Tham khảo tài liệu 'giáo trình cis+ part 92', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | complex. Every time interval Tc you get Bc tokens and Be tokens. In the case that you are not setting the DE on any frames data received by the FR switch decrements credits from the Bc pool until exhausted. Suppose the FR switch now receives a frame but there are no Bc tokens left you will get more Bc tokens in the next time interval at the time. The FR switch will check for a Be token and if you have one it will mark the DE field and transmit the frame across the network and decrement tokens from the Be pool. Keep in mind that the Be pool represents your burst capabilities over and above the CIR. IOW Be tokens keep track of the EIR and Bc tokens keep track of the CIR. Suppose the Be pool is exhausted and the Bc pool is exhausted and another frame arrives. It is dropped period. At the next time interval you will get more Bc and Be tokens to use. What happens if you mark your own DE frames Well when the ingress FR switch receives a non DE-marked frame it will subtract against the Bc token pool. If it receives a DE-marked frame it will subtract against the Be token pool. If it receives a non DE-marked frame but there are no Bc tokens left the FR switch will mark it DE transmit it and subtract Be tokens. If it receives any frame regardless of DE or non DE-marked and there are no Bc or Be tokens left the frame is dropped. So really the use of marking your own DE frames simply allows you to be the master of your own destiny by categorizing your own data intelligently instead of letting the FR switch do it based simply on the order of arrival. And the reason you want to mark your own packets has to do with how the network handles congestion see below where I talk about BECN etc. A couple of points are worth making. First you cannot accumulate tokens over time. There is a maximum amount which is the value of the committed burst Bc and this value has a mathematical relationship with the CIR CIR Bc Tc also EIR Be Tc . In almost all cases Tc is set to 1 second so the result
