Data and Computer Communications

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Data and Computer Communications
Chapter 2 Protocol Architecture, TCP/IP, and
Internet-Based Applications

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Protocol Architecture, TCP/IP, and Internet-Based
Applications

• To destroy communication completely, there must
  be no rules in common between transmitter and
  receiverneither of alphabet nor of syntax On
  Human Communication, Colin Cherry

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Need For Protocol Architecture

• data exchange can involve complex procedures,
  file transfer example
• better if task broken into subtasks
• implemented separately in layers in stack
• each layer provides functions needed to perform
  communications for layers above
• using functions provided by layers below
• peer layers communicate with a protocol

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Functions of Protocol Architecture

• breaks logic into subtask modules which are
  implemented separately
• modules are arranged in a vertical stack
• each layer in the stack performs a subset of
  functions
• relies on next lower layer for primitive
  functions
• changes in one layer should not require changes
  in other layers

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Key Elements of a Protocol
A protocol is a set of rules or conventions that
allow peer layers to communicate.

• syntax - data format
• semantics - control info error handling
• timing - speed matching sequencing

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A Simple Protocol
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Simplified Network Architecture
,Communications can be said to involve three
agents
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Communication Layers

• communication tasks are organized into three
  relatively independent layers
• Network access layer
• concerned with the exchange of data
• Transport layer
• provides reliable data transfer
• Application layer
• Contains logic to support applications

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Network Access Layer

• exchange of data between an end system and
  attached network
• concerned with issues like
• destination address provision
• invoking specific services like priority
• access to routing data across a network link
  between two attached systems
• allows layers above to ignore link specifics

The sending computer must provide the network
with the address of the destination computer
different standards have been developed for
circuit switching, packet switching (e.g., frame
relay), LANs (e.g., Ethernet), and others
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Application Layer
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Protocol Architecture and Networks
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Protocols in a Simplified Architecture
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Addressing and addressing Requirements
every entity in the overall system must have a
unique address.

• two levels of addressing required
• each host on a subnet needs a unique global
  network address
• its IP address
• each application on a (multi-tasking) host needs
  a unique address within the host
• known as a port or SAP(service acces point)

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Protocol Data Unit (PDU)

• the combination of data and control information
  is a protocol data unit (PDU)
• typically control information is contained in a
  PDU header
• control information is used by the peer transport
  protocol at computer B
• headers may include
• source port, destination port, sequence number,
  and error-detection code

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Network Access Protocol

• after receiving segment from transport layer, the
  network access protocol must request transmission
  over the network
• the network access protocol creates a network
  access PDU (packet) with control information
• header includes
• source computer address
• destination computer address
• facilities requests

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TCP/IP Protocol Architecture

• developed by US Defense Advanced Research Project
  Agency (DARPA)
• for ARPANET packet switched network
• used by the global Internet
• protocol suite comprises a large collection of
  standardized protocols

Built on the biases of the OSI
Open System Interconnection Reference Model
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TCP/IP Layers

• no official model but a working one
• Application layer
• Host-to-host, or transport layer
• Internet layer
• Network access layer
• Physical layer

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TCP/IP Layers and Example Protocols
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Physical Layer

• concerned with physical interface between
  computer and network
• concerned with issues like
• characteristics of transmission medium
• signal levels
• data rates
• other related matters

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Network Access Layer

• covers the exchange of data between an end system
  and the network that it is attached to
• concerned with issues like
• destination address provision
• invoking specific services like priority
• access to routing data across a network for two
  end systems attached to the same network

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Internet Layer (IP)

• This protocol is implemented not only in the end
  systems but also in routers
• Covers routing functions across multiple networks
• Used for systems attached to different networks
• routers connect two networks and (main function)
  relays data between them

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Host-to-Host (Transport) Layer
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Operation of TCP and IP
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TCP/IP Address Requirements

• Two levels of addressing are needed

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Operation of TCP/IP
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Transmission Control Protocol (TCP)

• usual transport layer is (TCP)
• provides a reliable connection(temporary logic)
  for transfer of data between applications
• a TCP segment is the basic protocol unit
• TCP tracks segments between entities for duration
  of each connection

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TCP Header
minimum of 20 octets or 160 bits.
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User Datagram Protocol(UDP)
In addition to TCP, (UDP) is one other
transport-level protocol that is in common use as
part of the TCP/IP protocol suite.

