TCPIP Transport and Application Layers

1
TCP/IP Transport and Application Layers

• Concepts
• By
• Adwoa Afful (Mrs)

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TCP/IP Transport Layer

• The Transport Layer reliably and accurately
  transports and regulates the flow of information
  between source and destination.
• sliding windows
• sequencing numbers
• acknowledgments

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TCP/IP Transport Layer

• The two primary duties of the transport layer are
  to provide flow control and reliability. Services
  include
• Segmentation of upper-layer application data
• Establishment of end-to-end operations
• Transportation of segments from one end host to
  another
• Flow control provided by sliding windows
• Reliability provided by sequence numbers and
  acknowledgments
• Segments reassembled at destination

4
Transport Layer Flow Control

• Flow control ensures that a source host does not
  overflow the buffers in a destination host.
• Too much data means lost data
• With flow control, the two hosts establish a data
  transfer rate.

5
Session Establishment, Maintenance, and
Termination

• Layer 4 allows different conversations to occur
  simultaneously over one connection.
• This is called multiplexing.
• different types of conversations are labelled
  with software port numbers
• Before data is transferred
• Synchronization occurs
• The connection is established
• Data is transferred

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A typical connection

• The first handshake requests synchronization.
• The second handshake acknowledges the initial
  request, and requests synchronization in the
  opposite direction.
• The third handshake is an acknowledgment
  informing the destination that a connection has
  been established.
• After the connection has been established, data
  transfer begins

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Flow Control

• Congestion occurs for one of two reasons
• A PC transmits data faster than the network can
  transmit it.
• Many devices transmit data to the same
  destination.
• If data arrives too quickly it is stored in
  memory.
• If it continues to arrive too quickly, data will
  be discarded.

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Flow Control

• Instead of allowing data to be lost, the
  destination sends a not ready indicator to the
  sender.
• When it can handle more data, it sends a ready
  transport indicator to the sender.
• At the end of data transfer, the source host
  sends a signal that indicates the end of the
  transmission.
• The destination acknowledges this and the
  connections is terminated.

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Three-way Handshake

• TCP is connection-oriented
• The connection is established before data
  transfer begins.
• Synchronization requires each side to send its
  own initial sequence number and to receive a
  confirmation of exchange in an acknowledgment
  (ACK) from the other side.

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Three-way Handshake

• The sending host (A) initiates a connection by
  sending a SYN packet to the receiving host (B)
  indicating its INS X
• A - gt B SYN, seq of A X
• B receives the packet, records that the seq of A
  X, replies with an ACK of X 1, and indicates
  that its INS Y. The ACK of X 1 means that
  host B has received all octets up to and
  including X and is expecting X 1 next
• B - gt A ACK, seq of A X, SYN seq of B Y, ACK
  X 1
• A receives the packet from B, it knows that the
  seq of B Y, and responds with an ACK of Y 1,
  which finalizes the connection process
• A - gt B ACK, seq of B Y, ACK Y 1

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Windowing

• Reliable data transfer is achieved by
  acknowledgments (ACK).
• If ACKs were sent after every packet, throughput
  would be low, so multiple packets are sent.
• The number of packets a sender can transmit
  before it receives an ACK is known as the window
  size, or window.

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Windowing Flow Control

• Expectational ACKs the ACK number refers to the
  next packet that is expected
• The window size is negotiated dynamically.

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Windowing Flow Control
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Windowing Flow Control
The ACK sent by the destination determines
whether the sender retransmits, or continues to
send as before.
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Acknowledgments
16
TCP Segment Format
Number of the called port
set to zero
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TCP/UDP Protocols

• TCP
• FTP
• HTTP
• SMTP
• Telnet

• UDP
• TFTP
• SNMP
• DHCP
• DNS

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UDP

• Connectionless
• No guaranteed delivery
• Reliability is provided by application layer
  protocols
• Applications that do not need sequencing
• UDP Fields
• Source port Number of the port that sends data
• Destination port Port number that receives data
  
• Length Number of bytes in 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

• Port numbers are used to keep track of different
  conversations.
• Numbers below 1024 are well-known ports numbers.
• Numbers above 1024 are dynamically-assigned ports
  numbers.
• Registered port numbers for vendor-specific
  applications are gt 1024

Memorise these port numbers! (Journal)
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TCP/IP Application Layer

• The Session, Presentation, and Application layers
  of the OSI model make up the TCP/IP Application
  layer.
• Therefore, representation, encoding, and dialog
  control are all dealt with by this layer.

