OSI (Open System Interconnection Model ) Model
•An architecture model based on the OSI protocol suite which defines and standardizes the flow of
data between computers
-Represents how network communication works
-7 different layers
-Standards maintained by the International Organization for Standardization(ISO)
Protocol Data Unit (PDU)
•The unit of data specified by a protocol at each layer of the OSI model
Layer 1 (OSI Model)
•Physical layer
-Defines hardware connection and turns binary into physical pulses
-Moves data from one system to another
-Responsible for transmitting signals over the network medium
-Signaling, Cabling, Connectors
-The PDU is bits
(Ex: Cable, Network Interface Card, Hub)
• "You have a physical layer problem"
-Fix the cabling, punchdown block
-Run loopback tests, test/replace cables, swap adapter cards
Layer 2 (OSI Model)
•Data Link Layer
-Identifies devices on the physical layer (NIC/MAC address)
-transfers data between adjacent network nodes on the same local area network (Frames)
,-Switches operate on this level
-The PDU is frames
•Has 2 sub-layers:
-Logical Link Control(LLC)
-Media Access Control(MAC)
Logical Link Control (LLC) sublayer
•A sublayer of the data link layer of the OSI model (Layer 2)
-Talks with the OS
-Places outbound data into frames
-Creates the FCS on each frame
-Deals with incoming frames by processing thoses addressed to the NIC and erasing ones meant for
other machines
Media Access Control (MAC) sublayer
•A sublayer of the data link layer of the OSI model (Layer 2)
-Adds the NIC's own MAC address
-Creates and addresses the frame
-Adds or checks the FCS
-Ensures frames are sent along the network cabling
Frame
•A defined series of binary data that is the basic container for a discrete amount of data moving
across the network
-Created in Layer 2 of the OSI model
-3 main components: Header, payload, trailer
,•Header
-The Recipient's/Sender's MAC address and type
•Payload
-The actual data being transmitted
•Trailer
-The frame check sequence
Frame Check Sequence (FCS)
A sequence of bits placed at the very end (trailer) of a frame that is used to check the primary data for
errors by implementing a cyclic redundancy check
unicast frame
Any frame addressed specifically to another device's MAC address
broadcast frame
A frame intended for every computer on the network
Layer 3 (OSI Model)
•Network Layer
-Creates/addresses packets so they can go from one network to another(IP)
-Responsible for the delivery of data to its final destination
-Routers/IP operate on this level
-The PDU are packets
, Packet
•An IP specific container inside of a frame that enables routers to determine where to send data
-Does not care about physical connection type
Internet Protocol (IP)
•Layer 3 protocol responsible for logical addressing and routing packets across the network,
including the Internet
-It is a connectionless protocol
-Has 2 versions: IPv4 & IPv6
IP address
•The numeric address of a computer connected to a TCP/IP network
-Also known as a logical address
Layer 4 (OSI Model)
•Transport Layer
-Breaks requested data down into manageable chunks and reassembles chunks of data for the
receiving system (segmentaion)
-Protocols used on this layer are TCP and UDP
-TCP segments and UDP datagrams are made at this layer
-Flow control operates at this level
-Have header fields that contain the port numbers of the applications that generated the data in the
packet and which will receive it
-The PDU are segments
TCP segments
•An architecture model based on the OSI protocol suite which defines and standardizes the flow of
data between computers
-Represents how network communication works
-7 different layers
-Standards maintained by the International Organization for Standardization(ISO)
Protocol Data Unit (PDU)
•The unit of data specified by a protocol at each layer of the OSI model
Layer 1 (OSI Model)
•Physical layer
-Defines hardware connection and turns binary into physical pulses
-Moves data from one system to another
-Responsible for transmitting signals over the network medium
-Signaling, Cabling, Connectors
-The PDU is bits
(Ex: Cable, Network Interface Card, Hub)
• "You have a physical layer problem"
-Fix the cabling, punchdown block
-Run loopback tests, test/replace cables, swap adapter cards
Layer 2 (OSI Model)
•Data Link Layer
-Identifies devices on the physical layer (NIC/MAC address)
-transfers data between adjacent network nodes on the same local area network (Frames)
,-Switches operate on this level
-The PDU is frames
•Has 2 sub-layers:
-Logical Link Control(LLC)
-Media Access Control(MAC)
Logical Link Control (LLC) sublayer
•A sublayer of the data link layer of the OSI model (Layer 2)
-Talks with the OS
-Places outbound data into frames
-Creates the FCS on each frame
-Deals with incoming frames by processing thoses addressed to the NIC and erasing ones meant for
other machines
Media Access Control (MAC) sublayer
•A sublayer of the data link layer of the OSI model (Layer 2)
-Adds the NIC's own MAC address
-Creates and addresses the frame
-Adds or checks the FCS
-Ensures frames are sent along the network cabling
Frame
•A defined series of binary data that is the basic container for a discrete amount of data moving
across the network
-Created in Layer 2 of the OSI model
-3 main components: Header, payload, trailer
,•Header
-The Recipient's/Sender's MAC address and type
•Payload
-The actual data being transmitted
•Trailer
-The frame check sequence
Frame Check Sequence (FCS)
A sequence of bits placed at the very end (trailer) of a frame that is used to check the primary data for
errors by implementing a cyclic redundancy check
unicast frame
Any frame addressed specifically to another device's MAC address
broadcast frame
A frame intended for every computer on the network
Layer 3 (OSI Model)
•Network Layer
-Creates/addresses packets so they can go from one network to another(IP)
-Responsible for the delivery of data to its final destination
-Routers/IP operate on this level
-The PDU are packets
, Packet
•An IP specific container inside of a frame that enables routers to determine where to send data
-Does not care about physical connection type
Internet Protocol (IP)
•Layer 3 protocol responsible for logical addressing and routing packets across the network,
including the Internet
-It is a connectionless protocol
-Has 2 versions: IPv4 & IPv6
IP address
•The numeric address of a computer connected to a TCP/IP network
-Also known as a logical address
Layer 4 (OSI Model)
•Transport Layer
-Breaks requested data down into manageable chunks and reassembles chunks of data for the
receiving system (segmentaion)
-Protocols used on this layer are TCP and UDP
-TCP segments and UDP datagrams are made at this layer
-Flow control operates at this level
-Have header fields that contain the port numbers of the applications that generated the data in the
packet and which will receive it
-The PDU are segments
TCP segments
