When ATM was developed in the early 1990s, its speed provided a key advantage over T-1 and T-3 services, which are based on time division multiplexing. It was also faster than routers available at that time. ATM's speed is due to its fixed-size cells, switching in hardware and asynchronous technology, which does not depend on timing. Rather, cells are forwarded based on priority and arrival time.
Fixed-Sized Cells - Less Processing: ATM packages data into discrete groups called cells. These cells are of a fixed size. Handling fixed-sized cells requires less processing than older routers with variable-sized packets. The ATM switch does not have to look for bits telling it when the cell is over. Each cell is 53 bytes long. Five of the 53 bytes contain header information. This includes bits that identify the type of information contained in the cell (for example, voice, data , or video) so that the cell can be prioritized. The remaining 48 bytes are the "payload" - user data such as voice, video, or sales proposals.
Switching in Hardware - Less Address Lookup: ATM cells are switched in hardware. This means that an ATM switch does not have to look up each cell's address in software. Rather, an ATM switch sets up a route through the network when it sees the first cell of a transmission. It puts this information into its hardware and sends each cell with the same header routing information down the virtual path previously established. For example, all cells with XXX in the header use route 234. Using the same path for each cell makes ATM a connection-oriented service.
Asynchronous Switching - Improving Network Utilization: With asynchronous switching, every bit of network capacity is available for every cell. This is different than synchronous multiplexing technology such as T-1/E-1 and T-3/E-3. With T-3 multiplexing, every one of the 672 input transmissions is assigned a time slot. If device A has nothing to send, its slot is sent through the network empty. ATM has no synchronous requirements. It statistically multiplexes cells onto the network path based on quality-of-service information in the header. With ATM, network capacity is not wasted forwarding empty cells.
Source: The Essential Guide to Telecommunications, 4th Edition by Annabel Z. Dodd
Tuesday, November 25, 2008
Monday, November 24, 2008
ATM (Asynchronous Transfer Mode)
ATM (Asynchronous Transfer Mode): a high-speed switching service capable of carrying voice, data, video, and multimedia images. ATM is used primarily in frame relay networks, carrier networks and enterprises for private lines. The key advantage of ATM is that it enables providers and end users to carry multiple types of traffic at assigned quality-of-service levels. ATM carries parallel streams of traffic at different levels of service quality over the same circuit. In frame relay networks, carriers deploy multiplatform switches with both frame relay and ATM ports. The switch converts the frames from enterprise sites to ATM cells and transports them through the network. It converts them back to the frame relay format before sending data to the enterprise site to which the frames were addressed.
Because of improvements in IP protocols - in particular, MPLS's (Multi-Protocol Label Switching) capability to "tag" traffic so that voice and video can be prioritized - and the lower cost and easier programming of IP, ATM is becoming displaced by IP equipment. In addition, in carrier networks, IP services achieve higher speeds. On the enterprise side, Gigabit Ethernet and individual wavelengths offer lower-cost options than ATM for end users who need to send large files between sites. However, GigE and individual wavelength services are still not universally available, and wavelength service has distance limitations. (We'll elaborate on these technologies/services in the future.)
ATM is expensive and complex for carriers to install and program. As older equipment is depreciated, carriers will transition to IP with MPLS for voice, data and video traffic.
Source: The Essential Guide to Telecommunications, 4th Edition by Annabel Z. Dodd
Because of improvements in IP protocols - in particular, MPLS's (Multi-Protocol Label Switching) capability to "tag" traffic so that voice and video can be prioritized - and the lower cost and easier programming of IP, ATM is becoming displaced by IP equipment. In addition, in carrier networks, IP services achieve higher speeds. On the enterprise side, Gigabit Ethernet and individual wavelengths offer lower-cost options than ATM for end users who need to send large files between sites. However, GigE and individual wavelength services are still not universally available, and wavelength service has distance limitations. (We'll elaborate on these technologies/services in the future.)
ATM is expensive and complex for carriers to install and program. As older equipment is depreciated, carriers will transition to IP with MPLS for voice, data and video traffic.
