The Langley Research Center's (LaRC) Local Area Network (LAN) effort is discussed. LaRC initiated the development of a LAN to support a growing distributed computing environment at the Center. The purpose of the network is to provide an improved capability (over inteactive and RJE terminal access) for sharing multivendor computer resources. Specifically, the network will provide a data highway for the transfer of files between mainframe computers, minicomputers, work stations, and personal computers. An important influence on the overall network design was the vital need of LaRC researchers to efficiently utilize the large CDC mainframe computers in the central scientific computing facility. Although there was a steady migration from a centralized to a distributed computing environment at LaRC in recent years, the work load on the central resources increased. Major emphasis in the network design was on communication with the central resources within the distributed environment. The network to be implemented will allow researchers to utilize the central resources, distributed minicomputers, work stations, and personal computers to obtain the proper level of computing power to efficiently perform their jobs

Riddle, E. P.

English

NASA Technical Reports Server

LaRC Local Area Networks to Support Distributed Computing
by: Ed P. Riddle
Langley Research Center
INTRODUCTION
LaRC has initiated the development of a Local Area Network (LAN) to support
a growing distributed computing environment at the Center. The purpose
of the network is to provide an improved capability (over interactive and
RJE terminal access) for sharing multi-vendor computer resources. Specifical-
ly, the network will provide a data highway for the transfer of files between
mainframe computers, minicomputers, work stations, and personal computers.
An important influence on the overall network design has been the vital
need of LaRC researchers to efficiently utilize the large CDC mainframe
computers in the central scientific computing facility. Although there
has been a steady migration from a centralized to a distributed computing
environment at LaRC in recent years, the work load on the central resources
has increased. This same experience has been noted at other large computing
facilities. Therefore, major emphasis in the network design has been placed
on communication with the central resources within the distributed environ-
ment. The network to be implemented will allow researchers to utilize the
central resources, distributed minicomputers, work stations, and personal
computers to obtain the proper level of computing power to efficiently per-
form their jobs.
LaRC requirements for a local area network cannot be met with a commercially
available system. As with almost all local area networks of any size, a
custom design is required, including both hardware and software. LaRC has
elected to minimize hardware design by building a network around commercially
available Ethernet products. However, network and application level software
for the network gateways and various resources on the network will be devel-
oped in-house. With today's LAN technology, an in-house design of the net-
work software appears to be the only viable approach to meet LaRC require-
ments. Following is a review of LaRC plans for the development of a center-
wide local area network.
NETWORKCONFIGURATION
Figure I defines a proposed framework within which an integrated data network
to support distributed computing at LaRC will be developed. The top half
of Figure 1 depicts the central scientific computing resources which include
multiple CDC Cyber mainframe computers and a large mass storage system with
a current capacity of 16 billion words. A major resource at the central
facility is a CDC Cyber 203 vector processing supercomputer. The bottom
half of Figure 1 depicts the growing distributed environment at LaRC.
The total network configuration consists of three levels of network with the
principal difference between the levels being transmission speed. Three dif-
ferent networks are used because it is not economically feasible to implement
a single network with today's technology to meet LaRC's networking require-
ment. The design goal will be to integrate the different levels of network
to form what will appear as a single networking environment to the user.
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TWo levels of the network are already in existence at LaRC. An interactive
computing low-speed network has been in operation for six years. The inter-
active network is shown in more detail in Figure 2. The network supports
up to 9600 baud interactive terminal traffic to various computing resources
at LaRC. The heart oF the network is a digital data switch from Micom Sys-
tems, Inc. located in the central scientific computing facility. The data
switch operates similarily to a telephone company central office switch.
Any terminal on the network can initiate a connection to any computer (or
terminal) on the network. Although installed initially to support scientific
computing, the network has in recent years been expanded to support adminis-
trative computing as well. Requirement for a low-speed networking is expect-
ed to continue into the foreseeable future, although the implementation
might, in the future, be part of an integrated voice/data PBX.
A high-speed mainframe computer network was installed in the computer center
last year. This network, Control Data Corporation's Loosely Coupled Network
(LCN), provides i nterconnection between the CDC mainframe computers and the
mass storage system in the central facility. Three parallel coax trunks,
each operating at a transmission rate of 50 megabaud, are used as the trans-
mission medium.
To optimize the value of a distributed computing environment, a means for
efficiently transferring large data files between all network resources
is required. The two existing networks are not suitable for this. The
interactive terminal network is too slow. It is limited to data rates of
9600 baud and typically does not provide a means for guaranteeing error-free
transmission. The high-speed LCN network, although fast enough, is too
expensive. The cost to interface a resource to LCN is $50,000 to $100,O00--
obviously not practical for workstations, personal computers, and most mini-
computers. A new medium-speed network is needed to fill the gap between
the existing networks and provide a reasonable and cost effective means for
