Chapter 2 Protocols and Architecture Protocols OSI 7

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

Protocols • Key elements – 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 2

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 3

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

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

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 6

Functions of Protocols (cont) 7

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

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

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 10

OSI Environment 11

OSI as Framework 12

Layer-specific Standards 13

Service Primitives (b) Non-confirmed 14

The OSI Layers 15

The OSI Layers (cont) • Physical 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 16

The OSI Layers (cont) • Session 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. 17

TCP/IP Protocol Suite • Application layer • Transport 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 18

TCP/IP PDU 19

Protocols in TCP/IP Suite 20