MMDS and LMDS

Chapter 18: MMDS and LMDS

Multichannel Multipoint Distribution System (MMDS)

             MMDS has been around since 1970s. This is another technology for wireless broadcasting to internet access. TV transmission has been using MMDS for more than 30 years. MMDS is using terrestrial-based radio transmission located at a highest location in a metropolitan to deliver its service. Every MMDS subscriber has a small, exclusive, digital receiver placed at the location that is at the line of sight to the transmitters.  MMDS  operates at higher portion of  the spectrum called the ultra high frequency which ranges from 2.1-2.7 Ghz. MMDS has been known as the substitute for cable television though there are some applications like Telephone/fax and data transmission that MMDS also has. MMDS is using omni-directional antenna located at the higher topographic that is intended to cover the area below which MMDS can transmit data. MMDS can run to license and unlicensed channel which can come in 6MHz chunks and has a transfer rate that would reach 27Mbps or up to 1Gbps when over licensed channels. It has a workable radius that is 70 miles in a flat terrain and significantly less in mountainous or in a hilly areas.

MMDS simple Topology:

               MMDS is known for its precise, clearer and wide-ranging signal coverage which is ideal to have in any provider. There are some instances that weather interferes with the provider; MMDS can protect users to that. Many of the carriers use a super-cell concept with a service area spanning a 35 mile radius from each of its MMDS transmitters. There are 33 analog video channels with 6MHz wide that MMDS originally consist of but now as the technology evolves video channels can now turn into digital and would convert these to 99 channels. The combination of super cells and sectors enable the carrier to reuse the same frequency many times by building multiple cell sites.

When enough customers sign on and as their bandwidth demands grow, the growth in traffic can be handled expeditiously through a new cell or a new sector

Architecture for MMDS

LMDS

LMDS (Local Multipoint Distribution Service) is a broadband wireless point-to-multipoint specification utilizing microwave communications.

LMDS operates on FCC licensed frequencies. The FCC divided the United States into 493 BTA's (Basic Trading Areas) and auctioned the rights to transmit on the LMDS bands in each of those areas to LMDS service providers. Each BTA is licensed to two LMDS service providers. 

What is LMDS?

The term LMDS stands for Local Multipoint Distribution Service. LMDS uses microwave signals to transmit voice, video, and data signals using low power which can reach distances no greater than a five mile range. It is a wireless broadband service that relies on microwave radios to send large amounts of information between each of the radios at very high speeds. It operates between the 28Ghz & 29Ghz bands (Specifically): 27.50Ghz - 28.35Ghz & 29.10Ghz - 29.25Ghz & 30.00Ghz & 31.075Ghz - 31.225Ghz. 

How does LMDS work?

Microwave radios designed to be used with LMDS are installed at two separate sites which are within a five mile range of each other. One of the radios is installed at the LMDS Hub or station and the other is installed at the customers site. The two radios can then transmit very large amounts of information between the two locations. The Hub or station is located at a key position to interface directly with land line fiber optic backbones as well as standard telephony. Video conferencing, Voice, Data, Internet access, and TV signals can all be provided even at the same time through this wireless service.

Why would I want to use LMDS?

One situation might occur when a large company has buildings which are spread out over a campus. However, a portion of the campus is divided by a freeway. In this example it is not cost effective to be able have land lines installed under the freeway to allow communication to the other half of the campus. LMDS radios can be installed on either side of the freeway to enable communications which were previously not feasible. In addition, the radios can be installed on each building throughout the campus to have direct communication internally rather than using the local phone company.

Another situation that may occur is a new high rise that is in need of fiber optic service. However, the building is far from the localfiber ring and it would take a large amount of money and over a year to have it installed. LMDS radios can be installed in as little as a weeks time and can provide fiber optic like services.

Viginia Tech purchased LMDS licenses and partnered with an equipment provider and has systems running.

M-R-R-S

Chapter 17: Microwave and radio Based System

History for Microwave

Percy Spencer open an idea for microwave. Under the company name Raytheon Company, Spencer discover the idea of  using microwave in preparing food. This idea that Percy Spencer has become big after the World War II. The microwave oven was that was invented by Percy Spencer has developed and become widely used in Radio systems.It become hit at the world market that has been expected to grow its market in global will reach to approximately $10 billion in 2006.Microwave has also become a vital link in the overall backbone networks over the years.

