brian@ucsd.EDU (Brian Kantor) (12/20/88)
RFC 1077 November 1988
not restrict the aggregate rates we can achieve over trunks, it
prevents delivery of high data rate flows to the host-based
applications, which will prevent the development of new applications
needing high bandwidth. The host bottleneck is thus a serious
impediment to networked use of supercomputers.
To build a GN we need to create new ways for hosts and their high
bandwidth peripherals to connect to networks. We believe that
pursuing research in the ways to most effectively isolate host and
LAN development paths from the GN is the most productive way to
proceed. By decoupling the development paths, neither is restricted
by the momentary performance of capability bottlenecks of the other.
The best context in which to view this separation is with the notion
of a network front end (NFE). The NFE can take the electronic input
data at many data rates and transform it into gigabit light data
appropriately packetized to traverse the GN. The NFE can accept
inputs from many types of gateways, hosts, host peripherals, and LANS
and provide arbitration and path set-up facilities as needed. Most
importantly, the NFE can perform protocol arbitration to retain
upward compatibility with the existing Internet protocols while
enabling those sophisticated network input sources to execute GN
specific high-throughput protocols. Of course, this introduces the
need for research into high-speed NFEs to avoid the NFE becoming a
bottleneck.
3.3.1. VLSI and Optronics Implementations
In a host interface, unless the host is optical (an unlikely prospect
in the near-term), the opportunities for optronic support are
limited. In fact, with a serial-to-parallel conversion on reception
stepping the clock rate down by a factor of 32 (assuming a 32-bit
data path on the host interface), optronic speeds are not required in
the immediate future.
One exception may be for encryption. Current VLSI implementations of
standard encryption algorithms run in the 10 Mbit/s range. Optronic
implementation of these encryption techniques and encryption
techniques specifically oriented to, or taking advantage of, optronic
capabilities appears to be an area of some potential (and enormous
benefit if achieved).
The potential of targeted VLSI research in this area appears limited
for similar reasons discussed above with its application in high-
speed switching. The major benefits will arise from work that is
well-motivated by other research (such as high-performance
parallelism) and by strong commercial interest. Again, we need to be
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open to imaginative opportunities not foreseen here while keeping
ourselves from being diverted into low-impact research without
further insights being put forward.
3.3.2. High-Performance Transport Protocols
Current transport protocols exhibit some severe problems for maximal
performance, especially for using hardware support. For example, TCP
places the checksum in the packet header, forcing the packet to be
formed and read fully before transmission begins. ISO TP4 is even
worse, locating the checksum in a variable portion of the header at
an indeterminate offset, making hardware implementation extremely
difficult.
The current Internet has thrived and grown due to the existence of
TCP implementations for a wide variety of classes of host computers.
These various TCP implementations achieve robust interoperability by
a "least common denominator" approach to features and options. Some
applications have arisen in the current Internet, and analogs can be
envisioned for the GN environment, which need qualities of service
not generally supported by the ubiquitous generic TCP, and therefore
special purpose transport protocols have been developed. Examples
include special purpose transport protocols such as UDP (user
datagram protocol), RDP (reliable datagram protocol), LDP
(loader/debugger protocol), NETBLT (high-speed block transfer
protocol), NVP (network voice protocol) and PVP (packet video
protocol). Efforts are also under way to develop a new generic
transport protocol VMTP (versatile message transaction protocol)
which will remedy some of deficiencies of TCP, without the need to
resort to special purpose protocols for some applications. Research
is needed in this area to understand how transport level protocols
should be constructed for a GN which provide adequate qualities of
service and ease of implementation.
A new transport protocol of reasonable success can be expected to
last for ten years more. Therefore, a new protocol should not be
over optimized for current networks and must not ignore the
functional deficiencies of current protocols. These deficiencies are
essential to remedy before it is feasible to deploy even current
distributed systems technology for military and commercial
applications.
Forward Error Correction (FEC) is a useful approach when the
bandwidth/delay ratio of the physical medium is high, as can be
expected in transcontinental photonic links. A degenerate form of
FEC is to simply transmit multiple copies of the data; this allows
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one to trade bandwidth for delay and reliability, without requiring
much intelligence. In fact, it is generally true that reliability,
bandwidth, and delay are interrelated and an improvement in one
generally comes at the expense of the others for a given technology.
Research is required to find appropriate operating points in networks
using transmission components which offer extremely high bandwidth
with very good bit-error-rate performance.
3.3.3. Network Adaptors
With the promised speed of networks, the future network adaptor must
be viewed as a memory interconnect, tying the memory in one host to
another, at least if the data rate and the low latency made possible
by the network is to be realized at the host-to-host or process-to-
process level. The challenge is too great to be met by just
implementing protocols in custom VLSI.
