ICN Research Challenges
Author(s): Ioannis Psaras, Dirk Kutscher, Daniel Corujo, Kostas Pentikousis, Damien Saucez, Suyong Eum
This memo describes research challenges for Information-Centric Networking. Information-centric networking is an approach to evolve the Internet infrastructure to directly support this use by introducing uniquely named data as a core Internet principle. Data becomes independent from location,...
Network Working Group D. Kutscher, Ed. Internet-Draft NEC Intended status: Standards Track S. Eum Expires: August 14, 2013 NICT K. Pentikousis Huawei I. Psaras UCL D. Corujo Universidade de Aveiro D. Saucez INRIA February 10, 2013 ICN Research Challenges draft-kutscher-icnrg-challenges-00 Abstract This memo describes research challenges for Information-Centric Networking. Information-centric networking is an approach to evolve the Internet infrastructure to directly support this use by introducing uniquely named data as a core Internet principle. Data becomes independent from location, application, storage, and means of transportation, enabling in-network caching and replication. Challenges include naming, security, routing, system scalability, mobility management, wireless networking, transport services, in- network caching, and network management. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 14, 2013. Copyright Notice Kutscher, et al. Expires August 14, 2013 [Page 1] Internet-Draft ICN Challenges February 2013 Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Problems with Information Distribution Today . . . . . . . . . 4 3. ICN Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. ICN Research Challenges . . . . . . . . . . . . . . . . . . . 6 4.1. Naming and Security . . . . . . . . . . . . . . . . . . . 6 4.2. Routing and Resolution System Scalability . . . . . . . . 8 4.2.1. Route-By-Name Routing (RBNR) . . . . . . . . . . . . . 9 4.2.2. Lookup-By-Name Routing (LBNR) . . . . . . . . . . . . 9 4.2.3. Hybrid Routing (HR) . . . . . . . . . . . . . . . . . 10 4.3. Mobility Management . . . . . . . . . . . . . . . . . . . 10 4.4. Wireless Networking . . . . . . . . . . . . . . . . . . . 12 4.5. Transport Services . . . . . . . . . . . . . . . . . . . . 12 4.6. In-Network Caching . . . . . . . . . . . . . . . . . . . . 13 4.6.1. Cache Placement . . . . . . . . . . . . . . . . . . . 13 4.6.2. Content Placement -- Content-to-Cache Distribution . . 14 4.6.3. Request-to-Cache Routing . . . . . . . . . . . . . . . 15 4.7. Network Management . . . . . . . . . . . . . . . . . . . . 15 5. Link to and Impact on IETF Technologies . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7. Informative References . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Kutscher, et al. Expires August 14, 2013 [Page 2] Internet-Draft ICN Challenges February 2013 1. Introduction Distributing and manipulating named information is a major application in the Internet today. In addition to web-based content distribution, other distribution technologies (such as P2P and CDN) have emerged and are promoting a communication model of accessing data by name, regardless of origin server location. In order to respond to increasing traffic volume in the current Internet for applications such as mobile video and cloud computing, a set of disparate technologies and distribution services are applied that employ caching, replication and content distribution in different specific ways. These approaches are currently deployed in separate silos -- different CDN providers and P2P applications rely on specific distribution technologies. It is not possible to uniquely and securely identify named information independently of the distribution channel; and the different distribution approaches are typically implemented as an overlay, potentially leading to unnecessary inefficiency. For example, creating and sharing multimedia content in a social networking application today, typically requires uploading data objects to centralized service provider platforms, from where it can be accessed individually by other users. Even if content sharing is intended to happen locally, e.g., in a local network or local area, the actual communication will require interactions from any interested user with the service provider. CDNs can alleviate the situation only partly, because, due to organizational and economic reasons, it is not common to deploy CDN gear ubiquitously. Moreover, since CDNs and the HTTP communication sessions form overlays, the actual communication, i.e., the requests for named content and the actual responses, are largely invisible to the network, i.e., it is not easily possible to optimize efficiency and performance. For example in a wireless access network, it is not possible to leverage inherent broadcast functionality (to avoid duplicate transmission of the same content) due to limitations from point-to-point and overlay communication. Information-centric networking (ICN) is an approach to evolve the Internet infrastructure to directly support this use by introducing uniquely named data as a core Internet principle. Data becomes independent from location, application, storage, and means of transportation, enabling in-network caching and replication. The expected benefits are improved efficiency, better support for provenance verification and name-content binding validation, better scalability with respect to information/bandwidth demand and better robustness in challenging communication scenarios. Kutscher, et al. Expires August 14, 2013 [Page 3] Internet-Draft ICN Challenges February 2013 ICN concepts can be