Subscriber plant 431 Subscriber loop

The subscriber plant has conventionally used twisted-pair copper. This provides the DC power to operate the basic telephone instrument from the Central Office, conveys the AC ringing voltage used to operate the telephone bell to indicate incoming calls and conveys loop signaling to the Central Office so as to indicate when the telephone is on- or offhook. This is used to indicate when the customer wishes to initiate a call, by going offhook or to terminate a call by replacing the telephone...

Aggregating bandwidth with ISDN

One of the most useful features of the ISDN network design is the ability to combine 64 kbps B-channels for applications that require larger amounts of bandwidth. As you add more B-channels to an ISDN installation, you need to choose a method of controlling and combining the channels into one connection. Each B-channel may travel a different path through the network to reach its destination. These different paths may introduce timing differences between data passed over different B-channels....

Protocols supporting VoIP Multicast IP

Normally IP is used for unicasting, i.e. messages are delivered on a one-to-one basis. IP multicasting delivers data on a one-to-many basis simultaneously. To support multicasting, the end stations must support the Internet group management protocol, IGMP, (RFC 1112), which enables multicast routers to determine which end stations on their attached Subnets are members of multicast groups. IPv4 Class D addresses ranging from 224.0.0.0 to 239.255.255.255 are reserved for multicasting. In order to...

Glossary

A1-Net Access control mechanism ACD Address Third generation partnership project for mobile telephony. IEEE 802.3 (or Ethernet) implementation on thin coaxial cable (RG58 Au). IEEE 802.3 (or Ethernet) implementation on thick coaxial cable. IEEE 802.3 (or Ethernet) implementation on unshielded 22AWG twisted-pair cable. The way in which the access to the physical transmission medium is managed by the LAN. A normally unique designator for location of data or the identity of a peripheral device,...

Receiving system figure of merit GT

The receiving system figure of merit (G T) describes the capability of a satellite or earth station to receive a signal. This is defined as follows G T is the figure of Merit measured in dB per degree Kelvin (dB K) G is the net antenna gain up to the reference plane, which is normally the input to LNA, in dB T is the effective noise temperature of the receiving system in degrees Kelvin. Net antenna gain The net antenna gain is the gross gain of the antenna less the losses of all of the...

Coaxial cable parameters Attenuation

Flat Braid Impedance

Attenuation of coaxial cables varies with frequency. A typical response curve for a coaxial cable used for cable TV applications is shown in Figure 3.13. It can be seen that there is an exponential increase in attenuation as the frequency increases. In the CATV industry this parameter is referred to as 'tilt'. Practical transmission systems need a relatively flat frequency response across the working bandwidth. To achieve this the system amplifiers provide equalization by amplifying the lower...

Conditioned lines

The leased circuits used for data transmission can be fitted with equalizers to improve the quality of their transmission characteristics to make them more suitable for data transmission. These circuits are said to be conditioned and various grades of conditioning are available to improve the frequency response and the envelope delay distortion. The differing grades of C-type conditioning available from AT& T are illustrated in Table 6.3. C-type conditioning applies only to frequency...

Network areas

The GSM network consists of geographic areas that include cells, location areas (LAs), mobile services switching center visitor location register (MSC VLR) service areas and public land mobile network (PLMNs) (Figure 10.9). These concepts will now be discussed individually. PLMN service area MSC VLR service area Location area A cell is the area covered by one base transceiver station and a cell global identity (CGI) number identifies it. A location area, in turn, is a group of cells, each...

Exchange hierarchy

An important national network design decision is to determine the number of hierarchical levels in a national switching network. The top level of the exchange hierarchy is the international switching center (ISC) and more than one of these may be necessary. The next level provides the long-distance switching using transit or toll exchanges while the bottom level would consist of the local exchanges and tandem exchanges to interconnect them. The objective of this hierarchy is to ensure that...

WEP cryptographic operations

Communications security has three important aims. It is extremely essential that any protocol that claims to provide secure data as it traverses across a network must assist network managers to obtain the following goals. Confidentiality denotes the data that is protected from interruption by malicious parties. Integrity denotes the data that is unmodified. Authentication bolsters the security strategy because a portion of data reliability is based on its origin. Users must ascertain that that...

