Original subtitles

0 In this section network access and we are gonna define how we can access to a network 1

briefly. 2

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... 4

... 5

in this lecture 6

In this lecture, firstly we are gonna focus on OSI-Layer 1 ; Physical layer. In the seven-layer OSI model of computer 7

networking, the physical layer or layer 1 is the first and lowest layer. The physical layer consists 8

of the electronic circuit transmission technologies of a network 9

It is a fundamental layer underlying the higher level functions in a network.. The physical layer defines 10

the means of transmitting raw bits rather than logical data packets over a physical data link connecting network 11

nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal 12

that is transmitted over a transmission medium. The physical layer provides an electrical, mechanical, and 13

procedural interface to the transmission medium and here are the fundamentals of the physical layer 14

We have three medias the first medium is copper cable the second media is fiber optic cable. 15

And the third is the wireless media. in a corporate cable media the physical components are maybe a utility 16

cable coaxial cable. 17

We have some connectors, we have Network Interface Cards, ports, interfaces and etc, in a fiber optic 18

cable media. 19

We have single multimode fibers, connectors again, Network Interface Cards, interfaces lasers 20

and LEDs and photoreceptors. 21

And in a wireless media our physical components are maybe access points maybe. 22

Again network interface cards which are the wireless network interface cards this time, maybe radios 23

bandwidth is the bit-rate of available or consumed information capacity expressed typically 24

in metric multiples of bits per second. 25

For example An internet connection with a larger bandwidth can move a set amount of data much faster 26

than an internet connection with a lower bandwidth. here as you can see the abbrv. as well. 27

If you want to talk about the kilobits per second we're using K.B.. 28

P.S. If you want to talk about the megabit per second we're using M.B.P.S. If you want to talk 29

about gigabit per second we're using the GBPS. let's move forward with the network media. network media 30

Network media refers to the communication channels used to interconnect nodes on a computer network 31

Typical examples of network media include copper coaxial cable, copper twisted pair cables and optical fiber 32

cables used in wired networks, and radio waves used in wireless data communications networks 33

Let's go ahead with UTP cable. 34

First Unshielded twisted pair (UTP) 35

TIPPY is a type of copper cabling used in telephone wiring and the local area networks incited you to 36

is a type of copper cabling used in telephone wiring and local area networks (LANs).Inside a 37

UTP cable is up to four twisted pairs of copper wires, enclosed in a protective plastic cover, 38

with the greater number of pairs corresponding to more bandwidth. The two individual wires in a single 39

pair are twisted around each other, and then the pairs are twisted around each other, as well. 40

This is done to reduce crosstalk and electromagnetic interference, each of which can degrade network 41

performance. Each signal on a twisted pair requires both wires. 42

here are the standards when we are using UTP cabling. UTP categories 43

are starting with cat one and finishing with the cat 7. 44

We have various rates for each categories as you can see for example if you are using cat 1 you can 45

use up to one megabit per second. 46

But if you're are using cat 7 cable you can use up to 10 gigabit per second. 47

data rate 48

The maximum lengths are almost the same as you can see it's almost 100 meters. 49

And the applications that are using the different categories are for example Cat 1 is used in old telephone 50

cables cat 2 is used in the token ring networks for for example Cat 6 is being used in gigabit 51

and ten gigabit networks. 52

Let's go ahead with UTP connectors. connector is the part of a cable that plugs into a port or 53

interface to connect one device to another. 54

Most connectors are either male (containing one or more exposed pins) or female (containing holes in which 55

or female (containing holes in which the male connector can be inserted). 56

The RJ-45 connector is an eight-wire connector that is commonly used to connect networking devices such 57

as switches , routers or PCs to a local area network (LAN). 58

This connector is used with Cat-5 or Cat-6 cables commonly and consists of 8 pins. 59

Here is the male connector. 60

And here as you can see this is a female connector. 61

Let's go with UTPcable types. T568A and T568B 62

are the two color codes used for wiring eight-position RJ45 modular plugs 63

The only difference between the two color codes is that the orange and green pairs are interchanged. 64

Straight-through cable is a type of CAT5 which the RJ-45 connectors at each end 65

have the same pin out. (color code use on both ends are the same)Straight-Through cable is also referred to 66

as a “patch cable.” Straight-through cable is used to connect computers and other end user devices to 67

networking devices such as hubs & switches. A Crossover cable is a type of CAT 68

where one end is T568A configuration and the other as T568B configuration. 69

Pin 1 is crossed with Pin 3 and Pin 2 is crossed with Pin 6.Crossover cable is used to connect two 70

same devices (for example routers) together 71

here as you can see the T 5 6 8 a pinout and as you can see 72

we have 8 pins in here. 73

If are using this pin out with the five six eight A in the first pin you're using white green cable. 74

