Aplication and Transport layer- a practical approach


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This presentation was done for a Networking course. It really shows from a more practical standpoint how the application layer and the transport layer communicates with each other and operates on a whole to get the job done. It gives the reader more insight of how the pieces come together in an IT networking world.

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Aplication and Transport layer- a practical approach

  1. 1. Practical Approach - Application Layer with Transport Layer
  2. 2. Agenda • Review of models • Application layer interacts with transport / Scenarios • Port Addressing • Responsibilities ofTransport Layer • Tools to help understand and monitor
  3. 3. The entire picture – top down approach • OSI – theoretical, reference model • Internet Protocol Suite – practical & widely used, protocol stack on which the internet works. Cisco Systems(2007),Application Layer Functionality and Protocols, Retrieved from http://ciscoserver.eastms.edu/scoleman/ccna1.html
  4. 4. Application layer protocols • DNS – Matches/ resolves domain names with IP addresses • HTTP – Used to transfer data between clients/servers using a web browser • SMTP & POP3 – used to send email messages from clients to servers over the internet • FTP – allows the download/upload of files between a client/server • Telnet – allows users to login to a host from a remote location and take control as if they were sitting at the machine (virtual connection) • DHCP – assigns IP addresses, subnet masks, default gateways, DNS servers, to users as they login the network Cisco Systems(2007),Application Layer Functionality and Protocols, Retrieved from http://ciscoserver.eastms.edu/scoleman/ccna1.html
  5. 5. Applications – Processes and Services DNS Server • Telnet Server DHCP • Email Server • Web Server • FTP Server DNS Telnet SMTP, POP, IMAP HTTP DHCP FTP In and IT Environment – Companies, Enterprises etc.
  6. 6. Examples DHCP Retrieved from http://wintips4u.blogspot.com/2 002/11/dhcp- gujaratikanudo.html TELNET DNS Retrieved from http://www.cisco.com/en/US/products/ hw/optical/ps2006/products_tech_note 09186a008052e85f.shtml Retrieved from http://ciscoserver.eastms.edu/s coleman/ccna1.html
  7. 7. Applications need transport Transport layer = LIAISON Protocols at this layer oversee the delivery of data from an application program on one computer to an application program on another computer. More importantly, they act as a liaison between the application-layer protocols and the services provided by the lower layers (network, data link, and physical). Retrieved from http://highered.mcgraw-hill.com/sites/0072397020/student_view0/chapter3/ Stallings (2010), Each application within a host must have an address that is unique within the host; this allows the host-to-host protocol (TCP) to deliver data to the proper process.These latter addresses are known as Ports. How is the application identified? –Transport layer uses application identifier – PORTS Internal address reserved for a specific application. It determines which application layer protocols is used.
  8. 8. Application connects to transport layer
  9. 9. Link layer Network IP Internet TCP port UDP port 20 21 80 69 53 FTP HTTP TFTP DNS Application TCP UDP Transport Socket interface Socket  IP address & TCP/UDP port
  10. 10. PORT ADDRESSINGTRANSPORT LAYER • Many common application have default port assignments. • Port numbers are assigned in different ways depending on whether it is a request or response. • The source port in a segment of a client request is generated randomly once it does not conflict with existing used ports. • The destination port is either assigned by default or manually IANA assignment ports – International Assigned Numbers Authority http://www.iana.org/ • 0 to 1023 - Well Known (Contact) Ports • 1024 to 49151 – Registered Ports • 49152 to 65535 – Private and/or Dynamic Ports
  11. 11. Responsibility ofTransport Layer – Port Addressing Retrieved from http://ciscoserver.eastms.edu/scoleman/ccna1.html
  12. 12. Other responsibilities - TRANSPORT Layer • Segmentation • Session Multiplexing • Identification of different applications • Sequencing • Flow Control • Connection Oriented • Reliability RELIABLE BEST EFFORT Connection Type Connection-oriented Connectionless Protocol TCP UDP Sequencing Yes No Uses Email / File Sharing /Downloading Voice Streaming / Video Streaming/ Online Gaming
  13. 13. TCP / UDP TCP TRANSPORT LAYER UDP TCP FTP – 20-21 Telnet – 23 SMTP – 25 DNS – 53 (BothTCP & UDP) HTTP – 80 UDP DHCP – 67 & 68 DNS - 53 TFTP – 69 www.iana.org RFC 1700 - http://www.cse.ohio-state.edu/cgi- bin/rfc/rfc1700.html
  14. 14. NETWORK UTILITIES TCP – 3WAY HANDSHAKE INTCP / Connection Oriented CONNECTION ESTABLISHMENT Retrieved from – http://blogs.ixiacom.com/ixia-blog/tcp-portals-the- handshakes-a-lie/
  15. 15. Protocol Analyzer Connection Request Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
  16. 16. Protocol Analyzer • Connection confirmation Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
  17. 17. Protocol Analyzer • Acknowledgement of confirmation Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
  18. 18. NetStat • Examine openTCP connections over the network host • UnexplainedTCP connections which can pose a threat by consuming resources Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.h tml
  19. 19. Troubleshooting Network Utility tools • FIDDLER • Microsoft Network monitor
  20. 20. SUMMARY • When we use apps over the internet the application layer protocols takes the request down to lower layers. • The transport layer is the liaison, responsible for delivering the segments to lower layer. • A port is what connects the application layer to the transport layer.Tells the transport layer which protocol is speaking and whether to use tcp/udp to deliver. • TCP – Reliable connection oriented • UDP – Connectionless • Application protocols + ports tells us whetherTCP/UDP to use. • Tools to use for monitoring and troubleshootingTCP connections.
  21. 21. REFERENCES Coleman S.. (2007), Application Layer Functionality and Protocols, In Network Fundamentals CCNACisco Systems– (Chapter 3) Retrieved from http://ciscoserver.eastms.edu/scoleman/ccna1.html Stallings ,W. (2010), Cryptography and Network Security, Fifth Edition William Stallings Prentice Hall. http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html http://wintips4u.blogspot.com/2002/11/dhcp-gujaratikanudo.html http://www.cisco.com/en/US/products/hw/optical/ps2006/products_tech_note09186a008052e85f.shtml http://blogs.ixiacom.com/ixia-blog/tcp-portals-the-handshakes-a-lie/ http://www.iana.org/numbers