Microwave

A microwave is ranges from 3-300Ghz which is the high way for any wireless data communication. Over the years, radio communication is the most common use for wireless communication and it is using the free space or the frequency spectrum. In radio and telecommunications, the frequency spectrum can be shared among many different broadcasters. Each broadcast radio and TV station transmits a wave on an assigned frequency range, called a channel. When many broadcasters are present, the radio spectrum consists of the sum of all the individual channels, each carrying separate information, spread across a wide frequency spectrum


As the wireless communication progresses though years, the spectrum that is suppose to transport data in wireless could be over populated. The engineers were able to use the idea that Raytheon company was first been developed, the microwave oven by Percy Spencer. Engineers uses the idea that was implemented in microwave oven and make it as the solution for the frequency spectrum problem. Microwave radio communication provide a much higher spectrum to be use for data transmission. Microwave communication is known as a form of "line of sight" communication, because there must be nothing obstructing the transmission of data between these towers for signals to be properly sent and received.




Microwave communication has a wide bandwidth that  VHF cant provide. Microwave could have a multiple channels to accumudate and this is one way to lessen the traffic happening in the spectrum.  It also has no cable use that it could transmit data even way far in distance. Though microwave has its own delimitation or the scope where as microwave could not be able to penetrate against any obstacle like buildings, mountains, and other stuff.  In many situations, microwave systems provide more reliable service than land lines, which are vulnerable to everything including flooding, rodent damage,backhoe cuts, and vandalism. Using a radio system, a developing country without a wired communications infrastructure can install a leading−edge telecommunications system within a matter of months. For these reasons, regions with rugged terrain or without any copper land-line backbone in place find it easier to leap into the wireless age and provide the infrastructure at a fraction of the cost of installing wires.

xDSL

Chapter 16: xDSL




What is xDSL?


 The term DSL is an acronym for Digital Subscriber Lines and the term xDSL is the name of the family that provide technology for digital data transmission through the network over the wires of the local telephone network, which are usually made up of copper wires. 

• Asymmetrical digital subscriber line (ADSL)
• ISDN (like) digital subscriber line (IDSL)
• High bit−rate Digital Subscriber Line (HDSL)
• Consumer Digital Subscriber Line (CDSL)
• Single High Speed DSL (SHDSL)
• Rate−adaptive digital subscriber line (RADSL)
• Very high−bit rate digital subscriber line (VDSL)
• Single or symmetric digital subscriber line (SDSL)

The two main categories of this xDSL are ADSL or Asymmetric Digital Subscriber Line and SDSL or Symmetric digital subscriber line. Apart from these two major categories, there are two other types of categories present in the market as well, named HDSL or High Data Rate DSL and VDSL or Very High DSL. These two types of the DSL are quite expensive and are installed only in the large sized enterprise, as they installation and the operational costs are both high. The most common type of the DSL that is used by many people throughout the world is ADSL, as it is cheaper and the operational costs are also low.

This DSL technology basically pack the data on to the copper wire by using a sophisticated modulation technique and schemes and this technology is only used for connection from the telephone lines to homes and offices but not for providing connections between the switching stations. This xDSL technology is quite similar to the ISDN technology as they both operate on the copper wires and both require the short run to the telephone office. However, the major difference between these two lies in the matter of speed.

The xDSL technology is capable of giving speed up to 32 Mbps for upstream traffic and max speed of 1 Mbps for the downstream traffic. This technology is currently undergoing revision and it is quite possible that the speed that this technology has to offer to the users might even increase drastically, after all the main thing is loading the cables with the data packets with the help of modulation schemes.

What is a Modem?

 A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device.

Why do the DSL technology needs modem technology?

A modem is a communications device that can be either internal or external to your computer. It allows one computer to connect another computer and transfer data over telephone lines. The original dial-up modems are becoming obsolete because of their slow speeds and are being replaced by the much faster cable and DSL modems. The modem acts as the Data Circuit terminating Equipment (DCE) for the link.The modem then converts the data from a computer terminal into a voice−equivalent analog signal.Newer technologies will produce much higher compressed speeds of up to 230 to 300 Kbps on a modem, but these are now in their infancy. They are not a major factor in our communications networks yet.