Research is required to investigate the impact of network
interconnection on a machine architecture and to define and evaluate
new network adaptor architectures. Of key importance is integration
of network adaptor into the operating system so that process-to-
process communications performance matches that offered by the
network. In particular, we conjecture that the transport level will
be implemented largely, if not entirely, in the network adaptor,
providing the host with reliable memory-to-memory transfer at memory
speeds with a minimum of interrupt processing bus overhead and packet
processing.
Drawing an analogy to RISC technology again, maximal performance
requires a well-designed and coordinated protocol, software, and
hardware (network adaptor) design. Current standard protocols are
significantly flawed for hardware compatibility, suggesting a need
for considerable further research on high-performance protocol
design.
3.3.4. Host Operating System Software
Conventionally, communication has been an add-on to an operating
system. With the GN, the network may well become the fastest
"peripheral" connected to most nodes. High-performance process-to-
process (or application to application) communication will not be
achieved until the operating system is well designed for fast access
to and from the network. For example, incorporating templates of the
network packet header directly in the process descriptor may allow a
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process to initiate communications with minimal overhead. Similarly,
memory mapping can be used to eliminate copies between data arriving
from the network and it being delivered to the applications. With a
GN, an extra copy forced by the operating system may easily double
the perceived transfer time for a packet between applications.
Besides matching data transfer mechanisms, operating systems must be
well-matched in security design to that supported by the host
interface and network as well. Otherwise, all but the most trivial
additional security actions by the operating system in common case
communication can easily eliminate the performance benefits of the
GN. For example, if the host has to do further encryption or
decryption, the throughput is likely to be at least halved and the
latency doubled.
Research effort is required to further refine operating systems for
the level of performance offered by the GN. This effort may well be
best realized with coupling existing efforts in distributed systems
with the GN activities, as opposed to starting new separate efforts.
3.4. Advanced Network Management Algorithms
An important emphasis for research into network management should be
on decentralized approaches. The ratio of propagation delay across
the country to data rates in a GN appear to be too great to deal
effectively with resource management centrally when traffic load is
bursty and unstable (and if it is not, one might argue there is no
problem). In addition, important principles of fault containment and
minimal privilege for reliability and security suggest that a
centralized management approach is infeasible. In particular,
compromising the security of one portion of the network should not
compromise the security of the whole network. Similarly, a failure
or fault should affect at most a local region of the network.
The challenge is clearly to provide decentralized management
techniques that lead to good global behavior in the normal case and
acceptable behavior in expected worst-case failures, traffic
variations and security intrusions.
3.4.1. Control Flow vs. Data Flow
Network operational communications can be separated into flow of user
data and flow of management/control data. However, the user data
must contain some amount of control data. One question that needs to
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be explored in light of changes in communications and computing costs
and performance is the trade-off between these two flows. An example
of a potential approach is to use data units which contain predefined
path indicators. The switch can perform a simple table look-up which
maps the path indicator onto the preferred outbound link and
transmits the packet immediately. There is a path set-up packet
which fills in the appropriate tables. Path set-up occurs before the
first data packet flows and then, while data is flowing, to improve
the routes during the lifetime of the connection. This concept has
been discussed in the Internet engineering group under the name of
soft connections.
We note that separating the data flow from the control flow in the GN
has security and reliability advantages as well. We could encrypt
most of the packet header to provide confidentiality within the GN
and to limit the ability of intruders to perform traffic analysis.
And, by separating the control flow, we can encrypt all the control
exchanges between switches and the host front ends thereby offering
confidentiality and integrity. No unauthorized entity will be able
to alter or examine the control traffic. By employing a path set-up
procedure, we can assure that the GN NFE-to-NFE path is functioning
and also include user-specific requirements in the route. For
example, we could request a certain bandwidth allocation and simplify
the job of the switches in handling flow control. We could also set
up backup paths in case the output link will be busy for so many
microseconds that the packet cannot be stored until the link is
freed.
3.4.2. Resource Management Algorithms
Most current networks deliver one quality of service. X.25 networks
deliver a reliable byte-stream. Most LANs deliver a best-effort
unreliable service. There are few networks today that can support
multiple types of service, and allocate their resources among them.
Indeed, for many networks, such as best-effort unreliable service,
there is little management of resources at all. The next generation
of network will require a much more controlled allocation of
resources.
There will be a much wider range of desired types of service, with
current services such as remote procedure call mixing with new
services such as video streams. Unless these are separately
recognized and controlled, there is little reason to believe that
effective service can be delivered unless the network is very lightly
loaded.
