Tài liệu Protocols and Transmission Theory pptx

Protocol History• The key principle behind Ethernets success was not it’s speed early on or the way it transmitted within a network, but Metcalfe’s vision to have a standardized platform

• Protocol History

• Signalling – Frequency vs Bit Rate

Protocols Explained

• Ethernet conception

• StarLAN

• Token Ring

• Cell vs Packets – ATM vs Ethernet

• Ethernet comes of age

Protocol History

Protocol History

• Born from the original Aloha Network in 1972

• Xerox, who pioneered the first PC with a GUI

commission Bob Metcalfe to develop networking from

their ALTO computers to Arpanet

• The breakthrough was a device that could listen before

transmitting, which allowed for full utilization of the

bandwidth speed (2.94Mbps)

• In 1977 they were issued the patent on CSMA/CD

(Carrier-Sense Multiple Access with Collision Detection)

Protocol History

• The key principle behind Ethernets success was not it’s

speed early on or the way it transmitted within a

network, but Metcalfe’s vision to have a standardized

platform that WAS NOT proprietary

• This was pushed further by joint efforts between Intel,

DEC and Xerox in the late 70’s through to the early 80’s

• Simultaneously the IEEE began working on

standardizing protocol developments, starting with

Ethernet, as Xerox continued to turn it’s patents over to

them in an effort to drive global adoption with a

standard platform

Protocol History

• Metcalfe and others broke off on their own to form

3COM in 1979

• They released their first TCP/IP transceivers for UNIX

a full 18 Months before the IEEE standard

• The 3C100 Transceivers were being produced for DEC,

Intel and Sun Microsystems

• Both Apple and IBM were approached in an effort to

push networking for the developing PC market

• Apple said yes, but IBM said no because of their own

Token Ring developments

Protocol History

• 3COM, without the cooperation of IBM, decided to

produce the highly successful ISA EtherLink adaptors for

IBM PC’s

• This was highly cost effective at the time ($950 USD)

and gained large acceptance

• Demand was driven not by “Personal” computing, but

rather by businesses adopting the PC

• Of course with so many computers within companies

the need to network grew

• 3COM met these demands and become the NIC

champion in the mid 80’s

• Although the distances were reduced using 10Base2,

acceptance was better due to reduced costs in cabling

infrastructure, as well as active hardware

• It was quickly realized that LAN connections did not

require 500m distances in the horizontal

Protocol History – Thick vs Thin

Cable AUI

Transceptor Dispositive Connection

NIC 10Base5 Transceptor

Dispositive Connection NIC 10Base2

Terminator

Terminator Vampire

RG 8 Coax Ethernet cable

RG 8 Coax Ethernet cable

Vampire Clamp

Terminator

Protocol History - StarLAN vs Thick/Thin Bus

• Thin Ethernet had advantages over regular (thick)

Ethernet, in that the cables were cheaper and the

electronics were all located within the NIC Both still had

drawbacks with their Bus architecture MAC’s were

difficult Cables could not be severed or the entire

network would go down Termination at both ends was a

must!

• Intel and AT&T saw this as an opportunity to change

the architecture to a “Star” configuration

Centralized Controller

Protocol History StarLAN - Bus vs Star

Protocol History - StarLAN

• StarLAN offered advantages in its flexibility through

the ability to run on UTP cables (standard telephone

wire)

• The star configuration allowed the addition of circuits

without disturbing others

• It also offered a more cost effective means of network

deployment

• StarLAN had drawbacks in speed, only running at

1Mbps 3COM did not adopt this technology for this very

reason

• The 386 processor speed would end StarLAN, but Star

Typology was born!

Protocol History - Token Ring

• In 1985 IBM released 4Mbps Token

Ring, several years after Bob Metcalfe

approached IBM with Ethernet!

• At the time the speed was less than

half that of 10Mbps Ethernet, but had

the advantage of using a centralized

hub, similar to StarLAN

• It also used “structured cabling”

IBM shielded cable

• 1Mbps StarLAN had the same

centralized structure, but was 4 times

slower

Centralized Controller

Protocol History - Bus vs Star vs Ring

Protocol History - Token Ring

• While Token Ring offered advantages over

Ethernet Bus Topology IBM made several mistakes

during the “War

• Licensing and standardization of Ethernet early on

meant that the technology was more cost effective

• Adoption of Ethernet by main industry players,

such as Sun, 3COM and Texas Instruments made

Token Ring less attractive

• IBM’s push to ATM Cell (vs Ethernet Frames) had

several disadvantages

• Ethernet was, at the same time, becoming a Fibre

and UTP technology vs STP only!

