ch01.htm

this describes managing multivendor networks

<UL>
	<LI><I>Resource locking.</I> This allows various levels of locking on a clusterwide
	basis. It allows file-level, record-level, and even field-level locking.<BR>
	<BR>
	
	<LI><I>Disaster rollback.</I> After a disaster, this restores information to a previous
	point at which it was known to be good. This feature usually works with recovery
	processing, as described next.<BR>
	<BR>
	
	<LI><I>Recovery processing.</I> After information has been restored to a known good
	state, this feature reapplies the updates that occurred after that point and before
	the disaster. For example, if an application inadvertently corrupted the information
	at 12:05, the disk could be rolled back and then have the updates that occurred before
	12:00 reapplied.<BR>
	<BR>
	
	<LI><I>Security. </I>Maintaining an audit trail of what program applied what update
	at what time is often a critical part of preventing a disaster from repeating. An
	audit trail can find the offending program so it can be corrected.
</UL>

<P>On a much broader level, another technique to help maintain a high degree of data
integrity and availability is disk shadowing. With this technique, you attach two
disks to at least one (but preferably two) hierarchical storage controllers in a
cluster so identical information is maintained on both disk drives. Please note,
however, that you should use shadowing with the above recovery mechanisms to handle
situations in which the application corrupts both copies of the information.</P>
<P>As previously discussed, VAXclusters initially were developed to help Digital
compete in the higher end of the market. The advent of high-end systems from Digital,
however, will not make the cluster obsolete. Instead, systems like the Alpha 8000
Series will be used in clusters to maximize and even increase their high performance.</P>
<P>To sum up the salient difference between SMP and clusters, SMP is an architecture
that enables multiple applications within a computer to run in parallel (to a degree),
sharing common memory and disk resources. Clusters, on the other hand, enable multiple
applications on separate computers to share the same information stored on disk.
With clusters, there is no need to redesign or DECompose programs to take advantage
of the shared disk facility. Finally, SMP can be implemented within a cluster to
achieve maximum performance (provided the computers in the cluster support multiple
processors).
<H2><A NAME="Heading9"></A><FONT COLOR="#000077">Strategy for Connectivity</FONT></H2>
<P>Digital Equipment Corporation's strategy for connectivity is built upon DECnet.
<I>DECnet</I> is a set of products and services designed and implemented based on
the Digital Network Architecture (DNA). DECnet was originally implemented using proprietary
protocols, but in the early 1990s, Digital shifted DECnet into the open network environment
by incorporating support for both OSI protocols and for TCP/IP.</P>
<P>The shift toward open networking was the fifth major &quot;phase&quot; (revision)
in the DECnet specifications. The original DECnet phase (Phase I) was introduced
in 1976, and provided simple services for file transfer and program-to-program communication
between PDP-11 machines running the RSX-11M operating system. At the time, this was
fairly revolutionary, as software portability was almost non-existent. The subsequent
phases added more networking and interoperability services, bringing DECnet up to
the level of where it is today.</P>
<P>Phase II was released in 1978, and brought the capabilities of Phase I to all
major operating systems (including VMS). Additional features included remote file
access, network management tools, and support for point-to-point network configurations.
Phase III, released in 1980, introduced a dynamic adaptive routing algorithm, which
automatically calculated the best route to a message's destination. Under Phase II,
a direct connection had to be created between systems. Phase III also offered support
for X.25 packet switching networks as a method to connect systems, record-level access
over the network, and downline loading. A Phase III network could include up to 255
nodes.</P>
<P>Introduced in 1982, Phase IV was a major jump in technology. Under this phase,
Digital came to support ethernet, large LANs and WANs, virtual terminal services,
and various communications servers and gateways.</P>
<P>Digital's Phase IV approach to combining DNA with Ethernet (resulting in DECnet)
was the most revolutionary and sweeping networking architecture since IBM's Systems
Network Architecture (SNA). Ethernet, the result of a collaboration among Digital
Equipment, Intel Corporation, and Xerox Corporation, defines a physical interface
that supports a data rate of 10 million bps over a shielded coaxial cable. Up to
1,024 nodes (addressable attachments) are supported. One of the major benefits of
Phase IV was conformance with Open Systems Interconnect (OSI) standards.</P>
<P>The second important aspect of Ethernet is the collision-detection mechanism.
Because any node on the network could transmit at any time, a regulation mechanism
had to be created to recover from the inevitable collisions (which result in garbled
information). The technique Digital and Xerox put in place was termed the Carrier
Sense Multiple Access with Collision Detection (CSMA/CD).</P>
<P>Using the CSMA/CD technique, a node with information to transmit first listens
to the network. If no one else is transmitting, that node goes ahead and sends. If,
however, another node is transmitting on the network, that node waits for a predetermined
length of time before attempting to transmit again. If two nodes transmit simultaneously,
the collision is detected and both nodes wait for a random time period before attempting
to retransmit.</P>
<P>The CSMA/CD technique is also used in the IEEE 802.3 network implementation. In
fact, Ethernet and IEEE 802.3 are similar enough that nodes of both types can coexist
on the same physical network (although the two implementations are also different
enough that one type of node can't &quot;understand&quot; the other type's information).</P>
<P>Phase V was made available in 1991. It made significant changes to accommodate
TCP/IP as an alternative to OSI standards for open networking. Digital had three
goals in releasing Phase V: to permit a network to grow up to a million systems,
to incorporate both OSI and TCP/IP standard protocol suites to provide for a higher
level of system integration, and to support a distributed mode of operation. Although
a Phase IV network could accommodate up to 64,000 nodes, the industry's move towards
distributed, client/server computing soon limited Phase IV's viability. Phase V introduced
a new routing algorithm, which can potentially support millions of nodes. This algorithm
has since been adopted as a routing standard for both OSI and TCP/IP networks. Phase
V also set out to provide a distributed networkwide naming service, and to permit
nodes to generate their own addresses and register themselves automatically.</P>
<P>The Digital Distributed Name Service (DECdns) provides the following features:
distribution (so naming information does not have to be stored in a single location),
replication, dynamic updating, automatic updating, and a hierarchical naming structure.
Adding a new node to a Digital Equipment network is remarkably simple when using
DECnet with DECdns. The combination of these two products permit full autoconfiguration.
Where DECdns assigns names to computer systems, X.500 names extend to naming individuals
within a naming framework.</P>
<P>DECnet can be implemented on a LAN using Ethernet or over a WAN using a variety
of routers and/or gateways to bridge the distant LANs. Technicalities notwithstanding,
the primary function of DECnet is to deliver the following capabilities:

