MS TN related study

8/19/2019 MS TN related study

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Advanced Computer Networks

DR IMRAN SHAFI

2

SEQUENCE

• REVIEW

– PHYSICAL LAYERCOVERED

• TCP/IP PROTOCOL SUITE

• ADDRESSING

• TCP/IP VERSIONS• SWITCHED WANs


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Physical layer

• Handles the transmission of bits over a

communication channel from one hop to

the next

• Includes voltage levels, connectors, media

choice, modulation techniques

• Also defines the procedures and functions

that physical devices and interfaces haveto perform for transmission to occur

4

Physical layer (cont..)

• The phy layer is concerned with – Physical char of interfaces and media

– Representation of bits

– Data rate

– Synchronization of bits

– Line configuration

– Physical topology• Mesh topology

• Star topology• Ring topology

• Bus topology

– Transmission mode• Simplex

• Half-duplex

• Full-duplex


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Figure 2-4

Physical Layer

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Data link Layer

• Responsible for taking the data and

transforming it into a frame with header,

control and address information, and error

detection code

• Transforms the phy layer, a raw tx facility,

to a reliable link


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Data link Layer

• The responsibilities include – Framing

• Convert stream of bits received from

network layer to manageable data units

called frames

– Physical addressing

• Adds a header to the frame to define

– the sender and/or receiver of the frameonsame network

– Receiver address is of the connecting device of

next networkon different networks

8

Data link Layer

• Other responsibilities include

– Flow control

• Imposes a flow con mech to prevent

overwhelming the receiver for diff data rates

– Error control

• Adds reliability to the phy layer by adding

mech to detect and retx damaged/lost frames

• Also recognize duplicate frames

• Gen achieved by adding a trailer

– Access control

• Which device has con on link at any time


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Data Link Layer

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Node-to-node delivery


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Network Layer

• Responsible for source2destination delivery of a packet,

possibly across multiple networks, whereas Data link layer

deliver b/w 2 systems on same network

• Not needed if systems connected to same link


– Logical addressing

• Physical addressing by data link layer handles address problem

locally. NL adds logical addressing of sender & receiver

– Routing

• For independant networks, the connecting devices route or switch

packets to final destination

12

Network Layer


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End-to-end delivery

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Transport Layer

• Provides an end-to-end error-free network

connection

• Makes sure data arrives at destination exactly as it

left the source

• Responsible for process-to-process delivery in

contrast to network layer responsible for source-to-

destination delivery• NL treats each packet independently, as though

each piece belonged to separate message,

whereas TL ensures whole message arrives intact

& in order overseeing both error & flow control at

source-to-destination level


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Transport Layer


– Service point addressing (port address)

• To ensure delivery to correct process (runningprogram) as host to host delivery is made by NL

– Segmentation & reassembly

• Message divided into transmittable segments, eachcontaining sequence no. which enable TL toreassemble correctly & to identify and replace lostpackets

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–Connection control

• Transport Layer is either connectionless

or connection-oriented

• Connectionless Towards Enhancing Reliability in Hybrid Mobile Ad-Hoc Network – Treats each segment as independent packet and

deliver to Transport Layer at destination

• Connection-oriented – First establish connection with Transport Layer at

destination before delivering packet

– On completion of data delivery, connection is

terminated

Transport Layer cont..


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–Flow control• End-to-end flow con rather than across a

single link like Data Link Layer

–Error control

• Process-to-process rather than across a

single link like Data Link Layer

• Message is received without error

(damage, loss or duplication) achieved byre-Transmission

Transport Layer cont..

18

Transport Layer


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Reliable end-to-end delivery of a message

20

The Open Systems Interconnection

(OSI) Model (continued)

• Application layer

– Where the application using the network

resides

– Common network applications include web

browsing, e-mail, file transfers, and remote

logins• Presentation layer

– Performs a series of miscellaneous functions

necessary for presenting the data package

properly to the sender or receiver


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• Session layer

– Responsible for establishing sessions between users

• Transport layer

– Provides an end-to-end error-free network connection

– Makes sure data arrives at destination exactly as it left

the source

• Network layer

– Responsible for creating, maintaining and ending

network connections

– Transfers data packet from node to node within network

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• Data link layer

– Responsible for taking the data and

transforming it into a frame with header,

control and address information, and error

detection code

• Physical layer – Handles the transmission of bits over a

communications channel

– Includes voltage levels, connectors, media

choice, modulation techniques


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23Network worker perform their job duties at each layer in the model

The Open Systems Interconnection (OSI)

Model (continued)

