two mor questioins about bridge/switch and hub

pengbinpengbin Posts: 5Member ■□□□□□□□□□
1. When discussing about Ethernet CSMA/CD method, one book I read says "Only bridge and router can effectively prevent a transmission from propagating throughout the entire network". My question is if bridge can, why not switch? Swithc can be considered as an advanced bridge, so it should do anything bridge can do. right?

2. One book specifies that "If a hub is attached to a switch, it must operate in half-duplex mode because the end stations must be able to detect collision." But I can't understand the reason the author gave. Why does the end stations must be able to detect collision result in use half-duplex mode.


  • BubbaJBubbaJ Posts: 323Member
    1. In this instance, a switch is a bridge. You will find that Cisco uses the term bridge interchangeably with Layer 2 switch. Multilayer switches and routers can bridge, too, but Cisco does not use bridge to identify these devices.

    2. In full-duplex mode, there is no possibility of detecting collisions because separate pairs are used for transmitting and receiving. By definition, collision detection is turned off in full-duplex. You can only use it as a point-to-point connection. When there is a possibility of more than two devices sharing a channel, you must use half-duplex so that every end-device can listen to see if the line is clear before sending, and each can hear if there is a collision. A hub is a Layer 1 device just like the wire. It is merely a conectration of the wire. Look up CSMA-CD if you are still confused.
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