Unit-4

2.5G Mobile Data Networks

Q1) What are IEEE802.11 standards and what other standards do they support?

A1) IEEE 802.11 is a set of standards carrying out wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802)

802.11a — an extension to 802.11 that applies to wireless LANs and provides up to 54-Mbps in the 5GHz band. 802.11a uses an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS.

802.11b — an extension to 802.11 that applies to wireless LANS and provides 11 Mbps transmission in the 2.4 GHz band. 802.11b uses only DSSS. 802.11b was a 1999 ratification to the original 802.11 standard, allowing wireless functionality comparable to Ethernet.

802.11e — a wireless draft standard that defines the Quality of Service support for LANs, and is an enhancement to the 802.11a and 802.11b wireless LAN (WLAN) specifications. 802.11e adds QoS features and multimedia support to the existing IEEE 802.11b and IEEE 802.11a wireless standards, while maintaining full backward compatibility with these standards.

802.11g — applies to wireless LANs and is used for transmission over short distances at up to 54-Mbps in the 2.4 GHz bands.

802.11n — 802.11n builds upon previous 802.11 standards by adding multiple-input multiple-output. The additional transmitter and receiver antennas allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity through coding schemes like Alamouti coding. The real speed would be 100 Mbit/s (even 250 Mbit/s in PHY level), and so up to 4-5 times faster than 802.11g.

Q2) Explain the difference between IEEE 802.11 and 802.16?

A2)

Q3) What are the mobile IP entities and technologies used in mobile IP?

A3) Mobile IP Entities

Following section defines several entities and terminologies used in mobile IP.

(i) Mobile node

• A MN (Mobile Node) is an router or end system that can change its point of attachment to the internet using mobile IP.
• Mobile node can be any device such as laptop or mobile phone. Mobile node have its IP address and can communicate with another systems.

(ii) Correspondent node

A CN can be a Mobile Node (MN) or it can be a fixed IP host linked to a router. CN can be considered as a communication partner and at least one partner is needed for the communication purpose.

(iii) Home network

HN is a network having an address prefix matching that of a mobile node’s home address. Mobile IP support is not needed within the home network.

(iv) Foreign network

The Foreign Network (FN) is the current subnet of the MN visits and which is not belongs to the home network.

(v) Foreign agent (FA)

• Foreign agent is used to provide the various services to the Mobile Node (MN), when MN visits to the foreign network.
• Foreign agent can have care-of-address  (COA), that is acting as tunnel end points and forwarding the packets to the mobile node.

(vi) Care of address (COA)

• It is used to define the current location of mobile node from an  IP point of view.
• All the IP packets sent to the MN are first delivered to the COA, that is not directly send to the IP address of the MN.

(vii) Home Agent (HA)

HA is located in home Network and provides various services for the mobile node. Home agent maintains a location registry that used to give MNs location by the current COA.

Q4) Explain IMT 2000 the third generation mobile services?

A4)

It is called international mobile telecommunication 2000. For indoor and outdoor operation it has high data rate. It is for symmetrical and asymmetrical data transmission. It can be implemented for circuit switched and packet switched services. It can be implemented for multimedia services.

Fig: IMT Family structure

Q5) Explain the architecture of WCDMA network?

A5)

International mobile telecommunication-2000 is ITU globally co-ordinated term for 3G with some constraints like frequency spectrum uses and technical specifications.

Fig. Specification of IMT-2000 (radio interface)

Similarities :

• For higher data rate uses turbo code.
• Convolutional code used as baseline.
• Complex QPSK spreading on downlink.
• Soft handoff and mobile assisted procedure for inter frequency hard handoff proceed.

W-CDMA Features

Radio Interface  

It occupies 5 MHz channels. It has format for synchronization, power control etc.

CDMA Technology  

It allows multiple handset to get access at one base station same time. It uses DSSS for access.

Handover  

It is handoff from one cell to another. Different strategies needed to handle inter-cell intra-cell movements of users lies under same or different BTS, MSC in handoff mechanism.

Network Architecture  

Network architecture is designed in such a way that it supports packet data transmission.

User equipment in W-CDMA is radio frequency circuitry, baseband processing, battery Universal Subscribers Identity Module (USIM).

Fig.  WCDMA network architecture overview

Q6) What are features of HSCSD?

A6)

• HSCSD stands for high-speed circuit switched data. It is enhanced version of circuit switched data; it helps to improve error correction in various level of quality of radio links.
• HSCSD provides data rate up to 14.4 kbps by using multiple time slot at same time. It transfers time sensitive images or video at high speed.
• In generate some latency compared to GPRS while in transmission of normal voice and data traffic.

Features

1. High speed circuit switched data technology gives four times faster compare to typical GSM networks.

2. 38.8 kbps speed for all type of non-voice application.

3. It works with multiple slot which makes allow for data transmission at higher rate.

4. With all standard conditions (UL, DL) user can attain 40 to 57.4 kbps in specific area.

Q7) Explain GPRS network?

A7)

• General Packet Radio System (GPRS) is a packet based data services for wireless communication.
• A packet radio principle is used to transfer subscriber data packet within GSM mobile station and external packet data network.
• Data is split and transmitted at sender node and reassembled at receiving end. GPRS support IP and X.25, these operate over cellular connection of a GSM.
• According to peter Rysavy, Rysavy Research 1998 GPRS network is as follows :

Fig: GPRS network (1)

• GPRS system has a base of GSM communication and somewhat of circuit switched phone connection, Short Message Service (SMS).

Fig: GPRS Network (2) (by Peter Rysavy)

Q8) Explain working of GPRS?

A8) