Exploration Network Chapter2hkm

8/3/2019 Exploration Network Chapter2hkm

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1© 2007 Cisco Systems, Inc. All rights reserved. Cisco© 2007 Cisco Systems, Inc. All rights reserved. Cisco 1

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Communicating over

the Network

Network Fundamentals – Chapter 2



2© 2007 Cisco Systems, Inc. All rights reserved. Cisco

Objectives

§ Describe the structure of a network, including thedevices and media that are necessary for successfulcommunications.

§ Explain the function of protocols in network

communications.§ Explain the advantages of using a layered model to

describe network functionality.

§ Describe the role of each layer in two recognizednetwork models: The TCP/IP model and the OSImodel.

§ Describe the importance of addressing and namingschemes in network communications.




Elements of Communication

§ All methods of communication have three things incommon.

– There is source for the message or a sender. – There is a destination for the message or a receiver . – There is a channel that consists of the media thatprovides the pathway for the message.

ABC

Sender

Channel

Receiver




Elements of Communication•

Devices communicate in exactly the same way.




Communicating the Messages

• In theory, a networkcommunication couldbe sent as onecontinuous streamof 1’s and 0’s.

• No other devicewould be able tosend or receivemessages on thesame network.

– Significant delays

– Inefficient use of the channel

– A lost message entirely retransmitted.




Communicating the Messages• A better approach

is calledSegmentation.

• The data stream isdivided into smaller,

more manageablesegments.

• Segmentation hastwo benefits:

–

Multiplexing:• Different transmissions can be interleaved on the network.

– Reliability

• Pieces can travel different ways, avoiding congestions

• If a piece fails, just resend the failed or missing parts


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Communicating the Messages

• Segmentation Disadvantage: Increased level of complexity. – The label is a unique sequence number.

– Handled by protocols that format and address the message.



Network Components

Devices (end devices, intermediary devices) – end devices that send and receive messages (e.g.,computers, VoIP phones)

– intermediary devices (e.g., hubs, switches, routers)that move messages among different parts of the

network. – Each type of device plays an important role inmoving messages. Different symbols to representeach device

Media (Cable or wireless)

Services and processes (Software)

HARDWARE

SOFTWARE



devices

services

media



Components of the Network



End Devices

– End devices form interface with human network &communications network

– Role of end devices (a.k.a. hosts): client, server, or both• client - request and display the information obtained from theserver

• server - provide information and services (E-mail, Web Pages)to other hosts on the network



Wireless

scanners

Network PrintersNotebooks

Mobile PhonesVOIP Phones

Blackberry

PC

SecurityCameras

Server



Intermediary Device

–

Role of an intermediary device• provides connectivity and ensures data flowsacross network• it directs the path of the data but do not generate or change the data



Intermediary Device

§ Processes running on the intermediary network devicesperform these functions:

– Regenerate and retransmit data signals – Maintain information about what pathways exist throughthe network and internetwork

– Notify other devices of errors and communication failures – Direct data along alternate pathways when there is a linkfailure

– Classify and direct messages according to QoS priorities – Permit or deny the flow of data, based on security settings



KC KHOR, MultimediaUniv. Cyberjaya

Intermediary DeviceExamples:

- Network Access Devices (Hubs, switches, and wirelessaccess points)

- Internetworking Devices (routers)

- Communication Servers and Modems

- Security Devices (firewalls)

Cisco PixFirewall

Routers

Modems

Switches

Wireless Access

Point



Network Media

§ Network media - the channel over which a messagetravels

Metallic wires within cables

Glass or plastic fibers (fiber optic cable)

Wireless transmission



Network Media•

The signal encoding that must occur is different for each type of media. Electricalimpulses withspecific patterns

Pulses of light in theinfrared or visibleranges

Patterns of electromagnetic waves



• Different network media have different features and

benefits.• Not all network media are appropriate for the same

purpose.

§ Criteria for choosing a network media are: –

The distance the media can successfully carry asignal.

– The environment in which the media is to be installed. – The amount of data and the speed at which it must betransmitted.

– The cost of the media and installation



Network Types

§

Networks infrastructures can vary greatly interms of: – The size of the area covered – The number of users connected –

The number and types of services available§ Network types include

– LAN – WAN – Internetworks



§ Local Area Networks (LANs)-

A network serving a home, building or campus is considered aLocal Area Network (LAN)

§ Wide Area Networks (WANs)- LANs separated by geographic distance are connected by anetwork known as a Wide Area Network (WAN)



§ InternetworkThe internet is defined as a global mesh of interconnected networks



Network Representations




• Network Interface Card (NIC): – Provides the physical connection to the network at the PC or other host device.

• Physical Port:• A connector or outlet on a networking

device where the media is connected to ahost or other networking device.





• Interface: –

Specialized ports on an internetworking device that connect toindividual networks.

• Because routers are used to interconnect networks, the portson a router are referred to as network interfaces.




Rules That Govern Communications•

Protocols: – Are the rules that govern communications.

The format or structure of the message.

How and when error and system messages are passed between

devices.

