Loose tube cables are primarily used in outside plant applications. They are designed to protect the fibers from damage stretching and kinking that might result from an overly aggressive cable puller.
The tube arrangement also allows for easier transition to fiber drops at buildings or communication cabinets. The fiber strands float within the buffer tubes and are not part of the cable structure. Loose tube cables are ideal for metropolitan and long distance cable installations. Tight buffer cables are specified for inside plant use. These types of cables are designed for use within a controlled environment such as a building or inside plant equipment cabinets.
Because the cable is used within a building the cable it requires less physical protection and has greater flexibility. The fibers within the cable are susceptible to damage from aggressive cable pulls because the fiber strands are part of the cable structure. The strands are tightly bound in a central bundle within the outer cable sheath. Fibers are assembled into either stranded or ribbon cables.
Stranded cables are individual fibers that are bundled together. Ribbon cable is constructed by grouping up to 12 fibers and coating them with plastic to form a multi fiber ribbon.
Stranded and ribbon fiber bundles can be packaged together into either loose or tight buffering cable. Fiber strands are produced in two basic varieties: Multimode and Single mode. Each variety is used to facilitate specific requirements of the communication system. Multimode is optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the optical fiber core.
Multimode fiber transmission is used for relatively short distances because the modes tend to disperse over longer lengths this is called modal dispersion. Multimode fiber is used for requirements of less than 15, feet.
Multimode fiber became available during the early 's and is still being used in many older systems. With the advances in fiber technology and the number of product choices available, multimode fiber is almost never deployed for new systems. There are mechanical devices available that accommodate a transition from multimode fiber to single mode fiber.
Single mode is optical fiber that is designed for the transmission of a single ray or mode of light as a carrier. Single mode fiber has a much smaller core than multimode fiber. Single mode fiber is produced in several variations. The variations are designed to facilitate very long distances, and the transmission of multiple light frequencies within a single light ray. Single mode fiber is generally manufactured with core diameters between 7 and 9 microns.
Note: SMF is a trademarked nomenclature of Corning Cable, that has become a generic term used to describe an all purpose single mode fiber. Nearly all traffic signal and freeway management systems will use an all purpose single mode fiber. Fiber optic product characteristics are in a constant state of change. Investigate before finalizing system specifications. The Resource Section of this handbook contains a list of fiber optic cable manufacturers and their web sites.
During the past 10 years, a number of variants of single mode fiber have been developed. Some of the fibers are used for long distance systems, and others are used for metropolitan systems. Each of these has been developed with special characteristics designed to enhance performance for a specific purpose.
Freeway Management and Traffic Signal Control would be considered — from a communications perspective — as general purpose systems. Designers of Transportation Management Systems using fiber should strongly consider specifying SMF type single mode fiber. This fiber is very available and normally is lowest in price. Fiber optic cable is priced on the basis of strand feet. A 5, foot cable with two fiber strands is 10, fiber strand feet.
A 5, foot cable with 24 fibers is , strand feet. Therefore, when purchasing fiber optic cable, it is always best to consider potential system additions in order to incur a lower overall materials cost. Remember, price per fiber strand foot is not the only factor to consider in overall system costs.
Items not included in this calculation are the costs associated with splicing, optimization and engineering. Single mode fiber has a very small core causing light to travel in a straight line and typically has a core size of 8 to 10 microns. It has theoretically unlimited bandwidth capacity, that can be transmitted for very long distances 40 to 60 miles. Multimode fiber supports multiple paths of light and has a much larger core — 50 or Because multimode fibers are five to six times the diameter of single mode, transmitted light will travel along multiple paths, or modes within the fiber.
Multimode fiber can be manufactured in two ways: step-index or graded index. Step-index fiber has an abrupt change or step between the index of refraction of the core and the index of refraction of the cladding. Multimode step-index fibers have lower bandwidth capacity than graded index fibers. Graded index fiber was designed to reduce modal dispersion inherent in step index fiber. Modal dispersion occurs as light pulses travel through the core along higher and lower order modes.
Graded index fiber is made up of multiple layers with the highest index of refraction at the core. Each succeeding layer has a gradually decreasing index of refraction as the layers move away from the center. High order modes enter the outer layers of the cladding and are reflected back towards the core. Multimode graded index fibers have less attenuation loss of the output pulse and have higher bandwidth than multimode step-index fibers. Single mode fibers are not affected by modal dispersion because light travels a single path.
Single mode step-index fibers experience light pulse stretching and shrinking via chromatic dispersion. Chromatic dispersion happens when a pulse of light contains more than one wavelength.
Wavelengths travel at different speeds, causing the pulse to spread. Dispersion can also occur when the optical signal gets out of the core and into the cladding, causing shrinking of the total pulse. Single mode shifted fiber uses multiple layers of core and cladding to reduce dispersion. Dispersion shifted fibers have low attenuation loss , longer transmission distances, and higher bandwidth.
