Chapter 18

MMDS and LMDS

      The  Multichannel Multipoint Distribution Service (MMDS) is a broadcasting and communications service that operates in the ultra-high-frequency (UHF) portion of the radio spectrum between 2.1 and 2.7 GHz. MMDS is also known as wireless cable. It was conceived as a substitute for conventional cable television (TV). However, it also has applications in telephone/fax and data communications. Allows two-way voice, data and video streaming. It operates at a lower frequency than LMDS (typically within specified bands in the 2-10GHz range) and therefore has a greater range and requires a less powerful signal than LMDS. MMDS is a less complicated, cheaper system to implement.

     

         MMDS band uses microwave frequencies from 2 GHz to 3 GHz in range. Reception of MMDS-delivered television signals is done with a special rooftop microwave antenna and a set-top box for the television receiving the signals. The antenna usually has an integrated down-converter to transmit the signals at frequencies compatible with terrestrial TV tuners down on the coax (much like on satellite dishes where the signals are converted down to frequencies more compatible with standard TV coaxial cabling), some larger antennas utilise an external down-converter. The receiver box is very similar in appearance to an analogue cable television receiver box. is a wireless telecommunications technology, used for general-purpose broadband networking or, more commonly, as an alternative method of cable television programming reception.

Transmission line

   Transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that their wave nature must be taken into account. Transmission lines are used for purposes such as connecting radio transmitters and receivers with their antennas, distributing cable television signals, and computer network connections.

        

          Local Multipoint Distribution Service (LMDS) is an ideal solution for bringing high-bandwidth services to homes and offices within the last-mile—an area where cable or optical fibre may not be convenient or economical. Having architectural similarities with cellular networks, LMDS is a fixed (non-mobile) point-to-multipoint wireless access technology that typically operates in the 28 GHz band and offers Line-of-Sight (LoS) coverage up to 3-5 km. Depending on the local licensing regulations in a country, such broadband wireless systems may operate anywhere from 2 to 42 GHz. Though data transfer rates for LMDS can reach 1.5 to 2 Gbps, in reality it is designed to deliver data at speeds between 64 Kbps to 155 Mbps (as against 9.6 Kbps offered by 2G cellular networks like GSM), a more realistic downstream average being around 38 Mbps. At such speeds, LMDS may be the key to bringing multimedia data—supporting voice connections, the Internet, videoconferencing, interactive gaming, video streaming and other high-speed data applications—to millions of customers worldwide over the air.

              

The services possible with LMDS include the following:

· Voice dial−up services

· Data

· Internet access

· Video

Head-End Equipment

The Head-End equipment can be broken down into two main categories:

Digital television equipment and Internet and VoIP equipment.

   

     The digital television equipment can provide MPEG-2 encoded video/audio streams from live television feeds, and optionally from video servers with VOD or other pre-recorded content.  The encoded streams are multiplexed into a DVB compliant MPEG-2 ASI transport stream and delivered to the transmission site through a variety of distribution networks including IP networks, microwave links and satellite delivery.

          The Internet and VoIP Head-End equipment requires a robust IP network connection to the DOCSIS 2.0/3.0 Wireless Modem Termination System at the transmission site.  The connection must exceed the total bandwidth   (>30Mbit/sec) of the wireless data network.

http://en.wikipedia.org/wiki/Local_Multipoint_Distribution_Service 

http://www.angelfire.com/nd/ramdinchacha/DEC00.html

http://www.uniquesys.com/MMDS/MMDS_Triple_Play.php

http://www.digital-kaos.co.uk/forums/f10/what-mmds-simple-explanation-23214/

http://www.mobilecomms-technology.com/projects/mmds/

Chapter 17

                               

      Microwave− and Radio−Based Systems

        A radio base system (1000) is multi-path-connected to a plurality of mobile terminal devices to transmit/receive signals. When a communication channel establishment request is sent from one of the plurality of mobile terminal devices, a control unit (80) detects the presence or absence of a mobile terminal device to which a communication channel is already connected for each of a plurality of slots.

