> >The network may be 10Mbps, but it's well-known that Ethernet , being a
> >CSMA/CD type network, will not achieve anything like that in practice,
> >although 2Mbps does seem extremely low. The figure I had in mind was
> >something like 50%-70% of the available bandwidth, but one reference I
> >found quoted 40%:
> >The CSMA/CD article wrote:
> >"Performance of CSMA / CD
> >"It is simple to calculate the performance of a CSMA/CD network where
> >only one node attempts to transmit at any time. In this case, the node
> >may saturate the network and near 100% utilisation of the network may
> >be achieved, providing almost 10 Mbps of throughput on a 10 Mbps LAN.
> >"However, when two or more nodes attempt to transmit at the same time,
> >the performance of Ethernet is less predictable (and not covered by
> >this course). The fall in utilisation and throughput occurs because
> >some bandwidth is wasted by collisions and back-off delays. In
> >practice, a busy shared 10 Mbps Ethernet network will typically supply
> >2-4 Mbps of throughput to the nodes connected to it.
> >"As the level of utilisation of the network increases, particularly if
> >there are many nodes competing to share the bandwidth, an overload
> >condition may occur. In this case, the throughput of Ethernet LANs
> >reduces very considerably, and much of the capacity is wasted by the
> >CSMA/CD algorithm, and very little is available for sending useful
> >data. This is the reason why a shared Ethernet LAN should not connect
> >more than 1024 computers. Many Engineers use a threshold of 40%
> >Utilisation to determine if a LAN is overloaded. A LAN with a higher
> >utilisation will observe a high collision rate, and likely a very
> >variable transmission time (due to back off). Separating the LAN in to
> >two or more collision domains using bridges or switches would likely
> >provide a significant benefit (assuming appropriate positioning of the
> >bridges or switches).
> >"Shared networks may also be constructed using Fast Ethernet, operating
> >at 100 Mbps. Since fast Ethernet always uses fibre or twisted pair, a
> >hub or switch is always required."
> >A home network with a handful of nodes would not normally be considered
> >a "busy network", so it does raise the question of what protocols are
> >in use on the network? Is a lot of unnecessary traffic being generated?
> >On the face of it, it does seem unlikely that a 10Mbps Ethernet should
> >not be able to keep pace with your 2Mbps/256kbps ADSL connection.