Chapter 18: MMDS and LMDS

Multichannel Multipoint Distribution Service (MMDS)

    MMDS (Multichannel Multipoint Distribution Service) is a Multichannel broadcast service that operates in the 2.0 to 2.9 GHz. Frequency range. It’s designed to be a point to multipoint broadcast service that is capable of delivering multiple channels of television programming for digital or analogue mode together with internet access, telephone and data transfer services to individual receive sites. Channels containing video, audio and data transmitter from a central site to individual residences, multiple dwelling units, and business locations. MMDS systems, which can be configured to offer just television, are commonly referred to as “Wireless Cable Television”.

Specifications of MMDS

Fixed/Mobile	Fixed
Circuit/Packet	n/a
Max Bandwidth	10Mb
Range	70 miles
Frequency	2.5GHz-2.686Ghz
Host Network	None
Definer	IEEE (Institute of Electrical and Electronic Engineers)

How does MMDS System work?

     The architecture of a typical wireless cable system can be divided into two basic nodes: transmitting sites and receiving sites. Transmitting sites are the main or “HUB” node of MMDS system.

     Programming information is generally delivered to an MMDS system from satellites, it can also be generated locally or come from pre-recorded video tapes, these signals are fed into discrete transmitters where they are modulated up converted and amplified. Transmitter powers range 1 to 200 watts per channel and 15 to 100 watts average power per digital channel, individual microwave channels are then multiplexed or combined together and are passed to a transmitting antenna via low loss coaxial cable or waveguide. A centrally located transmitting antenna radiates the MMDS signal to the desired receiving sites, generally in an omni directional (360 degrees) pattern.

Advantages of MMDS

     Construction of the MMDS transmit site can generally be accomplished in a few weeks to a few months whereas a conventional cable TV system may require in excess of three years. A conventional cable TV system requires a dedicated coaxial “wire” to be connected to each subscriber.

      Another advantage of an MMDS system is the picture quality. A properly designed MMDS system will deliver clear, distortion free pictures to each subscriber’s home. Since the signals do not have to pass through many kilometers of coaxial cable and numerous amplifier chains, the noise associated with typical cable systems is not introduced to MMDS signals. The overall result is better picture quality and greater subscriber satisfaction.

     The third advantage of an MMDS system is the reduced capital expenditure. The majority of the capital invested in an MMDS system is goes directly into the subscriber’s receive equipment. A minimal capital investment is required to install a transmit station. Therefore, as soon as a subscriber is installed, revenue is immediately generated.

    The fourth advantage of an MMDS system is greater reliability. Since conventional cable signals are delivered through many chains of line amplifiers, there is a greater chance for service interruptions (amplifiers are pole and strand mounted). MMDS electronic equipment is generally co-located, yielding much easier system maintenance. MMDS transmit sites are located in climate controlled equipment shelters for maximum performance and greater system reliability.

Local Multipoint Distribution Service (LMDS)

    It is a type of high-speed wireless internet transmission which works using microwaves. At one time, it was seen as a potential solution for expanding home broadband services, particularly in the united States. Today it appears somewhat outdated and has generally been over taken by rival technologies.

    The microwave used by the LMDS system are of a much higher frequency than radio waves. whereas most current wireless internet services broadcast on frequencies of around 2 to 3GHz, LMDS uses frequencies around 26 to 31GHz. The exact frequencies used vary from location to location and ranges may be limited by local regulation and licensing.

    The main uses of LMDS is a point-to-multipoint communication system. This Means that information can be transferred from one point, the local Station, to multiple users. Information transmitted back by any one user only goes back to the local station, rather than to all other users.

LMDS Specifications

Fixed/Mobile	Fixed
Circuit/Packet:	n/a
Max Bandwidth	1.5Gb downstream, 200Mb upstream
Range	4 miles
Frequency	27.5GHz-28.35Ghz, 29.1Ghz-29.25Ghz, 31.075Ghz-31.225Ghz, 31.Ghz-31.075Ghz, 31.225Ghz-31.3Ghz
Host Network	None
Definer	IEEE (Institute of Electrical and Electronic Engineers)

Advantages of LMDS Technology

    The biggest advantage of LMDS technology is derive from the wireless nature: it gave operators an opportunity to provide consumers with access bandwidth and two-way capability without digging up streets. This one fact that no right-of-way clearances are required to deploy it makes it sufficiently inclining as a technology. LMDS has huge chunks of under-utilized spectrum ready to go, more than to satisfy pent-up demand for voice, private data networks, and high speed internet access.

    In addition, this advantage has provided today cellular operators across the globe an economical way to quickly deploy cell sites to provide next generation of bandwidth intensive data services, beyond the traditional voice service.

Why LMDS?

