Alice in Telecomland

Fiber to the x (FTTX) is a generic term for any network architecture that uses optical fiber to replace all or part of the usual copper local loop used for telecommunications where “X” stands for termination point.The increased bandwidth demand in turn creates interest in deploying more fiber to the home (FTTX) equipment. FTTX offers much greater bandwidth than other broadband technologies such as DSL, VDSL and Cable Modems also it is more reliable and secure and has the longest life span then any other transmission system. The three main technologies are,

• Fiber to the node / neighborhood (FTTN) / Fiber to the cabinet (FTTCab)
• Fiber to the curb (FTTC) / Fibre to the kerb (FTTK)
• Fiber To The Premises
• Fiber to the building (FTTB)
• Fiber to the home (FTTH)

FIBER TO THE NODE

Fiber to the node (FTTN), also called fiber to the neighborhood or fiber to the cabinet (FTTCab), is a telecommunication architecture based on fiber-optic cables run to a cabinet serving a neighborhood. Customers connect to this cabinet using traditional coaxial cable or twisted pair wiring. The area served by the cabinet is usually less than 1,500 m in radius and can contain several hundred customers. Fiber to the node allows delivery of broadband services such as high speed internet. High speed communications protocols such as broadband cable access or some form of DSL are used between the cabinet and the customers. The data rates vary according to the exact protocol used and according to how close the customer is to the cabinet.
Unlike the competing fiber to the premises (FTTP) technology, fiber to the node can use the existing coaxial or twisted pair infrastructure to provide last mile service. For this reason, fiber to the node costs less to deploy. However, it also has lower bandwidth potential than fiber to the premises.

FIBER TO THE CURB

Fiber to the curb (FTTC), also called fibre to the kerb (FTTK), is a telecommunications system based on fiber-optic cables run to a platform that serves several customers. Each
of these customers has a connection to this platform via coaxial cable or twisted pair.
Fiber to the curb allows delivery of broadband services such as high speed internet. High speed communications protocols such as broadband cable access (typically DOCSIS) or some form of DSL are used between the cabinet and the customers. The data rates vary according to the exact protocol used and according to how close the customer is to the cabinet.
FTTC is subtly distinct from FTTN. The chief difference is the placement of the cabinet. FTTC will be placed near the “curb” but not fully to the customer’s residence which differs from FTTN which is placed far from the customer.
Unlike the competing fiber to the premises technology, fiber to the curb can use the existing coaxial or twisted pair infrastructure to provide last mile service. For this reason, fiber to the curb costs less to deploy. However, it also has lower bandwidth potential than fiber to the premises.

FIBER TO THE PREMISES

Fiber to the premises (FTTP) is a form of fiber-optic communication delivery in which an optical fiber is run directly onto the customers’ premises
Fiber to the Building (FTTB) is the deployment of fiber (optical) cable to a specific location within a building, then connected to the buildings existing copper, cable facilities. This deployment is also referred to as FTTB (Fiber to the Basement) & FTTB (Fiber to the Business).
Fiber to the Home (FTTH) is the complete deployment of fiber to the customer’s home, with replacement of there existing NID (Network Interface Device). This replacement device is called an ONT (Optical Network Terminator).

TECHNOLOGIES

The two main technologies used for these architectures are;
1. VDSL
2. PON

• VDSL

VDSL is commonly used as the last mile solution for Fiber-to-the-premise and allow premises to enjoy fiber speed connection. It solves the problem of hard-to-wire environment where fiber is hard to bend and install in building environment. VDSL improves on data rate and longer distance where Ethernet connection will deteriorate in data rate as distance is increased. VDSL connection running on normal telephone line can preserve that loss as distance increases. VDSL is the newest and most advanced standard of DSL broadband wire line communications designed to support the wide deployment of Triple Play services such as voice, video, data, high definition television (HDTV) and interactive gaming. It has been standardized as ITU G.993.2.

• PON

A passive optical network is a point-to-multi-point architecture for delivering last-mile connectivity without any active components in the distribution network. No powered equipment means less cost, less network management, longer reach and no need for an upgrade. A PON configuration reduces the amount of fiber and central office equipment required compared with point to point architectures.