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TCP/IP Application Layer

• Applications
• DNS
• FTP
• HTTP
• SMTP
• SNMP
• Telnet

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Domain Name System - DNS

• It is difficult to associate an IP address with a
  particular site, let alone lots of them.
• DNS is a system used for translating domain names
  and their network nodes into IP addresses.
• A domain is a group of computers that are
  associated by their geographical location or
  their business type.

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Domain Name System - DNS

• .edu educational sites
• .com commercial sites
• .gov government sites
• .org non-profit sites
• .net network service
• .au Australia
• .nz New Zealand

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FTP and TFTP

• FTP
• Connection-oriented
• Reliable
• FTP protocol
• Data transfer can occur in ASCII mode or in
  binary mode
• After the file transfer, the data connection
  terminates automatically.

• TFTP
• Connectionless
• Unreliable
• UDP protocol
• No authentication
• Faster than TCP

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HTTP

• HyperText Transfer Protocol
• Requires a web browser
• a client server application
• Multimedia format
• HTML (HyperText Markup Language)
• Determines the content and layout of web pages
• URL Uniform Resource Locator
• http//www.cisco.com/edu/

protocol
Folder location on the server
Hostname and IP address
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HTTP
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Simple Mail Transfer Protocol - SMTP

• Transports email messages in ASCII format using
  TCP
• Mail servers store mail until the client collects
  it.
• SMTP usually used to send mail
• POP3 and IMAP4 are mail client protocols used to
  receive mail
• SMTP has little security and no authentication.

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Simple Network Management Protocol (SNMP)

• Application Layer protocol used to remotely learn
  about other devices.
• Uses UDP
• Allows administrators to
• Manage network performance
• Find and plan network problems
• Plan for network growth

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SNMP Three Main Components

• Network management system (NMS) NMS executes
  applications that monitor and control managed
  devices. One or more NMSs must exist on any
  managed network.
• Managed devices Managed devices are nodes that
  contain an SNMP agent. They collect and store
  management information and make it available to
  NMSs using SNMP. Can be routers, access servers,
  switches, and bridges, hubs, computer hosts, or
  printers.
• Agents Agents are network-management software
  modules in managed devices. An agent translates
  management information into a form compatible
  with SNMP.

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Telnet

• Telnet is a TCP/IP Application protocol.
• OSI Application layer commands
• OSI Presentation layer formatting (ASCII)
• OSI Session layer transmission
• A telnet client can log into a remote host
  (telnet server) and execute commands.
• A telnet client is called a local host
• A telnet is a remote host
• Runs software called a daemon.

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Internet Layer Protocols
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Features of IP

• IP provides connectionless, best-effort delivery
  routing of packets. IP is not concerned with the
  content of the packets but looks for a path to
  the destination.
• Internet Control Message Protocol (ICMP) provides
  control and messaging capabilities.

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Contd

• Address Resolution Protocol (ARP) determines the
  data link layer address, or MAC address, for
  known IP addresses.
• Reverse Address Resolution Protocol (RARP)
  determines the IP address for a known MAC
  address.

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Contd

• IP performs the following operations
• Defines a packet and an addressing scheme
• Transfers data between the Internet layer and
  network access layer
• Routes packets to remote hosts

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Contd

• IP is sometimes referred to as an unreliable
  protocol. This does not mean that IP will not
  accurately deliver data across a network.

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Contd

• IP is unreliable because it does not perform
  error checking and correction. That function is
  handled by upper layer protocols from the
  transport or application layers.

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Internet Path Determination
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IPv4 Address Allocation
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Contd

• Meanwhile, an even more extendible and scalable
  version of IP, IP Version 6 (IPv6), has been
  defined and developed.
• IPv6 uses 128 bits rather than the 32 bits
  currently used in IPv4. IPv6 uses hexadecimal
  numbers to represent the 128 bits.

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Contd

• IPv6 provides 640 sextrillion addresses. This
  version of IP should provide enough addresses for
  future communication needs.

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IPv4 and IPv6
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IPv4 and IPv6 Addresses
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Contd

• shows an IPv4 address and an IPv6 address. IPv4
  addresses are 32 bits long, written in decimal
  form, and separated by periods. IPv6 addresses
  are 128-bits long and are identifiers for
  individual interfaces and sets of interfaces.
  IPv6 addresses are assigned to interfaces, not
  nodes.