In the second you're using green third white orange blue white blue orange white brown and brown. 75

If you're using five six eight b in the first pin ur using white orange cable this time. 76

Then orange white green blue white blue green and white brown and they're brown. 77

Let's go ahead with the Shielded twisted pair . Shielded twisted pair is a special kind 78

of copper cable used in telephone or LAN systems. 79

An outer covering or shield is added to the ordinary twisted pair wires prevent 80

electromagnetic interference and the shield functions as a ground. 81

Coaxial cable is a type of copper cable specially built with a metal shield and other components 82

engineered to block signal interference. 83

It is primarily used by cable TV companies to connect their satellite antenna facilities to customer 84

homes and businesses. Some homes and offices use coaxial cable, too, but 85

its widespread use as an Ethernet connectivity medium in enterprises and data centers has 86

been supplanted by the deployment of twisted pair cabling. A fiber optic cable is a network cable that contains 87

strands of glass fibers inside an insulated casing. 88

They're designed for long distance, 89

very high performance data networking and telecommunications.Compared to wired cables, fiber optic cables 90

provides higher bandwidth and can transmit data over longer distances. 91

The two primary types of fiber cables are called single mode and multi mode fiber. 92

Single mode fiber uses very thin glass strands and a laser to generate light 93

while multi mode fibers use LEDs. Single mode fiber networks often use Wave Division Multiplexing (WDM) techniques techniques 94

to increase the amount of data traffic that can be sent across the strand. as I told you multimode fibers 95

use LED as light source and provide multiple paths for light. 96

If you compare with the single mode they provide lowe bw and higher attenuation. 97

And here are the connection types that we can use in the fiber optic cables. 98

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let's compare the fiber optic with the copper cable. 100

As you can see in here the first let's take a look to the distance. optical fiber can provide communication 101

up to 12 miles while copper provides communication up to 300 feeets 102

The weight is almost 4 LBS is in here while the copper is thirty nine. 103

The maximum bandwidth that optical fiber can provide 69 tbps per second which is much higher than 104

the 10 gigabit per second. 105

but optical fiber is hard to tap and easy to alarm but copper emits the EMI electromagnetic interface. 106

Let's go ahead with the wireless communication .wireless communication is the transfer of information 107

between two or more points that are not connected by a cable. 108

The most common wireless technologies use radio waves. With radio waves speeds may be low as 3 mbps 109

per seconds. 110

for bluetooth, or may be really high up to 1 gbps for Wi-MAX 111

and let's take a look to 802.11 wifi standards. 112

Standards are Set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless 113

local area network communication. In the chart you 114

can see the evolution of the standards. In the first standard 802.11, maximum data rate is 115

2mbps, 116

but in 802.11ac 117

max data rate is 7gbps. 118

... 119

And here you can see the frequency bands , bandwidths modulation types and advanced antenna technologies 120

for each standard as well. let's go with the datalink layer protocols and media access control. 121

The data link layer or layer 2 is the second layer of the seven-layer OSI model of computer 122

networking and provides access to media via mac addresses. 123

Guys This layer is the protocol layer that transfers data between adjacent network nodes. The data link layer 124

provides the functional and procedural means to transfer data between network entities and might provide the 125

means to detect and possibly correct errors that may occur in the physical layer. 126

Protocols like Ethernet, PPP and HDLC operate at this layer. 127

The most important standards used in Layer-2 are, Ethernet 128

bluetooth which are created by IEEE and ADSL and MPLS which are created 129

by ITU-T and we have HDLC and MAC which are created by ISO and we have FDDI which is created by ANSI 130

see these are the most important ones. 131

The data link layer functionality is usually split it into 2 logical sub-layers as you can see we have logically 132

control and media access control. the upper sub-layer, termed as LLC, that interacts 133

with the network layer above and the lower sub-layer, termed as MAC media access control is the one that 134

interacts with the physical layer below. 135

While LLC is responsible for handling multiple Layer3 protocols (multiplexing/de-multiplexing) and link services 136

like reliability and flow control, the MAC is responsible for framing 137

and the media access control for broadcast media 138

Ethernet is the most widely installed local area network (LAN) technology. Ethernet is a protocol in the describing 139