As to increase the Band width by providing high-speed file sharing, High Definition Television, video-on-demand and other high-speed services increase. Using passive optical networking (PON) results in bandwidth improvements that are orders of magnitude greater than today’s broadband technologies.

The three main elements in the PON networks are the Optical Line Terminal (OLT), the passive optical splitters, and the Optical Network Terminal (ONT). The OLT at the central office connects the subscriber’s local loop to the network. A Splitter divides the single line into 32 equal channels. The ONT provides the interface between the optical network and the home/business.

OPTICAL NETWORK COMPONENTS

Optical Line Terminal (OLT) is the networks control card. This card resides in the local CO (Central Office) cross connected to the video and data networks that will be delivered to your home. This control card handles traffic from 32 subscribers

Fiber Distribution Hub (FDH) is the cross point for the Fiber CO Trunk and Distribution Fiber to the individual homes. Generally be the 144 / 216 user format

Optical Network Terminal (ONT) is an Optical to Electrical to Optical device that delivers your triple play services. It will replace your existing copper NID (Network Interface Device).

Optical Network Unit (ONU) is a transceiver at the subscriber premise. It contains 12 - 24 POTS Lines.

Signaling System Number 7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world’s public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls. Other uses include number translation, prepaid billing mechanisms, short message service (SMS), and a variety of other mass market services

There are two essential components to all telephone calls. The first, and most obvious, is the actual content—our voices, faxes, modem data, etc. The second is the information that instructs telephone exchanges to establish connections and route content to an appropriate destination. SS7 is designed to operate in two modes:

• Associated Mode
• Quasi-Associated Mode

When operating in the Associated Mode, SS7 signaling progresses from switch to switch through the PSTN following the same path as the associated facilities that carry the telephone call. This mode is more economical for small networks.

When operating in the Quasi-Associated Mode, SS7 signaling progresses from the originating switch to the terminating switch following a path through a separate SS7 signaling network composed of STPs. This mode is more economical for large networks with lightly loaded signaling links.

SS7 clearly splits the signaling planes and voice circuits. An SS7 network has to be made up of SS7-capable equipment from end to end in order to provide its full functionality. The network is made up of several link types (A, B, C, D, E, and F) and three signaling nodes - Service switching point (SSPs),
- Signal transfer point (STPs),
- Service Control Point (SCPs).

Each node is identified on the network by a number, a point code. Extended services are provided by a database interface at the SCP level using the SS7 network. The links between nodes are full-duplex 56, 64, 1,536, or 1,984 kbit/s graded communications channels.

Route Management

This function provides a means for rerouting traffic around failed or congested nodes. Route management works together with link management. Route management informs other nodes of the status of the affected node. It uses Message Signal Units (MSUs) generated by adjacent nodes and is not usually generated by the affected nodes.

Traffic Management

This function provides flow control if a node has become congested. It allows the network to control the flow of certain messages based on protocol. Traffic management deals with a specific user part within an affected node.

Message Routing

Message discrimination will pass messages to message routing if it determines the message is not local. Message routing reads the called and calling party addresses to determine the physical address in the form of a point code. Every SS7 node must have its own unique point code. Message routing determines the point code from an address contained in the routing table.

Message Transfer Part

Protocols are used within the layers of the SS7 protocol to accomplish functions called for at each level. Levels 1, 2 and 3 are combined into one part, the Message Transfer Part (MTP). MTP provides the rest of the levels with node-to-node transmission, including basic error detection and correction schemes and message sequencing. It provides routing, message discrimination and distribution functions within a node.

SS7 OVER IP
• Integrate IP-based nodes into the SS7 network.
• No special hardware requirements for the IP-based nodes.
• Interworking at different protocol layers.
• A common transport protocol is used.
• Similar performance requirements as the classical SS7 network
• Minimize end-to-end delay.
• Short failover time in case of network failures.

SS7 can be transported over IP. Ss7 is fast, accurate and secure protocols system for the network .it has wide range of applications

To carry a demand between two nodes on a SONET ring, traffic is routed simultaneously clockwise and counter-clockwise, one as the primary path and the other as the backup path. The master ring problem (MRP) is to find such a ring, whenever it exists. The goal is to find a master ring whenever it exists. As a network evolves with growing traffic, it expands from an initially small number of SONET rings. As a result, the network may have unnecessarily complex topology. To replace a spaghetti-like network, one simple topology is a master ring. Another problem is to perform load balancing using a linear programming based formulation in SONET dual ring.

