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diff --git a/doc/rfc/rfc6392.txt b/doc/rfc/rfc6392.txt new file mode 100644 index 0000000..4b30d4f --- /dev/null +++ b/doc/rfc/rfc6392.txt @@ -0,0 +1,2467 @@ + + + + + + +Internet Engineering Task Force (IETF) R. Alimi, Ed. +Request for Comments: 6392 Google +Category: Informational A. Rahman, Ed. +ISSN: 2070-1721 InterDigital Communications, LLC + Y. Yang, Ed. + Yale University + October 2011 + + + A Survey of In-Network Storage Systems + +Abstract + + This document surveys deployed and experimental in-network storage + systems and describes their applicability for the DECADE (DECoupled + Application Data Enroute) architecture. + +Status of This Memo + + This document is not an Internet Standards Track specification; it is + published for informational purposes. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Not all documents + approved by the IESG are a candidate for any level of Internet + Standard; see Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc6392. + +Copyright Notice + + Copyright (c) 2011 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. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + + + +Alimi, et al. Informational [Page 1] + +RFC 6392 DECADE Survey October 2011 + + +Table of Contents + + 1. Introduction ....................................................3 + 2. Survey Overview .................................................3 + 2.1. Terminology and Concepts ...................................3 + 2.2. Historical Context .........................................3 + 3. In-Network Storage System Components ............................5 + 3.1. Data Access Interface ......................................5 + 3.2. Data Management Operations .................................5 + 3.3. Data Search Capability .....................................6 + 3.4. Access Control Authorization ...............................6 + 3.5. Resource Control Interface .................................6 + 3.6. Discovery Mechanism ........................................7 + 3.7. Storage Mode ...............................................7 + 4. In-Network Storage Systems ......................................7 + 4.1. Amazon S3 ..................................................7 + 4.2. BranchCache ................................................9 + 4.3. Cache-and-Forward Architecture ............................11 + 4.4. Cloud Data Management Interface ...........................12 + 4.5. Content Delivery Network ..................................14 + 4.6. Delay-Tolerant Network ....................................16 + 4.7. Named Data Networking .....................................18 + 4.8. Network of Information ....................................19 + 4.9. Network Traffic Redundancy Elimination ....................22 + 4.10. OceanStore ...............................................23 + 4.11. P2P Cache ................................................24 + 4.12. Photo Sharing ............................................26 + 4.13. Usenet ...................................................28 + 4.14. Web Cache ................................................29 + 4.15. Observations Regarding In-Network Storage Systems ........31 + 5. Storage and Other Related Protocols ............................32 + 5.1. HTTP ......................................................32 + 5.2. iSCSI .....................................................33 + 5.3. NFS .......................................................34 + 5.4. OAuth .....................................................36 + 5.5. WebDAV ....................................................37 + 5.6. Observations Regarding Storage and Related Protocols ......39 + 6. Conclusions ....................................................40 + 7. Security Considerations ........................................40 + 8. Contributors ...................................................40 + 9. Acknowledgments ................................................41 + 10. Informative References ........................................41 + + + + + + + + + +Alimi, et al. Informational [Page 2] + +RFC 6392 DECADE Survey October 2011 + + +1. Introduction + + DECADE (DECoupled Application Data Enroute) is an architecture that + provides applications with access to provider-based in-network + storage for content distribution (hereafter referred to as only + "in-network storage" in this document). With access to in-network + storage, content distribution applications can be designed to place + less load on network infrastructure. As a simple example, a peer of + a Peer-to-Peer (P2P) application may upload to other peers through + its in-network storage, saving its usage of last-mile uplink + bandwidth. See [1] for further discussion. + + A major motivation for DECADE is the substantial increase in capacity + and reduction in cost offered by storage systems. For example, over + the last two decades, there has been at least a 30-fold increase in + the amount of storage that a customer can get for a given price (for + flash memory and hard disk drives) [2] [3] [4]. + + High-capacity and low-cost in-network storage devices introduce + substantial opportunities. One example of in-network storage is + content caches supporting Web and P2P content. DECADE differs from + existing content caches whose control fully resides with the owners + of the caching devices in that DECADE also allows applications to + control access to their allocated in-network storage, as well as the + resources consumed while accessing that storage (bandwidth, + connections, storage space). While designed in the context of P2P + applications, DECADE may be useful to other applications as well. + This document provides details on deployed and experimental + in-network storage solutions, and evaluates their suitability for + DECADE. + + We note that the survey presented in this document is only + representative of the research in this area. Rather than trying to + enumerate an exhaustive list, we have chosen some typical techniques + that lead to derivative works. + +2. Survey Overview + +2.1. Terminology and Concepts + + This document uses terms defined in [1]. + +2.2. Historical Context + + In-network storage has been used previously in numerous scenarios to + reduce network traffic and enable more efficient content + distribution. This section presents a brief history of content + distribution techniques and illustrates how DECADE relates to past + + + +Alimi, et al. Informational [Page 3] + +RFC 6392 DECADE Survey October 2011 + + + approaches. Systems have been developed with particular use cases in + mind. Thus, this survey is not meant to point out shortcomings of + existing solutions, but rather to indicate where certain capabilities + required in DECADE [5] are not provided by existing systems. + + In the early stage of Internet development, most Web content was + stored at a central server, and clients requested Web content from + the central server. In this architecture, the central server was + required to provide a large amount of bandwidth. As more and more + users access Web content, a central server can become overloaded. + The use of Web caches is one technique to reduce load on a central + server. Web caches store frequently requested content and provide + bandwidth for serving the content to clients. + + The ongoing growth of broadband technology in the worldwide market + has been driven by the hunger of customers for new multimedia + services as well as Web content. In particular, the use of audio and + video streaming formats has become common for delivery of rich + information to the public, both residential and business. + + To overcome this challenge of massive multimedia consumption, just + installing more Web caches will not be enough. Moving content closer + to the consumer results in greater network efficiency, improved + Quality of Service (QoS), and lower latency, while facilitating + personalization of content through broadband content applications. + In these edge technologies, Content Delivery Networks (CDNs) are a + representative technique. CDNs are based on a large-scale + distributed network of servers located closer to customers for + efficient delivery of digital content, including various forms of + multimedia content. + + Although CDNs are an effective means of information access and + delivery, there are two barriers to making CDNs a more common + service: cost and replication integrity. Deploying a CDN with its + associated infrastructure is expensive. A CDN also requires + administrative control over nodes with large storage capacity at + geographically dispersed locations with adequate connectivity. CDNs + can be scalable, but due to this administrative and cost overhead, + they are not rapidly deployable for the common user. + + The emergence and maturation of P2P has allowed improvements to many + network applications. P2P allows the use of client resources, such + as CPU, memory, storage, and bandwidth, for serving content. This + can reduce the amount of resources required by a content provider. + Multimedia content delivery using various P2P or peer-assisted + frameworks has been shown to greatly reduce the dependence on CDNs + and central content servers. However, the popularity of P2P + applications has resulted in increased traffic on ISP networks. P2P + + + +Alimi, et al. Informational [Page 4] + +RFC 6392 DECADE Survey October 2011 + + + caches (both transparent and non-transparent) have been introduced as + a way to reduce the burden. Though they can be effective in reducing + traffic in certain areas of ISP networks, P2P caches have their + shortcomings. In particular, they are application-dependent and thus + difficult to keep up to date with new and evolving P2P application + protocols. Second, applications may benefit from explicit control of + in-network storage, which P2P caches do not provide. See [1] for + further discussion. + + DECADE aims to provide a standard protocol allowing P2P applications + (including content providers) to make use of in-network storage to + reduce the traffic burden on ISP networks, while enabling P2P + applications to control access to content they have placed in + in-network storage. + +3. In-Network Storage System Components + + Before surveying individual technologies, we describe the basic + components of in-network storage. For consistency and for ease of + comparison, we use the same model to evaluate each storage technology + in this document. + + Note that the network protocol(s) used by a given storage system are + also an important part of the design. We omit details of particular + protocol choices in this document. + +3.1. Data Access Interface + + A set of operations is made available to a user for accessing data in + the in-network storage system. Solutions typically allow both read + and write operations, though the mechanisms for doing so can differ + drastically. + +3.2. Data Management Operations + + Storage systems may provide users the ability to manage stored + content. For example, operations such as delete and move may be + provided to users. In this survey, we focus on data management + operations that are provided to users and omit those provided to + system administrators. + + + + + + + + + + + +Alimi, et al. Informational [Page 5] + +RFC 6392 DECADE Survey October 2011 + + +3.3. Data Search Capability + + Some storage systems may provide the capability to search or + enumerate content that has been stored. In this survey, we focus on + search capabilities that are provided to users and omit those + provided to system administrators. An example of a search would be + to find the list of items stored by a given user over a given period + of time. + +3.4. Access Control Authorization + + Storage systems typically allow a user, content owner, or some other + entity to define the access policies for the in-network storage + system. The in-network storage system then checks the authorization + of a user before it stores or retrieves content. We define three + types of access control authorization: public-unrestricted, public- + restricted, and private. + + "Public-unrestricted" refers to content on an in-network storage + system that is widely available to all clients (i.e., without + restrictions). An example is accessing Wikipedia on the Web, or + anonymous access to FTP sites. + + "Public-restricted" refers to content on an in-network storage system + that is available to a restricted (though still potentially large) + set of clients, but that does not require any confidential + credentials from the client. An example is some content (e.g., a TV + show episode) on the Internet that can only be viewable in selected + countries or networks (i.e., white/black lists or black-out areas). + + "Private" refers to content on an in-network storage system that is + only made available to one or more clients presenting the required + confidential credentials (e.g., password or key). This content is + not available to anyone without the proper confidential access + credentials. + + Note that a combination of access control types may be applicable for + a given scenario. For example, the retrieval (read) of content from + an in-network storage system may be public-unrestricted, but the + storage (write) to the same system may be private. + +3.5. Resource Control Interface + + This is the interface through which users manage the resources on + in-network storage systems that can be used by other peers, e.g., the + bandwidth or connections. The storage system may also allow users to + indicate a time for which resources are granted. + + + + +Alimi, et al. Informational [Page 6] + +RFC 6392 DECADE Survey October 2011 + + +3.6. Discovery Mechanism + + Users use the discovery mechanism to find the location of in-network + storage, find an access interface or resource control interface, or + find other interfaces of in-network storage. + +3.7. Storage Mode + + Storage systems may use the following modes of storage: file system, + object-based, or block-based. + + A file system typically organizes files into a hierarchical tree + structure. Each level of the hierarchy normally contains zero or + more directories, each with zero or more files. A file system may + also be flat or use some other organizing principle. + + We define an object-based storage mode as one that stores discrete + chunks of data (e.g., IP datagrams or another type of aggregation + useful to an application) without a pre-defined hierarchy or + meta-structure. + + We define a block-based storage mode as one that stores a raw + sequence of bytes, with a client being able to read and/or write data + at offsets within that sequence. Data is typically accessed in + blocks for efficiency. A common example for this storage mode is raw + access to a hard disk. + + In this survey, we define "storage mode" to refer to how data is + structured within the system, which may not be the same as how it is + accessed by a client. For example, a caching system may cache + objects with hierarchical names, but may internally use an object- + based storage mode. + +4. In-Network Storage Systems + + This section surveys in-network storage systems using the methodology + defined above. The survey includes some systems that are widely + deployed today, some systems that are just being deployed, and some + experimental systems. The survey covers both traditional client- + server architectures and P2P architectures. The surveyed systems are + listed in alphabetical order. Also, for each system, a brief + explanation of the relevance to DECADE is given. + +4.1. Amazon S3 + + Amazon S3 (Simple Storage Service) [6] provides an online storage + service using Web (HTTP) interfaces. Users create buckets, and each + bucket can contain stored objects. Users are provided an interface + + + +Alimi, et al. Informational [Page 7] + +RFC 6392 DECADE Survey October 2011 + + + through which they can manage their buckets. Amazon S3 is a popular + backend storage service for other services. Other related storage + services are the Blob Service provided by Windows Azure [7], Google + Storage for Developers [8], and Dropbox [9]. + +4.1.1. Applicability to DECADE + + Amazon S3 is a very widely used (deployed) example of in-network + storage. Amazon S3 leases the storage to third-party companies for + disparate services. In particular, Amazon S3 has a rich model for + authorization (using signed queries) to integrate with a wide variety + of use cases. A focus for Amazon S3 is scalability. Particular + simplifications that were made are the absence of a general, + hierarchical namespace and the inability to update the contents of + existing data. + +4.1.2. Data Access Interface + + Users can read and write objects. + +4.1.3. Data Management Operations + + Users can delete previously stored objects. + +4.1.4. Data Search Capability + + Users can list contents of buckets to find objects matching desired + criteria. + +4.1.5. Access Control Authorization + + All methods of access control are supported for clients: public- + unrestricted, public-restricted, and private. + + For example, access to stored objects can be restricted by an owner, + a list of other Amazon S3 Web Service users, or all Amazon S3 Web + Service users; or can be open to all users (anonymous access). + Another option is for the owner to generate and sign a query (e.g., a + query to read an object) that can be used by any user until an owner- + defined expiration time. + +4.1.6. Resource Control Interface + + Not provided. + + + + + + + +Alimi, et al. Informational [Page 8] + +RFC 6392 DECADE Survey October 2011 + + +4.1.7. Discovery Mechanism + + Users are provided a well-known DNS name (either a default provided + by Amazon S3, or one customized by a particular user). Users + accessing S3 storage use DNS to discover an IP address where S3 + requests can be sent. + +4.1.8. Storage Mode + + Object-based, with the extension that objects can be organized into + user-defined buckets. + +4.2. BranchCache + + BranchCache [10] is a feature integrated into Windows (Windows 7 and + Windows Server 2008R2) that aims to optimize enterprise branch office + file access over WAN links. The main goals are to reduce WAN link + utilization and improve application responsiveness by caching and + sharing content within a branch while still maintaining end-to-end + security. BranchCache allows files retrieved from the Web servers + and file servers located in headquarters or data centers to be cached + in remote branch offices, and shared among users in the same branch + accessing the same content. BranchCache operates transparently by + instrumenting the HTTP and Server Message Block (SMB) components of + the networking stack. It provides two modes of operation: + Distributed Cache and Hosted Cache. + + In both modes, a client always contacts a BranchCache-enabled content + server first to get the content identifiers for local search. If the + content is cached locally, the client then retrieves the content + within the branch. Otherwise, the client will go back to the + original content server to request the content. The two modes differ + in how the content is shared. + + In the Hosted Cache mode, a locally provisioned server acts as a + cache for files retrieved from the servers. After getting the + content identifiers, the client first consults the cache for the + desired file. If it is not present in the cache, the client + retrieves it from the content server and sends it to the cache for + storage. + + In the Distributed Cache mode, a client first queries other clients + in the same network using the Web Services Discovery multicast + protocol [11]. As in the Hosted Cache mode, the client retrieves the + file from the content server if it is not available locally. After + retrieving the file (either from another client or the content + server), the client stores the file locally. + + + + +Alimi, et al. Informational [Page 9] + +RFC 6392 DECADE Survey October 2011 + + + The original content server always authorizes requests from clients. + Cached content is encrypted such that clients can decrypt the data + only using keys derived from metadata returned by the content server. + In addition to instrumenting the networking stack at clients, content + servers must also support BranchCache. + +4.2.1. Applicability to DECADE + + BranchCache is an example of an in-network storage system primarily + targeted at enterprise networks. It supports a P2P-like mode + (Distributed Cache) as well as a client-server mode (Hosted Cache). + Integration into the Microsoft OS will ensure wide distribution of + this in-network storage technology. + +4.2.2. Data Access Interface + + Clients transparently retrieve (read) data from a cache (on a client + or a Hosted Cache), since BranchCache operates by instrumenting the + networking stack. In the Hosted Cache mode, clients write data to + the Hosted Cache once it is retrieved from the content server. + +4.2.3. Data Management Operations + + Not provided. + +4.2.4. Data Search Capability + + Not provided. + +4.2.5. Access Control Authorization + + The access control method for clients is private. For example, + transferred content is encrypted, and can only be decrypted by keys + derived from