Network Fundamentals: Ch4 - Transport Layer

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Transport layer is responsible for the overall end-to-end transfer of application data.
Because different applications have different requirements, there are multiple Transport layer protocols.
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
TCP and UDP headers.
Port Addressing, socket pair.
Types of port numbers: Well Known Ports (0 to 1023), Registered Ports (1024 to 49151) and Dynamic or Private ‘Ephemeral’ Ports (49152 to 65535).
Netstat command : examines the open connections on a host.
Transport Layer Functions.
TCP Connection Establishment (3-way handshake).
Connection Management - Flow Control through buffering, congestion avoidance, and windowing.
Flow Control – Reducing the window size .
TCP Connection Termination (4-way Handshake).


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Network Fundamentals: Ch4 - Transport Layer

  1. 1. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Network Fundamentals Abdelkhalik Elsaid Mosa abdu.elsaid@yahoo.com http://abdelkhalik.staff.scuegypt.edu.eg/ Last Update: 10/7/2011 “In God we trust, all others bring data” - W. Edwards Deming
  2. 2. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Introduction • Layer 4, responsible for the overall end-to-end transfer of application data. • Transport layer also encompasses these functions: 1. Enables multiple applications to communicate over the network at the same time on a single device. 2. Ensures that, if required, all the data is received reliably and in order by the correct application. 3. Employs error handling mechanisms.
  3. 3. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Applications Requirements Vary • Because different applications have different requirements, there are multiple Transport layer protocols.
  4. 4. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Data Encapsulation Transport Data Link Physical Network Data Header Data Presentation Application Session Segment-Datagram Packet Bits Frame Header Segment / Datagram Header Packet Trailer 1000000111111000001110000
  5. 5. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy TCP and UDP • UDP  is a simple, low overhead, connectionless protocol, RFC 768  Pieces of communication in UDP are called datagrams.  Datagrams are sent as "best effort“ “Unreliable”.  Applications that use UDP include:  DNS,DHCP,SNMP,RIP, TFTP, Online games, Video Streaming, and VoIP. • TCP  is a connection-oriented, RFC 793, additional overhead  Reliable delivery.  Flow control which prevents overflow  Applications that use TCP are:  Web Browsers, E-mail, File Transfers.
  6. 6. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Transport Layer Header
  7. 7. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy TCP Header Fields • Source port : a random value above 1023. • Destination port: Identifies the destination protocol or application. • Sequence number: the first byte in the current segment. Is the SYN flag set or not?? • Acknowledgement number: specifies the next expected byte by the receiver. • Window size: determines how many bytes can be sent before waiting for acknowledgement. • H.length (Offset): the length of the segment header in bytes. • Checksum: used for error checking. • Reserved: Reserved for future use and should be set to zero.
  8. 8. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Port Addressing • Port Number (L4 Addressing): Uniquely identifies applications.  Server processes have static port numbers assigned to them.  Clients dynamically choose a port number for each conversation. • Socket: is the combination of the port number and the IP address, Ex: 198.16.23.213:80. • Socket Pair: consists of the source and destination IP addresses and port numbers, is also unique and identifies the conversation between the two hosts. • IANA is responsible for assigning various addressing standards.
  9. 9. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Types of port numbers 1. Well Known Ports (0 to 1023): are reserved for services and applications such as HTTP (80), SMTP (25), DNS (53), ... . 2. Registered Ports (1024 to 49151): are assigned to user processes or applications such as MSN Messenger (1863). 3. Dynamic or Private ‘Ephemeral’ Ports (49152 to 65535): assigned dynamically to client applications when initiating a connection. Well Known UDP Ports 69 - TFTP 520 - RIP Well Known TCP/UDP Ports 53 - DNS 161 - SNMP Well Known TCP Ports Telnet: 23, SMTP:25, HTTP: 80, POP3: 110, HTTPS:443
  10. 10. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Identifying Applications and hosts • Netstat: examines the open connections on a host 192.168.1.101 172.16.5.5 Destination Port 80 80 Source Port 49890 49888 198.133.219.25 49888 www.cisco.com 66.13.29.25 80 Source Port
  11. 11. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Transport Layer Functions • TCP/UDP Functions. 1.Segmentation and Reassembly. 2.Conversation Multiplexing using port numbers. 3.Error detection. • TCP Additional functions 1.Connection Establishment (3-way handshake) 2.Connection Management.  Reliability (acknowledgements).  Flow control (Buffering, congestion avoidance, windowing).  Error correction . 3. Connection Termination (4-way handshake)
  12. 12. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy At the source: Segmentation • divides application data into blocks of data that are of appropriate size
  13. 13. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy At the Destination: TCP in order Reassembly • The Transport layer reassembles the data before sending it to the destination application or service.
  14. 14. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy At the Destination: UDP Out of order Reassembly • The Transport layer reassembles the data before sending it to the destination application or service.
  15. 15. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Conversation Multiplexing • Multiple Applications can use the network at the same time where each application is identified by unique port number.
  16. 16. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy TCP Connection Establishment (3-way handshake) • When two hosts communicate using TCP, a connection (Three-way handshake) is established before data can be exchanged.
  17. 17. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Connection Management - Reliability • At the Transport layer the three basic operations of reliability are: 1. Tracking transmitted data: keep track of all the data pieces of each conversation. 2. Acknowledging received data: The destination sends acknowledgements to the source for the segments that it receives. 3. Retransmitting any unacknowledged data: Retransmit any of data that were not acknowledged by the destination. If the source does not receive an acknowledgement within a predetermined amount of time, it retransmits that data to the destination.
  18. 18. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Connection Management - Flow Control • Flow Control: the management of data flow between devices in the network.  is a method of making sure that an excessive amount of data doesn't overrun the end station.  Example: imagine that PC A is running at 100 Mbps and PC B is running at 10 Mbps. If PC A sends something to PC B at full speed, 90 percent of the information will be lost because PC B cannot accept the information at 100 Mbps. This is the reason for flow control. • Flow control Methods: 1. Buffering 2. Congestion Avoidance 3. Windowing
  19. 19. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Flow Control - Buffering & Congestion Avoidance
  20. 20. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Flow Control - Windowing • Window Size: The amount of data that a source can transmit before an acknowledgement must be received
  21. 21. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Flow Control - Windowing • Flow control assists the reliability of TCP transmission by adjusting the effective rate of data flow between the two services in the session.
  22. 22. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy Flow Control – Reducing the window size • If a receiving host has congestion, it may respond to the sending host with a segment with a reduced window size.
  23. 23. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy TCP Connection Termination (4-way Handshake)
  24. 24. Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy

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