 be 1/622.08 X 106 = 1.60 ns UI. These 1.6 ns correspond to a phase of 360°. If 100 ps of jitter are present in the signal, the equivalent in UI will be 0.062208 UI, and the jitter phase will be 22.394°. A typical specification for jitter limits for a digital transmission system comprising many regenerators is given in Figure 2.20. In this figure, peak-to-peak jitter is expressed in clock periods and is plotted against jitter frequency. This representative example is based on figures given in ITU-T Recommendations G.823 and G.824. The figure serves to Chapter 2 Data Transmission (1.5) (0.2) 10,000 Jitter Frequency (Hz) Intermediate Fig. 2.20 Typical jitter limits for a digital transmission system. highlight the low-frequency timing jitter (or wander), which can amount to many clock intervals. Trends in Data Transmission Data transmission communications are evolving according to demand and advances in technology. With the aim of interconnecting everybody to everywhere, complex networks at different levels have appeared. Some examples of these types of data networks are Eth- ernet and 10G Ethernet, IP over DWDM, and video codecs. 10G Ethernet Ethernet is clearly the most widely understood LAN technology. The speed of Ethernet data transmission has grown enormously during the past years. Gigabit Ethernet delivers the scalable performance of Ethernet technology. Currently 10-Gbit/s Ethernet (10G Ethernet) is the highest standardized transmission speed in current use, although there is significant effort to raise this to 100 Gbit/s. 10G Ethernet links adopt full-duplex operation and use a fiber optic medium. SONET/SDH equipment can be used to provide long-distance data communications (see Chapter 10). Potentially carrier-class Ethernet (see Chapter 14) can simplify the architecture of communications networks. Applications like multimedia (videoconferencing and real-time backup) require a high amount of bandwidth from the LAN, which will demand far higher speeds. Ethernet local-area networks (LANs) usually operate from