Source: The Essential Guide to Telecommunications, 4th Edition by Annabel Z. Dodd
Friday, November 21, 2008
DSL Access Multiplexers (DSLAMs)
DSLAMs (DSL Access Multiplexers) aggregate traffic from multiple DSL modems and combine it into higher speeds before sending it to the Internet of data networks. DSLAMs are located in carriers' COs or digital loop carriers, also referred to as remote terminals, in neighborhoods and in the wiring closets of large apartment and office buildings. DSLAMs combine DSL traffic into higher-speed streams. These are, for the most part, ATM speeds of optical carrier level 3 (OC-3), 155 million bits per second, but some DSLAMs use slower DS-3 44 Mbps connections.
Customers have dedicated capacity between their DSL modem and the DSLAM that they don't share with other customers. However, capacity between the DSLAM and the Internet or the ISP (Internet Service Provider) is shared by data from other customers. The connection between the DSLAM and an ISP is a potential site for network congestion. If not enough capacity is available, a customer might experience delays. DSLAMs have been manufactured by Adtran, Alcatel, Catena, Lucent, Paradne and Westell.
The links below are the pictures of various DSLAMs
http://www.pssi-us.com/DSLInfo.gif
http://www.tsninternet.com.au/webpages/Prices/images/dslam-image2lg.gif
http://www.nag.ru/2002/2309/img/dslam.jpg
MiniRAM-Mini Remote Access Multiplexer: A newer, lower cost, smaller DSLAM is being deployed to provide DSL over short copper telephone lines. These MiniRAMs are about the size of two pizza boxes stacked on top of each other. They can be located on telephone poles or in standalone boxes on the ground and serve 10 to 24 customers. Power is fed to MiniRAMs through copper telephone lines on the pole or underground.
Because they are closer to customers, MiniRAMs avoid most of the impairments found on copper lines further from COs. These impairments are caused by crosstalk, loading coils that boost signals, and bridge taps used to share copper lines among customers. The dilemma is that the closer the fiber and MiniRAMs are to customers, the higher the overall costs. As they get closer to customers, MiniRAMs serve fewer customers. Overall there are more fiber runs, more MiniRAMs, and more equipment to maintain and install.
Smaller MiniRAMs are connected to CO-based aggregation switches that packetize the data and send it to ISPs. Traffic from larger MiniRAMs is aggregated in DSLAMs. In the future, switches in the DSLAM will provide more of the aggregation function.
Customers have dedicated capacity between their DSL modem and the DSLAM that they don't share with other customers. However, capacity between the DSLAM and the Internet or the ISP (Internet Service Provider) is shared by data from other customers. The connection between the DSLAM and an ISP is a potential site for network congestion. If not enough capacity is available, a customer might experience delays. DSLAMs have been manufactured by Adtran, Alcatel, Catena, Lucent, Paradne and Westell.
The links below are the pictures of various DSLAMs
http://www.pssi-us.com/DSLInfo.gif
http://www.tsninternet.com.au/webpages/Prices/images/dslam-image2lg.gif
http://www.nag.ru/2002/2309/img/dslam.jpg
MiniRAM-Mini Remote Access Multiplexer: A newer, lower cost, smaller DSLAM is being deployed to provide DSL over short copper telephone lines. These MiniRAMs are about the size of two pizza boxes stacked on top of each other. They can be located on telephone poles or in standalone boxes on the ground and serve 10 to 24 customers. Power is fed to MiniRAMs through copper telephone lines on the pole or underground.
Because they are closer to customers, MiniRAMs avoid most of the impairments found on copper lines further from COs. These impairments are caused by crosstalk, loading coils that boost signals, and bridge taps used to share copper lines among customers. The dilemma is that the closer the fiber and MiniRAMs are to customers, the higher the overall costs. As they get closer to customers, MiniRAMs serve fewer customers. Overall there are more fiber runs, more MiniRAMs, and more equipment to maintain and install.
Smaller MiniRAMs are connected to CO-based aggregation switches that packetize the data and send it to ISPs. Traffic from larger MiniRAMs is aggregated in DSLAMs. In the future, switches in the DSLAM will provide more of the aggregation function.
