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.

1. Practical Approach -
Application Layer with Transport Layer

2. Agenda
• Review of models
• Application layer interacts with transport / Scenarios
• Port Addressing
• Responsibilities ofTransport Layer
• Tools to help understand and monitor

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. 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. 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. 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. 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. Application connects to transport layer

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. 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. Responsibility ofTransport Layer – Port Addressing
Retrieved from
http://ciscoserver.eastms.edu/scoleman/ccna1.html

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. 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. 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. Protocol Analyzer
Connection Request
Retrieved from -
http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html

16. Protocol Analyzer
• Connection confirmation
Retrieved from -
http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html

17. Protocol Analyzer
• Acknowledgement of
confirmation
Retrieved from -
http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html

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. Troubleshooting Network Utility tools
• FIDDLER
• Microsoft Network monitor

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. 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