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Chapter Contents
Protocol architecture & operation
TCP/IP
OSI
Standards
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How to Communicate ?
Dr Wong
Interested in XY
Speaks only Chinese
Dr Raymond Expert in XY
Speaks only French
Ms Leong
Chinese-English
translator
Mr Henry
French-English
translator
Chinese
document
Exchanging
documents
in English
French
document
Discussing XY
research in China
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Why Need Protocol Architecture?
• File transfer
• Source must activate communication path or inform network of the identity of
the desired destination
• Source must ascertain that the destination is prepared to receive data
• File transfer application on source must ascertain that the destination’s filemanagement program is prepared to accept and store file
• May need file format translation if file format used on source & destination are
incompatible
• Instead of implementing in single module, the task is broken into
subtasks
• Each subtask is implemented separately
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Protocol Architecture
• Modules arranged in vertical stack
• Each layer performs a subset of the
functions required to communicate with
another system
• Relies on the next lower layer to perform
more primitive functions & to conceal the
details of those functions
• Provides services to the next higher layer
• Changes in one layer should not requirechanges in other layers
Subtask A
Subtask B
Subtask C
Layer 3
Layer 2
Layer 1
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Protocol
• Data communication usually occurs between entities in different
system
• Entities : anything capable of sending or receiving information
• Different entities can’t simply send data to each other & expect to be understood
• For communication to occur, the entities must agree on a protocol
• Protocol : set of rules or conventions that allow peer layers to
communicate
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Key Elements of a Protocol
• 3 elements of a protocol are :
• Syntax
• Refers to structure/format of the data
•Semantics
• Refers to the meaning of each section of bits
• Includes control information for coordination & error handling
• Timing
• Refers to when data should be sent & how fast they can be
sent
• Includes sequencing and speed matching
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Protocol Architecture
• The same set of layered functions must exist in two systems if those systems
want to communicate
• Communication is achieved by having the peer layers in the two systems
communicate
• The peer layers communicate by means of formatted blocks of data that obey aset of rules conventions known as a protocol
Subtask A
Subtask B
Subtask C Layer 3
Layer 2
Layer 1
Subtask A
Subtask B
Subtask C
Communications
network
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Standardized Protocol Architectures
• Required for devices to communicate
• Vendors have more marketable products
• Customers can insist on standards based equipment
• Two standards:
• TCP/IP protocol architecture
• OSI model
• Also:
• Internetwork Packet eXchange/Sequenced Packet eXchange
(IPX/SPX),• NetBIOS Enhanced User Interface (NetBEUI)
• AppleTalk
• IBM Systems Network Architecture (SNA)
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TCP/IP Model
• Transmission Control Protocol / Internet Protocol
• Result of protocol research & development conducted on the
experimental packet-switched network, ARPANET, funded by
Defence Advanced Research Projects Agency (DARPA)• Generally referred as the TCP/IP protocol suite
• Consists of a large collection of protocols that have been issued
as Internet standards by the Internet Architecture Board (IAB)
• Most widely used interoperable network protocol architecture
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TCP/IP Model
Physical
Network access
Internet
Layer 1
Transport
Application
Layer 2
Layer 3
Layer 4
Layer 5
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TCP/IP Layers
Physical
Network access
Internet
Transport
Application
Physical layer
Covers the physical interface between a data
transmission device (e.g. workstation, computer) &
transmission medium or network
Concerns with specifying the characteristics of the
transmission medium, nature of the signals, data
rate etc
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TCP/IP Layers
Physical
Network access
Internet
Transport
Application
Network Access layer
Concerns with the exchange of data between end
system (server, workstation, etc) and the network
to which it is attached
Concerns with access to and routing data across a
network for two end systems attached to the same
network
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TCP/IP Layers
Physical
Network access
Internet
Transport
Application
Internet layer
Implements procedures needed to allow data to
travel across multiple interconnected networks
Internet Protocol (IP) is used to provide routing
function across multiple networks
Implemented in end systems and routers
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TCP/IP Layers
Physical
Network access
Internet
Transport
Application
Transport layer
Concerns about the reliability requirement of
exchanged data
E.g. Data arrive at destination application, in thesame order in which they were sent
Transmission Control Protocol (TCP) is the most
commonly used protocol to provide reliability
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TCP/IP Layers
Physical
Network access
Internet
Transport
Application
Application layer
Responsible for providing services to the user
Contains the logic needed to support various user
applications
Example of applications :
Simple Mail Transfer Protocol (SMTP)
File Transfer Protocol (FTP)
TELNET
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TCP/IP Layers and Protocol Examples
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Provides ccess to the
TCP/IP environment for
users and also provides
distributed information
services.
Application
Transfer of data between
end points. May provide
error control, flow control,
congestion control, reliable
delivery.
Transport
Shield higher layers from
details of physical network
configuration. Provides
routing. May provide QoS,
congestion control.
