Abstract
This article presents the comparison of different transport level congestion control schemes, including variants of the TCP (Postel, 1981). The protocol mechanisms, implemented in various protocols are hard to investigate in a uniform manner (Hosszú, 2005); therefore, the simulator SimCast (Simulator for multicast) is developed for traffic analysis of the unicast (one-to-one communication) and multicast (one-to-many communication) streams. In this article, the TCP and other transport protocol mechanisms will be compared using the SimCast simulator (Orosz & Tegze, 2001). The simulated results are presented through examples.
TopIntroduction
Internet streaming media changed the Web from a static medium into a multimedia platform, which supports audio and video content delivery. Today, streaming media turns into the standard way of global media broadcasting and distribution. The low costs, worldwide accessibility, and technical simplicity of this telecommunication way make media streams very attractive for content providers.
Streaming works by cutting the compressed media content into packets that are sent to the receiver. Packets are reassembled and decompressed on the receiver side into a format that can be played by the user. To achieve smooth playback, packets are buffered on the receiver side. However, in case of network congestion, the stream of packets slows down and the player application runs out of data, which results in poor playback quality.
This article presents the comparison of different transport level congestion control schemes, including variants of the TCP (Postel, 1981). The protocol mechanisms, implemented in various protocols are hard to investigate in a uniform manner (Hosszú, 2005); therefore, the simulator SimCast (Simulator for multicast) is developed for traffic analysis of the unicast (one-to-one communication) and multicast (one-to-many communication) streams. In this article, the TCP and other transport protocol mechanisms will be compared using the SimCast simulator (Orosz & Tegze, 2001). The simulated results are presented through examples.
Due to spreading of traffic lacking end-to-end congestion control, congestion collapse may arise on the Internet (Floyd & Fall, 1999). This form of congestion collapse is caused by congested links that are sending packets to be dropped only later in the network. The essential factor behind this form of congestion collapse is the absence of end-to-end feedback. On the one hand, an unresponsive flow fails to reduce its offered load at a router in response to an increased packet drop rate, and on the other hand, a disproportionate-bandwidth flow uses considerably more bandwidth than other flows in time of congestion. In order to achieve accurate multicast traffic simulation—because it is not so TCP-friendly yet—the effects of the flow control of the TCP protocol should be determined. However, there are many different kinds of TCP and other unicast transport protocol implementations with various flow control mechanisms, which make this investigation rather difficult (He, Vicat-Blanc Primet, & Welzl, 2005).
Until now, a lot of comparisons have been done. For example, Wang et al. reviewed the TCP-friendly congestion control schemes on the Internet (Wang, Long, Cheng, & Zhang, 2001). They differentiated two groups of the TCP-friendly congestion control algorithms as follows: (1) end-to-end and (2) hop-by-hop congestion control mechanisms. The end-to-end mechanisms are grouped into (a) additive increase multiplicative decrease (AIMD)-based schemes with the window- and rate-adaptation schemes, (b) modeling-based schemes, including equation based congestion control schemes and the so called model-based congestion schemes, and (c) a combination of AIMD-based and modeling-based mechanism. Wang’s classification is mostly used in our discussion, too.
Yu (2001) proposes another important approach about the survey on TCP-friendly congestion control protocols for media streaming applications, in which several TCP-friendly congestion control protocols were discussed via a comparison of many important issues that determine the performance and fairness of a protocol.
It is an important advantage of the simulator SimCast that the latest TCP congestion control mechanisms are also implemented. In this way, the cooperation among different TCP protocol entities or various other transport level protocols can be examined (Shalunov, Dunn, Gu, Low, Rhee, Senger, Wydrowski, & Xu 2005).
In this article, various TCP congestion control mechanisms as well as congestion control mechanisms for media streams are reviewed. Then a novel simulator for transport protocols is described and the various simulation results summarized. Lastly, conclusions are drawn and future work is identified.
Key Terms in this Chapter
Transceiver: An electronic device which is both a TRANSmitter and a reCEIVER.