IFG 8 Bytes 6 Bytes 6 Bytes 2 Bytes 46-1500Bytes 4 Bytes IFG 8 Bytes 6 Bytes 6 Bytes 2 Bytes 46-1500Bytes 4 Bytes Preamble Destination

Address

Source Address Type/Length Data/Payload CRC/FCS Preamble

Destination Address

Source Address Type/Length Data/Payload CRC/FCS

5 Bytes 48Bytes 5 Bytes 48Bytes 5 Bytes 48Bytes 5 Bytes 48Bytes 5 Bytes 48Bytes Destination

Header Data

Destination Header Data

Destination Header Data

Destination Header Data

Destination Header Data

Ethernet

Packet

ATM

Cell

• The Ethernet packet has far more overhead than the ATM cell

• The nature of ATM is to setup the conversation/connection and

stream the data between two nodes This allows for QoS at a

90% efficiency

• The Ethernet packet does offer a larger payload, but also has

inter-frame gaps for timing

•The packet relies on Best-Effort Transmission and does not

offer true QoS and has a 98% efficiency

Protocol History - Cell vs Packet – ATM vs Ethernet

• ATM was developed in the late 70’s as a Carrier WAN transmission protocol for both Voice and Data

• It was based on Broadband ISDN principles of offering QoS

• In the mid 90’s it was thought that WAN technology, because of QoS and the ability to deliver real-time

applications such as voice reliably, would take over the LAN

Protocol History - Ethernet Comes of Age

• While other protocols offered advantages over Ethernet in

different areas such as QoS and speed, during different

stages of development, standardisation made Ethernet more

cost effective through the ease of technology licensing from

the IEEE

• Full Duplex transmission enabled Ethernet to talk and

listen simultaneously and greatly increase efficiency

• The development of Gigabit Ethernet increased speeds

within the LAN to levels that could support any real-time

application and increased bandwidth requirements of the

time

• QoS has been addressed through sheer pipe size and

prioritized packeting

Protocol History - Ethernet Comes of Age

• Gigabit horizontal, 10Gig backbone, Layer 3 switching,

broadband wireless, migration into SAN’s, MAN’s and now

WAN’s have proliferated Ethernet from traditional Enterprise

networks out

• This has pushed infrastructure to develop and grow at an

incredible rate to keep up with speed and quantity demands

• We are now used to Ethernet increasing in speed 10 times

every few years

• What begins as a backbone technology to support

increasing numbers of horizontal connections, quickly

becomes the next horizontal speed to support newer, faster

peripheral devices

Frequency vs Bit Rate

• The True about protocol speeds and the

frequencies they require

• Encoding Schemes and how they really

work

• Sensitivity of new technology

• Why a Standard Platform is so important

Technology TX Pairs

Used

Data Rate

in Mbps Per Pair

Total Data Rate Encoding

Zero of Freq Spectrum (=clock frequency)

Nyquist Min Channel Bandwidth

Cable Category

Cable Bandwidth 10Base-T 1 10Mbps 10Mbps Manchester 20MHz 10MHz 3 16MHz

Frequency vs Bit Rate

• There has always been a misperception that frequency and

bit rate have a direct linear correlation This is simply not

true

• As a result, several industry misnomers have lived on that

can easily be dispelled

• ATM is a perfect example of misperception and industry

hype The data rate for ATM 155, for example, is 155Mbps

• There were several technologies that played on a direct

correlation between the 155Mbps data rate and the 155MHz

frequency range having a direct correlation

• As in Ethernet, the Nyquist bandwidth is what is needed

for the receiver to interpret the data at half the clock speed

e.g 77MHz!

• This is why Cat 5 cable, characterised to 100MHz, not

155MHz, is be used to support a 155Mbps protocol and Cat

5e cable for ATM 622

Technology TX Pairs

Used

Data Rate

in Mbps Per Pair

Total Data Rate Encoding

Zero of Freq Spectrum (=clock frequency)

Nyquist Min Channel Bandwidth

Cable Category

Cable Bandwidth

ATM 155 1 155Mbps 155Mbps MLT 3 (4B5B) 155MHz 77MHz 5 100MHz

ATM 622 4 155Mbps 622Mbps MLT 3 (4B5B) 155MHz 77MHz 5e 100MHz

Frequency vs Bit Rate

Frequency vs Bit Rate

• Despite this industry misperception several marketers took

advantage of the 155Mbps data rate increase of 55Mbps

over 100BaseT and introduced cables and test solutions that

were rated to 155MHz!

• The WireScope 155 (Now the WireScope 350) is a perfect

example of testing to the 155MHz max frequency for

“assured ATM compliance”

• Some cable vendors followed suit and released Cat 5

cables that were tested to 155MHz, despite having no

standards requirement and no protocol need

• The same happened at the 350MHz frequency range, but

simply because a doubling of 155MHz to 310MHz did not

create an attractive “marketing message”!

Definition of a Data Bit (RS232)

Figure 1 Digital Data Signal Representation and Bit Rate

Information is coded into groups of bits; generally groups of 8 bits A

group of 8 bits is called a byte of information.

The text letter “E” is coded in 8 bits as “01001001” in one encoding scheme

called the ASCII.

