OSI Layers

Open Systems Interconnection.
Links
http://en.wikipedia.org/wiki/OSI_model

Please Do Not Throw Sausage Pizza Away.

1. Physical
2. Data
3. Network
4. Transport
5. Session
6. Presentation
7. Application

1. Physical - Bits
2. Data Link - Frames
3. Network - Packets
4. Transport - Segments

Physical

Physical Topology. Moves Bits between devices. NIC Card. Hub. Repeaters. Wires.

Data Link

Logical Topology. Framing. Error Detection, Notification (NOT Correction). Flow Control. Delivery on LAN using MAC, Physical Addresses. Switches and Bridges. Switches Break up Collision Domains. Data Frames have source and destination MAC Address in header. LLC (Logical Link Control) Header. MAC (Media Access Control) Header.

Network

Routed Protocols IP (Header) and IPV6 transport Data Packets through an internetwork (devices that aren't locally attached). Logical Addressing. Routing Protocols update neighboring routers with Route Update Packets. Examples are RIP Routing Information Protocol, EIGRP Enhanced Interior Gateway Routing Protocol, and OSPF Open Shortest Path First. Routers break up Broadcast Domains, will not forward broadcast or Multicast packets. Routing Table Holds Network Address, Interface, Metric

Transport

TCP, UDP (header). Reliable or Unreliable Delivery. Error Correction before re-transmit. Connection Oriented Communication. Virtual Circuit. SYN, SYN/ACK, ACK. Three way handshake. Flow Control. Receiver governs amt of data sent by sender by sending ack for each segment. Segments are ordered - delivered in the order they are transmitted. Window is the # of segments that can be sent without waiting for a Flow Control ack. Positive acknowledgement with retransmission.

Session

simplex, half duplex,full duplex.

Presentation

Translation. Compression. Encryption. EBCDIC to ASCII

Application

FTP, HTTP, SMTP, SNMP, Telnet, DNS, DHCP.