The Internet is currently passively pushing bits between end-host machines, be it servers, fixed or mobile user devices, or sensors. The network does not "understand" what is being transferred, i.e., it is not content-aware. This agnostic mode of operation affects several of its key functionalities, for example, efficient content distribution and content-aware traffic engineering. As a result, the network is not able to cope well with the exponentially increasing amounts of multimedia content access which constitute the major mode of use in recent years. Fixed and mobile network providers keep continuously upgrading their infrastructures but the situation has become unsustainable due to their eroding profit margins. There is an urgent need to rethink traffic management under the umbrella of active content management, rather than passive content transfer, allowing ISPs to control traffic better and achieve a sustainable model for the long-term evolution of their networks. New approaches that maximise traffic localisation are essential for long-term global network sustainability.
In this context, Information-Centric Networking (ICN) has emerged as an alternative to the current host-to-host communication paradigm and proposes direct communication between user applications and the content itself, putting the actual information or content in the forefront and disregarding location. In ICN, the network transfers individual, identifiable content chunks, instead of data containers, i.e. packets, with opaque data. Contents are identified by name and relevant packets contain a part of a content chunk; the latter can be retrieved from the hosting server or from an in-network router cache, given that in-network caching is a key aspect of the ICN paradigm. Popular content tends to stay longer in network caches and "anycast routing" based on content names retrieves the closest copy to the user. This increases dramatically traffic localisation, avoids flash crowd effects and gives to network providers control over the information transferred, allowing them to engineer their networks based on the actual demand for named content.
Despite the considerable amount of effort that has been invested to date by the research community in location-independent routing based on content names, a widely acceptable and scalable solution is yet to be found. Any naming scheme would have to be able to accommodate 10**12 or more objects and content resolution and routing based solely on content names raises serious scalability concerns. In addition, the current IP-based Internet represents a massive infrastructure that cannot be easily replaced by a new, clean slate design. Having this in mind, and given our considerable research experience in the ICN area, we believe it is possible to achieve the ICN benefits of traffic localisation and sustainable network evolution without radical ICN approaches but by introducing, in an evolutionary manner, a "content layer" in the Internet architecture which will operate above the current network layer and below the transport layer, i.e. layer 3.5.
This layer will intercept communication, will produce unique location-independent names for requested content and will store the latter within the network according to sophisticated caching policies. Content will be accessed in an anycast fashion using ICN style of operation but overlaid over IP, exploiting the existence of scalable IP-based routing, maintaining full backwards compatibility and protecting current investment. In addition, congestion control will be dealt with in a hop-by-hop rather than an end-to-end basis within the content layer, maintaining at the same time compatibility with current end-to-end operation while maximizing the use of available network resources, increasing user quality of experience and paving the way for future Internet applications with stringent real-time requirements.
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