Communicating over
the Network
Network 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
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
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:
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.
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)
Media
End devices: PCs, printers, PDAs, mobile phones
Intermediary devices: router, switch, hub, firewall
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
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.
Each host on a network is identified by an address.
People access the network through an end device.
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
Intermediary Devices and
Their Roles
Provide connectivity to the network.
Connect individual network.
Connect segments (links) within the same network.
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 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
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
Copper
Fiber-optic
Wireless
Example
Twisted-pair
cable
Glass or plastic
fibers
Connect local
user through air
Encoding
Electrical pulses
Light pulses
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 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 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
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).
Internetworks
An internetwork is a global mesh of interconnected
networks for communication.
Example: The Internet.
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
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
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
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.
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.
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.
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
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
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.
Protocols in the TCP/IP model are cooperatively
developed by researchers and members of the
industry.
A protocol model is a model that closely matches the
structure of a particular protocol suite.
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.
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
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
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.
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