CISCO NETWORKING ACADEMY PROGRAM CNAP

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TCP/IP Application and Transport
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TCP/IP Application and Transport
Introduction to Transport Layer

• The TCP/IP transport layer does the work of
  transporting data between applications on source
  and destination devices.
• Ensure that segments delivered will be
  acknowledged to the sender
• Provide for retransmission of any segments that
  are acknowledged
• Put segments back into their correct sequence at
  the destination
• Provide congestion avoidance and control

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TCP/IP Transport Layer

• The primary functions that occur
• To transport and regulate the flow of information
  from source to destination, reliably and
  accurately.
• To provide end-to-end control, provided by
  sliding windows and
• To ensure a reliability in sequencing numbers and
  acknowledgments
• There are two protocols in TCP/IP
• transport layer
• User Datagram Protocol (UDP)
• Transmission Control Protocol (TCP)

Flow Control Analogy
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Flow Control

• To regulate the flow of information from source
  to destination, reliably and accurately, host
  tries to ensure that data is not lost
• The two hosts then establish a data-transfer rate
  that is agreeable to both
• End-to-end control, provided by sliding windows,
  and reliability in sequencing numbers and
  acknowledgments

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Session Establishment, Maintenance and Termination

• Multiple applications can share the same
  transport connection in the OSI reference model.
• Transport functionality is accomplished on a
  segment-by-segment basis
• Transport layer can multiplex upper-layer
  conversations based on a segment-by-segment
  basis.

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Session Establishment, Maintenance and Termination
Three-Way Handshake

• One function of the transport layer is to
  establish a connection-oriented session between
  similar devices at the application layer.
• The connection is established and the transfer of
  data begins after all synchronization has
  occurred.
• During transfer, the two machines continue to
  communicate with their protocol software to
  verify that data is received correctly.
• Congestion can occur during data transfer for two
  reasons.
• high-speed computer might be capable of
  generating traffic faster than a network can
  transfer it.
• many computers simultaneously need to send
  datagrams to a single destination

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Session Establishment, Maintenance and Termination

• When datagrams arrive too quickly for a host or
  gateway to process, the host or gateway
  eventually exhausts its memory and must discard
  additional datagrams that arrive (Congestion).
• the transport function can issue a not ready
  indicator to the sender. When the receiver can
  handle additional data, the receiver sends a
  ready transport indicator. When this indicator
  is received, the sender can resume the segment
  transmission

Flow Control
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Three-Way Handshake

• TCP is a connection-oriented protocol.
• TCP requires connection establishment before data
  transfer begins.
• For a connection to be established or
  initialized, the two hosts must synchronize their
  Initial Sequence Numbers (ISNs).
• Each side must also receive the INS from the
  other side and send a confirming ACK.

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Windowing and Acknowledgement
Low throughput

• Windowing is a flow control mechanism requiring
  that the source device receive an acknowledgment
  from the destination after transmitting a certain
  amount of data.

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Windowing and Acknowledgement

• The number of data packets the sender is allowed
  to have outstanding without having received an
  acknowledgment is known as the window size, or
  window.
• Windowing requires that the source device receive
  an acknowledgment from the destination after
  transmittinga certain amount of data.
• The receiving TCP process reports a window to
  the sending TCP.
• TCP window sizes are variable during the
  lifetime of a connection.
• Each acknowledgement contains a window
  advertisement that indicates the number of bytes
  the receiver can accept.

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Windowing and Acknowledgement

• Reliable delivery guarantees that a stream of
  data sent from one device is delivered through a
  data link to another device without duplication
  or data loss.
• Positive acknowledgment with retransmission is
  one technique that guarantees reliable delivery
  of data.
• TCP uses expectational acknowledgments.
• Expectational acknowledgements mean that the
  acknowledgment number refers to the packet that
  is next expected.

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Acknowledgement

• Each segment is numbered before transmission
• At the receiving station, TCP reassembles the
  segments into a complete message.

• If a sequence number is missing in the series,
  that segment is retransmitted.
• Segments that are not acknowledged within a given
  time period will result in a retransmission.

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Positive Acknowledgement and Retransmission

• It is used to provide reliability.
• Positive acknowledgment requires a recipient to
  communicate with the source and send back an
  acknowledgment message when the data is received.
  
• The sender keeps a record of each data packet
  (TCP segment), that it sends and expects an
  acknowledgment.
• Once the source sends a packet, it starts a timer
  and waits for an acknowledgment before sending
  the next packet.
• If the timer expires before the source receives
  an acknowledgment, the source retransmits the
  packet and starts the timer over again.

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TCP Congestion Control

• TCP also maintains a congestion-control window.
• This window is normally the same size as the
  window of the receiver.
• However, this window is cut in half when a packet
  is lost, perhaps as a result of network
  congestion.
• This approach permits the window to be expanded
  or contracted as necessary to manage buffer space
  and processing.

