Netgear XSM4324FS Software Administration Manual Software Version 12.x - Page 681

M4300 Series and M4300-96X Fully Managed Switches packet comes in to the device and is added to the correction field when the packet leaves the device. The result is that the correction field is updated with the period that the packet spends in the device. Two types of hardware time stamp operation exist, one of which is supported by the M4300 switches: • 1-step hardware time stamp. The hardware supports corrections, allowing the PTP packets to be modified as they pass through the device. The M4300 series switches support 1-step hardware time stamps only: The switch supports PTPv2 packets with a destination MAC address that is set to 01:1B:19:00:00:00. The switch does not support PTPv1 packets and drops those packets. The time stamp counter is 32 bits in length. • 2-step hardware time stamp. The hardware supports recording of time stamps of the PTP event packets. This time stamp is then retrieved by the local CPU on a device that supports the PTP firmware and is sent in a separate message. The M4300 series switches do not support 2-step hardware time stamps. PTP Transparent Clocks A transparent clock is a PTP device that does not process PTP packets, but modifies them to account for the residence time correction. That is, the device measures the period that the PTP packets require to pass through the device, and then adds that time span to the PTP packets. A transparent clock measures the variable delay as the PTP packets pass through a device. The measured delay is calculated by adding the residence time into the correction field of the PTP packet. A transparent clock can be an end-to-end (E2E) clock or a peer-to-peer (P2P) clock. An E2E transparent clock updates the correction field of the PTP packet only with the residence time. A P2P clock can update the correction field with the residence time of packet and the path delay. All M4300 series models support a PTP E2E transparent clock, with the exception of models M4300-24X24F, M4300-48X, and M4300-48XF. The following limitations apply to a PTP E2E transparent clock on an M4300 series switch: • You cannot configure a PTP E2E transparent clock at VLAN level. However, the feature functions well for VLAN-tagged packets. • The PTP E2E transparent clock is intended for a standalone switch only. In a switch stack, a PTP E2E transparent clock is enabled by default only on the master unit. You cannot enable the feature on member ports. • The PTP E2E transparent clock supports only the following three types of PTP event packets: Sync, Delay_Req, and Delay_Resp. PTP End-to-End Transparent Clock 681 Software Administration Manual