taylor@ecsvax.UUCP (Steven Taylor) (07/30/85)
The following are a report description and a sample summary
report for a report series which my company, Distributed Networking,
is considering producing. These reports will provide the data
communications industry with the first in depth, technically
competent analysis of the wide area networking market.
I would very much appreciate the net.dcom readers reviewing this information.
In particular, I am looking for feedback about the feasibility of
such a study, especially concerning the marketability once it is
completed. Consequently, your comments from a technical viewpoint
and from a potential purchaser's viewpoint would be most valuable
to me.
I also have enclosed a sample "management report" about one of
the packet switching systems. This summary report is an actual
preliminary evaluation of a real network, but the names of the
network and the products have been changed to protect the
interests of all parties.
Thank you in advance for your help.
Steven Taylor
Distributed Networking Associates
119 Doncaster Lane
Charlottesville, VA 22901
(804) 979-0656
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TECHLINK Reports on Data Communications Networks
Distributed Networking Associates' TECHLINK Reports on Data
Communications Networks provide an analysis of networking systems
in previously unavailable technical detail. The initial set of
reports covers two of the most popular types of networks - high
speed "T-1" networks and private packet switching netowrks.
The TECHLINK Report on T-1 Networks examines the technology
recently made available to end users to utilize high speed
digital transmission facilities. Systems included here are
primarily high speed multiplexing networks designed to carry
voice and data over a wide variety of facilities such as
telephone company T-1 facilities, private microwave, and private
local area facilities. The TECHLINK Report on Private Packet
Switching Networks examines systems commonly referred to as X.25
packet switches, distributed data switches, and switching
multiplexers.
The reports have a primary goal of assisting the user to
determine which networking system, if any, best fits his
organization's unique needs. As such, TECHLINK significantly
reduces the time needed for evaluation of networking systems by
providing detailed information about the major systems currently
in the marketplace. Essentially, TECHLINK provides the user with
the equivalent of a detailed consulting report on the state of
the art in this technology at a fraction of the price that a
"dedicated" consulting report would cost.
The reports are highly tutorial in nature, helping the user make
sense of all the trade jargon which often makes the data
communications field somewhat difficult to understand. Because
the TECHLINK reports are prepared by a vendor-independent
consulting firm, they provide objective third-party technical
analysis.
Report Description
Each TECHLINK report consists of four basic sections. The
opening section is a detailed technical specification of the
"ideal" system, coupled with an explanation of why each part of
the specification is important. The explanation not only assists
the report user in understanding the vendor responses, but also
helps cut through the technical nomenclature by clearly defining
all terminology. Consequently, this section serves the dual
purposes of setting a framework for the remainder of the report
and providing users with a set of specifications which may be
customized for use in their own procurement procedures.
The second major section contains summary "management reports"
detailing the strongest and weakest features of each system,
together with other commentary about each system's unique
capabilities. This section is a quick reference guide in which it
is assumed that most of the standard features found in such a
network are provided and only the exceptional capabilities are
noted.
The results of the technical specification for each vendor
constitute the third major section. This section is more than a
typical vendor response to a questionnaire. Each vendor will be
invited to have extensive conferences with the Distributed
Networking Associates staff in the completion of the
questionnaire to ensure accurate responses. Additionally, the
completed text of the questionnaire will be presented to the
vendor prior to publication for verification of all information.
Finally, since there may be outstanding issues on which the
Distributed Networking Associates staff and the vendor have
professional differences of opinion, a fourth section is reserved
for the unedited remarks of the vendor. The vendor may choose to
include pricing information in this section, as pricing will not
be discussed in the body of the report due to the tendancy for
relatively frequent price fluctuations in this market. The
vendor may also wish to include comments about field support for
the product in this section.
Scope of Report
TECHLINK is planned to include reports on most major private
network vendors. Specifically, the TECHLINK Report on T-1
Networks is planned to include T-1 multiplexing and networking
systems offered by at least (alphabetically) Avanti, Bayly, Case
Rixon, Codex, Datatel, DCA, Gandalf, General Datacom, Infotron,
M/A-Com Linkabit, Paradyne, Racal-Milgo, Spectrum, Tellabs, and
Timeplex.
The TECHLINK Report on Private Packet Switching Networks is
planned to include systems offered by at least (alphabetically)
BBN, Case Rixon, Codex, ComDesign, DCA, Develcon (Develnet),
Doelz Networks, Dynapac, Equinox Systems, Gandalf, Infotron,
Micom, Network Products, Northern Telecom, Paradyne, Penril,
Siemens-Databit, Telematics, Tellabs, and Timeplex.
Additional Services
Additional support services regarding this report are available
to purchasers of the reports. In particular, there are plans for
quarterly updates to the reports. These updates are an essential
part of the product due to the rapid changes in the data
communications industry. The updates will add new information
about systems in the report and add entire new systems as these
systems are announced.