applied to different layers of the protocol stack: name-based data access can be implemented on top of the existing IP infrastructure, e.g., by providing resource naming, ubiquitous caching and corresponding transport services, or it can be seen as a packet-level internetworking technology that would cause fundamental changes to Internet routing and forwarding. In summary, ICN is expected to evolve the Internet architecture at different layers. This document describes research challenges for ICN that need to be addressed in order to achieve these goals. The objective of this document is to document these challenges and corresponding current approaches and to expose requirements that should be addressed by future research work. 2. Problems with Information Distribution Today The best current practice to manage this growth in terms of data volume and devices is to employ application-layer overlays such as CDNs, P2P applications, and M2M application platforms that cache content, provide location-independent access to data, and optimize its delivery. In principle, such platforms provide a service model of accessing named data objects (NDOs) (replicated web resources, M2M data in data centers) instead of a host-to-host packet delivery service model. However, since this functionality resides in overlays only, the full potential of content distribution and M2M application platforms cannot be leveraged as the network is not aware of data requests and data transmissions, leading to: o data having to travel sub-optimal routes depending on the overlay, and not the Internet layer, topology; o multicast and broadcast features of wireless networks cannot be leveraged, i.e., request and delivery for the same object have to be made multiple times; o overlays typically require a significant amount of infrastructure support, e.g., authentication portals, content storage, and applications servers, making it often impossible to establish local, direct communication; o the network not being aware of the nature of data objects and thus being unable to manage access and transmission (without layer violations); o provenance validation uses host authentication today, so that even if there are locally cached copies available, it is normally not Kutscher, et al. Expires August 14, 2013 [Page 4] Internet-Draft ICN Challenges February 2013 easily possible to validate their authenticity; and o many applications providing their own approach to caching, replication, transport, authenticity validation (if at all), although they all share similar models of accessing named data objects in the network. 3. ICN Concepts Fundamentally, ICN is providing access to named data as a first-order network service, i.e., the network is able to serve requests to named data natively. That means, network nodes can receive requests for named data and act on it, for example by forwarding the request to a suitable next-hop. Consequently, the network processes requests for named data objects (and corresponding responses) natively, i.e., it can see requests and responses. Every network nodes on a path is enabled to perform forwarding decisions, to cache objects etc. This enables the network to forward such requests on optimal paths, employing optimal transmission technologies at every node, e.g., broadcast/multicast transmission in wireless networks to avoid duplicate transmission of both requests and responses. In ICN, like in the Internet Protocol, there is a set of common concepts and node requirements beyond this basic service model. Naming data objects is a key concept. In general, ICN names do not represent neither network nodes nor interfaces -- they represent NDOs independent of their location. Names are the keys for forwarding decisions -- and they are used for matching requests to responses: In order to provide better support for accessing copies of NDOs regardless of their location, it is important to be able to validate that a response actually delivers the bits that correspond to an original request for named data. Name-content binding validation is a fundamental security service in ICN, and this is often achieved by establishing a verifiable binding between the object name and the actual object or an identity that has created the object. ICN can support other security services, such as provenance validation, encryption -- depending on the details of naming schemes, object models and assumptions on infrastructure support. Security services such as name-content binding validation are available to any node, i.e., not just the actual receivers. This is an important feature, for enabling ingress gateways to check object authenticity to prevent denial-of-service attacks. Based on these fundamental properties it is possible to leverage network storage ubiquitously: every node and every device can cache data objects and respond to requests for such objects -- it is not required to validate the authenticity of the node itself since name- Kutscher, et al. Expires August 14, 2013 [Page 5] Internet-Draft ICN Challenges February 2013 content bindings can be validated. Ubiquitous in-network storage can be used for different purposes: it can enable sharing, i.e., the same object copy can be delivered to multiple users/nodes as in today's proxy caches and CDNs. It can also be used to make communication more robust (and perform better) by enabling the network to answer requests from local caches (instead of from origin servers). In case of disruption (message not delivered), a node can re-send the request, and it could be answered by an on-path cache, i.e., on