<UL>
	<LI><I>Task-to-task communications.</I> The capability of two programs (possibly
	running on dissimilar systems or written in dissimilar languages) to exchange information.<BR>
	<BR>
	
	<LI><I>Remote file access.</I> The capability to transfer files to and from remote
	locations and to perform read and write (record-level) operations to a remote file.<BR>
	<BR>
	
	<LI><I>Network terminal access.</I> The capability of terminals to access a remote
	system and run programs on that system as if they were locally attached terminals.<BR>
	<BR>
	
	<LI><I>Network management.</I> The capability to locate and isolate network problems
	without bringing the whole network down.<BR>
	<BR>
	
	<LI><I>Downline loading.</I> The capability to load a program or task from one system
	onto another and run it on that system.<BR>
	<BR>
	
	<LI><I>Upline dumping.</I> The capability of a system during abnormal termination
	to send pertinent system information to an adjacent system. When the failed node
	has been restored, this information can then be downloaded to help it resume its
	normal operations.
</UL>

<P>Understanding the importance of DECnet is the key to understanding Digital's approach
to data processing. It is much rarer to find a single, isolated, non-networked VAX
than to find two or more Digital nodes communicating via ethernet.</P>
<P>Digital uses an X.500-based Directory Service, a general-purpose distributed directory
similar to Banyan's StreetTalk and Novell's NetWare Distributed Services. Digital
goes further than these two products in making the service accessible from any Web
browser or messaging system. Digital's service can be used to hold any information
that an organization wants to make public; sensitive data can be restricted. The
directory can be divided between multiple directory servers, with each server having
the ability to pass directory tasks to other servers that possess the relevant data.
Digital X.500 Directory Service supports Internet and X.400-based networks, and can
function as a superset of other directory services to form a global directory for
messaging and other applications. The service is integrated with Digital's MAILbus
400 backbone, which acts as a bridge between SMTP and other enterprise mail systems.
Developers can write applications to access the directory using the industry standard
X/Open XDS API. With the Digital X.500 Directory Synchronizer, directory information
can be exchanged and synchronized in a multivendor environment. Directories from
many popular e-mail products can be synchronized, and it can also support legacy
e-mail, Internet mail, and custom systems.
<H2><A NAME="Heading10"></A><FONT COLOR="#000077">Messaging</FONT></H2>
<P>Digital accommodates enterprisewide messaging in a multivendor environment with
a range of products that adhere to industry standards. Digital's messaging strategy
comprises a three-tier, client/server architecture, consisting of the enterprise
backbone, departmental system, and the desktop.</P>
<P>The messaging infrastructure lives at the Enterprise Backbone Server tier, and
provides mission-critical transport and directory services for heterogeneous mail
environments, as well as management of the messaging network. Connectivity to X.400
and the Internet is also achieved at this level.</P>
<P>At the Departmental Server tier, a mail or groupware server is deployed, and access
to the enterprise directory is achieved through a variety of servers, including MailWorks
(a client/server messaging system for LAN mail connectivity), Microsoft Exchange
Server, and ALL-IN-1. At the Desktop tier. E-mail clients can select from various
products such as Microsoft Mail, Lotus cc:Mail, TeamLinks, and Windows 95.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>The Digital and Microsoft Alliance</B></FONT><BR>
	Recently, Digital entered into a messaging alliance with Microsoft to develop a joint
	enterprise mail infrastructure. The result of this alliance will be the eventual
	integration of ALL-IN-1 and MailWorks, with the Microsoft Exchange Server through
	MAILbus 400 and Digital X.500 Directory Service. <I>MAILbus 400</I> is a store-and-forward
	message transfer agent (MTA) that connects with other systems and services. MAILbus
	is based on the X.400 standard, and can therefore connect to a wide variety of other
	X.400 MTAs. DEC EDI (Electronic Data Interchange) provides connectivity between a
	company and its customers or suppliers.</P>
	<P>Digital and Microsoft's alliance further ensures the interoperability of all Digital
	and Microsoft products. The Microsoft Exchange Server mail technology will be integrated
	with Digital's ALL-IN-1 and MailWorks products, and Digital's mail backbone will
	support Exchange Server. Digital will also support Microsoft's Windows Open Systems
	Architecture (WOSA) API in OpenVMS, which will permit application developers to write
	to both operating environments more easily. The alliance will contribute significantly
	to the integration of Windows NT into the enterprise. 
<HR>


</BLOCKQUOTE>