Dielectrics: Materials, such as liquids, that are not able to conduct electricity. These materials interfere with the transmission of radio frequency waves.
EAN (13-digit UPC code): Provides more flexibility than original UPC code.
RFID: RFID, or radio frequency identification, is a form of Auto ID in which radio waves are used to gather information from electronic tags attached to items such as vehicles, merchandise, or animals.
Semi-active Tag: Type of RFID tag with a built-in battery power source which provides power to the electronic circuitry while the tag is communicating with the reader. Semi-active tags do not have enough power to autonomously generate radio waves.
Reader: One of the two components of an RFID system. The reader generates and sends a radio wave signal to the tag, and captures and decodes the reflected signal from the tag in order to identify the object to which the tag is attached. All readers have some power source. Also known as an interrogator.
Tag: One of the two components of an RFID system. The tag, a radio frequency transponder, is affixed to the product that needs to be identified and is actuated by receiving a radio wave sent to it by the reader. See passive tag, semi-active tag, and active tag.
EAS (Electronic Article Surveillance): The use of an RFID tag to identify valuable property in order to reduce theft.
Transponder: Also known as a tag, a transponder electronically TRANSmits and resPONDs.
Passive Tag: Type of RFID tag that does not have a battery incorporated and therefore must rely on power contained in the radio wave transmitted by the reader. Passive tags are the lowest cost tags, but also perform at the lowest level.
Air Interface: Air, the medium through which radio waves are transmitted.
Auto ID: Auto ID, also called “Automatic Identification,” is a form of ICT that enables identifying information about objects to be gathered through the agency of scanners and readers. Auto ID encompasses barcodes, RFID, and similar tagging technology which can be read and interpreted automatically by a mechanical device. A bar code reader can interpret a printed bar code; an RFID reader can interpret an RFID tag.
EPC (Electronic Product Code): Encoded on RFID tags and tied to a multiplicity of data concerning the object tagged. Standards are still being developed and proposed for EPC by EPCGlobal, an international organization devoted to creating a community of supply chain firms cooperating to consistent end-to-end partnerships of product movement and tracking.
UPC (Universal Product Code): UPCs are used to identify consumer goods and consist of a manufacturer’s number combined with a product number. The manufacturer’s identification number is assigned by the Uniform Code Council; the manufacturer can then assign its own product number.
EDI (Electronic Data Interchange): The electronic transmission of business information from one supply chain member to another, using a standard data format and standard transaction codes. An EDI transaction, known as Advance Shipment Notice, or ASN, is being coordinated with data tracked by RFID tags on products moving through supply chains.
HF (High Frequency): The original range of frequencies used with case and pallet level tagging in supply chains. The signals exchanged between HF tags and readers are subject to attenuation due to dielectrics.
Bar Code: Automatic identification technology that generally employs a series of black vertical bars separated by vertical white spaces as a method of encoding numeric and alphanumeric data. Commonly used forms of barcodes are placed on consumer goods to identify universal product codes (UPCs). Newer technologies of barcodes include 2D (two dimensional) which allow more information to be encoded using a smaller area. There must be a line of sight between barcodes and barcode scanners in order for information to be read.
Alignment: How the reader is oriented to the tag.
Frequency: Frequencies constitute the rate at which electromagnetic waves, such as light, television, and radio waves, oscillate. Electromagnetic waves are comprised of a continuum of emanations, including light waves which are visible, and invisible frequencies such as television and radio waves which are lower frequency than light, and x-rays and gamma rays which are higher frequency. Frequencies are measured in Hertz (Hz), kilohertz (kHz), megahertz (MHz), or gigahertz (GHz), and represent the rate of oscillation of the waves.
UHF (Ultra High Frequency): UHF is being tested with Gen 2 chips as a means of overcoming problems with RF tags because the UHF emanations are not affected by dielectric materials in the same way in which RF is affected.
Gen 2: Second generation tags. Uses ultra high frequency range of radio waves.
Active Tag: Type of RFID tag that contains a battery power source that is used for all of its functioning. Active tags can autonomously produce radio waves without the presence of a reader.