Carrier Ethernet is a marketing term for extensions to Ethernet for communications service providers that utilize Ethernet technology in their networks.
92-491: Ethernet has a long history. It has become dominant in enterprise networks. This dominance has led to high production-volume components, which in turn have allowed extremely low cost per bit. Likewise, Ethernet has a long history of re-inventing itself. From the original copper coaxial cable format (" thicknet ") it has extended its scope to nearly all copper, optical fiber and wireless physical media . Bit rates have continued to increase, traditionally growing tenfold each time
184-486: A carrier network. Despite the advantages described above, Ethernet has traditionally had a number of limitations in the WAN application. The "bridge" and "spanning tree" concepts described above do not scale to large international networks. Moreover, Ethernet has lacked some of the dependability features necessary in this application (in particular, mechanisms to isolate one customer's traffic from another, to measure performance of
276-791: A characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the lowest insertion loss impedance drops down to a value between 52 and 64 Ω. Maximum power handling is achieved at 30 Ω. The approximate impedance required to match a centre-fed dipole antenna in free space (i.e., a dipole without ground reflections) is 73 Ω, so 75 Ω coax was commonly used for connecting shortwave antennas to receivers. These typically involve such low levels of RF power that power-handling and high-voltage breakdown characteristics are unimportant when compared to attenuation. Likewise with CATV , although many broadcast TV installations and CATV headends use 300 Ω folded dipole antennas to receive off-the-air signals, 75 Ω coax makes
368-423: A common ground at the house. See ground loop . External fields create a voltage across the inductance of the outside of the outer conductor between sender and receiver. The effect is less when there are several parallel cables, as this reduces the inductance and, therefore, the voltage. Because the outer conductor carries the reference potential for the signal on the inner conductor, the receiving circuit measures
460-869: A concerted effort to resolve the limitations of Ethernet in the WAN described above, so as to allow the use of "native" Ethernet technologies by network providers. The key roles have been played by the Institute of Electrical and Electronics Engineers (IEEE) 802.1 and 802.3 standards committees. IEEE 802.1 has addressed the scalability and management issues in the standards for Provider Bridges (802.1ad) and Provider Backbone Bridges (802.1ah). These standards allow for Ethernet networks of planetary scale. Associated standards ( IEEE 802.1ag , and related ITU-T standard Y.1731) provide Operations and Maintenance (OAM) capabilities allowing connectivity verification, rapid recovery, and performance measurement. Current work on PBB-TE (802.1Qay: Provider Backbone Bridging-Traffic Engineering)
552-416: A convenient 4:1 balun transformer for these as well as possessing low attenuation. The arithmetic mean between 30 Ω and 77 Ω is 53.5 Ω; the geometric mean is 48 Ω. The selection of 50 Ω as a compromise between power-handling capability and attenuation is in general cited as the reason for the number. 50 Ω also works out tolerably well because it corresponds approximately to
644-673: A customer service instance, and to rapidly detect and repair failures in large networks). Because of these limitations, and because of the need to make use of pre-existing equipment, Ethernet services have been carried across wide area networks using other technologies. Two types of technology have been widely used, while a third (Carrier-Ethernet transport) is rapidly emerging as a viable and logical option for Carrier-Ethernet services. Point-to-point Ethernet links are carried over SDH/SONET networks, making use of virtual concatenation (ITU-T G.707) and LCAS (Link Capacity Adjustment Scheme - ITU-T G.7042) to create an appropriate size carrier bundle, of
736-521: A framework for firms to do so in Sections 251 and 252. Section 252(c)(1) for example ("Duty to Negotiate") requires Incumbent local exchange carriers (ILECs) to negotiate in good faith about matters such as resale and access to rights of way. New emerging technologies such as 5G bring new complexities to the network operators. With more stringent SLAs and customer expectations, problem resolutions must be prioritized based on impacted subscribers. With
828-409: A function of frequency, voltage handling capability, and shield quality. Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost. The inner conductor might be solid or stranded; stranded is more flexible. To get better high-frequency performance, the inner conductor may be silver-plated. Copper-plated steel wire
920-493: A good choice both for carrying weak signals that cannot tolerate interference from the environment, and for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits. Larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections. The characteristic impedance of
