chapter 2 communicating over the network. chapter 2 elements of communication people communicate in...

Chapter 2

Communicating Over the Network

Chapter 2

Elements of Communication• People communicate in many different ways.

– Vocal, a look, a hand signal, …

• All of the methods have three things in common.– 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 that

provides the pathway for the message.

Chapter 2

Elements of Communication• Devices communicate in exactly the same way.

Chapter 2

Communicating the Messages• In theory, a network

communication 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– Any lost, message entirely retransmitted.

Chapter 2

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

Chapter 2

Interconnections

• Over time, 2 different techniques have been developed for multiplexing

– "circuit switching" : used by telephone network

– "packet switching" : used by the internet

Chapter 2

Interconnections

• The transmission of information in circuit-switching networks occurs in two phases

– Setup phase : a path is allocated from source to destination

– Information transfer phase : the frames are actually sent

Chapter 2

Interconnections

• Our objective: to allow for any sender to transmit data at any time WHILE allowing the link to be shared

• Solution : Packet switching

– Uses a tantalizingly simple idea: adding to each frame of data a little bit of information that tells the switch HOW to forward it => this is what we call header

Chapter 2

Communicating the Messages

• Segmentation and Reliability:– Increases the reliability of network communications. – Separate pieces of each message can travel across

different paths to destination. – Path fails or congested, alternate path can be used. – Part of the message fails to make it to the destination,

only the missing parts need to be retransmitted.

In a packet switched network like the

Internet.

Chapter 2

Communicating the Messages

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

Chapter 2

Components of the Network

Chapter 2

End Devices

• Work Stations, Servers, Laptops, Printers, VoIP Phones, Security Cameras, ...

• Any device that allows us to interface with the network.• End devices are referred to as hosts and are either the

source or destination of a message.

Chapter 2

End Devices• End Devices:

– A host can be aclient, a server orboth.

– The softwareinstalled on the device determines its role.

• Servers:– Software that enables them to provide information and

services (E-mail, Web Pages) to other hosts on the network.

• Client:– Software installed that enables them to request and

display the information obtained from the server.

Servers

Clients

Chapter 2

Intermediary Devices

• Routers, Switches, Hubs, Wireless Access Points, Security Devices.

• Any device that provides connectivity to other networks or links between network segments.

Chapter 2

Intermediary Devices• Manage data as it flows through the network.• Some use the destination host address and

network interconnection information to find the best path through the network.

RoutersRouters

Access PointsAccess Points

SwitchesSwitches

HubsHubs

FirewallsFirewalls

Chapter 2

Media•The medium provides the channel over which the

messages travel from source to destination.Metallic wires within cablesGlass or plastic

fibers

Wireless Transmission

Chapter 2


ProtocolsProtocols

Chapter 2

Rules That Govern Communications• Protocols:

– Are the rules that govern communications.

The format or structure of the message.The format or structure of the message.

How and when error and system messages are How and when error and system messages are passed between devices.passed between devices.

The setup and termination of data transfer sessions.The setup and termination of data transfer sessions.

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

Chapter 2

Protocol Suites• Protocol Suite:

– A group of inter-related protocols that are necessary to perform a communication function.

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

– 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

Chapter 2

2 .Protocol, service and other fancy definitions• Peer entities

– two (or more) instances of the same layer• Protocol and a PDU:

– the rules of the operation followed by peer entities– the data exchanged is called PDU (Protocol Data Unit)there is one protocol (or more) at every layer

Examples of protocols are: TCP; UDP;IP; Ethernet• Connection

– a protocol is connection oriented if the peer entities must be synchronized before exchanging useful data (connection set up); otherwise it is connectionless.The telephone system is connection oriented: before A can send some information to B, A has to call B (or vice versa) and say “hello”. The postal (mail) system is connectionless. If A wants to send some information to B, A can write a letter and mail it, even if B is not ready to read it.

2020

Chapter 2

Interaction of Protocols

• operation rules between peer entities are calledoperation rules between peer entities are called protocol protocol

• Layering of protocol entitiesLayering of protocol entities is reflected by the term of is reflected by the term of a a protocol stackprotocol stack. .