           Microwave frequencies range from 300 MHz to 30 GHz, corresponding to wavelengths of 1 meter to 1 cm.  These frequencies are useful for terrestrial and satellite communication systems, both fixed and mobile.  In the case of point-to-point radio links, antennas are placed on a tower or other tall structure at sufficient height to provide a direct, unobstructed line-of-sight (LOS) path between the transmitter and receiver sites. In the case of mobile radio systems, a single tower provides point-to-multipoint coverage, which may include both LOS and non-LOS paths.  LOS microwave is used for both short- and long-haul telecommunications to complement wired media such as optical transmission systems.

         Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do.

  

   Advantages:

Ø  High frequency of microwaves gives the microwave band a very large information-carrying capacity.

Ø  The microwave band has a bandwidth 30 times that of all the rest of the radio spectrum.

     Disadvantage:

Ø  Microwaves are limited to line of sight propagation.

Ø  They cannot pass around hills or mountains as lower frequency radio waves can.

  

Principles and Operation

Microwave Link Structure

        

      The basic components required for operating a radio link are the transmitter, towers, antennas, and receiver. Transmitter functions typically include multiplexing, encoding, modulation, up-conversion from baseband or intermediate frequency (IF) to radio frequency (RF), power amplification, and filtering for spectrum control. Receiver functions include RF filtering, down-conversion from RF to IF, amplification at IF, equalization, demodulation, decoding, and demultiplexing. To achieve point-to-point radio links, antennas are placed on a tower or other tall structure at sufficient height to provide a direct, unobstructed line-of-sight (LOS) path between the transmitter and receiver sites.

Microwave System Design

    

     The design of microwave radio systems involves engineering of the path to evaluate the effects of propagation on performance, development of a frequency allocation plan, and proper selection of radio and link components. The frequency allocation plan is based on four elements: the local frequency regulatory authority requirements, selected radio transmitter and receiver characteristics, antenna characteristics, and potential intrasystem and intersystem RF interference.

 Microwave Propagation Characteristics

       

     The various phenomena associated with propagation, such as multipath fading and interference, affect microwave radio performance.  The modes of propagation between two radio antennas may include a direct, line-of-sight (LOS) path but also a ground or surface wave that parallels the earth's surface, a sky wave from signal components reflected off the troposphere or ionosphere, a ground reflected path, and a path diffracted from an obstacle in the terrain.

       A simple and cost-effective demultiplexing approach for a subcarrier multiplexed radio-over-fiber (RoF) system is proposed, analyzed, and experimentally demonstrated. A microwave photonic filter based on multiple optical sources is integrated into the RoF system, and by simply controlling the time delay in the remote antenna unit, the subcarrier with desirable frequency can be filtered out, and undesirable ones are suppressed. An experimental demonstration has been carried out by implementing a two-optical-source-based microwave photonic filter in an RoF downlink transmitting a 2.5-GHz subcarrier modulated with 150-Mb/s on-off keying (OOK) data, showing that it works well as a subcarrier demultiplexer. The proposed demultiplexing approach enjoys high flexibility, tunability, and cost-effectiveness and has good potential applications in the multiplexed RoF systems.

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5711628

http://www.eogogics.com/talkgogics/tutorials/microwave-line-of-sight-systems

http://www.google.com.ph/search?q=Microwave%E2%88%92+and+Radio%E2%88%92Based+Systems&hl=tl&rlz=1C1ECBA_enPH471PH471&prmd=imvns&source=lnms&tbm=isch&ei=kqs8T_S6OLCRiQfNv823BA&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CBQQ_AUoAQ&biw=1366&bih=624

Chapter 16

       

                                                                    xDSL

       DSL   is a family of technologies that provide internet access by transmitting digital data over the wires of a local telephone network. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line (ADSL), the most commonly installed DSL technology. DSL service is delivered simultaneously with wired telephone service on the same telephone line. This is possible because DSL uses higher frequency bands for data separated by filtering. On the customer premises, a DSL filter on each outlet removes the high frequency interference, to enable simultaneous use of the telephone and data.

       The data bit rate of consumer DSL services typically ranges from 256 kbit/s to 40 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and service-level implementation. In ADSL, the data throughput in the upstream direction, (the direction to the service provider) is lower, hence the designation of asymmetric service. In Symmetric Digital Subscriber Line (SDSL) services, the downstream and upstream data rates are equal.