the other side of the disrupted link. The network itself would thus support retransmissions -- enabling shorter round-trip times and offloading origin servers and other parts of the network. The request/response model and ubiquitous in-network storage also enables new options for implementing transport services, i.e., reliable transmission, flow control etc. First of all, a request/ response model can enable receiver-driven transport regimes, i.e., receivers (the requestors of NDOs) can control message sending rates by regulating the request sending rate (assuming that every response message has to be triggered by a request message). Retransmission would be achieved by re-sending requests, e.g., after a timeout. Because objects can be replicated, object transmission and transport sessions would not necessarily have end-to-end semantics: requests can be answered by caches, and a node can select one or multiple next-hop destination for a particular request -- depending on configuration, observed performance or other criteria. This receiver-driven communication model potentially enables new interconnection and business models: a request for named data can be linked to an interest of a requestor (or requesting network) in data from another peer, which could suggest modeling peering agreements and charging accordingly. 4. ICN Research Challenges 4.1. Naming and Security Naming data objects is as important for ICN as naming hosts is for today's Internet. Fundamentally, ICN requires unique names for individual NDOs, since names are used for identifying objects independently of its location or container. It is important to establish a verifiable binding between the object and its name (name- data integrity ), so that a receiver can be sure that received bits actually represent the NDO (object authenticity). Information about an object's provenance, i.e., who generated or published it, is also useful to associate to the name. The above functions are fundamentally required for the information- Kutscher, et al. Expires August 14, 2013 [Page 6] Internet-Draft ICN Challenges February 2013 centric network to work reliably -- otherwise neither network elements nor receivers can trust objects' authenticity, which would enable several attacks including critical DoS attacks by injecting spoofed content into the network. There are different ways to use names and cryptography to achieve the desired functions [ICNNAMING] [ICNSURVEY], and there are different ways to manage namespaces correspondingly. Two naming schemes have largely been proposed: one with a hierarchical and one with a flat namespace. The hierarchical scheme has a structure similar to current URLs, where the hierarchy is rooted in a publisher prefix. The hierarchy enables aggregation of routing information, improving scalability of the routing system. In some cases, the names are human-readable, which makes it possible for users to manually type in names, reuse, and, to some extent, mapping name to a user's intent. The other naming scheme is self-certifying, meaning that the object's name-data integrity can be verified without needing a public key infrastructure (PKI) or other third party to first establish trust in the key. Self-certification is achieved by binding the hash of the content closely to the object's name. This can be done by directly embedding the hash of the content in the name. Another option is an indirect binding, which embeds the public key of the publisher in the name and signs the hash of the content with the corresponding secret key. The resulting names are typically non-hierarchical, or flat, although the publisher field provides structure that can be used for routing aggregation. There are design trade-offs for ICN naming affecting routing and security. Self-certifying names are not human readable nor hierarchical. They can however provide some structure for aggregation, for instance, a name part corresponding to a publisher. Without self-certification, as mentioned above, the infrastructure depends on a PKI for its operation, which can be impede a large-scale deployment. Specific research challenges include: o naming static data objects can be performed by using content hashes as part of object names, so that publishers calculate the hash over existing data objects and receivers (or any ICN node) can validate the name-content binding by re-calculating the hash and comparing it to the name (component). [I-D.farrell-decade-ni] specifies a concrete naming format for this. o naming dynamic objects is referring to use cases where the name has to be generated before the object is created (for example, Kutscher, et al. Expires August 14, 2013 [Page 7] Internet-Draft ICN Challenges February 2013 this could be the case for live streaming, when a publisher wants to make the stream available by registering stream chunk names in the network). One approach to this can be self-certified names as described above. o requestor privacy protection can be a challenge in ICN as a direct consequence of the accessing-named-data-objects paradigm: if the network can "see" requests and responses, it can also log request history for network segments or individual users, which can be undesirable, especially since name are typically expected to be long-lived. I.e., even if the name itself does not reveal much information, the assumption is that the name can be used to retrieve the corresponding data objects in the future. o Updating and versioning NDO can be challenging because it can contradict fundamental ICN assumptions: if an NDO can be replicated and stored in in-network storage for later retrieval, names have to be long-lived -- and the name-content binding must not change: updating an object (changing the content without generating a new name) is impossible. Versioning can be seen as one possible solution, possibly requiring a naming scheme that supports versioning (and a way for requestors to learn about versions). o Managing accessibility: whereas in ICN the general assumption is to enable ubiquitous access to NDOs, there can be relevant use cases where access to objects should be restricted, for example to a specific user group. There are different approaches for this, such as object encryption (requiring key distribution and related mechanisms) or the concept of scopes, e.g., based on names that can only be used/resolved under some constraints. 