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Topic: Plesiochronous Digital Hierarchy

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	Plesiochronous Digital Hierarchy
		The Plesiochronous Digital Hierarchy (PDH) is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio[?] systems.
		The term plesiochronous is derived from Greek plesio, meaning near, and chronos, time, and refers to the fact that PDH networks run in a state where different parts of the network are almost, but not quite perfectly, synchronised.
		PDH allows transmission of data streams that are nominally running at the same rate, but allowing some variation on the speed around a nominal rate.
	www.ebroadcast.com.au /lookup/encyclopedia/pd/PDH.html (556 words)

	PDH - Plesiochronous Digital Hierarchy
		Plesiochronous Digital Hierarchy: PDH (plesiochronous means nearly synchronous), was developed to carry digitized voice over twisted pair cabling more efficiently.
		This evolved into the North American, European, and Japanese Digital Hierarchies where only a discrete set of fixed rates is available, namely, nxDS0 (DS0 is a 64 kbps rate) and then the next levels in the respective multiplex hierarchies.
		PDH (plesiochronous means nearly synchronous), was developed to carry digitized voice over twisted pair cabling more efficiently.
	www.auditmypc.com /acronym/PDH.asp (284 words)

	PLESIOCHRONOUS DIGITAL HIERARCHY digital
		Early core transmission facilities used frequency division multiplexing, but in the 1960s this system was largely replaced with the PDH (plesiochronous digital hierarchy), which is a system of multiplexing numerous individual channels into higher-level channels.
		These features were based on high-order multiplexing through a hierarchy of increasing bit rates up to 140 Mbps or 565 Mbps in Europe and had been defined in the late 1960s and early 1970s along with the introduction of digital transmission over coaxial cables.
		The Synchronous digital hierarchy as developed by the ITU-T is also covered and the North American SONET implementation of it is analysis in order to obtain a better insight of the complexity of this new technology.
	digilander.libero.it /a_digital/Plesiochronous_Digital_Hierarchy.html (591 words)

	Plesiochronous Digital Hierarchy (Site not responding. Last check: 2007-10-11)
		PDH was the old standard derived from the days of multiplexing telephone calls.
		The figures shown here are the European standard and are based on the 64kbit/s channel which was used to transmit a single voice call digitally.
		NOTE: The PDH standards in the USA and JAPAN are different although both are based on the same Level 0 rate.
	www-users.aston.ac.uk /~blowkj/photonicnetworks/lecture4/sld002.htm (282 words)

	DIGITAL MULTIPLEX HIERARCHY digital
		Pleisosynchronous Digital Hierarchy abbreviation for pain-drug-hypnosis, a behavioral modification technique used by military and intelligence services in which pain, drugs or hypnosis, or any combination of these, are administered to drive an individual into a state whereby he can be given suggestions or commands subconsciously.
		SDH Synchronous Digital Hierarchy is an ITU standard used in Europe.
		Description of the Prior Art Digital transmission networks and a multiplex hierarchy are known from the periodical "Telcom Report", Vol.
	digilander.libero.it /a_digital/Digital_multiplex_hierarchy.html (863 words)

	RFC 4197 (rfc4197) - Requirements for Edge-to-Edge Emulation of Time Divis
		TDM Circuits Belonging to the PDH Hierarchy The bit rates traditionally used in various regions of the world are detailed in the normative reference [G.702].
		The Synchronous Digital Hierarchy (SDH) is the international equivalent and enhancement of SONET and is specified by [G.707].
		Structure-Aware Transport of Signals out of the PDH Hierarchy Structure-aware transport is considered for the following signals: o E1/T1 with one of the structures imposed by framing as described in [G.704].
	www.faqs.org /rfcs/rfc4197.html (4387 words)

	OFC Communication
		This introduction of justification 'dummy' bits occurs at all levels of multiplexing in the hierarchy, and this plesiochronous (almost synchronous) mode of transmission multiplexing is termed Plesiochronous Digital Hierarchy (PDH).
		Plesiochronous Digital Hierarchy was intended as a solution for voice telephony channel multiplexing and is not suited for the high-bandwidth connections that the applications of today need.
		An important difference between PDH and SDH is that higher order streams are obtained in SDH by byte-interleaving the lower streams, instead of bit-interleaving as is done in PDH.
	msridhar.freeshell.org /ofc.htm (973 words)

	limitations of the plesiochronous digital hierarchy (Site not responding. Last check: 2007-10-11)
		The problem of flexibility in a plesiochronous network is illustrated by considering what a network operator may need to do in order to be able to provide a business customer with a 2 Mbit\s leased line.
		The use of justification bits at each level in the PDH means that identifying the exact location of the frames in a single 2 Mbit\s line within say a 140 Mbit\s channel is impossible.
		Another limitation of the PDH is its lack of performance monitoring capability.
	www2.rad.com /networks/1994/sdh/doc33.htm (341 words)

	[No title]
		Digital data and voice transmission is based on a 2.048Mbit/s bearer consisting of 30 time division multiplexed (TDM) voice channels, each running at 64Kbps (known as E1 and described by the CCITT G.703 specification).
		Plesiochronous transmission is now often referred to as plesiochronous digital hierarchy (PDH).
		PDH links are generally limited to point-to-point configurations with full demultiplexing at each switching or cross connect node.
	www.gare.co.uk /technology_watch/sdh.htm (1759 words)

	What is SDH
		Because of PDH disadvantages, It was obvious That a new multiplexing method is needed.
		Further more there is no inband management in the PDH protocol if we need to know the status of 1 of the multiplexers, or if we need to change the route of 1 of the trails we have to go to the site or build an
		In order to be able to do the same things with the PDH network, one should build another separated network for the management and the remote control.
	www.pulsewan.com /data101/sdh_basics.htm (1999 words)

	Plesiochronous Digital Hierarchy - Wikipedia, the free encyclopedia
		PDH is now being replaced by Synchronous Digital Hierarchy (SDH) equipment in most telecommunications networks.
		However, there is no link between watches to guarantee they run at exactly the same rate, and it is highly likely that one is running slightly faster than the other.
		This allows the receiving multiplexer to correctly reconstruct the original data for each of the four 2 Mbit/s data streams, and at the correct, different plesiochronous, rates.
	en.wikipedia.org /wiki/Plesiochronous_Digital_Hierarchy (584 words)

	Synchronous Digital Hierarchy, Synchronous Transport Model, Plesiochronous Digital Hierarchy
		As bandwidth demand grew the technology called Plesiochronous Digital Hierarchy (PDH) was developed by ITU-T G.702, whereby the basic primary multiplexer 2.048Mb/s trunks were joined together by adding bits (bit stuffing) which synchronised the trunks at each level of the PDH.
		Multiplexers on the same level of the hierarchy remove the spare bits and are synchronised with each other at that level only.
		The 2Mb/s PDH first enters a container C12 which compensates for the varying speeds via the use of stuff bits (R).
	www.rhyshaden.com /sdh.htm (1046 words)

	Plesiochronous Digital Hierarchies (PDH) (Site not responding. Last check: 2007-10-11)
		Plesiochronous Digital Hierarchy (PDH) refers to the three, digital communication standards of the world which use point-to-point, 2-wire-pair links and are based on the fundamental concepts of Time Division Multiplexing (TDM).
		In the PSTN, PDH carriers are used for trunking and transporting voice channels.
		Hence, digital information (voice or data) can be exchanged between geographically dispersed office locations and access to the World Wide Web is provided.
	www.xilinx.com /esp/wired/optical/net_tech/pdh.htm (234 words)

	What is SDH? - a definition from Whatis.com - see also: Synchronous Digital Hierarchy
		- SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media.
		In digital telephone transmission, "synchronous" means the bits from one call are carried within one transmission frame.
		"Plesiochronous" means "almost (but not) synchronous," or a call that must be extracted from more than one transmission frame.
	searchnetworking.techtarget.com /sDefinition/0,,sid7_gci214191,00.html (240 words)