how networked devices can format data for transmission to other network devices on the same network segment, and 140

how to put that data out of network connection. 141

Ethernet defines two units of transmission, packet and frame. 142

The frame includes not just the "payload" of data being transmitted but also addressing information 143

identifying the physical "Media Access Control" (MAC) addresses of both sender and receiver, VLAN tagging 144

and quality of service information, and error-correction information to detect problems in 145

transmission. Each frame is wrapped in a packet, which affixes several bytes of information used 146

in establishing the connection and marking where the frame starts. 147

Another protocol used in the data link layer player is the point to point protocol. Point-to-Point Protocol (PPP) is a data link layer (layer 2) 148

communications protocol used to establish a direct connection between two nodes. 149

For example these devices are routers 150

It connects two routers directly without any host or any other networking device in between. 151

It can provide connection authentication, transmission encryption and compression. 152

we are going to focus on the topologies So what is a topology? A network topology is the arrangement 153

of a network, including its nodes and connecting lines. 154

There are two ways of defining network geometry: the physical topology and the logical topology 155

Here we are seeing a physical topology.Physical topology is the placement of the various components 156

of a network, including device location and cable installation. 157

Here we can see a physical topology and what we are seeing is just the cable connections and name and 158

symbols of the devices. 159

As you can see. for example we have an Apple II Mac connected to gigabit switch we have an iPad which 160

is connect to Apple Airport Extreme. 161

We have an iPhone also connected to Apple Airport Extreme and we have Tivo premier which are connected 162

to our gigabit switch. 163

We have printer in here which is connected to gigabit switch and etc That's the physical view 164

of the topology. 165

We have three types of physical LAN topologies and they are Ring, Bus and Star. 166

In the ring network topology, the workstations are connected in a closed loop configuration. as you can see in here 167

. Adjacent pairs of workstations are directly connected. Other pairs of workstations are indirectly connected, the data passing through one or more intermediate nodes. 168

... 169

For example lets say that here is the PC one wants to communicate with the PC two: here the direction 170

of the packets. 171

Pc1 is going to this guy then this guy and this guy. 172

But what if this guy fails? if this guys fails if there is an interruption on this guy, you can send the 173

packet also from this way on the ring topology. in the bus network topology every workstation is connected 174

to the main cable called the bus. 175

Therefore, in effect, each workstation is directly connected to every other workstation in the network. 176

as you can see. in the Star topology. 177

There is a central computer server this guy to reach all the workstations are directly connected to 178

Every workstation is indirectly connected to every other through the central computer. 179

For example if this PC one wants to communicate with the PC two that should send the packet to this guy 180

and this guy should forward the packet to the PC2. 181

OK that seems like good but if theres a problem on the central device all the devices will fail as you 182

can see and here are the physical WAN topologies. point to point 183

Topology is the first one. 184

That's the simplest topology with a dedicated link. 185

between two endpoints. as you can see the second one is hub and spoke topology. hub and spoke here in 186

a Hub-and-spoke Site-to-Site Wide Area Network (WAN) network topology, one physical 187

site act as Hub while other physical sites act as spokes. Spoke sites are connected to each 188

other via Hub as you can see in here and In Hub-and-spoke Wide Area Network (WAN) topology, the network communication 189

between two spokes always travel through the hub. 190

And here is the lastly we are going to focus on full mesh topology. full mesh topology connects each 191

node to all other cluster nodes. This topology is highly reliable and fast, but it does not scale well. 192

It is reliable because it provides many paths through the fabric in case of cable or node failure. 193

It is fast with low latency because you can get to any node in the fabric in just one hop. 194

It does not scale well because each additional node increases the number of fabric links and switch 195

ports exponentially. as you can see in here we have r1 -2 -3 196

4-5 and they're connected each other. 197

And that provides really really big reliablity in this network. 198

There's a really big redundancy for example if router one wants to communicate with router 2 to this path 199

can be used. 200

This path can be used or this path can be used because we are of various ways as you can see. 201

So that means no matter if this link fails the traffic will go through from here from here from here 202

or something like that. 203

And lastly we're going to talk about logical topology.logical topology is the arrangement of devices 204

computer network and how they communicate with one another.Logical topologies describe how signals act 205

on the network. in a logical topology we can see IP addresses as you can see in here we can see 206

Tunnell types we can see subnetmask and something like that. 207

That's the logical view of the topology.