The figure above are the modems that are installed at the customer's location and use the existing telephone wires to transmit data across the voice network.

There are types of Modems 

1. Analog dial-up modem, came with all laptops until 2-3 years ago. Used for dial-in connections ONLY. Not needed much anymore with Wireless and Ethernet connections. If you have dial-in and NO modem you can always buy a USB modem.

2. Cable/DSL Modem. By far far the most used today Required for Cable or DSL service. It is an EXTERNAL device not part of the computer. It will convert the signal to either a USB output, Ethernet output or a wireless output or a combination of all three (depending on the modem you get.)
All you need to connect a Cable/DSL modem to your computer is an Ethernet port. (Wide Phone jack) or a USB connection. Use Ethernet port if available (Greater Speed)
You can also connect wireless if you have a wireless modem
and a wireless card in the computer. 

This is HDSL is impervious to the bridge and splices. The T1 is split onto two pairs.

As already mentioned, HDSL runs at 1.544 Mbps (T1 speeds) in North America and at 2.048 Mbps

(E1 speeds) in other parts of the world. Both speeds are symmetric (simultaneous in both

directions). Originally, HDSL used two wire pairs at distances of up to 15K. HDSL at 2.048 Mbps

uses three pairs of wire for the same distances, but no longer. The most recent version of HDSL

uses only one pair of wire and is expected to be more accepted by the providers. Nearly all the

providers today deliver T1 capabilities on some form of HDSL.

xDSL Coding Techniques

There are a lots of approaches that the xDSL has in encoding the data. One of that is the Carrierless Amplitude Phase Modulation (CAP) and the Discreet multitone (DMT) modulation. another technique that the xDSL has is the Quadrature with Phase Modulation (QAM).  The industry, as a rule, selected DMT, but several developers and providers have used CAP. It is, therefore, appropriate to summarize both of these techniques. The SHDSL technology uses a trellis−coded pulse amplitude modulation (TCPAM) technique to gain the benefits of the single−pair services or two−pair service.

Asynchronous Transfer Mode

Chapter 12: Asynchronous Transfer Mode (ATM)

The Origin of ATM

The ATM platform enables multimedia transmission via fixed-sized 53-byte packets called cells in network environments ranging from desk area networks (DANs) to global implementations. The term  Asynchronous refers to ATM support of intermittent bit rates and traffic patterns in accordance with actual demand. The phrase  Transfer Mode  denotes ATM multiplexing capabilities in transmitting and switching multiple types of network traffic.

Bell Labs initiated work on ATM research projects in the 1960s and subsequently developed cell relay technology and cell switching architecture for handling bursty transmissions. Originally, ATM was called Asynchronous Time-Division Multiplexing (ATDM) and regarded as a successor to TDM (Time-Division Multiplexing). As with TDM, ATDM supports transmission of delay-sensitive and delay-insensitive traffic. TDM and ATDM assign each fixed-sized cell or information packet to a fixed timeslot. By contrast, ATM supports dynamic allocation of timeslots to cells ondemand. In comparison to ATM, TDM and ATDM protocols are limited in optimizing utilization of available bandwidth for effectively handling volume-intensive multimedia applications.

What is Asynchronous Transfer Mode (ATM)?

 An  ATM or the Asynchronous Transfer Mode is one of the fast packet-switching family called cell relay. ATM demands for its  fast and dependable access to Web-based applications and real-time delivery of multimedia transmissions.  ATM is a statistical time−division multiplexed(STDM) form of traffic that is designed to carry any form of traffic and enables the traffic to be delivered asynchronously to the network. The time-division multiplex is mainly the concept in functioning an ATM. ATM using STDM that enable to have a smooth traffic that the previous chapters was sighted as a problem.

The figure below is showing how ATM uses the TMD:

The purpose of ATM 

ATM technology employs a priority switching technique for enabling ATM cells carrying delay-sensitive signals to access the first available timeslot. Because the ATM cell size is fixed and the buffer memory size is constant for each cell, switch queuing delays are predictable and jitter or the variation in signal delay is minimized. By contrast, signal delays degrade performance of real-time applications such as videoconferencing and interactive video-on-demand (IVOD) in networks such as Frame Relay (FR) and Ethernet that transport variable length packets.