	SDH PDH SONET - SONET - High Speed Synchronous Digital Multiplexing Systems - Goals of SONET,Elements of an ...
		digital multiplexing hierarchy consisted of the components shown in Figure 1.
		The multiplexing hierarchy intended by the original SONET proposal would allow for any combination of input tributaries, thereby eliminating the requirement of homogeneous tributaries of asynchronous multiplexers.
		Figure 3 shows the concept of a synchronous multiplexer, where the STS-n represents a signal that has a bit rate or frame size that is "n" times greater than that of the basic (SONET frame) STS-1.
	www.2cool4u.ch /sdh_pdh_sonet/sonet_hispeed/sonet_hispeed.htm (2070 words)

	Siemens Communications Lexicon - plesiochronous digital hierarchy (PDH)
		Plesiochronous digital hierarchy (PDH) refers to a digital transmission technology for transmission between two network nodes that are not clocked identically.
		PDH was standardized in 1972 by the CCITT and supports various bitrates.
		To support the basic E1 bitrate of 2.048 Mbps and the T1 bitrate used in North America and Japan of 1.544 Mbps, G.702 uses time division multiplexing of 64 kbps channels.
	networks.siemens.com /communications/lexicon/0/f000140.htm (150 words)

	Plesiochronous Digital Hierarchy
		(PDH) A transmission system for voice communication using plesiochronous synchronisation.
		PDH is the conventional multiplexing technology for network transmission systems.
		PDH is being replaced by SONET and other SDH (Synchronous Digital Hierarchy) schemes.
	burks.bton.ac.uk /burks/foldoc/34/90.htm (84 words)

	NADH (North American Digital Hierarchy) (Linktionary term)
		In this scheme, a circuit is divided into a continuous stream of time slots and multiple channels are multiplexed into the circuit.
		Traditionally, each channel was a digitized voice call, but video information and data may also occupy a channel.
		The basic channel is 64 Kbits/sec, which is the amount of bandwidth required to transmit a voice call that has been converted from analog to digital using a sampling rate of 8,000 times per second with the sample represented as an 8-bit value (8 × 8,000 = 64 Kbits/sec).
	www.linktionary.com /n/nadh.html (462 words)

	synchronous_digital_hierarchy (Site not responding. Last check: 2007-10-11)
		It was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting large amounts of telephone and data traffic and to allow for interoperability between equipment from different vendors.The more recent synchronous digital hierarchy (SDH) standard developed by the International Telecommunication Union (ITU) is built on experience in the development of SONET.
		SONET differs from PDH in that the exact rates that are used to transport the data are tightly synchronized across the entire network, made possible by atomic clocks.
		Three OC-1 (STS-1) signals are multiplexed by time-division multiplexing to form the next level of the SONET hierarchy, the OC-3 (STS-3), running at 155.52 Mbit/s.
	hondparts.com /wiki/?title=Synchronous_Digital_Hierarchy (2544 words)

	Transmission Systems
		PDH: Data rates, telecommunications terminology and standards: 2 Mbit/s to 565 Mbit/s, E0, E1, OC 192, etc.
		disuss the data rates associated with PDH, telecommunications terminology and standards: 2 Mbit/s to 565 Mbit/s, E1, E3, OC 192, etc. together with typical applications of their usage.
		Entry requirements for this unit are at the discretion of the centre.
	www.amerc.ac.uk /telecomms/unit11.html (949 words)

	Synchronous Digital Hierarchy from FOLDOC (Site not responding. Last check: 2007-10-11)
		The SDH specifies how payload data is framed and transported synchronously across optical fibre transmission links without requiring all the links and nodes to have the same synchronized clock for data transmission and recovery (i.e.
		SDH offers several advantages over the current multiplexing technology, which is known as Plesiochronous Digital Hierarchy.
		Where PDH lacks built-in facilities for automatic management and routing, and locks users into proprietary methods, SDH can improve network reliability and performance, offers much greater flexibility and lower operating and maintenance costs, and provides for a faster provision of new services.
	foldoc.org /?SDH (259 words)

