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Topic: Physical layer

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In the News (Sun 16 Jun 19)

  Managing the Physical Layer
All things considered, the physical layer is essentially the true “edge” of the network, but unfortunately has the least amount of visibility of all of the critical components making up the network infrastructure.
If a physical layer management system (such as one with the attributes described in the previous sections) is in place, an unauthorized access event would be generated and sent to the NOC.
To make matters worse, for the physical layer it is not the equipment side cabling or the OSP/horizontal cabling that is the item that is the most prone to changes and errors; it is the cross-connects on the patch panels.
www.panduit.com /enabling_technologies/070240.asp   (3538 words)

 Howstuffworks "How OSI Works"
Application - This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network-related activities.
Flow control means that the Transport layer looks to see if data is coming from more than one application and integrates each application's data into a single stream for the physical network.
Data - In this layer, the appropriate physical protocol is assigned to the data.
computer.howstuffworks.com /osi1.htm   (291 words)

 TCP/IP Networks - The seven-layer Open Systems Interconnection (OSI) Reference Model
The physical layer describes the bit patters to be used, but does not define the medium, it describes how data are encoded into media signals and the characteristics of the media attachment interface.
This layer synchronises the transmission and is responsible for error-control on frame-level (a frame is a block of data within network-specific addressing information), also error-correction so that information can be transmitted from the physical layer.
The network layer operates independently of the physical medium, which is a concern of the physical layer.
www.citap.com /documents/tcp-ip/tcpip006.htm   (4733 words)

 Physical Sciences Research   (Site not responding. Last check: 2007-10-08)
During the last 50 years, physical sciences research at Bell Labs has played a crucial role in enabling modern communication networks through the creation of much of its physical layer material and component infrastructure.
While a substantial part of our research can be described as being associated with the physical layer of the network, we have an increasing presence at the system level, where, in recent years, we have been making significant contributions synergistic with those of other laboratories.
Understanding the physical limits of communication technologies is part of the mission of physical research.
www.bell-labs.com /org/physicalsciences   (366 words)

 Seven Layer Model
The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity, and small enough that the architecture does not become unwieldy.
Layer 6 specifies whether it's a request for a GIF or an HTML document, and treats the Layer 7 header, data, and footer as its own data, prepending that with a header and appending it with a footer.
Physical layer specifications define such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and the physical connectors to be used.
networking.ringofsaturn.com /Protocols/sevenlayer.php   (1739 words)

 The Physical Layer   (Site not responding. Last check: 2007-10-08)
  The physical layer is made up of two separate functions : (1) functions that depend on the actual type of medium used, which are contained in the physical medium sublayer ; (2) functions that change the bits to ATM cells, which are contained in the transmission convergence sublayer.
Once the cells are found and checked the cells must be decoupled from the transmission rate of the medium and this is achieved by the insertion and deletion of idle cells in the stream, which can also be seen in Figure 1.7.
While all the physical attributes of the physical medium should be dealt with in the physical layer, this is not really possible.
www.eeng.dcu.ie /~murphyj/the/the/node6.html   (461 words)

 Webopedia: The 7 Layers of the OSI Model
Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control.
This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level.
www.webopedia.com /quick_ref/OSI_Layers.asp   (426 words)

 ' + pPage + '
By segmenting the tasks that each layer performs, it is possible to change one of the layers with little or no impact on the others.
This layer is the main interface for the user to interact with the application and therefore the network.
This layer's primary function is the syntax and semantics of the data transmission.
www.officewizard.com /books/network/ch02.htm   (3759 words)

 The TCP/IP Guide - Physical Layer (Layer 1)
The physical layer is special compared to the other layers of the model, because it is the only one where data is physically moved across the network interface.
All of the other layers perform useful functions to create messages to be sent, but they must all be transmitted down the protocol stack to the physical layer, where they are actually sent out over the network.
In general, then, physical layer technologies are ones that are at the very lowest level and deal with the actual ones and zeroes that are sent over the network.
www.tcpipguide.com /free/t_PhysicalLayerLayer1.htm   (659 words)

 Physical layer - Wikipedia, the free encyclopedia
The physical layer is level one in the seven level OSI model of computer networking as well as in the five layer TCP/IP reference model.
The physical layer is the most basic network layer, providing only the means of transmitting raw bits rather than packets over a physical data link connecting network nodes.
The physical layer determines the bit rate in bit/s, also known as channel capacity, digital bandwidth, maximum throughput or connection speed.
en.wikipedia.org /wiki/Physical_layer   (470 words)

 Physical Layer   (Site not responding. Last check: 2007-10-08)
The physical layer (layer 1) of the OSI reference model serialises the frame (i.e.
The physical layer defines the representation of ecah bit as a voltage, current, phase, or frequency.
A clock (timing signal) is needed to identify the boundaries between the bits (in practice it is preferable to identify the centre of the bit - since this usually indicates the point of maximum signal power).
www.erg.abdn.ac.uk /users/gorry/course/phy-pages/phy.html   (332 words)

 3rd GPP Physical layer - General description
In the FDD mode a physical channel is characterised by the code, frequency and in the uplink the relative phase (I/Q).
A physical channel is therefore defined as a code (or a number of codes) and additionally in TDD mode the sequence of time slots completes the definition of a physical channel.
A physical channel is therefore defined as a code(or a number of codes) and additionally in TDD mode, the sequence of time slots completes the definition of a physical channel.
www.fortunecity.com /business/tisch/1301/id55.htm   (2951 words)