       A DSL circuit provides digital service. The underlying technology of transport across DSL facilities uses high-frequency sinusoidal carrier wave modulation, which is an analog signal transmission. A DSL circuit terminates at each end in a modem which modulates patterns of bits into certain high-frequency impulses for transmission to the opposing modem. Signals received from the far-end modem are demodulated to yield a corresponding bit pattern that the modem retransmits, in digital form, to its interfaced equipment, such as a computer, router, switch, etc.

Benefits & Applications

Benefits

• High-speed data service

– DSL typically >10x faster than

56-kbps analog modem

• Always on connection

– No need to “dial-up”

• Uses existing copper wires

– Co-exists w/ POTS service

• Reasonably priced today and

getting cheaper

Applications

• High speed Internet access

• SOHO

• Multimedia, Long distance

learning, gaming

• Video on Demand

• VPN

• VoDSL

          Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call.[1] A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the telephone exchange (the last mile), typically less than 4 kilometres (2 mi),[2] but has been known to exceed 8 kilometres (5 mi) if the originally laid wire gauge allows for further distribution.

           IDSL is a system in which digital data is transmitted at 128 Kbps on a regular copper telephone line (twisted pair) from a user to a destination using digital (rather than analog or voice) transmission, bypassing the telephone company's central office equipment that handles analog signals. IDSL uses the Integrated Services Digital Network (Integrated Services Digital Network) Basic Rate Interface in ISDN transmission code.

           HDSL (High bit-rate Digital Subscriber Line), one of the earliest forms of DSL, is used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions. HDSL can carry as much on a single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.

         SDSL (Symmetric Digital Subscriber Line) is high-speed Internet access service with matching upstream and downstream data rates. That is, data can be sent to the Internet from the client machine or received from the Internet with equal bandwidth availability in both directions.

         RADSL is an implementation of ADSL that automatically adjusts the connection speed to adjust for the quality of the telephone line. As line conditions change, you can see the speeds changing in each direction during the transmission.

         SHDSL technology can transport data symmetrically at data rates from 192 Kbps to 2,320 Kbps. SHDSL utilizes a single copper wire pair, making it an affordable DSL option attractive to small businesses.This service delivers voice and data services based on highly innovative communication technologies and will thus be able to replace older communication technologies such as T1, E1, HDSL, HDSL2, SDSL, ISDN, and IDSL in the future.

          VDSL was developed to support exceptionally high-bandwidth applications such as High-Definition Television (HDTV). VDSL is not as widely deployed as other forms of DSL service. However, VDSL can achieve data rates up to approximately 51,840 Kbps, making it the fastest available form of DSL.

http://compnetworking.about.com/od/dsldigitalsubscriberline/l/bldef_vdsl.htm

http://www.wisegeek.com/what-is-sdsl.htm

http://www.xilinx.com/esp/wired/optical/collateral/DSL.pdf

http://en.wikipedia.org/wiki/Digital_subscriber_line

Chapter 12

ASYNCHRONOUS TRANSFER MODE

    Asynchronous Transfer Mode (ATM) is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that use variable sized packets or frames. ATM provides data link layer services that run over a wide range of OSI physical Layer links. ATM has functional similarity with both circuit switched networking and small packet switched networking. It was designed for a network that must handle both traditional high-throughput data traffic (e.g., file transfers), and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins. ATM is a core protocol used over the SONET/SDH backbone of the public switched telephone network (PSTN) and Integrated Services Digital Network (ISDN), but its use is declining in favour of all IP.

       Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.

      ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path.

            ATM creates a fixed channel, or route, between two points whenever data transfer begins. This differs from TCP/IP, in which messages are divided into packets and each packet can take a different route from source to destination. This difference makes it easier to track and bill data usage across an ATM network, but it makes it less adaptable to sudden surges in network traffic.

       Asynchronous Transfer Mode (ATM) represents a relatively recently developed communications technology designed to overcome the constraints associated with traditional, and for the most part separate, voice and data networks. ATM has its roots in the work of a CCITT (now known as ITU-T) study group formed to develop broadband ISDN standards during the mid-1980s. In 1988, a cell switching technology was chosen as the foundation for broadband ISDN, and in 1991, the ATM Forum was founded.

         The ATM Forum represents an international consortium of public and private equipment vendors, data communications and telecommunications service providers, consultants, and end users established to promote the implementation of ATM. To accomplish this goal, the ATM Forum develops standards with the ITU and other standards organizations.

