The OSI ModelJuly 25, 2024 OSI 7 Layer Model Physical Data Link Network Transport Session Presentation Application Physical Layer Make sure 1’s & 0’s get between host Think Wires Getting info from one system to another Ethernet Frame: Preamble and FCS are read at this layer to see where frame needs to go Data Link layer Allow individual systems to be addressed so ethernet frames go to the right spot Based on MAC Address Ethernet Frame: Check Destination (send too) and Source (send back) MAC Addresses Used for local area network NICs operate at this layer Network Layer For large distributed networks like the internet Uses IP addresses to find sources and destination Look at packets and check IP addresses Ethernet Frame: Destination and Source IP addresses Routers operate at this level because they deal with IP addresses Transport Layer Assemble and Disassemble data Ethernet Frame: each ethernet frame can hold 1500 bytes of data maximum Ex. When sending a video the Transport layer will chop the frames up into 1500 byte chucks to send, if a video is coming in the transport layer will assemble the frames into the video. Session Layer Makes the connection to the remote host (ex web server, email client, etc) Once connection is established, data can flow between the two connections Ports in the session layer get the data to the right application Ethernet Frame: Destination and Source Ports Presentation Layer Makes sure data gets to the application in a format that the application can view it Not that important anymore Ethernet Frame: Data Application Layer Applications that read the data Ethernet Frame: Data Frames Devices on a network send and receive data in discrete chunks called frames or (packets) Frames are a maximum of 1500 bytes Frames are created and destroyed inside the network interface card (NIC) MAC Addresses Unique 48-bit identifier for a NIC Frames have destination and source MAC addresses NICs use MAC addresses to decide whether or not to process a frame Broadcast vs Unicast A unicast transmission is addresses to a single device on a network A broadcast transmission is sent to every device in a broadcast domain A broadcast address looks like this: FF-FF-FF-FF-FF-FF (12 F’s) IP Addressing An IPv4 address looks like this: 31.44.17.231 A router connects multiple local area networks (LANs) The IP packet within the frame never changes Packets & Ports Port numbers help direct packet traffic between the source and destination Packets have sequence numbers so the network software can reassemble the file correctly TCP is connection-oriented, UDP is connectionless