Internet
Logical interface to actual
network hardware. May be
stream or packet oriented.
May provide reliable
delivery.
Network Access
Transmission of bit stream;
specifies medium, signal
encoding technique, data
rate, bandwidth, and
physical connector.
Physical
Twisted pair, optical fiber, satellite,
terrestrial microwave
Ethernet, WiFi, ATM, frame relay
IPv4, IPv6
TCP, UDP
SMTP, FTP, SSH, HTTP
ARP
ICMP,
OSPF,
RSVP
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Operations of TCP/IP
• For successful communication, two levels of addressing are
needed
• Each host on a subnetwork must have a unique global
internet address IP address• Each process with a host must have an address that is
unique within the host to allow TCP to deliver data to proper
process ports
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Operations of TCP/IP
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Router J
TCP
IP
Physical Physical
IP
NAP 1 NAP 2
Physical Physical
Network Access
Protocol #1
Host A
App XApp Y
TCP
IP
Network Access
Protocol #2
Host B
App YApp X
Network 1 Network 2
Global internet
address
1 2 2 4 63
Subnetwork attachment
point address
Logical connection
(e.g., virtual circuit)
Logical connection
(TCP connection)
Port
A process associated with
port 3 at host A wishes to
send a message to another
process, associated with port
2 at host B
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Operations of TCP/IP
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Router J
TCP
IP
Physical Physical
IP
NAP 1 NAP 2
Physical Physical
Network Access
Protocol #1
Host A
App XApp Y
TCP
IP
Network Access
Protocol #2
Host B
App YApp X
Network 1 Network 2
Global internet
address
1 2 2 4 63
Subnetwork attachment
point address
Logical connection
(e.g., virtual circuit)
Logical connection
(TCP connection)
Port
The process at A hands the
message down to transport
layer with instructions to
send it to port 2 host B
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Operations of TCP/IP
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Router J
TCP
IP
Physical Physical
IP
NAP 1 NAP 2
Physical Physical
Network Access
Protocol #1
Host A
App XApp Y
TCP
IP
Network Access
Protocol #2
Host B
App YApp X
Network 1 Network 2
Global internet
address
1 2 2 4 63
Subnetwork attachment
point address
Logical connection
(e.g., virtual circuit)
Logical connection
(TCP connection)
Port
TCP in transport layer
hands the message down
to Internet layer with
instructions to send it to
host B
IP in Internet layer need not be
told the identity of the
destination port, it only needs
to know that the data are
intended for host B
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Operations of TCP/IP
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Router J
TCP
IP
Physical Physical
IP
NAP 1 NAP 2
Physical Physical
Network Access
Protocol #1
Host A
App XApp Y
TCP
IP
Network Access
Protocol #2
Host B
App YApp X
Network 1 Network 2
Global internet
address
1 2 2 4 63
Subnetwork attachment
point address
Logical connection
(e.g., virtual circuit)
Logical connection
(TCP connection)
Port
IP hands the message
down to network
access layer with
instructions to send it
to router J
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Operations of TCP/IP
To control this operation, control information as
well as user data must be transmitted
The sending process generates a block of data &
passes this to transport layer
TCP may break this block into smaller pieces to
make it more manageable
To each of these pieces, TCP appends control
information known as TCP header, forming a TCP
segment
The control information is to be used by the peer
TCP protocol entity at host B
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TCP
IP
Physical
Network Access
Protocol #1
Host A
App XApp Y
1 2 3
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Operations of TCP/IP
Items in the TCP header include the following :
Destination port
Sequence number
Checksum
Next TCP hands each segment to Internet layer with
instructions to transmit it to host B
Application byte stream
TCP segmentCPheader
User data
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TCP
IP
Physical
Network Access
Protocol #1
Host A
App XApp Y
1 2 3
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Operations of TCP/IP
IP appends a header of control information to each
segment to form IP datagram
IP header contains the destination host address (inthis example is host B)
Each IP datagram is presented to the network access
layer for transmission across the first subnetwork in its
journey to the destination
Application byte stream
TCP segment
IP
header
IP datagram
TCP
header
User data
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TCP
IP
Physical
Network Access
Protocol #1
Host A
App XApp Y
1 2 3
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Operations of TCP/IP
NA layer appends its own header, creating a packet or frame The packet is transmitted across the subnetwork 1 to router J
Items that may be contained in network access header :
Destination subnetwork address
Facilities requests, e.g. priority
Application byte stream
TCP segment
IP
header
IP datagram
Network
header
Network-level packet
TCP
header
User data
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TCP
IP
Physical
Network Access
Protocol #1
Host A
App XApp Y
1 2 3
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Router J
TCP
IP
Physical Physical
IP
NAP 1 NAP 2
Physical Physical
Network Access
Protocol #1
Host A
App XApp Y
TCP
IP
Network Access
Protocol #2
Host B
App YApp X
Network 1 Network 2
Global internet
address
1 2 2 4 63
Subnetwork attachment
point address
Logical connection
(e.g., virtual circuit)
Logical connection
(TCP connection)
Port
Operations of TCP/IP
At router J, the packet
header is stripped off and
the IP header is examined
Base on destination
address info in the IP
header, the IP module inthe router directs the
datagram out across
subnetwork to host B
To do this, the datagram is
again encapsulated with a
network access header
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Router J
TCP
IP
Physical Physical
IP
NAP 1 NAP 2
Physical Physical