       The first ATM Forum standard was released in 1992. Various ATM Forum working groups are busy defining additional standards required to enable ATM to provide a communications capability for the wide range of LAN and WAN transmission schemes it is designed to support. This standardization effort will probably remain in effect for a considerable period due to the comprehensive design goal of the technology, which was developed to support voice, data, and video on both local and wide area networks.

Benefits of ATM

      ATM provides a flexible and scalable solution to the increasing need for quality of service in networks where multiple information types (such as data, voice, and real-time video and audio) are supported. With ATM, each of these information types can pass through a single network connection.        

ATM can provide the following:

1.    High-speed communication

2.    Connection-oriented service, similar to traditional telephony

3.    Fast, hardware-based switching

4.    A single, universal, interoperable network transport

5.    A single network connection that can reliably mix voice, vedio, and data

6.    Flexible and efficient allocation of network bandwidth  

http://technet.microsoft.com/en-us/library/cc740081(WS.10).aspx

http://www.techfest.com/networking/atm/atm.htm

http://technet.microsoft.com/en-us/library/bb726929.aspx

http://www.webopedia.com/TERM/A/ATM.html

http://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode

     CHAPTER 11 ( FRAME RELAY )

             Frame Relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology. Network handles the transmission over a frequently-changing path transparent to all end-users. Has become one of the most extensively-used WAN protocols. Its cheapness (compared to leased lines) provided one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay's popularity.

             Frame Relay aimed to provide a telecommunication service for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame Relay puts data in variable-size units called "frames" and leaves any necessary error-correction (such as re-transmission of data) up to the end-points. This speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service-provider figures out the route each frame travels to its destination and can charge based on usage.

          Packet switching is a store and forward switching technology for queuing networks where user messages are broken down into smaller pieces called packets. Each packet has its own associated overhead containing the destination address and control information. Packets are sent from source to destination over shared facilities and use a statistical time−division multiplexing (TDM) concept to

share the resources.

           Fast packet switching is a combination of packet switching and faster networking using high−speed communications and low−delay networking. Fast packet is a "hold and forward" technology designed to reduce delay, reduce overhead and processing, improve speed, and reduce costs. It is designed to run on high−speed circuits with low (or no) error rates.

Frame Relay Speeds
          It is appropriate to discuss the speed that can be achieved with the use of Frame Relay. It was stated that Frame Relay was designed for speeds up to T−1/E−1 (1.544—2.048 Mbps); it later evolved to speeds of up to 50 Mbps. Actually, few end users have ever implemented Frame Relay at the higher speeds; this is more of a speed for the carrier community, but the need for stepped increments has always been a requirement for data transmission.


Frame Relay Access
         A link is installed between the end−user location and the network carrier's node. The normal link speed is T−1, although many locations can and do use Integrated Services Digital Network (ISDN) or leased lines at lower rates. Some customers may choose to install a local loop at speeds up to T−3(45Mbps approximately) to support higher−speed access and faster data throughput. The use of the T−3 will also allow for consolidation on the same link. Many of the carriers (and in particular the LECs) will offer the T−3 access and enable Frame Relay throughput atrates up to 37 or 42 Mbps.


   Provisioning PVCs and SVCs

        The primary difference between PVCs and switched virtual circuits (SVCs) is whether the connections are provisioned or established. Both types of connections need to be defined. The difference is when the connections are defined and resources allocated.The network operator typically provisions PVCs. The network operator can be the carrier (public services) or the MIS manager (private networks). Once the PVC is provisioned, the connection is available for use at all times unless there is a service outage.  

               

        SVCs are ideal for networks with highly meshed connectivity, highly intermittent applications, remote site access, and interenterprise communications. Each of these applications will be discussed in more detail in the succeeding slides. SVCs are also ideal for networks that are not primarily dependent on resources housed at a single location such as the headquarters site or at regional offices. In a nonhierarchical networking environment where there is a need to communicate
with many locations, SVCs can offer a viable solution.
       
  Advantages of SVCs
- magnified as the number of locations and the degree of connectivity requirements increase.
-Highly meshed networks are becoming more common as more and more companies deploy intranets.
-It isconceivable that all end users will have their own Web page within the corporation. This will
increase the amount of peer−to−peer intracompany traffic.



http://en.wikipedia.org/wiki/Frame_Relay