CCNA 1 v3'0 Module 11 TCPIP Transport and Application Layers

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CCNA 1 v3.0 Module 11 TCP/IP Transport and
Application Layers
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Objectives

• TCP/IP Transport Layer
• TCP/IP Application Layer

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TCP/IP Transport Layer
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Introduction to Transport Layer

• Five basic services
• Segmenting upper-layer application data
• Establishing end-to-end operations
• Transporting segments from one end host to
  another end host
• Ensuring data reliability
• Providing flow control

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Reliability

• Reliable transport can accomplish the following
• Ensure the segments delivered will be
  acknowledged to the sender
• Provide for retransmission of any segments that
  are not acknowledged
• Put segments back into their correct sequence at
  the destination
• Provide congestion avoidance and control

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Flow Control

• Avoids the problem of a host at one side of the
  connection overflowing the buffers in the host at
  the other side
• Ensures the integrity of the data

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Session Establishment

• One function of the transport layer is to
  establish a connection-oriented session between
  similar devices at the application layer.

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Session Maintenance and Termination

• Congestion can occur during data transfer
• To terminate, the sending host sends a signal
  that indicates the end of the transmission, which
  is acknowledged by the receiver.

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Three-Way Handshake
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Windowing

• 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.
• A method of controlling the amount of information
  transferred end to end
• Information can be measured in terms of the
  number of packets or the number of bytes

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Synchronisation

• Hosts use segments called SYNs for
  synchronisation. SYNs carry a control bit also
  called SYN and the Initial Sequence Number (ISN)
• The synchronization requires each side to send
  its own ISN and to receive a confirmation of
  exchange in an acknowledgment (ACK) from the
  other side.
• Each side must also receive the ISN from the
  other side and send a confirming ACK.

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The sequence is as follows

• A?B SYN(A) initial sequence number is X, ACK
  number is 0, SYN bit is set, but ACK bit is not
  set.
• B?A ACK(A) sequence number is X 1, (B) initial
  sequence number is Y, and SYN and ACK bit are
  set.
• A?B ACK(B) sequence number is Y 1, (A)
  sequence number is X 1, the ACK bit is set, but
  the SYN bit is not set.

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Window Size

• TCP window sizes are variable during the lifetime
  of a connection.
• Larger window sizes increase communication
  efficiency.

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Acknowledgment

• Positive acknowledgment requires a recipient to
  communicate with the source, sending back an
  acknowledgment message when it receives data.
• Sender keeps a record of each data packet that it
  sends and expects an acknowledgment.

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TCP Sequence and Acknowledgment
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Transmission Control Protocol (TCP)

• The protocols that use TCP include
• FTP (File Transfer Protocol)
• HTTP (Hypertext Transfer Protocol)
• SMTP (Simple Mail Transfer Protocol)
• Telnet

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TCP Segment Format
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The following are the definitions of the fields
in the TCP segment

• 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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fields in the TCP segment (cont)

• 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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UDP

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

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UDP Segment Format
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The following are the definitions of the fields
in the UDP segment

• Source port Number of the calling port
• Destination port Number of the called port
• Length Number of bytes including header and
  data
• Checksum Calculated checksum of the header and
  data fields
• Data Upper-layer protocol data

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TCP and UDP Port Numbers

• Both TCP and UDP use port (socket) numbers to
  pass information to the upper layers.
• 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.

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TCP and UDP Port Numbers
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Port Numbers
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TCP/IP Application Layer
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Introduction to Application Layer
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Responsibilities of Application Layer

• Identifying and establishing the availability of
  intended communication partners
• Synchronizing cooperating applications
• Establishing agreement on procedures for error
  recovery
• Controlling data integrity

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Application Layer Examples

• Domain Name System
• File Transfer Protocol
• Hypertext Transfer Protocol
• Simple Mail Transport Protocol
• Simple Network Management Protocol
• Telnet

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DNS

• The Domain Name System (DNS) is a system used for
  translating names of domains into IP addresses.
• There are more than 200 top-level domains on the
  Internet, examples of which include the
  following

.us United States .uk United Kingdom .edu
educational sites .com commercial sites
.gov government sites .org non-profit sites
.net network service
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FTP and TFTP

• FTP is a reliable, connection-oriented service
  that uses TCP to transfer files between systems
  that support FTP.
• TFTP is a connectionless service that uses User
  Datagram Protocol (UDP).
• TFTP is used on routers to transfer configuration
  files and Cisco IOS images.
• TFTP is designed to be small and easy to
  implement.

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HTTP
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SMTP

• E-mail servers communicate with each other using
  the Simple Mail Transport Protocol (SMTP) to send
  and receive mail.

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SNMP

• The Simple Network Management Protocol (SNMP) is
  an application layer protocol that facilitates
  the exchange of management information between
  network devices.

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Telnet

• Telnet client software provides the ability to
  log in to a remote Internet host that is running
  a Telnet server application and then to execute
  commands from the command line.

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Summary

• The functions of the TCP/IP transport layer
• Flow control
• The processes of establishing a connection
  between peer systems
• Windowing
• Acknowledgment
• Transport layer protocols
• TCP and UDP header formats
• TCP and UDP port numbers
• The processes and protocols at the TCP/IP
  application layer
• Domain Name Services
• File Transfer Protocols
• Simple Mail Transfer Protocol
• Simple Network Management Protocol
• Telnet