1012-482: A high degree of transparency, EPL is often used to provide point-to-point transparent LAN service (TLS), where the service frame's header and payload are identical at both the source and destination UNI. Some implementations tunnel most Ethernet Layer 2 control protocols (L2CPs) except for some link-layer L2CPs such as IEEE 802.3x pause frames . Unlike EPL, EVPL allows for service multiplexing, i.e., multiple EVCs or Ethernet services per UNI. The other difference between
SECTION 10
#17327981826461104-814: A market in Ethernet services, it is necessary to clarify and standardise the services to be provided. Recognising this, the industry created the MEF. This played a key role in defining: All these services provide standard definitions of such characteristics as bandwidth, resilience and service multiplexing, allowing customers to compare service offerings and facilitating service level agreements (SLAs). Analogous definitions for wireless networks are defined in IEEE 802.21 and IEEE 802.11u , though these are intended for much shorter time commitments and services appropriate for mobile users only. Ethernet Virtual Private Tree or E-Tree
1196-488: A much larger enterprise segment commands. Carrier-Ethernet Transport (CET) usually involves an evolution of conventional Ethernet and comprises multiple technology components. Provider Backbone Bridges (PBB) provides the scalability and a secure demarcation, while Provider Backbone Bridge Traffic Engineering (PBB-TE, commonly called PBT) provides for traffic-engineering and an effective transport for protected Ethernet services. Connectivity-Fault Management (CFM-OAM) provides
1288-523: A new rate is defined. Gigabit Ethernet interfaces are widely deployed in PCs and servers, and 10 Gbit/s in local area network (LAN) backbones. Rates up to 100 Gigabit Ethernet were standardized in 2010 and 2011. Ethernet's dominance is partly attributed to the simple advantages for the industry of adopting a single standard to drive up volumes and drive down prices. In part, it is also due to ease of deployment, using its ability to self-configure based on
1380-444: A non-circular conductor to avoid current hot-spots. While many cables have a solid dielectric, many others have a foam dielectric that contains as much air or other gas as possible to reduce the losses by allowing the use of a larger diameter center conductor. Foam coax will have about 15% less attenuation but some types of foam dielectric can absorb moisture—especially at its many surfaces—in humid environments, significantly increasing
1472-480: A number of basic transport protocols, including SDH and (increasingly) Ethernet. Proponents of Carrier-Class Ethernet argue Ethernet is the best for Metro Area Networks because all data traffic originates as Ethernet. Ethernet's ubiquitous presence in the LANs worldwide drives down the cost of Ethernet as a technology. Thus, the use of Ethernet in a metro network allows service providers to take advantage of volumes that
1564-406: A periodic (annual) revisitation to make changes. Since the late 1980s SLAs have been used by fixed-line telecom operators. SLAs are so widely used these days that larger organizations have many different SLAs existing within the company itself. Two different units in an organization script an SLA with one unit being the customer and another being the service provider. This practice helps to maintain
1656-484: A point-to-point or point-to-multipoint connection between a pair of UNIs. The services are categorized as an E-line service type, with an expectation of low frame delay , frame delay variation and frame loss ratio . EPL is implemented using a point-to-point EVC with no service multiplexing at each UNI (physical interface), i.e., all service frames at the UNI are mapped to a single EVC (a.k.a. all-to-one bundling). Due to
1748-416: A result, must-have Carrier Ethernet demarcation features include sophisticated traffic management and hierarchical quality of service (QoS) mechanisms, standard end-to-end operations, administration and maintenance (OAM) and performance monitoring, extensive fault management and diagnostics, and SDH/SONET-like resiliency to reduce service provider operating costs and capital expenses. The industry has made
1840-485: A solid copper, stranded copper or copper-plated steel wire) surrounded by an insulating layer and all enclosed by a shield, typically one to four layers of woven metallic braid and metallic tape. The cable is protected by an outer insulating jacket. Normally, the outside of the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor. When using differential signaling , coaxial cable provides an advantage of equal push-pull currents on
1932-423: A solid metal tube. Those cables cannot be bent sharply, as the shield will kink, causing losses in the cable. When a foil shield is used a small wire conductor incorporated into the foil makes soldering the shield termination easier. For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward. The outer conductor
SECTION 20
#17327981826462024-673: A transmission line. Coaxial cable was used in the first (1858) and following transatlantic cable installations, but its theory was not described until 1880 by English physicist, engineer, and mathematician Oliver Heaviside , who patented the design in that year (British patent No. 1,407). Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers to their antennas, computer network (e.g., Ethernet ) connections, digital audio ( S/PDIF ), and distribution of cable television signals. One advantage of coaxial over other types of radio transmission line