Communications systems consulting regarding customized areas of
the reports will be made available. Seminars, both public and
in-house, also will be available to help educate staff in the use
of the reports.
Price and Availability
The initial release of TECHLINK is planned for publication during
the first quarter of 1986. Quarterly updates will follow. A
special prepublication price $895.00 per report or $1495.00 for
both reports is offered for orders received prior to October 1,
1985. The first year of update service may be ordered in advance
for $200.00 per report per quarter. Customers who order both the
basic report package and first year's update service will receive
a 50% discount on conference fees for seminars detailing the
results of each report. Additional in-house seminars and
consulting will be priced separately.
Distributed Networking Associates Staff
Distributed Networking Associates is involving a consortium of
consultants, educators, and end users in the preparation and
editing of this report. These individuals constitute an "Industry
Advisory Board" which is involved in all aspects of the report
preparation. A "Manufacturers Advisory Board" is also providing
vendors with a mechanism for recommending that certain areas be
given special attention in the specification and evaluation
process.
This unique blend of users and vendors should enable the
professional quality of the report to yield extremely high
quality information, both in asking the right questions and in
obtaining accurate answers to the questions.
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Management Overview - "Generic" Networks
This report provides a brief technical description of the
networking product offered by "Generic" Networks. In general,
the product is very similar to most packet switching and
switching multiplexer products which are currently on the market
(or at least announced). However, there are four areas in which
this product is sufficiently unique that special attention is
required. These areas are the specialized link protocol, the
ability to handle multidropped lines, the ability to support any
synchronous protocol without a specialized handler, and network
management capabilities.
There are two basic hardware versions. The "Mini-Net" is the
smaller product, consisting of up to two composite high speed
data links per node and up to 32 ports. Data links are rated at
up to 72 kbps. The "Maxi-Net" is the larger system, and calls
for support of up to 67 data links to "Mini-Net" systems and up
to 8 data links to other "Maxi-Net" systems. Composite data link
speed is also 72 kbps for the "Maxi-Net," although 1.544 mbps is
planned. The "Maxi-Net" also features a quite elaborate
redundancy structure, including redundant data buses.
Specialized Link Protocol
The "Generic" data link protocol is indeed a fairly radical
departure from the way that packet switching traditionally has
been approached. At the port level, the data from each
individual session is packetized in "small, fixed-length"
packets. These packets are similar to X.25 Level 3 packets.
Error checking, if desired, occurs end to end only. (Window size
was not immediately available.)
The data links in a statistical multiplexer or packet switch are
typically a variation of X.25 Level 2. As such, they are
optimized for point to point operation. They also perform error
checking on the data link level. The "Generic" products don't
really use a Level 2 protocol at all. Instead, they use a
combination of stat muxing and local area network architecture.
When data from a particular port is ready to be placed on the
network, the packetized data, with its network address, is placed
on the outgoing circuit (transmit data leads.) At this point, a
"ring architecture" takes over. Imagine a "daisy chain" of about
five "Mini-Net" nodes. ("Generic" calls this a "network link.")
The middle node receives some data on a port and places this on
the "transmit data" pair. The next node receives the data on its
"data link 1." If the data belongs to that node, the data is
shipped off to the appropriate port. If the data does not belong
to a port on that node, the entire packet is immediately
forwarded to the transmit pair of "data link 2." This process
continues to the end of the chain, where all data not destined
for the end node is turned around and retransmitted.
"Generic" believes that this architecture is extremely efficient
because the data is not reframed at each intermediate node for
the Level 2 protocol. This efficiency is realized primarily
because less processor power is used in each node for reframing
the data. There are some technical concerns about the additional
loading on the data links caused by the ring architecture. This,
combined with the short packets, could result quite significant
overhead.
The architecture allows for rerouting of calls in the event of a
failure. This rerouting uses a primary circuit and a secondary
circuit for each "network link." A standby circuit links the
endpoint of the "normal" network link with the saxi-Net" system. The major change is that each
endpoint on an "Maxi-Net" terminates a "network link," and the
"Mini-Net" may then pass data among multiple "network link"
rings. "Maxi-Net" to "Maxi-Net" communication consists of a
simple two-point ring. At this point there may be only one
"Maxi-Net" per network link.
Multipoint Support
The "Generic" protocol described above enables the support of
multidropped terminals. At this time, however, all multidropped
terminals on a single "virtual multipoint circuit" must be on the
same network link.
This capability is quite unique within the packet switching
marketplace. In environments where multidropping is very firmly
entrenched, such as the banking systems using ATM's, this is
indeed an attractive feature. In all fairness, however, it
should be mentioned that there are questions about the
advisability of multidropping in many situations from both
technical and financial viewpoints.