Chapter 2

Technology Independent Protocols

• Protocols are not dependent upon any specific technology.– They describe what must be done to communicate but not

how it is to be carried out.

Chapter 2


Using Layered ModelsUsing Layered Models

Chapter 2

Layered Models

•Divide and conquer – make things manageable.

Chapter 2

Protocol and Reference Models• Protocol Model:

– The TCP/IP model is a protocolmodel because it describes thefunctions that occur at eachlayer of protocols only within theTCP/IP suite.

Chapter 2

Protocol and Reference Models• Reference Model:

– Provides a common referencefor maintaining consistency withinall types of network protocols andservices.

– Not intended to be animplementation specification.

– Primary purpose is to aid inclearer understanding of thefunctions and process involved.

Chapter 2

TCP/IP Model• Open Standard

• No onecompanycontrols it.

• Governed byIETF WorkingGroups

• Standards proposedusing Request for Comments (RFCs).

Chapter 2

Request For Comments RFC

Chapter 2

The Communication Process

Segment and Segment and EncapsulateEncapsulate

Generate on Generate on to the mediato the media

Create DataCreate Data

Transport through the segmentTransport through the segment

Pass data to Pass data to applicationapplication

Receive from Receive from the mediathe media

Decapsulate and Decapsulate and ReassembleReassemble

Chapter 2

Protocol Data Units and Encapsulation

HeaderHeader

HeaderHeader DataData

HeaderHeader TrailerTrailer

Email MessageEmail Message

DataData DataData DataData

DataData

DataData

00101001110110010100000111110101000101010010100111011001010000011111010100010101

Segmentation and EncapsulationSegmentation and Encapsulation

Chapter 2


HeaderHeader

HeaderHeader



DataData DataData DataData

DataData

DataData

DataData

Decapsulation and ReassemblyDecapsulation and Reassembly

DataData

00101001110110010100000111110101000101010010100111011001010000011111010100010101

Chapter 2


HeaderHeader

HeaderHeader



DataData

DataData

DataData

Protocol Data UnitsProtocol Data Units

DataData

SegmentSegment

PacketPacket

FrameFrame

Chapter 2


Chapter 2


The OSI ModelThe OSI Model

Chapter 2

OSI Model

• The International Organization for Standardization (ISO) released the Open Systems Interconnection (OSI) reference model in 1984.

• www.iso.org for more information

Chapter 2

OSI Model• Breaks network communication into

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

understand.– Prevents changes in one layer from

affecting other layers.• Standardizes network components

to allow multiple vendor developmentand support.

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

• It is a descriptive scheme.

Chapter 2

OSI Model – Example - FYI•Descriptive Scheme: Can be used to describe the

functionality and interaction of different protocol suites.

TCP/IPTCP/IP

PhysicalPhysical

Data LinkData Link

NetworkNetwork

TransportTransport

SessionSession

PresentationPresentation

ApplicationApplication

LAN / Wan Physical Media

ARP / RARPLLC

IPICMP RIP

IGMP

TCP UDP

NETBIOS DNS

FTP, Telnet, SMTP, POP3, IMAP4, HTTP, X-Windows

SNMP, TFTP, BOOTP, DHCP

Chapter 2

OSI Model

LayersLayers CISCOCISCO MICROSOFTMICROSOFT

7 Application AllAll AwayAway

6 Presentation PeoplePeople PizzaPizza

5 Session SeemSeem SausageSausage

4 Transport ToTo ThrowThrow

3 Network NeedNeed NotNot

2 Data Link DataData DoDo

1 Physical ProcessingProcessing PleasePlease

Usually Usually referenced by referenced by layer numberlayer number

These two layers These two layers are not commonly are not commonly referred to in most referred to in most

instances.instances.

