Synchronous Ethernet
Synchronous Ethernet, also referred as SyncE, is an ITU-T standard for computer networking that facilitates the transference of clock signals over the Ethernet physical layer.
Synchronous Ethernet Overview
Synchronous Ethernet (ITU-T G.8261 and ITU-T G.8264) is a physical layer technology that functions regardless of the network load and supports hop-by-hop frequency transfer, where all interfaces on the trail must support Synchronous Ethernet. It enables you to deliver synchronization services that meet the requirements of the present-day mobile network, as well as future Long Term Evolution (LTE)–based infrastructures.
Synchronization is a key requirement for circuit (emulation) services and mobile radio access technologies. Traditionally, mobile networks used SONET/SDH technologies to backhaul voice and data traffic, and the native support for frequency of SONET/SDH to synchronize their radio network. With the need for greater-capacity backhaul networks, packet-based technologies such as Carrier Ethernet (which do not support the transfer of frequency) and wireless technologies such as frequency division duplex and time-division duplex require not only frequency synchronization but also proper time and phase alignment. This requirement is fulfilled by Synchronous Ethernet, which is used for physical layer frequency synchronization of connected access devices (such as base stations, access nodes, and so on). Synchronous Ethernet supports sourcing and transfer of frequency for synchronization purposes for both wireless and wireline services and is primarily used for mobile backhaul and converged transport.
Synchronous Ethernet is used to transfer clock signals over Ethernet interfaces. The Synchronous Ethernet operation is described in three ITU recommendations:
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G.8261—Defines the architecture and wander performance of Synchronous Ethernet networks.
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G.8262—Specifies timing characteristics of synchronous Ethernet equipment clock (EEC).
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G.8264—Describes the Ethernet Synchronization Message Channel (ESMC).
Synchronous Ethernet is not supported in the following instances on an MX Series router:
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Slot 10 on an MX Series router with Switch Control Board (SCB).
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RJ45 ports
However, note that Synchronous Ethernet is supported on slot 10 on an MX Series router with SCBE and SCBE2.
Unified in-service software upgrade (unified ISSU) is currently not supported when clock synchronization is configured for PTP and Synchronous Ethernet on MX80 Universal Routing Platforms and on the MICs and MPCEs on MX240, MX480, MX960, MX2010, and MX2020 routers.
The following sections explain Synchronous Ethernet:
- Synchronous Ethernet Configuration
- Synchronous Ethernet over LAG
- Synchronous Ethernet on Routers
- Ingress Monitoring on Routers
- Supported Platforms
Synchronous Ethernet Configuration
SyncE configuration can be performed under the [edit chassis
synchronization] hierarchy. A configuration snippet is provided
below:
set chassis synchronization network-option option-1 set chassis synchronization selection-mode received-quality set chassis synchronization quality-mode-enable set chassis synchronization source interfaces ifname priority priority wait-to-restore sec quality-level quality-level set chassis synchronization esmc-transmit ifname
Synchronous Ethernet over LAG
Link aggregation enables to group Ethernet interfaces to form a single, aggregated Ethernet interface, also known as a link aggregation group (LAG) or bundle. The aggregated Ethernet interfaces that participate in a LAG are called member links.To configure synchronous ethernet over LAG, an aggregated-ether (AE) group shall be defined as the clock source. Any number of interfaces from the same AE group can be configured as the clock source. The ESMC transmit shall be configured on individual link.
A configuration snippet is provided below:
set interfaces ae0 aggregated-ether-options link-speed mixed set interfaces ae0 unit 0 family inet address 2.2.0.1/24 set interfaces et-0/0/2 ether-options 802.3ad ae0 set interfaces et-0/0/4 ether-options 802.3ad ae0 set chassis synchronization network-option option-1 set chassis synchronization source interfaces et-0/0/2 aggregated-ether ae0 set chassis synchronization source interfaces et-0/0/2 quality-level sec
Synchronous Ethernet on Routers
Synchronous Ethernet is supported on the ACX Series routers with Gigabit Ethernet and 10-Gigabit Ethernet SFP and SFP+ transceivers and is compliant with ITU-T Recommendation G.8261: Timing and synchronization aspects in packet networks and ITU-T Recommendation G8264: Distribution of timing through packet networks.Synchronous Ethernet is a physical layer frequency transfer technology modeled after synchronization in SONET/SDH. Traditional Ethernet nodes, which do not support Synchronous Ethernet, do not carry synchronization from one node link to another. Synchronous Ethernet–capable nodes however can synchronize their chassis clock to a clock recovered from an interface connected to an upstream primary clock . After this, the clock is used to time data sent to downstream clock secondary clocks, forming a synchronization trail from a Primary Reference Clock (PRC) to Ethernet equipment clocks (EECs) and transferring frequency synchronization along the trail.
The ITU-T G.8264 specification defines the Synchronization Status Message (SSM) protocol and its format for Synchronous Ethernet to ensure interoperability between Synchronous Ethernet equipment used for frequency transfer—for example, SONET/SDH. Synchronous Ethernet provides stable frequency synchronization to a PRC and is not affected by load on the network. However, it requires that all the nodes from the PRC to the last downstream node are Synchronous Ethernet capable. Synchronous Ethernet is a recommended technology for mobile networks that require frequency-only synchronization—for example, 2G or 3G base stations.
Ingress Monitoring on Routers
The ingress clock monitoring feature is supported on all MX Series routers including the 16-port 10-Gigabit Ethernet MPC. On these routers, the incoming Synchronous Ethernet signals cannot be monitored on the 16-port 10-Gigabit Ethernet MPC but are monitored by other Modular Port Concentrators (MPCs) in the chassis. Therefore, you can use the 16-port 10-Gigabit Ethernet MPC for incoming Synchronous Ethernet signals if at least one other MPC with an Ethernet Equipment Clock (EEC) is present in the chassis. This behavior is referred to as ingress clock monitoring. Note that the 16-port 10-Gigabit Ethernet MPC does not have a built-in EEC or internal clock; therefore, it can only input (accept) a clock signal but cannot act as a clock source.
When an MX Series router is configured for Synchronous Ethernet on the 16-port 10-Gigabit Ethernet MPC and no other MPC with an EEC is present in the chassis, the Synchronous Ethernet feature cannot be supported by the system. The system notifies the user through log messages and CLI output and justifies its inability to support Synchronous Ethernet.
Supported Platforms
Synchronous Ethernet (SyncE) summarizes the first Junos OS release that supports Synchronous Ethernet on the various Juniper Networks routers and their components.