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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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The default for time servers is the non-courier role. As long as enough local time<br />

servers can be contacted, they will not contact a global time server.<br />

In a large or distributed network, local time servers, global time servers, <strong>and</strong><br />

courier time servers automatically <strong>and</strong> accurately make the process of time<br />

synchronization function.<br />

13.3.5 Additional information<br />

For additional information about DCE, refer to the <strong>IBM</strong> Redbook DCE Cell<br />

Design Considerations, SG24-4746.<br />

For information about the most current release of DCE (Version 1.2.2), view the<br />

Open Group Web site at:<br />

http://www.opengroup.org/dce<br />

13.4 Distributed File Service (DFS)<br />

The Distributed File Service is not really a core component of DCE, but it is an<br />

application that is integrated with, <strong>and</strong> uses, the other DCE services. DFS<br />

provides global file sharing. Access to files located anywhere in interconnected<br />

DCE cells is transparent to the user. To the user, it appears as though the files<br />

were located on a local drive. DFS servers <strong>and</strong> clients can be heterogeneous<br />

computers running different operating systems.<br />

The origin of DFS is Transarc Corporation's implementation of the Andrew File<br />

System (AFS) from Carnegie-Mellon University. DFS conforms to POSIX 1003.1<br />

for file system semantics <strong>and</strong> POSIX 1003.6 for access control security. DFS is<br />

built onto, <strong>and</strong> integrated with, all of the other DCE services, <strong>and</strong> was developed<br />

to address identified distributed file system needs, such as:<br />

► Location transparency<br />

► Uniform naming<br />

► Good performance<br />

► Security<br />

► High availability<br />

► File consistency control<br />

► NFS interoperability<br />

Chapter 13. Remote execution <strong>and</strong> distributed computing 509

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