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Contd

• Since each interface belongs to a single node,
  any of the unicast addresses assigned to the
  interfaces of the node may be used as an
  identifier for the node. IPv6 addresses are
  written in hexadecimal, and separated by colons.
  IPv6 fields are 16 bits long.

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Contd

• To make the addresses easier to read, leading
  zeros can be omitted from each field. The field
  0003 is written 3. IPv6 shorthand
  representation of the 128 bits uses eight 16-bit
  numbers, shown as four hexadecimal digits.

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Contd

• After years of planning and development, IPv6 is
  slowly being implemented in select networks.
  Eventually, IPv6 may replace IPv4 as the dominant
  Internet protocol.

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Network access layer

• The network access layer allows an IP packet to
  make a physical link to the network media. It
  includes the LAN and WAN technology details and
  all the details contained in the OSI physical and
  data link layers.

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Contd

• Drivers for software applications, modem cards,
  and other devices operate at the network access
  layer. The network access layer defines the
  procedures used to interface with the network
  hardware and access the transmission medium.
  Modem protocol standards such as Serial Line
  Internet Protocol (SLIP) and Point-to-Point
  Protocol (PPP) provide network access through a
  modem connection.

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Contd

• Many protocols are required to determine the
  hardware, software, and transmission-medium
  specifications at this layer. This can lead to
  confusion for users. Most of the recognizable
  protocols operate at the transport and Internet
  layers of the TCP/IP model.

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Contd

• Network access layer protocols also map IP
  addresses to physical hardware addresses and
  encapsulate IP packets into frames. The network
  access layer defines the physical media
  connection based on the hardware type and network
  interface.

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Contd

• Here is an example of a network access layer
  configuration that involves a Windows system set
  up with a third party NIC. The NIC would
  automatically be detected by some versions of
  Windows and then the proper drivers would be
  installed.

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Contd

• In an older version of Windows, the user would
  have to specify the network card driver. The card
  manufacturer supplies these drivers on disks or
  CD-ROMs.

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Network Access Protocols
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The OSI model and the TCP/IP model

• The OSI and TCP/IP models have many similarities
  
• Both have layers.
• Both have application layers, though they include
  different services.
• Both have comparable transport and network
  layers.

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Contd

• Both use packet-switched instead of
  circuit-switched technology.
• Networking professionals need to know both
  models.

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Circuit-Switched

• A circuit-switched network creates a closed
  circuit between two nodes in the network to
  establish a connection. The established
  connection is thus dedicated to the communication
  between the two nodes.

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Contd

• One of the immediate problems with dedicated
  circuits is wasted capacity, since almost no
  transmission uses the circuit 100 percent of the
  time. Also, if a circuit fails in the middle of a
  transmission, the entire connection must be
  dropped and a new one established.

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Contd
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Packet-Switched

• IP-based networks on the other hand utilize a
  packet-switched network technology, which uses
  available capacity much more efficiently and
  minimizes the risk of possible problems, such as
  a disconnection.

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Contd

• Messages sent over a packet-switched network are
  first divided into packets containing the
  destination address. Then, each packet is sent
  over the network with every intermediate node and
  router in the network determining where the
  packet goes next.

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Contd

• A packet does not need to be routed over the same
  links as previous related packets. Thus, packets
  sent between two network devices can be
  transmitted over different routes in the event of
  a link breakdown or node malfunction.

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Illustration
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Differences of the OSI and TCP/IP

• Here are some differences of the OSI and TCP/IP
  models
• TCP/IP combines the OSI application,
  presentation, and session layers into its
  application layer.
• TCP/IP combines the OSI data link and physical
  layers into its network access layer.

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Contd

• TCP/IP appears simpler because it has fewer
  layers.
• When the TCP/IP transport layer uses UDP it does
  not provide reliable delivery of packets. The
  transport layer in the OSI model always does.

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Contd

• The Internet was developed based on the standards
  of the TCP/IP protocols. The TCP/IP model gains
  credibility because of its protocols. The OSI
  model is not generally used to build networks.
  The OSI model is used as a guide to help students
  understand the communication process.

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Comparing TCP/IP with the OSI Model
67
questions

• Answers