Implementing switched 56 service

To provide dial-up capable digital lines for support of switched 56 requires special CSU DSUs to be installed on the 56 kbps circuit at the Central Office. The channel service unit (CSU) is a device that is installed between the customer's multiplexer and the service provider's network switch. It manages the physical characteristics of the signal such as the network protection, diagnostics, signal format, clocking and one's density. It is also used here to extract signaling information from the...

Copper subscriber loop plant

The conventional subscriber distribution plant is made up of twisted-pair copper. The diameter of the copper wire determines its resistance and distribution networks commonly comprise either 0.5 mm (24 AWG) or 0.63 mm (22 AWG) conductors. Access points are designed into the network in the form of cross connection cabinets to give more flexibility in the network and provide cost-effective circuit provision. The dedicated distribution cable to the customer's premises is generously provisioned to...

CTI components

The CTI architecture consists of three components. They are 1. The switch-to-host interface which provides connection between the telephone switch and the controlling host (the CTI server) 2. The application programing interface (API) which allows a software developer to create new functions and services for the system 3. The CTI resource architecture which manages the telephony and computing resources (building blocks) such as speech recognition and fax boards. These building blocks will now...

Telecommunications standards

Telecommunications standards are essential to enable the global PSTN to function. It is clear that when a telephone call or data message originates in one country and terminates in another, both the sender and recipient need to understand each other's messages. This is most easily achieved by using standardized message formats. This enables a message to be successfully passed through a number of countries, as necessary, along the way. This standardization is provided by two international...

Advantages of wireless data networks

The most important advantage of wireless networking is mobility. Wireless data users are free from the restriction of working from a fixed place. They can carry out their work in the conference room, in their project laboratory room, in their car and so on. The only requirement is that the wireless users should be within the specified range of the base station. The range that is covered by the simplest available equipment is a campus domain. As the equipment gets slightly sophisticated, the...

Twistedpair copper cables

Twisted-pair cable is widely used, inexpensive, and easy to install. Twisted-pair cable used for telecommunication purposes is generally unshielded (UTP). It can transmit data at an acceptable rate - up to 100 Mbps in some network architectures. The most common twisted-pair wiring is telephone cable, which is unshielded and is usually voice-grade, rather than the higher-quality category 5 cable used for data networks. In a twisted-pair cable, two conductor wires are wrapped around each other....

Disadvantages

There can be a security problem, since every node may see every message, even those that are not destined for it. Diagnosis troubleshooting (fault isolation) can be difficult, since the fault can be anywhere along the bus. There is no automatic acknowledgment of messages, since messages get absorbed at the end of the bus and do not return to the sender. The bus cable can be a bottleneck when network traffic gets heavy. This is because nodes can spend much of their time trying to access the...

Components of twistedpair cable

A twisted-pair cable is made from pairs as illustrated in Figure 3.7 and the pairs are bundled to form a cable as illustrated in Figure 3.6. The components are The signal wires for this cable are conductors that are wrapped around each other. The conductor wires are usually made of copper. They are normally solid (consisting of a single wire) but can be stranded (consisting of many thin wires wrapped tightly together) for short, flexible patch cords. A twisted-pair cable contains multiple...

Fiberoptic cable parameters Attenuation

The attenuation of a multimode fiber depends on the wavelength and the fiber construction, and ranges from around 3-8 dB km at 850 nm and 1-3 dB km at 1300 nm. The attenuation of single-mode fiber ranges from around 0.4-0.6 dB km at 1300 nm and 0.25-0.35 dB km at 1550 nm. The fiber diameter is either 50 or 62.5 microns for multimode fiber or 8.5 microns for single mode. Multimode fibers (50 or 62.5 microns) In multimode fibers a beam of light has room to follow multiple paths, which are called...

Simplex halfduplex and fullduplex 221 Simplex

A simplex channel is unidirectional and allows data to flow in one direction only, as shown in Figure 2.3. Public radio broadcasting is an example of a simplex transmission. The radio station transmits the broadcast program, but does not receive any signals back from the radio receiver. This has limited use for data transfer purposes, as invariably the flow of data is required in both directions in order to control the transfer process, acknowledge data, etc. Output signal, channel bandwidth 1...

Intelligent bridges

Intelligent bridges (also referred to as transparent or spanning-tree bridges) are the most commonly used bridges because they are very efficient in operation and do not need to be taught the network topology. A transparent bridge learns and maintains two address lists corresponding to each network it is connected to. When a frame arrives from the one Ethernet network, its source address is added to the list of source addresses for that network. The destination address is then compared to that...