2116-550: A type of waveguide . Power is transmitted through the radial electric field and the circumferential magnetic field in the TEM mode. This is the dominant mode from zero frequency (DC) to an upper limit determined by the electrical dimensions of the cable. Coaxial connectors are designed to maintain a coaxial form across the connection and have the same impedance as the attached cable. Connectors are usually plated with high-conductivity metals such as silver or tarnish-resistant gold. Due to
2208-616: A weaker signal at the end of the cable and radio frequency interference to nearby devices. Severe leakage usually results from improperly installed connectors or faults in the cable shield. For example, in the United States, signal leakage from cable television systems is regulated by the FCC, since cable signals use the same frequencies as aeronautical and radionavigation bands. CATV operators may also choose to monitor their networks for leakage to prevent ingress. Outside signals entering
2300-438: Is a point-to-multipoint Ethernet Virtual Connection defined by the MEF — an Ethernet VLAN configuration suitable for multicast services. Ethernet private line ( EPL ) and Ethernet virtual private line ( EVPL ) are data services defined by the MEF. EPL provides a point-to-point Ethernet virtual connection (EVC) between a pair of dedicated user–network interfaces (UNIs), with a high degree of transparency. EVPL provides
2392-522: Is a good approximation at radio frequencies however for frequencies below 100 kHz (such as audio ) it becomes important to use the complete telegrapher's equation : Applying this formula to typical 75 ohm coax we find the measured impedance across the audio spectrum will range from ~150 ohms to ~5K ohms, much higher than nominal. The velocity of propagation also slows considerably. Thus we can expect coax cable impedances to be consistent at RF frequencies but variable across audio frequencies. This effect
2484-466: Is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield , with the two separated by a dielectric ( insulating material); many coaxial cables also have a protective outer sheath or jacket. The term coaxial refers to the inner conductor and the outer shield sharing a geometric axis. Coaxial cable is a type of transmission line , used to carry high-frequency electrical signals with low losses. It
2576-451: Is allowing such an Ethernet to be controlled by an external control or management application (for example, a network management application or a transport control plane such as GMPLS (IETF RFC 3945)), so as to allow the full range of traffic engineering policies and strategies to a network provider. The IEEE 802.3 Working Group in close cooperation with the ITU have been working to simplify
2668-631: Is also a common metric, often used for data services such as shared hosting , virtual private servers and dedicated servers . Common agreements include percentage of network uptime, power uptime, number of scheduled maintenance windows , etc. Many SLAs track to the ITIL specifications when applied to IT services. It is not uncommon for an internet backbone service provider (or network service provider ) to explicitly state its SLA on its website. The U.S. Telecommunications Act of 1996 does not expressly mandate that companies have SLAs, but it does provide
2760-423: Is also used as an insulator, and exclusively in plenum-rated cables. Some coaxial lines use air (or some other gas) and have spacers to keep the inner conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield. This allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because
2852-568: Is corrugated like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric. One brand name for such cable is Heliax . Coaxial cables require an internal structure of an insulating (dielectric) material to maintain the spacing between the center conductor and shield. The dielectric losses increase in this order: Ideal dielectric (no loss), vacuum, air, polytetrafluoroethylene (PTFE), polyethylene foam, and solid polyethylene. An inhomogeneous dielectric needs to be compensated by
Carrier Ethernet - Misplaced Pages Continue
2944-418: Is often used as an inner conductor for cable used in the cable TV industry. The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of the dielectric insulator determine some of the electrical properties of the cable. A common choice is a solid polyethylene (PE) insulator, used in lower-loss cables. Solid Teflon (PTFE)
3036-553: Is referenced in IEC 61917. A continuous current, even if small, along the imperfect shield of a coaxial cable can cause visible or audible interference. In CATV systems distributing analog signals the potential difference between the coaxial network and the electrical grounding system of a house can cause a visible "hum bar" in the picture. This appears as a wide horizontal distortion bar in the picture that scrolls slowly upward. Such differences in potential can be reduced by proper bonding to
