Defining the Bandwidth Product
Answer the following questions to define the bandwidth
product.
- How will buyer traffic
be identified? Merkato must be able to distinguish between data
belonging to each buyer so that bandwidth can be apportioned correctly.
The most common identifier is an IP subnet—identified by an IP address
and subnet mask. Traffic can also be identified by the physical port or
logical interface to which a buyer is connected, by VLAN tags on the buyers’
data streams, or by the MAC address of the next-hop router from which
a buyer’s traffic flows. (All buyers within the same marketplace should
use a common method for identification of their traffic to avoid unnecessary
complexity.)
- In what direction will
bandwidth be apportioned? Although buyer traffic nearly always flows
both in and out of any interface, it is often unnecessary to apportion
bandwidth in both directions. Generally, there is an obvious direction
that corresponds to the application being addressed. For example, if you
use Merkato to apportion bandwidth among content providers, the direction
to control would be from the source of content to the receivers of that
content. If there is no obvious direction, Merkato can be used to apportion
bandwidth in both directions simultaneously. It is also possible to use
Merkato to create separate markets for incoming and outgoing traffic,
but you should be careful that, if you grant bandwidth in one direction,
you allow sufficient bandwidth for protocol acknowledgements in the other
direction.
- How strictly do you
want to limit bandwidth? The most common method of enforcing bandwidth
limits is the least forgiving—to discard any traffic that exceeds the
amount of bandwidth purchased. In some cases, however, you may wish to
allow excess traffic to be sent if there is sufficient unused capacity.
We only recommend allowing this permissive behavior in unique applications.
When taken to extremes, any buyer could use the whole amount of bandwidth
for sale during periods when no other buyers happen to be sending data.
The result is that your buyers will not be purchasing bandwidth, but rather
be purchasing bandwidth insurance—guarantees of a minimum amount of bandwidth
during periods of congestion. Buyers may discover that they need to purchase
only the absolute minimum amount of bandwidth except during times of network
congestion, so the market for bandwidth tends to be very limited unless
congestion is very common.