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Track 6: Network Technology and Engineering Panel: Active Networks By Paul Gillingwater, 22 July 1998 What is an active network? According to Richard A. Carlson of Argonne National
Laboratories, its the next big thing that could replace the current Internet
architecture. Traditional networks use source and destination addresses to help packets
find their way, but this is very much a passive operation, with devices known as
"routers" actually doing all the work. Packets themselves are sent on their way
based on the best available route to their destination, which is encoded in their header.
The next generation of "Active Networks" takes a different approach, where each
packet is smart embedded within the header is a small piece of program code, which
allows the packet to decide where, and more importantly how, it should go through the
network. In order to test these new types of networks (and allow researchers to try out many
other types of new networking techniques), Argonne has built the MORPHNet ( http://www.anl.gov:80/ECT/Public/research/morphnt2.htm
), which is intended to allow production network operations (such as e-mail, web and
backups) to co-exist peacefully with developers and network researchers. Another challenge they faced was to build and deploy test networks that could easily be
migrated into production, once they were sufficiently stable. In order to achieve this,
several layers of network infrastructure had to be considered. Starting with the hardware,
Argonne selected Dense Wave Division Multiplexing along with Sonet block multiplexing to
keep signals separate within the optical fiber paths that form the backbone of their net.
On top of this they provide ATM (Asynchronous Transfer Mode) at the media layer, to
provide control over Quality of Service (QOS) and both virtual and permanent paths. The
bearer service is presently IPv4, but of course IPv6 and other non-IP protocols can also
be used. A key goal of the project was to ensure that any experimental network protocol that
might accidentally "run amok" would not adversely affect the normal 24 hour a
day production applications, and vice versa, so that sufficient bandwidth would be
available for researchers during heavy production runs such as backups. This was partly
achieved using multiple SONET channels to guarantee separation. Achieving this
segmentation of infrastructure, with a single application as the point of control,
requires considerable cooperation with the hardware vendors of the switches and routers,
as well as the Telcos for the wide area networking. The issues of QOS (both requesting and
verification) needs some form of cross-layer signaling, combined with a mechanism for
encoding and enforcing policy, which the MORPHNet architecture attempted to address. In
summary, users and network administrators need and want more control, and building
"object-based" active networks with smart packets is one potentially effective
way to give it to them. The second speaker was Hilarie K. Orman, from Defense Advanced Research Projects
Agency. Originally one of the developers of the Internet and related technologies, DARPA
has shown that it is actively pursuing key research into future networks with this
presentation, which focused on the concept of "Active Packets." (The speaker
showed an amusing graphic depiction of flying Turing tapes, each with a payload of data,
and jokingly explained that the project had already shown a positive financial return in
the number of Tee-shirts with that picture sold to other researchers.) The DARPA vision of Active Networks (http://www.sds.lcs.mit.edu/darpa-activenet/) is
"Networks that turn on a dime." ( http://www.darpa.mil/ito/research/anets/index.html
). Such networks must be capable of rapid reconfiguration on the fly, allowing them
to be responsive to the needs of its applications. To achieve this, additional computation
is placed into the network, by associating small programs with each packet of data. The
tradeoffs (in terms of computational load, latency and increased packet size) seem to be
compensated for by the benefits of offering smarter services, especially as new
technologies (such as wireless LANs) become more sophisticated, with more demanding
applications. Traditional packet switching is the basis for most current Internet networking, which
is passive, address-based routing with all packets treated the same way. In Active
Networks, the Active Packets carry "how" information. These delivery
instructions are called a "method", and methods are applied to the data they
accompany by being executed within network devices such as routers or switches. An example of where Active Networks may be beneficial is with a multicast
videoconference that links participants in many different locations. The packets
associated with that application could be sent out onto the network containing the
instructions necessary to adjust bandwidth and quality of service dynamically, in order to
ensure the optimum usage of the network resources. Other types of dynamic methods could be
applied to eligible packets, depending upon the demands of the application, such as
caching, error correction, data compression and of course encryption. The Active Networks research group is developing detailed high-level specifications in
three areas: Node Architecture, API and Development tools, Security Architecture. One final example of a smart packet at work is a traceback using Active Packets to the
source of a denial-of-service attack on the Internet. Such an Active Packet would find its
way to the router nearest to the origin of the attack, requesting a small filter or
firewall to be dynamically installed in that router to prevent future attacks. The third speaker was Christian Tschudin of the University of Zuerich, Switzerland. He
described work that has been going on in Zuerich since 1993, under the "Messenger
Project." This features a mobile program (typically less than 1500 bytes in size,
around the size of a typical Ethernet packet), written in a purpose-developed language
called M0. The messenger project has been quite successful, establishing several nodes in Japan,
the USA and Europe, of the Active Networking ( http://cuiwww.unige.ch/tios/msgr/msgr.html
). Messengers are "autonomous flows of control that can spawn across the
network." Starting with a "stupid network", messengers are like a germ or
worm that propagate across the network, copying themselves from node to node to deploy
services throughout the network. In this model, a single Messenger contains (DNA-like) all
the information necessary to replicate itself, and even if all the nodes but one in the
network were purged, it would begin again to re-deploy itself. A crucial finding of the Messenger Project was that the network should start as dumb as
possible, thereby reducing biased choices, and that all services should where possible be
deployed as mobile code. At this point, Mr Tschudin drew parallels from the Science
Fiction world of Star Trek, contrasting the centralized control of the "Borg"
against the co-operative collective of the "Federation." Using this model, he
identified two areas where some choices needed to be made in advance of messenger
deployment, that is, security and resource allocation. Security appears to impose choices about the trust and authenticity of both packets and
nodes. Such authentication, which could be implemented by "hardening" packets
with both encrypted contents and methods, was generally computationally expensive, but
necessary where a network is not under complete control. Resource allocation, which was
identified as probably the most difficult and urgent problem of Active Networks, looks at
questions of Quality of Service, and how much of a esource a packet could consume (where
resources might include bandwidth, cache RAM, computation capability or certificate
administration.) The essential solution to the resource issue seems to be based on an economic model,
where the packet equivalent of money (in terms of Teleclicks, a TTL counter or even
out-of-band reservation) dictates how packets could negotiate for resources. Such use of
artificial money could be vital as both a signaling mechanism, and as an audit function
for possible linking to "real" money. The final speaker, Ian Wakeman from the University of Sussex, presented a new
programming language called "Safetynet", which was developed from the ground up
as a semantically safe and strongly typed language for implementation of the methods
within Active Packets. Using the latest analytical and semantic techniques of Higher Order
Programming, Wakeman and his colleagues developed a design for a language which makes key
assumptions about its environment, and that forces most of the important checking to be
done at the compilation stage, rather than at run-time. After thinking seriously about how the Internet presently operates (accompanied by a
few beers in the local pub), the team developed guidelines for the language design that
excluded the possibility to modify routing or IP addressing, that took into account the
dynamic (i.e., failure prone) nature of todays Internet, and that seeks to protect
resources against unintentional program effects during run-time. Bugs (or even malicious
code) in an Active Network program should not be able to over-consume or destroy resources
shared with other applications. By enforcing very strong typing at the compile stage, the
Safetynet language seeks to replace run-time checking with static checking as much as
possible, and to fix important policy into programs up front, thereby resulting in higher
performance and safer code. The language design is now finalized, and a prototype compiler
(producing Java code) is nearing completion. In summary, this session, with its four capable speakers, offered an excellent
introduction to the field of Active Networking, with some very interesting examples of
techniques and methodologies that will be crucial to the success of "smart
packets" in making future networks more responsive to the needs and choices of users.
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