What is ATM Cell

ATM networks employ a standard, fixed-size 53-byte cell comprised of a 5-byte header and a 48-byte payload or information field as the basic unit of transmission. The 5-byte header includes an error detection field and a Virtual Channel Identifier (VCI) or Virtual Path Indicator (VPI) for transporting a cell payload to a destination address.

Through utilization of a common cell format, ATM enables real-time services, public and private network interconnectivity, and global interoperability. ISDN employs STDM (Statistical Time-Division Multiplexing) for enabling transmission of frames via designated timeslots at specified intervals. In contrast to ISDN installations, the ATM protocol supports dynamic allocation of timeslots to cells on-demand for optimizing traffic throughput in high-performance network configurations.

ATM technology employs a priority switching technique for enabling ATM cells carrying delay-sensitive signals to access the first available timeslot. Because the ATM cell size is fixed and the buffer memory size is constant for each cell, switch queuing delays are predictable and jitter or the variation in signal delay is minimized. By contrast, signal delays degrade performance of real-time applications such as videoconferencing and interactive video-on-demand (IVOD) in networks such as Frame Relay (FR) and Ethernet that transport variable length packets.

The ATM Forum defines procedures for monitoring the effectiveness of network transmission based on cellular throughput. Cell Loss Ratio (CLR) describes the percentage of cells that are not transported to their destination addresses as a consequence of buffer overloads and network congestion. Cell Transfer Delay (CTD) refers to propagation and queuing delays experienced by cells transiting the network.
Cell Delay Variation (CDV) measures variations in transmission delay between adjacent cells. Minimum Cell Rate (MCR) refers to the lowest cell rate supported by ABR (Available Bit Rate) service. In addition, metrics for Cell Delay Variation Tolerance (CDVT) and parameters for Maximum Cell Transfer Delay (MCTD) are also defined. The effectiveness of QoS delivery in ATM networks depends on such variables as Cell Transfer Delay (CDT) and Cell Delay Variation (CDV).

ATM Protocols

ATM is a complex cell multiplexing and switching technology. This chapter provides a high-level introduction to ATM technical attributes, features, and functions. Representative ATM implementations that support a diverse and powerful mix of applications are examined. Wireless ATM (WATM) configurations are described, and the capabilities of next-generation ATM networks are explored.


The ATM layer is responsible for relaying cells from the Architectural Area Lighting (AAL) to the physical layer for transmission and from the physical layer to the AAL for use at the end systems, it determines where the incoming cells should be forwarded to, resets the corresponding connection identifiers and forwards the cells to the next link, as well as buffers cells, and handles various traffic management functions such as cell loss priority marking, congestion indication, and generic flow control access. It also monitors the transmission rate and conformance to the service contract (traffic policing).


The physical layer of ATM defines the bit timing and other characteristics for encoding and decoding the data into suitable electrical/optical waveforms for transmission and reception on the specific physical media used. In addition, it also provides frame adaptation function, which includes cell delineation, header error check (HEC) generation and processing, performance monitoring, and payload rate matching of the different transport formats used at this layer. SONET , DS3, Fiber, twisted-pair are few media often used at the physical layer.

Frame Relay

Chapter 11: Frame Relay


A frame relay is a telecommunication service designed 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 a variable-size unit called a frame and leaves any necessary error correction (re-transmission of data) up to the end-points, which 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. An enterprise can select a level of service quality - prioritizing some frames and making others less important. Frame relay is offered by a number of service providers, including AT&T. Frame relay is provided on fractional T-1 or full T-carrier system carriers. Frame relay complements and provides a mid-range service between ISDN, which offers bandwidth at 128 Kbps, and Asynchronous Transfer Mode(ATM), which operates in somewhat similar fashion to frame relay but at speeds from 155.520 Mbps or 622.080 Mbps.

• Virtual circuits consume bandwidth only when they transport data. Consequently, many virtual circuits can exist across a given transmission line, which is an improvement compared to dedicated leased lines. In addition, each device can use more than the allowed bandwidth as necessary, and thus operate at higher speeds.
• The increased error-handling sophistication at end stations and the improved reliability of communication lines allows the Frame Relay protocol to discard bad frames and thus eliminate time-consuming error-handling processing.

