aplication and transport layer- a practical approach
DESCRIPTION
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.TRANSCRIPT
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Practical Approach - Application Layer with Transport Layer
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Agenda
• Review of models
• Application layer interacts with transport / Scenarios
• Port Addressing
• Responsibilities of Transport Layer
• Tools to help understand and monitor
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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
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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
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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.
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Examples DHCP
Retrieved from http://wintips4u.blogspot.com/2002/11/dhcp-gujaratikanudo.html
TELNET DNS
Retrieved from http://www.cisco.com/en/US/products/hw/optical/ps2006/products_tech_note09186a008052e85f.shtml
Retrieved from http://ciscoserver.eastms.edu/scoleman/ccna1.html
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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.
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Application connects to transport layer
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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
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PORT ADDRESSING TRANSPORT 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
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Responsibility of Transport Layer – Port Addressing
Retrieved from http://ciscoserver.eastms.edu/scoleman/ccna1.html
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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
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TCP / UDP
TCP
TRANSPORT LAYER
UDP
TCP FTP – 20-21 Telnet – 23 SMTP – 25 DNS – 53 (Both TCP & 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
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NETWORK UTILITIES
TCP – 3 WAY HANDSHAKE IN TCP / Connection Oriented CONNECTION ESTABLISHMENT
Retrieved from – http://blogs.ixiacom.com/ixia-blog/tcp-portals-the-handshakes-a-lie/
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Protocol Analyzer
Connection Request
Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
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Protocol Analyzer
• Connection confirmation
Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
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Protocol Analyzer
• Acknowledgement of confirmation
Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
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NetStat
• Examine open TCP connections over the network host
• Unexplained TCP connections which can pose a threat by consuming resources
Retrieved from - http://www.highteck.net/IT/Transport/Livello_OSI_Transport.html
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Troubleshooting Network Utility tools
• FIDDLER
• Microsoft Network monitor
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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 whether TCP/UDP to use.
• Tools to use for monitoring and troubleshooting TCP connections.
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REFERENCES
Coleman S.. (2007), Application Layer Functionality and Protocols, In Network Fundamentals CCNA Cisco 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