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In order to support multiple types of service, two things must
happen, both a change from current practice. First, the application
must describe to the network what type of service is required.
Second, the network must use this information to make resource
allocation decisions. Both of these practices present difficulties.
Past experience suggests that application code is not prepared to
know or specify what service it needs. By custom, operating systems
provide a virtual world, and the applications in this world are
unaware of the relation between this and the reality of time and
space. Resource requests must be in real terms. Allocation of
resources in the network is difficult, because it requires that
decisions be made in the network, but as network packet throughput
increases, there is less time for decisions.
The resolution of this latter conflict is to observe that decisions
must be made on larger units than the unit of multiplexing such as
the packet. This in turn implies that packets must be visible to the
network as being part of a sequence, as opposed to the pure datagram
model previously exploited. As suggested earlier in this report,
research is required to support this more complex form of switch
without compromising robustness.
To permit the application to specify the service it needs, it will be
necessary to propose some abstraction of service class. By clever
design of this abstraction, it should be possible to allow the
application to describe its needs effectively. For example, an
application such as file transfer or mail has two modes of operation;
bulk data transfer and remote procedure call. The application may
not be able to predict when it will be in which mode, but if it just
describes both of them, the system may be able to adapt by observing
its current operation.
Experimentation needs to be done to determine a suitable service
specification interface. This experimentation could be done in the
context of the current protocols, and could thus be undertaken at
once.
3.4.3. Adaptive Protocols
Network operating conditions can vary quickly and over a wide range.
This is true of the current Internet, and is likely to affect the GN
too. Protocols that can adapt to changing circumstances would
provide more even and robust service than is currently possible. For
example, when error rates increased, a protocol implementation might
decide to use smaller packets, thus reducing the burden caused by
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retransmissions.
The environment in which a protocol operates can be described in
terms of the service it is getting from the next lower layer. A
protocol implementation can adapt to changes in that service by
tuning its internal mechanisms (time-outs, retransmission strategies,
etc.). Therefore, to design adaptive protocols, we must understand
the interaction between protocol layers and the mechanisms used
within them. There has been some work done in this area. For
example, the SATNET measurement task force has looked at the
interactions between the protocol used by the SIMP, IP, and TCP.
What is needed is a more complete characterization of the
interactions at various layer boundaries, and the development of
appropriate protocol designs and mechanisms to provide for necessary
adaptations and renegotiations.
3.4.4. Error Recovery Mechanisms
Being large and complex, GNs will experience a variety of faults such
as link or nodal failure, excessive buffer overflow due to faulty
flow and congestion control, and partial failure of switching fabric.
These failures, which also exist in today's networks, will have a
stronger effect in GNs where a large amount of data will be "stored"
in transit and, to expedite the switching, nodes will apply only
minimal processing to the packets traversing them. In source
routing, for example, a link failure may cause the loss of all
packets sent until the source is notified about the change in
topology. The longer is the delay in recovering from failures, the
higher is the degradation in performance observed by the users.
To minimize the effects of failures, GNs will need to employ error
recovery mechanisms whereby the network detects failures and error
conditions, reconfigures itself to adapt to the new network state,
and notifies peripheral devices of the new configuration. Such
protocols, which have to be developed, will respond quickly, will be
decentralized or distributed to minimize the possibility of fatal
failures, and will complement, rather than replicate, the error
correction mechanisms of the end-to-end protocols, and the two must
operate in coordinated manner. To this end, the peripheral devices
will have to be knowledgeable about the intranet recovery mechanisms
and interact continuously with them to minimize the effect on the
connections they manage.
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3.4.5. Flow Control
As networks become faster, two related problems arise. First,
existing flow control mechanisms such as windows do not work well,
because the window must be opened to such an extent to achieve
desired bandwidth that effective flow control cannot be achieved.
Second, especially for long-haul networks, the larger number of bits
in transit at one time becomes so large that most computer messages
will fit into one window. This means that traditional congestion
control schemes will cease to work well.
What is needed is a combination of two approaches, both new. First,
for messages that are small (most messages generated by computers
today will be small, since they will fit into one round-trip time of
future networks), open-loop controls on flow and congestion are
needed. For longer messages (voice or video streams, for example),
some explicit resource commitment will be required.
3.4.6. Latency Control and Real-Time Operations
Currently, there are several distinct approaches to latency control.
First, there are some networks which are physically short, more like
multiprocessor buses. Applications in these networks are built
assuming that delays will be short.
Second, there are networks where the physical length is not
constrained by the design and may differ by orders of magnitude,
depending on the scope of the network. Most general purpose networks
fall in this category. In these networks, one of two things happens.
