DHCP

The Dynamic Host Configuration Protocol is used by computers for requesting Internet Protocol parameters, such as an IP address from a network server. The protocol operates based on the client-server model. DHCP is very common in all modern networks ranging in size from home networks to large campus networks and regional Internet service provider networks. Most residential network routers receive a globally unique IP address within the provider network. Within a local network, DHCP assigns a local IP address to devices connected to the local network.

When a computer or other networked device connects to a network, its DHCP client software in the operating system sends a broadcast query requesting necessary information. Any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, and time servers. On receiving a request, the server may respond with specific information for each client, as previously configured by an administrator, or with a specific address and any other information valid for the entire network, and the time period for which the allocation (lease) is valid. A host typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When an assignment is refreshed by the client computer, it initially requests the same parameter values, but may be assigned a new address from the server, based on the assignment policies set by administrators.

On large networks that consist of multiple links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets.

Depending on implementation, the DHCP server may have three methods of allocating IP-addresses:

·    Dynamic allocation:  A network administrator reserves a range of IP addresses for DHCP, and each client computer on the LAN is configured to request an IP address from the DHCP server during network initialization. The request-and-grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim (and then reallocate) IP addresses that are not renewed.

·   Automatic allocation: The DHCP server permanently assigns an IP address to a requesting client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had.

·       Static allocation: The DHCP server allocates an IP address based on a preconfigured mapping to each client's MAC address. This feature is variously called static DHCP assignment by DD-WRT, fixed-address by the dhcpd documentation, address reservation by Netgear, DHCP reservation or static DHCP by Cisco and Linksys, and IP address reservation or MAC/IP address binding by various other router manufacturers.

DHCP is used for Internet Protocol version 4 (IPv4), as well as IPv6. While both versions serve the same purpose, the details of the protocol for IPv4 and IPv6 are sufficiently different that they may be considered separate protocols.

3D Printing

Additive manufacturing or 3D printing is a process of making a three-dimensional solid object of virtually any shape from a digital model. 3D printing is achieved using an additive process, where successive layers of material are laid down in different shapes. 3D printing is also considered distinct from traditional machining techniques, which mostly rely on the removal of material by methods such as cutting or drilling (subtractive processes).

 

A 3D printer is a limited type of industrial robot that is capable of carrying out an additive process under computer control.

                                                   

 

General principles

·         Modeling: Additive manufacturing takes virtual models (3D blueprints) from computer aided design (CAD) or animation modeling software and "slices" them into digital cross-sections for the machine to successively use as a guideline for printing. Depending on the machine used, material or a binding material is deposited on the build bed or platform until material/binder layering is complete and the final 3D model has been "printed."

                                                        

 

3D model slicing

 

·         Printing: To perform a print, the machine reads the design from an stl file and lays down successive layers of liquid, powder, paper or sheet material to build the model from a series of cross sections. These layers, which correspond to the virtual cross sections from the CAD model, are joined or automatically fused to create the final shape. The primary advantage of this technique is its ability to create almost any shape or geometric feature.

 

·         Finishing: Though the printer-produced resolution is sufficient for many applications, printing a slightly oversized version of the desired object in standard resolution and then removing material with a higher-resolution subtractive process can achieve greater precision.

 

Applications

Additive manufacturing's earliest applications have been on the toolroom end of the manufacturing spectrum. Standard applications include design visualization, prototyping/CAD, metal casting, architecture, education, geospatial, healthcare, and entertainment/retail.

 

·         Industrial uses

o   Rapid prototyping: Industrial 3D printers have existed since the early 1980s and have been used extensively for rapid prototyping and research purposes. These are generally larger machines that use proprietary powdered metals, casting media (e.g. sand), plastics, paper or cartridges, and are used for rapid prototyping by universities and commercial companies.

o   Rapid manufacturing: Advances in RP technology have introduced materials that are appropriate for final manufacture, which has in turn introduced the possibility of directly manufacturing finished components. One advantage of 3D printing for rapid manufacturing lies in the relatively inexpensive production of small numbers of parts.

o   Mass customization: Companies have created services where consumers can customize objects using simplified web based customization software, and order the resulting items as 3D printed unique objects.

o   Mass production: The current slow print speed of 3D printers limits their use for mass production. To reduce this overhead, several fused filament machines now offer multiple extruder heads. These can be used to print in multiple colors, with different polymers, or to make multiple prints simultaneously.