Cutthrough vs storeandforward

Switches have two basic architectures, cut-through and store-and-forward. In the past, cut-through switches were faster because they examined the packet destination address only before forwarding the frame to the destination segment. A store-and-forward switch, on the other hand, accepts and analyses the entire packet before forwarding it to its destination. It takes more time to examine the entire packet, but it allows the switch to catch certain packet errors and keep them from propagating...

Fiberoptic cable components

The major components of a fiber-optic cable are core, cladding, buffer, strength members and jacket. Some types of fiber-optic cable even include a conductive copper wire that can be used to provide power to a repeater. The core of an optical fiber carries the light signal. The most common core sizes are 50 and 62.5 m (microns) which are used in multimode cables. Fibers of 8.5 micron size are used in single mode systems. The cladding is a larger of glass surrounding the core. The core and...

Protocols 931 Introduction

TCP IP is the de facto global standard for the network and transport layer implementation of internetwork applications because of the popularity of the Internet. The Internet (in its early years known as ARPANet), was part of a military project commissioned by the Advanced Research Projects Agency (ARPA), later known as the Defence Advanced Research Agency or DARPA. The communications model used to construct the system is known as the ARPA model. Whereas the OSI model was developed in Europe by...

Virtual channel

A virtual channel (VC) is used to describe an entity used for unidirectional transport of ATM cells. The virtual channel identifier (VCI) identifies a virtual channel link for a specific virtual path connection (VPC). Each VC link has a VCI assigned when the link is originated and the VC link is terminated when the VCI is removed. Virtual channels are routed by means of a VC switch crossconnect. This is done by translation of the VCI of the incoming virtual channel links into the VCI values of...

Frame format

In order to meet the challenges caused by a wireless data link, the MAC was enforced to embrace certain unique features. All the frames do not utilize all the address fields, and the values allocated to the address fields may be transformed on the basis of the MAC frame that is being transmitted. The basic 802.11 frame is illustrated in Figure 11.7. Fields are transmitted from left to right, and the most significant digit appears last. We will now have a detailed look at each of the fields...

ATM services

ATM networks can have the following different service types Constant bit rate (CBR) which operates similar to fixed time division multiplexing but is subject to varying delay, which causes jitter. Variable bit rate (VBR) which operates within certain traffic constraints without specific cell flow control from the network. Virtual path and virtual channel switching Virtual path and virtual channel switching Available bit rate (ABR) which is used for data applications. This operates between...

Local multipoint distribution system

Local multipoint distribution system (LMDS) uses millimeter wave radio transmission in the Ka-band (28 GHz) to transmit voice, data and video signals within cells of up to 3 miles or 5 km in diameter. LMDS can deliver services ranging from one-way video distribution and telephony to fully interactive switched broadband multimedia applications such as video-on-demand, interactive video, video conferencing and high speed Internet access. The basic LMDS configuration is shown in Figure 7.17. LMDS...

Channel associated information signaling

Inter-exchange information signals transfer the address or telephone number of the called subscriber plus other call progress and control signals around the network. These can include, amongst others, the type of subscriber, the type of call, automatic number identification requests, clear forward and clear back signals, re-seize and re-answer signals in response to a hook-switch flash, and trunk offer signals whereby an assistance operator can gain access to busy lines. The early exchanges...

Call processing control

There are two fundamental types of switching control methods used in telephone exchange systems - direct progressive control and common control. Direct progressive control systems such as step-by-step exchanges are controlled directly by the telephone dial. As each digit is dialed the switch, called a group selector, is stepped upward in accordance with each pulse to select the appropriate digit level. During the interdigit pause the group selector then hunts for an outlet (1 out of 20) to a...

Exterior gateway protocols

One of the earlier EGPs was in fact called EGP. The current de facto Internet standard for interdomain (AS) routing is Border Gateway Patrol version 4, or simply BGP-4. BGP-4, as detailed in RFC 1771, performs intelligent route selection based on the shortest AS path. In other words, whereas IGPs such as RIP make decisions on the number of routers to a specific destination, BGP-4 bases its decisions on the number of ASs to a specific destination. It is a so-called path vector protocol, and runs...

