Full Duplex: Two way traffic. Not a shared

Switch

Legacy Ethernet

Full Duplex:
Two way traffic.
Not a shared media.
Dedicated switch connection.
A device can transmit

and receive at the same time.
No Collisions.
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Legacy Ethernet Ethernet with hubs is designed to work with collisions.

Legacy Ethernet

Ethernet with hubs is designed to work with collisions.
Collisions occur

when devices transmit at the same time.
Managed by CSMA/CD.
As more devices are added, more collisions occur.
As more collisions occur, network performance degrades.
Half Duplex communication.
Ethernet with switches is designed to eliminate collisions.
Each device attached to switch only receives frames destined for that device.
Full Duplex communication.
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Moving to 1 Gbps and Beyond Gigabit Ethernet is used to

Moving to 1 Gbps and Beyond

Gigabit Ethernet is used to describe

implementations that provide bandwidth of 1000 Mbps (1 Gbps) or greater.
Built on the full-duplex capability and the UTP and fiber-optic media technologies of earlier Ethernet.

New networking services require high bandwidth LANs.

Does not always mean replacement of existing switches and cables .

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Moving to 1 Gbps and Beyond Increased cabling distances enabled by

Moving to 1 Gbps and Beyond

Increased cabling distances enabled by the

use of fiber-optic cable in Ethernet-based networks has resulted in a blurring of the distinction between LANs and WANs.
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Ethernet Ethernet Frame

Ethernet

Ethernet Frame

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Encapsulating the Packet The Ethernet protocol defines the frame format. Adds

Encapsulating the Packet

The Ethernet protocol defines the frame format.
Adds headers and

trailers around the Layer 3 packet.
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Encapsulating the Packet The IEEE 802.3 Ethernet Frame format: Minimum Size:

Encapsulating the Packet

The IEEE 802.3 Ethernet Frame format:
Minimum Size: 64 Bytes
Maximum

Size: 1518 Bytes
If the frame is less than the minimum or greater than the maximum, it is considered corrupt and will be dropped.

Header

Trailer

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Encapsulating the Packet Preamble and Start of Frame Delimiter (SFD) –

Encapsulating the Packet

Preamble and Start of Frame Delimiter (SFD) – 8

bytes:
Used to synchronize the NIC with the media in preparation for receiving a frame.
Is not considered part of the frame length.
Will not appear in any capture of the frame.
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Encapsulating the Packet Destination MAC Address – 6 bytes: Identifies the

Encapsulating the Packet

Destination MAC Address – 6 bytes:
Identifies the node that

is to receive the frame.
A receiving device compares its MAC address to the contents of this field.
If the addresses match, the frame is accepted.
Also used by switches to determine the interface to be used to forward the frame.
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Encapsulating the Packet Source MAC Address – 6 bytes: Identifies the

Encapsulating the Packet

Source MAC Address – 6 bytes:
Identifies the node that

originated the frame.
Also used by switches to add addresses to their internal Port / MAC address tables.
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Encapsulating the Packet Length / Type – 2 bytes: DIX used

Encapsulating the Packet

Length / Type – 2 bytes:
DIX used this for

type, the original IEEE 802.3 standard used it for length. The later IEEE standard (Ethernet II) allows it to be used for either.
Ethernet II is the frame type used in TCP/IP networks.
If the value is greater than 1518 (0x600), it contains a code identifying the encapsulated upper layer protocol.
Any other value defines the length of the frame.
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Encapsulating the Packet Data and Pad – 46 to 1500 bytes:

Encapsulating the Packet

Data and Pad – 46 to 1500 bytes:
The encapsulated

data from Layer 3.
Most commonly an IPv4 packet.
If the total frame length is less than 64 bytes, the field is padded to the right with enough null characters to meet the minimum frame length.
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Encapsulating the Packet Frame Check Sequence (FCS)– 4 bytes: Used to

Encapsulating the Packet

Frame Check Sequence (FCS)– 4 bytes:
Used to detect errors

in a frame that may have occurred during transmission along the media.
The result of a Cyclic Redundancy Check (CRC) is placed in the frame by the sending node.
The receiving node performs the same CRC and compares the values….they should be equal.
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Ethernet MAC Address In order for a transmission to be received