data received from the original content server. Though + data may be transferred to unauthorized clients, end-to-end security + is maintained by only allowing authorized clients to decrypt the + data. + +4.2.6. Resource Control Interface + + The storage capacity of caches on the clients and Hosted Caches is + configurable by system administrators. The Hosted Cache further + allows configuration of the maximum number of simultaneous client + accesses. In the Distributed Cache mode, exponential back-off and + throttling mechanisms are utilized to prevent reply storms of popular + content requests. The client will also spread data-block access + among multiple serving clients that have the content (complete or + partial) to improve latency and provide some load balancing. + + + +Alimi, et al. Informational [Page 10] + +RFC 6392 DECADE Survey October 2011 + + +4.2.7. Discovery Mechanism + + The Distributed Cache mode uses multicast for discovery of other + clients and content within a local network. Currently, the Hosted + Cache mode uses policy provisioning or manual configuration of the + server used as the Hosted Cache. In this mode, the address of the + server may be found via DNS. + +4.2.8. Storage Mode + + Object-based. + +4.3. Cache-and-Forward Architecture + + Cache-and-Forward (CNF) [12] is an architecture for content delivery + services for the future Internet. In this architecture, storage can + be exploited on nodes within the network, either directly on routers + or deployed near the routers. CNF is based on the concept of store- + and-forward routers with large storage, providing for opportunistic + delivery to occasionally disconnected mobile users and for in-network + caching of content. The proposed CNF protocol uses reliable hop-by- + hop transfer of large data files between CNF routers in place of an + end-to-end transport protocol such as TCP. + +4.3.1. Applicability to DECADE + + CNF is an example of an experimental in-network storage system that + would require storage space on (or near) a large number of routers in + the Internet if it was deployed. As the name of the system implies, + it would provide short-term caching and not long-term network + storage. + +4.3.2. Data Access Interface + + Users implicitly store content at CNF routers by requesting files. + End hosts read content from in-network storage by submitting queries + for content. + +4.3.3. Data Management Operations + + Not provided. + +4.3.4. Data Search Capability + + Not provided. + + + + + + +Alimi, et al. Informational [Page 11] + +RFC 6392 DECADE Survey October 2011 + + +4.3.5. Access Control Authorization + + The access control method is public-restricted (to any client that is + part of the CNF network). + +4.3.6. Resource Control Interface + + Not provided. + +4.3.7. Discovery Mechanism + + A query including a location-independent content ID is sent to the + network and routed to a CNF router, which handles retrieval of the + data and forwarding to the end host. + +4.3.8. Storage Mode + + Object-based, with objects representing individual files. The + architecture proposes to cache large files in storage within the + network, though objects could be made to represent smaller chunks of + larger files. + +4.4. Cloud Data Management Interface + + The Cloud Data Management Interface (CDMI) is a specification to + access and manage cloud storage. CDMI is specified by the Storage + Networking Industry Association (SNIA). + + CDMI is a functional interface that applications can use to create, + retrieve, update, and delete data elements from the cloud. As part + of this interface, the client will be able to discover the + capabilities of the cloud storage offering and use this interface to + manage containers and the data that is placed in them. In addition, + metadata can be set on containers and their contained data elements + through this interface [13]. + + CDMI follows a traditional client-server model, and operates over an + HTTP interface using the Representational State Transfer (REST) + model. Similar to Amazon S3 buckets (see Section 4.1), users may + create containers in which data objects may be stored. Even though + data objects may be accessed via a user-defined name within a + container, it is also possible to access data objects via a storage- + defined Object ID, which is provided in the response upon creation of + a data object. + + + + + + + +Alimi, et al. Informational [Page 12] + +RFC 6392 DECADE Survey October 2011 + + +4.4.1. Applicability to DECADE + + CDMI is an important initiative to standardize storage interfaces for + cloud services, which are rapidly becoming an important type of + storage service. In particular, it specifies a set of operations for + creating, reading, writing, and managing data objects at a remote + server (or set of servers) via HTTP. + +4.4.2. Data Access Interface + + Users can read and write data objects, and also update data in + existing data objects. CDMI data objects are sent on the wire + embedded as a field in a JavaScript Object Notation (JSON) object. + The protocol also defines interfaces in which the contents of data + objects can be written via simple HTTP GET/PUT operations. + +4.4.3. Data Management Operations + + Users can delete already-existing data objects. The create operation + also supports modes in which the created object is copied or moved + from an existing data object. + + Data system metadata also allows users to configure policies + regarding time-to-live, after which a data object is automatically + deleted, as well as the redundancy with which a data object is + stored. + +4.4.4. Data Search Capability + + Users may list the contents of containers to locate data objects + matching any desired criteria. + +4.4.5. Access Control Authorization + + All methods of access control for clients are supported: public- + unrestricted, public-restricted, and private. + + In particular, CDMI allows access to data objects to be protected by + Access Control Lists (ACLs) that can allow or restrict access based + on user name, group, administrative status, or whether a user is + authenticated or anonymous. + +4.4.6. Resource Control Interface + + CDMI supports attributes 'cdmi_max_latency' and 'cdmi_max_throughput' + (set at either the level of containers, or a specific data object), + which control the level of service offered to any users accessing a + particular data object. + + + +Alimi, et al. Informational [Page 13] + +RFC 6392 DECADE Survey October 2011 + + +4.4.7. Discovery Mechanism + + Users are provided a well-known DNS name. The DNS name is resolved + to determine the IP address to which requests may be sent. + +4.4.8. Storage Mode + + Object-based, with the extension that objects can be organized into + user-defined containers. + +4.5. Content Delivery Network + + A CDN provides services that improve performance by minimizing the + amount of data transmitted through the network, improving + accessibility, and maintaining correctness through content + replication. CDNs offer fast and reliable applications and services + by distributing content to cache or edge servers located close to + users. See [14] for an additional taxonomy and survey. + + A CDN has some combination of content delivery, request routing, + distribution, and accounting infrastructures. The content-delivery + infrastructure consists of a set of edge servers (also called + surrogates) that deliver copies of content to end users. The + request-routing infrastructure is responsible for directing client + requests to appropriate edge servers. It also interacts with the + distribution infrastructure to keep an up-to-date view of the content + stored in the CDN caches. The distribution infrastructure moves + content from the origin server to the CDN edge servers and ensures + consistency of content in the caches. The accounting infrastructure + maintains logs of client accesses and records the usage of the CDN + servers. This information is used for traffic reporting and usage- + based billing. + + In practice, a CDN typically hosts static content including images, + video, media clips, advertisements, and other embedded objects for + Web viewing. A focus for CDNs is the ability to publish and deliver + content to end users in a reliable and timely manner. A CDN focuses + on building its network infrastructure to provide the following + services and functionalities: storage and management of content; + distribution of content among surrogates; cache management; delivery + of static, dynamic, and streaming content; backup and disaster + recovery solutions; and monitoring, performance measurement, and + reporting. + + Examples of existing CDNs are Akamai, Limelight, and CloudFront. + + + + + + +Alimi, et al. Informational [Page 14] + +RFC 6392 DECADE Survey October 2011 + + + The following description uses the term "content provider" to refer + to the entity purchasing a CDN service, and the term "client" to + refer to the subscriber requesting content via the CDN from the + content provider. + +4.5.1. Applicability to DECADE + + CDNs are a very widely used (deployed) example of in-network storage + for multimedia content. The existence and operation of the storage + system are totally transparent to the end user. CDNs typically + require a strong business relationship between the content providers + and content distributors, and often the business relationship extends + to the ISPs. + +4.5.2. Data Access Interface + + A CDN is typically a closed system, and generally provides only a + read (retrieve) access interface to clients. A CDN typically does + not provide a write (store) access interface to clients. The content + provider can access network edge servers and store content on them, + or edge servers can retrieve content from content providers. Client + nodes can only retrieve content from edge servers. + +4.5.3. Data Management Operations + + A content provider can manage the data distributed in different cache + nodes, such as moving popular data objects from one cache node to + another cache node, or deleting rarely accessed data objects in cache + nodes. User nodes, however, have no right to perform these + operations. + +4.5.4. Data Search Capability + + A content provider can search or enumerate the data each cache node + stores. User nodes cannot perform search operations. + +4.5.5. Access Control Authorization + + All methods of access control (for reading) are supported for + clients: public-unrestricted, public-restricted, and private. Some + CDN edge servers allow usage of HTTP basic authentication with the + origin server or restrictions by IP address, or they can use a token- + based