Leased analog data services

Dedicated or leased analog lines are available for permanent connection across the PSTN. Most of these lines are used for data services although others are used for permanent analog connections such as for example music distribution or control circuits. In this section we will only consider the special requirements for data applications. To utilize these circuits for data, a leased line modem is used in a similar manner to dial-up circuits. The only difference between a leased line and dial-up...

Frame processing

When a frame is received for data transferred, the frame handler within each exchange reads the DLCI from the frame header, determines the corresponding outgoing link and the new DLCI. This is inserted into the frame header and the frame is queued for transmission on the new outgoing link. If the DLCI is not defined for this frame, the frame is discarded. The use of DLCI is illustrated in Figure 6.18. Use of data link connection identifiers

Pv4 addressing

The ultimate responsibility for the issuing of IP addresses is vested in the Internet assigned numbers authority (IANA). This responsibility is, in turn, delegated to the three regional Internet registries (RIRs) viz. APNIC (Asia-Pacific Network Information Center), ARIN (American Registry for Internet Numbers) and RIPE NCC (Reseau IP Europeans). RIRs allocate blocks of IP addresses to Internet service providers (ISPs) under their jurisdiction, for subsequent issuing to users or subISP's. The...

Interframe spacing and priority

Atomic operations commence like regular transmissions they have to wait for the DIFS prior to commencing. Later on, the second and the remaining steps in an atomic operation occur using the SIFS, rather than during the DIFS. This essentially means that second and the remaining steps of an atomic operation seize the medium prior to another frame type being transmitted. By utilizing the SIFS and the network allocation vector (NAV), stations can grab the medium for as long as they want. The...

ISDN channel types

ISDN defines two types of user interfaces the basic rate interface (BRI) primarily for residential customers and the primary rate interface (PRI) for commercial users with greater data requirements. In this section the basic rate interface will be discussed and the primary rate interface is discussed in detail in Section 6.12. The user access link is made up of combinations of the following user channels B-channel 64 kbps. This channel can be used to carry digital data, digitally encoded voice,...

Direct vs indirect delivery

When the source host prepares to send a message to another host, a fundamental decision has to be made, namely is the destination host also resident on the local network or not If the NetID portions of the source and destination IP addresses match, the source host will assume that the destination host is resident on the same network, and will attempt to forward it locally using the hardware (Mac) address. This is called direct delivery. If not, the message will be forwarded to the default...

Time division switching

Time division switching is accomplished by interchanging time slots between digital data streams. You will recall that in digital systems each speech channel is sampled at 8000 times per second with each 8-bit sample placed in a time slot. Time switching involves storage of the data from the various incoming time slots then placing that data in a different sequence in the outgoing time slots. This is shown diagrammatically in Figure 4.9. In this simple example the time division multiplexer on...

Baseband vs broadband 241 Baseband

Baseband refers to a communication method where all the traffic shares a single channel hence when a given user transmits on the channel, the entire bandwidth is occupied and nobody else can use the channel. If more than one user wish to use the channel, they need to do it sequentially i.e. they have to use a time-related multiplexing scheme such as TDM. The signal is placed on the medium without using a high-frequency carrier signal (Figure 2.6). In the case of analog signals, such as on an...

The RTP header format

The first section (12 bytes fixed) is present in all RTP headers. The second section is optional (and variable length) and consists of CSRC identifiers inserted by a mixer. The third section is also optional and variable in length, and is used for experimental purposes (Figure 9.13). Synchronization source (SSRC) identifier Contributing source (CSRC) identifier Version (V) 2 bits. This field identifies the version of RTP. The current version is 2. Padding (P) 1 bit. If the padding bit is set,...

Gprs

General packet radio service (GPRS) is a data service (non-voice) that supplements circuit switch data (CSD) and short message service (SMS) on GSM networks. It can theoretically run at speeds of up to 171.2 kbps, achievable by using all the eight time slots on a GSM network. In practice the maximum speed is about 150 kbps. This is in contrast with circuit switched data that runs at 9.6 kbps. Because of its bandwidth, GPRS suitable for sending and receiving small bursts of data such as e-mail,...

Integrated services digital network Isdnbri

ISDN was developed to initially utilize the existing copper distribution plant to provide an integrated digital transmission system between the customer and the integrated digital telecommunications network (IDN). ISDN extends 64 kbps digital channels right to the customer and it enables them to carry any combination of digital voice telephony, digital data, telex, facsimile, etc. This is illustrated in Figure 6.10. ISDN is simply an interface specification for digital communication between the...

