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User Datagram Protocol UDP

User Datagram Protocol UDP. Capitulo 11, TCP/IP Forouzan. McGraw Hill. Protocolos para capa transporte. TCP/IP especifica 2 protocolos para la capa de transporte: TCP y UDP. Forouzan, cap. 11. Transport Layer. Funciones de la capa Transporte:

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User Datagram Protocol UDP

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  1. User Datagram ProtocolUDP Capitulo 11, TCP/IP Forouzan. McGraw Hill

  2. Protocolos para capa transporte • TCP/IP especifica 2 protocolos para la capa de transporte: TCP y UDP. Forouzan, cap. 11

  3. Transport Layer • Funciones de la capa Transporte: • Proveer mecanismos para lograr la comunicación “process-to-process”. • Proveer mecanismos de control de flujo y errores. • UDP utiliza puertos para establecer comunicación process-to-process, pero no tiene mecanismo de control de flujo ni se lleva a cabo el acuse de recibo de los paquetes. Si provee un mecanismo de control de errores.

  4. Por que UDP. • UDP es un protocolo no orientado a conexión, no ofrece muchos servicios de IP solo establece la comunicación process-to-process. Su mecanismo de control de errores es muy limitado. • Sin embargo, UDP es un protocolo muy simple, produce poco overhead, sirve para enviar pequeños mensajes y es muy útil para aplicaciones de tiempo real.

  5. Comunicacion proceso-a-proceso • Comunicacion host-to-host --> IP. • Comunicacion process-to-process --> UDP. Forouzan, cap. 11

  6. PUERTOS • Paradigma cliente-servidor. • Ambientes multiusuarios y multiprogramas. • Partes involucradas: • Local host. • Local process. • Remote host. • Remote process. • Para identificar los procesos se utilizan puertos (en TCP/IP van de 0 a 65,535). • Tipos de puertos: “ephemeral” y “well-know”

  7. Port numbers Figure 11-3 Forouzan

  8. IP addresses versus port numbers Figure 11-4 Forouzan.

  9. IANA ranges Figure 11-5 Forouzan

  10. Well-Known UDP Ports. • http://www.networksorcery.com/enp/protocol/ip/ports00000.htm

  11. SOCKETS • UDP necesita 2 identicadores para establecer la conexion: la direccion IP y un numero de puerto. La combinacion de estos dos se llama: “Socket address”. • Por lo tanto se necesita un “client-socket” y un “server-socket”.

  12. Socket addresses Figure 11-6 Forouzan

  13. User datagram format Figure 11-7 Forouzan

  14. Checksum • El calculo del checksum de UDP incluye: • Pseudoheader (parte del header de IP que encapsula al datagrama). • UDP header. • Datos.

  15. Pseudoheader added to the UDP datagram Figure 11-8

  16. Checksum calculation of a simple UDP user datagram Figure 11-9

  17. OPERACION • Conceptos involucrados en la operacion de UDP: • Servicios no-orientados a conexion. • Control de flujo y error (nulo o muy simple). • Encapsulacion / Desencapsulacion. • Filas de espera. • Multiplexion / Demultiplexion.

  18. Encapsulation and decapsulation Figure 11-10

  19. Queues in UDP Figure 11-11

  20. Multiplexing and demultiplexing Figure 11-12

  21. UDP package Figure 11-13

  22. Control-block table at the beginning State Process ID Port Number Queue Number -------- ------------ -------------- ------------ IN-USE 2,345 52,010 34 IN-USE 3,422 52,011 FREE IN-USE 4,652 52,012 38 FREE

  23. Example 1 The first activity is the arrival of a user datagram with destination port number 52,012. The input module searches for this port number and finds it. Queue number 38 has been assigned to this port, which means that the port has been previously used. The input module sends the data to queue 38. The control-block table does not change.

  24. Example 2 After a few seconds, a process starts. It asks the operating system for a port number and is granted port number 52,014. Now the process sends its ID (4,978) and the port number to the control-block module to create an entry in the table. The module does not allocate a queue at this moment because no user datagrams have arrived for this destination.

  25. Modified table after Example 2 State Process ID Port Number Queue Number -------- ------------ -------------- ----------IN-USE 2,345 52,010 34 IN-USE 3,422 52,011 IN-USE 4,978 52,014 IN-USE 4,652 52,012 38 FREE

  26. Example 3 A user datagram now arrives for port 52,011. The input module checks the table and finds that no queue has been allocated for this destination since this is the first time a user datagram has arrived for this destination. The module creates a queue and gives it a number (43).

  27. Modified table after Example 3 State Process ID Port Number Queue Number -------- ------------ -------------- --------------- IN-USE 2,345 52,010 34 IN-USE 3,422 52,011 43 IN-USE 4,978 52,014 IN-USE 4,652 52,012 38 FREE

  28. Example 4 After a few seconds, a user datagram arrives for port 52,222. The input module checks the table and cannot find the entry for this destination. The user datagram is dropped and a request is made to ICMP to send an “unreachable port” message to the source.

  29. Example 5 After a few seconds, a process needs to send a user datagram. It delivers the data to the output module which adds the UDP header and sends it.

  30. Uso de UDP • En procesos que requieren comunicacion simple sin importar control de flujo y error. • En procesos que cuentan ya con mecanismos de control de flujo y error internos (TFTP). • Para multicast y broadcast. • Para procesos de administracion como SNMP. • Actualizaciones de rotocolos de ruteo (RIP).

  31. TAREA • Leer capitulo 11, TCP/IP - Forouzan.

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