Elastic traffic marking for multi-priority packet streams in a communications network
Routers in a communications network mark packets of a multi-priority stream to establish a drop precedence of the packets during network congestion. For each packet received, a router employs one of two types of packet-marking mechanisms to associate low drop precedence with a high-priority, out-of-profile packet. One type, called “token bucket with loan bucket,” uses a token bucket to determine whether a packet is in conformance, i.e., in-profile, with a traffic profile and at least one loan bucket to determine whether a high priority, out-of-profile packet may borrow bandwidth. Another mechanism type, called “token bucket with color-exchange queue,” uses a color-exchange queue to delay packet forwarding for a fixed period. During this delay, a high-drop-precedence marking of an out-of-profile, high-priority packet may be exchanged with a low-drop-precedence marking of an in-profile, low-priority packet. The packet-marking mechanisms are useful in improving the quality of video viewing.
1. In a communications network, a method for marking a packet of a multi-priority stream to establish a drop precedence of the packet, the method comprising:
receiving a first packet and a second packet of the multi-priority stream, the first packet having a higher priority than the second packet;
determining that the first packet is non-conforming with respect to a traffic profile and that the second packet is conforming with respect to the traffic profile;
determining whether bandwidth can be borrowed for the first packet; and
if borrowing bandwidth for the first packet is permitted, associating the non-conforming, higher priority first packet with low drop precedence and the conforming second packet with high drop precedence; otherwise, associating the non-conforming, higher priority first packet with high drop precedence and the conforming second packet with low drop precedence.
2. The method of claim 1 , wherein the step of determining whether bandwidth for the first packet can be borrowed includes examining a loan bucket to determine whether a number of tokens in the loan bucket is less than a predetermined threshold.
3. The method of claim 1 , further comprising the step of adding at least one token to a loan bucket when the non-conforming first packet is associated with low drop precedence.
4. The method of claim 1 , wherein the step of associating the conforming second packet includes examining a loan bucket to determine whether the loan bucket contains any tokens.
5. The method of claim 1 , further comprising the step of forwarding the first packet over the communications network before the second packet is received.
6. The method of claim 1 , wherein the step of associating includes:
marking the non-conforming first packet with high drop precedence and the conforming second packet with low drop precedence; and
exchanging the high drop precedence marking of the first packet with the low drop precedence marking of the second packet before forwarding the first packet to the communications network.
7. The method of claim 1 , further comprising the step of placing each packet into a queue for a fixed period.
8. The method of claim 7 , further comprising the step of exchanging a marking of the first packet with a marking of the second packet when one of the first and second packets enters the queue.
9. The method of claim 7 , further comprising the step of exchanging a marking of the first packet with a marking of the second packet when one of the first and second packets exits the queue.