Either the application takes special steps to deal with variable
latency, such as echo suppression in voice networks, or these
applications are not supported.
For most applications today, the latency in the network is not an
obvious issue so long as the network is not overloaded (which leads
to losses and long queues), because the protocol overhead masks the
variation in the network latency. This balance will change. The
latency due to the speed of light will obviously remain the same, but
the overhead will drop (of necessity if we are to achieve high
performance) which will leave speed of light and queueing as the most
critical sources of delay.
This conclusion implies that if queueing delay can be controlled, it
will be possible to build networks with stable and controlled
latency. If applications exist that require this class of service,
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it can be supported. Either the network must be underloaded, so that
queues do not develop at all, or a specific class of service must be
supported in which resources are allocated to stabilize the delay.
If this service is provided, it will still leave the application with
delays that can vary by several orders of magnitude, depending on the
physical size of the network. Research at the application level will
be required to see how applications can be designed to cope with this
variation.
3.4.7. High-Speed Internetworking and Administrational Domains
Internetworking recognized that the value of communication services
increases significantly with wider interconnection but ignored
management and the role of administrations. As a consequence we see
that:
1. The Internet is more or less unmanageable, as evidenced by
performance, reliability, and security problems.
2. The Internet is being stressed by administrators that are
building networks to match their organization rather than the
geography. An example is a set of Ethernets at different
company locations operating as a single Internet network but
geographically dispersed and connected by satellite or leased
lines.
The next generation of internetworking must focus on administration
and management. Internetworking must support cohesion within an
administration and a healthy separation between administrations. To
illustrate by analogy, the American and Soviet embassies in Mexico
City are geographically closer to each other than to their respective
home countries but further in administrational distance, including
security, accounting, etc. The emerging revolution in WANs makes
this issue that much more critical. The amount of communication to
exchange the state of systems is bound to increase enormously. The
potential cost of failures and security violations is frightening.
A promising approach appears to be high-level gateways that guard
between administrations and require negotiations to set up access
paths between administrations. These paths are set up, and labeled
with agreements on authorization, security, accounting, and possible
resource limits. These administrative virtual circuits provide
transparency to the physical and geographical interconnection, but
need not support more than datagram packet delivery. One view is
that of communication contracts with high-level gateways acting as
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contract monitors at each end. The key is the focus on controlled
interadministrational connectivity, not the conventional protocol
concerns.
Focus is required on developing an (inter)network management
architecture and the specifics of high-level gateways. The
structures of such gateways will have to take advantage of advances
in multi-processor architectures to handle the processing load.
Moreover, a key issue is being able to optimize communication between
administrations once the contract is in place, but without losing
control. Related is the issue of allowing high-speed interconnection
within a single administration, although geographical dispersed.
Another issue is fault-tolerance. High-level gateways contain state
information whose loss typically disrupts communication. How does
one minimize this problem?
A key goal of these administrational gateways has to be failure
containment: How to protect against external (to administration)
problems and how to prevent local problems imposing liability on
others. A particular area of concern is the self-organizing problems
of large-scale systems, observed by Van Jacobson in the Internet.
Gateways must serve to damp out oscillations and control wide load
swings. Rate control appears to be a key area to investigate as a
basis for buffer management and for congestion control, as well as to
control offered load.
Given the speed of new networks, and the sophistication of the
gateways suggested above, another key area to investigate is the
provision of high-speed network interface adaptors.
3.4.8. Policy-Based Algorithms
Networks of today generally select routes based on minimizing some
measure such as delay. However, in the real world, route selection
will commonly be constrained at the global level by policy issues,
such as access rights to resources and accounting and billing for
usage.
It is difficult for connectionless protocols such as Internet to deal
with policy controls, because a lack of state in the gateway implies
that a separate policy decision must be made for each packet in
isolation. As networks get faster, the cost of this processing will
be intolerable. One possible approach, discussed above, is to move
to a more sophisticated model in which there is knowledge in the
gateways of the ongoing flows. Alternatively, it may be possible to
design gateways that simply cache recent policy evaluations and apply
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them to successive packets.
Routing based on policy is particularly difficult because a route
must be globally consistent to be useful; otherwise it may loop.
This implies that the every policy decision must be propagated
globally. Since there can be expected to be a large number of
policies, this global passing of information might easily lead to an
information explosion.
There are at least two solutions. One is to restrict the possible
classes of policy. Another is to use some form of source route, so
that the route consistent with some set of policies is computed at
one point only, and then attached to the packet. Both of these
approaches have problems. A two-pronged research program is needed,
in which mechanisms are proposed, and at the same time the needed
policies are defined.