Thursday, November 20, 2008
DSL (Expanded Definition)
Digital subscriber line (DSL) service is used primarily for high-speed Internet access. (The most commonly used types of DSL services are listed in the attached table.) Asymmetric DSL (ADSL) counts for the largest installed base. Asymmetric services have higher download speeds away from the Internet to the customer and slower uploading speeds from the consumer to the Internet. Business customer, for the most part, lease symmetric DSL with equal speeds upstream to the Internet and downstream. ADSL shares the same copper cabling already in place for voice. This made it an appealing technology for telephone companies that can, for the most part, use existing cabling to provide broadband access. However, copper cabling is not suitable for carrying video over long distances.
Now, however, newer versions of ADSL are available that support television on shorter cabling runs of 5,000 to 8,000 feet (5-8 kft). However, DSL works only on copper, not fiber. To create short copper cabling runs, telephone companies extend fiber closer to customers. They convert DSL signals to those compatible with fiber, where fiber connects to the copper cabling carrying DSL signals.
Interest in new DSL standards has been spurred by competition from cable TV, wireless, and VoIP providers. Cable TV operators are starting to steal more voice telephony along with Internet access, television, and video on demand. To compensate for lines lost each year since 2001 to competitive services, incumbent telephone companies are putting in place strategies for new infrastructure that will enable them to sell television, voice telephony, and Internet access plus enhanced services.
There is disagreement in the industry about whether DSL is an interim technology and whether fiber should be run to people's homes and businesses. Some telephone companies are planning to bring fiber to every customer location in their territory. They believe that bringing fiber to the premises (FTTP) is less expensive in the long run because it is more reliable, less costly to maintain, and supports higher speeds. However, in the short run, the labor involved in digging trenches for fiber and purchasing materials will cost billions of dollars. SBC and BellSouth (now combined AT&T) and Qwest have announced they will bring fiber closer to customers and use DSL for the last few thousand feet (Fiber to the Node-FTTN is SBC's, i.e. AT&T's, plan and Fiber to the Curb-FTTC was BellSouth's plan). They will build fiber to premises at new housing developments. Verizon has taken a different tack. They have announced a nationwide initiative to lay fiber to all of their residential and business customers' premises instead of using new ADSL technology to reach customers.
Although DSL modems often use the same copper cabling that carries voice, data carried on DSL service is handled separately from voice in carriers' networks. When DSL traffic hits the central office, it is routed on data networks that are separate from the PSTN. Equipment at the CO packetizes DSL traffic and sends it to Internet service providers (ISPs) or other data networks.
Now, however, newer versions of ADSL are available that support television on shorter cabling runs of 5,000 to 8,000 feet (5-8 kft). However, DSL works only on copper, not fiber. To create short copper cabling runs, telephone companies extend fiber closer to customers. They convert DSL signals to those compatible with fiber, where fiber connects to the copper cabling carrying DSL signals.
Interest in new DSL standards has been spurred by competition from cable TV, wireless, and VoIP providers. Cable TV operators are starting to steal more voice telephony along with Internet access, television, and video on demand. To compensate for lines lost each year since 2001 to competitive services, incumbent telephone companies are putting in place strategies for new infrastructure that will enable them to sell television, voice telephony, and Internet access plus enhanced services.
There is disagreement in the industry about whether DSL is an interim technology and whether fiber should be run to people's homes and businesses. Some telephone companies are planning to bring fiber to every customer location in their territory. They believe that bringing fiber to the premises (FTTP) is less expensive in the long run because it is more reliable, less costly to maintain, and supports higher speeds. However, in the short run, the labor involved in digging trenches for fiber and purchasing materials will cost billions of dollars. SBC and BellSouth (now combined AT&T) and Qwest have announced they will bring fiber closer to customers and use DSL for the last few thousand feet (Fiber to the Node-FTTN is SBC's, i.e. AT&T's, plan and Fiber to the Curb-FTTC was BellSouth's plan). They will build fiber to premises at new housing developments. Verizon has taken a different tack. They have announced a nationwide initiative to lay fiber to all of their residential and business customers' premises instead of using new ADSL technology to reach customers.
