The advent of high-speed networks with quality of service guarantees, will enable the deployment of data-server distributed systems over wide-area networks. Most implementations of data-server systems have been over local area networks. Thus it is important, in this context, to study the performance of existing distributed data management protocols in the new networking environment, identify the performance bottlenecks and develop protocols that are capable of taking advantage of the high speed networking technology. In this paper, we examine and compare the scalability of the server-based two-phase locking protocol (s-2PL), and the group two-phase locking protocol (g-2PL). The s-2PL protocol is the most widely used concurrency control protocol, while the g-2PL protocol is an optimized version of the s-2PL protocol, tailored for high-speed wide-area network environments. The g-2PL protocol reduces the effect of the network latency by message grouping, client-end caching and data migration. Detailed simulation results indicate that g-2PL indeed scales better than s-2PL. For example, upto 28% improvement in response time is reported.