3128-448: Is researching aspects of multi-level, multi-provider SLAs within service-oriented infrastructure and cloud computing, while another EU-funded project, VISION Cloud, has provided results concerning content-oriented SLAs. FP7 IRMOS also investigated aspects of translating application-level SLA terms to resource-based attributes to bridge the gap between client-side expectations and cloud-provider resource-management mechanisms. A summary of
3220-506: Is responsible for reporting faults or paying fees; responsibility for various data rates; throughput ; jitter ; or similar measurable details. A service-level agreement is an agreement between two or more parties, where one is the customer and the others are service providers. This can be a legally binding formal or an informal "contract" (for example, internal department relationships). The agreement may involve separate organizations or different teams within one organization. Contracts between
3312-400: Is roughly inversely proportional to the cutoff frequency . A propagating surface-wave mode that only involves the central conductor also exists, but is effectively suppressed in coaxial cable of conventional geometry and common impedance. Electric field lines for this TM mode have a longitudinal component and require line lengths of a half-wavelength or longer. Coaxial cable may be viewed as
3404-439: Is still a seam running the length of the cable. Foil becomes increasingly rigid with increasing thickness, so a thin foil layer is often surrounded by a layer of braided metal, which offers greater flexibility for a given cross-section. Signal leakage can be severe if there is poor contact at the interface to connectors at either end of the cable or if there is a break in the shield. To greatly reduce signal leakage into or out of
3496-449: Is supported by a spiral strand of polyethylene, so that an air space exists between most of the conductor and the inside of the jacket. The lower dielectric constant of air allows for a greater inner diameter at the same impedance and a greater outer diameter at the same cutoff frequency, lowering ohmic losses . Inner conductors are sometimes silver-plated to smooth the surface and reduce losses due to skin effect . A rough surface extends
3588-484: Is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors . This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference . Coaxial cable conducts electrical signals using an inner conductor (usually
3680-553: Is that the services should be provided to the customer as agreed upon in the contract. As an example, Internet service providers and telcos will commonly include service level agreements within the terms of their contracts with customers to define the level(s) of service being sold in plain language terms. In this case, the SLA will typically have a technical definition of mean time between failures (MTBF), mean time to repair or mean time to recovery (MTTR); identifying which party
3772-418: Is used for straight-line feeds to commercial radio broadcast towers. More economical cables must make compromises between shield efficacy, flexibility, and cost, such as the corrugated surface of flexible hardline, flexible braid, or foil shields. Since shields cannot be perfect conductors, current flowing on the inside of the shield produces an electromagnetic field on the outer surface of the shield. Consider
Carrier Ethernet - Misplaced Pages Continue
3864-435: Is used in such applications as telephone trunk lines , broadband internet networking cables, high-speed computer data busses , cable television signals, and connecting radio transmitters and receivers to their antennas . It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as
3956-775: The Generic Framing Procedure of SDH equipment, and takes advantage of the management and recovery features of SDH to provide high availability and resilience to failures. Ethernet services are carried over IP / MPLS networks making use of a wide range of IP-related protocols (see IETF pseudowire standards, e.g. RFC 3985, RFC 4448). Ethernet links are transported as "pseudowires" using MPLS label-switched paths (LSPs) inside an outer MPLS "tunnel". This strategy can support both point-to-point (Virtual Private Wire Service - VPWS) and multipoint (Virtual Private LAN service - VPLS) services, and has recently achieved significant deployment in routed networks. It makes use of
4048-461: The cloud , they need to achieve the same even more demanding levels of service than classical installations. SLAs for cloud services focus on characteristics of the data center and more recently include characteristics of the network (see carrier cloud ) to support end-to-end SLAs. Any SLA management strategy considers two well-differentiated phases: negotiating the contract and monitoring its fulfillment in real-time. Thus, SLA management encompasses
4140-536: The skin effect , the RF signal is only carried by the plating at higher frequencies and does not penetrate to the connector body. Silver however tarnishes quickly and the silver sulfide that is produced is poorly conductive, degrading connector performance, making silver a poor choice for this application. Coaxial cable is a particular kind of transmission line , so the circuit models developed for general transmission lines are appropriate. See Telegrapher's equation . In
