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8/2/2019 4.Network Protocols and Architectures
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Data Communications andComputer Networks
Chapter 4
Network Protocols and
Architecture
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Outline:
Protocol CharacteristicsOSI reference model
TCP/IP reference model
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Communicating the Message
In theory, a single communication, such as a musicvideo or an e-mail message, could be sent across anetwork from a source to a destination as onemassive continuous stream of bits.
Problem??
Solution - Data is sent across a network in smallchunks called segmentsSegmentation helps
Interleaving/multiplexing messages (many conversation on onenetwork)
increase the reliability of network communications - If aparticular path becomes congested with data traffic or fails,individual pieces of the message can still be directed to the
destination using alternate pathways. 4
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Components of the Network
Network componentshardware: Devices and media such as laptop,
a PC, a switch, or the cabling used to connectthe devices
software: run on the networked devices todeliver Services and do some processes
Services include many of the common networkapplications
Processes provide the functionality that directs andmoves the messages through the network.
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Cont..
End Devices and their Role in the NetworkEnd devices (host networking context) form
interface with human network &communications network
Role of end devices:
client
server
both client and serversoftware installed on the host determines
which role it plays on the network.6
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Cont..
Servers are hosts that have software installed thatenables them to provide information and services
Clients are hosts that have software installed thatenables them to request and display the information
obtained from the server. Role of an intermediary device
provides connectivity and ensures data flows across network
Network Access Devices (Hubs, switches, and wireless accesspoints)
Internetworking Devices (routers)
Communication Servers and Modems
Security Devices (firewalls)
The management of data as it flows through the
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Cont..
Processes running on the intermediary network devicesperform these 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 alink failure
Classify and direct messages according to QoS priorities
Permit or deny the flow of data, based on securitysettings
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Function of Protocol in Network
Communication
The importance of protocols and how they are used tofacilitate communication over data networks
All communication, whether face-to-face or over anetwork, is governed by predetermined rules called
protocols.A group of inter-related protocols that are necessary to
perform a communication function is called a protocolsuite.
The protocols are viewed as a layered hierarchy, witheach higher level services depending on the functionalitydefined by the protocols shown in the lower levels.
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Standards and Protocols
A standard is - a process or protocol that hasbeen endorsed by the networking industry andratified by a standards organization - such asthe Institute of Electrical and Electronics
Engineers (IEEE) or the Internet EngineeringTask Force (IETF).
The use of standards in developing and
implementing protocols ensures that productsfrom different manufacturers can work togetherfor efficient communications.
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Why Standards?
Communication requires a common language Standards specify how things are done to the
smallest detail
Standardized things are easier to develop inthe future
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Protocols
One form of network standardsA protocol
Is a language spoken between computers toexchange information
Is a formal description of message formats and therules that two computers must follow in order toexchange those messages.
Example: The HTTP protocol defines the formatfor communication between web browsers andweb servers
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Network models
Specify how networks are implemented One famous model is the Open Systems
Interconnection (OSI) reference model
Another famous model is TCP/IP model
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Benefits of using a layered
model
Benefits include assists in protocol design
fosters competition
changes in one layer do not affect other layers provides a common language
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OSI model
Used to specify a networking framework forimplementing protocols
Facilitates communication betweenheterogeneous systems
Implemented by almost most network systems
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Explaining the OSI layer
Breaks network communication to small partsto make it manageable and easier to understand
Consists of seven well defined layers
Prevents changes in one layer from affectingothers
Proprietary - one or a small group ofcompanies controls all usage of the technology
OSI is proprietary, developed by InternationalOrganization for Standardization (ISO)
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Physical
Concerned with transmission of data across media wires
connectors
voltages data rates
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Data link
Concerned with physical addressing
network topology
error notification flow control
reliable transfer of data across media
Divided into two sub layers: Logical Link Control(LLC) and Media Access Control (MAC)
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Network
Concerned with network addressing
best path determination
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Transport
Concerned with transportation with hosts
data transport reliability
establish, maintain, terminate virtual circuits Fault detection, flow control, recovery
information
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Session
Concerned with establishing, managing and terminating
sessions
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Presentation
Concerned with format of data
data structures
data transfer syntax
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Application
Concerned with providing network service toapplications like
File transfer Terminal emulation
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Encapsulation
Data Packets or packets are information sentover a network.