Metasearch Engine

A metasearch engine is a search tool that sends user requests to several other search engines and/or databases and aggregates the results into a single list or displays them according to their source. Metasearch engines enable users to enter search criteria once and access several search engines simultaneously. Metasearch engines operate on the premise that the Web is too large for any one search engine to index it all and that more comprehensive search results can be obtained by combining the results from several search engines. This also may save the user from having to use multiple search engines separately. The process of fusion also improves the search results.

Metasearch engines create what is known as a virtual database. They do not compile a physical database or catalogue of the web. Instead, they take a user's request, pass it to several other heterogeneous databases and then compile the results in a homogeneous manner based on a specific algorithm.

No two metasearch engines are alike. Some search only the most popular search engines while others also search lesser-known engines, newsgroups, and other databases. They also differ in how the results are presented and the quantity of engines that are used. Some will list results according to search engine or database. Others return results according to relevance, often concealing which search engine returned which results. This benefits the user by eliminating duplicate hits and grouping the most relevant ones at the top of the list.

Search engines frequently have different ways they expect requests submitted. For example, some search engines allow the usage of the word "AND" while others require "+" or only a space to combine words. The better metasearch engines try to synthesize requests appropriately when submitting them.                                                       

Architecture of a metasearch engine

Examples of Metasearch Engine

·         Info.com – It provides results from leading search engines and pay-per-click directories, including Google, Yahoo!, Bing.com, Ask, LookSmart, About and Open Directory.

·         HotBot.com – In the 1990s, it was one of the most popular search engines on the World Wide Web.

·         Yippy.com – Offers clusters of results.

Beacons

A beacon is an intentionally conspicuous device designed to attract attention to a specific location.

 

Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon or of pending weather as indicated on a weather beacon mounted at the top of a tall building or similar site. When used in such fashion, beacons can be considered a form of optical telegraphy.

 

Usage

· For Navigation – Beacons help guide navigators to their destinations. Types of navigational beacons include radar reflectors, radio beacons, sonic and visual signals.

· For defensive communications – Classically, beacons were fires lit at well-known locations on hills or high places, used either as lighthouses for navigation at sea, or for signalling over land that enemy troops were approaching, in order to alert defenses. As signals, beacons are an ancient form of optical telegraphy, and were part of a relay league.

· On vehicles – Vehicular beacons are rotating or flashing lights affixed to the top of a vehicle to attract the attention of surrounding vehicles and pedestrians. Emergency vehicles such as fire engines, ambulances, police cars, tow trucks, construction vehicles, and snow-removal vehicles carry beacon lights.

 

In wireless networks, a beacon is a type of frame which is sent by the access point (or wifi router), to indicate that is on.

 

Beaconing is the process that allows a network to self-repair network problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.

HLR , VLR

A Home Location Register (HLR) is a database of user (subscriber) information, i.e., customer profiles, used in mobile (cellular) networks. It is a key component of mobile networks such as GSM, TDMA, and CDMA networks. A HLR contains user information such as account information, account status, user preferences, features subscribed to by the user, user’s current location, etc. The data stored in HLRs for the different types of networks is similar but does differ in some details.

 

HLRs are used by the Mobile Switching Centers (MSCs) to originate and deliver arriving mobile calls.

 

A Visiting Location Register (VLR) is a database, similar to a HLR, which is used by the mobile network to temporarily held profiles of roaming users. This VLR data is based on the user information retrieved from a HLR. MSCs use a VLR to handle roaming users.

 

How HLR & VLR are used

Each mobile network has its own HLRs and VLRs. When a MSC detects a mobile user’s presence in the area covered by its network, it first checks a database to determine if the user is in his/her home area or is roaming, i.e., the user is a visitor.

·         User in Home Area: HLR has the necessary information for initiating, terminating, or receiving a call.

·         User is Roaming: VLR contacts the user’s HLR to get the necessary information to set up a temporary user profile.

 

The user’s location is recorded in the HLR, and in case the user is roaming, it is also recorded in the VLR.

