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In the section we're going to talk about Ethernet.
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as we discussed in our previous section.
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Ethernet is the most widely installed local area network (LAN) technology. Ethernet is a protocol in the describing 
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how networked devices can format data for transmission to other network devices on the same network network
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segment and how to put data on our network connection.
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Again as we talked before, data Link layer has 2 sublayers and they are L.L.C. logical link control and
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MAC: Media Access Control . Organizes communication with upper / lower  laysers and  Provides common 
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interface, reliability and flow control and MAC  Appends physical address to frame and Provides data encapsulation 
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and error detection
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A collision domain is a network segment connected by a shared
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medium or through repeaters where data packets may collide with one another while being sent.
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A network collision occurs when more than one device attempts to send a packet on a network segment
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at the same time. Members of a collision domain may be involved in collisions with one another. 
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Guys Only one device in the collision domain may transmit at any one time, 
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and the other devices in the domain listen to the network and refrain from transmitting while others are 
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already transmitting in order to avoid collisions. Because only one device may be transmitting at any one 
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time.
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total network bandwidth is shared among all devices on the collision domain. 
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Collisions also decrease network efficiency on a collision domain as collisions require devices 
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to abort transmission and retransmit at a later time.
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Collisions are often in a hub environment, because each port on a hub is in the same collision domain. 
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By contrast, each port on a bridge, a switch or a router is in a separate collision domain.
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here we have a switch and this switch has four ports , four different ports. each port of the switch is a
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separate collision domain.
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As you can see in here this is collusion.
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Domain one.
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This is collision domain 3.
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This is collision domain t2o and this is collision domain four.
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But as you can see in a here separate ports of the hub is not as seperate collision domain.  all parts of
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the hub are in the same collision domain which is collision domain
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In a shared media , Devices may want to send data at the same time 
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CSMA 
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method is used for sharing the media, but collisions may ocur
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if two devices try to send data at the same time.
on the screen as you can see that all workstations are
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saying that I send my data when I want.
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And they don't want to share the media.
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So we have a method named CSMA/CD collision detection used for detecting collisions
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for ethernet networks . Logic behind this is : Check media, 
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If it is free send.
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If not wait for idle and send them later.
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For example in here if workstation a wants to communicate with the server it sends a message saying
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that I need to send something.
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Is there anything currently on the wire or
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Not
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CSMA CA Used for detecting collisions for 802.11 wireless networks. . Logic behind 
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This is check media if it is free.
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Send the notification to use it and then send your data and here how it is going on
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For example if the tablet want to send data to a wireless medium it's checking the data checking the
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medium I'm sorry first then it's sending a notification to the medium saying hey guys I'm going to send
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that data then it's sending whatever it's going to send and let's  take a look to Ethernet Frame.
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in the first fields of Ethernet, we have preamble and SFD
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between source and destination devices.
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Secondly we have destination and source address fields.
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And they are the source and destination MAC address. and the other field is the VLAN Tag which
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is used for quality of services and carries the VLAN information that is an optional field.
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And the other field is length and type which keeps the length of data and the type of the protocol we
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are using.
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And the other field is the data field which gives the encapsulated data information from Layer 3 and
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the last field is fcs, frame check sequence and frame check sequence bits must match for source and
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destination.
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If no error occured and this field is used for the error detection. Lets take a look to the MAC addr.
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now.
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A media access control address (MAC address) of a device is a 48 bit unique identifier assigned to network 
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interfaces for communications at the data link layer of a network segment. MAC addresses are used as a 
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network address for most network technologies, including Ethernet and Wi-Fi. 
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MAC Address is Shown in hexadecimal format ,  hexadecimal is a positional numeral system
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with a radix, or base, of 16. 
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It uses 16
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distinct symbols, most often the symbols 0–9 to 
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As you can see in here
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A, B, C, D, E, F to represent values ten to fifteen.
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MAC addresses are assigned to network devices such as PCs, printers, servers etc. And consists 
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of two portions as you can see in here the first portion is all you OUI..
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And the second UAA.
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...
