Thursday, September 10, 2009

PSTN - Public Switched Telephone Network

The public switched telephone network (PSTN) is collection of interconnected public telephone networks that was designed primarily for voice traffic.

The PSTN is a circuit-switched network. That is, a dedicated circuit (also referred to as a channel) is established for the duration of a transmission, such as a telephone call. This contrasts with packet switching networks, in which messages are divided into small segments called packets and each packet is sent individually.The Internet is based on a packet-switching protocol, TCP/IP.

Originally only an analog system, the PSTN is now almost entirely digital, even though most subscribers are connected via analog circuits, and it now includes mobile phones in addition to fixed-line phones. Only the very oldest and most backward parts of the PSTN still use analog technology for anything other than the final mile connections to individual homes and other end users. In recent years digital connections have been increasingly been made available to end users through such services such as ISDN (integrated services digital network), DSL (digital subscriber line) and cable.

In recent years, however, it has become increasingly apparent that the long-term future of the PSTN is to become just another application of the Internet. That is, the voice traffic that is currently carried by the PSTN will be shifted to VoIP (voice over Internet protocol), thus allowing the PSTN infrastructure to be converted from circuit switching to packet switching. However, it will be necessary to make additional progress on improving the quality of VoIP before this can become a reality.

Tuesday, September 8, 2009

CDMA - Code Division Multiple Access

CDMA is a form of Direct Sequence Spread Spectrum communications. In general, Spread Spectrum communications is distinguished by three key elements:
1. The signal occupies a bandwidth much greater than that which is necessary to send the information. This results in many benefits, such as immunity to interference and jamming and multi-user access.
2. The bandwidth is spread by means of a code which is independent of the data. The independence of the code distinguishes this from standard modulation schemes in which the data modulation will always spread the spectrum somewhat. 3. The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.

In order to protect the signal, the code used is pseudo-random. It appears random, but is actually deterministic, so that the receiver can reconstruct the code for synchronous detection. This pseudo-random code is also called pseudo-noise (PN).

In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.
CODINGCDMA uses unique spreading codes to spread the baseband data before transmission. The signal is transmitted in a channel, which is below noise level. The receiver then uses a correlator to despread the wanted signal, which is passed through a narrow bandpass filter. Unwanted signals will not be despread and will not pass through the filter. Codes take the form of a carefully designed one/zero sequence produced at a much higher rate than that of the baseband data. The rate of a spreading code is referred to as chip rate rather than bit rate.

CDMA codes are not required to provide call security, but create a uniqueness to enable call identification. Codes should not correlate to other codes or time shifted version of itself. Spreading codes are noise like pseudo-random codes, channel codes are designed for maximum separation from each other and cell identification codes are balanced not to correlate to other codes of itself.

Mobile Number Portability (MNP)

Number portability is a circuit-switch telecommunications network feature thatenables end users to retain their telephone numbers when changing service providers,service types, and/or locations. When fully implemented nationwide by both wirelineand wireless providers, portability will remove one of the most significant deterrentsto changing service, providing unprecedented convenience for consumers, andencouraging unrestrained competition in the telecommunications industry.

NGN -Next Generation Networking

Next Generation Networking (NGN) is a broad term to describe some key architectural evolutions in telecommunication and access networks. The general idea behind NGN is that one network transports all information and services (voice, data, and all sorts of media such as video) by encapsulating these into packets, like it is on the Internet. NGNs are commonly built around the Internet Protocol.
NGNs will allow carriers’ networks to cost effectively support a new suite of sophisticated services by building on core competencies related to traditional transport services. In addition, a unified and consistent NGN approach will help reduce costs by eliminating the inefficiencies of current service-specific, proprietary, and non-reusable solutions. NGN approaches will also reduce the time to market and life-cycle costs of offering new services.

Sunday, September 6, 2009


NGOSS defines a comprehensive, integrated framework for developing, procuring and deploying operational and business support systems and software for communications service providers and their suppliers.
It is the industry’s standard for development and deployment of OSS/BSS system.For NGOSS TMF has provided with a set of documents that make up a toolkit of industry-agreed specifications and guidelines that cover key business and technical areas and a defined methodology for use of the tools.
The TMF is further developing NGOSS artefacts to address new business requirements based on fast growing industry.
The Tele Management Forum’s New Generation Operations Systems and Software (NGOSS) is an architectural framework for organising, integrating and implementing telecom systems.
NGOSS is a component based framework consisting of the following elements:

• The enhanced Telecom Operations Map (eTOM) is a business process framework, (i.e., a model for categorizing all the business activities that a service provider might use).
• The Shared Information Data (SID) model provides a comprehensive information/data model that may be specialized for the needs of a particular organization.
• The Technology Neutral Architecture (TNA) and contract interface are the components make up the heart of the NGOSS integrated framework. TNA is an architecture that is sustainable through the technology changes. The contract interface defines APIs for interfacing across the architecture from different software vendors.
• NGOSS compliance element provides a suite of tests for compliance to the eTOM, SID, TNA and contract interface components. These tests allow vendors to achieve certification for complying with one or more NGOSS standards.

Telecom OSS/BSS

Operations Support Systems (OSS) is a suite of software designed specifically to manage a large network infrastructure, connecting individual sub-systems. OSS supports processes such as management, inventory, engineering, planning, billing and repair functions for telecom service provider’s networks.
A complementary term Business Support Systems (BSS) typically refers to ‘business systems’ dealing with customers supporting processes such as taking orders, processing bills and collecting payments.
OSS and BSS systems together are often abbreviated as OSS/BSS. Component-based OSS/BSS solutions improve the management of service planning, deployment and operations in a multi-service, multi-vendor, multi-technology environment.

