Computer Networks I CSE 502

Computer Networks I CSE 502
Dr:- Rania Abul Seoud

r-abulseoud@k-space.org
2004, Cisco Systems, Inc. All rights reserved.
Lecture 2
Network Terminology + OSI Model
Dr:- Rania Abul Seoud
r-abulseoud@k-space.org
hr
Network Technology
It is related to the signal encoding Techniques.
LAN Technologies
1. Ethernet 2. Token Ring 3. FDDI (Fiber Distributed Data Interface)
WAN Technologies
1. Modems (dial up). 2. Integrated Services Digital network (ISDN). 3. Digital subscribe Line (DSL). 4. Frame Relay. 5. T1 , E1,T3,E3 6. Synchronous optical network (SoNET)
Bandwidth
It is the amount of information that can flow through a network connection in a given period of time. B.W. = Data (Amount of data that can flow)\ Time
Measuring Bandwidth
Importance of Bandwidth
Throughput
It refers to actual measured bandwidth. It is often far less than the maximum possible digital bandwidth of the medium that is being used. P = Amount of data being sent\ Time Some of the factors that determine throughput:
Internetworking devices. Type of data being transferred. Network topology. Number of users on the network. User computer. Server computer. Time of the day .
Transfer Time Calculation
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Open Systems
Interconnection Model - OSI Model
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Network Reference Models

Network Fundamentals
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Why do we need Reference Models?

The early 1980s number and size of networks are increased. It was difficult for networks that used different specifications and implementation to exchange information. The same problem with the companies that developed private networking model or technology. They follow rules could not communicate with technologies that follow different rules.
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Reference Model
Importance of reference model: Better understanding of data transfer. A framework (guideline) for network implementation and troubleshooting. Vendor:- for providing a set of standards for network communication- standardization. OSI (Open System Interconnection) Reference model:
It divides complex functions into simpler components.
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Open Systems Interconnection (OSI) Model

The International Organization for Standardization (ISO) created the Open Systems Interconnection - OSI model in 1984. It is a network model to create networks that are compatible with other networks. It allows different types of network hardware and software to communicate with each other. Term open denotes the ability to connect any two systems which conform to the reference model and associated standards.
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OSI Model
It describes how information or data makes its way from application programmes through a network medium to another application programme located on another network. It divides network communication into smaller parts to make learning it easier to understand. PC A PC B
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OSI layers
The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable functions (layering). It explains how packets travel through the various layers to another device on the network even the sender and the destination have different types of the network media.
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OSI Model
PC A PC B
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OSI Model
Top-Down Approach
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Layer 7 - The Application Layer

7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Its the S\w on our PCs that is used to represent a user interface to the network & so aids the user to make applications. Examples: Email (SMTP,POP3) Web browsers (HTTP) File transfer - FTP Remote login - Telnet
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Layer 6 - The Presentation Layer

7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
It is responsible for presenting the data in the proper format in which the data is to be exchanged between the two entities. Examples: ASCII, AVI,JPG,. It Also handles data compression and data encryption (cryptography).
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Layer 5 - The Session Layer

7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Ensure that all information required for opening a session is available. Controlling the dialogue between the two end systems. It gives orders for: Establishment, Management, Termination of the session.
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Layer 4 - The Transport Layer

Provide a reliable mechanism for the exchange of data :1.Establishment of connection. 2.Management of connection: Segmentation- Breaks the outgoing data into
segments and reassemble the received segments. Sequencing- Ensures that data units are delivered in sequence.
End-to-end check. Error detection & correction- Ensures that the

data units are delivered error free. Flow control- Ensures that there is no loss or duplication of data units.
3.Termination of connection.
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OSI Model
Transport Layer Protocols

TCP (transmission control protocol). UDP (User Datagram Protocol).
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Layer 3 - The Network Layer

1.Breaks the outgoing data into packets and reassemble the received packets. 1.End-to-end delivery. 2.Logical addressing EX:IPv4, IPv6, IPX, APPLETALK 4. Implements routing of packets (choose the best path to destination.) EX:RIP,OSPF,IS-IS,EIGRP. 5. The network layer also defines how to fragment a packet into smaller packets to accommodate different media.
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Layer 2 - The Data Link Layer

Responsible for: 1. Breaks the outgoing data into frames and reassemble the received frames. 2. Create and detect frame boundaries. 1. Hop-to hop data delivery. 2. Hop-to-hop addressing (MAC Address in Ethernet). 3. Hop-to-hop error detection 4. Hop-to-hop flow control- by
implementing an acknowledgement and retransmission scheme.
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Layer 1 - The Physical Layer

Its responsible for all Physical properties of the network : 1. Cable length. 2. Cable type. 3. Bit rate. 4. Voltage levels. 5. H/W interface types.
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OSI Model
OSI: A Layered Network Model
The upper three layers of the OSI model are orientated more toward services to the applications. The lower 4 layers are concerned with the flow of data from end to end through the network.
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OSI Layers
S/W
S/W H/W H/W

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Using Layers to Describe Data Communication
The concept of layers is used to describe communication from one computer to another.
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Using Layers to Describe Data Communication

Each layer performs a certain set of operations on data as it prepares the data to be sent over the network. The data is then passed to the next layer to perform another different set of operations. Once the data has been sent to destination, it undoes the construction of the data that was done on the source side. Each layer on the destination return the information to its original form, so the application can read the data.
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Computer Networks I CSE 502

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Computer Networks I CSE 502

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Computer Networks I CSE 502

Dr:- Rania Abul Seoud

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

Transfer Time Calculation

2004, Cisco Systems, Inc. All rights reserved.

Network Reference Models

2004, Cisco Systems, Inc. All rights reserved.

Why do we need Reference Models?

2004, Cisco Systems, Inc. All rights reserved.

Open Systems Interconnection (OSI) Model

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

2004, Cisco Systems, Inc. All rights reserved.

Layer 7 - The Application Layer

2004, Cisco Systems, Inc. All rights reserved.

Layer 6 - The Presentation Layer

Layer 5 - The Session Layer

2004, Cisco Systems, Inc. All rights reserved.

Layer 4 - The Transport Layer

End-to-end check. Error detection & correction- Ensures that the

Transport Layer Protocols

2004, Cisco Systems, Inc. All rights reserved.

Layer 3 - The Network Layer

2004, Cisco Systems, Inc. All rights reserved.

Layer 2 - The Data Link Layer

Layer 1 - The Physical Layer

OSI: A Layered Network Model

2004, Cisco Systems, Inc. All rights reserved.

S/W H/W H/W

Using Layers to Describe Data Communication

Using Layers to Describe Data Communication

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