AoIP Clocking
AES67 and ST 2110-30 AoIP networks require devices to be synchronized to a common external clock source using IEEE 1588-2008 Precision Time Protocol (PTPv2). One device on a network will need to function as the 'Primary Leader' clock and all other devices will sync to this across the network. Most of the time a specialized PTP leader clock, synced to GPS for timing reference, is used to enable precise timing accuracy lower than 1 microsecond in many instances. Before enabling AES67 streaming it is necessary to ensure the codec is synced to a PTP leader clock source which is running. Most of the time the default settings will work fine. The codec can also act as the Primary Leader PTP clock source. Tieline recommends no more than 10 PTP followers are used in this mode. It is also possible to select Livewire as the AoIP clock source.
Tieline codecs support packet timing from 125 microseconds to 5 milliseconds. WheatNet-IP uses 250 microsecond packet timing by default and this is also supported by Telos xNodes and many other AES67 devices. At the time of writing Dante does not support this packet size and neither do Comrex AES67 codecs. The 1.25 millisecond (surround streams) frame size is unique to Livewire.
Sample Rates
The AES67 standard supports 44.1kHz, 48kHz and 96kHz sampling frequencies and most of the time AoIP systems run using 48kHz, 24 bit PCM digital audio. The rate of the media clock should also be the same as the sampling frequency. AES67 compatible devices should support:
•16 bit, 44.1kHz sampling.
•16 bit and 24 bit, 48kHz sampling.
•24 bit, 96kHz sampling.
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Important Notes: It is not possible to enable Livewire as a service if the sample rate is not configured as 48kHz. If Livewire is running the sample rate cannot be changed from 48kHz. |
PTP Settings
PTP Domain Number
A domain is an interacting set of clocks that synchronize to each other using PTP. Clocks are assigned to a domain using the Domain number and the default domain is 0 which is usually ok unless there is a requirement for multiple clock domains in a network. Adjust as required when on a network with multiple leader clocks in different domains.
PTP Delay Mechanism
PTP provides three different methods of calculating delay within a network: End-to-End (E2E), End-to-End Hybrid (E2E Hybrid), and Peer-to-Peer (P2P).
The default setting is usually E2E and this is automatically configured in the codec. If connected to a large PTP network without boundary clocks, End-to-End Hybrid mode may sometimes be preferred to support other AoIP devices that do not support delay request loads. This mode is more efficient with regard to PTP messages. It includes a mix of multicast and unicast PTP messages, to avoid follower clocks being bombarded by delay requests and responses.
Time to Live (TTL)
To avoid network congestion Time to Live configures the number of times a packet is allowed to pass through a multicast router before it will no longer pass the packet.
Announce Interval
The Announce Interval is configured by a PTP Leader and sets the announce message rate for a Precision Time Protocol (PTP) follower.
Announce Receipt Timeout
Use the Announce Receipt Timeout setting to configure the timeout value for receiving announce messages.
Allow Primary Leader
Select the Allow Leader check-box to set the codec as a PTP Leader clock across an AES67 AoIP network.
Priority 1 and 2
Priority 1 and Priority 2 configure the user-assigned priority, ranging from 0-255, given to each PTP clock. The default setting is 255 which is appropriate for the codec as a PTP follower and this can be adjusted as required.
Sync Interval
The Sync Interval sets the mean interval to send synchronization messages across the AoIP network.
PTP status
The PTP clocking status is displayed in the Synchronization panel.
If a Livewire Clock is in use then status is displayed in the Livewire Clock Status pane.
Livewire Clock Settings and Status
When streaming using Livewire+ the codec can be synced to a PTP clock or a Livewire device acting as the clock leader. Livewire systems can automatically change to a different clock leader if the current leader clock is disconnected or otherwise inoperable. This can be managed using the Leader Priority setting. Livewire Clock Settings are displayed for a follower codec.
Leader Priority
With Livewire each node has a clock leader configuration setting ranging from 0 to 7. Livewire clock Leader Priority 3 is the default suggested for a typical Livewire network. When a higher priority number is given to a node this will define which device becomes the network clock leader. A value of 7 insists a device becomes the clock leader. In summary:
•‘0’ means never a leader - follower only
•‘7’ means always - forced leader (note, do not use multiple forced leaders in a system)
•Factory default is 3. So all units have equal priority out of the box, and the following is used to break ties (in descending order): lowest Livewire+ audio transmit base channel, then lowest IP address, then lowest Ethernet address.
If no clock is present then devices negotiate a clock leader using Leader Priority settings and the lowest MAC address.
Sync to PTP
Sync to PTP is usually selected if your network uses PTP for synchronization. All devices should enable this setting if PTP is in use, unless the Leader Priority setting is 0. When Sync to PTP is configured in Livewire Clock Settings it synchronizes the Livewire clock to the PTP clock when the codec is the Livewire clock master.
Enable VLAN Tagging
Select Enable VLAN Tagging to configure VLAN tagging for packet prioritization across the network.
VLAN Priority
The recommended setting for AES67 is to set the VLAN Priority level at 6. Note: When operating in AVB networks the recommended setting is 5.
QoS DSCP
The QoS DSCP field in an IP packet header allows the network to easily recognize packets that need to be treated preferentially when traversing IP networks. AF41 (34) is the default setting and recommended for AES67. EF (46) is used for expedited forwarding of PTP clock packets.
Livewire Clock Status
Livewire Clock Status is displayed for leader and follower codecs when Livewire is in use.
When Livewire is not in use the Livewire Clock Status panel displays as follows.
