Brainstorm Electronics DXD/GPS, Руководство по эксплуатации

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DXD/PTP/GPS User Manual (rev 2.10) Page 17
12.7. DELAY MEASUREMENT MECHANISM
To synchronize clocks, the delay between the clocks must be known. There are two mechanisms to measure the delay called
End to End (E2E) and Peer to Peer (P2P).
•The E2E delay mechanism was the only one included in the original IEEE1588-2002. It measures the delay between
the master and the slave.
E2E uses the following messages, as described in 1.6. above: Sync, Follow-up (optional), Delay_Req, and Delay_Resp.
It can be used with switches or routers that are not 1588 capable.
•The P2P delay mechanism was introduced in IEEE15880-2008. It measures the delay between directly connected
ports. Peer-to-peer delay measurement works “locally”, from every node to each of its neighbors. For each pair of
directly connected ports, each end periodically measures the round-trip network delay by sending a Pdelay_Req
message and receiving in response a Pdelay_Resp message. This way all ports learn the delay on their link.
P2P uses messages Pdelay_Req, Pdelay_Resp, and Pdelay_Resp_Follow_Up (optional).
NOTE: An ordinary clock, which has just one port, can be configured for end-to-end or for peer-to-peer; a boundary clock,
which can have a single slave port and multiple master ports, can be configured for E2E on some ports and P2P on others.
While a single domain can have both end-to-end and peer-to-peer delay mechanisms running simultaneously, all clocks on a
single PTP communication path must use the same method to measure the time delay.
12.8. TYPES OF CLOCKS
IEEE 1588 defines three different types of clocks:
•Ordinary Clock (OC)
•Boundary Clock (BC)
•Transparent Clock (TC)
Ordinary Clocks (OC) are devices with a single port, usually at either end of a network such as A/V equipment, DAW’s or
speakers. They can be master or slave.
Boundary (BC) and Transparent (TC) Clocks are network devices such as switches or routers.
Since the DXD-8 has 1 Ethernet port, it is an ordinary clock (OC).
12.9. PTP DOMAINS
A PTP domain is a network (or a portion of a network) within which all of the clocks are in sync. A single network can have
multiple PTP domains operating separately, e. g., one set of clocks synchronized to one time scale and another set of clocks
synchronized to an other time scale.
12.10. PTP PROFILES
A PTP Profile defines the range and default values of all configurable attributes as well as all required, permitted, or prohibited
clock types and options for a specific application area. Profiles can be created by recognized standards associations such as
AES or SMPTE. The DXD supports the AES67 Media profile and the SMPTE ST-2059-2 profile. The DXD also support the 1588
default profile.
12.11. EPOCH
PTP uses the concept of an Epoch clock. This is an absolute time value when the clock was set to zero, and the number of
1GHz clock pulses that have occurred since provides the current time, converted with software into year, month, day, hours,
minutes and seconds. The Epoch (or zero time) for PTP was set at midnight on the 1st January 1970.