Encoding – Manchester for 10Base-T

• Encoding schemes are used to

signify a bit of data as either a 0 or

a 1 in a binary sense

• Depending on rules, voltage and

phase changes and the number of

these changes that take place

dictates how many bits can be

transmitted in a frequency range

• Manchester, used for 10Base-T

transmission over Cat 3 cable, uses

- and + voltage changes in the clock

period to determine a 0 or a 1

• For 100Base-TX transmission

three voltage levels are used to

create additional bit capabilities in

the same clock period

• Any change in voltage

represents a 1 and any constant

• This is why frequency didn’t

need to increase by 10x from

10Mbps to 100Mbps

Encoding – MLT 3 for 100Base-TX

• PAM 5 (Pulse Amplitude

Modulation) is used in 5 voltage

states for Gigabit Ethernet

transmission

• The addition of two voltage

levels enables the encoding

scheme to transmit 250Mbps on a

single pair, without increasing the

Nyquist frequency range from

100Base-TX

• Because all 4 pairs are now

used instead of 1, the full

transmission speed capable is

increased to 1000Mbps or 1Gig

Encoding – PAM 5 for 1000Base-T

• Nominal voltage remains the

same as MLT 3 The voltage

change levels are decreased from

1V to 0.5V

• This means the accuracy of the

transceivers need to be greater

• The quality of the cabling used

is also greater, as the protocol is

more sensitive to minor changes

that can corrupt the bit period

• Eye patterns are a great way to

show correct signaling across the

multiple frequencies used to

make up the Square Wave

Encoding – PAM 5 for 1000Base-T

Encoding – PAM 5 Eye Pattern

• In a PAM 5 Eye Patter you can measure

multiple wave forms from the transmitter

to the receiver

• This is a good way to measure the

signaling quality and the cabling solution

impact on different frequencies used in

the Square Wave

• The larger the “Eye” pattern, the

cleaner the signal and the lesser chance

for error in the bit period

• This was the reason for TrueNet’s

impedance matching across the entire

frequency spectrum

10G - PAM16 2-Dimensional (2D) Code

• With technology increasing by 10x

every few years we are now beginning to

implement the next “phase” in protocol

technology (pardon the pun)

• 10GBase-T transmission has been

designed to use the most complex

transmission protocol to date

• Similar to MLT 3 and PAM 5, voltage

stepping has been used, but to a total of

16 different levels!

• This means that the voltage differential

between each step has been decreased

greatly, resulting in more sophisticated

electronics being required to read the

small voltage changes

10G - DSQ128 Code

• To achieve this a change in Phase is

used to pack a double punch into the

amount of possible data that can be

transmitted in a single clock period

• The frequency range has also been

increased greatly to 500MHz, from the

100MHz range used for 100 and

1000Mbps transmission

• With smaller voltage increments, phase

shifts the sensitivity of the transceivers

needs to be much better than ever

before

• The increased frequency also increases

potential noise, which will be covered in

Active Equipment Developments

• Development of TOE’s (Transport Offload Engine) to

offload the burden of processing TCP/IP packets from

CPUs

• Development of 10 Gbps copper-media transceivers

• KeyEye’s Echowave

technology

When Devices Speak Different Protocols

• There’s no advantage today in

selecting various protocol platforms for

specific needs

• This simply leads to additional costs in

translation from one technology to

another (More Routers)

Backwards Compatible and Interoperable

It’s all 1’s and 0’s

Industry standardization on Ethernet allows for

faster progression in technology and allows

consultants and customers to focus in on needs

more easily

10001011100101011100010101001110110101001000

01010100101001111001010010101001010001011110

01011100101001010010100010100101100

When Devices Speak a Common Protocols

• When all of the devices being deployed

within a network can speak a common

language economies of scale can be

realized

• Ethernet is that common language

• Standard Infrastructure platforms are

also more economical than supporting

multiple technologies with several

different cable types

• Material and installation costs are

minimized through having one common

structured cabling solution that can

handle all voice, video and data needs

Fully Integrated Common Platforms

If you can’t let go of the past

• It’s very cheap to deploy a

Token Ring network

• Dead Technologies are

always cheap

If you can’t let go of the past

• Anyone for 68 ATM

switches?

• Only $99 for the lot, but

you must pay the shipping!

• I think this seller is just

looking for a way to get rid

of the pallet!

If you really, really, really can’t let go of the past

• If ATM and Token Ring

interest you I also have

some other technologies to

Transmission over Copper and Fibre Cables

• Test parameters and how they relate to

cable design and installation

• How legacy cabling systems worked in

support of the original networking protocols

• Migration to UTP solutions for standard

Ethernet platforms

• Issues associated with transmission rate

increases

Balanced and Unbalanced Cable Pairs

Figure 2 Unbalanced Pair

Balanced and Unbalanced Cable Pairs

Figure 3 Balanced Pair