 

In case the user wants to make a call:

·         User in Home Area: MSC contacts the HLR prior to setting up the call.

·         User is Roaming: MSC contacts the VLR prior to setting up the call.

 

In case there is a call for the user (call goes to the home MSC):

·         User in Home Area: Home MSC delivers the call immediately.

·         User is Roaming: Home MSC contacts the VLR to determine the appropriate switch in the roaming area to handle the arriving call and then transfers the call to the roaming area MSC.

 

Issues with HLRs:

·      Slow Performance, due to lookups.

·     Questionable adaptability in handling different types of networks, including 3G networks.

·         Limited capability/data to support user authentication.

·         Limited Support for data backups, fault tolerance, and reliability.

·         Scalability.

Bluetooth LE

Bluetooth low energy, Bluetooth LE, or BLE, marketed as Bluetooth Smart, is a wireless personal area network technology aimed at novel applications in the healthcare, fitness, security, and home entertainment industries. Compared to "Classic" Bluetooth, BLE is intended to provide considerably reduced power consumption and cost while maintaining a similar communication range.

Mobile operating systems including iOS, Android, Windows Phone and BlackBerry, as well as OS X and Windows 8, natively support Bluetooth low energy. The Bluetooth SIG predicts more than 90 percent of Bluetooth-enabled smartphones will support the low energy standard by 2018.

Bluetooth low energy is not backward-compatible with the previous, often called Classic, Bluetooth protocol. The Bluetooth 4.0 specification permits devices to implement either or both of the LE and Classic systems. Those that implement both are known as Bluetooth 4.0 dual-mode devices.

Technical Details

Bluetooth low energy technology operates in the same spectrum range (the 2.400 GHz-2.4835 GHz ISM band) as Classic Bluetooth technology, but uses a different set of channels. Instead of Bluetooth's 79 1-MHz channels, Bluetooth low energy technology has 40 2-MHz channels. Within a channel, data is transmitted using Gaussian frequency shift modulation, similar to Classic Bluetooth's Basic Rate scheme. The bit rate is 1Mbit/s, and the maximum transmit power is 10 mW.

Bluetooth low energy technology uses frequency hopping to counteract narrowband interference problems. Classic Bluetooth also uses frequency hopping but the details are different; as a result, while both FCC and ETSI classify Bluetooth technology as a Frequency-hopping spread spectrum scheme, Bluetooth low energy technology is classified as a system using digital modulation techniques or a direct-sequence spread spectrum.

Software model

All Bluetooth low energy devices use the Generic Attribute Profile (GATT). GATT has the following terminology:

·         Client - A device that initiates GATT commands and requests, and accepts responses, for example a computer or smartphone.

·         Server - A device that receives GATT commands and requests, and returns responses, for example a temperature sensor.

·         Characteristic - A data value transferred between client and server, for example the current battery voltage.

·         Service - A collection of related characteristics, which operate together to perform a particular function. For instance, the Health Thermometer service includes characteristics for a temperature measurement value, and a time interval between measurements.

·         Descriptor - A descriptor provides additional information about a characteristic. For instance, a temperature value characteristic may have an indication of its units (e.g. Celsius), and the maximum and minimum values which the sensor can measure.

Services, characteristics, and descriptors are collectively referred to as attributes and identified by UUIDs (Universally unique identifiers).

The GATT protocol provides a number of commands for the client to discover information about the server. These include:

·         Discover UUIDs for all primary services
·         Find a service with a given UUID
·         Find secondary services for a given primary service
·         Discover all characteristics for a given service
·         Find characteristics matching a given UUID
·         Read all descriptors for a particular characteristic

 Applications:

Borrowing from the original Bluetooth specification, the Bluetooth SIG defines several profiles — specifications for how a device works in a particular application — for low energy devices.

All current low energy application profiles are based on the generic attribute profile or GATT.

·         Health care profiles

o   HTP — for medical temperature measurement devices

o   GLP — for blood glucose monitors

o   BLP — for blood pressure measurement

·         Sports and fitness profiles

o   HRP — for devices which measure heart rate

o   CSCP — for sensors attached to a bicycle or exercise bike to measure cadence and wheel speed

o   RSCP — running speed and cadence profile

o   CPP — cycling power profile

o   LNP — location and navigation profile

·         Proximity sensing

o   FMP — the "find me" profile — allows one device to issue an alert on a second misplaced device.

o   PXP — the proximity profile — allows a proximity monitor to detect whether a proximity reporter is within a close range.

