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Communicating over
the Network
Network FundamentalsNetwork Fundamentals
Chapter 2
Objectives
� Describe the structure of a network, including the devices and media that are necessary for successful communications.
� 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 recognized network models: The TCP/IP model and the OSI model.
� Describe the importance of addressing and naming schemes in network communications.
Outline
� The platform for communications� The elements of communication
� Communicating the messages
� Component of the network
� End devices and their role on the network
� Intermediary devices and their role on the network
� Network media
� LANs, WANs and internetworks� Local are networks
� Wide area networks
� The Internet: a network of networks
� Network representation
Outline
� Protocols
� Rules that govern communication
� Network protocols
� Protocol suite and industry standards
� Interaction of protocols
� Technology-independent protocols
� Using layered models
� The benefits of layered model
� Protocol and reference models
� TCP/IP model
Outline
� Communicating process
� Protocol data units and encapsulation
� Sending and receiving process
� OSI model
Comparing OSI model to the TCP/IP model� Comparing OSI model to the TCP/IP model
� Network addressing
� Addressing in the network
� Getting data to the end device
� Getting data through the internetwork
� Getting data to the right application
The Elements of Communication
� Three elements of communication:
� Message source / sender
� Destination / receiver
� A channel� A channel
Communicating the Messages
� Data is divided into smaller pieces during transmission.� The process of dividing data into smaller pieces is called
segmentation.
� Benefits of segmentation:� Benefits of segmentation:� Multiplexing
� Enable transmission medium to be shared.
� Reliability
� Different packets can use different paths. If path fails or congested, alternate paths can be used.
� If part of the message fails to make it to destination, only the missing parts need to be retransmitted.
Communicating the Messages
Communicating the Messages
Communicating the Messages
� Disadvantages of segmentation: added level of complexity.
� Must ensure each segment can:
� Get to the correct destination.Get to the correct destination.
� Be reassembled back into the content of the original
message.
� Example: similar like sending a 100-page letter one page at a time.
� Each letter needs separate envelop
� Need to label the envelopes with a sequence number
Communicating the Messages
Components of the Network
� Devices (hardware)
� End devices: PCs, printers, PDAs, mobile phones
� Intermediary devices: router, switch, hub, firewall
� MediaMedia
� Can be wired or wireless
� Service (software)
� Network applications
� Routing protocols
� Processes
� Algorithms
End Devices and Their Roles
End Devices and Their Roles
� End devices are also referred to as hosts.
� A host device is either the source or destination of a message.
� Examples:Computers (workstations, laptops, file servers, Web � Computers (workstations, laptops, file servers, Web servers)
� Network printers
� VoIP phones
� Cameras on a network
� Mobile handheld devices (PDAs, wireless barcode scanners)
End Devices and Their Roles
� End device forms an interface between human and communication network.
� People access the network through an end device.
� Each host on a network is identified by an address.Each host on a network is identified by an address.
� In the Internet, this address is called an IP address.
� A host can act as a client, server or both.
� Client: request and display information obtained from
server.
� Server: provide information and services.
� Role is determined based on software installed on the host.
Intermediary Devices and Their Roles
switch
or hub
switch
or hub
routers
or hub or hub
Intermediary Devices and Their Roles
� Provide connectivity to the network.
� Connect individual network.
� Connect segments (links) within the same network.
� Examples:� Examples:
� Network access devices: hubs, switches, wireless access
points.
� Interconnecting devices: routers.
� Communication servers and modems.
� Security devices: firewalls
Intermediary Devices and Their Roles
� Processes running on intermediary devices perform the following functions:
� Regenerate and retransmit data signals
� Maintain information about what pathways exist through
the network and internetworkthe network and internetwork
� Notify other devices of errors and communication failures
� Direct data along alternate pathways when there is a link
failure
� Classify and direct messages according to QoS priorities
� Permit or deny the flow of data, based on security settings
Network Media
� Network media provides the channel over which message travels from source to destination.
� There are three types of network media:� Metallic wires
� Fiber optics� Fiber optics
� Wireless
� Each media has different physical properties and uses different methods to encode message.� Encoding refers to the way data is converted to patterns of
electrical, light or electromagnetic energy and carried on the medium.
