Load Shedding

The term load shedding is borrowed from electrical power supplies - if not all demand can be met, some section is deliberately disadvantaged.

The approach is to discard packets when they cannot all be managed. If there is inadequate router memory (on queues and/or in buffers) then discard some incoming packets.

Load shedding must be performed under many constraints:

• Must balance 'reasonable delay' and 'user freedom'.
• Maintain fair access to the network for all users.
• Respect rights (privileges) of priority users.

A number of reasonable strategies exist for discarding packets:

• consider the priority of each packet (don't drop high priority packets). We also need a strategy to encourage senders to send low-priority packets.
• don't discard ACKs, throw out DATA instead.
• make packets carry a hop counter, don't discard a DATA packet if it has travelled a long way. Instead discard one that has only travelled a short distance.
• examine the type of traffic being carried (perhaps by its priority). File transfers must eventually see all frames - all discarded frames will be retransmitted. Discard frames with high sequence numbers, not low numbers. Multimedia data will likely not retransmit old frames, only new frames are of interest.