Although DSL modems often use the same copper cabling that carries voice, data carried on DSL service is handled separately from voice in carriers' networks. When DSL traffic hits the central office, it is routed on data networks that are separate from the PSTN. Equipment at the CO packetizes DSL traffic and sends it to Internet service providers (ISPs) or other data networks.
Wednesday, November 19, 2008
SDSL (Symmetric DSL) and variants
Symmetric: Same Speed Both Ways
HDSL (High Bit Rate DSL)
The most mature DSL, HDSL provides T1 transmission over existing twisted pair without the additional provisioning typically required for setting up T1 circuits, such as bridged tap removal and repeater installation. HDSL requires two cable pairs up to 12,000 feet, while HDSL-2 requires only one cable pair and spans 18,000 feet. HDSL does not allow line sharing with analog phones.
SDSL (Symmetric DSL)
SDSL is an HDSL variation that is rate adaptive, uses one cable pair and is offered in speeds from 144 Kbps to 1.5 Mbps. Like HDSL, SDSL does not share lines with analog phones.
IDSL (ISDN DSL)
IDSL is a slightly faster basic BRI ISDN service. It uses the 16 Kbps "D" channel for data rather than call setup to achieve 144 Kbps instead of 128 Kbps. It also offers the longest distance of 26,000 feet. Unlike standard ISDN, IDSL does not support analog phones, and signals are not switched through the telephone network. Since IDSL uses the same 2B1Q line coding as ISDN, ISDN customers can use existing BRI terminal adapters and routers.
HDSL (High Bit Rate DSL)
The most mature DSL, HDSL provides T1 transmission over existing twisted pair without the additional provisioning typically required for setting up T1 circuits, such as bridged tap removal and repeater installation. HDSL requires two cable pairs up to 12,000 feet, while HDSL-2 requires only one cable pair and spans 18,000 feet. HDSL does not allow line sharing with analog phones.
SDSL (Symmetric DSL)
SDSL is an HDSL variation that is rate adaptive, uses one cable pair and is offered in speeds from 144 Kbps to 1.5 Mbps. Like HDSL, SDSL does not share lines with analog phones.
IDSL (ISDN DSL)
IDSL is a slightly faster basic BRI ISDN service. It uses the 16 Kbps "D" channel for data rather than call setup to achieve 144 Kbps instead of 128 Kbps. It also offers the longest distance of 26,000 feet. Unlike standard ISDN, IDSL does not support analog phones, and signals are not switched through the telephone network. Since IDSL uses the same 2B1Q line coding as ISDN, ISDN customers can use existing BRI terminal adapters and routers.
Tuesday, November 18, 2008
ADSL (Asymmetric DSL) and variants
ADSL shares ordinary telephone lines by using frequencies above the voice band, but the higher frequencies interfere with regular telephone usage. The first versions required a visit from the phone company to install a POTS (Plain Old Telephone Service) splitter that divides the line into separate lines for DSL and telephone. Subsequent splitterless versions (also known as G.Lite, Universal ADSL and ADSL Lite) eliminate the phone company visit, but require that the user plug DSL low-pass filters into every telephone outlet that serves ordinary telephones, answering machines and faxes. ADSL is available in two modulation schemes: Discrete Multitone (DMT) or Carrierless Amplitude Phase (CAP).
ADSL Transmission: The higher frequencies of DSL have to be filtered out for regular telephones, answering and fax machines. Low-pass DSL filters split the line between phone and DSL modem and must be used wherever a telephone is plugged into the wall.
RADSL (Rate Adaptive DSL): RADSL is a version of ADSL that adjusts speeds based on signal quality. Many ADSL technologies are actually RADSL.
VDSL/VHDSL (Very High Bit Rate DSL): VDSL is used as the final drop from a fiber optic junction point to nearby customers. VDSL lets an apartment or office complex obtain high-bandwidth services using existing copper wires without having to replace the infrastructure with optical fiber. Like ADSL, VDSL can share the line with the telephone.
ADSL Transmission: The higher frequencies of DSL have to be filtered out for regular telephones, answering and fax machines. Low-pass DSL filters split the line between phone and DSL modem and must be used wherever a telephone is plugged into the wall.
RADSL (Rate Adaptive DSL): RADSL is a version of ADSL that adjusts speeds based on signal quality. Many ADSL technologies are actually RADSL.