    Point-to-point fixed wireless networks have been commonly deployed to offer high-speed dedicated links between high-density nodes in a network. More recent advances in a point-to-multipoint technology is that it offer service providers a method of providing high-capacity local access that is less capital-intensive than a wireline solution, faster to deploy than a wireline, and able to offer a combination of applications. Moreover, as a large part of a wireless network's cost is not incurred until the costumer premises equipment(CPE) is installed, the network services operator can time capital expenditures to coincide with the signing of new costumers. LMDS provides an effective last-mile solution for the incumbent service provider and can be used by competitive service providers to deliver services directly to end users. Benefit can be summarize as follows:

• Lower entry and deployment cost
• Ease and speed of deployment(system can be deployed rapidly with minimal disruption to the community and the environment).
• Fast realization of revenue(as a result of rapid deployment).
• Demand-based build-out.
• Cost shift from fixed to variable components.
• No stranded capital when costumers churn
• cost-effective network maintenance, management, and operating costs.

    Via the transmission of microwave signals, LMDS networks can provide two-way broadband services including video, high-speed internet access, and telephony services. LMDS leap frogs all the hurdles encountered when wired networks must be deployed. It  really could be the answer to the long sought solution to last mile broadband in the world. Breakthroughs in radio technology, along with increased industry confidence following the success of personal communication service(PCS) and cellular mobile service, have dramatically improved confidence in radio as a reliable local access technology. LMDS, as a technology is mature and reliable and delivers compelling advantages for adoption in the world.

Chapter 17: Microwave Based and Radio Based System

Microwave Radio Based System

     

     The term Microwave radio Based System refers to the electromagnetic energy having a frequency higher than 1 GHz, corresponding to wavelength shorter than 30cm. Microwave signals propagate in straight lines and are effected very little by the troposphere. they are not the refracted or reflected by ionized regions in the upper atmosphere. Microwave beams not really diffract around the barriers such as hills and large human made structures. some attenuation occurs when microwave energy through trees and frame bases.

Microwave Frequency Bands

    

Advantages and Disadvantages of Microwave Radio Based System

Advantages:

  1. Able to transmit Large Quantities of Data

    

        Microwave radio system have the capacity to broadcast great quantities of information because of their higher frequencies. They use repeaters a device that receives the transmitting signal through one antenna, converts it into an electrical signal and re transmits to large volumes of data over great distance. Microwave radio communication systems propagate signals through the earth's atmosphere. these signals are sent between transmitters and receivers that lie on top of towers. This allows microwave radio systems to transmit thousands of data channels between two points without relying on a physical transmitting medium.

  2. Relatively Low Costs

      Microwave communication systems have relatively low construction costs compared with other forms of data transmission, such as wire-line technologies. A microwave communication system does not require physical cables or expensive attenuation equipment.

Disadvantages:

  1. Line of Sight Technology

       Microwave Radio System are line of sight technology, meaning the signals will not pass through objects like mountains, buildings and airplanes. The drawback limits microwave communication system to line of sight operating distances. Signals flow between one fixed point to another, provided no solid obstacles disrupts the flow.

  2. Subject to Electromagnetic and Other Interference

      Microwave radio system are affected by electromagnetic interference(EMI). EMI is any disturbance that dis grades, obstructs or interrupts the performances of a microwave signals. Microwave signal disruption EMI is caused by electric motors, electric power transmission lines, wind turbines, TV/radio Stations and Cellphone transmission tower. Microwave radio communication is also affected by heavy moisture, snow and others.

Although Microwave Radio Based System can offer a good level of quality, convenience, resilience and security to integrator's and end users. This systems support safe, secure and speedy flow in traffic and people. The nature of the underpinning technologies leads to a different industries.

ATM and xDSL

Chapter 16: Digital Subscriber Line


Digital Subscriber Line(xDSL)


     Is the term for the Broadband Access technologies based on Digital Subscriber Line (DSL) technology, "x" signifies that there are various flavors of DSL. It provides always-on, high speed data services over existing copper wires to residences and businesses.

Line-length limitations on DSL signal transmission from the telephone exchanges speeds have resulted in many types of DSLs.

