Pipeline forwarding (PF) [1] applies to packet forwarding Forwarding is the relaying of packets from one network segment to another by nodes in a computer network in computer networks A computer network, often simply referred to as a network, is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Networks may be classified according to a wide variety of characteristics. This article provides a general the basic concept of pipelining In computing, a pipeline is a set of data processing elements connected in series, so that the output of one element is the input of the next one. The elements of a pipeline are often executed in parallel or in time-sliced fashion; in that case, some amount of buffer storage is often inserted between elements, which has been widely and successfully used in computing — specifically, in the architecture of all major central processing units The Central Processing Unit or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPUs have changed (CPUs) — and manufacturing — specifically in assembly lines of various industries starting from automotive to many others. Pipelining is known to be optimal independent of the specific instantiation. In particular, PF is optimal from various points of view:
- High efficiency in utilization of network resources, which enables accommodating a larger amount of traffic on the network, thus lowering operation cost and being the foundation for accommodating the exponential growth of modern networks.
- Low implementation complexity, which enables the realization of larger and more powerful networking systems at low cost, thus offering further support to network growth.
- High scalability, which is an immediate consequence of the above two features.
- Deterministic and predictable operation with minimum delay and no packet loss even under full load condition, which is key in supporting the demanding requirements of the new and valuable services that are being deployed, or envisioned to be deployed, on modern networks, such as telephony, videoconferencing, virtual presence, video on demand, distributed gaming.
Various aspects of the technology are covered by several patents issued by both the United States Patent and Trademark Office The United States Patent and Trademark Office is an agency in the United States Department of Commerce that issues patents to inventors and businesses for their inventions, and trademark registration for product and intellectual property identification and the European Patent Office The European Patent Office is one of the two organs of the European Patent Organisation (EPOrg), the other being the Administrative Council. The EPO acts as executive body for the Organisation while the Administrative Council acts as its supervisory body as well as, to a limited extent, its legislative body. The actual legislative power to revise.[citation needed]
Operating principles
As in other pipelining implementations, a common time reference (CTR) is needed to perform pipeline forwarding. In the context of global networks the CTR can be effectively realized by using UTC Coordinated Universal Time is a time standard based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation. Leap seconds are used to allow UTC to closely track UT1, which is mean solar time at the Royal Observatory, Greenwich (coordinated universal time Coordinated Universal Time is a time standard based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation. Leap seconds are used to allow UTC to closely track UT1, which is mean solar time at the Royal Observatory, Greenwich) that is globally available via GPS The Global Positioning System is a space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely (global positioning system The Global Positioning System is a space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely) or Galileo Galileo is a global navigation satellite system currently being built by the European Union (EU) and European Space Agency (ESA). The €3.4 billion project is an alternative and complementary to the U.S. Global Positioning System (GPS) and the Russian GLONASS. On 30 November 2007 the 27 EU transportation ministers involved reached an agreement in the near future. For example the UTC second is divided into fixed duration time frames, which are grouped into time cycles so that in each UTC second there is a predefined integer number of time cycles. Alternatively, or complementary, the CTR can be obtained through the network by means of synchronization protocols such as IEEE 1588.
Packets are forwarded from node to node according to predefined schedules, as shown in the figure below, i.e., each node forwards packets of a certain flow during predefined time frames. The time cycles define the periodic re-occurrence of the various predefined schedules. The periodic scheduling within each node results in a periodic packet forwarding across the network, which is referred to as pipeline forwarding for the ordered, step-by-step fashion with which packets travel toward their destination.
Through a resource reservation procedure transmission capacity is booked for a flow on each link it traverses during the time frame (or time frames) predefined for its forwarding, thus setting up a synchronous virtual pipe (SVP). The capacity during each time frame can be is partially or totally reserved to one or more flows. Consequently, the time cycle provides the basis for a periodic repetition of the reservation that ensures enough transmission resources to be available on each link to forward the packets of each flow, which prevents delays due to resource contention and loss resulting to congestion.
Forwarding options
As exemplified in the figure above, which depicts the journey of a packet from node A to node D along three pipeline forwarding switches, the forwarding delay may have different values for different nodes, due to different propagation delays on different links (e.g., Tab, Tbc, and Tcd), and different packet processing and switching times in heterogeneous nodes (e.g., Tbb and Tcc). Moreover, two variants of the basic pipeline forwarding operation are possible. When node n deploys immediate forwarding the forwarding delay has the same value for all the packets received by node n on input link i and it is the minimum necessary to accommodate the packet propagation, processing, and switching time. When implementing non-immediate forwarding, node n may use different forwarding delays for different packets.
Two implementations of the pipeline forwarding were proposed: Time-Driven Switching (TDS) - a.k.a. Fractional lambda switching (FλS) in the context of optical networks - [2] and time-driven priority Time-driven priority is a synchronous packet scheduling technique that implements UTC-based pipeline forwarding and can be combined with conventional IP routing to achieve the higher flexibility than another pipeline forwarding implementation known as time-driven switching (TDS) or fractional lambda switching (FλS).[clarification needed] Packets (TDP) [3] and can be used to create pipeline forwarding parallel network in the future Internet [4].
References
- ^ [|Baldi, M.]; Marchetto, G.; Ofek, Y. (2007), "A Scalable Solution for Engineering Streaming Traffic in the Future Internet", Computer Networks (COMNET) 51 (14), http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRG-4NR18MX-3&_user=1002983&_coverDate=10%2F10%2F2007&_rdoc=9&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236234%232007%23999489985%23664619%23FLA%23display%23Volume)&_cdi=6234&_sort=d&_docanchor=&view=c&_ct=15&_acct=C000050171&_version=1&_urlVersion=0&_userid=1002983&md5=098456d09df1a406819b5260772c1f26
- ^ [|Baldi, M.]; Ofek, Y. (2004), "Fractional Lambda Switching - Principles of Operation and Performance Issues" (PDF Portable Document Format is a generic computer term.[citation needed] The best-known PDF implementation is Adobe PDF, a file format created by Adobe Systems in 1993 for document exchange. The remainder of this article discusses Adobe PDF exclusively), SIMULATION: Transactions of The Society for Modeling and Simulation International 80 (10), http://staff.polito.it/mario.baldi/publications/TSMS2004_FLS.pdf
- ^ Li, C.-S.; Yung, M. (1996), "Time-driven priority flow control for real-time heterogeneous internetworking" (PDF Portable Document Format is a generic computer term.[citation needed] The best-known PDF implementation is Adobe PDF, a file format created by Adobe Systems in 1993 for document exchange. The remainder of this article discusses Adobe PDF exclusively), IEEE Int. Conf. on Computer Communications (INFOCOM 1996), IEEE, http://www.synchrodyne.com/papers/Infocom96.pdf
- ^ [|Baldi, M.]; Ofek, Y. (2009), "Time for a 'Greener' Internet" (PDF Portable Document Format is a generic computer term.[citation needed] The best-known PDF implementation is Adobe PDF, a file format created by Adobe Systems in 1993 for document exchange. The remainder of this article discusses Adobe PDF exclusively), 1st International Workshop on Green Communications (GreenComm'09) in conjunction with the IEEE International Conference on Communications (IEEE ICC 2009), IEEE, http://staff.polito.it/mario.baldi/publications/2009GreenComm_PF.pdf
Categories: Computer networking
