System Connection (ESCON) are commonly used in modern Storage Area Networks (SANs), and for video distribution, Digital Video Broadcast-Asynchronous Serial Interface (DVB-ASI) is popular. Some of these protocols use line coding to communicate control codes between the end devices for various functions. If the frames from these protocols were carried with GFP-F, the 8B/10B control code information would be lost. Another consideration for the SAN protocols is that they are typically very sensitive to transmission delay (latency) between the two SAN nodes. Framed GFP requires the buffering of an entire client data frame to determine the payload length for the PLI field of the GFP header. For most applications, this is not a problem, but where transparency and low latency are required, transparent GFP should be employed. Conclusion As this chapter explained, the early deficiencies of Synchronous Digital Hierarchy have largely been addressed through the introduction of VCAT, LCAS, and GFP into what is now termed "next generation" SDH. The exponential growth in packet-based data and storage services will continue, and there will be competing technologies to NG-SDH in the next decade. However, with such a huge installed base of SDH worldwide, NG-SDH has fueled the continued growth of SDH equipment and is regarded as a trusted and robust technology for providing carrier-class wide-area networking of packet and storage services. Resources ANSI (2001) T1X1.5/2001/062, Revised Draft T105 Sonet Base Standard. IEEE Commun. Mag. May 2002, IEEE (1998) 802.3: CSMA/CD Access Method and Physical Layer Specifications. IETF (1990) RFC 2615, PPP over Sonet/SDH. ITU-T (2002) G.7041/Y.1303, Generic Framing Procedure. ITU-T (2001) G.709, Network Node Interface for Optical Transport Network. ITU-T (2001) Recommendation X.83/Y.1323, Ethernet over LAPS. ITU-T (2001) Recommendation X.85/Y.1321, IP over SDH Using LAPS. ITU-T (2000) G.707/Y.1322, Network Node Interface for the Synchronous Digital Hieracrchy. This page intentionally left blank