technique to allow the origin server to apply its own + authorization criteria. + + As mentioned previously, clients typically cannot write to the CDN. + Writing is typically a private operation for the content providers. + + + + +Alimi, et al. Informational [Page 15] + +RFC 6392 DECADE Survey October 2011 + + +4.5.6. Resource Control Interface + + Not provided. + +4.5.7. Discovery Mechanism + + Content providers can directly find internal CDN cache nodes to store + content, since they typically have an explicit business relationship. + Clients can locate CDN nodes through DNS or other redirection + mechanisms. + +4.5.8. Storage Mode + + Though the addressing of objects uses URLs that typically refer to + objects in a hierarchical fashion, the storage mode is typically + object-based. + +4.6. Delay-Tolerant Network + + The Delay-Tolerant Network (DTN) [15] is an evolution of an + architecture originally designed for the Interplanetary Internet. + The Interplanetary Internet is a communication system envisioned to + provide Internet-like services across interplanetary distances in + support of deep space exploration. The DTN architecture can be + utilized in various operational environments characterized by severe + communication disruptions, disconnections, and high delays (e.g., a + month-long loss of connectivity between two planetary networks + because of high solar radiation due to sun spots). The DTN + architecture is thus suitable for environments including deep space + networks, sensor-based networks, certain satellite networks, and + underwater acoustic networks. + + A key aspect of the DTN is a store-and-forward overlay layer called + the "Bundle Protocol" or "Bundle Layer", which exists between the + transport and application layers [16]. The Bundle Layer forms a + logical overlay that employs persistent storage to help combat long- + term network interruptions by providing a store-and-forward service. + While traditional IP networks are also based on store-and-forward + principles, the amount of time of a packet being kept in "storage" at + a traditional IP router is typically on the order of milliseconds (or + less). In contrast, the DTN architecture assumes that most Bundle + Layer nodes will use some form of persistent storage (e.g., hard + disk, flash memory, etc.) for DTN packets because of the nature of + the DTN environment. + + + + + + + +Alimi, et al. Informational [Page 16] + +RFC 6392 DECADE Survey October 2011 + + +4.6.1. Applicability to DECADE + + The DTN is an example of an experimental in-network storage system + that would require fundamental changes to the Internet protocols. + +4.6.2. Data Access Interface + + Users implicitly cause content to be stored (until successfully + forwarded) at Bundle Layer nodes by initiating/terminating any + transaction that traverses the DTN. + +4.6.3. Data Management Operations + + Users can implicitly cause deletion of content stored at Bundle Layer + nodes via a "time-to-live" type of parameter that the user can + control (for transactions originating from the user). + +4.6.4. Data Search Capability + + Not provided. + +4.6.5. Access Control Authorization + + The access control method is public-restricted (to any client that is + part of the DTN) or private. + +4.6.6. Resource Control Interface + + Not provided. + +4.6.7. Discovery Mechanism + + A Uniform Resource Identifier (URI) approach is used as the basis of + the addressing scheme for DTN transactions (and subsequent store-and- + forward routing through the DTN network). + +4.6.8. Storage Mode + + Object-based. DTN applications send data to the Bundle Layer, which + then breaks the data into segments. These segments are then routed + through the DTN network, and stored in Bundle Layer nodes as required + (before being forwarded). + + + + + + + + + +Alimi, et al. Informational [Page 17] + +RFC 6392 DECADE Survey October 2011 + + +4.7. Named Data Networking + + Named Data Networking (NDN) [17] is a research initiative that + proposes to move to a new model of addressing and routing for the + Internet. NDN uses "named data"-based routing and forwarding, to + replace the current IP-address-based model. NDN also uses name-based + data caching in the routers. + + Each NDN Data packet will be assigned a content name and will be + cryptographically signed. Data delivery is driven by the requesting + end. Routers disseminate name-based prefix announcements by using + routing protocols such as Intermediate System to Intermediate System + (IS-IS) or the Border Gateway Protocol (BGP). The requester will + send out an "Interest" packet, which identifies the name of the data + that it wants. Routers that receive this Interest packet will + remember the interface it came from and will then forward it on a + name-based routing protocol. Once an Interest packet reaches a node + that has the desired data, a named Data packet is sent back, which + carries both the name and content of the data, along with a digital + signature of the producer. This named Data packet is then forwarded + back to the original requester on the reverse path of the Interest + packet [18]. + + A key aspect of NDN is that routers have the capability to cache the + named data. If a request for the same data (i.e., same name) comes + to the router, then the NDN router will forward the named data stored + locally to fulfill the request. The proponents of NDN believe that + the network can be designed naturally, matching data delivery + characteristics instead of communication between endpoints, because + data delivery has become the primary use of the network. + +4.7.1. Applicability to DECADE + + NDN is an example of an experimental in-network storage system that + would require storage space on a large number of routers in the + Internet. Named Data packets would be kept in storage in the NDN + routers and provided to new requesters of the same data. + +4.7.2. Data Access Interface + + Users implicitly store content at NDN routers by requesting content + (the named Data packets) from the network. Subsequent requests by + different users for the same content will cause the named Data + packets to be read from the NDN routers' in-network storage. + + + + + + + +Alimi, et al. Informational [Page 18] + +RFC 6392 DECADE Survey October 2011 + + +4.7.3. Data Management Operations + + Users do not have the direct ability to delete content stored in the + NDN routers. However, there will be some type of time-to-live + parameter associated with the named Data packets, though this has not + yet been specified. + +4.7.4. Data Search Capability + + Not provided. + +4.7.5. Access Control Authorization + + All methods of access control for clients are supported: public- + unrestricted, public-restricted, and private. + + The basic security mechanism in NDN is for the sender to digitally + sign the content (the named Data packets) that it sends. It is + envisioned that a complete access control system can be built on top + of NDN, though this has not yet been specified. + +4.7.6. Resource Control Interface + + Not provided. + +4.7.7. Discovery Mechanism + + Names are used as the basis of the addressing and discovery scheme + for NDN (and subsequent store-and-forward routing through the NDN + network). NDN names are assumed to be hierarchical and to be able to + be deterministically constructed. This is still an active area of + research. + +4.7.8. Storage Mode + + Object-based. NDN sends named Data packets through the network. + These Data packets are routed through the NDN network and stored in + NDN routers. + +4.8. Network of Information + + Similar to NDN (see Section 4.7), Network of Information (NetInf) + [19] is another information-centric approach in which the named data + objects are the basic component of the networking architecture. + NetInf is thus moving away from today's host-centric networking + + + + + + +Alimi, et al. Informational [Page 19] + +RFC 6392 DECADE Survey October 2011 + + + architecture where the nodes in the network are the primary objects. + In today's network, the information objects are named relative to the + hosts they are stored on (e.g., + http://www.example.com/information-object.txt). + + The NetInf naming and security framework builds the foundation for an + information-centric security model that integrates security deeply + into the architecture. In this model, trust is based on the + information itself. Information objects (IOs) are given a unique + name with cryptographic properties. Together with additional + metadata, the name can be used to verify the data integrity as well + as several other security properties, such as self-certification, + name persistency, and owner authentication and identification. The + approach also gives some benefits over the security model in today's + host-centric networks, as it minimizes the need for trust in the + infrastructure, including the hosts providing the data, the channel, + or the resolution service. + + In NetInf, the information objects are published into the network. + They are registered with a Name Resolution Service (NRS). The NRS is + also used to register network locators that can be used to retrieve + data objects that represent the published IOs. When a receiver wants + to retrieve an IO, the request for the IO is resolved by the NRS into + a set of locators. These locators are then used to retrieve a copy + of the data object from the "best" available source(s). NetInf is + open to use any type of underlying transport network. The locators + can thus be a heterogeneous set, e.g., IPv4, IPv6, Medium Access + Control (MAC), etc. + + NetInf will make extensive use of caching of information objects in + the network and will provide network functionality that is similar to + what overlay solutions such as CDNs and P2P distribution networks + (e.g., BitTorrent) provide today. + +4.8.1. Applicability to DECADE + + NetInf is an example of an experimental information-centric network + architecture that will require storage space for storage and caching + of information objects on a large number of NetInf nodes in the + Internet. + + + + + + + + + + + +Alimi, et al. Informational [Page 20] + +RFC 6392 DECADE Survey October 2011 + + +4.8.2. Data Access Interface + + Users will publish IOs with specific IDs into the network. This is + done by the client sending a register message to the NRS stating that + the IO with the specific ID is available. When another user wishes + to retrieve the IO, they will use the given ID to make a request for + the IO. The ID is then resolved by the NRS, and the IO is delivered + from a nearby in-network storage location. + +4.8.3. Data