Table of Contents. Figure RJ Connector. Figure Twisted Pair Cable. Figure Co-Axial Cable Illustration. Figure Fiber Optic Cable Illustration. Previous Next. One exemplary system embodiment includes a multi-drop Ethernet network. What is claimed is: 1. A network adapter configured to connect a host device to a network, the network adapter comprising: an Ethernet media access controller configured to implement a data link layer and process Ethernet compatible signals to and from the host device; a non-Ethernet physical layer interface configured to provide communication between the Ethernet media access controller and a non-Ethernet transceiver, the non-Ethernet transceiver being configured to allow the host device that is an Ethernet device to be connected as a node in a multi-d A network adapter configured to connect a host device to a network, the network adapter comprising: an Ethernet media access controller configured to implement a data link layer and process Ethernet compatible signals to and from the host device; a non-Ethernet physical layer interface configured to provide communication between the Ethernet media access controller and a non-Ethernet transceiver, the non-Ethernet transceiver being configured to allow the host device that is an Ethernet device to be connected as a node in a multi-drop network, where the multi-drop network is a non-Ethernet network; and the non-Ethernet physical layer interface being further configured to convert signals between the Ethernet compatible signals and signals compatible with the non-Ethernet transceiver.
The network adapter of claim 1 where the non-Ethernet transceiver is a serial transceiver. The network adapter of claim 2 where the serial transceiver includes an RS transceiver and the signals compatible with the non-Ethernet transceiver includes signals compatible with RS protocol. The network adapter of claim 1 where the non-Ethernet physical layer interface includes an electrical interface for converting signals between the Ethernet compatible signals and signals compatible with an RS transceiver.
The network adapter of claim 1 further including a Media Independent Interface MII connected between the Ethernet media access controller and the non-Ethernet physical layer interface.
The network adapter of claim 1 where the non-Ethernet transceiver includes a differential electrical pair that allows multiple host devices to be on a network bus to form the multi-drop network.
The network adapter of claim 1 where the non-Ethernet transceiver includes one of: an RS transceiver, an RS transceiver, or an RS transceiver.
A method comprising: forming a multi-drop network by connecting a plurality of Ethernet devices as nodes in the multi-drop network where the nodes are connected to a non-Ethernet multi-drop bus; when transmitting signals to the multi-drop network: converting Ethernet based signals from the Ethernet devices into non-Ethernet based signals; and communicating the non-Ethernet based signals to a non-Ethernet transceiver where the non-Ethernet transceiver provides network connection to the multi-drop network for a node; and when receiving signals from the multi-drop network: converting non-Ethernet based signals to Ethernet based signals; and communicating the Ethernet based signals to the Ethernet based device.
The method of claim 8 where the non-Ethernet transceiver is an RS transceiver and the non-Ethernet based signals are RS based signals. The network adapter can also be configured external to the host device In one embodiment, the network adapter can be configured with an Ethernet media access controller MAC The Ethernet MAC includes logic configured to implement a data link layer layer 2 based on the seven layers of the networking framework defined by the OSI model Open System Interconnection.
In accordance with the OSI model, the data link layer is divided into two sub-layers including the media access control MAC layer and the logical link control LLC layer. The MAC sub-layer controls how a computer on the network gains access to data and controls permission rights to transmit the data.
The LLC layer controls frame synchronization, flow control, and error checking. The data link layer is defined by IEEE In order to provide a physical connection to a network, a physical layer interface is provided. A physical layer interface is also referred to as a PHY and includes logic that implements the physical layer layer 1 of the OSI model.
In particular, the physical layer interface is a non-Ethernet physical layer interface in that it is configured to implement the physical layer in accordance with a protocol different from Ethernet. This configuration facilitates providing communication between the Ethernet media access controller and a non-Ethernet transceiver In this manner, the type of the non-Ethernet transceiver can be selected that allows the host device to be connected as a node in a multi-drop network, rather than a common Ethernet network.
Since the Ethernet media access controller is configured based on Ethernet protocol, it processes data that is Ethernet-based or generically speaking, Ethernet-compatible data. The non-Ethernet transceiver , however, is not configured to interpret or process Ethernet-compatible data, but rather, processes data according to its own protocol.
As such, the non-Ethernet physical layer interface is configured with logic that converts data between the Ethernet-compatible data and data compatible with the non-Ethernet transceiver In one embodiment, the non-Ethernet transceiver can be a serial transceiver that can be based on various protocols such as RS, RS, RS, or other desired transceiver capable of being connected to a multi-drop network.
For purposes of discussion, the following example embodiments will be described based on a transceiver that is an RS transceiver. It will be appreciated by one of ordinary skill in the art that the RS transceiver can be substituted with other types of transceivers to implement similar configurations as described.
Based on the type of transceiver used, appropriate modifications to the non-Ethernet physical layer interface will be needed to properly convert data between the Ethernet protocol and the protocol of the selected transceiver. By using the RS transceiver , the host device can be configured into a multi-drop Ethernet network since the RS specification provides for multi-point communications.