There are different topologies of SONET that enables a number of different networks to solve networking requirements, including survivability, cost, and bandwidth efficiencies. The SONET configurations include:

• Point-to-point configuration
• Hub configuration
• Linear Add/Drop configuration
• Ring configuration

SONET technology has made the ring a popular network topology. To carry a demand between two nodes on a SONET ring, traffic is routed simultaneously clockwise and counter-clockwise, one as the primary path and the other as the backup path. Often an optical network consists of a collection of interconnected SONET rings. A master ring contains every node in the network exactly once and respects the node ordering of every individual SONET ring. The master ring problem (MRP) is to find such a ring, whenever it exists.

Management & protection techniques in the optical networks are becoming more and more important with increasing demand for the availability of high-speed networks. A master ring respects the node ordering of every existing SONET ring; it has the advantage of preserving the routing label of every demand intra to an existing SONET ring. By reconfiguring the network, overall utilization can be improved. Ring topology has advantages over mesh but rings are considered for poor routing so the reconfiguring rings may increase the efficiency of the network. By combining highly accurate network synchronization systems with advanced optical network technology, high-speed transport systems like SDH or SONET.

Reduction of cross talk

In WDM there may be a problem of cross talk because the signals may mix up while travelling from the window. The work is being done to increase the number of multiplexed channels, by decreasing the channel spacing, and increasing the bit (data) rate of a single channel reduce the crosstalk in WDM optical communication systems. Both these factors, decrease in the channel spacing and increase in the data rate, increases the crosstalk of the systems.

WDM consists of Ring topology. Once the WDM ring is up, light paths need to be established in accordance with the traffic pattern to be supported. This helps to solve the problem of routing and wavelength assignment. Essentially, the light path routes need to be determined. WDM is employed by carriers to boost the data rates of their networks dramatically. The frequency increases as the wavelength is shortened. The WDM promises of unlimited bandwidth and fast protection capabilities. The deployment of WDM devices thus must be economically well justified, as well as well planned.

METHOD & SOLUTION

To reduce cross talk the authors are using return-to-zero (RZ) format in place of NRZ format. The RZ format is more advantageous, because the RZ-modulated signal can withstand better the impact of fiber nonlinearity and polarization-mode dispersion. The most widely used being is the polarization interleaving method. In dispersion interleaving method, the signals in the odd channels are delayed by a half-bit period relative to the signals in the even channels. Thus, the interference from the adjacent channels near sampling point is greatly reduced.

In Polarization & Dispersion Interleaved WDM systems the total channels (N) are separated into two odd and even channels in a single stage and then separated odd and even channels are multiplexed separately. In polarization interleaving model the separation of channels into odd and even channels improves capacity and spectral efficiency of WDM systems. So modifications in PI and DI systems are proposed. Separation of total number of channels into odd and even channels is done in several stages instead of a single stage. In first stage, N channels are divided into two odd and even channels of number N/2.  In second stage, each N/2 channel is again divided into two odd and even channels of number N/4. This process is continued till the divided odd and even channels have only one number. The proposed design is for eight channels (N = 8). The odd and even channels are routed through optical polarizer’s having vertical and horizontal polarizations, respectively, before interleaving with each other.

 The fiber channel is used to serve both networks and channels.

FIBER CHANNEL DESIGNS:

1.      Point -to- point: It is used for the transmission of large blocks of data and also as a mass data storage device.

 2.      Switched fabric:It is used to cluster a number of devices through a switching fabric.

3.      Attributed loop: It is also known as FC-AL. it is used to connect three or more devices without fabric. It allows the connection of several devices in a ring forming a “virtual single device.”

CLASS OF SERVICES:Fiber channel has three classes to satisfy the large number of data communication.

Class 1: it is based on circuit switched or hard switched connection. It is a dedicated link that connects two devices and is capable of providing a continuous and graduate delivery of data with acknowledgement of receipt.

Class 2: this connection is based on frame switched service. It is not a dedicated connection. It is not a dedicated connection. In frame switching mechanism reads the switching mechanism reads the frame header code, and then makes a decision for the pay load destination. It also provides guaranteed delivery with acknowledgement of receipt.

