Chapter 5

Making Networks Work

OSI & 802 Network Models

• Open Systems Interconnect (OSI )
• ISO - International Standards Organization
• ISO/OSI model
• IEEE 802 networking model
• Open ended to allow for new types
• Reference Model Role
  • A framework to assist in choosing a network
  • Similar to buying a car

OSI Reference Model

• Layers are the essence of OSI
• Comparable to a conference call
  • Conference call time
  • Identify & notify involved parties
  • Obtain a number & ID
  • Conduct the call
  • Follow up action after call

Protocol Stacks

• TCP/IP- the internet
• IPX/SPX- NetWare
• NetBEUI- Microsoft
• AppleTalk- Macintosh
• SNA- IBM mainframe

OSI Layer Relationships

Data Units

• Packets
• Payloads
• PDU
  • Protocol data unit
  • packet data unit
  • Payload data unit

Application Layer (Layer 7)

• Applications interface to network
• Direct applications support
• General network access
• Error recovery at the user level

Presentation Layer (Layer 6)

• Data format for communications
• Protocol conversion
• Data encryption/decryption
• Graphics commands

Session Layer (Layer 5)

• Two party communication-session
• Session setup
• Data exchange
• Session tear down

Transport Layer (Layer 4)

• Manages data flow
• Chunks & re-chunks data
• Flow control
• Error handling

Network Layer (Layer 3)

• Addresses for delivery
• Translates logical data into physical
• Packet switching
• Congestion control

Data Link Layer (Layer 2)

• Sends special PDUs -data frames
• Sends data frames from 1 to 3
• Packages raw data into data frames
• Cyclical redundancy check (CRC)

Physical Layer (Layer 1)

• Translates bits to signals & signals to bits
• Manages NIC to medium attachment
• Governs connector type
• Regulates transmission technique

IEEE 802 Specifications

• Project 802
  • Year 1980
  • Month -February ( 2 )
• In concert with ISO
• Standardized 1982-1983

IEEE 802 Extensions

• LLC - Logical Link Control
• MAC - Media Access Control

IEEE 802 OSI Map