The American National Standards Institute ANSI

2 SONETSDH and the Generic Frame Procedure GFP So far, we have witnessed the development of three generations of digital transport tech- nologies for telephony: PDH, SONETSDH, and G.709. The first generation of digital transport technology was the plesiochronous digital hierarchy PDH, of which the North American standard T1 and the ITU-T equivalent standard E1 are probably the most well-known transport schemes. T1E1 was first deployed in the early 1960s to transport voice traffic. The synchronous optical net work SONET was proposed by Bellcore now Telecordia in 1985, and it can be seen as the second generation of digital transport networks. SONET was designed to multiplex PDH signals and transmit them optically between equipment made by different manufacturers. SONET was not designed, however, to address the needs of the European community, which used the ITU-T plesiochronous digital hierarchy. In view of this, ITU-T adopted the synchronous digital hierarchy SDH as the international standard. SONET is compliant with SDH. SONET and SDH were also defined to carry ATM cells and PPP and HDLC frames. The third generation digital transport network is the ITU-T standard G.709, other- wise known as the digital wrapper. This is a new standard that takes advantage of the wavelength division multiplexing WDM technology. It can carry IP packets, ATM cells, Ethernet frames, and SONETSDH synchronous traffic. In this chapter, we focus on the SONETSDH transport technology. The G.709 standard is described in Section 9.3, since the reader is required to have knowledge of the WDM optical technology. We first start with a description of T1 and E1, and then we present in detail the SONETSDH hierarchy, the SONET STS-1 frame structure, overheads, payload, and the SONET STS-3 frame structure. Subsequently, we describe the SONETSDH devices and SONETSDH rings. One of the main features of SONETSDH rings is that they are self-healing. That is, a SONETSDH ring can recover automatically when a fiber link fails. This failure can occur when a fiber is accidentally cut, when the optical components used to transmit on a fiber fail, or the SONETSDH switch fails. We will describe various architectures for self-healing rings, such as two-fiber and four-fiber protection schemes. We conclude this chapter with a description of the generic framing procedure GFP and data over SONETSDH DoS. GFP is a lightweight adaptation scheme that permits the transmission of different types of traffic over SONETSDH and, in the future, over Connection-oriented Networks Harry Perros  2005 John Wiley Sons, Ltd ISBN: 0-470-02163-2