4232-418: The skin effect . The magnitude of an alternating current in a conductor decays exponentially with distance beneath the surface, with the depth of penetration being proportional to the square root of the resistivity. This means that, in a shield of finite thickness, some small amount of current will still be flowing on the opposite surface of the conductor. With a perfect conductor (i.e., zero resistivity), all of
4324-608: The EVPL and EPL is the degree of transparency: while EPL is highly transparent, filtering only the pause frames, EVPL is required to either peer or drop most of the Layer 2 control protocols. Ethernet Virtual Private LAN (EVP-LAN) is a multipoint-to-multipoint Ethernet Virtual Connection defined by the MEF — a Carrier Ethernet equivalent of Virtual Private LAN Service (VPLS) or Transparent LAN Services . EVP-LAN enables any-to-any communication between all customer locations associated with
4416-470: The RG-series designations were so common for generations that they are still used, although critical users should be aware that since the handbook is withdrawn there is no standard to guarantee the electrical and physical characteristics of a cable described as "RG-# type". The RG designators are mostly used to identify compatible connectors that fit the inner conductor, dielectric, and jacket dimensions of
4508-537: The SLA contract definition: the basic schema with the QoS parameters; SLA negotiation; SLA monitoring; SLA violation detection; and SLA enforcement—according to defined policies. The main point is to build a new layer upon the grid, cloud, or SOA middleware able to create a negotiation mechanism between the providers and consumers of services. An example is the EU–funded Framework 7 research project, SLA@SOI, which
4600-457: The area inside the cable. Coaxial lines can therefore be bent and moderately twisted without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them, so long as provisions are made to ensure differential signalling push-pull currents in the cable. In radio-frequency applications up to a few gigahertz , the wave propagates primarily in the transverse electric magnetic (TEM) mode , which means that
4692-611: The bottleneck remains in the wide area links to other offices and online services. Thus wide area network (WAN) and metropolitan area network (MAN) providers find themselves with three needs: They are also constrained as services cannot be migrated from local to wide area services too fast lest they exceed the total provisioning available and result in unacceptable quality. Services that try to expand too fast lose money while those that wait too long lose customers. Accordingly, carriers must expand their services conservatively and pay close attention to quality of service (QoS). The MEF
SECTION 50
#17327981826464784-466: The braid cannot be flat. Sometimes the braid is silver-plated. For better shield performance, some cables have a double-layer shield. The shield might be just two braids, but it is more common now to have a thin foil shield covered by a wire braid. Some cables may invest in more than two shield layers, such as "quad-shield", which uses four alternating layers of foil and braid. Other shield designs sacrifice flexibility for better performance; some shields are
4876-535: The cable ( Z 0 ) is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. In radio frequency systems, where the cable length is comparable to the wavelength of the signals transmitted, a uniform cable characteristic impedance is important to minimize loss. The source and load impedances are chosen to match the impedance of the cable to ensure maximum power transfer and minimum standing wave ratio . Other important properties of coaxial cable include attenuation as
4968-401: The cable can cause unwanted noise and picture ghosting. Excessive noise can overwhelm the signal, making it useless. In-channel ingress can be digitally removed by ingress cancellation . An ideal shield would be a perfect conductor with no holes, gaps, or bumps connected to a perfect ground. However, a smooth solid highly conductive shield would be heavy, inflexible, and expensive. Such coax
5060-505: The cable from water infiltration through minor cuts in the jacket. For internal chassis connections the insulating jacket may be omitted. Twin-lead transmission lines have the property that the electromagnetic wave propagating down the line extends into the space surrounding the parallel wires. These lines have low loss, but also have undesirable characteristics. They cannot be bent, tightly twisted, or otherwise shaped without changing their characteristic impedance , causing reflection of
5152-536: The cable, by a factor of 1000, or even 10,000, superscreened cables are often used in critical applications, such as for neutron flux counters in nuclear reactors . Superscreened cables for nuclear use are defined in IEC 96-4-1, 1990, however as there have been long gaps in the construction of nuclear power stations in Europe, many existing installations are using superscreened cables to the UK standard AESS(TRG) 71181 which
5244-451: The capabilities of Ethernet networks, and would like to extend these capabilities to multi-site networks. Meanwhile, the needs of such networks have expanded to include many services previously handled only on the LAN or by specialized connections, notably video and backup. It is not practical to expand most small networks beyond 1G or at most 2G ( dual teaming gigabit) capacity per segment, since