·         Alerts and time profiles

o   The phone alert status profile and alert notification profile allow a client device to receive notifications such as incoming call alerts from another device.

o   The time profile allows current time and time zone information on a client device to be set from a server device, such as between a wristwatch and a mobile phone's network time.

Firewalls

A firewall is a software or hardware-based network security system that controls the incoming and outgoing network traffic by analyzing the data packets and determining whether they should be allowed through or not, based on a rule set. Generally, firewalls are configured to protect against unauthenticated interactive logins from the outside world. This helps prevent hackers from logging into machines on a network.

Firewalls also provide logging and auditing functions; often they provide summaries to the administrator about what type/volume of traffic has been processed through.

Network Layer Firewalls

Network layer firewalls, also called packet filters, operate at a relatively low level of the TCP/IP protocol stack, not allowing packets to pass through unless they match the established rule set. Network layer firewalls generally make their decisions based on the source address, destination address and ports in individual IP packets.

“Stateful” network layer firewalls maintain context about active sessions, and use that "state information" to speed packet processing. If a packet does not match an existing connection, it will be evaluated according to the ruleset for new connections. If a packet matches an existing connection based on comparison with the firewall's state table, it will be allowed to pass without further processing.

“Stateless” network layer firewalls require less memory, and can be faster for simple filters that require less time to filter than to look up a session. However, they cannot make more complex decisions based on what stage communications between hosts have reached.

Application Layer Firewalls

Application-layer firewalls work on the application level of the TCP/IP stack (i.e., all browser traffic, or all telnet or ftp traffic), and may intercept all packets traveling to or from an application.

Application firewalls function by determining whether a process should accept any given connection. Application firewalls accomplish their function by hooking into socket calls to filter the connections between the application layer and the lower layers of the OSI model. Also, application firewalls further filter connections by examining the process ID of data packets against a ruleset for the local process involved in the data transmission.

Proxies

A proxy server (running either on dedicated hardware or as software on a general-purpose machine) may act as a firewall by responding to input packets (connection requests, for example) in the manner of an application, while blocking other packets. A proxy server is a gateway from one network to another for a specific network application, in the sense that it functions as a proxy on behalf of the network user.

Computers establish a connection to the proxy, which serves as an intermediary, and initiate a new network connection on behalf of the request. This prevents direct connections between systems on either side of the firewall and makes it harder for an attacker to discover where the network is, because they will never receive packets directly by their target system.

Telecommunications Management Network

The Telecommunications Management Network (TMN) is a protocol model defined by ITU-T for managing open systems in a communications network. It is part of the ITU-T recommendation series M.3000 and is based on the OSI management specifications in ITU-T recommendation series X.700.

TMN provides a framework for achieving interconnectivity and communication across heterogeneous operations systems and telecommunication networks. To achieve this, TMN defines a set of interface points for elements which perform the actual communications processing (such as a call processing switch). It also allows for management workstations, to monitor and control them. The standard interface allows elements from different manufacturers to be incorporated into a network under a single management control.

For communication between Operations Systems and NEs (Network Elements), it uses the Common management information protocol (CMIP) or Mediation devices when it uses Q3 interface.

The TMN layered organization is used as the basis for the management software of ISDN, B-ISDN, ATM, SDH/SONET and GSM networks. It is not as commonly used for purely packet-switched data networks such as GPRS.

Modern telecom networks offer automated management functions and are run by OSS software. These manage modern telecom networks and provide the data that is needed in the day-to-day running of a telecom network. OSS software is also responsible for issuing commands to the network infrastructure to activate new service offerings, commence services for new customers, detect and correct network faults.

The framework identifies four logical layers of network management:

 

· Business management – Includes the functions related to business aspects, analyzes trends and quality issues, for example, or to provide a basis for billing and other financial reports.

· Service management – Handles services in the network: definition, administration and charging of services.

· Network management – Distributes network resources, performs tasks of: configuration, control and supervision of the network.