The same trade-off can be seen for accounting and billing. A single
accounting metric, such as "bytes times distance", could be proposed.
This might be somewhat simple to implement, but would not permit the
definition of individual billing policies, as is now done in the
parts of the telephone system. The current connectionless transport
architectures such as TCP/IP or the connectionless ISO configuration
using TP4 do not have good tools for accounting for traffic, or for
restricting traffic from certain resources. Building these tools is
difficult in a connectionless environment, because an accounting or
control facility must deal with each packet in isolation, which
implies a significant processing burden as part of packet forwarding.
This burden is an increasing problem as switches are expected to
operate faster.
The lack of these tools is proving a significant problem for network
design. Not only are accounting and control needed to support
management requirements, they are needed as a building block to
support enforcement of such things as multiple qualities of service,
as discussed above.
Network accounting is generally considered to be simply a step that
leads to billing, and thus is often evaluated in terms of how simple
or difficult it will be to implement. Yet an accounting and billing
procedure is a mechanism for implementing a policy considered to be
desirable for reasons beyond the scope of accounting per se. For
example, a policy might be established either to encourage or
discourage network use, while fully recovering operational cost. A
policy of encouraging use could be implemented by a relatively high
monthly attachment charge and a relatively low per-packet charge. A
policy of discouraging use could be implemented by a low monthly
charge and a high per-packet charge.
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Network administrators have a relatively small number of variables
with which to implement policy objectives. Nevertheless, these
variables can be combined in a number of innovative ways. Some of
the possibilities include:
1. Classes of users (e.g., large or small institutions, for-
profit or non-profit).
2. Classes of service.
3. Time varying (e.g., peak and off-peak).
4. Volume (e.g., volume discounts, or volume surcharges).
5. Access charges (e.g., per port, or port * [bandwidth of
port]).
6. Distance (e.g., circuit-miles, airline miles, number of hops).
Generally, an accounting procedure can be developed to support
voluntary user cooperation with almost any single policy objective.
Difficulties most often arise when there are multiple competing
policy objectives, or when there is no clear policy at all.
Another aspect of accounting and billing procedures which must be
carefully considered is the cost of accumulating and processing the
data on which billing is based. Of particular concern is collection
of detailed data on a per-packet basis. As network circuit data
rates increase, the number of instructions which must be executed on
a per-packet basis can become the limiting factor in system
throughput. Thus, it may be appropriate to prefer accounting and
billing policies and procedures which minimize the difficulty of
collecting data, even if this approach requires a compromise of other
objectives. Similarly, node memory required for data collection and
any network bandwidth required for transmission of the data to
administrative headquarters are factors which must be traded off
against the need to process user packets.
3.4.9. Priority and Preemption
The GN should support multiple levels of priority for traffic and the
preemption of network resources for higher priority use. Network
control traffic should be given the highest priority to ensure that
it is able to pass through the network unimpeded by congestion caused
by user-level traffic. There may be additional military uses for
multiple levels of priority which correspond to rank or level of
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importance of a user or the mission criticality of some particular
data.
The use of and existence of priority levels may be different for
different types of traffic. For example, datagram traffic may not
have multiple priority levels. Because the network's transmission
speed is so high and traffic bursts may be short, it may not make
sense to do any processing in the switches to deal with different
priority levels. Priority will be more important for flow- (or
soft-connection-) oriented data or hard connections in terms of
permitting higher priority connections to be set up ahead of lower
priority connections. Preemption will permit requests for high
priority connections to reclaim network resources currently in use by
lower priority traffic.
Networks such as the Wideband Satellite Network, which supports
datagram and stream traffic, implement four priority levels for
traffic with the highest reserved for network control functions and
the other three for user traffic. The Wideband Network supports
preemption of lower priority stream allocations by higher priority
requests. An important component of the use of priority and
preemption is the ability to notify users when requests for service
have been denied, or allocations have been modified or disrupted.
Such mechanisms have been implemented in the Wideband Network for
streams and dynamic multicast groups.
Priority and preemption mechanisms for a GN will have to be
implemented in an extremely simple way so that they can take effect
very quickly. It is likely that they will have to built into the
hardware of the switch fabric.
3.5. User and Network Services
As discussed in Section 2 above, there will need to be certain
services provided as part of the network operation to the users
(people) themselves and to the machines that connect to the network.
These services, which include such capabilities as white and yellow
pages (allowing users to determine what the appropriate network
identification is for other users and for network-available computing
resources) and distributed fault identification and isolation, are
needed in current networks and will continue to be required in the
networks of the future. The speed of the GN will serve to accentuate
this requirement, but at the same time will allow for new
architectures to be put in place for such services. For example,
Ethernet speeds in the local environment have allowed for more usable
services to be provided.