VDSL/VHDSL (Very High Bit Rate DSL): VDSL is used as the final drop from a fiber optic junction point to nearby customers. VDSL lets an apartment or office complex obtain high-bandwidth services using existing copper wires without having to replace the infrastructure with optical fiber. Like ADSL, VDSL can share the line with the telephone.
Monday, November 17, 2008
DSL (Digital Subscriber Line)
A technology that dramatically increases the digital capacity of ordinary telephone lines (the local loops) into the home or office. DSL speeds are based on the distance between the customer and telco central office. There are two main categories. Asymmetric DSL (ADSL) is for Internet access, where fast downstream is required, but slow upstream is acceptable. Symmetric DSL (SDSL, HDSL, etc.) is designed for connections that require high speed in both directions.
Typically, the download speed of consumer DSL services ranges from 256 kilobits per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, line conditions and service level implemented. For the most part, upload speed is lower than download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to download speed for the rarer Symmetric Digital Subscriber Line (SDSL).
DSL provides "always-on" operation. At the telco central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network. DSL arrived in the late 1990s with more versions and "alphabet soup" than most any other new transmission technology. We will explore the "flavors" of DSL this week.
Typically, the download speed of consumer DSL services ranges from 256 kilobits per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, line conditions and service level implemented. For the most part, upload speed is lower than download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to download speed for the rarer Symmetric Digital Subscriber Line (SDSL).
DSL provides "always-on" operation. At the telco central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network. DSL arrived in the late 1990s with more versions and "alphabet soup" than most any other new transmission technology. We will explore the "flavors" of DSL this week.
Friday, November 14, 2008
Amplifier
When telephone conversations travel through a medium, such as a copper wire, they encounter resistance and thus become weaker and more difficult to hear. An amplifier is an electrical device which strengthens the signal. Unfortunately, amplifiers in analog circuits also strengthen noise and other extraneous garbage on the line. Cascading amplifiers, therefore, compound, or accumulate, noise. Digital systems make use of regenerative repeaters, which regenerate (i.e. reshape or reconstruct) the signal before amplifying it and sending it on its way. As a result, noise is much less prevalent and less likely to be amplified in digital systems, whether one or many repeaters are in place. The ultimate yield of a repeater in a digital environment is that of improved error performance, which also yields improved throughput, assuming that error correction involves retransmission.
Thursday, November 13, 2008
Repeater Coil (and Repeater)
Repeater Coil: Also called a Repeat Coil. It's really just a transformer, which converts AC power to the voltages used to charge batteries and to power various devices such as PBXs. Repeater coils also are used for impedance matching, which serves to maximize the power transfer of a signal where two electrical circuits (e.g, twisted pair) are interconnected. The power transfer is improved through the elimination of echo, which is signal reflection back towards the signal source.
Different than a Repeater…
Repeater: Also known as a Regenerative Repeater and a Regenerator. A device inserted at intervals along a digital circuit to regenerate the transmitted signal. As the digital signal transverses the circuit, it loses its shape due to the combined effects of attenuation and noise. Attenuation is weakening of the signal as it transverses the circuit. Noise, or distortion, can be caused by EMI (ElectroMagnetic Interference), RFI (Radio Frequency Interference) frequency shifts internal to the circuit, and various other factors. At some point, the original signal becomes incoherent unless a repeater is placed on the circuit at specific intervals, which are sensitive to the specifics of the circuit design. The repeater is capable of reading the signal, even though it is somewhat attenuated and distorted, reshaping it into proper "ones" and "zeros," and repeating (i.e., retransmitting) it at the proper level of signal strength. Repeaters are used exclusively in digital circuits, whether they are metallic (e.g., twisted pair and coaxial), radio (e.g., cellular, microwave, and satellite), or optical (e.g., optical fiber). Analog circuits make use of amplifiers, which simply serve to boost the signal strength, and which cannot reshape it.
