Transit delay and queueing
The recently finalized sFlow Transit Delay Structures extension provides visibility into the performance of packet forwarding in a switch or router using the industry standard sFlow protocol.
The diagram provides a logical representation of packet forwarding. A packet is received at an Ingress Port, the packet header is examined and a forwarding decision is made to add the packet to one of the queues associated with an Egress Port, finally the packet is removed from the queue and sent out the Egress Port to be received by the next device in the chain.
The time between sending and receiving a packet is the packet's transit delay. The transit delay is affected by the time it takes to make the forwarding decision and the time the packet spends in the queue. Identifying the specific queue selected and the number of bytes already in the queue fills out the set of performance metrics for the forwarding decision. The sFlow Transit Delay Structures extension adds these performance metrics to the metadata associated with each packet sample.
The following output from sflowtool shows that data contained in a packet sample:
startSample ----------------------
sampleType_tag 0:1
sampleType FLOWSAMPLE
sampleSequenceNo 91159
sourceId 0:2216
meanSkipCount Continue reading
