Precision Time Protocol (PTP)

The transition from synchronous transport methods to IP for production quality video and audio services implies a deterioration of the timing quality of the signals, since IP is a completely asynchronous transport format. IEEE 1588 (PTP) has been introduced to convey precise timing over an IP network. In the Studio LAN, reaching the required quality level of timing transport with PTP is manageable, but doing it in the WAN is very challenging. In practice the only wide area solution today is to use GPS controlled Grand Master (GM) clocks at each remote location to provide synchronization with sufficient quality. This scheme has some disadvantages in that it depends on that a GPS signal is always available, which may not be the case, for several reasons. The industry also needs solutions for PTP transport over the terrestrial WANs. We will describe the challenges with PTP over the WAN, but also show how a synchronous overlay on top of the IP network can provide sufficient PTP quality over the WAN for professional Audio and Video services without resorting to GPS controlled GMs at each end point. Real operational cases using this functionality will be described.

Synchronization networks have been critical components of wireless networks for many years. Introduction of advanced LTE services and G services poses new requirements for synchronization networks. This white paper describes synchronization requirements, technologies, as well as, synchronization standards and test and measurement applications. The paper closes with a description of ITU G.x/G.x standards for synchronization in wireless networks and highlights some of the main metrics and network limits relevant for deployment in field applications.

O artigo faz uma descrição sucinta dos protocolos IRIG-B e NTP, ressaltando suas vantagens e desvantagens, e
apresenta o protocolo IEEE1588 Precision Time Protocol (PTP), explicando sua filosofia de funcionamento,
vantagens e perspectivas do seu uso no setor elétrico brasileiro.

For the past two decades, the design of high-performance
stratum-1 NTP servers, those with internal means of
synchronization to hardware clocks, have involved the use
of specialized bus interface cards often utilizing
proprietary device drivers. Those commercially available
bus clocks provide memory-mappable time registers
synchronized to GPS or Master Clock time code (such as
IRIG-B and, more recently, IEEE 1588). Providing an
essentially global NTP service has proven costly for
timing labs as at the U.S. Naval Observatory. In 2007 a
trio of Hewlett-Packard Unix servers, each with two bus
clocks, and fronted by a redundant pair of IP load
balancers cost over $53 thousand in 2014 dollars. A
growing number of LAN-on-Motherboard (LoM) and bus
card Ethernet adapters are now providing support for
IEEE 1588 Precise Time Protocol, perhaps obviating the
need for costly synchronized bus clocks. Open-source
development projects at ntp.org, linuxptp.org, and
kernel.org have resulted in widespread access to PPS and
PTP hosted on low-cost platforms. To investigate the
utility of inexpensive network timing a pair of Supermicro
SYS-5015A-EHF-D525 servers with Intel® Atom
processors were integrated with PTP-enabled NICs, GPS,
and NTP and Linux PTP to test network timing in a PTP
Grandmaster/Slave configuration. Results of long-term
tests show quite satisfactory timing stability, well within
the range of NTP timing requirements.

Tight synchronization timing is expected to play a crucial role for the realization of emerging Internet of Things (IoT) high value real-time applications such as smart transportation and smart grid. Most packet-based synchronization protocols require two-way communications delay symmetry for precise accuracy. The Precision Time Protocol (PTP) provides mechanisms to measure and take into account the delay asymmetry problem, such as the residence time measurements, but recommend  PTP support at all nodes. In this paper, we consider partial on-path PTP support, where a subset of the nodes are PTP unaware. We propose probing-based mechanisms in order to estimate asymmetry and improve the synchronization performance. The extensive simulation results show that the proposed lightweight per-packet asymmetry mitigation (PPAM) mechanism, aiming at estimating the per-packet delay components, outperforms the other considered protocols mainly at low to mid network loads, while under certain conditions the regular PTP with QoS support provides more stable synchronization accuracy.

This work addresses an optimal Global Positioning System (GPS)-based synchronization loop for local clocks utilizing the one pulse per second (1PPS) timing signals. To eliminate sawtooth errors peculiar to the 1PPS signals and optimally steer the clock errors each M seconds, we propose using a ramp predictive finite impulse response (FIR) filter that is known to be optimal for clock models on large averaging horizons. A low-pass filter is used to smooth the hold filter output between the optimally predicted points. A GPS locked crystal clock has been investigated in detail in terms of the time interval error and precision time protocol (PTP) variance. A high efficiency implementation of the proposed synchronization algorithm is demonstrated experimentally.

A Mobile Ad hoc Network (MANET) is a collection of mobile stations with wireless interfaces which form a temporary network without using any central administration. MANETs are more vulnerable to attacks because they have some specific characteristics as complexity of wireless communication and lack of infrastructure. Hence security is an important requirement in mobile ad hoc networks. One of the attacks against network integrity in MANETs is the Black Hole Attack. In this type of attack all data packets are absorbed by malicious node, hence data loss occurs. In this paper we investigated the impacts of Black Hole attacks on the network performance. We have simulated black hole attacks using Network Simulator 2 (NS-2) and have measured the packet loss in the network without and with a black hole attacks. Also, we measured the packet loss when the number of black hole attacks increases.

If all clocks within a distributed system share the same notion of time, the application domain can gain several advantages. Among those is the possibility to implement real-time behavior, accurate time stamping, and event detection. However, with the wide spread application of clock synchronization another topic has to be taken into consideration: the fault tolerance. The well known clock synchronization protocol IEEE1588 (precision time protocol, PTP), is based on a master/slave principle, which has one severe disadvantage. This disadvantage is the fact that the failure of a master automatically requires the re-election of a new master. The start of a master election based on timeout and thus takes a certain time span during which the clocks are not synchronized and thus running freely. Moreover the usage of a new master also requires new delay measurements, which prolong the time of uncertainty as well. This paper analyzes the results of such a master failure and proposes democratic master groups instead of hot-stand-by masters to overcome this problem by. It is shown by means of simulation that the proposed solution will not deteriorate the accuracy of the slave clocks in case of a master failure.

This paper analyzes the factors that affect the synchronization performance in peer-to-peer precision time protocol (PTP). We first study the influence of frequency drift in the absence of jitter and compare the gravity of the master drift with that of the slave drift. Then, we study the influence of jitter under the assumption of constant frequencies and the effect of