5-Application:
 Provides network services to application processes (email, file transfer, etc.)
 Interacts with operating system and interfaces with system (FTP, Telnet, SMTP)
 Handles general network access, flow control, error recovery, and file transfer
 Agreement procedures for error recovery and controls data integrity
 Responsible for meaningful exchange of data
 Ensures data is readable by receiver
 Format of data/data structures
 Negotiates data transfer syntax for application layer
 Provides encryption, text compression, and reformatting? Support of connections between sessions, administrative tasks,  and security
 Control structure for communication between applications
 Establishes, manages, and terminates connections between applications
 Data expeditions, class of service, exception reporting
 Inter-host communication

4-Transport:
 Responsible for reliable, transparent transfer of data between end points
 End-to-end error recovery and flow control
 Packet handling, repackaging of messages, dividing messages into smaller packets, and error handling
 Concerned with transportation issues between hosts
 Establishing, maintaining, and terminating virtual circuits
 Fault detection and recovery
 Deals with segments

3-Network:
 Responsible for addressing and control functions (routing)
 Establishing, maintaining, and terminating connections (packet switching, routing, data congestion, reassembly of data, translation of logical addresses to physical addresses)
 Provides connectivity and path selection between two end systems
 Domain of routing
 Deals with packets


2-Data Link:
 Responsible for error-free transmission and establishing logical connections between stations
 Packaging raw bits of data from physical into blocks of data (frames)
 Sending frames with necessary synchronization, error control, and flow control
 Physical addressing, network topology, and media access (interface to cable)
 Reliable transfer of data, error notification, and flow control
1-Physical:
 Responsible for the transmission of unstructured bit streams over physical media
 Defines the mechanical, electrical, and procedural characteristics required to establish, maintain, and deactivate physical links of end systems
Describes the media
 Wires, connectors, voltages, data rates, and binary transmission