4.2. Routing and Resolution System Scalability ICN routing locates a data object based on its name which is initially provided by a requester. ICN routing is composed of three steps: a name resolution step, a discovery step, and a delivery step. The name resolution step translates the name of requesting data object into its locator. The discovery step routes user request to data object based on its name or locator. The last delivery step routes the data object back to the requester. Depending on how these steps are combined, ICN routing schemes can be categorized as: Route- By-Name Routing (RBNR), Lookup-By-Name Routing (LBNR), and Hybrid Routing (HR). Kutscher, et al. Expires August 14, 2013 [Page 8] Internet-Draft ICN Challenges February 2013 4.2.1. Route-By-Name Routing (RBNR) RBNR omits the first name resolution step. The name of data object is directly used to route user request to the data object. Therefore, routing information to each data object basically has to be maintained in the routing table. Since the number of data objects is huge (The number of originally published content files that ICN is expected to support was estimated as 10^11 back in 2007 [DONA]. However, there are still many people in ICN research community who believe that the number should be larger than 10^11 , e.g. 10^15 -- 10^22.), the size of routing table tends to be proportional to the number of data object unless any aggregation mechanism is introduced to the name of data object. On the other hand, RBNR reduces overall latency and simplifies the routing process due to the omission of the resolution process. For the delivery step, RBNR needs another identifier (ID) of either host or location to forward the requested data object back to the requester. Otherwise, an additional routing mechanism has to be introduced such as bread-crumb routing [BREADCRUMBS]: a request leaves behind a trail of breadcrumbs along its forwarding path, and then the response is forwarded back to the requester consuming the trail. Specific challenges include: o How to aggregate the names of data objects to reduce the number of routing entries? o How does user learn the name which is designed for aggregation by provider? (For example, although we name our contribution as "ICN research challenge", IRTF (provider) may want to change the name to "/IETF/IRTF/ ICN/Research challenge" for aggregation. In this case, how does a user learn the name "/IETF/IRTF/ICN/Research challenge" to retrieve the contribution initially named "ICN research challenge" without any resolution process?) o Without introducing the name aggregation scheme, can we still achieve a scalable routing by taking advantage of topological structure and distributed copies? e.g. compact routing [COMPACT], random walk [RANDOM] or Greedy routing [GREEDY], etc. o How to incorporate copies of a data object in in-network caches in this routing scheme? 4.2.2. Lookup-By-Name Routing (LBNR) LBNR uses the first name resolution step to translate the name of requesting data object into its locator. Then, the second discovery step is carried out based on the locator. Since IP address could be used as locators, the discovery step can depend on the current IP infrastructure. The delivery step can be implemented same as IP Kutscher, et al. Expires August 14, 2013 [Page 9] Internet-Draft ICN Challenges February 2013 routing. The locator of requester is included in the request message, and then the requested data object is delivered to the requester based on the locator. Specific challenges include: o How to build a scalable resolution system which provides * Fast lookup: mapping the name of data object to its locators (copies as well). * Fast update: the location of data object is expected to change frequently. Also, multiple data objects may change their locations at the same time, e.g. data objects in laptop. o How to incorporate copies of a data object in in-network caches in this routing scheme? 4.2.3. Hybrid Routing (HR) HR combines both RBNR and LBNR to benefit from their advantages. For instance, within a single administrative domain, e.g. ISP where scalability issue is not serious problem, RBNR can be adopted to reduce overall latency by omitting the resolution process. On the other hand, LBNR can be used to route among the domains which have their own prefix (locator). A specific challenge here is: o How to design a scalable mapping system, which given the name of data object, it should return a destination domain locator so that a user request can be encapsulated and forwarded to the domain? 