5336-461: The cloud and are offered by service providers as a service-based agreements rather than a customer-based agreements. Measuring, monitoring and reporting on cloud performance is based on the end UX or their ability to consume resources. The downside of cloud computing relative to SLAs is the difficulty in determining the root cause of service interruptions due to the complex nature of the environment. As applications are moved from dedicated hardware into
5428-478: The coax itself, affecting the radiation pattern of the antenna. With sufficient power, this could be a hazard to people near the cable. A properly placed and properly sized balun can prevent common-mode radiation in coax. An isolating transformer or blocking capacitor can be used to couple a coaxial cable to equipment, where it is desirable to pass radio-frequency signals but to block direct current or low-frequency power. The characteristic impedance formula above
5520-425: The coaxial cable is terminated in a pure resistance equal to its impedance. Signal leakage is the passage of electromagnetic fields through the shield of a cable and occurs in both directions. Ingress is the passage of an outside signal into the cable and can result in noise and disruption of the desired signal. Egress is the passage of signal intended to remain within the cable into the outside world and can result in
5612-409: The current path and concentrates the current at peaks, thus increasing ohmic loss. The insulating jacket can be made from many materials. A common choice is PVC , but some applications may require fire-resistant materials. Outdoor applications may require the jacket to resist ultraviolet light , oxidation , rodent damage, or direct burial . Flooded coaxial cables use a water-blocking gel to protect
SECTION 60
#17327981826465704-430: The current would flow at the surface, with no penetration into and through the conductor. Real cables have a shield made of an imperfect, although usually very good, conductor, so there must always be some leakage. The gaps or holes, allow some of the electromagnetic field to penetrate to the other side. For example, braided shields have many small gaps. The gaps are smaller when using a foil (solid metal) shield, but there
5796-399: The customer's Ethernet Virtual Connections (EVC). It is categorized as an E-LAN service type, with an expectation of low Frame Delay, Frame Delay Variation and Frame Loss Ratio. Service multiplexing is allowed at the UNI and EVPL and EVP-LAN service types may share the same port. CE-VLAN IDs are maintained across the network. The MEF does not specify how Ethernet services are to be provided in
5888-451: The customer, it is not an "SLA". SLAs commonly include many components, from a definition of services to the termination of agreement. To ensure that SLAs are consistently met, these agreements are often designed with specific lines of demarcation and the parties involved are required to meet regularly to create an open forum for communication. Rewards and penalties applying to the provider are often specified. Most SLAs also leave room for
5980-454: The electric and magnetic fields are both perpendicular to the direction of propagation. However, above a certain cutoff frequency , transverse electric (TE) or transverse magnetic (TM) modes can also propagate, as they do in a hollow waveguide . It is usually undesirable to transmit signals above the cutoff frequency, since it may cause multiple modes with different phase velocities to propagate, interfering with each other. The outer diameter
6072-522: The feedpoint impedance of a half-wave dipole, mounted approximately a half-wave above "normal" ground (ideally 73 Ω, but reduced for low-hanging horizontal wires). RG-62 is a 93 Ω coaxial cable originally used in mainframe computer networks in the 1970s and early 1980s (it was the cable used to connect IBM 3270 terminals to IBM 3274/3174 terminal cluster controllers). Later, some manufacturers of LAN equipment, such as Datapoint for ARCNET , adopted RG-62 as their coaxial cable standard. The cable has
6164-448: The fields before they completely cancel. Coax does not have this problem, since the field is enclosed in the shield. However, it is still possible for a field to form between the shield and other connected objects, such as the antenna the coax feeds. The current formed by the field between the antenna and the coax shield would flow in the same direction as the current in the center conductor, and thus not be canceled. Energy would radiate from
6256-399: The following components: A service-level agreement can track multiple performance metrics . In this context, these metrics are called service level indicators (SLIs). The target value of a given SLI is called a service-level objective (SLO). In IT-service management , a common case is a call center or service desk . SLAs in such cases usually refer to the following SLIs: Uptime
6348-404: The following section, these symbols are used: The best coaxial cable impedances were experimentally determined at Bell Laboratories in 1929 to be 77 Ω for low-attenuation, 60 Ω for high-voltage, and 30 Ω for high-power. For a coaxial cable with air dielectric and a shield of a given inner diameter, the attenuation is minimized by choosing the diameter of the inner conductor to give