transferring data files within LaRC's distributed computing environment.
Therefore, a network is being developed to support throughput up to one
megabaud at a hardware cost-per-device of less than $3000. The new network,
shown at the bottom of Figure i, will have a gateway to the high-speed LCN
mainframe network. A description of the proposed medium-speed network fol-
1ows.
MEDIUM-SPEEDFILE TRANSFERNETWORK
The proposed configuration of the medium-speed file transfer network is
shown in Figure 3. The network is designed around Ethernet technology and
products. Ethernet was chosen because it has received by far the greatest
amount of commercial acceptance and support. Ethernet hardware is currently
available commercially to interface with more computer systems, (including
DEC minicomputers and IBM personal computers), than any other LAN product.
The number of supported devices is growing rapidly.
116
The design concept is that each building, or group of buildings, will contain
an independent Ethernet network to which minicomputers, workstations, and
personal computers will be attached. The individual Ethernet clusters will
then be interconnected via gateways to a ring network using token-passing
LAN technology. Both the Ethernet and ring networks operate at a 10 megabaud
transmission rate. Two network technologies will be integrated because
it is not technically feasible to implement a single Ethernet extending
to all of the LaRC buildings. The total distance exceeds the one mile limita-
tion of Ethernet. The token-passing ring does not have this distance limita-
tion. The multiple Ethernet design allows local data traffic within an
Ethernet cluster to be confined to that cluster and not impact traffic on
other parts of the network. This is an important consideration since our
surveys have indicated that 50-70% of total data traffic will be local.
A dedicated gateway on the ring network will provide access to the high-speed
CDC LCN mainframe network. The integrated network as configured in Figure
3 will allow interconnectivity between network devices.
NETWORKCHARACTERISTICSAND CAPABILITIES
It has been necessary to set boundaries on network capability in order to
develop and implement a LaRC network using reasonable resources (manpower
and money). The following summarizes the capabilities of the network.
The network will support full interconnectivity: any network device will
be able to communicate with any other device at both a network and applica-
tion level. To provide that interconnectivity, however, it has been neces-
sary to limit (at least initially) the kinds of equipment and the applica-
tions that will be supported. Initial implementation will accommodate only
CDC Cyber mainframe computers, DED PDP/VAX minicomputers, and IBM personal
computers. File transfers will be the only application initially supported.
Even though the transmission rate on the network will be I0 megabaud, the
maximum throughput between any two network devices will be limited by the
device throughput, which typically has been found to be less than one mega-
baud. All network gateways will be designed to support throughputs up to
one megabaud.
The packet scheme of transmission on both the Ethernet and ring networks
provides for re-transmission of data when communication errors are detected,
resulting in negligible error rates on the network.
An important design criteria has been that no modifications to the computer
operating systems should be required to accommodate the network software.
All network software has been designed to operate external to the computer
operating systems.
Finally, the network is being designed with the future in mind. The goal
of the design is a network that is easily expandable and adaptable to new
LAN technologies. The latter is important because rapid advancements in
LAN technology result in new and improved concepts and products almost daily.
117
IMPLEMENTATIONPLAN AND SCHEDULE
The development and implementation of the network will be in four phases.
The first phase, which is now well underway, is a pilot implementation in
LaRC's central scientific computing facility. The pilot effort will be
completed by the end of this calendar year. The second phase will be a
production implementation of the network, beginning next year, at three
to six selected sites. Refinements to network design are expected to be
made as a result of experience gained during the first year of production
activity. The third and fourth phases of network implementation will be
a continuation of production implementation at additional sites. The last
phase is expected to be completed by the end of calendar year 1986.
STATUS OF NETWORKDEVELOPMENT
Installation of a ten-station Ethernet pilot network in the central computing
facility has been completed. The pilot includes a CDC Cyber mainframe com-
puter, four DEC minicomputers, and five IBM personal computers. This equip-
ment was not purchased for the network project but is equipment that was,
and continues to be used for production work. An initial, simplified version
of network and file transfer software has been developed in-house for all
network devices. Throughput rates of 100-450 kilobaud between network de-
vices have been demonstrated. Typically, the limiting factor on throughput
has been found to be disk I/0 on the network devices. The pilot network
is operational during normal working hours and is available for limited
production use.
Two Ethernet clusters on the pilot have been connected to a two-node ring
and primitive operation of that configuration has been demonstrated. A
fully-operational three-node pilot ring with three Ethernet clusters is
expected to be operational in the central computing facility by the end of
this calendar year.
The work remaining during this calendar year will be to refine the network
software that has been developed, adding multi-user capability and providing
routing and flow control protocols that are required for the ring network.
118
1983 - 1992 LaRC NETWORKTOPOLOGY
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ACD CENTRALCOMPUTERS DECEMBER 1983
LaRC MEDIUM SPEED DATA NETWORK
(PROPOSEDCONFIGURATION)
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PROGRAM SUPPORT GW = GATEWAY
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MW = MICROWAVE


LaRC local area networks to support distributed computing

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