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Transmission Control Protocol (TCP)

• connection-oriented
• reliable
• divides outgoing messages into segments
• reassembles messages at the destination station
• re-sends anything not received
• reassembles messages from incoming segments
• The protocols that use TCP include
• FTP (File Transfer Protocol)
• HTTP (Hypertext Transfer Protocol)
• SMTP (Simple Mail Transfer Protocol)
• Telnet

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Transmission Control Protocol

• Source port Number of the calling port
• Destination port Number of the called port
• Sequence number Number used to ensure correct
  sequencing of the arriving data
• Acknowledgment number Next expected TCP octet
• HLEN Number of 32-bit words in the header
• Reserved Set to zero

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Transmission Control Protocol

• Code bits Control functions, such as setup and
  termination of a session
• Window Number of octets that the sender is
  willing to accept
• Checksum Calculated checksum of the header and
  data fields
• Urgent pointer Indicates the end of the urgent
  data
• Option One option currently defined, maximum
  TCP segment size
• Data Upper-layer protocol data

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User Datagram Protocol

• connectionless
• unreliable
• transmit messages (called user datagrams)
• provides no software checking for message
  delivery (unreliable)
• does not reassemble incoming messages
• uses no acknowledgments
• provides no flow control

UDP Segment Format
No sequence or acknowledgement fields
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User Datagram Protocol

• The protocols that use TCP include
• TFTP (Trivial File Transfer Protocol)
• SNMP (Simple Network Management Protocol)
• DHCP (Dynamic Host Control Protocol)
• DNS (Domain Name System)

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Port Number

• Both TCP and UDP use port (socket) numbers to
  pass information to the upper layers.
• Port numbers are used to keep track of different
  conversations crossing the network at the same
  time.
• Port numbers have the following assigned ranges
• Numbers below 1024 are considered well-known
  ports numbers.
• Numbers above 1024 are dynamically assigned ports
  numbers.
• Registered port numbers are those registered for
  vendor-specific applications. Most of these are
  above 1024.
• The source host dynamically assigns originating
  source port numbers. These numbers are always
  greater than 1023.

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Port Numbers
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Introduction to Application Layer

• TCP/IP application layer combine the functions of
  three upper layers together.
• This design assures that the TCP/IP model
  provides maximum flexibility at the application
  layer for developers of software.
• Application Layer is responsible for
• Identifying and establishing the availability of
  intended communication partner
• Synchronizing cooperating applications
• Establishing agreement on procedures for error
  recovery
• Controlling data integrity

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Introduction to Application Layer

• TCP/IP application Examples
• Domain Name System (DNS)
• File Transfer Protocol (FTP)
• Hypertext Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• Simple Network Management Protocol (SNMP)
• Telnet

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Domain Name System

• The Domain Name System (DNS) is a system used on
  the Internet for translating names of domains and
  their publicly advertised network nodes into IP
  addresses.
• Examples
• .th Thailand, .us United States , .uk
  United Kingdom

• Domain name server is a device on a network
• It responds to requests from clients to translate
  a domain name into the associated IP address.
• The DNS system is set up in a hierarchy that
  creates different levels of DNS servers.
• If a local DNS server is able to translate a
  domain name into its associated IP address, it
  does so, and returns the result to the client.
• If it cannot translate the address, it passes the
  request up to the next higher-level DNS server on
  the system

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Domain Name System

• There are also generic names, which examples
  include the following
• .edu educational sites
• .com commercial sites
• .gov government sites
• .org non-profit sites
• .net network service

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File Transfer Protocol and Trivial File Transfer
Protocol

• FTP
• FTP is a reliable, connection-oriented service
  that uses TCP to transfer files between systems
  that support FTP
• FTP is designed to download files or upload
  files.

• TFTP
• is a connectionless service that uses UDP.
• TFTP is used on the routers and switches to
  transfer files between systems that support TFTP
• TFTP operates faster than FTP
• TFTP has no provisions for user authentication.

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Hypertext Transfer Protocol

• HTTP works with the World Wide Web, which is the
  fastest growing and most used part of the
  Internet.
• One of the main reasons for the extraordinary
  growth of the Web is the ease with which it
  allows access to information.
• A Web browser (along with all the other network
  applications covered in this chapter) is a
  client-server application, which means that it
  requires both a client and a server component in
  order to function.
• The Web pages are created with a format language
  called Hypertext Markup Language (HTML).
• The Web page contains, often hidden within its
  HTML description, an address location known as a
  Uniform Resource Locator (URL).

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Simple Mail Transfer Protocol

• Email servers communicate with each other using
  the Simple Mail Transfer Protocol (SMTP) to send
  and receive mail.
• The SMTP protocol transports email messages in
  ASCII format using TCP.
• Mail can be collected by using program that
  access the mail server files directly or collect
  their mail using one of many network protocols
• POP3 and IMAP4, which both use TCP to
  transport data.

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Simple Network Management

• The Simple Network Management Protocol (SNMP) is
  an application layer protocol that facilitates
  the exchange of management information between
  network devices.
• SNMP enables network administrators to manage
  network performance, find and solve network
  problems,and plan for network growth.
• SNMP uses UDP as its transportlayer protocol.

• SNMP three components
• Network management system (NMS)
• Managed devices
• Agents

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Telnet

• Terminal emulation (Telnet) software provides the
  ability to remotely access another computer.
• It allows you to log in to an Internet host and
  execute commands.
• A Telnet client is referred to as a local host,
  and a Telnet server, which uses special software
  called a daemon, is referred to as a remote host.