The setup and termination of data transfer sessions.

The method by which networking devices share information aboutpathways with other networks.




Protocol Suites•

Protocol Suite: – A group of inter-related protocols that are necessary to perform acommunication function.

– Cannot function without a set of standards that network vendors canfollow.

–

Institute of Electrical and Electronics Engineers (IEEE):• Develops standards in telecommunications, information technology

and power generation.

• Examples: 802.3 (Ethernet), 802.11 (WLAN) – Internet Engineering Task Force (IETF)

•

Internet standards, RFCs (Request for Comments)• Example: TCP, IP, HTTP, FTP




Protocol Suites




Function of Protocol in Network Communication

§ The protocols are viewed as a layered hierarchy, witheach higher level service depending on the functionalitydefined by the protocols shown in the lower levels.

§ The lower layers of the stack are concerned with –

moving data over the network and – providing services to the upper layers

§ the upper layers are focused on – the content of the message being sent and

– the user interface.




Function of Protocol in Network Communication

Layer 1

Layer 2

Layer 3




Layered

The Interaction of Protocols




Technology Independent Protocols

§Many diverse types of devices can communicate usingthe same sets of protocols.

§This is because protocols specify network functionality, not the underlying technology to support this

functionality.




Layered Models :: TCP/IP and OSI

§ A layered model – depicts the operation of the protocols occurring withineach layer,

– as well as the interaction with the layers above andbelow it.

§ Benefits of using a layered modelü assists in protocol designü fosters competitionü changes in one layer do not affect other layersü provides a common language




Layered Models

• Layered models separate the functions of specific protocols.




Protocol & Reference Model

§ Two basic types of networking models:: protocol models andreference models.

A protocol model provides amodel that closely matches thestructure of a particular protocol suite.

The hierarchical set of related

protocols in a suite typicallyrepresents all the functionalityrequired to interface thehuman network with the datanetwork. Ex: TCP/IP model

§ A reference model provides acommon reference for maintaining consistency withinall types of network protocolsand services.

§

The primary purpose of areference model is to aid inclearer understanding of thefunctions and process involved.Ex: OSI model




Protocol and Reference Models

A protocol model provides amodel that closely matches thestructure of a particular protocolsuite.

The hierarchical set of relatedprotocols in a suite typicallyrepresents all the functionalityrequired to interface the humannetwork with the data network.




Protocol and Reference Models

• Reference Model: – Provides a common referencefor maintaining consistency withinall types of network protocols and

services. – Not intended to be animplementation specification.

– Primary purpose is to aid inclearer understanding of the

functions and process involved.




Protocol & Reference Model

A protocol model

provides a model thatclosely matches thestructure of aparticular protocolsuite.

A reference model

provides acommon referencefor maintainingconsistency withinall types of

network protocolsand services.

OSITCP/IP




Layers with TCP/IP and OSI Model




Protocol data units and encapsulation

§ As application data is passeddown the protocol stack,various protocols addinformation to it at each level.This is commonly known asthe encapsulation process.

§ The form that a piece of datatakes at any layer is called aProtocol Data Unit (PDU).

§ During encapsulation, thelower layer encapsulates the

PDU that it receives from thelayer above in accordancewith the protocol being used.

§ At each stage of the process,a PDU has a different name toreflect its new appearance.

§ Data – Application Layer PDU

§ Segment - Transport Layer

PDU§ Packet - Internetwork Layer

PDU

§ Frame - Network AccessLayer PDU

§ Bits - A PDU used whenphysically transmitting dataover the medium




The Communication Process

Segment andEncapsulate

Generate onto the media

Create Data

Transport through the segment

Pass data toapplication

Receive fromthe media

Decapsulate andReassemble




Segmentation and Encapsulation

Header

Header Data

Header Trailer

Email Message

Data Data Data

Data

Data

001010011101100101000001111101010001010

1




Decapsulation and Reassembly

Header

Header

Header Trailer

Email Message

Data Data Data

Data

Data

Data

Data

001010011101100101000001111101010001010

1




Layers with TCP/IP and OSI Model§

The process of sending and receiving messagesStart

HTML formatted web page data

data is broken into TCP segments. Each TCP segment is given a label, called aheader

the entire TCP segment is encapsulated within an IP packet, which addsanother label, called the IP header.the IP packet is sent to the Network Access layer Ethernet protocolwhere it is encapsulated within a frame header and trailer.

Change to bits




data is broken into TCP segments. Each TCP segmentis given a label, called a header

Start

HTML formatted web page data

the entire TCP segment is encapsulated within an IP packet, which adds another label, called the IP header.




Change to bits

the IP packet is sent to the Network Access layer Ethernet protocol where it is encapsulated within aframe header and trailer.

This process is reversed at the receiving host.The data is decapsulated as it moves up thestack toward the end user application.




OSI Model• Breaks network communication into

smaller, more manageable parts. – Makes learning it easier tounderstand.

– Prevents changes in one layer fromaffecting other layers.

• Standardizes network componentsto allow multiple vendor developmentand support.