4.3. Mobility Management IP was not designed to consider node mobility originally, forcing new connections towards the content sources to be made. With the proliferation of mobile terminals equipped with different kinds of access technologies, mobility became a highly sought solution to be available at the network layer, berthing Mobile IP [RFC5944] based protocols. However, this addition also placed a higher degree of complexity on the network operations due to the need for new network entities, new signaling messages and resulting side-mechanisms, such as tunneling. In that sense, novel content-centric network architectures that go beyond host-based mobility control, provide the ample grounds for the definition of operating mechanisms considering mobility as a prime requirement, right at the start. ICN naming for reaching content intrinsically supports mobility. For example, CCN [CCN] does not share the IP restriction of forwarding on spanning trees, so it is able to take advantage of multiple interfaces or adapt to the changes produced by rapid mobility (i.e., Kutscher, et al. Expires August 14, 2013 [Page 10] Internet-Draft ICN Challenges February 2013 there is no need to bind a layer 3 address into a layer 2 address). In fact, client mobility is simplified by allowing requests for new content to normally flow from different interfaces, or through newly connected points of attachment to the network. However, that simplicity may not be reflected when the node moving is the content source, requiring more complex support from the networking mechanisms in respect to different aspects, such as forwarding update and caching rebuilding. Furthermore, requirements become more stringent when support for seamless mobility is required, especially in cases such as real-time voice/video communications. These requirements are further exacerbated when mobile nodes are able to connect through wireless access interfaces of different technologies, where the performance and link conditions can vary widely depending of numerous factors. Here mobility management has an important role in terms of not only optimizing the handover process, but also to ideally ensure seamless transition from one point of attachment to the other. In this way, "seamless transition" ensures that the content reception by the user occurs in an unperceptive way to the user and/or application receiving that content. Moreover, this transition needs to be executed in parallel with ICN content identification and reaching mechanisms enabling scenarios, such as, preparation of the content reaching process at the target connectivity point, prior to the handover (to reduce link switch disturbances). Finally, these mobility aspects can also be tightly coupled with network management aspects, in respect to policy enforcement, link control and other parameters necessary for establishing the node's link to the network. The resulting mobility management process can thus enhance and evolve ICN aspects by making them aware (or able to contribute) to not only allow but also enhance possible mobility procedures. From this, a set of research challenges on ICN Mobility Management can be derived: o How can content reaching mechanisms interface with specific link operations, such as identifying which links are available for a certain content o How to make mobility as a service that is only activated when the specific user/content/conditions require it (i.e., a possible solution to maintain the mobility-agnostic aspect of generic ICN) o How to coordinate mobility management between the node and the network for optimization and policing procedures? Kutscher, et al. Expires August 14, 2013 [Page 11] Internet-Draft ICN Challenges February 2013 4.4. Wireless Networking Today, all wireless network/radio access technologies (L2) are developed with a clear assumption in mind: the waist of the protocol stack is (and will be) IP. This translates into answering a large set of questions, from how to handle broadcast to how to support multicast in a rather straightforward manner. Arguably, if one designs a future wireless access technology with an information- centric "layer 3", most of these answers would no longer be valid. Although this is clearly outside the scope of this document, a few research challenges that the wider community may be interested in include: o In the context of wireless access, how can we leverage the broadcast nature of the medium in an information-centric network? o Is it possible that by changing the network paradigm to ICN we can in practice increase the spectral efficiency (bits/s/Hz) of a wireless network beyond what would be possible with today's host- centric approaches? o How can a conversational service be supported at least as efficiently as today's SoA wireless network deliver? 4.5. Transport Services ICN's receiver-driven communication model as described above creates new option for transport protocol design -- it does not rely on end- to-end communication path from a sender to a receiver, because a requested object can be accessible in multiple different network locations. A node can thus decide how to utilize multiple sources, e.g., by sending parallel requests for the same object or by switching sources (or next hops) in a suitable schedule for a series of requests. In this model the requestor would control data rate by regulating its request sending rate and next by performing source/next-hop selections. Specific challenges are depending on the specific ICN approach in use, but general challenges for receiver-driven transport protocols (or mechanisms, since dedicated protocols might not be required) include flow and congestion control, fairness, network utilization, stability (of data rates under stable conditions) etc. [HRICP] describes a sample