"Any" Protocol Support
The "Generic" approach of using short, fixed length packets to
minimize throughput delay is key to their claim of being able to
support any protocol, including bit synchronous protocols such as
SNA/SDLC. The delays inherent in the multiplexing are compensated
for by the use of a fixed duration delay timer. Consequently,
there are no protocol-specific data handlers.
The throughput for synchronous channels is further enhanced by
the utilization of "selective ARQ." The selective ARQ enables or
disables the ARQ function on a channel by channel basis. Since
most synchronous protocols have inherent error detection and
retransmission capabilities, the error checking by the network is
not needed. Thus, in bypassing this step, the "Generic" product
decreases the delay which would be encountered while
retransmitting blocks of data containing transmission errors.
At this point, host/terminal emulation, or "spoofing," is not a
part of the synchronous capabilities. All data is passed through
the network. "Generic" reportedly has an "auto-emulator" under
development, however. The "auto-emulator" would decipher the
normal polling pattern and then emulate the pattern. Like a
currently available emulator, the "auto-emulator" would only pass
data and would not pass polls. However, because of the
"self-learning" process, the emulator would not have to be
specific for each protocol.
This approach is indeed interesting. The basic idea seems to be
that if the data is delivered fast enough, no protocol-specific
handlers are needed. However, with high levels of congestion of
the data links due to peak traffic periods, deteriorating
communications facilities, etc., problems such as device timeouts
may be experienced much more frequently than when emulation is
used. The real question, consequently, is whether the price paid
for enough bandwidth to ensure "fast enough" delivery is
economically advantageous over the price paid for
protocol-specific emulation.
"Generic" partially addresses the problem of delays when there is
heavy bandwidth contention by allowing the network manager to
assign priorities to each session. Consequently, it is possible
to help preserve synchronous device response assigning a higher
priority to synchronous devices than is assigned to asynchronous
devices. This approach is fine so long as better response is
indeed desired for synchronous devices than asynchronous devices
in the network under consideration. In some network operations,
however, it is desirable to have better response on interactive
aysnchronous terminals than on synchronous batch terminals.
One final philosophical note on this issue. The "Generic"
approach relies on using the error checking mechanisms of the
synchronous protocol for error detection and retransmission.
This indeed represents a significant savings over "dual error
correction" seen by using methods which pass all of the
synchronous data over error checked data links. However, the
savings in terms of decreased delay, increased compaction ratios,
etc, have not been demonstrated versus a system which uses
protocol-specific emulation. Here, one would expect issues such
as block length, number of intermediate nodes, etc., also to have
a severe impact on the determination of which method provided the
better performance.
Network Management
Network management is one of the strongest features of the
"Generic" network. "Generic" estimates that up to half of the
processor power utilized in the system is devoted to network
management tasks. While insufficient data is available to
evaluate fully the merits of the management system in this
preliminary report, the fact that network management is designed
as an integral part of the system instead of an afterthought
provides significant advantages.
Summary and Primary Applications
The "Generic" networking products offer some significant new
ideas in handling synchronous protocols. While the intent of the
network is to remain transparent to all protocols, it remains to
be seen whether this can be accomplished while still providing
acceptable performance under stressed data link conditions. The
intended transparency also significantly limits the ability to
offer protocol-specific services, such as switching (selection)
functions for synchronous devices.
Major advantages include the ability to support large networks,
protocol-independent synchronous transmission, multidrop
(multipoint) support, failure compensation, and network
management. Possible limitations include unproven performance on
stressed data links due to overhead considerations and delays in
synchronous data and questionable efficiency of bandwidth
utilization on "network links" due to the ring architecture.
These advantages and limitations will probably make this network
most attractive to users with relatively large networks utilizing
multiple data links at speeds of 56 kbps or greater. Greatest
advantages will also be found for networks with a large
percentage of interactive synchronous devices, such as ATM's and
3270-type terminals, which require good response time but have
relatively light absolute network loading.sjl@amdahl.UUCP (Steve Langdon) (08/03/85)
> > The following are a report description and a sample summary > report for a report series which my company, Distributed Networking, > is considering producing. These reports will provide the data > communications industry with the first in depth, technically > competent analysis of the wide area networking market. > ... > I also have enclosed a sample "management report" about one of > the packet switching systems. This summary report is an actual > preliminary evaluation of a real network, but the names of the > network and the products have been changed to protect the > interests of all parties. ^^^^^^^^^^^ > > Thank you in advance for your help. > > > Steven Taylor > Distributed Networking Associates > 119 Doncaster Lane > Charlottesville, VA 22901 > (804) 979-0656 All parties except the net.dcom readers who are curious about which company makes the product described in the report. For those who do not recognize the product, the company selling the network described is Doelz Networks Inc. -- Stephen J. Langdon ...!{ihnp4,hplabs,sun,nsc}!amdahl!sjl [ The article above is not an official statement from any organization in the known universe. ]