## 1 Introduction  
Since its first application in 1980, the global positioning system (GPS) has been recognized as an efficient tool for time and frequency transfer [1]. The GPS technique has been applied for time transfer with pseudo range measurements in the early days, which is referred to as common-view (CV) and all-in-view (AV) [1,2]. Due to the high-precision of the carrier phase measurement, the techniquesbased on code observations no longer provide the optimal time transfer solutions. Another approach, which could improve TAI (International Atomic Time) time links and TAI computation, was proposed in 2006 [3]; it is referred to as the carrier phase (CP) technique. By virtue of the precise orbit and clock products distributed freely and routinely by the IGS (International GNSS Service), precise point positioning (PPP) is one of the most promising time comparison techniques available, primarily because of its high-accuracy, cost-effectiveness, and global coverage [3; 4; 5]. PPP time transfer results have been used in TAI at BIPM (Bureau international des poids et mesures) since September 2009, and are involved in over 50% of the more than 70 timing laboratories' contributions to TAI and UTC (Coordinated Universal Time) [3; 6]. The PPP strategy has better short-term stability compared to code-only techniques. The statistical uncertainty is approximately 0.3 ns for PPP links in BIPM circular T, and the frequency comparison is approximately \(1\times 10^{-15}\) with a 1-d averaging time [6; 7]. In recent years, the research community has shown a growing interest in the PPP technique [8; 9; 10; 11]. To meet the increasing requirements of real-time PPP applications, the IGS initiated the IGS Real-Time Pilot Project (IGS-RTPP) in 2007 and provided the precise orbit and clock corrections [12; 13; 14]. [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] (2018) evaluated real-time precise orbits and clock products from different IGS analysis centres (ACs). The results indicated that the root-mean-square error (RMSE) of a satellite orbit ranges from 3.8 cm to 7.5 cm for different real-time service (RTS) products, while the mean standard deviations of errors (STDE) of the satellite clocks range from 1.9 cm to 5.6 cm. These data show that RTS products are suitable for PPP applications. [PERSON], [PERSON], [PERSON], and [PERSON] (2018) proposed models, algorithms and ionosphere applications of real-time PPP (RT-PPP). Their studies reveal that slant ionosphere delays from RT-PPP are more precise and have a much better convergence performance than those from the carrier-to-code levelling (CCL) method in real-time processing. Currently, PPP is mainly utilized in post processing as a crucial time transfer technique. A limited number of researchers attach great importance to RT-PPP time transfer techniques [15; 16; 17], employing continuous observation and products. However, as far as the practical application of RT-PPP time transfer is concerned, the problem is more complicated. There are numerous cases, which will significantly affect statistical uncertainty in RT-PPP time transfer. One case involves a data discontinuity from network problems [18] that leads to product loss or a delay in processing. The data discontinuity will cause a re-convergence of the clock parameters and the ambiguity parameters, or a clock jump. This is true for both static and kinematic models when the clock offset is modelled as white noise. This consequently gives rise to a degradation of the RT-PPP time transfer performance, as evidenced by the fact that ambiguity parameters will be initialized at the time of the data interruption, presenting a strong correlation with clock offset parameters. Until now, there has been no body of literature investigating the problem. These deficiencies of previous studies are the main drivers of this contribution, in which we demonstrate the efficiency of the clock model for instantly recovering clock offset, avoiding re-convergence when there is a data discontinuity in the RT-PPP time transfer data processing.