In one embodiment, the host device can be a computing device configured to be connectable to a multi-drop network using an RS transceiver where the computing device is configured to convert Ethernet compatible signals at a media access control MAC layer to RS compatible signals at a physical layer that can be processed by the RS transceiver In general, the system can be considered to include an Ethernet communication logic, an RS communication logic, and a conversion logic that translates data between the Ethernet protocol and the RS protocol.
For example, system can include a media access controller MAC that is configured based on Ethernet specifications. The data interface includes a channel for a transmitter and a separate channel for a receiver. Each channel has its own clock, data, and control signals. The MII data interface uses 16 signals and the management interface uses a 2-signal interface, where one signal is for clocking and the other signal is for data.
As previously explained, the PHY is not directly connected to the network bus as a typical Ethernet PHY would be, but rather, is connected to the RS transceiver , which is the component that is directly connected to the network bus. Since the RS specification configures the data signal and the clock signal on the same differential wire pair, the conversion logic will include an encoder to encode the separate clock signal and data signal from the MII into a synchronous signal for transmission to the RS transceiver The conversion logic will also include a decoder to decode the clock and data signals from the receive line RX into separate data and clock signals to function with the MII A more detailed embodiment will be described with reference to FIG.
It will be appreciated that the conversion logic may be configured differently. One or more of the components of system may be directly attached to the Ethernet-based host device , attached to a separate device such as a system board, or combinations of these. Similar signal lines are identified with the same references.
It will be appreciated by those of ordinary skill in the art that other configurations of an RS transceiver can be implemented. For example, different types and connections for resistors can be used and the like. The components may be viewed in terms of their functions as being part of an Ethernet media access controller MAC , a media independent interface MII , and a physical interface that controls and connects with an RS transceiver The physical interface is also configured to convert signals between Ethernet-compatible signals and RS compatible signals as previously described.
Example components that may be part of the Ethernet MAC can include a media independent interface MII control logic , a data transmit logic , and a data receive logic These components can be configured in accordance with Ethernet specifications for the data link layer layer 2 of the OSI model. Components that may be part of the media independent interface MII can include a variety of registers such as an MII register , a transmit TX register , and a receive RX register Of course, one or more registers can be used to implement the illustrated registers.
In one embodiment, the registers , , and are implemented based on IEEE Components that may be part of the physical interface and conversion logic can include a state machine , an encoder , and a decoder The state machine can be implemented in logic that controls the signal processes for data transmission, reception, and collision detection.
The encoder is configured to receive data signals and clocking signals from the data transmit logic and encode the signals together for transmission to the RS transceiver Conversely, the decoder receives data from the RS transceiver and decodes the signals into data signals and clocking signals Manchester encoding is a synchronous clock encoding technique used by the OSI physical layer to encode the clock and data of a synchronous bit stream.
N that can be inserted or removed into slots within the rack In one example, the Ethernet devices can be servers. The data link layer creates packets appropriate for the network architecture being used.
Requests and data from the network layer are part of the data in these packets or frames, as they are often called at this layer.
These packets re passed down to the physical layer and from there, the data is transmitted to the physical layer on the destination machine. Network architectures such as Ethernet, ARCnet, Token Ring, and FDDI encompass the data link and physical layers, which is why these architectures support services at the data link level. These architectures also represent the most common protocols used at the data link level. The IEEE The LLC sub-layer must provide an interface for the network layer protocols, and control the logical communication with its peer at the receiving side.
The MAC sub-layer must provide access to a particular physical encoding and transport scheme. Physical layer The physical layer is the lowest layer in the OSI reference model. This layer gets data packets from the data link layer above it, and converts the contents of these packets into a series of electrical signals that represent 0 and 1 values in a digital transmission. These signals are sent across a transmission medium to the physical layer at the receiving end.
At the destination, the physical layer converts the electrical signals into a series of bit values. These values are grouped into packets and passed up to the data link layer. The mechanical and electrical properties of the transmission medium are defined at this level. Cable may be coaxial, twisted pair, or fiber optic. The encoding scheme used to signal 0 and 1 values in a digital transmission or particular values in an analog transmission depend on the network architecture being used.
Historically, SCADA system communication protocols have been developed as proprietary protocols, each created by a manufacturer as part of a proprietary system, to meet the specific needs of a particular industry.
This was a matter of necessity, as suitable standards had not hitherto existed. However, proprietary protocols have disadvantages for the user. Arising from this underlying disadvantage and the increasing use of SCADA systems generally, the need for open standards became recognized.
This recognition has translated into efforts by a number of organizations in a number of countries. However, the emergence of standards that have wide acceptance has been a slow process. The key benefit of an open standard is that it provides for interoperability between equipment from different manufacturers.
This means for example that a user can purchase system equipment such as a master station from one manufacturer, and be able to add RTU equipment sourced from another manufacturer. The RTU in turn may have a number of control relays connected to it which are intelligent electronic devices and also use the protocol.
All of this equipment may be sourced from different manufacturers, either in an initial installation, or progressively as the system is developed over time.
Some of the different benefits arising from the use of open protocols are listed below, grouped into immediate and long-term effects. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous.
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