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Copyright,1995-2004
1
Issues from Internet Technologies
2 – Apps for Collaboration & Subversion
Roger Clarke, Xamax Consultancy, CanberraVisiting Prof/Fellow, Unis of N.S.W., Hong Kong,
A.N.U.
http://www.anu.edu.au/people/Roger.Clarke/ ........ II/CCCS-2-ACS.ppt
UofQ CCCS, 6 December 2004
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Copyright,1995-2004
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Apps for Collaboration & Subversion
Agenda
• From Master-Slave to Client-Server• From Client-Server to Peer-to-Peer• Proxy-Servers, incl. Nymity• Open Source and Open Content
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Star Topology / Master-Slave Architecture
1950s Onwards
HubDumb
Terminal
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Client-Server Architecture1970s Onwards
Intra-Organisational
Server
Client
LargeCentralDevice
SmallRemote
PC
LocalArea
Network
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Client-Server Architecture1980s Onwards
Internet-Mediated
Server
Client
Server
Server
TheInternet
Client
Client
Client
Client
Client
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Multiply-Connected Topology / P2P Architecture
1970s but esp. 1990s Onwards Internet-Mediated
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The Essential Nature of P2P• In principle, Any Device is a client and/or a server• In practice, Many Devices perform server-functions• Collaboration inherent to the software• Clients can find Servers• ‘Single Points-of-Failure’, Bottlenecks / Chokepoints are
avoided by means of networking dynamics • Enough Devices with Enough Resources participate as
Servers for discovery, and as Servers for services• 'Free-Riding' / 'Over-Grazing' of the 'Commons'
is restrained through software and psych. features
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Why P2P Is Attractive
• Much-reduced Dependence on individual devices and sub-networks (no central servers)
• Improved Resilience (inbuilt redundancy)• Much-improved Scalability (proportionality)• Much-improved ability to service highly-peaked
demand (more devices on the demand-side represent more server-resources)
• resistance to denial of service (DDOS) attacks (no central servers)
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Issues in P2P
• Vulnerability to masquerade, pollution attacks (decoys)
• Unpredictability of, and Volatility in, the locations of processing services and digital objects
• Lack of Central Control, hence challenges to the imposition of authority, reduction in accountability
• Security Challenges, esp. embedded malware• Surreptitious Enlistment of Devices (at least potential)• Reticulation of Digital Objects in breach of the wishes
of copyright-owners, governments, and individuals
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Internet Nodes at Work
Repeateror Hub
Bridgeor Switch
Gateway,Proxy-Server,
Network Cache
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Proxy-Servers
• A intermediating node that performs functions on behalf of the sending and/or receiving node
• Proxies can filter content, or substitute content
• A nymous proxy passes on a substituteIP-address and perhaps identifiers and even data
• A nym is:• Anonymous if unbreakable• Pseudonymous if the link can be discovered
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Closed, ‘Lock in’ Software
• Copyright Licences with very restrictive terms re reproduction, adaptation, re-distribution
• Source-Code is commonly not provided• The objective of the copyright owner is
to maximise revenue, by imposing constraints on both competitors and customers
• Such software is generally very expensive
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Open Source Software = Liberal Licence Terms
• The rationale is to enable cumulative improvements and enhancement, by exposing the source-code to ‘more eyes’
• The ‘Free Software’ movement, since 1982:Richard Stallman and Comrades – http://www.fsf.org/
‘free as in speech, not free as in beer’‘copyleft’, so that derivatives are free too
• The ‘Open Source Initiative’, since 1998Eric Raymond and Friends – http://www.opensource.org/
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Open Source Software – Licence Terms
• Ready Availability of:• a licence• executable code and source-code
• Licence Permissions to:• run the executable• reproduce both executable and source• re-distribute both executable and source• adapt the source• distribute adapted executables and source• distribute within larger software packages
• Licence Constraints to:• ensure that redistribution is no less liberal• prevent subversion of the objectives
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Open Content = Liberal Licence Terms
What It Is• Content available under liberal licensing terms,
and without technological protections
Motivations• to enable access
e.g. shared Learning-and-Teaching Materials• to encourage improvements and
enhancement by exposing the content to ‘more eyes’e.g. Wikipedia
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