Types of DSL

DSL Type	Description	Data Rate Downstream; Upstream	Distance Limit	Application
IDSL	ISDN Digital Subscriber Line	128 Kbps	18,000 feet on 24 gauge wire	Similar to the ISDN BRI service but data only (no voice on the same line)
CDSL	Consumer DSL	1 Mbps downstream; less upstream	18,000 feet on 24 gauge wire	Splitterless home and small business service; similar to DSL Lite
DSL Lite (same as G.Lite)	"Splitterless" DSL without the "truck roll"	From 1.544 Mbps to 6 Mbps downstream, depending on the subscribed service	18,000 feet on 24 gauge wire	The standard ADSL; sacrifices speed for not having to install a splitter at the user's home or business
G.Lite (same as DSL Lite)	"Splitterless" DSL without the "truck roll"	From 1.544 Mbps to 6 Mbps , depending on the subscribed service	18,000 feet on 24 gauge wire	The standard ADSL; sacrifices speed for not having to install a splitter at the user's home or business
HDSL	High bit-rate Digital Subscriber Line	1.544 Mbps duplex on two twisted-pair lines; 2.048 Mbps duplex on three twisted-pair lines	12,000 feet on 24 gauge wire	T1/E1 service between server and phone company or within a company; WAN, LAN, server access
SDSL	Symmetric DSL	1.544 Mbps duplex; 2.048 Mbps  on a single duplex line   downstream and upstream	12,000 feet on 24 gauge wire	Same as for HDSL but requiring only one line of twisted-pair
ADSL	Asymmetric Digital Subscriber Line	1.544 to 6.1 Mbps downstream; 16 to 640 Kbps upstream	1.544 Mbps at 18,000 feet; 2.048 Mbps at 16,000 feet; 6.312 Mpbs at 12,000 feet; 8.448 Mbps at 9,000 feet	Used for Internet and Web access, motion video, video on demand, remote LAN access
RADSL	Rate-Adaptive   DSL	Adapted to the line, 640 Kbps to 2.2 Mbps downstream; 272 Kbps to 1.088 Mbps upstream	Not provided	Similar to ADSL
UDSL	Unidirectional DSL	Not known	Not known	Similar to HDSL
VDSL	Very high Digital Subscriber Line	12.9 to 52.8 Mbps downstream; 1.5 to 2.3 Mbps upstream; 1.6 Mbps to 2.3 Mbps downstream	4,500 feet at 12.96 Mbps; 3,000 feet at 25.82 Mbps; 1,000 feet at 51.84 Mbps	ATM networks; Fiber to the Neighborhood

Asymmetric Digital Subscriber Line (ADSL)

is a technology for transmitting digital information at a high bandwidth on existing phone lines to homes and businesses. Unlike regular dial up phone service, ADSL provides continuously-available,"always on" connection. ADSL is asymmetric in that it uses most of the channel to transmit downstream to a user and only a small part to received information from the user.

ISDN Digital Subscriber Line (IDSL)

is a system in which digital data is transmitted at 128 Kbps on a regular copper telephone line from user to a destination using digital transmission, bypassing the telephone company's central office equipment that handles analog signals. IDSL uses the ISDN Basic rate Interface in ISDN code transmission.

High Bit-rate Digital Subscriber Line (HDSL)

One of the earliest form 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 direction.

Symmetric Digital Subscriber Line (SDSL)

is similar to HDSL with a single twisted-pair line, carrying 1.544 Mbps or 2.048Mbps each direction on a duplex line. It's symmetric because the data rate is the same in both direction. 

Rate Adaptive Digital Subscriber Line (RADSL)

a technology in which software is able to determine the rate at which signal can be transmitted on a given customer phone line and adjust the delivery rate accordingly. RADSL delivers from 640 Kbps Downstream and from 272Kbps to 1.088Mbps upstream over an existing line.

Consumer Digital Subscriber Line (CDSL)

It is somewhat slower than ADSL (1Mbps downstream and less upstream) and has the advantage that a "splitter" does not need to be installed at the user's end.

Symmetric High-bit rate Digital Subscriber Line (SHDSL) or (G.lite DSL)

Provides for sending and receiving high-speed symmetrical data stream over a single pair of copper wires at rates between 192 Kbps and 2.31 Mbps.

Very High-bit rate Digital Subscriber Line (VDSL)

transmits data in 13Mbps - 55 Mbps range over short distance, usually between 1000 and 45000 feet, of twisted pair copper wire. the shorter distance, the faster the connection rate.

ATM and xDSL

Chapter 12: 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. 

     Because ATM is designed to be easily implemented by hardware , faster processing and switch speed are possible. The prespecified bit rates are either 155.520 MBps or 622.080Mbps. Speeds on ATM networks can reach 10 Gbps. Along with Synchronous Optical Network(SONET) and other technologies, ATM is a key component of Broadband ISDN(BISDN).




Comparing Network Features

Feature	Data    Communications	Telecommunications	ATM
Traffic support	Data	Voice	Data, voice, video
Transmission unit	Packet	Frame	Cell
Transmission length	Variable	Fixed	Fixed
Switching type	Packet	Circuit	Cell
Connection type	Connectionless or Connection-oriented	Connection-oriented	Connection-oriented
Time sensitivity	None to some	All	Adaptive
Delivery	Best effort	Guaranteed	Defined class or guaranteed
Media and operating rate	Defined by protocol	Defined by class	Scalable
Media access	Shared or dedicated	Dedicated	Dedicated

ATM provides a mechanism for merging voice data and video onto LANs, CANs, MANs and WANs. you can gain an appreciation for how ATM accomplishes this by learning about its architecture.




