Netwroking

Protocol A deifned set of standards tht computers must follow in order to comminicate properly.
Computer Networking The name we’ve given to full scope of how computers comminicate with each other.

#	Layer Name	Protocol	Protocol Data Unit	Addressing
5	Application	HTTP, SMTP, etc.	Messages	n/a
4	Transport	TCP/UDP	Segment	Port #‘s
3	Network	IP	Datagram	IP address
2	Data Link	Ethernet, Wi-Fi	Frames	MAC Address
1	Physical	10 Base T, 802.11	Bits	n/a

Physical Layer Represents the Physical devices that interconnect computers
Data Link Layer responsible for defining a common way of interpreting these signals so network devices can comminicate
The Ethernet standards also defines a protocol responsible for getting data to nodes on same on the network or link.
Network layer Allows different network to comminicate with each other through devices known as routers.
Internetwork A collection of networks connected together through routers, the most famous of these being the internet.
Internet - Network layer
IP is the heart of the internet and most smaller networks around the world.
Transport layer Sort out which client and server programs are supposed to get that data
UDP
Physical -> Data Link -> Network -> Transport -> Application

Cables Connect different devices to each other, allowing data to be transmitted over them
Copper
Fiber
The most common forms of copper twisted-pair cables used in networking are Cat5, Cat5e, and Cat6 cables.
Cat3 - cat5 - Cat5e - cat6 - Cat6a - Cat7
crosstalk When an electrical pulse on one wire is accidently detected on another wire.
Fire cables Contain individual optical fibers, which are tiny tubes made out of glass about the width of a human hair
Copper cable - Fiber optic

Hub A physical layer device that allows for connections from many computers at once.
Sending to machine 3 -> Workstation 1 -> Hub -> Workstation 4, Workstation 2, Workstation 3
Collision domain A network segment where only one device can communicate at a time.
If multiple systems try sending data at the same time, the electrical pulses sent acress the cable can interfere with each other.
Data Collision (Hub) -> Workstation 1 -> Hub -> Workstation 2, Workstation, Workstation, Workstation, Workstation
Network switch

Hubs and Switches The primary devices used to connect computers on a single network, usually referred to as a LAN, or local area netwrok.
Routers A device that knows how to forward data between independent netwroks
Internet -> ISP -> Workstation -> Router -> Laptop
Border Gateway Protocol(BGP) Router share data with each other via this protocol, which lets them learn about the most optimal paths to forward traffic

Bit The smallest representation of data that a computer can understabd; it’s a one ora zero
Modulation A way of varying the voltage of this charge moving across the cable
Line coding Sender -> Digital Data -> Encoder -> Digital Signal -> Decoder -> Digital Data -> Receiver

Duplexing Communication The concept that information can flow in both directions across the tables
Simplex Communication This proess is unidirectional
Client Computer -> Only sends(Simples) -> Server
Client Computer -> Simulataneous(Full-Duplex) -> Server
Client Computer -> Taken turns(Half-Duplex) -> Server

RJ45 Ports
RJ45 Plugs
Network ports
Link LED - Cable properly connected to two devices that are both powered on - RJ45 Port
Activity LED - Would flash whhen data actively transmitted across the cable - RJ45 Port
Patch Panel

Ethernet as a protocol solved this problem by using a technique known as carrier sense multiple access with collision detection.

CSMA/Cd Used to determine when the communications channels are clear, and when a device is free to transmit data
Media Access Control Address(MAC) A globally unique identifier attached to an individual network interface
It’s a 48 bit number normally represented by six brouping of two hexadecimal numbers.
Hexadecimal A way to represent numbers using 16 digits
Octet In computer networking, any number that can be represented by 8 bits
Organizationally Unique Indetifier(OUI) The first three octects of a MAC address

	Organizational Unique Identifier	Vendor Assigned (NIC Cards, Interfaces)
Size, in bits	24 Bits	24 Bits
Size in hex digits	6 Hex Digits	6 Hex Digits
Example	00 60 2F	3A 07 BC
Structure	Cisco	Particular Device

Ethernet uses MAC addresses to ensure that the data it sends has both an address for that sent the transmission, as well as the one the transmission was intended for.

A unicast transmission is always meant for just one receiving address.
If the least significant bit in the first octet af a destination address is set to zero, it means that ethernet frame is intended for only the destination address.
If the least significant bit in the first octet of a destination address is set to one, it means you’re dealing with a multicats frame.
Ethernet broadcats address FF:FF:FF:FF:FF:FF

Data Packet An all-ancompassing term that represents any single set of binary data being sent across a network link.
Ethernet Frame A highly structured collection of information presented in a specific order
Preamle 8 bytes - SFD 1 byte - Destination address 6 bytes - Source address 6 bytes - VLAN header 4 bytes - Ether-type 2 bytes - Payload 0-1500 bytes - FCS 4 bytes
Preabmle 8 bytes (or 64 bits) long, and can itself be split into two sections.
Start frame delimeter (SFD) Signals to receiving device that the preamble is over and that the actual frame contents will now follow
Destination MAC address The hardware address of the intended recipient
Ether Tyoe field 16 bits long and used to describe the protocols of the frame
If a VLAN header is present, the EtherType field follows it.
Virtual LAN(VLAN) A technique that lets you have multiple logical LANs operating on the same physical equipment
Payload In networking in terms, i the actual data being transported, which is everything that isn’t a header
Frame Check Sequence A 4-byte or( 32-bit) number that represents a checksum value for the entire frame
The checksum value is calculated by performing what’s known as a cyclical redundancy check against the frame.
cyclical redundancy Check(CRC) An importanr concpet for data integrity, and is used all over computing, not just network transmissions