 Chapter 6: The OSI Physical Layer (via CobWeb/3.1 planet03.csc.ncsu.edu)   (Site not responding. Last check: 2007-10-08)
Physical - This layer has 7 topics and is associated with bits.
Physical topology is the way the network is wired (or wireless-ed?) together.
In a physical bus network (we'll talk about a logical bus in the next chapter), think of the bus as being one long network access channel that all the devices connected to it have to tap into.
home.att.net.cob-web.org:8888 /~s.k.vincent/250_6.htm   (1591 words)

 OSI model - Wikipedia, the free encyclopedia
Usually, the implementation of a protocol is layered in a similar way to the protocol design, with the possible exception of a 'fast path' where the most common transaction allowed by the system may be implemented as a single component encompassing aspects of several layers.
The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport layer.
The Data Link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical layer.
en.wikipedia.org /wiki/OSI_model   (1477 words)

 OSI Layer 1 - Physical Layer   (Site not responding. Last check: 2007-10-08)
The Physical layer communicates directly with the various types of actual communication media.
The Physical layer specifications specify the electrical, mechanical and functional requirements for activating, maintaining and deactivating a physical link between end systems.
The Physical layer's connectors (RJ-45, BNC e.c.t) and different physical topologies (Bus, Star, Hybrid networks) are defined by the OSI as standards, allowing different systems to communicate.
www.netcolony.com /clifford/osi_layer_1__physical_layer.htm   (197 words)

 OSI Model - Physical Layer
Transmission and receipt of data from the physical medium (copper wire, fiber, radio frequencies, barbed wire, string etc.) is managed at this layer.
The physical layer receives data from the data link Layer, and transmits it to the wire.
The physical layer controls the electrical and mechanical functions related to the transmission and receipt of a communications signal.
www.inetdaemon.com /tutorials/theory/osi/physical.shtml   (193 words)

 Physical Layer
The Physical layer of B-ISDN can have several different forms but its essential purpose is to collect and organize ATM cells sent down from the ATM layer, transport them to the physical medium and also perform the reverse of the process.
The physical medium can be optical with an extension capability of 0 - 800m or coaxial cable with an extension capability of 0 - 100m.
Conversion of data bit flow into a waveform adapted to a physical medium, or the reverse conversion process, insertion or extraction of timing information and line coding and decoding.
ganges.cs.tcd.ie /undergrad/4ba2/atm/ATMphys.html   (744 words)

 Physical Layer
This layer is composed of the electrical, optical, and physical components of the network.
The physical layer carries the signals for all of the higher layers.
The physical means of transmission,such as a network adapter or fiber optic adapter, determines whether it is appropriate to transmit bits as electrical or optical signals.
www.microsoft.com /technet/prodtechnol/windows2000serv/reskit/cnet/cnfh_osi_obcs.mspx   (187 words)

 IEee 802.11 Physical layer
Members of the 802.11 working group felt that a choice of PHY layer implementations was necessary so that systems designers can choose a technology that matches the price, performance, and operations profile of a specific application.
The infrared PHY layer provides for peak data rates of 1 Mbps (in 850 nanometer spectrum) with an optional 2-Mbps rate, and relies on pulse position modulation (PPM).
One of the key advantages of RF PHY layers is the ability to have a number of distinct channels.
www.cs.rit.edu /~aat0995/project/levine/physical_layer.html   (758 words)

 The Physical Layer   (Site not responding. Last check: 2007-10-08)
The physical later is concerned with transmitting raw bits over a communication channel.
The design issues here deal largely with mechanical, electrical, and procedural interfaces, and the physical transmission medium, which lies below the physical layer.
Physical layer design can properly be considered to be within the domain of the electrical engineer.
www2.rad.com /networks/1994/osi/physic.htm   (85 words)

 CAN physical layer
The Controller Area Network (CAN) protocol defines the data link layer and part of the physical layer in the OSI model, which consists of seven layers.
The physical media most commonly used to implement CAN networks is a differentially driven pair of wired with common return.
In order to achieve physical compatibility all nodes in the network must use the same or a similar bit-timing.
www.can-cia.org /can/physical-layer   (1995 words)

 Physical layer (via CobWeb/3.1 planet03.csc.ncsu.edu)   (Site not responding. Last check: 2007-10-08)
The physical layer is level one in the seven level OSI model of computer networking.
The physical layer is the very simplest, defining only exactly what a bit is: in other words how to transmit a one or a zero.
For example, you would specify at this layer things like what shapes the electrical connectors are, what frequencies to broadcast at, and what frequencies are allowed and will not blow up the network cards.
physical-layer.iqnaut.net.cob-web.org:8888   (275 words)

 What is the Physical Layer?
The Physical Layer is layer one of the OSI model.
The Physical Layer is responsible for bit-level transmission between network nodes.
In fiber optic networks, the Physical Layer is responsible for defining the characteristics of light signals.
www.tech-faq.com /physical-layer.shtml   (412 words)

 PHYsical Layer Solutions   (Site not responding. Last check: 2007-10-08)
An important type of physical layer device used in high speed communications links is the serializer/deserializer (SerDes) which, as its name suggests, serializes and deserializes the data stream.
The physical layer is involved when data needs to be sent either across the line or between line cards across the backplane to the switch fabric.
Next generation physical layers are moving to serial technologies with clock and data recovery.
www.xilinx.com /esp/wired/optical/xlnx_net/phy_lay.htm   (353 words)

 INFO370 Fundamentals of Datacommunications
From a network perspective, the Physical Layer is Layer 1 of the OSI model, receiving the raw data stream that has been packaged into frames by the Data Link Layer, Layer 2.
The Physical Layer carries the signal thru the network medium where the stream of bits is reconstructed into frames by the remote node's Data Link Layer.
All aspects of the physical layer are defined by protocols and specifications that describe the type of cable and connectors used.
www.people.vcu.edu /~gasaunde/info370/PhysicalLayer.html   (9211 words)

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