OSI Model Flashcards
Layer 1
Physical.
Protocol Data Unit (PDU) = Bit.
Transmission and reception of raw bit streams over a physical medium.
Layer 2
Data Link.
Protocol Data Unit (PDU) = Frame.
Reliable transmission of date frames between two nodes connected by the physical layer. Two sub-layers MAC and Logical Link Layer.
Layer 3
Network.
Protocol Data Unit (PDU) = Packet.
Addressing (host), routing, and traffic control.
Layer 4
Transport.
Protocol Data Unit (PDU) = Segment (TCP) and Datagram (UDP).
Reliable transmission of data segments between points on a network including segmentation, acknowledgement and multiplexing. Uses ports for addressing.
Layer 5
Session.
PDU = Data.
Managing communication sessions - continuous exchange of information between two nodes.
Layer 6
Presentation.
PDU = Data.
Translation of data between a networking service and an application; character encoding, data compression and encryption / decryption.
Layer 7
Application.
PDU = Data.
High level API, including resource sharing remote file access.
Bit
Smallest unit in computer networking.
0 or 1
Byte
Composed of 8 bits.
Letter, number, or other ASCII character.
Frames (L2) and Packets (L3)
Frames and Packets are formatted units of data that are transmitted in a packet-switched network. The way they are transmitted depends on the protocols and transmission methods used.
Both are used interchangeably but frames are L2 and packets L3.
Datagrams
Are very similar to frames and packets but usually describe those of an “unreliable” protocol, such as UDP.
Binary
Base 2 numbering system.
1 and 0s.
Decimal
Base 10 numbering system.
0-9.
Hexadecimal
Base 16 numbering system.
0-9 and A-F.