Network Media
Media Example Encoding
Copper Twisted-pair Electrical pulsesCopper Twisted-pair cable
Electrical pulses
Fiber-optic Glass or plastic fibers
Light pulses
Wireless Connect local user through air
Electromagnetic waves
Network Media
Network Media
� Criteria of choosing a network media:
� The distance the media can carry the signal
� The environment in which the media works
� The bandwidth� The bandwidth
� The cost of medium and installation
� The cost of connector and compatible equipment
LANs, WANs and Internetwork
� Networks come in many sizes and serve a wide variety of functions.
� Three basic differences:� The size of the area covered
� The number of users connected� The number of users connected
� The number and types of services available
� Based on these differences, networks can be divided into three types:� Local area network (LAN)
� Wide area network (WAN)
� Internetwork
Local Area Network (LAN)
� A network serving a home, building or campus.
� A more formal definition:
� An individual network that usually spans a single
geographical area, providing services and applications to
people within a common organizational structure such as a people within a common organizational structure such as a
single business, campus or region.
� LAN devices:
� Switches / hubs
� Routers
� Multilayer switches
Wide Area Network (WAN)
� LANs separated by geographic distance are connected by a network known as the wide area network (WAN).
� A WAN is owned by a telecommunication service provider (TSP).provider (TSP).
Internetworks
� An internetwork is a global mesh of interconnected networks for communication.
� Example: The Internet.
� The Internet is created by the interconnection of � The Internet is created by the interconnection of networks belonging to Internet Service Providers (ISPs).
� ISPs connect customers to the Internet.
� ISPs cooperate with other ISPs and TSPs to make sure their customers have access to all Internet networks.
Internetworks
Network Representations
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 an outlet on a networking device where the media is connected to a host or other networking device.
� Interface – Specialized ports on an internetworking device that connect to individual networks.
� Because routers are used to interconnect networks, the
ports on a router are referred to as network interfaces.
Network Representations
Protocols: Rules that Govern Communication
� Communication in networks is governed by
pre-defined rules called protocol.
� A protocol suite is a group of inter-related
protocols that are necessary to perform protocols that are necessary to perform
communication.
� Protocols are implemented in software or
hardware that is loaded on each host and
network device.
Protocols: Rules that Govern Communication
� Network protocol suites describe processes such as:
� The format or structure of the message.
� The process by which networking devices share
information about pathways to other networks.
How and when error or system messages are passed � How and when error or system messages are passed
between devices.
� The setting up and termination of data transfer sessions.
� A protocol can either be open standard or proprietary (vendor-specific).
Protocol Suite and Industry Standard
� Many of the protocols in a protocol suite are actually widely utilized protocols or industry standards.
� Networking protocols are standardized by organizations such as:
� Institute of Electrical and Electronics Engineers (IEEE)
� Internet Engineering Task Force (IETF)
� The use of standard protocols ensures that networking devices from different manufacturers can work together.
Interaction of Protocols
� A successful communication can only be achieved with the use of a number of protocols in a protocol suite.
� The different protocols work together to � The different protocols work together to ensure that the message are received and understood by both parties.� Different protocols take care of different
communication tasks.
� Example: Interaction between a Web server and Web browser.
Interaction of Protocols
Interaction of Protocols
� Application protocol – HTTP� Governs communication between a Web server
and Web client.
� Defines the content and format of the request and response messages between client and server.response messages between client and server.
� Implemented in the Web server and Web client application.
� Need to rely on other protocols for other communication tasks: transport data to the correct receiver, taking care of errors and losses, etc.
Interaction of Protocols
� Transport protocol – TCP
� Manages the individual conversation betweens servers and
clients (not just between Web servers and Web clients).
� Divide HTTP message (or any application message) into
smaller messages called segments.smaller messages called segments.
� Responsible for controlling the information exchanged
between the server and the client.
� Size of data in a segment
� Flow control – how much data can be sent and received
� Reliability – what to do when packet is lost / missing
Interaction of Protocols
� Internet protocol – IP� Responsible for making sure data can travel the
network to the correct receiver.
� Takes TCP segments and encapsulate them into a packet. a packet. � The packet header will contain information to carry the
packet to the receiver over the network.