Management Operations + + Users do not have the direct ability to delete content stored in the + NetInf nodes. However, there can be some type of time-to-live + parameter associated with the information objects, though this has + not yet been specified. + +4.8.4. Data Search Capability + + Not provided. + +4.8.5. Access Control Authorization + + All methods of access control for clients are supported: public- + unrestricted, public-restricted, and private. The basic security + mechanism in NetInf is for the publisher to digitally sign the + content of the information object that it publishes. It is + envisioned that a complete access control system can be built on top + of NetInf, though this has not yet been specified. + +4.8.6. Resource Control Interface + + Not provided. + +4.8.7. Discovery Mechanism + + NetInf IDs are used for naming and accessing information objects. + The IDs are resolved by the NRS into locators that are used for + routing and transport of data through the transport networks. This + is still an active area of research. + +4.8.8. Storage Mode + + Object-based. From an application perspective, NetInf can be used + for publishing entire files or chunks of files. NetInf is agnostic + to the application perspective and treats everything as information + objects. + + + + + +Alimi, et al. Informational [Page 21] + +RFC 6392 DECADE Survey October 2011 + + +4.9. Network Traffic Redundancy Elimination + + Redundancy Elimination (RE) is used for identifying and removing + repeated content from network transfers. This technique has been + proposed to improve network performance in many types of networks, + such as ISP backbones and enterprise access links. One example of an + RE proposal is SmartRE [20], proposed by Anand et al., which focuses + on network-wide RE. In packet-level RE, forwarding elements are + equipped with additional storage that can be used to cache data from + forwarded packets. Upstream routers may replace packet data with a + fingerprint that tells a downstream router how to decode and + reconstruct the packet based on cached data. + +4.9.1. Applicability to DECADE + + RE is an example of an experimental in-network storage system that + would require a large amount of associated packet processing at + routers if it was ever deployed. + +4.9.2. Data Access Interface + + RE is typically transparent to the user. Writing into storage is + done by transferring data that has not already been cached. Storage + is read when users transmit data identical to previously transmitted + data. + +4.9.3. Data Management Operations + + Not provided. + +4.9.4. Data Search Capability + + Not provided. + +4.9.5. Access Control Authorization + + The access control method is public-restricted (to any client that is + part of the RE network). Note that the content provider still + retains control over which peers receive the requested data. The + returned data is "compressed" as it is transferred within the + network. + +4.9.6. Resource Control Interface + + Not provided. The content provider still retains control over the + rate at which packets are sent to a peer. The packet size within the + network may be reduced. + + + + +Alimi, et al. Informational [Page 22] + +RFC 6392 DECADE Survey October 2011 + + +4.9.7. Discovery Mechanism + + No discovery mechanism is necessary. Routers can use RE without the + users' knowledge. + +4.9.8. Storage Mode + + Object-based, with "objects" being data from packets transmitted + within the network. + +4.10. OceanStore + + OceanStore [21] is a storage platform developed at the University of + California, Berkeley, that provides globally distributed storage. + OceanStore implements a model where multiple storage providers can + pool resources together. Thus, a major focus is on resiliency, self- + organization, and self-maintenance. + + The protocol is resilient to some storage nodes being compromised by + utilizing Byzantine agreement and erasure codes to store data at + primary replicas. + +4.10.1. Applicability to DECADE + + OceanStore is an example of an experimental in-network storage system + that provides a high degree of network resilience to failure + scenarios. + +4.10.2. Data Access Interface + + Users may read and write objects. + +4.10.3. Data Management Operations + + Objects may be replaced by newer versions, and multiple versions of + an object may be maintained. + +4.10.4. Data Search Capability + + Not provided. + +4.10.5. Access Control Authorization + + Provided, but specifics for clients are unclear from the available + references. + + + + + + +Alimi, et al. Informational [Page 23] + +RFC 6392 DECADE Survey October 2011 + + +4.10.6. Resource Control Interface + + Not provided. + +4.10.7. Discovery Mechanism + + Users require an entry point into the system in the form of one + storage node that is part of OceanStore. If a hostname is provided, + the address of a storage node may be determined via DNS. + +4.10.8. Storage Mode + + Object-based. + +4.11. P2P Cache + + Caching of P2P traffic is a useful approach to reduce P2P network + traffic, because objects in P2P systems are mostly immutable and the + traffic is highly repetitive. In addition, making use of P2P caches + does not require changes to P2P protocols and can be deployed + transparently from clients. + + P2P caches operate similarly to Web caches (Section 4.14) in that + they temporarily store frequently requested content. Requests for + content already stored in the cache can be served from local storage + instead of requiring the data to be transmitted over expensive + network links. + + Two types of P2P caches exist: transparent P2P caches and + non-transparent P2P caches. + + For a transparent cache, once a P2P cache is established, the network + will transparently redirect P2P traffic to the cache, which either + serves the file directly or passes the request on to a remote P2P + user and simultaneously caches that data. Transparency is typically + implemented using Deep Packet Inspection (DPI). DPI products + identify and pass P2P packets to the P2P caching system so it can + cache and accelerate the traffic. + + A non-transparent cache appears as a super peer; it explicitly peers + with other P2P clients. + + To enable operation with existing P2P software, P2P caches directly + support P2P application protocols. A large number of P2P protocols + are used by P2P software and hence are supported by caches, leading + to higher complexity. Additionally, these protocols evolve over + time, and new protocols are introduced. + + + + +Alimi, et al. Informational [Page 24] + +RFC 6392 DECADE Survey October 2011 + + +4.11.1. Applicability to DECADE + + A P2P cache is an example of in-network storage for P2P systems. + However, unlike DECADE, the existence and operation of the storage + system are totally transparent to the end user. + +4.11.2. Transparent P2P Caches + +4.11.2.1. Data Access Interface + + The data access interface allows P2P content to be cached (stored) + and supplied (retrieved) locally such that network traffic is + reduced, but it is transparent to P2P users, and P2P users implicitly + use the data access interface (in the form of their native P2P + application protocol) to store or retrieve content. + +4.11.2.2. Data Management Operations + + Not provided. + +4.11.2.3. Data Search Capability + + Not provided. + +4.11.2.4. Access Control Authorization + + The access control method is typically public-restricted (to any + client that is part of the P2P channel or swarm). + +4.11.2.5. Resource Control Interface + + Not provided. + +4.11.2.6. Discovery Mechanism + + The use of DPI means that no discovery mechanism is provided to P2P + users; it is transparent to P2P users. Since DPI is used to + recognize P2P applications' private protocols, P2P cache + implementations must be updated as new applications are added and + existing protocols evolve. + +4.11.2.7. Storage Mode + + Object-based. Chunks (typically, the unit of transfer among P2P + clients) of content are stored in the cache. + + + + + + +Alimi, et al. Informational [Page 25] + +RFC 6392 DECADE Survey October 2011 + + +4.11.3. Non-Transparent P2P Caches + +4.11.3.1. Data Access Interface + + The data access interface allows P2P content to be cached (stored) + and supplied (retrieved) locally such that network traffic is + reduced. P2P users implicitly store and retrieve from the cache + using the P2P application's native protocol. + +4.11.3.2. Data Management Operations + + Not provided. + +4.11.3.3. Data Search Capability + + Not provided. + +4.11.3.4. Access Control Authorization + + The access control method is typically public-restricted (to any + client that is part of the P2P channel or swarm). + +4.11.3.5. Resource Control Interface + + Not provided. + +4.11.3.6. Discovery Mechanism + + A P2P cache node behaves as if it were a normal peer in order to join + the P2P overlay network. Other P2P users can find such a cache node + through an overlay routing mechanism and can interact with it as if + it were a normal neighbor node. + +4.11.3.7. Storage Mode + + Object-based. Chunks (typically, the unit of transfer among P2P + clients) of content are stored in the cache. + +4.12. Photo Sharing + + There are a growing number of popular online photo-sharing (storing) + systems. For example, the Kodak Gallery system [22] serves over + 60 million users and stores billions of images [23]. Other well- + known examples of photo-sharing systems include Flickr [24] and + ImageShack [25]. There are also a number of popular blogging + + + + + + +Alimi, et al. Informational [Page 26] + +RFC 6392 DECADE Survey October 2011 + + + services, such as Tumblr [26], that specialize in sharing large + numbers of photos as well as other multimedia content (e.g., video, + text, audio, etc.) as part of their service. All of these in-network + storage systems utilize both free and paid subscription models. + + Most photo-sharing systems are based on a traditional client-server + architecture. However, a minority of systems also offer a P2P mode + of operation. The client-server architecture is typically based on + HTTP, with a browser client and a Web server. + +4.12.1. Applicability to DECADE + + Photo sharing is a very widely used (deployed) example of in-network + storage where the end user has direct visibility and extensive + control of the system. The typical end-user interface is through an + HTTP-based Web browser. + +4.12.2. Data Access Interface + + Users can read (view) and write (store) photos. + +4.12.3. Data Management Operations + + Users can delete previously stored photos. + +4.12.4. Data Search Capability + + Users can