Class 3: it is data gram transfer. This service has no connection and that allows data to be transmitted very quickly to a number of devices. Class 3 does not provide acknowledgement of receipt.

EFFICIENCY:Fiber channel is based on IBM 8B/10 B scheme and was specifically designed for data transmission over optical fiber.

FIBER CHANNEL STANDARDS: The set of standards for fiber channel are as follow:

1. The fiber channel’s physical standards. It is subdivided into five sub levels FC-0 to FC-4. FC-0 performs within physical layer.FC-1 is a transmission protocol. Fc-2 is signaling protocol. FC-3 is a common service. FC-4 is a bus interface.

2. The fiber channel arbitrated loop standard (FC-AL)

THE FIBER CHANNEL TRANSCIEVER:

At the transmitter input, the applied 10 bit parallel TTL data is encoded into 8B/10 B format and then multiplexed into high speed serial data stream. The PLL circuit in the transmitter section locks onto the 106.25 MHz clock frequency supplied by the user, then multiples it by ten to generate the required clock signal for high speed serial output signal.At the receiver end, the PLL circuit locks onto the incoming 1.0625 GBd serial data, from which it recovers both the data and clock signals. It also recovers two 53.125 MHz bytes clock signals with a phase difference of 180 degree which is used to align the parallel data at the positive going transition.

DETAILED OPERATION OF FIBER CHANNEL:

The transceiver is capable of transmitting and receiving 10 bit parallel data over high speed line in accordance with the fiber channel standards for FC-0 layer specifications. The transceiver incorporates the following:

• TTL parallel inputs/outputs (I/Os)
• High speed PPL circuits (transmitter receiver)
• High speed serial clock and data recovery circuitry
• Parallel-to-serial converters
• Comma character recognition circuitry
• Byte alignment circuitry
• Serial to paralle conversion circuitry

The functions are accomplished by building block within transceiver blocks. These are:

Transmitter:

• Input latch
• PLL/clock generator
• Frame multiplexer
• Output select

Receiver:

• Input select
• PLL/clock recovery
• Input sampler
• Frame de multiplexer and byte synchronization
• Output drivers
• Signal detect

Ray tracing is a method for calculating the path of waves or particles through a system with regions of varying propagation velocity, absorption characteristics, and reflecting surfaces. Under these circumstances, wave fronts may bend, change direction, or reflect off surfaces, complicating analysis. Ray tracing solves the problem by repeatedly advancing idealized narrow beams called rays .

Technique:

Ray tracing works by assuming that the particle or wave can be modeled as a large number of very narrow beams and that exists at some distance over which such a ray is locally straight. The ray tracer will advance the ray over this distance, and then use a local derivative of the medium to calculate the ray’s new direction. From this location, a new ray is sent out and the process is repeated until a complete path is generated. If the simulation includes solid objects, the ray may be tested for intersection with them at each step, making adjustments to the ray’s direction if a collision is found.

Algorithm
The basic ray tracing algorithm is called a “recursive” algorithm. Recursion is a means of obtaining a result in which a given process repeats itself an arbitrary number of times. Infinite recursion is recursion that never ends, and this is almost never useful. The algorithm begins by shooting a ray from the eye and through the screen, determining all the objects that intersect the ray, and finding the nearest of those intersections. It then repeats itself by shooting more rays from the point of intersection to see what objects are reflected at that point, what objects may be seen through the object at that point, which light sources are directly visible from that point, and so on.

1) Reflection
If the surface that the ray intersected was reflective, like a mirror, the ray tracer must determine the color at that point by finding, not only the color of the surface, but also the color of the reflection of any objects at that point.

2) Transparency
Transparency is modeled similarly to reflection, but instead of bouncing the new ray off of the surface, the ray is bent into and through the surface to model refraction. Refraction is an optical phenomenon caused when light bends as it travels through a given substance.

3) Shadows
Shadows are the third standard feature in ray tracing. Imagine the surface of an object. If seeing the light source, then there’s a clear path between you and the light, and at least some photons will certainly travel along this path. If any opaque objects are in way, then no light is coming directly from the light into your eye, and you are in shadow with respect to that light.

Methods:
Ray tracing with mirrors
Ray tracing with thin lenses

Applications:
a) Radio signals
b) Ocean acoustics
c) Optical design