• Allows different types of networkhardware and software to communicatewith each other.

• It is a descriptive scheme.




OSI Model

Layers

7 Application All Away

6 Presentation People Pizza

5 Session Seem Sausage

4 Transport To Throw

3 Network Need Not

2 Data Link Data Do

1 Physical Processing Please

Usually referenced by layer number

These two layers arenot commonlyreferred to in mostinstances.




OSI Model

Layers

7 Application All Away

6 Presentation People Pizza

5 Session Seem Sausage

4 Transport To Throw

3 Network Need Not

2 Data Link Data Do

1 Physical Processing Please

Primary concern:

Communications betweenapplications

Primary concern:Moving raw datacross the network




OSI and TCP/IP Models Comparison




OSI Model

OSI Model Layer Addressing

ApplicationEncoded Application Data

(Usually referred to as the Upper Layers)

Presentation

Session

Transport Source and Destination: Process Address

Network Source and Destination: Logical Network Address

Data Link Source and Destination: Device Physical Address

Physical Timing and Synchronization Bits




Addressing and Naming Schemes

§

There are various types of addresses that must be included tosuccessfully deliver the data from a source applicationrunning on one host to the correct destination applicationrunning on another

§ Using the OSI model as a guide, figure shows the different

addresses and identifiers that are necessary at each layer .




Getting Data to the End Device

Header

Header

Header Trailer

Email Message

Data

Data

Data

Encoded Data

Process

Logical

Physical

Encapsulation Process and Addressing

1.

2.

3.

4.

5.

6.

7.

Addressing always includes both the Source andDestination Addresses.




Addressing and Naming Schemes

§

The host physical address, is contained in the header of the Layer 2 PDU, called a frame.

§ Layer 2 is concerned with the delivery of messages on a singlelocal network.

§ The Layer 2 address is unique on the local network and

represents the address of the end device on the physical media.§ In a LAN using Ethernet, this address is called the Media Access

Control (MAC) address.

§ When two end devices communicate on the local Ethernetnetwork, the frames that are exchanged between them containthe destination and source MAC addresses.

§ Once a frame is successfully received by the destination host, theLayer 2 address information is removed as the data isdecapsulated and moved up the protocol stack to Layer 3.




Getting the Data Through the Internetwork

Layer 3 protocols are primarily designed to move datafrom one local network to another local network withinan internetwork.

Layer 3 addresses must include identifiers that enableintermediary network devices to locate hosts ondifferent networks

At the boundary of each local network, an intermediarynetwork device, usually a router , decapsulates theframe to read the destination host address contained inthe header of the packet, the Layer 3 PDU

Routers use the network identifier portion of thisaddress to determine which path to use to reach thedestination host.





1.

2.

3.

4.

5.

6.

7.

Layer 2 Addressing

• Delivery on a single local network .

• Unique on the network and representsthe device.

•

Codes placed on the NIC by themanufacturer.

• Referred to as the physical addressor the MAC address.

Header Trailer Data Source andDestination Physicalor MAC Address





DestinationMAC

Address

SourceMAC

AddressData

Layer 2 Header




Getting Data Through The Network

Header Data Source and Destination

Logical Network Address(IP, IPX, etc.)

1.

2.

3.

4.

5.

6.

7.

Layer 3 Addressing

• Move data from one local network toanother local network.

• Addresses must identify both thenetwork and the host on that network.

• Used by routers to determine the bestpath to the destination host.




Getting Data Through the Network

DestinationMAC

Address

SourceMAC

Address

DestinationLogical

Address

SourceLogical

AddressData

Layer 2 Header

Layer 3 Header




Getting Data to the Right Application

1.

2.

3.

4.

5.

6.

7.

Layer 4 Addressing

• Identifies the specific process or servicerunning on the destination host that will act on the data.

• Multiple, simultaneous applications.

Header Data Process

• Under TCP/IP, a port number to identify the

application.• Port 80: HTTP (Web Browser)• Port 25: SMTP (Email)• Port 194: IRC (Internet Relay Chat)




Getting Data to the Right Application

DestinationMAC

Address

SourceMAC

Address

DestinationLogical

Address

SourceLogical

Address

DestinationProcess

Address

SourceProcess

Address

Data

Layer 2 Header

Layer 3 Header

Layer 4 Header




Putting It All Together

DestinationMAC

Address

SourceMAC

Address

DestinationLogical

Address

SourceLogical

Address

DestinationProcess

Address

SourceProcess

AddressData

LogicalMAC

Port

MAC




Comparing the OSI and TCP/IP Models

OSI Model Layer FunctionProtocol

Data UnitDevice

TCP/IP

Model

7 Application User Functionality

Character Application6 Presentation Character Representation

5 Session Manage Data Exchange

4 TransportServices to segment, transfer andreassemble the data

Segment Transport

3 NetworkNetwork addressing and best pathdetermination

Packet Router Internet

2 Data LinkMethods for reliable frame exchangeover a common media

Frame SwitchNetwork Access

1 PhysicalDescribe physical characteristics totransmit bits over a common media

Bit Hub




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