Spider DSA User’s Manual
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PTP protocol to estimate delay, and, therefore, increase the precision to which the
clocks can be synchronized.
It is important to note the distinction between Ethernet “switches” and “hubs”.
Hubs are largely obsolete and work by blindly broadcasting transmissions
received on one port to every other port. They rely on collision detection among
the connected Ethernet devices themselves to allow multiple devices to
communicate. Switches, in contrast, use a store-and-forward mechanism to
transfer a transmitted packet received from one device to only the port (or ports,
for multicast messages) of the intended recipient. Switches can handle larger
amounts of traffic more reliably and are therefore more desirable than hubs.
Spider-HUB
The Spider-HUB is an advanced, managed
Ethernet switch (not a hub, despite its name)
manufactured by Crystal Instruments. It is
designed for the Spider platform. It fully
supports PTP and it can achieve a
synchronization precision of 20 ns with up to 8
Spider modules. In fact, it is the only switch that can synchronize Spider modules
this accurately.
Because it is PTP-enabled, it is aware of which ports are parts of the PTP sync
domain and which are not. It can then isolate the PTP multicast messages and
prevent external traffic from interfering with the synchronization.
The Spider-HUB does not have DHCP server, which means that when the Spider-
HUB is used, both the PC and all of the front-end hardware needs to be
configured with static IP addresses.
Cisco IE3000
The Cisco IE 3000 Series are also PTP-enabled managed Ethernet switches that
work with the Spider platform. Their performance is not as good as the Spider-
HUB, but they can still achieve synchronization
within 40 nanoseconds with up to 8 Spiders. A
drawback of these switches is that they require
a special power supply. They are also bulky and
less power efficient.
The Cisco IE 3000 has DHCP server support,
which means that the IP addresses of the host
PC and the front-end devices can be configured
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