Why does ATM uses cells?




Consider a speech signal reduced to packets, and forced to share a link with burst data traffic. No matter how small the speech packets could be made, they would have always encounter full size data packets, and under normal queuing conditions, might experience maximum queuing delays. That is why all packets or cells should have the same small size. in addition the fixed cell structure means that ATM can be always readily switched by hardware without the inherent delays introduced by the software switched and routed frames.




ATM SERVICES

Guarantees	ATM Service Feedback	Metrics	Loss	Delay	Bandwidth
Constant Bit Rate (CBR)	PCR, CDVT	Yes	Yes	Yes	No
Variable Bit Rate–Real Time (VBR–RT)	PCR, CDVT, SCR, BT	Yes	Yes	Yes	No
Variable Bit Rate–Non-Real Time (VBR-NRT)	PCR, CDVT, SCR, BT	Yes	Yes	Yes	No
Unspecified Bit Rate (UBR)	Unspecified	No	No	No	No
Available Bit Rate (ABR)	PCR, CDVT, MCR	Yes	No	Yes	Yes

Legend:


PCR = Peak Cell Rate
CDVT = Cell Delay Variation Tolerance
SCR = Sustained Cell Rate
BT = Burst Tolerance
MCR = Minimum Cell Rate




ATM Layered Architecture

Application Layer
User Layers
ATM Adaptation Layer:	Convergence Sublayer
	Segmentation and Reassembly Sublayer
ATM Layer
Physical Layer:	Transmission Convergence Sublayer
	Physical Medium Dependent Sublayer

The Physical Layer defines the medium for transmission, any medium-dependent parameters, and framing used to find the data contained within the medium.


The ATM Layer provides the basic 53-bytes cell format, by defining the 5-byte ATM header for each 48-byte payload segment handed down by the ALL.


The ATM Adaptation Layer adapts the higher level data into  formats compatible with the ATM Layer requirements; this layer segments the data and adds appropriate  error control information as necessary. It is dependent on the type of services being transported by the higher layer.




Several AAL protocols have been defined for specific types of data. these are loosely associated with the various classes of data. however, no AAL is restricted to a specific data class or type, all types of data could conceivable be handled by any of the AALs.


AAL 1


     Constant bit rate, connection-oriented, synchronous traffic.


AAL 2


    Definition never completed undefined, but envisioned to be for variable bit rate, connection-oriented,synchronous traffic.


AAL 3/4


    Variable bit rate,connection-oriented,asynchronous traffic or connectionless packet data with an additional 4 byte header in the information payload of the cell.


AAL 5


   Similar to AAL 3/4 with a simplified information header scheme that requires only one header per data unit and uses the PTI bit to indicate the last cell in a transmission. AAL 5 is the most widely used ATM Adaptation Layer Protocol.




5-byte Header ATM Cell

8	7	6	5	4	3	2	1
Generic Flow Control				Virtual Path Identifier
Virtual Path Identifier				Virtual Channel Identifier
Virtual Channel Identifier
Virtual Channel Identifier				Payload Type ID		CLP
Header Error Control
INFORMATION PAYLOAD

Generic Flow Control(GFC)


    The GFC field of the Header is only defined across the UNI. It is intended to control the traffic flow across the UNI to alleviates short term overload conditions. It is currently undefined and these 4 bits must be set to 0's.


Virtual Path Identifier(VPI)


    The VPI, an 8 bit field for the UNI and 12 bit for NNI, is used to identify virtual paths. In an idle cell, the VPI is set to all 0's.


Virtual Channel Identifier(VCI)


    This 16 bit field is used to identify a virtual channel. For idle cells, the VCI is set to all 0's. Together with the VPI, the VCI provides a unique local identification for the transmission.


Payload Type Identifier(PTI)


   The 3 bit for PTI are used for different purposes. Bit 4 is set to 1 to identify operation, administration, or maintenance cells. Bit 3 is set to 1 to indicate that congestion was experienced by a data cell in transmission and is only valid when bit 4 is set to 0. Bit 2 is used by AAL 5 to identify the data as type 0 when bit 4 is set to 0.


Cell Loss Priority(CLP)


   The 1 bit CLP field is used for explicit indication of the priority of the cell. It may be set by the AAL Layer to indicate cells to discard in cases of congestion, or by the network as part of the traffic management on commercial subscriber networks.


Header Error Control(HEC)


   The HEC is compared by each Switch as the ATM cell is received and all cells with HEC discrepancies are discarded. Cells with a single bit error may be subject to error correction.