tag photos and/or organize them using sophisticated Web + photo album generators. Users can then search for objects (photos) + matching desired criteria. + +4.12.5. Access Control Authorization + + The access control method for clients is typically either private or + public-unrestricted. For example, writing (storing) to a photo blog + is typically private to the owner of the account. However, all other + clients can view (read) the contents of the blog (i.e., public- + unrestricted). Some photo-sharing Websites provide private access to + read photos to allow sharing with a limited set of friends. + +4.12.6. Resource Control Interface + + Not provided. + + + + + + + + +Alimi, et al. Informational [Page 27] + +RFC 6392 DECADE Survey October 2011 + + +4.12.7. Discovery Mechanism + + Clients usually log on manually to a central Web page for the service + and enter the appropriate information to access the desired + information. The address to which the client connects is usually + determined by DNS using the hostname from the provided URL. + +4.12.8. Storage Mode + + File system (file-based). Photos are usually stored as files. They + can then be organized into meta-structures (e.g., albums, galleries, + etc.) using sophisticated Web photo album generators. + +4.13. Usenet + + Usenet is a distributed Internet-based discussion (message) system. + The Usenet messages are arranged as a set of "newsgroups" that are + classified hierarchically by subject. Usenet information is + distributed and stored among a large conglomeration of servers that + store and forward messages to one another in so-called news feeds. + Individual users may read messages from, and post messages to, a + local news server typically operated by an ISP. This local server + communicates with other servers and exchanges articles with them. In + this fashion, the message is copied from server to server and + eventually reaches every server in the network [27]. + + Traditional Usenet as described above operates as a P2P network + between the servers, and in a client-server architecture between the + user and their local news server. The user requires a Usenet client + to be installed on their computer and a Usenet server account + (through their ISP). However, with the rise of Web browsers, the + Usenet architecture is evolving to be Web-based. The most popular + example of this is Google Groups, where Google hosts all the + newsgroups and client access is via a standard HTTP-based Web + browser [28]. + +4.13.1. Applicability to DECADE + + Usenet is a historically very important and widely used (deployed) + example of in-network storage in the Internet. The use of this + system is rapidly declining, but efforts have been made to preserve + the stored content for historical purposes. + +4.13.2. Data Access Interface + + Users can read and post (store) messages. + + + + + +Alimi, et al. Informational [Page 28] + +RFC 6392 DECADE Survey October 2011 + + +4.13.3. Data Management Operations + + Users sometimes have limited ability to delete messages that they + previously posted. + +4.13.4. Data Search Capability + + Traditionally, users could manually search through the newsgroups, as + they are classified hierarchically by subject. In the newer Web- + based systems, there is also an automatic search capability based on + key-word matches. + +4.13.5. Access Control Authorization + + The access control method is either public-unrestricted or private + (to client members of that newsgroup). + +4.13.6. Resource Control Interface + + Not provided. + +4.13.7. Discovery Mechanism + + Clients usually log on manually to their Usenet accounts. DNS may be + used to resolve hostnames to their corresponding addresses. + +4.13.8. Storage Mode + + File system. Messages are usually stored as files that are then + organized hierarchically by subject into newsgroups. + +4.14. Web Cache + + Web cache [29] has been widely deployed by many ISPs to reduce + bandwidth consumption and Web access latency since the late 1990s. A + Web cache can cache the Web documents (e.g., HTML pages, images) + between server and client to reduce bandwidth usage, server load, and + perceived lag. A Web cache server is typically shared by many + clients, and stores copies of documents passing through it; + subsequent requests may be satisfied from the cache if certain + conditions are met. + + Another form of cache is a client-side cache, typically implemented + in Web browsers. A client-side cache can keep a local copy of all + pages recently displayed by a browser, and when the user returns to + one of these Web pages, the local cached copy is reused. + + + + + +Alimi, et al. Informational [Page 29] + +RFC 6392 DECADE Survey October 2011 + + + A related protocol for P2P applications to use Web cache is HPTP + (HTTP-based Peer to Peer) [30]. It proposes sharing chunks of P2P + files/streams using HTTP with cache-control headers. + +4.14.1. Applicability to DECADE + + Web cache is a very widely used (deployed) example of in-network + storage for the key Internet application of Web browsing. The + existence and operation of the storage system are transparent to the + end user in most cases. The content caching time is controlled by + time-to-live parameters associated with the original content. The + principle of Web caching is to speed up Web page reading by using + (the same) content previously requested by another user to service a + new user. + +4.14.2. Data Access Interface + + Users explicitly read from a Web cache by making requests, but they + cannot explicitly write data into it. Data is implicitly stored in + the Web cache by requesting content that is not already cached and + meets policy restrictions of the cache provider. + +4.14.3. Data Management Operations + + Not provided. + +4.14.4. Data Search Capability + + Not provided. + +4.14.5. Access Control Authorization + + The access control method for clients is public-unrestricted. It is + important to note that if content is authenticated or encrypted + (e.g., HTTPS, Secure Socket Layer (SSL)), it will not be cached. + Also, if the content is flagged as private (vs. public) at the HTTP + level by the origin server, it will not be cached. + +4.14.6. Resource Control Interface + + Not provided. + +4.14.7. Discovery Mechanism + + Web caches can be transparently deployed between a Web server and Web + clients, employing DPI for discovery. Alternatively, Web caches + could be explicitly discovered by clients using techniques such as + DNS or manual configuration. + + + +Alimi, et al. Informational [Page 30] + +RFC 6392 DECADE Survey October 2011 + + +4.14.8. Storage Mode + + Object-based. Web content is keyed within the cache by HTTP Request + fields, such as Method, URI, and Headers. + +4.15. Observations Regarding In-Network Storage Systems + + The following observations about the surveyed in-network storage + systems are made in the context of DECADE as defined by [1]. + + The majority of the surveyed systems were designed for client-server + architectures and do not support P2P. However, there are some + important exceptions, especially for some of the newer technologies + such as BranchCache and P2P cache, that do support a P2P mode of + operation. + + The P2P cache systems are interesting, since they do not require + changes to the P2P applications themselves. However, this is also a + limitation in that they are required to support each application + protocol. + + Many of the surveyed systems were designed for caching as opposed to + long-term network storage. Thus, during DECADE protocol design, it + should be carefully considered whether a caching mode should be + supported in addition to a long-term network storage mode. There is + typically a trade-off between providing a caching mode and long-term + (and usually also reliable) storage with regards to some performance + metrics. Note that [1] identifies issues with classical caching from + a DECADE perspective, such as the fact that P2P caches typically do + not allow users to explicitly control content stored in the cache. + + Certain components of the surveyed systems are outside of the scope + of DECADE. For example, a protocol used for searching across + multiple DECADE servers is out of scope. However, applications may + still be able to implement such functionality if DECADE exposes the + appropriate primitives. This has the benefit of keeping the core + in-network storage systems simple, while permitting diverse + applications to design mechanisms that meet their own requirements. + + Today, most in-network storage systems follow some variant of the + authorization model of public-unrestricted, public-restricted, and + private. For DECADE, we may need to evolve the authorization model + to support a resource owner (e.g., end user) authorization, in + addition to the network authorization. + + + + + + + +Alimi, et al. Informational [Page 31] + +RFC 6392 DECADE Survey October 2011 + + +5. Storage and Other Related Protocols + + This section surveys existing storage and other related protocols, as + well as comments on the usage of these protocols to satisfy DECADE's + use cases. The surveyed protocols are listed alphabetically. + +5.1. HTTP + + HTTP [31] is a key protocol for the World Wide Web. It is a + stateless client-server protocol that allows applications to be + designed using the REST model. HTTP is often associated with + downloading (reading) content from Web servers to Web browsers, but + it also has support for uploading (writing) content to Web servers. + It has been used as the underlying protocol for other protocols, such + as Web Distributed Authoring and Versioning (WebDAV). + + HTTP is used in some of the most popular in-network storage systems + surveyed previously, including CDNs, photo sharing, and Web cache. + Usage of HTTP by a storage protocol implies that no extra software is + required in the client (i.e., Web-based client), as all standard Web + browsers are based on HTTP. + +5.1.1. Data Access Interface + + Basic read and write operations are supported (using HTTP GET, PUT, + and POST methods). + +5.1.2. Data Management Operations + + Not provided. + +5.1.3. Data Search Capability + + Not provided. + +5.1.4. Access Control Authorization + + All methods of access control for clients are supported: public- + unrestricted, public-restricted, and private. + + The majority of Web pages are public-unrestricted in terms of reading + but do not allow any uploading of content. In-network storage + systems range from private or public-unrestricted for photo sharing + (described in Section 4.12.5) to public-unrestricted for Web caching + (described in