Despite the success of Internet technology and protocols, their deficiencies become apparent with growing and emerging applications like 3G mobile devices or pervasive environments. In these fields, there is a growing demand for additional support of mobility, multi- or anycast communication, or service composition. ..

Wehrle, Klaus

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Bridging today’s Internet Heterogeneitywith a Content-oriented ApproachKlaus WehrleProtocol Engineering and Distributed Systems??Wilhelm-Schickard-Institute for Computer ScienceUniversita¨t Tu¨bingen, GermanyKlaus.Wehrle@uni-tuebingen.de1 MotivationDespite the success of Internet technology and protocols, their deficiencies be-come apparent with growing and emerging applications like 3G mobile devices orpervasive environments. In these fields, there is a growing demand for additionalsupport of mobility, multi- or anycast communication, or service composition.The drawback of existing approaches to these problems like Mobile IP, IP-Multicast, and active networks is twofold: on the one hand, the necessary mod-ifications to existing software systems, in particular operating systems, are sub-stantial and have thus failed to fully disperse through to existing end-systems.On the other hand, central networking infrastructure like routers have to providesupport for these techniques. Thus, both their introduction and the increasedadministration effort cause high costs for Internet service providers.Another crucial disadvantage is the centralized management and administra-tion of these approaches. They do not adapt well and often only with human in-tervention to rapid and significant changes in the infrastructure or user demands.As a promising alternative, the last few years have seen the rise of peer-to-peer(P2P) technology in which end hosts also form part of the routing and com-munication infrastructure itself. Its properties of decentralized self-organization,scalability, and fault-resilience make it a promising approach for the problemsfaced in highly mobile and fluctuating communication environments of personaland pervasive devices. Also in ad-hoc and ubiquitous scenarios, an immediateset-up of services without the need for central instances or provides may be acrucial advantage.With already existing and emerging device classes and technologies, theseenvironments become increasingly diverse. Thus, a central challenge to main-taining ubiquitous and uniform service accessibility in these environments istheir increasing heterogeneity.On the network layer, the gap between transmission characteristics is widen-ing with high-speed fiber optical links on the one and slow and unreliable wirelesstechnology on the other side of the spectrum which require individual protocol?? Parts of this project are funded by DAAD and Landesstiftung Baden-Wu¨rttemberg.Dagstuhl Seminar Proceedings 04411Service Management and Self-Organization in IP-based Networkshttp://drops.dagstuhl.de/opus/volltexte/2005/100ID Rsend(ID,data)Sender SEmpfänger Rinsert(ID,R)send(R,data)i3-OverlayFig. 1. Communication Paradigm of i3 : Indirectionsupport. Furthermore, the widespread use of private networks, address transla-tion, and firewalls subvert the idea of global connectivity IP is based on. This isparticularly problematic in seamlessly integrating mobile devices into such frag-mented networking environments and providing global access to services for themobile end systems.The diversity of applications and data formats make it hard to provide a uni-form and consistent usage experience to users. Today’s systems do not transcodedata transparently to the required format nor do they provide adequate supportfor multi- or anycast communication becoming increasingly important e.g. incollaborative scenarios.Heterogeneity on the device and end-system layer comes from the vast num-ber of different hardware platforms and their capabilities. Also the differences ine.g. operating systems, user interfaces, or display facilities necessitate the adap-tation of content to the individual properties and needs of devices and users.Thus, the heterogeneity of today’s Internet manifests in many aspects of in-frastructure, implementation, and user interaction. In order to make servicesaccessible to users seamlessly and independent of the devices they use, a com-munication platform is required that provides mobility support, group commu-nication, and service composition.2 Indirection as Fundamental PrincipleThe Internet Indirection Infrastructure (i3 ) strives to achieve these requirementsas a generic distributed platform for implementing arbitrary forms of commu-nication and services based on a decentralized self-organizing infrastructure. Itsfundamental principle is to introduce a layer of indirection to the communi-cation between peers. This principle is based on the observation that existingapproaches like Mobile IP, IP Multicast, or IP Anycast all use a logical or physi-cal point of indirection to provide their services. By abstracting this observationinto a generic mechanism, i3 supports highly flexible forms of communicationand services.In i3, every communication connection runs across at least one point of in-direction. These indirection points are identified by globally unique IDs. Thus,i3 moves away from addressing based on the endpoints of the communication2SenderID R2send(ID,data)insert(ID,R2)send(R2,data)ReceiverÆ R2Sender ID R1send(ID,data)insert(ID,R1)Receiver R1send(R1,data)(a) Mobility SupportSender SID R2ID ID*ID R1ID* R4ID* R3R1R2R3R4(b) Multicast SupportFig. 