Different than a Repeater…
Repeater: Also known as a Regenerative Repeater and a Regenerator. A device inserted at intervals along a digital circuit to regenerate the transmitted signal. As the digital signal transverses the circuit, it loses its shape due to the combined effects of attenuation and noise. Attenuation is weakening of the signal as it transverses the circuit. Noise, or distortion, can be caused by EMI (ElectroMagnetic Interference), RFI (Radio Frequency Interference) frequency shifts internal to the circuit, and various other factors. At some point, the original signal becomes incoherent unless a repeater is placed on the circuit at specific intervals, which are sensitive to the specifics of the circuit design. The repeater is capable of reading the signal, even though it is somewhat attenuated and distorted, reshaping it into proper "ones" and "zeros," and repeating (i.e., retransmitting) it at the proper level of signal strength. Repeaters are used exclusively in digital circuits, whether they are metallic (e.g., twisted pair and coaxial), radio (e.g., cellular, microwave, and satellite), or optical (e.g., optical fiber). Analog circuits make use of amplifiers, which simply serve to boost the signal strength, and which cannot reshape it.
Wednesday, November 12, 2008
Loop Extender
Device in the CO (Central Office) that supplies augmented voltage out to subscribers who are at considerable distances. It provides satisfactory signaling and speech for such subscribers. More specifically, an ADSL (Asymmetric Digital Subscriber Line) loop extender increases the channel capacity of a DSL connection from the CO to the subscriber. ADSL repeaters are aggressively deployed by rural telephone companies trying to reach farms and small towns in areas where it is impractical to place the DSLAM (DSL Access Multiplexers) closer. The typical distance improvement with a loop extender is shown in the diagram below, with rate in Megabits per second and distance in thousands of feet. In future WotD's we will explore in more detail DSL (and ADSL) along with the market for these services.
For graph visit: http://www.strowger.com/images/moz-screenshot-8.jpg
[Note: ADSL2 and ipTV in this sense, refer to types/levels of service offered to DSL subscribers]
For graph visit: http://www.strowger.com/images/moz-screenshot-8.jpg
[Note: ADSL2 and ipTV in this sense, refer to types/levels of service offered to DSL subscribers]
Tuesday, November 11, 2008
Load Coil
Load coils are also known as impedance matching transformers. Load coils are used by the telephone companies on long analog POTS (Plain Old Telephone Service) lines to filter out frequencies above 4 kHz, using the energy of the higher frequency elements of the signal to improve the quality of the lower frequencies in the 4 kHz voice range. Load coils are great for analog voice grade local loops, but must be removed for digital circuits to function. Load coils must be removed for DSL loops, as the frequencies required are well above 4 kHz. Today many phone companies offer broadband service, but often tell their customers that they can't get the service because "you live too far from the telephone company's office." Tell the company to remove the loading coils and any bridging taps on your local loop and it will work. Or offer to pay for commercial ADSL service. (We'll explore the flavors of DSL in future WotDs.)
Monday, November 10, 2008
Jumper (and Jumper Cable)
Jumper:
1. A wire used to connect equipment and cable on a distributing frame.
2. Single twisted pairs used for cross connecting between 66, 110 or Krone blocks.
3. A patch cable or wire used to establish a circuit, often temporarily, for testing or diagnostics.
4. Jumpers are pairs or sets of small prongs on adapters and motherboards. Jumpers allow the user to instruct the computer to select one of its available operation options. When two pins are covered with a plug, an electrical circuit is completed. When the jumper is uncovered the connection is not made. The computer interprets these electrical connections as configuration information. When errors are found on printed circuit boards, a jumper cable is sometimes soldered in to correct the problem.
Jumper Cable: A short length of conductor or cable used to make a connection between terminals or around a break in a circuit, or around an instrument.
1. A wire used to connect equipment and cable on a distributing frame.
2. Single twisted pairs used for cross connecting between 66, 110 or Krone blocks.
3. A patch cable or wire used to establish a circuit, often temporarily, for testing or diagnostics.
4. Jumpers are pairs or sets of small prongs on adapters and motherboards. Jumpers allow the user to instruct the computer to select one of its available operation options. When two pins are covered with a plug, an electrical circuit is completed. When the jumper is uncovered the connection is not made. The computer interprets these electrical connections as configuration information. When errors are found on printed circuit boards, a jumper cable is sometimes soldered in to correct the problem.