Section 4.14.5). + + + + + + +Alimi, et al. Informational [Page 32] + +RFC 6392 DECADE Survey October 2011 + + +5.1.5. Resource Control Interface + + Not provided. + +5.1.6. Discovery Mechanism + + Manual configuration is typically used. Clients typically address + HTTP servers by providing a hostname, which is resolved to an address + using DNS. + +5.1.7. Storage Mode + + HTTP is a protocol; it thus does not define a storage mode. However, + a non-collection resource can typically be thought of as a "file". + These files may be organized into collections, which typically map + onto the HTTP path hierarchy, creating the illusion of a file system. + +5.1.8. Comments + + HTTP is based on a client-server architecture and thus is not + directly applicable for the DECADE focus on P2P. Also, HTTP offers + only a rudimentary toolset for storage operations compared to some of + the other storage protocols. + +5.2. iSCSI + + Small Computer System Interface (SCSI) is a set of protocols enabling + communication with storage devices such as disk drives and tapes; + Internet SCSI (iSCSI) [32] is a protocol enabling SCSI commands to be + sent over TCP. As in SCSI, iSCSI allows an Initiator to send + commands to a Target. These commands operate on the device level as + opposed to individual data objects stored on the device. + +5.2.1. Data Access Interface + + Read and write commands indicate which data is to be read or written + by specifying the offset (using Logical Block Addressing) into the + storage device. The size of data to be read or written is an + additional parameter in the command. + +5.2.2. Data Management Operations + + Since commands operate at the device level, management operations are + different than with traditional file systems. Management commands + for SCSI/iSCSI include explicit device control commands, such as + starting, stopping, and formatting the device. + + + + + +Alimi, et al. Informational [Page 33] + +RFC 6392 DECADE Survey October 2011 + + +5.2.3. Data Search Capability + + SCSI/iSCSI does not provide the ability to search for particular data + within a device. Note that such capabilities can be implemented + outside of iSCSI. + +5.2.4. Access Control Authorization + + With respect to access to devices, the access control method is + private. iSCSI uses the Challenge Handshake Authentication Protocol + (CHAP) [33] to authenticate Initiators and Targets when accessing + storage devices. However, since SCSI/iSCSI operates at the device + level, neither authentication nor authorization is provided for + individual data objects. Note that such capabilities can be + implemented outside of iSCSI. + +5.2.5. Resource Control Interface + + Not provided. + +5.2.6. Discovery Mechanism + + Manual configuration may be used. An alternative is the Internet + Storage Name Service (iSNS) [34], which provides the ability to + discover available storage resources. + +5.2.7. Storage Mode + + As a protocol, iSCSI does not explicitly have a storage mode. + However, it provides block-based access to clients. SCSI/iSCSI + provides an Initiator with block-level access to the storage device. + +5.3. NFS + + The Network File System (NFS) is designed to allow users to access + files over a network in a manner similar to how local storage is + accessed. NFS is typically used in local area networks or in + enterprise settings, though changes made in later versions of NFS + (e.g., [35]) make it easier to operate over the Internet. + +5.3.1. Data Access Interface + + Traditional file-system operations such as read, write, and update + (overwrite) are provided. Locking is provided to support concurrent + access by multiple clients. + + + + + + +Alimi, et al. Informational [Page 34] + +RFC 6392 DECADE Survey October 2011 + + +5.3.2. Data Management Operations + + Traditional file-system operations such as move and delete are + provided. + +5.3.3. Data Search Capability + + The user has the ability to list contents of directories to find + filenames matching desired criteria. + +5.3.4. Access Control Authorization + + All methods of access control for clients are supported: public- + unrestricted, public-restricted, and private. For example, files and + directories can be protected using read, write, and execute + permissions for the files' owner and group, and for the public + (others). Also, NFSv4.1 has a rich ACL model allowing a list of + Access Control Entries (ACEs) to be configured for each file or + directory. The ACEs can specify per-user read/write access to file + data, file/directory attributes, creation/deletion of files in a + directory, etc. + +5.3.5. Resource Control Interface + + While disk space quotas can be configured, administrative policy + typically limits the total amount of storage allocated to a + particular user. User control of bandwidth and connections used by + remote peers is not provided. + +5.3.6. Discovery Mechanism + + Manual configuration is typically used. Clients address NFS servers + by providing a hostname and a directory that should be mounted. DNS + may be used to look up an address for the provided hostname. + +5.3.7. Storage Mode + + As a protocol, there is no defined internal storage mode. However, + implementations typically use the underlying file-system storage. + Note that extensions have been defined for alternate storage modes + (e.g., block-based [36] and object-based [37]). + + + + + + + + + + +Alimi, et al. Informational [Page 35] + +RFC 6392 DECADE Survey October 2011 + + +5.3.8. Comments + + The efficiency and scalability of the NFS access control method are + concerns in the context of DECADE. In particular, Section 6.2.1 of + [35] states that: + + Only ACEs that have a "who" that matches the requester + are considered. + + Thus, in the context of DECADE, to specify per-peer access control + policies for an object, a client would need to explicitly configure + the ACL for the object for each individual peer. A concern with this + approach is scalability when a client's peers may change frequently, + and ACLs for many small objects need to be updated constantly during + participation in a swarm. + + Note that NFSv4.1's usage of RPCSEC_GSS provides support for multiple + security mechanisms. Kerberos V5 is required, but others, such as + X.509 certificates, are also supported by way of the Generic Security + Service Application Program Interface (GSS-API). Note, however, that + NFSv4.1's usage of such security mechanisms is limited to linking a + requesting user to a particular account maintained by the NFS server. + +5.4. OAuth + + Open Authorization (OAuth) [38] is a protocol that enriches the + traditional client-server authentication model for Web resources. In + particular, OAuth distinguishes the "client" from the "resource + owner", thus enabling a resource owner to authorize a particular + client for access (e.g., for a particular lifetime) to private + resources. + + We include OAuth in this survey so that its authentication model can + be evaluated in the context of DECADE. OAuth itself, however, is not + a network storage protocol. + +5.4.1. Data Access Interface + + Not provided. + +5.4.2. Data Management Operations + + Not provided. + +5.4.3. Data Search Capability + + Not provided. + + + + +Alimi, et al. Informational [Page 36] + +RFC 6392 DECADE Survey October 2011 + + +5.4.4. Access Control Authorization + + Not provided. While similar in spirit to the WebDAV ticketing + extensions [39], OAuth instead uses the following process: (1) a + client constructs a delegation request, (2) the client forwards the + request to the resource owner for authorization, (3) the resource + owner authorizes the request, and finally (4) a callback is made to + the client indicating that its request has been authorized. + + Once the process is complete, the client has a set of token + credentials that grant it access to the protected resource. The + token credentials may have an expiration time, and they can also be + revoked by the resource owner at any time. + +5.4.5. Resource Control Interface + + Not provided. + +5.4.6. Discovery Mechanism + + Not provided. + +5.4.7. Storage Mode + + Not provided. + +5.4.8. Comments + + The ticketing mechanism requires server involvement, and the + discussion relating to WebDAV's proposed ticketing mechanism (see + Section 5.5.8) applies here as well. + +5.5. WebDAV + + WebDAV [40] is a protocol designed for Web content authoring. It is + developed as an extension to HTTP (described in Section 5.1), meaning + that it can be simpler to integrate into existing software. WebDAV + supports traditional operations for reading/writing from storage, as + well as other constructs, such as locking and collections, that are + important when multiple users collaborate to author or edit a set of + documents. + +5.5.1. Data Access Interface + + Traditional read and write operations are supported (using HTTP GET + and PUT methods, respectively). Locking is provided to support + concurrent access by multiple clients. + + + + +Alimi, et al. Informational [Page 37] + +RFC 6392 DECADE Survey October 2011 + + +5.5.2. Data Management Operations + + WebDAV supports traditional file-system operations, such as move, + delete, and copy. Objects are organized into collections, and these + operations can also be performed on collections. WebDAV also allows + objects to have user-defined properties. + +5.5.3. Data Search Capability + + The user has the ability to list contents of collections to find + objects matching desired criteria. A SEARCH extension [41] has also + been specified allowing listing of objects matching client-defined + criteria. + +5.5.4. Access Control Authorization + + All methods of access control for clients are supported: public- + unrestricted, public-restricted, and private. + + For example, an ACL extension [42] is provided for WebDAV. ACLs + allow both user-based and group-based access control policies + (relating to reading, writing, properties, locking, etc.) to be + defined for objects and collections. + + A ticketing extension [39] has also been proposed, but has not + progressed since 2001. This extension allows a client to request the + WebDAV server to create a "ticket" (e.g., for reading an object) that + can be distributed to other clients. Tickets may be given expiration + times, or may only allow for a fixed number of uses. The proposed + extension requires the server to generate tickets and maintain state + for outstanding tickets. + +5.5.5. Resource Control Interface + + An extension [43] allows disk space quotas to be configured for + collections. The extension also allows WebDAV clients to query + current disk space usage. User