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Summary of layers


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TCP/IP

PROTOCOL

SUITE

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TCP/IP PROTOCOL SUITE

• Dev prior to the OSI model

– Therefore layers do not match

– First four layers correspond to first four layers of

OSI model

• Provide physical stds, network interface,

internetworking and transport functions – Three topmost layers of OSI are rep by a single

layer in TCP/IP


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The layers of the TCP/IP protocol suite compared to the layers of the OSI model

The TCP/IP Protocol Suite

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TCP/IP and OSI model

No spec protocol, sp all std/propriety protocols, can be LAN or WAN


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Internetworking Protocol (IP)• Transmission mechanism used by TCP/IP

• Unreliable and connectionless• Best effort delivery service – No error checking or tracking

• Transport data in packets called datagrams – Separate transmission and on different routes

– Can arrive out of sequence or duplicated

• IP does not keep track of routes, can’t reorderdatagrams

• Limited functionality – Shall Not be considered a weakness as

• It provides bare-bones transmission functionality and• Free the user to add missing facilities for a given application

and

– Thus get max efficiency

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Address resolution protocol (ARP)

• Used to associate an IP address with the

physical address

• Each device on network (e.g. LAN) is

identify by a physical or station address

– Usually imprinted on NIC

• ARP is used to find the physical address

of node when its Internet address is

known

• CHAPTER 6


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Reverse ARP

• Allows a host to recover its Internet

address when it knows its physical

address

• Used once a computer connects to

network first time or boots

• CHAPTER 7

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Internet control msg protocol (ICMP)

• A mechanism used by hosts & gateways

to send notification of datagram problem

back to sender

• Sends query and error reporting

messages

• CHAPTER 9


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Internet Gp msg protocol (IGMP)

• Facilitate the simultaneous transmission of

message to a group of recipients

• CHAPTER 10

34

ADDRESSINGrevisit


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Addresses in TCP/IP

36

Relation-

shipof

layers

and

addresses

in TCP/IP


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Physical Address

• Also known as link address, is the address of

node as defined by its LAN or WAN• Included in the frame used by DLL

• Lowest level address

• The size & format vary depend on the network – Ethernet uses 6-byte (48 bits) physical address

that is imprinted

– LocalTalk (Apple) uses 1-byte dynamic addressthat changes for each reboot

• Unicast, Multicast, and Broadcast Physical Addresses – Some networks support all three types e.g

ethernet

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burned-in address, Ethernet hardware

address (EHA), hardware address or

physical address, MAC addresses


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Example 1

Figure shows an example of physicaladdresses.

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Physical addresses


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Example 2

Most local area networks use a 48-bit (6 bytes) physical address written as 12

hexadecimal digits, with every 2 bytes

separated by a hyphen as shown below:

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address

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Logical Address

• Necessary for universal comm services

– That are indep of underlying phy networks

• Physical addresses not adequate in aninternetworking environment

– Where different networks have differentaddress format

– A universal addressing system where eachhost be identified uniquely, regardless ofunderlying physical network, is needed

– Logical address are designed for this

• Currently a 32-bit address to uniquelydefine a host connected to Internet


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Example 3

Figure shows an example of Internetaddresses.

44

IP addresses


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Example 4

As we will see in future, an Internet address(in IPv4) is 32 bits in length, normally

written as four decimal numbers, with each

number representing 1 byte. The numbers

are separated by a dot. Below is an example

of such an address.

132.24.75.9

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Port Address• First two addresses are necessary for qty of

data to travel from source to destination host

– Not sufficient as computers run multiple processes

at same time

• End objective of Internet communication is a

process communication

– computer A communicates with computer B using

TELNET & with computer C using FTP – We need to label processes

• In TCP/IP, label is called port address

– 16 bits long


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Example 5

Figure shows an example of transport layer communication.

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Port addresses


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Example 6

As we will see in future, a port address is a16-bit address represented by one decimal

number as shown below.

753 A 16-bit port address

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The TCP/IP Protocol Suite

(continued)

• Application layer

– Equivalent to OSI’s application and presentation and

session layers

• Transport layer

– Equivalent to OSI’s transport layer

• Network (Internet or internetwork) layer – Equivalent to OSI’s network layer

• Network access (data link/physical) layer

– Equivalent to OSI’s data link and physical layers


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The numerous network connections involved with a user downloading a web page at work

Network Connections in Action

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The TCP/IP Protocol Suite in

Action

• Note the flow of data from user to Web

browser and back

• At each layer, information is either added

or removed, depending on whether the

data is leaving or arriving at a workstation

• The adding of information over pre-

existing information is termed

encapsulation


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The TCP/IP Protocol Suite in Action

(continued)

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Path of a web page request as it flows from browser

to internet server and back bureaucracy


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TCP/IP

VERSIONS

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Versions:

• Version 4 (current)

• Version 5

• Version 6 (future)


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Summary

• Many services and products that we use every

day employ computer networks and data

communications in some way

• Field of data communications and computer

networks includes data networks, voice

networks, wireless networks, local area

networks, metropolitan area networks, wide

area networks, and personal area networks

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Summary (continued)

• Application areas can be understood in terms of

general network connections:

– Terminal/microcomputer-to-mainframe computer

– Microcomputer-to-local area network

– Microcomputer-to-Internet

– Local area network-to-local area network

– Personal area network-to-workstation

– Local area network-to-metropolitan area network – Local area network-to-wide area network

– Wide area network-to-wide area network

– Sensor-to-local area network

– Satellite and microwave

– Wireless telephone


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Summary (continued)

• A network architecture, or communications

model, places network pieces in layers

– Layers define model for functions or services that

need to be performed

• The International Organization for

Standardization (ISO) created the Open

Systems Interconnection (OSI) model

– OSI model is based on seven layers: application

layer, presentation layer, session layer, transport

layer, network layer, data link layer, physical layer

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Summary (continued)

• The TCP/IP protocol suite is also known

as the Internet model and is composed of

five layers:

– Application layer

– Transport layer

– Network layer

– Network access layer

• DLL

• Physical Layer


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TCP/IP and OSI model

No spec protocol, sp all std/propriety protocols, can be LAN or WAN

62

Underlying

Technologies


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MULTICASTING

• multicast is the delivery of a message

or information to a group of destination

computers simultaneously in a single

transmission from the source creating

copies automatically in other network

elements, such as routers, only when the

topology of the network requires it.

– IEEE 802.1D, IEEE MAC Bridges standard

– STP multicast address 01:80:C2:00:00:00

– BPDU, configuration, topologychange, ack

• Exchanged every 2 sec63

• Take quiz from STP, its states, purpose of

multicasting in physical address etc given

in the previous slide

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MULTICAST ADDRESS IN

ETHERNET•Ethernet frames with a value of 1 in

the least-significant bit of the first

octet of the destination address

• (01-00-0C-CC-CC-CC )are treated

as multicast frames and are flooded

to all points on the network.

•While frames with ones in all bits of

the destination address

• (FF:FF:FF:FF:FF:FF) are sometimes

referred to as broadcast packets,

Difference between OSI &

TCP/IP (DLL)

• The data link layer in

the OSI world makes

use of the Q.921 LapD

protocol

– which must support an

information field length

of at least 512 octets

according to G.784.

– LapD is based on HDLC

framing.

• In the internet world

there is no real data link

layer protocol, but the

subnet protocol which

has quite many

similarities.

– The subnet protocolconsists of the IMP-IMP

protocol which aims to

provide a reliable

connection between

neighbored IMPs.

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NO DIFFERENCE AT PHY

LAYER

For ethernet based networks e.g. LANs

(Local Area Network), the data link

protocol LLC (Logical Link Control) is

equally used in OSI and TCP/IP

networks.High-Level Data Link Control (HDLC) is a bit-

oriented synchronous data link layer protocol


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TCP/IP (NL)

• OSI uses the CLNS

(Connection Less

Network Service)

protocols

– ES-IS for communication

of an end system to an

intermediate system and

– IS-IS for communication

between intermediate

systems

• TCP divides messages

in datagrams of up to

64k length

– Each datagram consists

of a header and a text

part

– IP routes these

datagrams through the

network using e.g.

• the protocol OSPF (OpenShortest Path First) or

RIP (Route Information

Protocol) for path

calculation purposes

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TCP/IP (TL)

• TP4 uses nine different

TPDU (Transport

Protocol Data Unit)

types

• whereas the TP4

header takes at least 5

bytes• TP4 uses a different

flow control mechanism

for its messages,

– it also provides means

for quality of service

measurement.

• whereas TCP knows

only one

• This makes TCP

simpler but every TCP

header has to have all

possible fields and

therefore the TCPheader is at least 20

bytes long

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The OSI transport layer protocol (TP4) and the internet transport protocol

(TCP) have many similarities but also some remarkable differences


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Internet Header Length (IHL)

• The second field (4 bits) is the InternetHeader Length (IHL) telling the number of

32-bit words in the header.

• Since an IPv4 header may contain a

variable number of options, this field

specifies the size of the

• The minimum value for this field is 5

– which is a length of 5×32 = 160 bits = 20bytes.

