msis 4523 ch2.network models

8/3/2019 MSIS 4523 Ch2.Network Models

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Data Communications SystemsCh 2: Network Models

JinKyu Lee, Ph.D.

[email protected]


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Topic List

Network Architecture/Reference Models OSI 7-Layer Model

TCP/IP Protocol Suite 5-Layer Model

Purpose of Layered Models

Encapsulation & Decapsulation Layer-to-Layer (peer-to-peer) Processing

Devices in Each Layer

Addressing in Each Layer

2


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Network Architectures

Reference model

Describes the layers of hardware and software

necessary to transmit data between two points or for

multiple devices / applications to interoperate

Necessary to increase the likelihood that different

components from different manufacturers will

converse Two architectures are required learning: The OSI

Model, and the TCP/IP protocol suite


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The Open Systems Interconnection (OSI)model

An ISO standard that

covers all aspects of

network communications

is the Open Systems

Interconnection (OSI)

model. It was first

introduced in the late

1970s.

Layered Architecture

ISO is the organization.

OSI is the model.


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TCP/IP PROTOCOL SUITE

The layers in the TCP/IP protocol suite do not

exactly match those in the OSI model. The original

TCP/IP protocol suite was defined as having fourlayers: host-to-network, internet, transport, and

application. However, when TCP/IP is compared to

OSI, we can say that the TCP/IP protocol suite is

made of five layers: physical, data link, network,transport, andapplication.


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TCP/IP Protocol Layers


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Summary of Duties


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Figure 2.16 TCP/IP and OSI model


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An exchange using the Internet model

Encapsulation

Decapsulation


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Peer-to-Peer Processes


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Physical layer

The physical layer is responsible fortransmitting individual bits from one

node to the next.


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Data link layer

The data link layer is responsible fortransmitting frames from

one node to the next.


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Node-to-node delivery Nodes


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Delivery in Data Link Layer

A node with physical (MAC) address 10 sends a frame to a

node with physical address 87. The two nodes are connected

by a link.

At the data link level this frame contains physical addresses

in the header. These are the only addresses needed.


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Network layer

The network layer is responsible for the

delivery of packets from the original sourceto the

final destination.


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Source-to-destination deliveryNodes


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Delivery in Network Layer

A node with a physical

address 10 wants to send datato a node with a physical

address 95, located on a

different network. Physical

addresses only have localjurisdiction. We need

universal addresses that can

pass through the LAN

boundaries. The network

(logical) addresses have this

characteristic.


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Transport layer

The transport layer is responsible for

delivery of a message from one process

to another.


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Delivery in Transport Layer


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Application layer

The application layer is responsible for

providing services to the user.


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Devices in Each Layer

Physical Layer Repeaters & Hubs

Data Link Layer Devices

Bridges & (Layer-2) Switches

Network Layer Device

Routers & Layer-3 Switches

Transport Layer Device

(Packet filtering, SPI, NAT) Firewalls Application Layer Device

Proxy servers, (Content filtering) Firewalls,Application Gateways


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Addressing

Each sub-network on a network requires aunique address within that network

Each computer on a sub-network requires aunique address on that sub-network

Each application requires a unique addresswithin the computer to allow support for multipleapplications (service access points, or SAP)

Service Access Points (SAPs)

Addresses for applications using transport services

Commonly known as Ports


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ADDRESSING

Four levels of addresses are used in an internet

employing the TCP/IP protocols: physical, logical,port, andspecific.

Addresses in TCP/IP

e.g., Email addresss& URLs

User friendly

Converted to alogical & portaddress


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Relationship of layers and addresses in TCP/IP

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