· Element management – Handles individual network elements including alarm management, handling of information, backup, logging, and maintenance of hardware and software.

 
A network element provides agent services, mapping the physical aspects of the equipment into the TMN framework.

Network forensics

Network forensics is a sub-branch of digital forensics relating to the monitoring and analysis of computer network traffic for the purposes of information gathering, legal evidence, or intrusion detection. Unlike other areas of digital forensics, network investigations deal with volatile and dynamic information, making network forensics often a pro-active investigation.

Network forensics generally has two uses:

The first, relating to security, involves monitoring a network for anomalous traffic and identifying intrusions. An attacker might be able to erase all log files on a compromised host; network-based evidence might therefore be the only evidence available for forensic analysis. 

The second form of Network forensics relates to law enforcement. In this case analysis of captured network traffic can include tasks such as reassembling transferred files, searching for keywords and parsing human communication such as emails or chat sessions. 

Two systems are commonly used to collect network data:

"Catch-it-as-you-can" - This is where all packets passing through certain traffic point are captured and written to large storage with analysis being done subsequently in batch mode. 

"Stop, look and listen" - This is where each packet is analyzed by a faster processor in a rudimentary way in memory and only certain information saved for future analysis.

Types

Ethernet – Applying forensic methods on the Ethernet layer is done by eavesdropping bit streams with tools called monitoring tools or sniffers. The most common tool on this layer is Wireshark (formerly known as Ethereal). It collects all data on this layer and allows the user to filter for different events. With these tools, websites, email attachments and more that have been transmitted over the network can be reconstructed. An advantage of collecting this data is that it is directly connected to a host. If, for example, the IP address or the MAC address of a host at a certain time is known, all data for or from this IP or MAC address can be filtered.

 TCP/IP – For the correct routing of packets through the network (e.g., the Internet), every intermediate router must have a routing table which is the best source of information if investigating a digital crime. To do this, it is necessary to reverse the sending route of the attacker, follow the packets, and find where the computer the packet came from (i.e., the source of the attacker).

Another source of evidence on this layer is authentication logs. They show which account and which user was associated with an activity and may reveal who was the attacker or at least sets limits to the people who come into consideration of being the attacker.

The Internet – The internet can be a rich source of digital evidence including web browsing, email, newsgroup, synchronous chat and peer-to-peer traffic.

Wireless forensics is a sub-discipline of network forensics. The main goal of wireless forensics is to provide the methodology and tools required to collect and analyze (wireless) network traffic that can be presented as valid digital evidence in a court of law. The evidence collected can correspond to plain data or, with the broad usage of Voice-over-IP (VoIP) technologies, especially over wireless, can include voice conversations.

 

Second Screen or Multi Screen

Second screen, sometimes also referred to as "companion device" (or "companion apps" when referring to a software applications), is a term that refers to an additional electronic device (e.g. tablet, smartphone) that allows a television audience to interact with the content they are consuming, such as TV shows, movies, music, or video games. Extra data is displayed on a portable device synchronized with the content being viewed on television.

Several studies show a clear tendency of the consumer to use a device while watching television. They show high use of tablet or smartphone when watching television, and indicate a high percentage of comments or posts on social networks being about the content that's being watched.

Based on these studies, many companies both in content production and advertising have adapted their delivery content to the lifestyle of the consumer in order to get maximum attention and thus profits. Applications are becoming a natural extension of television programming, both live and on demand.

Applications

Many applications in the "second screen" are designed to give the consumer another way of interactivity. They also give the media companies another way to sell advertising content. Some examples:

·         Transmission of the Master's Golf Tournament, application for the iPhone (rating information and publicity)
·         TV programs broadcast live tweets and comment.
·         Synchronization of audiovisual content via web advertising.
·         Applications that extend the content information.
·         Shows that add on their websites, content devoted exclusively to the second screen.
·         Applications that synchronize the content being viewed to the portable device.
·         Video game console playing with extra data, such as a map or strategy data that synchronize with the content being viewed to the portable device.
·         TV discovery application with recommendation, EPG (live content), personalization.