Ethernet MAC Address

In order for a transmission to be received properly

at the destination computer, there must be a method of uniquely identifying that host.
A unique address is permanently programmed into ROM in each NIC ("burned in“ ) when it is manufactured.
Because of this, the MAC Address is often referred to as the burned in (BIA) address or physical address of a machine.
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Ethernet MAC Address 48 bits in length. Expressed as 12 hexadecimal

Ethernet MAC Address

48 bits in length.
Expressed as 12 hexadecimal digits.
The first 6

hexadecimal digits, which are administered by the IEEE, identify the manufacturer or vendor and thus comprise the Organizational Unique Identifier (OUI).
The remaining 6 hexadecimal digits comprise the interface serial number, or another value administered by the specific vendor.
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Ethernet MAC Address The OUI and the sequential number ensure that

Ethernet MAC Address

The OUI and the sequential number ensure that the

assigned MAC addresses remain unique.
You will see them expressed in different ways.

Cisco MAC Address
00-60-2F-3A-07-BC
00:60:2F:3A:07:BC
0060.2F3A.07BC

Intel MAC Address
00-20-E0-6B-17-62
00:20:E0:6B:17:62
0020.E06B.1762

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Ethernet MAC Address When a network device matches the destination address

Ethernet MAC Address

When a network device matches the destination address to

the address in the NIC, the NIC passes the frame up the OSI layers where the decapsulation process takes place.
The MAC address is essential to communications on a network. It is the only address that guarantees that the message will be accepted by the destination.
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Hexadecimal Numbering and Addressing A big problem with the binary system

Hexadecimal Numbering and Addressing

A big problem with the binary system was

verbosity. In order to represent the number 202:
Requires 3 decimal digits (202).
Requires 8 bits (11001010).
When representing large numbers, the binary system quickly becomes unwieldy.
We can also convert from decimal to binary but the conversion is not a trivial task.
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Hexadecimal Numbering and Addressing The hexadecimal numbering system addresses both of

Hexadecimal Numbering and Addressing

The hexadecimal numbering system addresses both of these

issues:
It is compact.
It easy to convert from binary to hexadecimal and vice versa.
Because of this most of the computers in use today use the hexadecimal system.
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Hexadecimal Numbering and Addressing You can expect to see hex numbers

Hexadecimal Numbering and Addressing

You can expect to see hex numbers represented

in documents and the web in different ways:
23A916 2eb6H 0FCDh ‘7b’
0xE0 0x23facb92 %0a000c834a >34ce
10-00-5a-29-16-ab (NIC – e.g. ipconfig –all)
00:00:0C:48:8C:11 (NIC – e.g. router MAC display
#FFFFFF (Web RGB Colour Code)
1080:0:0:0:8:800:200C:417A (IP Version 6 Address)
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Hexadecimal Numbering and Addressing BIT: 0 and 1 NIBBLE: BYTE: WORD: Binary Data Organization

Hexadecimal Numbering and Addressing

BIT: 0 and 1

NIBBLE:

BYTE:

WORD:

Binary Data Organization

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Hexadecimal Numbering and Addressing Hexadecimal and Binary: Hexadecimal numbering is base

Hexadecimal Numbering and Addressing

Hexadecimal and Binary:
Hexadecimal numbering is base 16 and

requires a way to represent the values 0 to 15:
Each hexadecimal digit is represented in binary by one nibble (4 bits).
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Hexadecimal Numbering and Addressing Hexadecimal and Binary: A byte is 8

Hexadecimal Numbering and Addressing

Hexadecimal and Binary:
A byte is 8 bits (2

nibbles).
Each byte is represented by a group of 2 hexadecimal digits and each word by a group of 4 digits.
e.g. 0x1234, 0xBEEF, 0xDEAF, 0xDEAD, 0xFEED
Bytes are usually, but not always, separated by a colon (:), a dash (–) or a space.
0x12:34 0xBE-EF 0xDE AF
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Hexadecimal Numbering and Addressing Converting Hexadecimal to Binary: Convert 0xCA to