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The first portion is OUI. An organizationally unique identifier (OUI) is a 24-bit number that 
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uniquely identifies a vendor, manufacturer, or other organization. 
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The second portion is 
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UAA or Extended / Device Identifier.
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This is a number unique to the vendor.
for example lets say that this first portion is unique for
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for example maybe Intel maybe Qualcomm
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then the MAC addresses that Intel manufactures or Qualcomm manufacturers are finishing with the
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arbitrary numbers that the Intel or Qualcomm says
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MAC Addresses can be represented in three ways mostly. In the first, dots are used between each four charachters. 
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as you can see here.
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And the second dashes are used between each two charachters 
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Correct.
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like here you can see as well and in the third double columns are used between each two charachters.
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There are also three different types of ethernet addresses and they are unicast multicast and broadcast
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a unicast frame contains the unique MAC address of the destination receiver and unicast
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address frame is all the send of the specific port leading to the receiver.
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For example if this computer,  computer one wants to communicate with the tree or the switch.
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And if this is a unicast, frame is going to here but not here and forwarded to here . 
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A multicast frame contains the unique multicast MAC address of an application, protocol, or data stream. A multicast 
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addressed frame is either flooded out all ports (if no multicast optimization is configured) or sent out 
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only the ports interested in receiving the traffic.
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. If you want to send a multicast layer-2 traffic, your destination MAC should start with 0100.5e
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...
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...
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Let's talk about the broadcast mac address. A broadcast frame is flooded
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A broadcast frame contains all binary 1’s as the destination address (FFFF.FFFF.FFFF)
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..
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For example if this guy wants to communicate with all these other guys, the source adress of the Ethernet frame is this guy's MAC address and the destination can be here.
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let's go with ARP.
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ARP (Address resolution protocol) is Used for resolution of IP address into MAC Address.
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ARP request is made via broadcast to FFFF.FFFF.FFFF 
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and ARP reply is made by related device as unicast.
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For example if PC one sends and arp request, the message this message is broadcast, comes to here
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And let's say the PC one is researching the physical address of the station that has the IP address 21.3 which is PC 3
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PC 3 takes this request and replies back with its MAC address
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and this packet is just sent to PC one as unicast.
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Let's take a look to the ARP table. On networking devices  A table, usually called the ARP cache or ARP 
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Table is used to maintain a correlation between each MAC address and its corresponding IP address
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. ARP provides the protocol rules for making this correlation and providing address conversion in both directions.
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In here you are seeing an arp table of a router and in here.
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You're seeing an ARP table of a PC. the command that we are using is show IP arp command to display
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the ARP cache of a router.
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And as you can see in here we are seeing the IP addresses and the MAC addresses of the same device on
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the table.
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Let's go ahead with LAN switches. A LAN switch is a networking device that connects devices together on 
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a computer network by using packet switching to receive, process, and forward data to the destination device. 
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...
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Switches mostly operate at Layer-2 of the OSI Model and Provides switching according to MAC addresses
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Layer-2 of the OSI Model and Provides switching according to MAC addresses
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using MAC address table. On the LAN switches, there is a table called MACaddress table and
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...
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what L2 switch is making is just switching between different ports by using MAC address information
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located in the MAC address table.
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Let's see how MAC address table is established on a switch right now.
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Firstly MAC address  table is empty.
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This is the switch guys and MAC address  table is empty.
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As you can see
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in the first step if PC one wants to forward the packet to PC 2, switch floods it out off all ports and
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adds PC ones MAC address to its MAC address table.
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Well what is going on in here is PC one wants to communicate with PC two, switch checks the frame and
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then checks the MAC address and immediately adds the PC1's MAC address  to the MAC address table
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and saying that hey on my first port have a MAC address of this
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Wants to communicate with this MAC address but I don't have this MAC address on this table so I'm flooding the
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requests out from all my ports.
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Then let's say the PC two sends unicast reply to PC 1 and switch adds the PC2's MAC address  to MAC address 
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stable to then after this process if PC one wants to send the data to PC two frame is forwarded directly
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in the end.