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3.5.1. Impact of High Bandwidth
One issue that will need to be addressed is the impact on the user of
such high-bandwidth capabilities. Users are already becoming
saturated by information in the modern information-rich environment.
(Many of us receive more than 50 electronic mail messages each day,
each requiring some degree of human attention.) Methods will be
needed to allow users to cope with this ever-expanding access to
data, or we will run the risk of users turning back to the relative
peace and quiet of the isolated office.
3.5.2. Distributed Network Directory
A distributed network directory can support the user-level directory
services and the lower-level name-to-address mapping services
described elsewhere in this report. It can also support distributed
systems and network management facilities by storing additional
information about named objects. For example, the network directory
might store node configurations or security levels.
Distributing the directory eases and decentralizes the administrative
burdens and provides a more robust and survivable implementation.
One approach toward implementing a distributed network directory
would be to base it upon the CCITT X.500/ISO DIS 9594 standard. This
avoids starting from ground zero and has the advantage of
facilitating interoperability with other communications networks.
However, research and development will be required even if this path
is chosen.
One area in which research and development are required is in the
services supplied by the distributed network directory. The X.500
standard is very general and powerful, but so far specific provisions
have been made only for storing information about network users and
applications. As mentioned elsewhere, multilevel security is not
addressed by X.500, and the approach taken toward authentication must
be carefully considered in view of DoD requirements. Also, X.500
assumes that administration of the directory will be done locally and
without the need for standardization; this may not be true of GN or
the larger national research network.
The model and algorithms used by a distributed network directory
constitute a second area of research. The model specified by X.500
must be extended into a framework that provides the necessary
flexibility in terms of services, responsiveness, data management
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policies, and protocol layer utilization. Furthermore, the internal
algorithms and mechanisms of X.500 must be extended in a number of
areas; for example, to support redundancy of the X.500 database,
internal consistency checking, fuller sharing of information about
the distribution of data, and defined access-control mechanisms.
4. Avenues of Approach
Ongoing research and commercial activities provide an opportunity for
more rapidly attacking some of the above research issues. At the
same time, there needs to be attention paid to the overall technical
approach used to allow multiple potential solutions to be explored
and allow issues to be attacked in parallel.
4.1. Small Prototype vs. Nationwide Network
The central question is how far to jump, and how far can the current
approaches get. That is, how far will connectionless network service
get us, how far will packet switching get us, and how far do we want
to go. If our goal is a Gbit/s net, then that is what we should
build. Building a 100 Mbit/s network to achieve a GN is analogous to
climbing a tree to get to the moon. It may get you closer, but it
will never get you there.
There are currently some network designs which can serve as the basis
for a GN prototype. The next step is some work by experts in
photonics and possibly high-speed electronics to explore ease of
implementation. Developing a prototype 3-5 node network at a Gbit/s
data rate is realistic at this point and would demonstrate wide-area
(40 km or more) Gbit/s networking.
DARPA should consider installing a Gbit/s cross-country set of
connected links analogous to the NSF backbone in 2 years. A Gbit/s
link between the east and west coasts would open up a whole new
generation of (C3I), distributed computing, and parallel computing
research possibilities and would reestablish DARPA as the premier
network research funding agency in the country. This will require
getting "dark" fiber from one or more of the common carriers and some
collaboration with these organizations on repeaters, etc. With this
collaboration, the time to a commercial network in the Gbit/s range
would be substantially reduced, and the resulting nationwide GN would
give the United States an enormous technical and economic advantage
over countries without it.
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Demonstrating a high-bandwidth WAN is not enough, however. As one
can see from the many research issues identified above, it will be
necessary to pursue via study and experiment the issues involved in
interconnecting high-bandwidth networks into a high-bandwidth
internet. These experiments can be done through use of a new
generation of internet, even if it requires starting at lower speeds
(e.g., T1 through 100 Mbit/s). Appropriate care must be given,
however, to assure that the capabilities that are demonstrated are
applicable to the higher bandwidths (Gbit/s) as they emerge.
4.2. Need for Parallel Efforts/Approaches
Parallel efforts will therefore be required for two major reasons.
First is the need to pursue alternative approaches (e.g., different
strategies for high-bandwidth switching, different addressing
techniques, etc). This is the case for most research programs, but
it is made more difficult here by the costs of prototyping. Thus, it
is necessary that appropriate review take place in the decisions as
to which efforts are supported through prototyping.