6440-488: The form "RG-#" or "RG-#/U". They date from World War II and were listed in MIL-HDBK-216 published in 1962. These designations are now obsolete. The RG designation stands for Radio Guide; the U designation stands for Universal. The current military standard is MIL-SPEC MIL-C-17. MIL-C-17 numbers, such as "M17/75-RG214", are given for military cables and manufacturer's catalog numbers for civilian applications. However,
6532-406: The image; multiple reflections may cause the original signal to be followed by more than one echo. If a coaxial cable is open (not connected at the end), the termination has nearly infinite resistance, which causes reflections. If the coaxial cable is short-circuited, the termination resistance is nearly zero, which causes reflections with the opposite polarity. Reflections will be nearly eliminated if
6624-399: The inner conductor and inside of the outer conductor that restrict the signal's electric and magnetic fields to the dielectric , with little leakage outside the shield. Further, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, if unequal currents are filtered out at the receiving end of the line. This property makes coaxial cable
6716-426: The inner conductor so that the two voltages can be cancelled by the receiver. Many senders and receivers have means to reduce the leakage even further. They increase the transformer effect by passing the whole cable through a ferrite core one or more times. Common mode current occurs when stray currents in the shield flow in the same direction as the current in the center conductor, causing the coax to radiate. They are
6808-466: The introduction of 5G network slicing , the need of having a 360º view of the 5G slices becomes imperative to deliver premium SLAs and monetize service faster. For fixed networks subscribers, service modeling appears to be one of the most suitable ways to effectively monitor SLA's and ensure they are met. A web service level agreement ( WSLA ) is a standard for service level agreement compliance monitoring of web services . It allows authors to specify
6900-492: The key concepts of "learning bridge" ( flooding , and associating learned destination addresses with bridge ports) and " spanning tree protocol " (the protocol used for avoiding bridging loops). Historically, competing protocols and cabling have been created in order to access higher speed devices than contemporary Ethernet-connected devices handled at an affordable price. Examples include FireWire and Light Peak . One motive to create competing standards has been to drive down
6992-451: The loss. Supports shaped like stars or spokes are even better but more expensive and very susceptible to moisture infiltration. Still more expensive were the air-spaced coaxials used for some inter-city communications in the mid-20th century. The center conductor was suspended by polyethylene discs every few centimeters. In some low-loss coaxial cables such as the RG-62 type, the inner conductor
7084-504: The lowest capacitance per unit-length when compared to other coaxial cables of similar size. All of the components of a coaxial system should have the same impedance to avoid internal reflections at connections between components (see Impedance matching ). Such reflections may cause signal attenuation. They introduce standing waves, which increase losses and can even result in cable dielectric breakdown with high-power transmission. In analog video or TV systems, reflections cause ghosting in
7176-472: The much-required OAM that makes Ethernet carrier grade . Carrier Ethernet demarcation is a key element in Carrier Ethernet services and transport networks for business, wholesale and mobile backhaul applications, as it enables service providers to extend their control over the entire service path, starting from the hand off points. This is achieved by connecting customer premises equipment (CPE) to
7268-583: The network with provider-owned demarcation devices that are deployed at customer locations, thereby enabling a clear separation between the user and provider networks. Carrier Ethernet demarcation devices (EDD) are required to support services, such as Ethernet Private Line (EPL), Ethernet Virtual Private Line (EVPL or E-LAN), and Ethernet Virtual Private Tree (E-Tree), as specified by the MEF. Such support needs to include service level agreement (SLA) management capabilities, with consistent performance over fiber, DSL, bonded PDH , and SDH/SONET access lines. As
7360-421: The old RG-series cables. (7×0.16) (7×0.1) (7×0.1) (7×0.16) (7×0.75) (7×0.75) (7×0.17) Service level agreement A service-level agreement ( SLA ) is an agreement between a service provider and a customer . Particular aspects of the service – quality, availability, responsibilities – are agreed between the service provider and the service user. The most common component of an SLA
7452-457: The opposite of the desired "push-pull" differential signalling currents, where the signal currents on the inner and outer conductor are equal and opposite. Most of the shield effect in coax results from opposing currents in the center conductor and shield creating opposite magnetic fields that cancel, and thus do not radiate. The same effect helps ladder line . However, ladder line is extremely sensitive to surrounding metal objects, which can enter