Connection orientated vs connectionless communication

Connectionless communication is a method of communication whereby data is simply sent without confirming whether the recipient is ready and willing to receive it. Because of this situation the sender cannot get immediate acknowledgment of receipt, and has to employ some other method for this purpose. An example of this technique is sending a telegram. In terms of networking protocols the TCP IP protocol suite's user datagram protocol (UDP) (see Chapter 9) performs such a function....

The hidden node problem

In Ethernet networks, stations rely on reception of transmissions in order to execute the carrier sensing functions of CSMA CD. Wires present in the physical medium carry signals and distribute them to all network nodes. Wireless networks, on the other hand, have unclear boundaries. In certain situations, the boundaries are so unclear that not all nodes present in the network are in a position to communicate with all other nodes. This aspect is illustrated in Figure 11.4. In Figure 11.4, node 2...

Coaxial cable components

A coaxial cable consists of the following layers (moving outward from the center) as shown in Figure 3.12. A carrier wire or signal wire is in the center of the cable. This wire is usually made of copper and is normally solid but may be stranded. There are restrictions regarding the wire composition for certain network configurations. The diameter of the signal wire is one factor in determining the attenuation of the signal over distance. The number of strands in a multi-strand conductor also...

Bluetooth

Bluetooth is a wireless technology for short-range radio links between various computing and communication devices such as mobile phones, PDAs, desktop computers, fax machines, printers, joysticks, etc. Bluetooth technology enables all of these devices to be connected by one universal short-range radio link. This means that many of the proprietary cables will not be required to connect these devices. Bluetooth also provides a universal bridge between existing data networks and a way of...

Audio voice Codecs

In order to transport the analog voice signal, it has to be digitized. The traditional approach is to sample it at 8000 samples per second, and then to quantize each sample into an 8-bit digital value, with a resolution of 1 (28) 1 25 6. Thus the basic bit rate becomes 8000 samples per second x 8 bits per sample 64 000 bps, known as the DS0 rate. Through an additional process called encoding, the 64 000 bps bandwidth requirement can be reduced considerably, by employing techniques such as data...

Asymmetric digital subscriber line

Bridge Tap Interference

Asymmetric digital subscriber line (ADSL) uses existing twisted-pair telephone cable to transmit data at up to 6 Mbps downstream to the subscriber and up to 640 kbps upstream from the subscriber. The basic ADSL system configuration is shown in Figure 7.1. ADSL uses standard unconditioned customer access cable pairs and performance primarily depends on the length of the copper circuit, its wire gage, the presence of any bridged taps and the noise environment. Typical ADSL performance for lines...

Digital dedicated circuit leased alternatives

Dedicated digital circuits can be obtained from the telecom service provider as various asynchronous (PDH) connections. These have the fixed bandwidth delivered to the customer's premises in various sizes Digital data services (DDS) in the range 2.4-56 kbps T-1 (1.544 Mbps) or E-1 (2.048 Mbps) Fractional T-1 E-1 which are multiples of 56 kbps Greater bandwidth T-3 at 44.736 Mbps. The advantage of these services is that the service provider delivers the digital bandwidth to the customer, with...

Switch concentration and expansion

The local switches utilize concentration whereby all of the individual subscribers are able to access a limited number of simultaneous switching paths to other subscribers or trunks to other exchanges, and expansion enabling a call on one of those limited paths or trunks to be connected to any one of the called subscribers. The concentration ratio is the same as the expansion ratio and may be in the order of 10 1 for residential subscribers or 3 1 for business subscribers. Switch design is...

Namps

Narrow band analog mobile phone service is a second-generation analog cellular system, designed as an upgrade to AMPS. Its major aim is to solve the problem of low calling capacity. It combines existing voice processing with digital signaling, tripling the capacity of existing AMPS systems. NAMPS uses FDM to fit three channels into the AMPS 30 kHz channel bandwidth, thereby increasing the capacity by a factor of three. Unfortunately, this increases the possibility of interference because...

Overview of existing systems

AMPS was developed by Bell Labs and first used commercially in the USA in 1983. It is currently the world's largest cellular standard and operates in the 800 MHz band. C-450 was installed in South Africa during the 1980s. It was known as Motorphone and run by Vodacom SA. It used the 450 MHz band. C-Netz is an older cellular technology, similar to C-450, and used in Germany and Austria. Comvik was introduced in Sweden by the Comvik Network in 1981. TACS (total access communication system) was...