In addition, it will be necessary to pursue the different aspects of
the program in parallel. It will not be possible to wait until the
high-bandwidth network is available before starting on prototyping
the high-bandwidth internet. Thus, a phased and evolutionary
approach will be needed.
4.3. Collaboration with Common Carriers
Computer communication networks in the United States today
practically ignore the STN (the Switched Telephone Network), except
for buying raw bandwidth through it. However, advances in network
performance are based on improvements in the underlying communication
media, including satellite communication, fiber optics, and photonic
switching.
In the past we used "their" transmission under "our" switching. An
alternative approach is to utilize the common-carrier switching
capabilities as an integral part of the networking architecture. We
must take an objective scientific and economic look and reevaluate
this question.
Another place for cooperation with the common carriers is in the area
of network addressing. Their addressing scheme ("numbering plan")
has a few advantages such as proven service to 300 million users [4].
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On the other hand, the common carriers have far fewer administrative
domains (area codes) than the current plethora of locally
administered local area networks in the internet system.
It is likely that future networks will eventually be managed and
operated by commercial communications providers. A way to maximize
technology transfer from the research discussed here to the
marketplace is to involve the potential carriers from the start.
However, it is not clear that the goals of commercial communications
providers, who have typically been most interested in meeting the
needs of 90+ percent of the user base, will be compatible with the
goals of the research described here. Thus, while we recommend that
the research program involve an appropriate amalgam of academia and
industry, paying particular attention to involvement of the potential
system developers and operators, we also caution that the specific
and unique goals of the DARPA program must be retained.
4.4. Technology Transfer
As we said above, it is our belief that future networks will
ultimately be managed and operated by commercial communications
providers. (Note that this may not be the common carriers as we know
them today, but may be value-added networks using common carrier
facilities.) The way to assure technology transfer, in our belief, is
to involve the potential system developers from the start. We
therefore believe that the research program would benefit from an
appropriate amalgam of university and industry, with provision for
close involvement of the potential system developers and operators.
4.5. Standards
The Internet program was a tremendous success in influencing national
and international standards. While there were changes to the
protocols, the underlying technology and approaches used by CCITT and
ISO in the standardization of packet-switched networks clearly had
its roots in the DARPA internet. Nevertheless, this has had some
negative impact on the research program, as the evolution of the
standards led to pressure to adopt them in the research environment.
Thus, it appears that there is a "catch-22" here. It is desirable
for the technology base developed in the research program to have
maximal impact on the standards activities. This is expedited by
doing the research in the context of the standards environment.
However, standards by their very nature will always lag behind the
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research environment.
The only reasonable approach, therefore, appears to be an occasional
"checkpointing" of the research environment, where the required
conversions take place to allow a new plateau of standards to be used
for future evolution and research. A good example is conducting
future research in mail using X.400 and X.500 where possible.
5. Conclusions
We hope that this document has provided a useful compendium of those
research issues critical to achieving the FCCSET phase III
recommendations. These problems interact in a complex way. If the
only goal of a new network architecture was high speed, reasonable
solutions would not be difficult to propose. But if one must achieve
higher speeds while supporting multiple services, and at the same
time support the establishment of these services across
administrative boundaries, so that policy concerns (e.g., access
control) must be enforced, the interactions become complex.
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APPENDIX
A. Current R and D Activities
In this appendix, we provide pointers to some ongoing activities in
the research and development community of which the group was aware
relevant to the goal of achieving the GN. In some cases, a short
abstract is provided of the research. Neither the order of the
listing (which is random) nor the amount of detail provided is meant
to indicate in any way the significance of the activity. We hope
that this set of pointers will be useful to anyone who chooses to
pursue the research issues discussed in this report.
1. Grumman (at Bethpage) is working on a three-year DARPA
contract, started in January 1988 to develop a 1.6 Gbit/s LAN,
for use on a plane or ship, or as a "building block". It is
really raw transport capacity running on two fibers in a
token-ring like mode. First milestone (after one year?) is to
be a 100 Mbit/s demonstration.
2. BBN Laboratories, as part of its current three-year DARPA
Network-Oriented Systems contract, has proposed design
concepts for a 10-100 Gbit/s wide area network. Work under
this effort will include wavelength division multiplexing,
photonic switching, self-routing packets, and protocol design.
3. Cheriton (Stanford) research on Blazenet, a high-bandwidth
network using photonic switching.
4. Acampora (Bell Labs) research on the use of wavelength
division multiplexing for building a shared optical network.
5. Yeh is reserching a VLSI approach to building high-bandwidth
parallel processing packet switch.