Telecom Mediation

Telecom Mediation is a system which acts as an interface or a middle layer between network elements and billing system/down stream applications like Fraud Management Systems, Revenue Assurance, Data Ware house etc.
The functionalities that are performed by Mediation are as follows.

  • Mediation collects the CDRs from the network elements (MSC, SGSN, GGSN etc).
  • Segregation of CDRs (separation of different kinds of CDRs).
  • Mediation performs data enrichment and format conversion.
  • Preprocessing and Post processing of CDRs.
  • Applies business rules such as Filtration, Aggregation, Correlation, and Duplicate check etc on the CDRs.
  • Sending SNMP traps in case of errors during the parsing, conversion, distribution and processing of CDRs in the mediation system.
  • Distribution of BDRs/CDRs to the billing systems or down-stream applications.
CDR Collection

Mediation collects the usage records/CDRs from the network elements. Mediation supports the collection of the usage records using various protocols that are widely supported namely FTP, SFTP, FTAM, X.25 Serial interface, MTP, SNMP. In the GSM networks the widely used interfaces to collect the CDRs are FTP/SFTP and FTAM. SFTP provides a secured way of collecting the CDRs as it uses SSL (secured socket layer) which encrypts the data while transferring the data in a secured way.

Preprocessing, Parsing and Validation

Preprocessing is a process of removal of headers/trailer information for further processing. Preprocessing also involves splitting the fields of the CDR, adding additional fields in the CDR required for processing. This may involve file or data base look ups to populate the route ID’s etc.
The collected or preprocessed CDR is parsed to identify whether all the required fields are present in the CDR and validated to the switch format to check whether it meets the specification. This involves checking the length of the CDR, usage field type (type of CDR) and fields are in proper order.

Business Rules (Processing Functions)

There are different types of business rules that are used in mediation.
· Sequence Validation
· Filtration
· Aggregation
· Duplicate CDR Check
· Correlation
· Time Gap DetectionTrunk Analysis

Thursday, September 3, 2009

GSM- Global System for Mobile Communications

GSM Network Architecture

GSM Network consists of three main parts:

  • Mobile Station (MS) carried by the subscriber
  • Base Station Subsystem(BSS) controls radio link with mobile station
  • Network and Switching Subsystems (NSS) mobility management and switching of calls between mobile users, and between mobile and fixed network users.
Mobile Station consists of:
  • Mobile Equipments(ME) such as hand portable and vehicle mounted unit.
  • Subscriber Identity Module (SIM) contains the entire customer related information.
Base Station Subsystem (BSS) consists of:
  • Base Transceiver Station (BTS) defines a cell and is responsible for radio link protocols with Mobile Station
  • Base Station Controller (BSC) controls multiple BTSs and manages radio channel setup, and handovers. The BSC is the connection between the Mobile Station and Mobile Switchning Center.
Network and Switching Subsystems consists of:
  • Mobile Switching Center (MSC) is the central component of the NSS. It operates all switching functions for the mobiles within its jurisdiction. Interface between mobile and other network including fixed network. Its functions:
  • Manages the location of mobiles.
  • Swtiches cells
  • Manages Security features.
  • Controls handover between BSCs.
  • Resource Management.
  • Interworks with and manages network databases
  • Collects call billing data and sends to billing system
  • Collects traffic statistics for performance monitoring.

  • Network Databases - Home Location Register and Visitor Location Register together with MSC provides the call routing and roaming capabilities of GSM.
  • Home Location Register(HLR) contains all the subscriber information for the purposes of call control and location determination. There is logically one HLR per GSM network although it may be implemented as adistributed database.
  • Visitors Location Register(VLR) is only a temporary storage while the particular subscriber is located in the geographical area controlled by the MSC/VLR. Contains on the necessary information provision of subscribed services.
  • Authentication Center (AuC) is a protected database that stores the security information for each subscriber ( a copy of the secrte key stored in each SIM).
  • Equipment Identity Register (EIR) is a list of all valid mobile equipment on the network.

Telecom Interconnect Billing

Telecom operators send/receives data to/from other operators. If these calls/SMS are within the network then telecom operator can send/receive them without interconnecting. If this sending/receiving of calls is to/from other operators then both the operators needs to be interconnected. This setup requires some kind of billing mechanism to monitor the actual amount of data (send/receive). It is known as Interconnect Billing.

Charging Policies
Voice or any other traffic can be charged according to different olicies. One of the common charging policies is Destination Baed Billing ( based on area code prefix of the destination). In this case, searate rates are assigned to each destination and the interconnect billing calculates charges on the basis of destination.

One more type of charging policy is Distance Based Billing ( based on the distance between source and the destination) and it is usually used within the country. In this type of billing, a matrix is used for calculating distance between all the possinle originating and terminating oints and billing system calculated charges on the basis of these points.

In destination based billing, service is charged on the basis of termination oint and irrespective of the origination point or distance covered. In the distance based billing, there are different zones that are made on the basis of the distance between the originating and the terminating points. Therefore, there can be a separate zone for smaller distances another for medium distances and aonther for larger distances.

Rates depend on the charging policy, if it is destination based billing then rates is specified according to the area code in the suorted destinations. In distance based billing, rates are specified according to different zones.
Sometimes rates can be simple like flat perminute billing but sometimes they can be more complex like peak and offpeak rates for some destinations and there can be special rates for different holidays or vacations for some secific area.