maller containers can be concatenated to form a larger container. The contain- ers, typically STS-1s, are then routed across the network towards the same destination where the individual STS-1s are realigned and sorted to form the original payload. In OSI terms this technique sounds like a layer four process, doesn't it? Virtual concatenation has been defined for VT1.5, VT2, VT3, VT6, STS-1 SPE and STS-3c SPE containers. A virtually concatenated group is referred to as a Base Container-nv, where "n" is a number that indi- cates the number of containers of the base container type. For example, VT1.5-4v indicates that the group consists of four VT1.5s that are Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Chapter 3 virtually concatenated. This process of "payload channelization" is per- formed at the end points in the network. There are two different forms of virtual concatenation. If the channel rate is STS-1 and greater for a channel in a group, then high-order vir- tual concatenation (HOVC) is used. If the channel rate is below STS-1, then low-order virtual concatenation (LOVC) is used. The LCAS is a complementary technology to virtual concatenation. It facilitates the adjustment of the size of a group of channels that have been virtually concatenated. LCAS synchronizes transmission between the sender and receiver so that the size of a virtually concatenated circuit can be increased or decreased without corrupting the data signal. GFP is an encapsulation technique that allows traffic from a fibre channel-based storage area network (SAN) to be carried directly onto the SONET network efficiently and cost-effectively. Previously, storage traffic had to be converted to an intermediary pro- tocol such as ATM, frame relay, or IP before being placed on a SONET network. This added overhead and issues related to security, resiliency, lat