request rate control protocol and corresponding design challenges. ICN offers routers the possibility to aggregate requests and can use several paths, meaning that there is no such thing as end-to-end communication path, e.g., a router that receives two requests for the Kutscher, et al. Expires August 14, 2013 [Page 12] Internet-Draft ICN Challenges February 2013 same content at the same time only sends one requests to its neighbor. The aggregation of requests has a general impact on transport service design. Achieving fairness for requestors can be one challenge as it is not possible to identify the number of clients behind one particular request. A second problem related to request aggregation is the management of request retransmissions. Generally, it is assumed that a router will not transmit a request if it transmitted an identical request recently and because there is no information about the requester, the router cannot distinguish the initial request form a client from a retransmission from the same client. In such a situation, how routers can adapt their timers to use the best of the communication paths. Finally, aggregation of requests has an impact on the server (producer) side. This last has no way to determine the number of clients actually consuming the content it is producing. This shift of model influence the business model of the server, e.g., how to implement pay-per-click? 4.6. In-Network Caching Explicitly named content objects allow for caching in virtually any network element, including routers, proxy caches and end-host machines. In-network caching can therefore improve network performance by fetching content from nodes geographically placed closer to the end-user. Several issues that need further investigation have been identified with respect to in-network caching. Here we list some of the most important challenges that relate to the properties of the new ubiquitous caching system. 4.6.1. Cache Placement The declining cost of fast memory gives the opportunity to deploy caches in network routers and take advantage of explicitly named cached contents. There exist two approaches to in-network caching, namely on-path and off-path caching. Both approaches have to consider the issue of cache location. Off-path caching is similar to traditional proxy-caching, or CDN server placement. Retrieval of contents from off-path caches requires redirection of requests and therefore, is closely related to the Request-to-Cache Routing problem discussed below. Off-path caches have to be placed in strategic points within a network in order to reduce the redirection delays and the number of detour hops to retrieve cached contents. Previous research on proxy-caching and CDN deployment is helpful in this case. On the other hand, on-path caching requires less network intervention and fits more neatly in an information-/content-centric network. However, on-path caching requires line-speed operation, a fact that Kutscher, et al. Expires August 14, 2013 [Page 13] Internet-Draft ICN Challenges February 2013 places more constraints on the design and operation of in-network caching elements. Furthermore, the gain of such a system of on-path in-network caches relies on opportunistic/accidental cache hits and has therefore been considered of limited benefit, given the huge amount of contents hosted in the Internet. For this reason, network operators might initially consider only a limited number of network elements to be upgraded to in-network caching elements. The decision on which nodes should be equipped with caches is an open issue and might be based, among others, on topological criteria, or traffic characteristics. These challenges relate to both the Content Placement Problem and the Request-to-Cache Routing Problem discussed next. 4.6.2. Content Placement -- Content-to-Cache Distribution Given a number of (on-path or off-path) in-network caching elements, content-to-cache distribution will affect both the dynamics of the system, in terms of request redirections (mainly in case of off-path caches) and the gain of the system in terms of cache hits. A straightforward approach to content placement is on-path placement of contents as they travel from source to destination. This approach reduces the computation and communication overhead of placing contents within the network, but on the other hand might reduce the chances of hitting cached contents. This relates to the Request-to- Cache Routing problem discussed next. Furthermore, the number of replicas held in the system brings up resource management issues in terms of cache allocation. For example, continuously replicating content objects in all network elements results in redundant copies of the same objects. The issue of redundant replication has been investigated in the past for hierarchical web-caches. However, in hierarchical web-caching, overlay systems co-ordination between the data and the control plane can guarantee increased performance in terms of cache hits. Line- speed, on-path in-network caching poses different requirements and therefore, new techniques need to be investigated. In this direction, there already exist some studies that attempt to reduce redundancy of cached copies. However, the issue of coordinated content placement in on-path caches still remains open. The Content-to-Cache Allocation problem relates also to the characteristics of the content to be cached. Popular content might need to be put in places where it is going to be requested next. Furthermore, issues of "expected content popularity" might need to be considered in