| 摘要 |
<p>As an IP packet traverses across a network each node adds timestamp information to the header of the packet as well as information identifying the node e.g. IP address. The destination node, or an inline device, e.g. firewall, near the destination node, can determine from the timestamp information and identifying information contained within a received packet the progress of the packet across the network and determine overall and individual link latency calculations or general application latency. The timestamp information is added so that it is in a compressed form and recorded in the header of the packet. As a packet traverses the network multiple timestamps may be present in the packet header. The main embodiment described is to record the time stamp in a modulo 600 (modular arithmetic) format but the format (and size of the timestamp information) can be adaptable based on the accuracy required for latency calculations e.g. nanosecond, microsecond, millisecond resolution. The arrangement also requires that the clocks of all the nodes that place timestamps in the headers are synchronised to a common clock e.g. in accordance with Precision Time Protocol, (PTP, IEEE 1588-2002). The timestamps may be added to an IP header in the Option field as defined in RFC 791.</p> |