H225 call signaling

The H.225 call signaling is used to establish a connection between two H.323 endpoints (terminals gateways), over which the real-time data can be transported. This is achieved by exchanging H.225 protocol messages on the call-signaling channel. The call-signaling channel is opened between two H.323 endpoints or between an endpoint and the gatekeeper. Call signaling involves the exchange of H.225 protocol messages over a reliable call-signaling channel, hence H.225 protocol messages are carried...

Bus multidrop topology

Physically, a bus describes a network in which all nodes are connected to a common single communication channel or 'bus'. This bus is sometimes called a backbone, as it provides the spine for the network. Every node can hear each message packet as it goes past. Logically, a bus is distinguished by the fact that packets are broadcast and every node gets the message at the same time. Transmitted packets travel in both directions along the bus, and need not go through the individual nodes, as in a...

Subscribers loop design limits

This section will consider the design limits of the subscriber's loop using twisted-pair cable, since this is the only reason for using such cable in a telecommunication network. The maximum attenuation allowed in the subscriber's loop is set in the national transmission plan. This is typically 8 dB measured at 1000 Hz. Using the values of attenuation for the low-capacitance cable (40 nF km) given in Table 3.1 for the different conductor sizes, we can derive the corresponding maximum cable...

Objectives

When you have completed studying this chapter you should be able to Describe the effects of attenuation on a digital signal Discuss the impact of induced magnetic fields on a twisted-pair cable Explain the various methods used to extend a subscriber's loop Discuss the implications of using loading coils on a subscriber plant Explain 'tilt' and how it is overcome in coaxial cable systems Identify the component parts of a fiber-optic cable Discuss the difference between single-and multi-mode...

Call accounting

Call accounting is useful for tracking employee productivity, the use (and abuse) of the telephone system by employees, billing for professional services, as well as ensuring that billed calls were actually made. Typically, call accounting software packages run on a PC (with Windows) connected to the station messaging detail reporting (SMDR) port of a phone system. If the phone system does not have an SMDR port, a hardware box such as Sandman's 'Whozz Calling' hardware can be placed on the...

IEEE 80212 Fast LANs

This specification covers the system known as 100VG AnyLAN. Developed by Hewlett-Packard, this system operates on voice grade (CAT3) cable - hence the VG in the name. The AnyLAN indicates that the system can interface with both IEEE 802.3 and IEEE 802.5 networks (by means of a special speed adaptation bridge). FDDI is a high sped token passing system that uses fiber optic as the medium. It is, in essence, a fast token ring system. It has the following characteristics It supports speeds up to...

North American TDM multiplex hierarchy

Higher level TDM multiplexing is used to combine DS-1 systems by interleaving bits from the various DS-1 inputs. For example, the DS-2 transmission system combines four DS-1 inputs into a 6.312 Mbps data stream byte interleaving 12 bits at a time from each stream. Additional bits are required for framing and control purposes. Table 6.4 illustrates the various circuit designations and their corresponding bit rates. North American TDM multiplex hierarchy North American TDM multiplex hierarchy

Remote subscriber unit

The remote subscriber unit RSU is increasingly being used to connect the distribution cable to the Central Office. It provides the subscriber line interface card SLIC for conventional plain old telephone service POTS . This is discussed in Section 4.5. The RSU can also carry out a concentrator function with an optional local switching capacity. The RSU may also provide independent interfaces for high-speed data circuits. The RSU is particularly useful for remote customers who would require the...

Broadcast vs pointtopoint topologies

Point Point Topology

Networks consist of several nodes workstations, printers, PLCs, etc. interconnected via some sort of medium. The way the nodes are interconnected is known as the topology. There are many possible topologies but they all form in one of two categories, broadcast and point-to-point. Broadcast topologies are those where the messages ripple out from the transmitter to reach all nodes. There is no active regeneration of the signal by the nodes and thus signal propagation is independent of the...

RTCP packet format

This specification defines several RTCP packet types to carry a variety of control information, namely SR A sender report, for transmission and reception statistics from participants that are active senders RR A receiver report, for reception statistics from participants that are not active senders SDES Source description items, including CNAME BYE Indicates end of participation APP Application specific functions. Each RTCP packet begins with a fixed part similar to that of RTP data packets,...