order for some contents to be given priority (e.g., popular content vs. one-timers). The criteria as to which contents should be given priority in in-network content caches relate also to the business relationships between content providers and network Kutscher, et al. Expires August 14, 2013 [Page 14] Internet-Draft ICN Challenges February 2013 operators. Such issues need to be investigated and relate also to the evaluation methodology discussed later on. 4.6.3. Request-to-Cache Routing In order to get advantage of cached contents, requests have to be forwarded to the nodes that temporarily host (cache) the corresponding contents. This challenge relates to name-based routing, discussed before. Requests should ideally follow the path to the cached content. However, instructions as to which content is cached where cannot be broadcast throughout the network. Therefore, the knowledge of a content's location at the time of the request might either not exist, or it might not be accurate (i.e., contents might have been removed by the time a request is redirected to a specific node). Co-ordination between the data and the control planes to update information of cached contents has been considered, but in this case scalability issues arise. We therefore, have two options. We either have to rely on opportunistic caching, where requests are forwarded to a server and in case the content they are looking for is found on the path, then content is fetched from this node (instead of the original server), or we employ cache-aware routing techniques. Cache-aware routing can either involve both the control and the data plane, or only one of them. Furthermore, cache-aware routing can be done in a domain-wide scale or can involve more than one individual AS. In the latter case, business relationships between ASes might need to be exploited in order to build a scalable model. 4.7. Network Management Managing networks has been a core craft in the IP-based host-centric paradigm ever since the technology was introduced in production networks. However, at the onset of IP, management was considered primarily as an add-on. Essential tools that are used daily by networkers, such as ping and traceroute, did not become widely available until more than a decade or so after IP was first introduced. Management protocols, such as SNMP, also became available much later than the original introduction of IP and many still consider them insufficient despite the years of experience we have running host-centric networks. Today, when new networks are deployed network management is considered a key aspect for any operator, a major challenge which is directly reflected in higher OPEX if not done well. If we want ICN to be deployed in infrastructure networks, development of management tools and mechanisms must go hand-in with the rest of the architecture design. Although defining FCAPS for ICN is clearly outside the scope of this Kutscher, et al. Expires August 14, 2013 [Page 15] Internet-Draft ICN Challenges February 2013 document, there is a need for creating basic tools early on while ICN is still in the design and experimentation phases that can evolve over time and help network operations centers (NOC) to define policies, validate that they are indeed used in practice, be notified early on about failures, determine and resolve configuration problems. AAA as well as performance management, from a NOC perspective, will also need to be considered. Given the expectations for a large number of nodes and unprecedented traffic volumes, automating tasks, or even better employing self-management mechanisms is preferred. The main challenge here is that all tools we have at our disposal today are node-centric, end-to-end oriented, or assuming a packet-stream communication environment. Rethinking reachability and operational availability, for example, can yield significant insights into how information-centric networks will be managed in the future. With respect to network management we see two different aspects. First, any operator needs to manage all resources available in the network, which can range from node connectivity to network bandwidth availability to in-network storage to multi-access support. In ICN, users will also bring into the network significant resources in terms of network coverage extension, storage, and processing capabilities. DTN characteristics should also be considered to the degree that this is possible (e.g. content dissemination through data mules). On the other hand, given that nodes and links are not at the center of an information-centric network, network management should capitalize on native ICN mechanisms. For example, in-network storage and name resolution can be used for monitoring, while native publish/subscribe functionality can be used for triggering notifications. However, the considerations on leveraging intrinsic ICN mechanisms and capabilities to support management operations go beyond a simple mapping exercise. In fact, not only it raises a series of challenges on its own, but also opens up new possibilities for both ICN and "network management" as a concept. For instance, naming mechanisms are central to ICN intrinsic operations, which are used to identify and reach content under different aspects (e.g., CCN uses a hierarchical namespace able to contain human-readable naming scheme, NetInf uses a flat naming structure, etc.). In this way, ICN is decoupled from host-centric aspects on which traditional networking management schemes rely upon. As such, questions are raised which can directly be translated into