2. Realizing Communication Patterns with i3partners to content-based addressing and data transfer using the IDs of theindirection points.Senders augment their data with a destination ID to which the packets arerouted by i3. Receivers insert tuples (triggers) of the form (ID, R) where R can beeither the IP address and port of an end-host or another i3 -ID. This informationis used by i3 to forward all data for ID to R, i.e. a receiving end-host or anotherindirection point.The nodes participating in the i3 infrastructure are organized in a distributedhash table (DHT) which provides decentralized and fault resilient routing ser-vices with the i3 IDs acting as keys into the DHT. The IDs and their associateddata are not implemented by a fixed node as the structure of the DHT can changedynamically. At the same time, the DHT layer guarantees scalability and relia-bility. The overhead introduced by the level of indirection can be mitigated formost packets by caching routing information and thus avoiding explicit routingvia the DHT.2.1 Realizing MobilityMobility is inherently supported by i3 as end-hosts are no longer directly ad-dressed. When the network address of a node changes due to a transition toa different physical network, it only needs to update its triggers with its newaddress. i3 will then route packets to the end-host using this new address.2.2 Realizing MulticastMulticast can be achieved in a similarly straight-forward manner. In i3, every IDmay be associated with multiple triggers and i3 forwards data to the destinationsin all triggers with the same ID. Thus every end-host interested in data fora specific ID simply inserts a trigger for this ID with its own address as thedestination. In order to maintain scalability even for large numbers of end-hosts,custom and flexible multicast trees can be formed using additional triggers thatmove the cascading of data closer to the receivers.3(ID, data_real)IDID(S1, R2)S1( (S1, R2), data_real)(R2, data_pcm)R1R2Service S1:TranscodingRealÆ PCMSender(S2, R2)S2(R1, data_real_small)( (S2 , R2 ), data_real)Service S2:Recoding tosmaller bandwidthFig. 3. Flexible Composition of Services with i32.3 Realizing AnycastA slight variation of the scheme enables i3 to support anycast: instead of usingexact matching when comparing packet IDs with trigger IDs, partial matching,e.g. longest prefix match, is employed. Thus, a packet is forwarded according tothe trigger best matching the packet ID. Different anycast strategies are modeledby choosing trigger IDs appropriately. For example, multiple trigger IDs with thesame prefix but a random suffix result in randomized anycast. Of course, choosingtrigger IDs based on certain metrics allows for optimizations with regard to e.g.link latency or reliability.2.4 Realizing Service CompositionWith an orthogonal extension to the trigger tuples, service composition can beachieved in i3 : the destination part may be not only a single address or IDbut a stack of them. Similar to IP source routing, this stack is attached to thepackets for such a trigger resulting in the packets being routed across all itemsin the stack. With this approach, flexible chains of services to operate on datacan be easily formed. Note how services can reuse other services transparentlyto the receiver and at the same time receivers can request customized servicecomposition according to their specific requirements.2.5 Integrating Applications without ModificationBy providing a single point of indirection for arbitrary services, i3 can helpto alleviate the problem of restricted network accessibility of end-hosts due tofirewalls and NAT routers. An i3 proxy [10] was developed which can be runinside such a restricted network to give access to services inside and outside thenetwork as a central and single point for authenticating and authorizing networkaccess.Another important functionality of the i3 proxy is to integrate legacy appli-cations with the i3 infrastructure in order to avoid source code modifications.4i3-OverlayProxy Proxy10.0.0.1 10.0.0.2IDAIDBTransparent IP „tunnel“ over i3Fig. 4. Transparent Tunneling of IP over i3Both existing client applications such as web browser and server applicationssuch as web servers are thus enabled to transparently make use of the advan-tages of i3.3 SummaryShortcomings of the existing IP technology, e.g. lack for mobility and multicast,have in practice not been successfully addressed. With the emergence of smallpersonal networked devices, these shortcomings negatively affect the connectiv-ity and usability of these devices. i3 tackles these problems as an overlay solutionto existing protocols and infrastructure. It provides a homogeneous decentralizedservice platform in a scalable, reliable, and self-organizing manner. With indi-rection as its fundamental principle, the diversity of end-systems can be bridgedand connectivity across private address space and firewalls can be ensured evenin mobile scenarios.References1. Steve Deering. Host Extensions for IP Multicasting. RFC 1112, August 1989.2. Internet Indirect Infrastructure, Project Homepage. http://i3.cs.berkeley.edu/.3. K. Lakshminarayanan, A. Rao, I. Stoica, and S. Shenker. Flexible and robust largescale multicast using i3. Technical Report CS-02-1187, UC Berkeley, 2002.4. C. Perkins. IP Mobility Support. RFC 2002, October 1996.5. L. Peterson, T. Anderson, D. Culler, and T. Roscoe. A blueprint for introducingdisruptive technology into the internet. In Proc. of ACM HotNets-I, Princeton,USA, October 2002.6. R. Steinmetz and K. Wehrle. Peer-to-Peer-Networking und -Computing. GI-Spektrum, 27(1), February 2004.7. I. Stoica, D. Adkins, S. Zhaung, et al. Internet Indirection Infrastructure. InProceedings of ACM SIGCOMM’02, August 2002. Pittsburgh, PA.8. I. Stoica, K. Lakshminarayanan, and K. Wehrle. Support for Service Compositionin i3. In Proceedings of ACM Multimedia, October 2004. New York.9. Ion Stoica, Robert Morris, David Karger, Frans Kaashoek, and Hari Balakrish-nan. Chord: A scalable Peer-To-Peer lookup service for internet applications. InProceedings of the 2001 ACM SIGCOMM Conference, pages 149–160, 2001.10. Klaus Wehrle, Jayanthkumar Kannan, Ayumu Kubota, Karthik Lakshmi-narayanan, and Ion Stoica. Supporting legacy applications over i3. TechnicalReport UCB/CS-04-1342, UC Berkeley, 2004.11. S. Zhuang, K. Lai, I. Stoica, et al. Host Mobility Using an Internet IndirectionInfrastructure. In Proceedings of ACM MobiSys, 2003.5

Bridging today\u27s Internet Heterogeneity with a Content-oriented Approach

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Bridging today\u27s Internet Heterogeneity with a Content-oriented Approach

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