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In the end of the day switch learns all of MAC address  connected to all of its ports and establishes a 
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full MAC address  as you can see in here. and saying that on my first port I have this MAC address on
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my third port.
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I have this MAC address on my forth this 7th this, and 8 this.from now on.
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If this PC 5 wants to communicate with PC one frame is directly forwarded to PC one.
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Let's go ahead with the duplex options.
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We have two duplex options :
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Half duplex and full duplex. Half-duplex is used to describe communication where only... one side can
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send data at at time.
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Once one side has finished transmitting its data, the other side can respond. Only one node can send 
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data at a time in half duplex.
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If both try to send data at the same time, a collision will occur on the network.
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On the other hand, full-duplex is used to describe communication where both sides are able to 
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send and receive data at the same time.
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In these cases, there is no danger of a collision and therefore the transfer of data is completed much 
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faster.
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Let's go ahead with the auto MDX feature. in today's networks using the appropriate cable type is way
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important guys and certain devices has a great feature to help us preventing wrong 
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Cabling.
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. Auto MDI-X ports on newer network interfaces detect 
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if the connection would require a crossover, and automatically chooses the MDI or MDI-X configuration  to properly match the other end of the link.
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and let's take a look to the frame forwarding types.
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We have 3 frame forwarding types.When we are forwarding a frame in our switches ; and they are store and forward, cut through and cut through
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and cut through fragment free. In store and forward method 
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The frame is forwarded after that whole frame received and there is no CRC. in cut through fast forward
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the Frame is forwarded after the destination MAC is checked. In cut through fragment free
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frame is forwarded after 6 to 4 bytes of the frame is checked.
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Let's go ahead with POE
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Power over Ethernet or PoE describes any of systems which pass electric power along with data on twisted pair Ethernet 
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cabling.
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This allows a single cable to provide both data connection and electric power to devices such 
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access points, IP cameras, and VoIP phones. To provide electric over data cables to end devices, End devices 
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also must be supporting POE  technology too 
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in here we are seeing a poe switch and we have an access point.
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IP camera, industrial sensor and voip phone connected to our poe switch.
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If this switch is supporting poe and also this VOIP phone sensor IP camera and access point are 
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the poe feature.too we don't need that extra power cable we don't need an extra power adapter we don't need anything
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else.
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We can provide the power of these devices by using the twisted pair of copper cables.
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...
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Let's take a look to the fixed and modular switches.
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These are the types of the switches guys. fixed configurations switches are fixed in their configuration
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what that means is that you cannot add features or options to the switch beyond those that orginally
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came with the switch.
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The particular model you purchase determines the features and options available
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For example, if you purchase a 24-port gigabit fixed switch, you cannot add additional ports when
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you need them. 
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There are typically different configuration choices that vary in how many and what types of ports 
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And let's take a look to modular switches. Modular switches:  offer more flexibility in their configuration. Modular 
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Modular switches:  offer more flexibility in their configuration. modular switches typically come with different 
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sized 
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chassis that allow for the installation of different numbers of modular line cards the line cards actually
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contain the ports. 
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The line card fits into the switch chassis 
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like expansion cards fit into a PC. 
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The larger the chassis, the more modules it can support.
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And mostly this modular switches can carry high traffic and let's take a look a great feature which is
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A stackable switch is a network switch that is fully functional operating standalone 
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but which can also be set up to operate together with one or more other network switches, with this group
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of switches showing the characteristics of a single switch 
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but having the port capacity of the sum of the combined 
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switches.
The term “stack” refers to the group of switches that have been set up in this way.
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The common characteristic of a stack acting as a single switch is that there is a single IP address for
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remote administration of the stack as a whole, not an IP address for the administration of each unit in the 
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stack.
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And then lastly we to talk about SFP small for Factor pluggable. this small form factor pluggable is a
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a compact, hot-pluggable optical module transceiver used for both telecommunication and data communications
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applications and SFP interface.
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on networking hardware provides the device with a modular interface that the user can easily 
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adapt to various fiber optic and copper networking standards. 
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This is the fiber optic SFP and there are also types of these SFP which supports the copper cables
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as well.