I don't really understand the difference, neither the necessity of including two fields (VCI and VPI) in asynchronous transfer mode. As far as I understand the main difference between a virtual path and a virtual channel is that a virtual channel has a dynamic bandwidth, while the allocated bandwidth of a virtual path is static. But why does an ATM cell need to include both fields? I thought that the VCI was enough to identify a channel on an ATM switch.
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Start by trying to understand [Why virtual circuits?](https://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode#Why_virtual_circuits.3F). – Ron Maupin Jan 10 '16 at 18:58
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All I've understood is that the ATM switch is able to identify the output interface through the VPI/CVI pair. But it's still unclear why a pair is needed instead of a single value. It is possible for two connections to have the same VCI but a different VPI? – Ramy Al Zuhouri Jan 11 '16 at 17:11
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1You can have multiple channels in a path. They do get combined to create a unique value, kind of like an IP address and TCP port number are combined to create a unique socket, but you still need each number separately. Look at this slideshow: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiV0ZmZoaLKAhXE3SYKHdEpC-UQFggdMAA&url=https%3A%2F%2Fwww.rivier.edu%2Ffaculty%2Fvriabov%2FATM_ATM_Layer.ppt&usg=AFQjCNGWUdL9xmAqxLjWJUDwd8HcnJJtkg&sig2=9fJBE1bQGfU0qCsQxRx2HQ&cad=rja – Ron Maupin Jan 11 '16 at 17:22