6. Bell Labs is working on a Metropolitan Area Network called
"Manhattan Street Net." This work, under Dr. Maxemchuck, is
similar to Blazenet. It is in the prototype stage for a small
number of street intersections; ultimately it is meant to be
city-wide. Like Blazenet, is uses photonic switching 2 x 2
lithium niobate block switches.
7. Ultra Network Technologies is a Silicon Valley company which
has a (prototype) Gbit/s fiber link which connects backplanes.
This is based on the ISO-TP4 transport protocol.
8. Jonathan Turner, Washington University, is working on a
Batcher-Banyan Multicast Net, based on the "SONET" concept,
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which provides 150 Mbit/s per pipe.
9. David Sincowskie, Bellcore, is working with Batcher-Banyan
design and has working 32x32 switches.
10. Stratacom has a commercial product which is really a T1 voice
switch implemented internally by a packet switch, where the
packet is 192 bits (T1 frame). This switch can pass 10,000
packets per second.
11. Stanford NAB provides 30-50 Mbit/s throughput on 100 Mbit/s
connection using Versatile Message Transaction Protocol (VMTP)
[see RFC 1045]
12. The December issue of IEEE Journal on Selected Areas in
Communications, provides much detail concerning interconnects.
13. Ultranet Technology has a 480 Mbit/s connection using modified
ISO TP4.
14. At MIT, Dave Clark has an architecture proposal of interest.
15. At CMU, the work of Eric Cooper is relevant.
16. At Protocol Engines, Inc., Greg Chesson is working on an XTP-
based system.
17. Larry Landweber at Wisconsin University is doing relevant
work.
18. Honeywell is doing relevant work for NASA.
19. Kung at CMU is working on a system called "Nectar" based on a
STARLAN on fiber connecting dissimilar processors.
20. Burroughs (now Unisys) has some relevant work within the IEEE
802.6 committee.
21. Bellcore work in "Switched Multimedia Datanet Service" (SMDS)
is relevant (see paper supplied by Dave Clark).
22. FDDI-2, a scheme for making TDMA channel allocations at 200
Mbit/s.
23. NRI, Kahn-Farber Proposal to NSF, is a paper design for high-
bandwidth network.
24. Barry Goldstein work, IBM-Yorktown.
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25. Bell Labs S-Net, 1280 Mbit/s prototype.
26. Fiber-LAN owned by Bell South and SECOR, a pre-prototype 575
Mbit/s Metro Area Net.
27. Bellcore chip implementation of FASTNET (1.2 Gbit/s).
28. Scientific Computer Systems, San Diego, 1.4 Gbit/s prototype.
29. BBN Monarch Switch, Space Division pre-prototype, chips being
fabricated, 64 Mbit/s per path.
30. Proteon, 80 Mbit/s token ring.
31. Toronto University, 150 Mbit/s "tree"--- really a LAN.
32. NSC Hyperchannel II, reputedly available at 250 Mbit/s.
33. Tobagi at Stanford working on EXPRESSNET; not commercially
available.
34. Columbia MAGNET-- 150 Mbit/s.
35. Versatile Message Transaction Protocol (VMTP).
36. ST integrated with IP.
37. XTP (Chesson).
38. Stanford Transport Gateway.
39. X.25/X.75.
40. Work of the Internet Activities Board.
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B. Gigabit Working Group Members
Member Affiliation
Gordon Bell Ardent Computers
Steve Blumenthal BBN Laboratories
Vint Cerf Corporation for National Research Initiatives
David Cheriton Stanford University
David Clark Massachusetts Institute of Technology
Barry Leiner (Chairman) Research Institute for Advanced Computer Science
Robert Lyons Defense Communication Agency
Richard Metzger Rome Air Development Center
David Mills University of Delaware
Kevin Mills National Bureau of Standards
Chris Perry MITRE
Jon Postel USC Information Sciences Institute
Nachum Shacham SRI International
Fouad Tobagi Stanford University
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End Notes
[1] Workshop on Computer Networks, 17-19 February 1987, San Diego,
CA.
[2] "A Report to the Congress on Computer Networks to Support
Research in the United States: A Study of Critical Problems and
Future Options", White House Office of Scientific and Technical
Policy (OSTP), November 1987.
[3] We distinguish in the report between development of a backbone
network providing gigabit capacity, the GB, and an
interconnected set of high-speed networks providing high-
bandwidth service to the user, the Gigabit Network (GN).
[4] Incidentally, they already manage to serve 150 million
subscribers in an 11-digit address-space (about 1:600 ratio).
We have a 9.6-digit address-space and are running into troubles
with much less than 100,000 users (less than 1:30,000 ratio).
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