Universidad Autónoma de Zacatecas
Programa de Ingeniería en Computación
Seguridad en Redes
8 º ”B”
Profesor: Carlos Héctor Castañeda Ramírez
Nombre del alumno: José de Jesús Gallegos Rodríguez
Tarea: Investigación de temas de redes
Fecha de entrega: domingo 14 de febrero de 2010
Índice
Índice .………………………………………………………………………………………… 2
Estructura de una trama Ethernet………………………………………………….. 3
El modelo OSI ……………………………………………………………………………… 3
Ruteadores ………………………………………………………………………………….. 5
MPLS ………………………………………………………………………………………….. 5
Comunicaciones orientadas a conexión y orientadas a no conexión …… 6
Servicios de Red …………………………………………………………………………… 6
Bibliografía …………………………………………………………………………………. 9
1.- Estructura de una tramaEthernet
Una trama Ethernet es un conjunto de pulsos digitales enviados en una transmisión de datos para transmitir información. Una trama Ethernet puede tener desde 64 hasta los 1,518 bytes de tamaño y se organiza en cuatro secciones:
? Preámbulo
? Cabecera
? Información
? Secuencia de verificación de trama (FCS)
Preámbulo
Se define como una serie de pulsos decomunicación que le dice a todas las máquinas que están en escucha “Alístense, tengo algo que enviar”. El preámbulo estándar es de 8 bytes.
Cabecera
Siempre contiene información a cerca de quién envía la trama y a dónde se dirige. Puede contener información como, cuántos bytes contiene la trama, esto se una para corrección de errores. Siempre es de 14 bytes.
Información
Contiene la información quese desea transmitir, así como información de protocolo tal como la IP destino. Puede tener un tamaño de 46 hasta 1,500 bytes. Si una computadora tiene más de 1,500 bytes de información para transferir, dividirá la información en partes y les identificará en el orden apropiado usando una secuencia numérica. Con esta información, el destinatario sabe como re-acomodar la información. Si la trama noalcanza los 46 bytes, la computadora rellena el fin de la sección con un 1.
Secuencia de Verificación de Trama
La FCS se usa para asegurar que la información recibida es la enviada. El sistema que envía información procesa la porción FCS de la trama a través de un algoritmo llamado Verificación de Redundancia Cíclica (CRC). El CRC toma los valores de los campos ya mencionados y crea un númerode 4 bytes. Cuando el sistema receptor recibe la trama, ejecuta el mismo CRC y lo compara con el valor contenido en el mismo campo. Si el sistema destino encuentra similitud, se asume que la trama está libre de errores y procesa la información. Si la comparación falla, el sistema destino asume que algo pasó en el trayecto de la trama y envía un aviso de que necesita que la trama sea nuevamenteenviada.
2.- El modelo OSI
Objetivo
El objetivo del modelo OSI es ayudar a mejorar las comunicaciones entre los diferentes distribuidores de sistemas. El ISO era un comité que representaba a diferentes organizaciones, cuya meta no estaba a favor de un método específico de comunicación, pero si a favor de desarrollar pautas que le permitieran a los distribuidores asegurar que sus productospudieran interoperar. ISO se estableció para simplificar la comunicación entre sistemas.
Capas
a) Física
b) Enlace de datos
c) Red
d) Transporte
e) Sesión
f) Presentación
g) Aplicación
Física
Describe las especificaciones de nuestros dispositivos de transmisión, conectores y pulsos de señal. Un repetidor o un hub se ubican en la capa física debido a que sóloamplifica la señal eléctrica en e cable.
Enlace de datos
Describe las especificaciones para la topología y comunicación entre los sistemas locales. El Ethernet es un buen ejemplo de un enlace de datos, también trabaja con múltiples especificaciones de la capa física (par trenzado, fibra óptica) y con muchas especificaciones de la capa de red (IPX, IP). La capa de enlace de datos es “la…
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