Encapsulation wraps data with the necessaryprotocol information before network transit.
As the data packet moves down through thelayers of the OSI model, it receives headers,trailers, and other information.
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Encapsulation process
As data travels through the layers, the followingprocedures are carried out
Build the data
Package the data for end-to-end transport Add the network IP address to the header
Add the data link layer header and trailer
Convert to bits for transmission
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Build the data
As a user sends an e-mail message, itsalphanumeric characters are converted to datathat can travel across the internetwork
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P k th d t f d t
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Package the data for end-to-
end transport
The data is packaged for internetworktransport.
By using segments, the transport functionensures that the message hosts at both ends ofthe e-mail system can reliably communicate.
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Add th t k IP dd t
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Add the network IP address to
the header
The data is put into a packet or datagram thatcontains a packet header with source anddestination logical addresses
Addresses help network devices send thepackets across the network along a chosen path
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Convert to bits for transmission
The frame must be converted into a pattern of1s and 0s (bits) for transmission on themedium.
A clocking function enables the devices todistinguish these bits as they travel across themedium.
The medium on the physical internetwork can
vary along the path used. Example: The e-mail message can originate on
a LAN, cross a campus backbone, and go out aWAN link until it reaches its destination on
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TCP/IP model
Developed by the U.S. Department of Defense Developed as an open standard anyone can
use it for free
Has four layers
Network access layer
Internet layer
Transport layer
Application layer
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Network access layer
Concerned with Logical addressing Transmission of data across media
wires
connectors voltages
data rates
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Internet layer
Concerned with network addressing
best path determination
Transport layer
Concerned with
-Reliability-Flow control
-Error correction
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Application layer
Concerned with Representation
Encoding
Dialogue control
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OSI and TCP/IP - similarities
Both have layers Both assume packets are switched (called
packet switched), i.e. that packets could takedifferent paths to reach to the same destination.Circuit switched is a case in which all packetstake the same path
Both should be known by network
professionals
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OSI and TCP/IP - differences
TCP/IP combines session, presentation andapplication layers into a single layer
TCP/IP combines physical and data link layerinto a single layer
TCP/IP is the standard in which the internethas grown
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Categorizing protocols
Application protocols work in Application layer
Presentation layer
Session layerTransport protocols work in
Transport layer
Network protocols work in Network layer
Data link layer
Physical layer45
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Application layer protocols
Hypertext Transfer Protocol (HTTP) Used for exchanging files (text, graphic
images, sound, video, and other multimediafiles) on the World Wide Web.
File Transfer Protocol (FTP)
Used for transferring files from one computerto another
Simple Mail Transfer (SMTP)
Used for transferring e-mail across theInternet.
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Application layer protocols
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Application layer protocols
(contd.)
Network File System (NFS) Used to transfer files from one computer to
another
Simple Network Management Protocol(SNMP)
Used to manage a network
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Transport layer protocols
Transmission Control Protocol (TCP) Enables two hosts to establish a connection
and exchange streams of data. It guaranteesdelivery of data and also guarantees that
individual units of data (called packets) will bedelivered in the same order in which they weresent
Net Bios Extended User Interface (NetBEUI) A communication protocol designed by IBM
and often used by Microsoft
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Network protocols
Internet Protocol (IP) Specifies the format of packets and the
addressing scheme. Most networks combine IPwith a Transport Control Protocol (TCP), which
establishes a virtual connection between adestination and a source. IP by itself issomething like the postal system. It allows you
to address a package and drop it in the system,but theres no direct link between you and therecipient
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Network protocols (contd.)
Ethernet The most common local area network (LAN)
protocol
X.25
Common wide area network (WAN) protocol
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