Frame relay is based on the older X.25 packet-switching technology which was designed for transmitting analog data such as voice conversations. Unlike X.25 which was designed for analog signals, frame relay is a fast packet technology, which means that the protocol does not attempt to correct errors. When an error is detected in a frame, it is simply "dropped." (thrown away). The end points are responsible for detecting and retransmitting dropped frames. (However, the incidence of error in digital networks is extraordinarily small relative to analog networks.)

Frame relay is often used to connect local area networks with major backbones as well as on public wide area networks and also in private network environments with leased lines over T-1 lines. It requires a dedicated connection during the transmission period. It's not ideally suited for voice or video transmission, which requires a steady flow of transmissions. However, under certain circumstances, it is used for voice and video transmission.

Frame Relay Structure

Standards for the Frame Relay protocol have been developed by ANSI and CCITT simultaneously. The separate LMI specification has basically been incorporated into the ANSI specification. The following discussion of the protocol structure includes the major points from these specifications.

The Frame Relay frame structure is based on the LAPD protocol. In the Frame Relay structure, the frame header is altered slightly to contain the Data Link Connection Identifier (DLCI) and congestion bits, in place of the normal address and control fields. This new Frame Relay header is 2 bytes in length and has the following format:

 How does Frame Relay differ from other Techniques?


The biggest difference in frame Relay from other techniques is the use of Virtual Connections rather than Static Connections. As shown before, each location can have one port into a Frame Relay Network. From this port, it can have multiple Virtual Connections to various locations. It can make multiple redundant connections possible through the use of PVC's between various routers, without having to use multiple physical links.
Also, since Frame relay is not media specific, and offers a way to buffer speed differences, it can make a good interconnect medium between various devices that run at various speeds.
The multiplexed nature of Frame Relay facilitates especially the transmission of Bursty Traffic. In a traditional fixed-bandwidth multiple connection scenario, a lot of bandwidth will be wasted at most times, since it is not actually being used. The bandwidth on frame is shared, allowing for multiple bursts to be handled sequentially, therefor allowing better utilization of bandwidth. The chance of congestion is however also greater, since the bandwidth in the Frame Relay Port may become a bottleneck.
frame Relay pricing is where things really get different: From the above discussion we know there are two elements to Frame Relay, the Access Port and the Private Virtual Circuits. Per port, we can feed as many circuits as we please (up to the equipment's limit..). The price of the port depends on it's bandwidth. A bigger port costs more money. The price of a PVC is fixed, and not dependent on bandwidth or usage. Data sent over the Frame Connection is not subject to additional charges. The interesting part about this pricing is that there is no distance charge involved. A Frame Relay Access Port is expensive. Two frame ports between two cities are usually also more expensive than a direct T-1 as long as there is only a one or two LATA Hop, say for example Knoxville to Nashville. However, when you feed multiple cities and Hop multiple Lata's, a Frame solution is an attractive one. In local traffic, Frame becomes attractive when you feed a large number of connections, at Fractional T-1 bandwidth generally 8 or more.

What is frame relay useful for?

Frame Relay can be used for various types of connections. It should be seen as a flexible protocol that lies on the Data Level of the Connections between routers. It can currently be used effectively for carrying all sorts of data, up to speeds of about 4 megabits per second.

Due to the implementation and cost of frame relay, it is most suitable for permanent or semi-permanent connections. It is not desirable as of yet to access frame relay on a dialup basis for economical purposes.

For a number of U.S. Internet clients, use of Frame Relay may allow for the connection of various remote sites using one technology. It is possible to connect the clients router to Frame Relay and access Internet Services over this circuit. At the same time, if the customer has other Frame Relay ports available in different locations, the same port may be used to connect to Wide Area offices the client has. This integrated approach can be attractive for both parties; from one Frame port, U.S. Internet can connect multiple customers. At the same time, the client can connect to multiple remote locations using the one port. Although there is a greater chance of connection then when dedicated lines are used, the economical advantage will in most cases compensate for this.

Typical Topology for Frame Relay:








souces link:

en.wikipedia.org/wiki/Frame_Relay 
www.protocols.com/pbook/frame.htm
www.alliancedatacom.com/fra... - Estados Unidos
www.arcelect.com/frame_relay-56kbps_ft1-t1...