� This information includes the source and destination addresses.
� The destination address will be used by the routers to find the best path to the receiver.
Interaction of Protocols
� Network access protocol (e.g. Ethernet)
� Controls physical transmission of data on the media.
� Takes packet from IP and format them to be transmitted
over the media.
Responsible for data transmission between two devices on � Responsible for data transmission between two devices on
the same network.
� Host to router
� Router to router
� Router to host
� Also responsible for converting the data (bits) into signals
used by the media.
Technology-independent Protocol
� Protocols are not dependent on any specific technology.
� Protocols specifies the tasks that need to be done to perform communication, not how the tasks are implemented.
� It is up to the programmer / device manufacturer to decide
on the best way to implement the protocol.
� As long as the same protocol is followed, network software / hardware developed by different parties should be able to work with each other.
Using Layered Model
� A layered model is used to visualize the interaction between various protocols.
� Benefits of using layered model:� Break network communication into smaller, more
manageable parts.
Provide a common language to describe networking � Provide a common language to describe networking functions and capabilities.
� Assist in protocol design because the functions of the protocol at a specific layer is clearly specified.
� Prevent changes in one layer from affecting the other layers.
� Allow products from different vendors that adhere to the specified protocol to work with each other.
TCP/IP Model
� The protocol model used in the Internet.� A protocol model is a model that closely matches the
structure of a particular protocol suite.
� Protocols in the TCP/IP model are cooperatively developed by researchers and members of the developed by researchers and members of the industry.� The documents describing the protocols are called RFCs
(Request for Comments).
� Protocols described in RFCs are open standards.
� RFC documents are publicly available.
� The RFC documents are maintained by IETF.
TCP/IP Model
Communication Process – On Sending Side
� Data originates from application layer of the source host.
� Segmentation and encapsulation is performed as it is passed down the protocol stack.
� Encapsulation: process of adding control information to the
data.
� At the network access layer, data is converted to signals to be transmitted by the transmission media.
� Data is transmitted through the internetwork, which consists of media and any intermediary device.
Communication Process – On Sending Side
Communication Process – On Receiving Side
� Data is received at the network access layer of the destination host.
� Decapsulation and reassembly is performed as it is passed up the protocol stack.as it is passed up the protocol stack.� Decapsulation: process of removing control
information of the data.
� Reassembly: process of combining the received data to produce the original data.
� Data is passed to the receiving application at the application layer of the destination host.
Communication Process – On Receiving Side
Protocol Data Units and Data Encapsulation
� As data is passed down the protocol stack, various control information is added.� This process is referred to as encapsulation.
� This happens at every layer of the protocol stack.
� The combination of data and control information is � The combination of data and control information is referred to as protocol data unit (PDU).
� At each layer, PDU received from upper layer is encapsulated with control information of that layer to form a new PDU.
� To distinguish between PDUs of different layers, they are given different names.
Protocol Data Units and Data Encapsulation
OSI Model
� OSI is a reference model.� A reference model
provides a common reference for maintaining reference for maintaining consistency within all types of network protocols and services.
� It divides network communication into smaller parts to make it easier to understand.
OSI Model
OSI Model vs. TCP/IP Model
Addressing in the Network
� To ensure successful data delivery, various types of addresses are used when sending data.
� Address to identify physical device / network interface
� Address to identify host
� Address to identify application
Getting Data to the End Device
� The host physical address is contained in Layer 2 PDU.
� Layer 2 is concerned with the delivery of messages on a single local network.
� 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.
Getting Data through the Internetwork
� Layer 3 protocols are primarily designed to move data from one LAN to another LAN through an internetwork.
� Intermediary network devices (routers) use Layer 3 address to locate hosts on different networks.
� Routers read the Layer 3 header of the packet and determine to which outgoing link the packet should be forwarded to.
� In the Internet, the Layer 3 address is called the IP address.
Getting Data through the Internetwork
Getting Data to the Right Application
� At the receiving end device, the data must be
sent to the correct network application.
� The end device may be running multiple network applications.applications.
� Information regarding the receiving
application is contained in Layer 4 PDU.
� In the Internet, the network applications are
identified using port numbers.
Getting Data to the Right Application