1Version 3.0

Module 7Ethernet

Technologies

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Legacy Ethernet

10BASE2 10BASE5 10BASE-T

Same Timing Parameters. . .

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Legacy Ethernet

10BASE2 10BASE5 10BASE-T

Same Frame Format. . .

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Legacy Ethernet

10BASE2 10BASE5 10BASE-T

Same Transmission Process. . .

Manchester

Line

Encoding

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Legacy Ethernet 10BASE2 10BASE5 10BASE-T

Same Basic Design Rule or common architectural features. . .

•5 segments connected on the network

•4 repeaters

•3 segments of the 5 segments can have stations connected. The other two segments must be inter-repeater link segments with no stations connected.

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10BASE5 & 10BASE2

10BASE5

• Thick Coax cable

• Inexpensive

• No configuration

• 500 m segment length

• Half-duplex mode

10BASE2

• Thin Coax cable• 185 m segment length• Half-duplex mode

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10BASE-T

• Cheaper & easier to install

• Used Category 3 UTP at first

• Can also use Category 5 or 5e UTP

• RJ-45 connectors

• Star or extended star topology

• Shared bus device (hub)

• Transmit pair on the receiving side are connected to the receiving pair

• Half (10 Mbps) or Full (20 Mbps) Duplex

• 100 m segment length

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Fast Ethernet

100BASE-TX 100BASE-FX

Copper UTP Multimode optical fiber

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Fast Ethernet

100BASE-TX 100BASE-FX

• Timing parameters are the same

• Frame format is the same

• 2 separate encoding steps– 4B/5B– 2nd part specific to the media (copper or fiber)

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4B/5B encoding is sometimes called 'Block coding'. Each 4-bit 'nibble' of received data has an extra 5th bit added. If input data is dealt with in 4-bit nibbles there are 24 = 16 different bit patterns. With 5-bit 'packets' there are 25 = 32 different bit patterns. This enables clock synchronizations required for reliable data transfer.

4Bit/5Bit Encoding

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Fast Ethernet

100BASE-TX 100BASE-FX

• Two separate transmit-receive paths

• Full-duplex or half-duplex

• Could be used for backbone applications, connections between floors and buildings where copper is less desirable (inter-building backbone), and also in high noise environments.

• Never really accepted because Gigabit Ethernet came into the picture

• First designed for inter-building backbone connectivity

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Class I Repeater

• Can use between media segments with different signaling techniques (100BASE-TX to 100BASE-FX)

• Only 1 Class I Repeater to be used per collision domain

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Class II Repeater

• Used between segment types that use the same signaling techniques (100BASE-TX to 100BASE-TX)

• May only use 2 with maximum cable lengths

• Cannot mix 2 different segments (100BASE-TX to 100BASE-FX)

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Gigabit Ethernet (1000BASE-X)(1000 Mbps or 1 Gbps)

• General infrastructure needs• High-speed cross-connects• Backbone installations• IEEE 802.3z specifies 1Gbps full

duplex over optical fiber• More complex encoding needed

because of the timing

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Gigabit Ethernet

• Gave more speed for intra-building backbones

• Inter-switch links

• Must be interoperable with 10BASE-T and 100BASE-TX

• All 4 pairs of wires used at the same time, full-duplex– Transmission and reception of data happens in both

directions on the same wire at the same time

All versions of Gigabit Ethernet share the same timing, frame format, and transmission

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1000BASE-X

• Uses NRZ line encoding– the determination of whether a bit is a zero or a one is made by

the level of the signal rather than when the signal changes levels.

• The NRZ signals are then pulsed into the fiber using either short-wavelength or long-wavelength light sources

Short wavelength

1000BASE-SX

Long wavelength

1000BASE-LX

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10 Gigabit (GbE) Ethernet

• 10 Gbps full duplex over fiber only (802.3ae)

• Frame format is same as all Ethernet

• CMSA/CD no longer a consideration

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10 Gigabit (GbE) Ethernet

• Each data bit duration is now 0.1 nanoseconds (1,000 GbE data bits in the same bit time as one data bit in a 10-Mbps Ethernet data stream)

• Uses 2 separate encoding steps

• 10GBASE-LX4 uses Wide Wavelength Division Multiplex (WWDM) to multiplex four bit simultaneous bit streams as four wavelengths of light launched into the fiber at one time.

• Further info http://www.spie.org/web/oer/october/oct97/multiplex.html)

• No repeater rules defined since half-duplex is not supported

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Wide Wavelength Division Multiplexing

• Wide wavelengths are diffracted into a fiber and then diffracted out the other end

• When the light propagation is reversed, the multiplexer becomes the demultiplexer.

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Development of fiber based Ethernet

• Mostly limited by :

– The actual electronics technology itself:• Emitters• Detectors

– And:• The manufacturing process itself

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Data Encapsulation Process

To prepare for Lab 7.1.2

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Data Encapsulation Process

• Application Layer– FTP (File Transfer Protocol) client PC sending

a text document to an FTP server PC

• Presentation Layer– Text is coded in ASCII (American Standard

Code for Information Interchange)

• Session Layer– Coordinates dialog between the two PCs

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Data Encapsulation Process

• Transport Layer– Segments the data stream from upper layers– Builds a virtual circuit between the two PCs– FTP is handled by TCP (Transmission Control

Protocol) at this layer– TCP tracks the conversation using destination and

source port numbers– FTP server ports are 20 for Data and 21 for Control– FTP client port is dynamically set by client PC using

IANA (Internet Assigned Numbers Authority) specified range of 49152 to 65535; each communication session referenced by a different port