Sports Broadcasting

Sports broadcasters, to stem the flight of the TV audience away from watching the main screen (new name for the television) to the second screen, are offering alternative and enhanced content to the main program. The idea is to present content related to the main program, such as unseen moments, alternative information, soundtrack, and characters. New technologies allow the viewer to see different camera angles while watching the game.

            

iBurst

Burst (or HC-SDMA, High Capacity Spatial Division Multiple Access) is a wireless broadband technology which optimizes the use of its bandwidth with the help of smart antennas.

Description

HC-SDMA was announced as considered by ISO TC204 WG16 for the continuous communications standards architecture, known as Communications, Air-interface, Long and Medium range (CALM), which ISO is developing for intelligent transport systems (ITS). ITS may include applications for public safety, network congestion management during traffic incidents, automatic toll booths, and more.

The HC-SDMA interface provides wide-area broadband wireless data-connectivity for fixed, portable and mobile computing devices and appliances. The protocol is designed to be implemented with smart antenna array techniques (called MIMO for multiple-input multiple-output) to substantially improve the radio frequency (RF) coverage, capacity and performance for the system.

Technology

The HC-SDMA interface operates on a similar premise as cellular phones, with hand-offs between HC-SDMA cells repeatedly providing the user with a seamless wireless Internet access even when moving at the speed of a car or train.

The protocol:

·         specifies base station and client device RF characteristics, including output power levels, transmit frequencies and timing error, pulse shaping, in-band and out-of band spurious emissions, receiver sensitivity and selectivity;

·         defines associated frame structures for the various burst types including standard uplink and downlink traffic, paging and broadcast burst types;

·         specifies the modulation, forward error correction, interleaving and scrambling for various burst types;

·         describes the various logical channels (broadcast, paging, random access, configuration and traffic channels) and their roles in establishing communication over the radio link; and

·         specifies procedures for error recovery and retry.

The protocol also supports Layer 3 (L3) mechanisms for creating and controlling logical connections (sessions) between client device and base including registration, stream start, power control, handover, link adaptation, and stream closure, as well as L3 mechanisms for client device authentication and secure transmission on the data links.

Usage

Various options are already commercially available using:

·         Desktop modem with USB and Ethernet ports (with external power supply)
·         Portable USB modem (using USB power supply)
·         Laptop modem (PC card)
·         Wireless Residential Gateway
·         Mobile Broadband Router

Assisted GPS

Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system that can under certain conditions improve the startup performance, or time-to-first-fix (TTFF), of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones to make the location of a cell phone available to emergency call dispatchers.

"Standalone" or "autonomous" GPS operation uses radio signals from satellites alone. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or are weakened by passing through atmospheric conditions, walls, or tree cover. When first turned on in these conditions, some standalone GPS navigation devices may not be able to fix a position due to the fragmentary signal, rendering them unable to function until a clearer signal can be received continuously for a long enough period of time.

An assisted GPS system can address these problems by using data available from a network to locate and use the satellites in poor signal conditions. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.

Basic Concepts

Standalone GPS provides first position in approximately 30–40 seconds. A Standalone GPS system needs orbital information of the satellites to calculate the current position. The data rate of the satellite signal is only 50 bits/s, so downloading orbital information like ephemeris and almanac directly from satellites typically takes a long time, and if the satellite signals are lost during the acquisition of this information, it is discarded and the standalone system has to start from scratch. In AGPS, the Network Operator deploys an AGPS server. These AGPS servers download the orbital information from the satellite and store it in the database. An AGPS capable device can connect to these servers and download this information using Mobile Network radio bearers such as GSM, CDMA, WCDMA, LTE or even using other wireless radio bearers such as Wi-Fi. Usually the data rate of these bearers is high; hence downloading orbital information takes less time.

AGPS has two modes of operation:

Mobile Station Assisted (MSA)

In MSA mode A-GPS operation, the A-GPS capable device receives acquisition assistance, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and sends the measurements to the A-GPS server. The A-GPS server calculates the position and sends it back to the A-GPS device.

Mobile Station Based (MSB)

In MSB mode A-GPS operation, the A-GPS device receives ephemeris, reference location, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and calculates the position.

Many mobile phones combine A-GPS and other location services including Wi-Fi Positioning System and cell-site multilateration and sometimes a hybrid positioning system.