network software & osi model

8/14/2019 Network Software & OSI Model

http://slidepdf.com/reader/full/network-software-osi-model 1/21

Topics Covered

Network SoftwareOSI Reference Model



Network Software

Basic activities :• reliability (error correction, messages order preservation),• flow control,• addressing (to refer to users),• connection and disconnection,• routing.

Secondary activities :• take the heterogeneity of the network into account,•

synchronization of the transmission,• multiplexing- de multiplexing,• error recovery,• congestion control,• failure management,



Layers, Protocols & Interfaces



Design issues for layers

• Identifying senders & receivers

• Rules of Data transfer

• Error control• Sequencing

• Speed regulation

• Inability to process long messages

• Multiplexing

• Routing



Interfaces & services

Service Provider

Service User Peer Entities

SAP-Service Access Point

IDU-Interface Data Unit

SDU-Service Data Unit

PDU-Protocol data UnitICI-Interface Control Information



Types of services

Connection-oriented services

Connectionless services

Service Primitives

Services/Protocols Relations



OSI Reference model

(7 layered )

• Principles

1. Different level of abstraction.

2. Well defined function.3. Defining international standard protocols.

4. Minimum information flow across interfaces.

5. No. of layers.

Not a network Architecture



OSI Model

Medium/Channel



Physical Layer

• Transmitting raw bits over a communication

channel.

• Design issues :Mechanical

Electrical

Procedural

• Protocols: Fast Ethernet, RS232, and ATM

http://www.webopedia.com/quick_ref/Fast_Ethernet.html

http://www.webopedia.com/TERM/R/RS_232C.html

http://www.webopedia.com/TERM/A/ATM.html

http://www.webopedia.com/TERM/A/ATM.html

http://www.webopedia.com/TERM/R/RS_232C.html

http://www.webopedia.com/quick_ref/Fast_Ethernet.html



Data Link Layer

• Handles errors in the physical layer

• Frame boundaries: special bit patterns

• Problem of damaged, lost & duplicate frames.

• Speed matching

• Transmission in both directions

• Broadcast n/w s

Data Link layer

MAC

Medium Access Layer

LLC

Logical Link Layer



Network Layer

• Controlling the operation of the subnet.

• Switching & Routing: Virtual circuits

• Congestion control

• Heterogeneous networks

• Billing purpose



Transport Layer (End to End layer)

• Insulates the upper layers

• Efficient transfer of data between layers.

• Establishing two types of connections:

network connections

transport connections

• Type of service to the service layer.

• Supports multiprogramming

• Flow control



Session Layer

• Establish the sessions.

• Dialogue control

• Token management

• Synchronization



Presentation Layer :compatibility problems

Application Layer : supports end user processes



Data Transmission



ENCAPSULATION



Criticism of the model

• It was not the right moment

• It was not the right technology

• It was not the right implementation

• It was not the right policy

network software & osi model

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