1. Chapter 2. Protocols and Architecture
OSI 7-layer Reference Model
TCP/IP Protocol Suite

2. Protocols Key elements Functions
Syntax: data format, coding, signal levels
Semantics: control information
Timing: speeding matching and sequencing
Functions
Segmentation and Reassembly,
Encapsulation, Connection Control,
Ordered delivery, Flow control, Error control,
Addressing, Multiplexing,
Transmission services

3. Functions of Protocols
Segmentation and Reassembly
Typical reasons for segmentations
Maximum size of transmitted data block
Error control may be more efficient with a smaller PDU
Shorter delay can be provided
A smaller PDU size means that receiving entities can allocate smaller buffers
Disadvantages of segmentation
The smaller the block, the greater the percentage overhead
Smaller blocks result in more interrupts
More time is spent processing smaller, more numerous PDUs

4. Functions of Protocols (cont)
Encapsulation
Control information in PDU
Address
Error-detecting code
Protocol control
Connection Control
Connectionless
E.g. Datagram
Connection-oriented

5. Functions of Protocols (cont)
Three phases
Connection request/accept
Data/Acknowledgment
Terminate request/accept
E.g. Virtual circuit
Key characteristic: sequencing
Supporting Ordered delivery, Flow/Error control
Ordered Delivery
For connection-oriented protocols
Finite sequence # field  sequence # repeat

6. Functions of Protocols (cont)
Flow Control
Performed by the receiving entity to limit the rate of data that is sent by a transmitted entity
Stop-and-wait, sliding window
Error Control
Error detection based on a frame check sequence and PDU retransmission
Addressing
Addressing level, Addressing scope,
Connection identifiers, Addressing mode

7. Functions of Protocols (cont)

8. Functions of Protocols (cont)
Advantages of connection identifiers
Reduce overhead
Routing: route identification
Multiplexing
Use of state information
End systems can enable functions such as flow/error control

9. Functions of Protocols (cont)
Multiplexing
Upward multiplexing
Downward multiplexing
Transmission services
Priority
Message basis, Connection basis
Quality of service
Security

10. OSI 7-Layer RM Open System Interconnection Reference Model
Layering architecture
Information hiding
Lower layers are concerned with greater details; upper layers are independent of these details
For each layer
Protocol specification
Service definition
Addressing

11. OSI Environment

12. OSI as Framework

13. Layer-specific Standards

14. Service Primitives
(b) Non-confirmed

15. The OSI Layers

16. The OSI Layers (cont) Physical layer Data Link layer Network layer
Mechanical, Electrical, Functional, Procedural
Data Link layer
e.g. Error detection and control
Network layer
Provides for the transfer of information between end systems across some sort of communications network (routing)
Transport layer
Provides a mechanism for the exchange of data between end systems

17. The OSI Layers (cont) Session layer Presentation layer
Provides the mechanism for controlling the dialogue between applications in end systems
Dialogue discipline, Grouping, Recovery
Presentation layer
Defines the format of the data to be exchanged between applications
Data compression and encryption
Application layer
General-purpose applications are considered to reside at this layer
File transfer, Electronic mail etc.

18. TCP/IP Protocol Suite Application layer Transport layer Internet layer
Provides end-to-end, data-transfer service
Internet layer
Routing data from source to destination host
Network access layer
Logical interface between an end system and a subnetwork
Physical layer
Tx medium, signaling rate, encoding scheme

19. TCP/IP PDU

20. Protocols in TCP/IP Suite