control of bandwidth and connections + used by remote peers is not provided. + +5.5.6. Discovery Mechanism + + Manual configuration is typically used. Clients address WebDAV + servers by providing a hostname, which can be resolved to an address + using DNS. + + + + + + + +Alimi, et al. Informational [Page 38] + +RFC 6392 DECADE Survey October 2011 + + +5.5.7. Storage Mode + + Though no storage mode is explicitly defined, WebDAV can be thought + of as providing file system (file-based) storage to a client. A + non-collection resource can typically be thought of as a "file". + Files may be organized into collections, which typically map onto the + HTTP path hierarchy. + +5.5.8. Comments + + The efficiency and scalability of the WebDAV access control method + are concerns in the context of DECADE, for reasons similar to those + stated in Section 5.3.8 for NFS. The proposed WebDAV ticketing + extension partially alleviates these concerns, but the particular + technique may need further evaluation before being applied to DECADE. + In particular, since DECADE clients may continuously upload/download + a large number of small-size objects, and a single DECADE server may + need to scale to many concurrent DECADE clients, requiring the server + to maintain ticket state and generate tickets may not be the best + design choice. Server-generated tickets can also increase latency + for data transport operations, depending on the message flow used by + DECADE. + +5.6. Observations Regarding Storage and Related Protocols + + The following observations about the surveyed storage and related + protocols are made in the context of DECADE as defined by [1]. + + All of the surveyed protocols were primarily designed for client- + server architectures and not for P2P. However, it is conceivable + that some of the protocols could be adapted to work in a P2P + architecture. + + Several popular in-network storage systems today use HTTP as their + key protocol, even though it is not classically considered as a + storage protocol. HTTP is a stateless protocol that is used to + design RESTful applications. HTTP is a well-supported and widely + implemented protocol that can provide important insights for DECADE. + + The majority of the surveyed protocols do not support low-latency + access for applications such as live streaming. This was one of the + key general requirements for DECADE. + + The majority of the surveyed protocols do not support any form of + resource control interface. Resource control is required for users + to manage the resources on in-network storage systems, e.g., the + bandwidth or connections, that can be used by other peers. Resource + control is a key capability required for DECADE. + + + +Alimi, et al. Informational [Page 39] + +RFC 6392 DECADE Survey October 2011 + + + Nearly all surveyed protocols did, however, support the following + capabilities required for DECADE: ability of the user to read/write + content, some form of access control, some form of error indication, + and the ability to traverse firewalls and NATs. + +6. Conclusions + + Though there have been many successful in-network storage systems, + they have been designed for use cases different from those defined in + DECADE. For example, many of the surveyed in-network storage systems + and protocols were designed for client-server architectures and not + P2P. No surveyed system or protocol has the functionality and + features to fully meet the set of requirements defined for DECADE. + DECADE aims to provide a standard protocol for P2P applications and + content providers to access and control in-network storage, resulting + in increased network efficiency while retaining control over content + shared with peers. Additionally, defining a standard protocol can + reduce the complexity of in-network storage, since multiple P2P + application protocols no longer need to be implemented by in-network + storage systems. + +7. Security Considerations + + This document is a survey of existing in-network storage systems, and + does not introduce any security considerations beyond those of the + surveyed systems. + + For more information on security considerations of DECADE, see [1]. + +8. Contributors + + The editors would like to thank the following people for contributing + to the development of this document: + + - ZhiHui Lv + + - Borje Ohlman + + - Pang Tao + + - Lucy Yong + + - Juan Carlos Zuniga + + + + + + + + +Alimi, et al. Informational [Page 40] + +RFC 6392 DECADE Survey October 2011 + + +9. Acknowledgments + + The editors would like to thank the following people for providing + valuable comments to various draft versions of this document: David + Bryan, Tao Mao, Haibin Song, Ove Strandberg, Yu-Shun Wang, Richard + Woundy, Yunfei Zhang, and Ning Zong. + +10. Informative References + + [1] Song, H., Zong, N., Yang, Y., and R. Alimi, "DECoupled + Application Data Enroute (DECADE) Problem Statement", Work + in Progress, October 2011. + + [2] Storage Search, "Flash Memory vs. Hard Disk Drives -- Which + Will Win?", <http://www.storagesearch.com/semico-art1.html>. + + [3] Brisken, W., "Hard Drive Price Trends", US VLBI Technical + Meeting, May 2008. + + [4] Woundy, R., "TSV P2P Efforts -- From an ISP's Perspective", + IETF 81, Quebec, Canada, July 2011, + <http://www.ietf.org/proceedings/81/slides/tsvarea-3.pdf>. + + [5] Gu, Y., Bryan, D., Yang, Y., and R. Alimi, "DECADE + Requirements", Work in Progress, September 2011. + + [6] Amazon Web Services, "Amazon Simple Storage Service + (Amazon S3)", <http://aws.amazon.com/s3/>. + + [7] Calder, B., Wang, T., Mainali, S., and J. Wu, "Windows Azure + Blob -- Programming Blob Storage", May 2009, + <http://www.microsoft.com/windowsazure/whitepapers/>. + + [8] Google, "Google Storage for Developers", + <http://code.google.com/apis/storage>. + + [9] Dropbox, "Dropbox Features", <http://www.dropbox.com/features>. + + [10] Microsoft Corporation, "BranchCache", + <http://technet.microsoft.com/en-us/network/dd425028.aspx>. + + [11] Microsoft Corporation, "Web Services Dynamic Discovery + (WS-Discovery)", April 2005, <http://specs.xmlsoap.org/ + ws/2005/04/discovery/ws-discovery.pdf>. + + + + + + + +Alimi, et al. Informational [Page 41] + +RFC 6392 DECADE Survey October 2011 + + + [12] Paul, S., Yates, R., Raychaudhuri, D., and J. Kurose, "The + Cache-and-Forward Network Architecture for Efficient Mobile + Content Delivery Services in the Future Internet", Innovations + in NGN: Future Network and Services, 2008. + + [13] SNIA, "Cloud Data Management Interface (CDMI)", + <http://www.snia.org/cdmi>. + + [14] Pathan, A.K. and Buyya, R., "A Taxonomy and Survey of Content + Delivery Networks", Grid Computing and Distributed Systems + Laboratory, University of Melbourne, Technical Report, + February 2007. + + [15] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R., + Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant Networking + Architecture", RFC 4838, April 2007. + + [16] Scott, K. and S. Burleigh, "Bundle Protocol Specification", + RFC 5050, November 2007. + + [17] Named Data Networking, "Named Data Networking Home Page", + <http://www.named-data.net/>. + + [18] Named Data Networking, "Named Data Networking (NDN) Project", + <http://www.named-data.net/ndn-proj.pdf>. + + [19] Network of Information, "NetInf Overview", + <http://www.netinf.org/home/overview/>. + + [20] Anand, A., Sekar, V., and A. Akella, "SmartRE: An Architecture + for Coordinated Network-wide Redundancy Elimination", + SIGCOMM 2009. + + [21] Rhea, S., Eaton, P., Geels, D., Weatherspoon, H., Zhao, B., and + J. Kubiatowicz, "Pond: the OceanStore Prototype", FAST 2003. + + [22] Kodak, "Kodak Gallery Home Page", + <http://www.kodakgallery.com/gallery/welcome.jsp>. + + [23] Wikipedia, "Kodak Gallery", + <http://en.wikipedia.org/wiki/Kodak_Gallery>. + + [24] Flickr, "Flickr Home Page", <http://www.flickr.com>. + + [25] ImageShack, "ImageShack Home Page", <http://imageshack.us>. + + [26] Tumblr, "Tumblr Home Page", <http://www.tumblr.com>. + + + + +Alimi, et al. Informational [Page 42] + +RFC 6392 DECADE Survey October 2011 + + + [27] Wikipedia, "Usenet", <http://en.wikipedia.org/wiki/Usenet>. + + [28] Google, "Google Groups", <http://groups.google.com>. + + [29] Huston, G., Telstra, "Web Caching", The Internet Protocol + Journal Volume 2, No. 3. + + [30] Shen, G., Wang, Y., Xiong, Y., Zhao, B., and Z-L. Zhang, "HPTP: + Relieving the Tension between ISPs and P2P", 6th International + Workshop on Peer-To-Peer Systems (IPTPS2007). + + [31] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., + Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- + HTTP/1.1", RFC 2616, June 1999. + + [32] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E. + Zeidner, "Internet Small Computer Systems Interface (iSCSI)", + RFC 3720, April 2004. + + [33] Simpson, W., "PPP Challenge Handshake Authentication Protocol + (CHAP)", RFC 1994, August 1996. + + [34] Tseng, J., Gibbons, K., Travostino, F., Du Laney, C., and J. + Souza, "Internet Storage Name Service (iSNS)", RFC 4171, + September 2005. + + [35] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network + File System (NFS) Version 4 Minor Version 1 Protocol", + RFC 5661, January 2010. + + [36] Black, D., Fridella, S., and J. Glasgow, "Parallel NFS (pNFS) + Block/Volume Layout", RFC 5663, January 2010. + + [37] Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel + NFS (pNFS) Operations", RFC 5664, January 2010. + + [38] Hammer-Lahav, E., Ed., "The OAuth 1.0 Protocol", RFC 5849, + April 2010. + + [39] Ito, K., "Ticket-Based Access Control Extension to WebDAV", + Work in Progress, October 2001. + + [40] Dusseault, L., Ed., "HTTP Extensions for Web Distributed + Authoring and Versioning (WebDAV)", RFC 4918, June 2007. + + [41] Reschke, J., Ed., Reddy, S., Davis, J., and A. Babich, "Web + Distributed Authoring and Versioning (WebDAV) SEARCH", + RFC 5323, November 2008. + + + +Alimi, et al. Informational [Page 43] + +RFC 6392 DECADE Survey October 2011 + + + [42] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web + Distributed Authoring and Versioning (WebDAV) + Access Control Protocol", RFC 3744, May 2004. + + [43] Korver, B. and L. Dusseault, "Quota and Size Properties + for Distributed Authoring and Versioning (DAV) Collections", + RFC 4331, February 2006. + +Authors' Addresses + + Richard Alimi (editor) + Google + + EMail: ralimi@google.com + + + Akbar Rahman (editor) + InterDigital Communications, LLC + + EMail: Akbar.Rahman@InterDigital.com + + + Yang Richard Yang (editor) + Yale University + + EMail: yry@cs.yale.edu + + + + + + + + + + + + + + + + + + + + + + + + + +Alimi, et al. Informational [Page 44] + |