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Data Encapsulation Process

• Network Layer– Places TCP segments into IP (Internet

Protocol) packets– Enables end-to-end routing from the source

network, over intermediate networks, to the destination network

– IP identifies TCP as its payload by placing a “6” in its protocol field

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Data Encapsulation Process

• Data Link Layer– Prepares IP packet for transmission on its directly

attached network, in this case an Ethernet LAN– The IP packet is placed in an Ethernet frame which

accesses the network using Ethernet’s CSMA/CD protocol

– The frame identifies its payload as IPv4 by placing a value of “0x0800” in its type field

– As the MAC sublayer transfers each individual octet of the frame to the Physical Layer, it reorders all but the FCS for encoding least-significant bit first

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Data Encapsulation Process

• Physical Layer– Encodes the Ethernet frame onto the physical medium– Ethernet utilizes Manchester encoding scheme– Binary value is determined by the direction of the edge

transition in the middle of the timing window– Ones are represented by a rise in voltage (copper

medium) or power level (fiber medium)– Zeroes are represented by a drop in voltage or power

level

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Data Encapsulation Process

• Data Link Layer / Physical Layer– Framing and encoding is changed at each

router hop as appropriate to the Layer 2 / Layer 1 protocols in use by the next network along the path to the destination

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Ethernet Frame

• Preamble (7 bytes)– Establish and maintain clock synchronization; although

faster versions are synchronous, Ethernet is asynchronous

– Avoid baseline wander– Hexadecimal “55 55 55 55 55 55 55”– Binary “0101 0101 … 0101 0101”

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Ethernet Frame

• Start of Frame Delimiter (1 byte)– Hexadecimal “D5”– Binary “1101 0101”– When reordered for Physical Layer encoding, it reads

“1010 1011”– The two consecutive one’s mark the boundary between

the Preamble and the frame’s Destination Address

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Ethernet Frame

• Destination Address (6 bytes)– MAC (Media Access Control) address of destination computer– The destination exists on the same LAN as the source computer– It may belong to the LAN’s router if the packet’s destination is on

another network– 48 bits in length, written as 12 hexadecimal digits– First 6 hexadecimal digits represent the OUI (Organizational

Unique Identifier) for the equipment manufacturer; the IEEE administers OUI assignments

– Last 6 hexadecimal digits indicate the serial number assigned by the manufacturer

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Ethernet Frame

• Source Address (6 bytes)– MAC (Media Access Control) address of source computer– The source exists on the same LAN as the destination computer– It may belongs to the LAN’s router if the packet’s source is on

another network– 48 bits in length, written as 12 hexadecimal digits– First 6 hexadecimal digits represent the OUI (Organizational

Unique Identifier) for the equipment manufacturer; the IEEE administers OUI assignments

– Last 6 hexadecimal digits indicate the serial number assigned by the equipment manufacturer

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Ethernet Frame

• Length/Type (2 bytes)– Early IEEE 802.3 versions of Ethernet used this field to indicate

the number of bytes in the data field– Later IEEE 802.3 versions of Ethernet allow this field to indicate

either the length of the data field or the Layer 3 protocol type being transported

– This allows compatibility between IEEE 802.3 and Ethernet version 2 developed by DIX (DEC, Intel, Xerox)

– A hexadecimal value < “0600” (decimal 1536) indicates length, while >= “0600” indicates an Ethernet II type code

– A hexadecimal value of “0800” indicates the frame is carrying an IPv4 packet

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Ethernet Frame

• Data / Padding (46 to 1500 bytes)– The Network Layer packet– Less than 46 bytes will result in an Ethernet “runt” which could

lead to an undetected collision– Greater than 1500 bytes will result in an Ethernet “giant” which

exceeds maximum frame length– For frames with a length/type < 0x0600, this field includes the

802.2 LLC (Logical Link Control) sublayer header to indicate the packet’s Layer 3 protocol

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Ethernet Frame

• Frame Check Sequence (4 bytes)– Used to ensure frames received without errors– Consists of a CRC (Cyclic Redundancy Check) ran against the

Destination Address, Source Address, Length/Type and Data fields

– Calculated by the source, value attached to frame– Calculated by the recipient and compared to source’s calculation

(= good / != bad)

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Lab 7.1.2 Decoding an Ethernet Waveform

• Locate Start of Frame Delimiter (SFD)– Immediately following the Preamble, there should be a

binary sequence of “1010 1011”– This sequence is the SFD– The Destination Address follows immediately after the

“11”

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Lab 7.1.2 Decoding an Ethernet Waveform

• Group binary values into octets starting with SFD– Place a marker around each binary octet working

backward and forward from the SFD– Grouping each octet simplifies the next step in which

you reorder the octet binaries from their Layer 1 “least-significant bit first” orderings into their Layer 2 “most-significant bit first” orderings

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Lab 7.1.2 Decoding an Ethernet Waveform

• Reorder octets into Layer 2 sequence– Write down the reverse bit order of each octet– This new ordering provides the actual Layer 2

frame

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Lab 7.1.2 Decoding an Ethernet Waveform

• Convert octets into hexadecimal digits– Each octet is represented by two hexadecimal

digits– For example, the Preamble’s Layer 2 binary

pattern of “0101 0101” is represented by the hex value “55”

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Lab 7.1.2 Decoding an Ethernet Waveform

• Use hex values to identify destination and source Organizational Unique Identifier (OUI), length/type, and initial portion of IP header– For the public OUI listing, reference

http://standards.ieee.org/regauth/oui/oui.txt– For the EtherTypes listing, reference the RFC Index at

http://www.rfc-editor.org/rfc-index.html• Enter a search for “Assigned Numbers” • Locate the latest version of document• Search the document for “EtherTypes”

– For the IP header format, reference RFC 791 page 10

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Module 7Ethernet

Technologies