• an alternative to TCP
• no guaranteed delivery
• no preservation of sequence
• no protection against duplication
• minimum overhead
• used in some simple transaction-oriented
  applications
• adds port addressing to IP
• it is connectionless

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UDP Header
UDP is connectionless and has very little to do
Adds a port addressing capability to IP
Optional to verify that no error occurs in the
data
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IP and IP v6 History

• IP v4 header format was the keystone for decades
• In 1995 the Internet Engineering Task (develops
  standards and protocols) issued specs for the
  next generation IP (IP ng).
• IP ng became IPv6 in 1996.
• IPv6 provided a number of functional enhancement
  over existing IP

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IP v4 Header
a minimum of 20 octets or 160 bits.
used in the fragmentation and reassembly
process
includes 32-bit source and destination addresses
Differentiated service field
Explicit congestion field
used to detect errors in the header to avoid
misdelivery
indicates which higher-layer protocol is using IP
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IPv6

• Provides enhancements over existing IP
• Designed to accommodate higher speeds and the mix
  of graphic and video data
• Driving force was the need for more addresses due
  to growth of the Internet
• IPv6 includes 128-bit source and destination
  address fields

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IPv6 Header
The current IP uses a 32-bit address to specify a
source or destination(not sufficient anymore)
all installations using TCP/IP are expected to
migrate from the current IP to IPv6, but this
process will take many years
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TCP/IP Applications

• have a number of standard TCP/IP applications
  such as (common ones)
• Simple Mail Transfer Protocol (SMTP)
• File Transfer Protocol (FTP)
• Telnet (provides a remote logon capability)

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Some TCP/IP Protocols
Each layer in the TCP/IP protocol suite interacts
with its immediate adjacent layers
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The Open Systems Interconnection OSI

• Open Systems Interconnection
• developed by the International Organization for
  Standardization (ISO)
• has seven layers
• is a theoretical system delivered too late!
• TCP/IP is the de facto standard

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OSI Standardization

• framework for standardization was motivator
• lower layers are concerned with greater levels of
  details
• each layer provides services to the next higher
  layer
• three key elements

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OSI Layers
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OSI v TCP/IP
Please Do Not Thru Sausage Pizza Away
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Standardized Protocol Architectures
Lower layers are concerned with greater levels of
detail upper layers are independent of these
details. Each layer provides services to the next
higher layer and implements a protocol to the
peer layer in other systems.
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Layer Specific Standards and the nature of the
standardization required at each layer.
defines what services are provided, but not how
the services are to be provided.
indicates a transport entity that is a user of
the network service.
because two different open systems are involved
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Service Primitives and Parameters
services between adjacent layers in the OSI
architecture are expressed in terms of primitives
and parameters

• primitives to specify function performed
• parameters to pass data and control info

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Primitive Types
four types of primitives are used in standards to
define the interaction between adjacent layers in
the architecture (X.210)
REQUEST A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service
INDICATION A primitive issued by a service provider either to indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or notify the service user of a provider-initiated action
RESPONSE A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user
CONFIRM A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user
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Traditional vs Multimedia Applications

• traditionally Internet dominated by info
  retrieval applications
• typically using text and image transfer
• eg. email, file transfer, web
• see increasing growth in multimedia applications
• involving massive amounts of data
• such as streaming audio and video

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Elastic and Inelastic Traffic

• Traffic on a network or internet can be divided
  into two broad categories elastic and inelastic.
• elastic traffic
• can adjust to delay throughput changes over a
  wide range
• eg. traditional data style TCP/IP traffic.
• common Internet-based applications, such as file
  transfer, electronic mail, remote logon, network
  management, and Web access
• some applications more sensitive though

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Elastic and Inelastic Traffic

• inelastic traffic
• does not adapt to such changes
• eg. real-time voice video traffic
• The requirements for inelastic traffic may
  include the following
• minimum throughput.
• may be delay-sensitive
• may require a reasonable upper bound on delay
  variation, may vary in the amount of packet loss
• These requirements are difficult to meet in an
  environment with variable queuing delays and
  congestion losses.

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Multimedia Technologies
a list of technologies relevant to the support of
multimedia applications.
multimedia from the perspective of three
different dimensions type of media,
applications, and the technology required to
support the applications.
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Summary

• introduced need for protocol architecture
• TCP/IP protocol architecture
• OSI Model protocol architecture standardization
• traditional vs multimedia application needs