Jumper Cable: A short length of conductor or cable used to make a connection between terminals or around a break in a circuit, or around an instrument.
Friday, November 7, 2008
Patch Cord (and Panel)
Patch Cord: A short length of wire or fiber cable with connectors on each end, a patch cord is used to join communication circuits at a cross connect point. A patch cord is much like an extension cord. In the context of telephony, it's much like the cords that the telephone operators in the early 1900s used to use on a manual switchboard. They would use a short cord with a plug on each end to connect to one jack for the calling party and another for the called party. Thereby, a unique physical and electrical path was established. When the call was concluded, the operator unplugged the cord from the jacks. The next call involved a repeat of the same process, and so on. Patch cords still have a very important purpose where semi-permanent and highly reliable connections must by made between links.
Patch Panel: A device in which temporary connections can be made between incoming lines and outgoing lines. It is used for modifying or reconfiguring a communications system or for connecting devices such as test instruments to specific lines. A patch panel differs from a distribution frame in that the connections on a distribution frame are intended to be permanent.
Source: http://www.americantechsupply.com/images/CAT%206%2048%20port%20patch%20panel.jpg
Patch Panel: A device in which temporary connections can be made between incoming lines and outgoing lines. It is used for modifying or reconfiguring a communications system or for connecting devices such as test instruments to specific lines. A patch panel differs from a distribution frame in that the connections on a distribution frame are intended to be permanent.
Source: http://www.americantechsupply.com/images/CAT%206%2048%20port%20patch%20panel.jpg
Thursday, November 6, 2008
Cross Connect
Cross Connect: Imagine you have an office that you need to wire up for voice and data. So you wire every desk with a bunch or wires. You punch one end of the wires into various plugs at the desk. You punch the other onto some form of punchdown block, for example a 66-block. That punchdown block may be in a closet on the same floor or it may be down in the basement. Then you bring the wires in from your telecom suppliers. The T-1s, the ATM, the FR, the local lines, the analog lines, the digital lines, etc. You punch them down on another punchdown block. Now you have two sets of blocks - one for those going to the office and those coming in from the outside world. You now have to join them in a process known as "cross-connecting" in the telecom world. You simply run wires from one punchdown device to the other. The reason you use cross-connect wires rather than just punching down an incoming phone line, for example, directly to your phone system is that moves, adds and changes would, over time, horribly confuse things, screw connections up, and eventually become a total mess. It's easier to simply have all the changes accomplished through the cross-connect wires and wiring. Follow the short wires. It's easy to see what's connected to what and provides for labeling, documentation, etc. In short, cross-connect is a connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers that attach to connecting hardware on each end. Cross-connection is the attachment of one wire to another usually by anchoring each wire to a connecting block and then placing a third wire between them so that an electrical connection is made. The TIA/EIA-568-A standard specifies that cross-connect cables (also called patch cords) are to be made out of stranded cable.
Cross Connect Equipment: Distribution system equipment used to terminate and administer communication circuits. In a wire cross connect, jumper wires or patch cords are used to make circuit connections. In an optical cross connect, fiber path cords are used. The cross connect is located in an equipment room, riser closet or satellite closet.
Cross Connect Field: Wire terminations grouped to provide cross connect capability the groups are identified by color-coded sections of blackboards mounted on the wall in equipment rooms, riser closets, or satellite closets, or by designation strips placed on the wiring block or unit. The color coding identifies the type of circuit that terminates at the field.
Cross Connect Equipment: Distribution system equipment used to terminate and administer communication circuits. In a wire cross connect, jumper wires or patch cords are used to make circuit connections. In an optical cross connect, fiber path cords are used. The cross connect is located in an equipment room, riser closet or satellite closet.
Cross Connect Field: Wire terminations grouped to provide cross connect capability the groups are identified by color-coded sections of blackboards mounted on the wall in equipment rooms, riser closets, or satellite closets, or by designation strips placed on the wiring block or unit. The color coding identifies the type of circuit that terminates at the field.
