OSIPhysical Layer: http://learn-networking.com/network-design/the-difference-between-straight-through-crossover-and-rollover-cablesThe Physical Layer is the copper, fiber, or wireless thatconnects network devices. The bits that arrive here areencoded according to the protocols that govern theirtype of end device. The control code is added toindicate the beginning and ending of each frame of bits.The encoded bits are transformed into signals(voltage, light, or radio waves) and sent to thedestination device.
The Data-Link layer arranges the bits it receives intoframes and provides synchronization, error control andflow control. It has two sub layers that are the logical linkcontrol and media access control. It begins the process ofencapsulation and adds a trailer and header. The sourceand destination addresses are included along with framecheck sequence values, quality of service, and type ofprotocol for whatever media is present. It links thehardware and software layers together.
Network LayerTranslates addresses from logical to physical and visa-versa the other way. This is where addressing thenetworks and subnetting comes into play.Encapsulation of frames: IP header, source IPaddress, destination IP address.All available common network layer protocols. can’t wait! Dynamically done for me
Type of service determines the priority of the packetand looks for the Quality of Service to decide who goesfirst. EX: Voice transmits faster than e-mail.Time to Live ensures a packet can’t get stuck looping into infinity.Protocol determines which type of data packet it is:ICMP, TCP, UDPThe header checksum provides a security measure tomake sure the data is exactly how it was fromorigination to destination.Packet Length is between
Source PortAddress or name of remote host destination Port Connection State
The top three layersApplication Layer: Is the first step to getting data ontothe network.Three primary functions:1. Coding and conversion of application layer data to ensure that data from the source device can be interpreted by the appropriate application on the destination device.2. Compression of the data so that it can be decompressed by the destination device.3. Encryption of the data for transmission and decryption of data by the destination device.Applications are computer programs with which the userinteracts and that initiate the data transfer process atthe user’s request.Services are background programs that provide theconnection between the application layer and the lowerlayers of the networking model.The most widely-known TCP/IP Application layerprotocols are those that provide for the exchange ofuser information. These protocols specify the formatand control information necessary for many of thecommon Internet communication functions. Amongthese TCP/IP protocols are:
DNS: TCP/UDP port 53Telnet: TCP port 23SMTP:TCP port 25, POP:UDP port 110 DHDHCP: UDP port 67 port 80a TCP ports 20 and 21