Network Access
Protocol #1
Host A
App XApp Y
TCP
IP
Network Access
Protocol #2
Host B
App YApp X
Network 1 Network 2
Global internet
address
1 2 2 4 63
Subnetwork attachment
point address
Logical connection
(e.g., virtual circuit)
Logical connection
(TCP connection)
Port
Operations of TCP/IP
When the data are
received at B, the
reverse process occurs
At each layer, the
corresponding header is
removed, and the remainder is
passed on to the next higher
layer until the original userdata are delivered to the
destination process
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OSI Reference Model
• Open System Interconnection OSI) reference model
• Designed by International Organization for Standardization
(ISO)
• A seven-layer model
• Never seriously implemented as a protocol stack
• A theoretical model designed to show how a protocol stack
should be implemented
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OSI Reference Model
Physical
Data Link
Network
Layer 1
Transport
Session
Presentation
Application
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
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OSI vs TCP/IP
Physical
Data Link
Network
Transport
Session
Presentation
Application
Physical
Transport
Application
Internet
Network access
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OSI Reference Model
Physical
Data Link
Network
Transport
Session
Presentation
Application
Application layer Provides access to the OSI
environment for users and also
provides distributed information
services
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OSI Reference Model
Physical
Data Link
Network
Transport
Session
Presentation
Application
Presentation layer Provides independence to the
application processes from
difference in data representation
(syntax)
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OSI Reference Model
Physical
Data Link
Network
Transport
Session
Presentation
Application
Transport layer Provides reliable, transparent
transfer of data between end
points; provides end-to-end error
recovery and flow control
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OSI Reference Model
Physical
Data Link
Network
Transport
Session
Presentation
Application
Network layer
Provides upper layers with
independence from the data
transmission and switching
technologies used to connect
systems; responsible for
establishing, maintaining and
terminating connection
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OSI Reference Model
Physical
Data Link
Network
Transport
Session
Presentation
Application
Physical layer
Concerned with transmission of
unstructured bit stream over
physical medium; deals with the
mechanical, electrical, functional
& procedural characteristics to
access the physical medium
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OSI Environment
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OSI Environment
• Each system contains the 7 layers
• Communications is between applications in the two computers, labeled
application X and application Y
• If application X wishes to send a message to application Y , it invokes the
application layer (layer 7)
• Layer 7 establishes a peer relationship with layer 7 of the target
computer using layer 7 protocol (application protocol)
• This protocol requires services from layer 6, so the two layer 6 entities
use a protocol of their own, and so on down to the physical layer, whichactually transmits bits over a transmission medium.
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OSI Environment
• No direct communication between peer layers except at the
physical layer
• Use of protocol data unit (PDU) within OSI architecture
•
PDU – combination of data from the next higher layer and control information
• When X has a message to send to Y, it transfers those data to
application layer (layer 7)
• A header is appended to the data that contains requiredinformation for the peer layer application protocol –
Encapsulation
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OSI Environment
• The original data plus header are now passed as a unit to presentation
layer (layer 6)
• The layer treats the whole unit as data and appends its own header
(second encapsulation)
• This process continues down through data link layer (layer 2) which
generally adds both a header & trailer
• This layer 2 unit, called a frame, is then passed onto the transmission
medium by the physical layer
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OSI Environment
• When the frame is received by the target system, the reverse process
occurs
• As the data ascend,
• each layer strips off the outermost header
• acts on the protocol information contained therein
• and passes the remainder up to the next layer
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Standards
• Required to allow for interoperability between equipment
• Provide guidelines to manufacturers, vendors, government agencies &
other service providers to ensure interconnectivity in international
communications
• Advantages
• Ensures a large market for equipment and software
• Allows products from different vendors to communicate
• Disadvantages
• Freeze technology
• May be multiple standards for the same thing
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Standards Organizations
• International Organization for Standardization (ISO)
• Multinational body
• Membership drawn mainly from standards creation committees of various governments
throughout the world
• Active in developing cooperation in the realms of scientific, technological and economic
activity
• International Telecommunication Union – Telecommunication
Standards Sector (ITU-T)
• Formerly Consultative Committee for International Telegraphy and Telephony (CCITT)
•UN agency
• Research & establishment of standards for telecommunications
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Standards Organizations
• Institute of Electrical & Electronics Engineers (IEEE)
• Largest professional engineering society in the world
• One of its goal : Oversees development & adoption of international standards for
computing & communications
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