Chapter 2

OSI Model

LayersLayers CISCOCISCO MICROSOFTMICROSOFT

7 Application AllAll AwayAway

6 Presentation PeoplePeople PizzaPizza

5 Session SeemSeem SausageSausage

4 Transport ToTo ThrowThrow

3 Network NeedNeed NotNot

2 Data Link DataData DoDo

1 Physical ProcessingProcessing PleasePlease

Primary concern: Primary concern: CommunicationsCommunications

between between applicationsapplications

Primary concern: Primary concern: Moving raw data Moving raw data cross the networkcross the network

Chapter 2


Network AddressingNetwork Addressing

Chapter 2

OSI Model

OSI Model LayerOSI Model Layer AddressingAddressing

ApplicationApplicationEncoded Application Data

(Usually referred to as the Upper Layers)PresentationPresentation

SessionSession

TransportTransport Source and Destination: Process Address

NetworkNetwork Source and Destination: Logical Network Address

Data LinkData Link Source and Destination: Device Physical Address

PhysicalPhysical Timing and Synchronization Bits

Chapter 2

Getting Data to the End Device

HeaderHeader

HeaderHeader

HeaderHeader Trailer


DataData

DataData

DataData

Encoded DataEncoded Data

ProcessProcess

LogicalLogical

PhysicalPhysical

Encapsulation Process Encapsulation Process and Addressingand Addressing

1.

2.

3.

4.

5.

6.

7.

Addressing always includes both the Addressing always includes both the Source and Destination AddressesSource and Destination Addresses..

Chapter 2


• Delivery on a single local network.• Hop by hop address• Unique on the network and represents

the device.• Codes placed on the NIC by the

manufacturer.• Referred to as the physical address

or the MAC address.

1.

2.

3.

4.

5.

6.

7.

Layer 2 AddressingLayer 2 Addressing

HeaderHeader TrailerDataData Source and Source and Destination Destination

Physical or MAC Physical or MAC AddressAddress

Chapter 2


Destination Destination MAC MAC

AddressAddress

SourceSourceMACMAC

AddressAddressDataData

Layer 2 HeaderLayer 2 Header

Chapter 2

Getting Data Through The Network

• Move data from one local network to another local network.

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

• Used by routers to determine the best path to the destination host.

HeaderHeader DataData

Source and Source and Destination Destination

Logical Network Logical Network AddressAddress

(IP)(IP)

1.

2.

3.

4.

5.

6.

7.


Chapter 2

Getting Data Through the Network


AddressAddress

SourceSourceMACMAC

AddressAddress

DestinationDestinationLogicalLogical

AddressAddress

SourceSourceLogicalLogical

AddressAddressDataData



Chapter 2

Getting Data to the Right Application

•Identifies the specific process or service running on the destination host that will act

on the data.•Differentiate Multiple, simultaneous

applications.

1.

2.

3.

4.

5.

6.

7.


HeaderHeader DataData ProcessProcess

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

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

Chapter 2

Getting Data to the Right Application


AddressAddress

SourceSourceMACMAC

AddressAddress


AddressAddress


AddressAddress

DestinationDestinationProcessProcessAddressAddress

SourceSourceProcessProcessAddressAddress

DataData




Chapter 2

Putting It All Together


AddressAddress

SourceSourceMACMAC

AddressAddress


AddressAddress


AddressAddress

DestinationDestinationProcessProcessAddressAddress

SourceSourceProcessProcessAddressAddress

DataData

LogicalLogicalMACMACPortPort

MACMAC

Chapter 2

Comparing the OSI and TCP/IP Models

OSI Model OSI Model Layer FunctionLayer Function Protocol Protocol Data UnitData Unit DeviceDevice TCP/IP TCP/IP

ModelModel

77 Application User Functionality

Character Application66 Presentation Character Representation

55 Session Manage Data Exchange

44 Transport Services to segment, transfer and reassemble the data Segment Transport

33 Network Network addressing and best path determination Packet Router Internet

22 Data Link Methods for reliable frame exchange over a common media Frame Switch

Network Access

11 Physical Describe physical characteristics to transmit bits over a common media Bit Hub

Chapter 2

Brain a little fuzzy?

• You need to learn tocrawl before you can walkand walk before you can run.

• We are starting with thetheory and concepts andwill move on to the actualdesign and implementationof networks.

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