Hexadecimal Numbering and Addressing

Converting Hexadecimal to Binary:
Convert 0xCA to Binary…….
Convert each

hexadecimal digit to its binary equivalent.
C = 1100 (12) A = 1010 (10)
Combine the nibbles in the same sequence to form the complete byte.
11001010
0xCA = 11001010 = 202
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Hexadecimal Numbering and Addressing Converting Binary to Hexadecimal: Convert 11001010 to

Hexadecimal Numbering and Addressing

Converting Binary to Hexadecimal:
Convert 11001010 to Hexadecimal…..
Beginning at

the left, divide the byte to form 4-bit nibbles.
1100 1010
Convert each nibble to its hexadecimal equivalent.
1100 = 12 = C 1010 = 10 = A
11001010 = 0xCA
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Hexadecimal Numbering and Addressing

Hexadecimal Numbering and Addressing

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Viewing the MAC Address

Viewing the MAC Address

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Another Layer of Addressing

Another Layer of Addressing

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Ethernet Unicast, Multicast and Broadcast Different MAC addresses are used to

Ethernet Unicast, Multicast and Broadcast

Different MAC addresses are used to provide

different types of communication.
Unicast:
A unique address identifying a specific host.
Multicast:
An address recognized by a specific group of hosts.
Broadcast:
An address used to send information to all hosts.
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Ethernet Unicast, Multicast and Broadcast

Ethernet Unicast, Multicast and Broadcast

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Ethernet Unicast, Multicast and Broadcast

Ethernet Unicast, Multicast and Broadcast

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Ethernet Unicast, Multicast and Broadcast

Ethernet Unicast, Multicast and Broadcast

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Ethernet Ethernet MAC CSMA/CD

Ethernet

Ethernet MAC
CSMA/CD

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Ethernet MAC method In a shared media environment, all devices have

Ethernet MAC method

In a shared media environment, all devices have guaranteed

access to the medium but they have no prioritized claim on it.
If more than one device transmits simultaneously
The physical signals collide.
The network must recover.
Collisions are the cost that Ethernet pays to get the low overhead associated with each transmission.
Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to detect and handle collisions and manage the resumption of communications.
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CSMA/CD: The Process To transmit, each host will listen on the

CSMA/CD: The Process

To transmit, each host will listen on the media.
If

a signal from another device is present, it will wait for a specific amount of time and listen again.
If no signal is present, it will transmit.
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CSMA/CD: The Process It can happen that two devices will determine

CSMA/CD: The Process

It can happen that two devices will determine that

it is safe to transmit at exactly the same time.
In that case, both will transmit their frame.
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CSMA/CD: The Process Both devices detect the collision and send out

CSMA/CD: The Process

Both devices detect the collision and send out a

jamming signal.
The jamming signal is detected by all devices and all devices now know that a collision has occurred on the network.
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CSMA/CD: The Process The jamming signal causes each device to invoke

CSMA/CD: The Process

The jamming signal causes each device to invoke a

backoff algorithm.
Devices wait a random amount of time before returning to listening mode.
The random time ensures that the original devices that caused the collision won’t repeat it.
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CSMA/CD: The Process

CSMA/CD: The Process

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Ethernet Timing Latency: Each transmission encounters a certain amount of delay

Ethernet Timing

Latency:
Each transmission encounters a certain amount of delay before reaching

the destination.
Every network device encountered in the path adds to the delay or increases the latency of the transmission.
Increases the chance of collisions.
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Ethernet Timing Timing and Synchronization: The 8 byte (64 bit) preamble

Ethernet Timing

Timing and Synchronization:
The 8 byte (64 bit) preamble is transmitted

at the start of the frame.
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Ethernet Timing Jam Signal: As soon as a collision is detected,

Ethernet Timing

Jam Signal:
As soon as a collision is detected, the sending

devices transmit a 32-bit "jam" signal - simply a repeating 1, 0, 1, 0 pattern.
Less than 64 bytes (runt).
Avoids detection of the jam signal as a frame.
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