IPA and IPTNetworkingGeneralRules of Thumb See below for more details. System sizes are forexample only^*. System Size System Switch Requirement Small 1-10 IPTs Up to 3 layer-2 hops between PTP Master and IPTs Clear-Com AES67 Traffic Only DiffServ QoS Medium 10-30 IPTs Up to 3 layer-2 hops between PTP Master and IPTs Clear-Com AES67 Traffic Only DiffServ QoS IGMP Snooping IGMP Querier Large > 25 IPTs > 4 layer-2 hops between PTP Master and IPTs Mixed network traffic DiffServ QoS IGMP Snooping IGMP Querier PTP-aware Transparent and/or Boundary Clocks *E.g. Even a "small" system would requirePTP-aware switches if using more than 3 switches between master and slave. In terms of tolerance, note the Offset fromMaster and Mean Path Delay shown per transceiver (IPT) in EHXMonitoring.



















The following figures are guidelines rather thanrigid rules. Tolerances will vary depending on the use of external PTP masterclocks and where transceivers (and IPA card) are located in the networkrelative to the master clock.
Parameter
Value (range) State Offset from Master (ns) ± 100 ns Excellent   ± 500 ns Potential for roaming issues   ± 1000 ns Issues with roaming likely   > ± 1000 ns Cannot roam between transceivers and intermittent loss-of-lock issues Mean Path Delay (ns) > 2000000 ns (2 ms) Issues with audio likely   QoS AES67 QoS values are used: Class name   Traffic type Default DiffServ class (DSCP decimal value) Clock IEEE 1588-2008 Announce, Sync, Follow_Up, Delay_Req, Delay_Resp, Pdelay_Req, Pdelay_Resp and Pdelay_Resp_Follow_Up packets   EF (46) (Expedited Forwarding) Media RTP and RTCP media stream data AF41 (34) (Assured Forwarding) Best Effort IEEE 1588-2008 signaling and management messages. Discovery and connection management messages.   DF (0) (Default Forwarding)
Note this is DiffServ (RFC2474)and a switch with CoS is not sufficient. QoS is mandatory for a system of anysize due to PTP clocking constraints. The switch must therefore supportDiffServ QoS and must be set to operate with the values above. Clock traffic mustbe configured in Strict Priority mode (not weighted round-robin)to ensure immediate delivery over other types of traffic.
IGMP andMulticast AES67 & PTP makes use of multicast.  To prevent multicast flooding (broadcast) thefollowing is required:·       IGMPSnooping Enabled (per switch).·       IGMP Querierenabled on the network (one only). For E-IPA & IPT, multicast is only used forDiscovery (mDNS) and PTP.Audio is sent Unicast but using IGMP is essentialfor other AES67 devices in the same VLAN as well as management of PTP traffic. Warning: If IGMPSnooping is enabled on any switch, there must be an IGMP querier enabledon the network. Multicast traffic can be blocked from reaching a certainendpoint if a querier is not enabled. A switch will eventually forget about amulticast group request from an endpoint. The switch would then stop forwardingthat multicast traffic to the endpoint. If PTP (which is multicast) stopsreaching a transceiver, it will disconnect from the system. All beltpacks wouldbe forced to roam and communications would fail if the beltpacks cannot allroam to a different transceiver. PTP E-IPA-HX uses the AES67 media profile. This is notuser configurable. The definition of the term “profile” may varydepending on switch manufacturers.  Forexample, the Cisco IE 4010 switch has the concept of “profile” but none of thepossible options includes a “AES67 media profile”.  In cases where the “AES67 media profile” is notavailable or specified, the user should make sure the boundary clock switch orgrand master clock respects the following criteria:-        PTPmessages sent using layer 3 IP packets-        PTPQoS setting must use DSCP tagging with type “expedited forwarding” (i.e. DSCP46)-        Syncmessages sent every 125 ms (Sync Interval overleaf)-        Masterannouncement messages sent every 2 seconds (Announce Interval overleaf)
The attribute values are detailed below.  Attribute Value Description Domain Number 0 The domain attribute of the local clock.   Announce Interval 1 The mean time interval between Announce messages. A shorter interval allows faster reactions to the changes in the master-slave hierarchy. The interval should be the same in the whole domain. It's specified as a power of two in seconds. So here 2¹ = 2 seconds between messages. Adapted from <https://linux.die.net/man/8/ptp4l> Sync Interval -3 The mean time interval between Sync messages. A shorter interval may improve accuracy of the local clock. It's specified as a power of two in seconds. 2^-3 = 0.125 = 8 per second. Adapted from <https://linux.die.net/man/8/ptp4l>   Min Delay Req Interval 0 The minimum permitted mean time interval between Delay_Req messages. A shorter interval allows faster reactions to the changes in the path delay. It's specified as a power of two in seconds. 2⁰ = 1 second. Adapted from <https://linux.die.net/man/8/ptp4l> Announce Receipt Timeout 3 The number of missed Announce messages before the last Announce messages expires. From <https://linux.die.net/man/8/ptp4l> Priority1 254 (IPT)   127 (IPA) The priority1 attribute of the local clock. It is used in the best master selection algorithm, lower values take precedence. Must be in the range 0 to 255. The default value for a generic AES67 device is 128. IPTs (transceivers) are priority 254. E-IPA-HXs (card) are priority 127. Adapted from <https://linux.die.net/man/8/ptp4l>  PTP Aware Switches To minimise jitter, larger systems require PTP-aware switches, which stamp PTP packets to account for the residence time in the switch. Such switches are termed Transparent clocks. To reduce load on the PTP Grandmaster Clock and clock offset  (Offset from Master), Boundary Clocks can be used. These receive PTP from a Master and serve PTP (as Master) to all other connected devices. Using the guidelines above will determine the need for PTP aware switches. The necessity of such switches depends on the physical size of the network (in terms of number of switches) and the number of devices on the network. Other Switch Parameters·        1 Gbps on all interfaces.·        Capable of switch full bandwidth of all ports.o   E.g. 24 1Gbps ports = 48 Gbps switching capacity.·        EEE (Energy Efficient Ethernet) disabled.
Example Switches·        PTP Aware:o   Luminex GigaCore26io   Cisco IE 4010·        Non PTP Aware:o   Cisco SG300 (EOL, being replaced by SG350)