Suppose $80$ desktop personal computers used by engineers and support personnel are

connected to an Ethernet LAN, which provides the following capabilities:

$200$ digital telephone service at $56kbps$

Retrieval time of $10ms$ for a $10-$MB $($megabyte$)$ file from a server attached to the

LAN.

$100$ e$-$mail messages per hour to and from a user. Assume $80$ percent of the

messages are less than $1MB($megabytes$)$ and $20$ percent contain a $10-MB$

attachment.

Internet access at $20Mbps.$

Full$-$duplex videoconferencing capabilities at $100Mbps.$

Estimate the bit rate requirements of the LAN.