7544-410: The performance metrics associated with a web service application, desired performance targets, and actions that should be performed when performance is not met. WSLA Language Specification, version 1.0 was published by IBM in 2001. The underlying benefit of cloud computing is shared resources, which are supported by the underlying nature of a shared infrastructure environment. Thus, SLAs span across
7636-814: The price of comparable-speed Ethernet devices. Once this purpose is achieved, competing standards tend to disappear or be confined to very specialized niches. Ethernet is a fairly simple protocol which has scaled to hundreds of thousands of times faster speeds and consistently been able to adapt to meet the needs and demands of new markets. For example, time domain capabilities are being added to IEEE 802.3 Ethernet to support IEEE 802.1 Audio Video Bridging (AVB), and these capabilities will be applicable to time sensitive carrier applications likewise IEEE 1588 . Customer LAN networks are increasingly connected to wide-area telecommunications networks over Ethernet interfaces or to devices that bridge digital subscriber line (DSL) or wireless to these. Moreover, customers are familiar with
7728-477: The results of various research projects in the area of SLAs (ranging from specifications to monitoring, management and enforcement) has been provided by the European Commission. Outsourcing involves the transfer of responsibility from an organization to a supplier. This new arrangement is managed through a contract that may include one or more SLAs. The contract may involve financial penalties and
7820-591: The right to terminate if any of the SLA metrics are consistently missed. The setting, tracking and managing SLAs is an important part of the outsourcing relationship management (ORM) discipline. Specific SLAs are typically negotiated upfront as part of the outsourcing contract and used as one of the primary tools of outsourcing governance. In software development, specific SLAs can apply to application outsourcing contracts in line with standards in software quality , as well as recommendations provided by neutral organizations like CISQ , which has published numerous papers on
7912-504: The same quality of service amongst different units in the organization and also across multiple locations of the organization. This internal scripting of SLA also helps to compare the quality of service between an in-house department and an external service provider. The output received by the customer as a result of the service provided is the main focus of the service level agreement. Service level agreements are also defined at different levels: A well-defined and typical SLA will contain
8004-399: The service provider and other third parties are often (incorrectly) called SLAs – because the level of service has been set by the (principal) customer, there can be no "agreement" between third parties; these agreements are simply "contracts." Operational-level agreements or OLAs, however, may be used by internal groups to support SLAs. If some aspect of service has not been agreed upon with
8096-414: The signal back toward the source. They also cannot be buried or run along or attached to anything conductive , as the extended fields will induce currents in the nearby conductors causing unwanted radiation and detuning of the line. Standoff insulators are used to keep them away from parallel metal surfaces. Coaxial lines largely solve this problem by confining virtually all of the electromagnetic wave to
8188-548: The transport of 40G and 100G technologies being developed by both bodies: 802.3 for LAN and ITU for the OTN . The OIF and the Ethernet Alliance have also been working cooperatively with their members to enable future enhancements to Ethernet for the WAN while looking to the future speed of Ethernet technologies and services. Coaxial cable Coaxial cable , or coax (pronounced / ˈ k oʊ . æ k s / ),
8280-413: The wrong voltage. The transformer effect is sometimes used to mitigate the effect of currents induced in the shield. The inner and outer conductors form the primary and secondary winding of the transformer, and the effect is enhanced in some high-quality cables that have an outer layer of mu-metal . Because of this 1:1 transformer, the aforementioned voltage across the outer conductor is transformed onto
8372-476: Was formed in 2001 in order to develop ubiquitous business services for Enterprise users principally accessed over optical metropolitan networks in order to connect their Enterprise LANs. The principal concept was to bring the simplicity and cost model of Ethernet to the wide area network. The success of Metro Ethernet Services caught the imagination of the world when the concept expanded to include worldwide services traversing national and global networks: To create
8464-505: Was manifested when trying to send a plain voice signal across the transatlantic telegraph cable , with poor results. Most coaxial cables have a characteristic impedance of either 50, 52, 75, or 93 Ω. The RF industry uses standard type-names for coaxial cables. Thanks to television, RG-6 is the most commonly used coaxial cable for home use, and the majority of connections outside Europe are by F connectors . A series of standard types of coaxial cable were specified for military uses, in
#645354