challenges for network management capability, such as, for example how to address a node or a network segment in a ICN naming paradigm, how to identify which node is connected "where", and if there is a host-centric protocol running from which the management process can also leverage upon. But, on the other hand, these same inherent ICN characteristics also Kutscher, et al. Expires August 14, 2013 [Page 16] Internet-Draft ICN Challenges February 2013 allow us to look into network management through a new perspective. By centering its operations around content, one can conceive new management operations addressing, for example, per-content management or access control, as well as analyzing performance per content name instead of per link or node. Moreover, such considerations can also be used to manage operational aspects of ICN mechanisms themselves. For example, [NDN-MGMT] re-utilizes inherent content-centric capabilities of CCN to manage optimal link connectivity for nodes, in concert with a network optimization process. Conversely, how these content-centric aspects can otherwise influence and impact management in other areas (e.g., security, resilience) is also important, as exemplified by in [ccn-access], where access control mechanisms are integrated into a prototype of the [PURSUIT] architecture. In this way, a set of core research challenges on ICN management can be derived as: o Manage and control content reception at the destination o Coordination of management information exchange and control between ICN nodes and ICN network control points Identification of management and controlling actions and items through information naming o Relationship between NDOs and host entities identification (i.e., how to identify a particular link, interface or flow that need to be managed) 5. Link to and Impact on IETF Technologies TBW later. 6. Security Considerations See naming and security challenges. 7. Informative References [BREADCRUMBS] Rosensweig, E. and J. Kurose, "Breadcrumbs: Efficient, Best-Effort Content Location in Cache Networks", In Proceedings of the IEEE INFOCOM 2009, April 2009. [CCN] Jacobsen, K, D, F, H, and L, "Networking Named Content", CoNEXT 2009 , December 2009. Kutscher, et al. Expires August 14, 2013 [Page 17] Internet-Draft ICN Challenges February 2013 [COMPACT] Cowen, L., "Compact routing with minimum stretch", In Journal of Algorithms, vol. 38, pp. 170--183, 2001. [DONA] Koponen, T., Ermolinskiy, A., Chawla, M., Kim, K., gon Chun, B., and S. Shenker, "A Data-Oriented (and Beyond) Network Architecture", In Proceedings of SIGCOMM 2007, August 2007. [GREEDY] Papadopoulos, F., Krioukov, D., Boguna, M., and A. Vahdat, "Greedy forwarding in dynamic scale-free networks embedded in hyperbolic metric spaces", In Proceedings of the IEEE INFOCOM, San Diego, USA, 2010. [HRICP] Carofiglio, G., Gallo, M., and L. Muscariello, "Joint hop- by-hop and receiver-driven interest control protocol for content-centric networks", In Proceedings of ACM SIGCOMM ICN 2012, DOI 10.1145/2342488.2342497, 2012. [I-D.farrell-decade-ni] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B., Keraenen, A., and P. Hallam-Baker, "Naming Things with Hashes", draft-farrell-decade-ni-10 (work in progress), August 2012. [ICNNAMING] Ghodsi, A., Koponen, T., Rajahalme, J., Sarolahti, P., and S. Shenker, "Naming in Content-Oriented Architectures", In Proceedings ACM SIGCOMM Workshop on Information-Centric Networking (ICN), 2011. [ICNSURVEY] Ahlgren, B., Dannewitz, C., Imbrenda, C., Kutscher, D., and B. Ohlman, "A Survey of Information-Centric Networking", In Communications Magazine, IEEE , vol.50, no.7, pp.26-36, DOI 10.1109/MCOM.2012.6231276, 2012. [NDN-MGMT] Corujo, D., Aguiar, R., Vidal, I., and J. Garcia-Reinoso, "A named data networking flexible framework for management communications", Communications Magazine, IEEE , vol.50, no.12, pp.36-43 , December 2012. [PURSUIT] Fotiou et al., N., "Developing Information Networking Further: From PSIRP to PURSUIT", In Proceedings of Proc. BROADNETS. ICST, 2010. [RANDOM] Gkantsidis, C., Mihail, M., and A. Saberi, "Random walks in peer-to-peer networks: algorithms and evaluation", Kutscher, et al. Expires August 14, 2013 [Page 18] Internet-Draft ICN Challenges February 2013 In Perform. Eval., vol. 63, pp. 241--263, 2006. [RFC5944] Perkins, C., "IP Mobility Support for IPv4, Revised", RFC5944, November 2010. [ccn-access] Fotiou, N., Marias, G., and G. Polyzos, "Access control enforcement delegation for information-centric networking architectures", In Proceedings of the second edition of the ICN workshop on Information-centric networking (ICN '12). ACM, New York, NY, USA, 85-90., 2012. Authors' Addresses Dirk Kutscher (editor) NEC Kurfuersten-Anlage 36 Heidelberg, Germany Phone: Email: firstname.lastname@example.org Suyong Eum National Institute of Information and Communications Technology 4-2-1, Nukui Kitamachi, Koganei Tokyo 184-8795 Japan Phone: +81-42-327-6582 Email: email@example.com Kostas Pentikousis Huawei Technologies Carnotstrasse 4 Berlin 10587 Germany Email: firstname.lastname@example.org Kutscher, et al. Expires August 14, 2013 [Page 19] Internet-Draft ICN Challenges February 2013 Ioannis Psaras University College London, Dept. of E.E. Eng. Torrington Place London WC1E 7JE United Kingdom Email: email@example.com Daniel Corujo Universidade de Aveiro Instituto de Telecomunicacoes, Campus Universitario de Santiago Aveiro P-3810-193 Portugal Email: firstname.lastname@example.org Damien Saucez INRIA Email: email@example.com Kutscher, et al. Expires August 14, 2013 [Page 20]