Wednesday, November 5, 2008
Inside Wiring
Inside Wiring: That telephone wiring located inside your premises or building. Inside Wiring starts at the telephone company's Demarcation Point and extends to the individual phone extensions. Traditionally, Inside Wiring was installed and owned by the telephone company but now you can install your own wiring. And most companies installing new phone systems are installing their own new wiring because of potential problems with reusing the old telephone company cable.
Inside Wire or Line Backer: names of products sold by LECs (Local Exchange Carriers) to their customers as "insurance" on their inside wire. Customers pay upwards of $5 per month in order not to have to pay the phone company a pile of cash if something goes wrong with their inside wiring.
Inside Wire or Line Backer: names of products sold by LECs (Local Exchange Carriers) to their customers as "insurance" on their inside wire. Customers pay upwards of $5 per month in order not to have to pay the phone company a pile of cash if something goes wrong with their inside wiring.
Tuesday, November 4, 2008
66 Block
The most common type of connecting block used to terminate and cross-connect twisted-pair cables. It was invented by Western Electric eons ago and has stood the test of time. It is still being installed. Its main claims to fame: Simplicity, speed, economy and space. You don't need to strip your cable of its plastic insulation covering. You simply lay each single conductor down inside the 66 block's two metal teeth and punch the conductor down with a special tool, called a punch-down tool. As you punch it down, the cable descends between the two metal teeth, which remove its plastic insulation (it's called insulation displacement) and the cable is cut. The installation is then neat and secure. 66 blocks are typically rated Category 3 and as such as used mostly for voice applications, although Category 5 66 blocks are available. 66 blocks are open plastic troughs with four pins across, and the conductors are more susceptible to being snagged or pulled than conductors terminated on other types of blocks (e.g., 110, Krone or BIX).
A note on the Bell Labs numbering system… They just started with "number 1" on whatever system they were working on. TD1 radio, TD2 radio, etc., Whenever there was a "hole" in the sequence, that meant that the labs had worked on something, but it didn't pan out for some reason.
A note on the Bell Labs numbering system… They just started with "number 1" on whatever system they were working on. TD1 radio, TD2 radio, etc., Whenever there was a "hole" in the sequence, that meant that the labs had worked on something, but it didn't pan out for some reason.
Monday, November 3, 2008
Drop (and variants of Drop)
Drop:
1. A wire or cable from a pole or cable terminal to a building.
2. That portion of a device that looks toward the internal station facilities, e.g., toward an AUTOVON 4-wire switch, toward a switchboard, or toward a switching center.
3. Single channel attachment to the horizontal wiring grid (wall plate, coupling, MOD-MOD adapter).
4. The CO (central office) side of test jacks.
5. To delete, intentionally or unintentionally, part of a signal for some reason, e.g., dropping bits.
Drop Cable:
1. The outside wire pair which connects your house or office to the transmission line coming from the phone company's CO.
2. In local area networks, a cable that connects a network device such as a computer to a physical medium such as an Ethernet network. Drop cable is also called transceiver cable because it runs from a network node to a transceiver (a transmit/receiver) attached to the trunk cable.
Drop Loop: The segment of wire from the nearest telephone pole to your home or business.
Drop Wire: Wires going from your phone company to the 66 Block (type of punchdown block used to connect sets of wires in a telephone system) or protector in your building.
1. A wire or cable from a pole or cable terminal to a building.
2. That portion of a device that looks toward the internal station facilities, e.g., toward an AUTOVON 4-wire switch, toward a switchboard, or toward a switching center.
3. Single channel attachment to the horizontal wiring grid (wall plate, coupling, MOD-MOD adapter).
4. The CO (central office) side of test jacks.
5. To delete, intentionally or unintentionally, part of a signal for some reason, e.g., dropping bits.
Drop Cable:
1. The outside wire pair which connects your house or office to the transmission line coming from the phone company's CO.
2. In local area networks, a cable that connects a network device such as a computer to a physical medium such as an Ethernet network. Drop cable is also called transceiver cable because it runs from a network node to a transceiver (a transmit/receiver) attached to the trunk cable.
Drop Loop: The segment of wire from the nearest telephone pole to your home or business.
Drop Wire: Wires going from your phone company to the 66 Block (type of punchdown block used to connect sets of wires in a telephone system) or protector in your building.
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