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 that exceeds agreed-up capacity? 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.