Twistedpair cable parameters Loop resistance

The resistance of a copper cable pair depends on the diameter of the conductors. Loop resistance is the total resistance in the conductors between the Central Office switch and the subscriber, that is twice the resistance of one individual conductor of that length. Cable diameters are normally measured either on millimeters or American wire gage AWG . A comparison of these different conductor sizes and their corresponding loop resistances is shown in Table 3.1. Typical twisted-pair cable...

Common channel signaling

With modern stored program controlled exchanges it is inefficient for the digital processor to handle channel associated signaling. A much more efficient method is to transfer all the signaling information between the processors over a high-speed data link. This is called common channel signaling CCS . This has many advantages including having a signaling path which is entirely separate from the switched speech paths, very fast signaling is possible because of the wide bandwidth 64 kbps of the...

Switched

Switched 56 or global switched digital services is a digitally switched or dial-up service, used primarily in North America, that has the capacity to provide a single data channel of 56 kbps on demand. Different telecommunications companies call the service by different names some of these are listed in Table 6.6. Switched 56 access lines were some of the first digital circuits installed by the telecommunication carriers. The low cost of switched 56 service relative to digital leased lines...

Star hub topology

Star Topology

In a physical star topology multiple nodes are connected to a central component, generally known as a hub. The hub usually is just a wiring center, that is, a common termination point for the nodes. In some cases, the hub may actually be a file server a central computer that contains a centralized file and control system , with all the nodes attached directly to the server. As a wiring center, a hub may in turn be connected to a file server or to another hub. All packets going to and from each...

European TDM multiplex hierarchy

Higher level TDM multiplexing is used to combine E1 systems by interleaving bits from the various E1 inputs. For example, the E2 transmission system combines four E1 inputs into an 8.448 Mbps data stream byte interleaving. Additional bits are required for framing and control purposes. Table 6.5 illustrates the various ITU-T circuit designations and their corresponding bit rates.

First party call control

First Party Call Control

In the first party configuration a call is controlled by the call parties. First party or phone oriented call control involves a direct interface between the user's PC and the telephone switch by intercepting line signaling between the telephone and the switch as shown in Figure 5.2. Because of this approach, it limits itself to conventional signaling conditions used in PSTN telephones. The telephone-to-computer interface is usually a phone line connection. This connection can be via RJ-11...

Local vs remote bridges

Multiport Bridge

Local bridges are devices that have two network ports and hence interconnect two adjacent networks at one point. Nowadays this function is usually performed by switches as they are basically multiport bridges, and are available with as few as two ports Figure 8.11 . A useful type of local bridge is a 10 100 Mbps Ethernet bridge, which allows interconnection of 10BaseT, 100BaseTX and 100BaseFX networks, thereby performing the required speed translation. These bridges typically provide...

IEEE 8025 Token ring

As in 802.4, data transmission can only occur when a station holds a token. The logical structure of the network wiring is in the form of a ring, and each message must cycle through each station connected to the ring. This standard is the ratified version of the IBM token ring LAN. However, where IBM token ring supports speed of 4 and 16 Mbps, IEEE 802.5 supports 1 and 4 Mbps. The physical media for the token ring can be either unshielded twisted pair, coaxial cable or optical fiber. The...

Radio path profile

Path Profile

The next step involves identification of the appropriate transmitting and receiving sites. Terminal sites need to be located close to the equipment they will serve, whereas intermediate repeaters are not constrained. The main site selection criteria will be Proximity of road access and above all Feasibility of the radio path. Preliminary site selection is often done from examination of topographical maps of the area, having a scale of at least 1 50 000. The next step is to draw a straight line...

The application programing interface

The second component of the CTI architecture is the application programing interface API . This is an interface that enables software developers to create new applications. Three standards will be discussed namely TAPI, TSAPI and JTAPI. Microsoft's telephony application programing interface TAPI enables Windows programmers to develop telephony applications in software. The current version is TAPI 3.0. The TAPI 3.0 component object model allows programmers to write TAPI applications in, for...

Local switches 451 Local switch overview

A local exchange or Central Office switch has inlets to serve incoming calls and outlets to serve outgoing calls. A call from the calling subscriber enters the switch via an inlet and is then connected to the calling subscriber on the outlet side of the switch. The switching function can be space-switched or time-switched or use combinations of the two. The switching function is initiated by the calling subscriber using line signaling conditions of either 'off-hook' or 'on-hook' together with...