- play_arrow Overview
- play_arrow Global Navigation Satellite System (GNSS)
- play_arrow GPS Systems on Routing Platforms
- play_arrow Integrated GNSS on Routing Platforms
- play_arrow GNSS Configuration for Routers Using External GNSS Receiver
- play_arrow Assisted Partial Timing Support (APTS) on Routing Platforms
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- play_arrow Network Time Protocol
- play_arrow NTP Concepts
- play_arrow NTP Configuration Examples
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- play_arrow Synchronous Ethernet
- play_arrow Synchronous Ethernet Overview
- play_arrow Synchronous Ethernet on 10-Gigabit Ethernet MIC
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- play_arrow Clock Synchronization
- play_arrow Clock Synchronization Concepts
- play_arrow Clock Synchronization for ACX Series Routers
- play_arrow Clock Synchronization for MX Series Routers
- play_arrow Clock Synchronization for PTX Series Routers
- play_arrow Centralized Clocking
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- play_arrow Hybrid Mode
- play_arrow Hybrid Mode Overview
- play_arrow Hybrid Mode and ESMC Quality-Level Mapping
- Configure Hybrid Mode and ESMC Quality-Level Mapping Overview
- Configure Hybrid Mode with Mapping of the PTP Clock Class to the ESMC Quality-Level
- Configure Hybrid Mode with a User-Defined Mapping of the PTP Clock Class to the ESMC Quality-Level
- Example: Configure Hybrid Mode and ESMC Quality-Level Mapping on ACX Series Router
- Example: Configure Hybrid Mode and ESMC Quality-Level Mapping on MX240 Router
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- play_arrow Configuration Statements and Operational Commands
- play_arrow Appendix
PTP over Ethernet Overview
PTP over Ethernet provides effective implementation of packet-based technology that enables the operator to deliver synchronization services on packet- based mobile backhaul networks that are configured in Ethernet rings.
Precision Time Protocol (PTP) is supported over IEEE 802.3 or Ethernet links on ACX Series routers. This functionality is supported in compliance with the IEEE 1588-2008 specification. Deployment of PTP at every hop in an Ethernet ring by using the Ethernet encapsulation method enables robust, redundant, and high-performance topologies to be created that enables a highly precise time and phase synchronization to be obtained.
The ACX Series routers can be directly connected to different types of base stations (for example, base transceiver station (BTS) in 2G, NodeB in 3G, and eNodeB in 4G networks) and different types of routers that hand off time- division multiplexing (TDM), ATM, and Ethernet traffic to the base station controller. ACX Series routers must extract the network clock from these sources and pass on synchronization information to the base stations to help the routers synchronize with the base station controller.
Most of the network deployments that use Ethernet contain a minimum of two Ethernet rings, while some of the network topologies might also contain up to three Ethernet rings. Consider a scenario in which the first ring contains aggregation routers (MX Series routers) and the second ring contains access routers (ACX Series routers). In such a network, about 10 or 12 nodes of MX Series routers and ACX Series routers are present in the aggregation and access Ethernet rings.
Some of the 4G base stations that are connected to ACX Series routers need to receive the timing and synchronization information in a packet-based form. Such base station vendors support only packet interfaces that use Ethernet encapsulation for PTP packets for time and phase synchronization. Therefore, any node (an ACX Series router) that is directly connected to a 4G base station must be able to use the Ethernet encapsulation method for PTP on a timeTransmitter port to support a packet-based timing capability.
PTP over Ethernet encapsulation also facilitates an easier, optimal network deployment model than PTP over IPv4. Using IPv4, the nodes (timeTransmitter and timeReceiver devices) participate in unicast negotiation in which the timeReceiver node is provisioned with the IP address of the timeTransmitter node and requests unicast messages to be sent to it from the timeTransmitter node. A timeTransmitter node is the router that functions as the PTP server where the timeTransmitter clock is located and a timeReceiver node is the router that functions as the PTP timeReceiver where the timeReceiver clock is located. Because PTP over Ethernet uses multicast addresses, the timeReceiver node automatically learns about the timeTransmitter nodes in the network. Also, the timeReceiver node is able to immediately receive the multicast messages from the timeTransmitter node and can begin sending messages to the timeTransmitter node without the need for any provisioning configuration.
An interface on which the timeTransmitter clock is configured is called a timeTransmitter interface and an interface on which the timeReceiver clock is configured is called a timeReceiver interface. A timeTransmitter interface functions as the timeTransmitter port and a timeReceiver interface functions as the timeReceiver port. For PTP over Ethernet, apart from configuring a port or a logical interface to operate as a timeTransmitter clock or a timeReceiver clock, you can also configure a port or a logical interface to function as both a timeTransmitter clock and a timeReceiver clock. This type of port is called a stateful port, or a bidirectional port. Such a stateful port enables the network to more efficiently adapt to the introduction and failure of timing sources by forming the shortest synchronization trees from a particular source. This behavior is implemented as defined by the best timeTransmitter clock algorithm (BTCA) in the ITU-T G.8265.1 Precision time protocol telecom profile for frequency synchronization specification.
On both MX Series and ACX Series routers, you can achieve the highest quality performance if you configure every node in a synchronization chain as a PTP boundary clock. In Ethernet ring-based topologies, you can configure a port or a logical interface to function either as a timeTransmitter port or as a timeReceiver port to enable redundancy when a node or link failure occurs. This stateful port or dual-port functionality is in accordance with the IEEE 1588-2008 standard and enables the implementation of PTP in data center or financial applications.
Apart from enabling every node to be available for configuration as a PTP boundary clock, it is also necessary to enable a logical interface to be configured either as a timeTransmitter port or a timeReceiver port. When you configure a logical interface or even a shared IP address to be a timeTransmitter port or a timeReceiver port, a PTP protocol stack can represent dynamic ports and the PTP application selects the correct state (timeTransmitter or timeReceiver) for any specific port in the system based on the output of the default PTP BTCA and the states of other ports in the system.
While an ACX Series router supports the PTP over Ethernet functionality, a TimeTransmitter such as an MX Series router or a TCA Series Timing TimeReceiver does not support PTP over Ethernet. In such a scenario, the ACX Series router functions as a boundary clock with a PTP timeReceiver port using IPv4 as the encapsulation mode and timeTransmitter ports using Ethernet as the encapsulation mode for PTP traffic. For example, consider an ACX Series router named ACX1 to have two potential timeReceiver interfaces, one that is fixed as a timeReceiver-only port using IPv4 on the link toward an MX Series router named MX1, and a stateful port that functions as a timeReceiver port using PTP over Ethernet on the link toward another ACX Series router named ACX2. In addition, ACX1 also contains a port that is a timeTransmitter-only port using PTP over Ethernet and connects to the base station.
Because PTP over Ethernet uses multicast addresses, a timeReceiver port can automatically start receiving the multicast announce messages transmitted by the timeTransmitter ports on a network and can also start communication with the timeTransmitter node with minimal or no configuration. Unlike PTP over IPv4 where IP addresses are used to identify the timeTransmitter and timeReceiver ports, with PTP over Ethernet, multicast MAC addresses are used in the forwarding of PTP traffic. The IEEE 1588 standard defines two types of multicast MAC addresses 01-80-C2-00-00-0E (link local multicast) and 01-1B-19-00-00-00 (standard Ethernet multicast) for PTP over Ethernet operations.