– Being a 4-bit value, the maximum length is

15 words (15×32 bits) or 480 bits = 60 bytes.69

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CONTENTS

• LANS

• POINT-TO-POINT WANS

• SWITCHED WANS

• CONNECTING DEVICES


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•Series of backbones

•Run by ISPs

•Connecting devices

•End users are either

•Local ISP LAN

•P2P networks to LAN

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Internet model

Conceptually, Internet is a set of switched

WANs (backbones (IBB)), LANs, P2P

WANs, and connecting or switching

devices

IBB are principal data routes between

large, strategically interconnected networks

and core routers in the Internet. Hosted by

commercial, government, academic and

other high-capacity network centers,

the Internet exchange points and networkaccess points, between the countries,

continents and across the oceans of the

world


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UNDERLYING TECHNOLOGIES

• TCP/IP concerned with only

– Network

– Transport

– Application layers

– Although shown as 5 layer stack

• It assumes existence of

– WANs

– LANs – Connecting devices

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LOCAL AREA

NETWORKS

(LANS)

•Wired LANs• Wireless LANs


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Wired LANs: Ethernet

• Most widely used LAN protocol

• Data rate of 10 Mbps and bus topology

designed in 1973 by xerox

• Today enhanced to 100 and 1000 Mbps

• Formally defined by IEEE 802.3

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Traditional Ethernet

• Access method (CSMA/CD)

– Topology (bus)

– One station talks all listen or receive

– How to sense two are using same time

• If yes, frame will collide

• The solution is CSMA/CD

– Every sta has an equal right to medium(multiple access)

– Every sta first listens before sending (carrier sense)

– Both senses and tx, collision occurs

– Protocol forces sta to keep listening to the line, & on collision

– Each sending sta send a jam signal to destroy data on line

– Wait different amount of time and resend


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CSMA/CD

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Minimum frame length/Transmission rate

is proportional to

Collision domain / Propagation speed

Min frame length is 520 bits, tx rate is 10 Mbps,

propagation speed is 2/3 of speed of light

Collision domain comes out to be 2500 m

The time station needs to wait to be sure that there is no data on the

line is the min frame length divided by txn rate(time req to send out the mi

frame length). This time is proportional to the time needed for the 1 st bitto travel the max network distance (collision domain)


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Ethernet layers

Flow & error

con

CSMA/CD

FramingEncoding

Detection & reporting

collisions

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Ethernet frame

No acknowledgment making it unreliable

Each station has NIC with 6 B address in

hexadecimal notation

07:01:02:01:2C:4B

Less than 1518 length field

Greater than 1536 (0x0600) defines

upper layer protocol in Ethernet v 2.0 by

DEC, Intel & xerox

46—1500 B


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For example, an EtherType value of 0x0800 signals that the

frame contains an IPv4 datagram. Likewise, an EtherType of0x0806 indicates an ARP frame, 0x8100 indicates an IEEE

802.1Q frame and 0x86DD indicates an IPv6 frame.

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Ethernet implementation

(4 in toto)

Transceiver responsible

for encoding, collision

detection and

transceiving


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FAST ETHERNET

• Need for higher data rate (100Mbps)

• Principles are same as traditional ethernet – CSMA/CD in MAC layer

– Data rate increased to 100 Mbps

• Variable are – Data rate

– Speed of light

– Frame length time to propagate

– Collision domain 2500 m traditional

• Less time to leave sender, for FRAME

• Sender has less time to hear collision

• For CSMA/CD to work – Either increase min frame length

– Or dec the collision domain


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FAST ETHERNET• Increasing frame length

– Involves additional overhead

• Extra bytes if data is short – Loss of efficiency

• Collision domain has been reduced by afactor of 10 – With a star topology

• 250 m is acceptable in many cases

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Fast Ethernet implementation

(Either 2 wire or 4 wire)

2 wire implementation is called 100BASE-X with

Either twisted pair cable (100BASE-TX)

Or fiber optic cable (100BASE-FX)


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90


The 4 wire implementation is only for twisted pair cable (100BASE-T4)


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GIGABIT ETHERNET• Need for even higher data rate (1000Mbps)

• To achieve this data rate

– Keeping CSMA/CD – Dropping CSMA/CD

• For CSMA/CD to work – Either increase min frame length

– Or dec the collision domain• 25 m is unacceptable

– Min frame length is increased

• If CSMA/CD is dropped

– Every sta is connected by 2 sep paths tocentral hub• Full duplex Ethernet

– No collision

– No need for CSMA/CD

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Gigabit Ethernet implementation

(either 2 wire or 4 wire)

2 wire implementation is called 100BASE-X with

Either optical fiber tx short wave laser signal (1000BASE-SX)

Or optical fiber tx long wave laser signal (1000BASE-LX)


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Gigabit Ethernet implementation

The 4 wire implementation uses twisted pair cable (1000BASE-T)

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