	Plesiochronous Digital Hierarchy - ierarhii digitale plesiocrone (English to Romanian translation glossary) ...
		Plesiochronous Digital Hierarchy - ierarhii digitale plesiocrone (English to Romanian translation glossary) telecommunication,Telecom(munications),Tech/Engineering
		The KudoZ network provides a framework for translators and others to assist each other with translations or explanations of terms and short phrases.
		The support of Asynchronous Transfer Mode (ATM) and Synchronous Digital Hierarchy (SDH) in the Plesiochronous Digital Hierarchy (PDH) bit rates is covered in this standard.
	www.proz.com /kudoz/511798 (127 words)

	CommsDesign - Ethernet ICs eye wireless service delivery (Site not responding. Last check: 2007-10-11)
		The initial opportunity lies in the upgrade of wireline PDH networks to Ethernet-centric services, said Matthew Coakeley, director of technical marketing at Galazar.
		In a backhaul termination application, the CopperNode would terminate multiple PDH lines and feed the output to an Ethernet switch or network processor in an edge router.
		Analog, Mixed-Signal and Digital ASIC, SoC and IP Design Solutions are available from Intrinsix Corp. Important numbers to consider: 21 Years in business.
	www.commsdesign.com /story/showArticle.jhtml?articleID=193600774 (481 words)

	Wilujeng Sumping - PDH (Pakaian Dinas Harian, bukan Plesiochronous Digital Hierarchy)
		Wilujeng Sumping - PDH (Pakaian Dinas Harian, bukan Plesiochronous Digital Hierarchy)
		PDH (Pakaian Dinas Harian, bukan Plesiochronous Digital Hierarchy)
		Nanti mulai tanggal 1 Desember, di kantor wajib pake PDH tiap hari Senen dan Rabu.
	ummuauliya.multiply.com /journal/item/178 (139 words)

	Synchronous Digital Hierarchy ( S D H and SDH) Definition
		DEFINITION: SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media.
		In digital telephone transmission, "synchronous" means the bits …
		SYNCHRONOUS DIGITAL HIERARCHY DEFINITION (continued): … SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media.
	www.bitpipe.com /tlist/Synchronous-Digital-Hierarchy.html (315 words)

	IEC: Synchronous Digital Hierarchy (SDH)
		This has resulted in new network applications, the deployment of new equipment in new network topologies, and management by operations systems of much greater power than previously seen in transmission networks.
		The 1984 breakup of the Bell operating companies (BOCs) in the United States produced competitive pressures that required a standard optical interface for interexchange carriers' use and new features for improved network management.
		It was widely accepted that the new multiplexing method should be synchronous and based not on bit interleaving as was the PDH, but on byte interleaving, as are the multiplexing structures from 64 kbps to the primary rates of 1,544 kbps (1.5 Mbps) and 2,048 kbps (2 Mbps).
	www.iec.org /online/tutorials/sdh/topic01.html (445 words)

	Roxen Community: RFC 4197 Requirements for Edge-to-Edge Emulation of Time Division Multiplexed (TDM) Circuits over ...
		This document defines the specific requirements for edge-to-edge emulation of circuits carrying Time Division Multiplexed (TDM) digital signals of the Plesiochronous Digital Hierarchy as well as the Synchronous Optical NETwork/Synchronous Digital Hierarchy over packet-switched networks.
		This document defines the specific requirements for edge-to-edge emulation of circuits carrying Time Division Multiplexed (TDM) digital signals of the Plesiochronous Digital Hierarchy (PDH) as well as the Synchronous Optical NETwork (SONET)/Synchronous Digital Hierarchy (SDH) over Packet-Switched Networks (PSN).
		The bit rates traditionally used in various regions of the world are detailed in the normative reference [G.702].
	community.roxen.com /developers/idocs/rfc/rfc4197.html (4369 words)

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