| > IEEE 1588 (PTP) in Communication |
This Application Note is about the new Precision Time Protocol (PTP), also know by the name of the corresponding standard, IEEE 1588. PTP is used for distributing synchronization over packet switched communication networks. This has become an important technology because of the recent move in telecommunications from traditional Time Division Multiplexed (TDM) networks to packet switched networks. In TDM networks the transfer of synchronization was a natural function of the physical layer of a traffic signal. With the introduction of packet-switched networks new protocol-based synchronization techniques were introduced because of the essentially asynchronous nature of packet switching. PTP is the result of a standardization effort which was initially done for industrial automation and measurement instrumentation.
With the second version of the standard, known as IEEE 1588-2008, this technology became available for other application spaces, including telecommunications.
The Application Note gives an overview of PTP technology and its applications. Companion Engineering Notes address more specific technical issues related to particular applications.
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| > Synchronization Networks Based on Synchronous Ethernet (SyncE) |
Telecommunication networks are evolving from TDM networks based on circuit-switched technology to so-called Next Generation Networks (NGN) based on packet-switching. The driver of this evolution is cost reduction; the technical goal is the transport of all telecommunication services over a unified and packet-switched platform. Ethernet is already playing an important role in the network convergence scenario. Ethernet started as a LAN technology for enterprise networks, and is now being used in base station backhaul and aggregation networks, and even in metro networks. It turns out that many access network technologies require some form of synchronization.
Traditional Ethernet is not designed for the transport of synchronization. Therefore the use of Ethernet in aggregation and backhaul networks is problematic for all access technologies in need of synchronization.
The answer to the problem for the case of frequency synchronization is Synchronous Ethernet (SyncE). Simply put, SyncE is traditional Ethernet plus a synchronization transport function similar to that in SDH and SONET. SyncE enables the transport of frequency synchronization. SyncE was standardized by the ITU-T in cooperation with IEEE. ITU-T recently published the three new recommendations dealing with SyncE.
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| > Cesium Clock and Hydrogen Maser Compared |
This Application Note compares two technologies often used as frequency sources in applications where highest frequency accuracy and stability are required.
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| > Holdover Autonomy of Synchronization Supply Units (SSU) |
This Application Note deals with the following question: "For how long may an SSU or SASE stay in holdover mode while guaranteeing normal operation of equipment and systems it synchronizes?" The answer to this question gives important indications on how fast synchronization failures should be repaired.
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| > The Synchronization of 3G UMTS Networks |
This Application Note presents a discussion of the synchronization issues in UMTS networks, and provides practical solutions for several UMTS network configurations. The paper addresses all variants of UMTS, i.e. UMTS-FDD and UMTS-TDD. In UMTS networks all network elements need some form of synchronization. The required synchronization accuracy and stability depend on the network element type. Most network elements must be synchronized in frequency. Base stations in the TDD variant of UMTS also require an external phase-alignment signal. The way to solve the synchronization question in UMTS networks depends very much on the transport network used to interconnect all the UMTS network elements. This Application Note details a number of practical solutions applicable to different transport network configurations. These solutions can be used for developing a synchronization design for any given real UMTS network.
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| > Synchronization Equipment for Power Distribution Networks |
This paper presents the power distribution network, its telecommunication network and the associated synchronization network as a layered system, in which lower network layers provide critical services for higher layer networks. The synchronization network distributes accurate, stable and reliable synchronization signals to all telecom equipment. This high quality synchronization supply is of paramount importance, since synchronization quality has a direct impact on the reliability and the real-time performance of the telecommunication services. These two properties are particularly important for telecommunication networks servicing power distribution networks, since they must be able to handle mission-critical communication traffic in failure situations such as over-voltage and short-circuit events. It appears that a well designed synchronization network is a pre-condition for the safe and reliable operation of any power distribution network.
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| > Holdover Autonomy of Timing Supply Generators and BITS Clocks |
This Application Note deals with the following question: "For how long may a TSG stay in holdover mode while guaranteeing normal operation of equipment and systems it synchronizes?" The answer to this question gives important indications on how fast synchronization failures should be repaired.
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| > Cellular Sync Networks for Telecom, based on GPS & SDH/SONET |
This paper presents a synchronisation method based on the Global Positioning System (GPS) for coarse distribution to a number of sub-networks, and on the SDH/SONET network for fine distribution to all nodes within the sub-networks. The method consists in partitioning the network at hand into sub-networks of predefined internal structure, and to interconnect the sub-networks according to well-defined rules.
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| > Retiming of PDH signals using the OSA RTU module |
Re-timing of PDH traffic signals using the Oscilloquartz Re-Timging Unit.
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| > How to Synchronise Telecommunications Networks |
To meet the telecommunication needs of a fast growing global economy, existing networks are being enhanced using new technologies and many new network operators are emerging after deregulation. Network synchronisation is very important for switching, transmission and data networks, such as telephony, Plesiochronous Digital Hierarchy (PDH), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), and Asynchronous Transfer Mode (ATM) networks. It is essential that the telecommunication systems in these networks are synchronised to meet the Quality of Service (QoS) demanded by network users. A network planner has to understand the object of network synchronisation, the related international specifications, the general synchronisation network design requirements, plus the merits and limits of different synchronisation methods before planning a synchronisation network.
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| > Applications of the Stand-Alone Synchronisation Equipment and SONET network |
Synchronous Digital Hierarchy (SDH) is a new international standard for transmission, agreed by the ITU-T in 1988. It is developed from Synchronous Optical Networks (SONET) previously defined by ANSI. Both SONET and SDH are designed to carry Plesiochronous Digital Hierarchy (PDH), and future transmission signals like Asynchronous Transfer Mode (ATM).
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| > Synchronisation of the Digital Telephony Network and the Plesiochonous Digital Hierarchy |
For the last several decades, the digital telephone switches, or exchanges, have been replacing the analogue mechanical exchanges. Digital exchanges are more reliable than the analogue exchanges. But they must be kept in close synchronisation with each other, in order to maintain their performance. For example, if the clock frequency of the transmitter exchange were running faster than the clock frequency of the receiver exchange, then some of the information transmitted would be lost. This phenomenon is referred to as slips.
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| > Evaluating measurement data from the OSA 5565 STS |
Evaluating measurement data to determine the effect of different noise sources generated by clock signals.
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| > OSA 5548B & SSMB Inter-working with SDH Equipment |
The OSA 5548B includes provisions for enhanced 2Mbit/s interfaces with Synchronisation Status Message (SSM) detection and generation. The SSMs are used in SDH networks to indicate the synchronisation quality carried by the aggregate STM-N signals.
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| > Multi-site PRC Systems |
Digital telecommunications networks require a reliable supply of accurate and stable synchronization. The synchronization reference frequency is usually generated by one or several Primary Reference Clocks (PRC) and distributed via a synchronisation network. The availability requirements of SDH based networks entail the use of multi-site PRC systems. This application note describes a step-by-step procedure for the design of an Oscilloquartz PRC system for a given network.
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