Questão 345241

• Banca: MOVENS
• Órgão: Prefeitura de Manaus - AM
• Ano: 2010
• Provas: MOVENS - 2010 - Prefeitura de Manaus - AM - Analista - Administração de Redes
• Disciplina: Redes de Computadores
• Assuntos: Equipamentos de Redes; Switches

Com a diminuição dos preços dos switchs, eles substituíram os hubs como principal equipamento de interconexão de computadores em uma rede local. Os switchs utilizam dois métodos para transmitir os pacotes: o Cut-through e o Store-and-forward.

Com relação aos dois métodos de funcionamento dos switchs, assinale a opção correta.

• A. No método Store-and-forward, o switch armazena cópias dos pacotes transferidos, para retransmiti-los, se necessário, acelerando assim as transferências de rede.
• B. No método cut-through, a integridade do pacote é verificada antes de transferi-lo para seu destino.
• C. No método cut-through, o switch inicia a transferência do pacote para seu destino antes de ter recebido todo o pacote.
• D. No método Store-and-forward, um pacote enviado é sempre armazenado e replicado para todas as portas do switch, de forma a garantir a transferência do pacote para o destino correto.

Gabarito: C

Comentários

• c-

  Cut-through switching, also called cut-through forwarding is a method for packet switching systems, wherein the switch starts forwarding a frame (or packet) before the whole frame has been received, normally as soon as the destination address and outgoing interface is determined. Compared to store and forward, this technique reduces latency through the switch and relies on the destination devices for error handling.

  Fragment free is a variation on cut-through switching that partially addresses the frame dropping issue by assuring that collision fragments are not forwarded. Fragment free will hold the frame until the first 64 bytes are read from the source to detect a collision before forwarding. This is only useful if there is a chance of a collision on the source port.

  In Store and forward, information is sent to an intermediate station where it is kept and sent at a later time to the final destination. The intermediate station, or node in a networking context, verifies the integrity of the message before forwarding it. In general, this technique is used in networks with intermittent connectivity, especially in the wilderness or environments requiring high mobility.

  An adaptive switch is a network switch designed to normally operate in cut-through mode but if a port's error rate jumps too high, the switch automatically reconfigures the port to run in store-and-forward mode.

  https://en.wikipedia.org/wiki/Adaptive_switching

  https://en.wikipedia.org/wiki/Cut-through_switching

  https://en.wikipedia.org/wiki/Store_and_forward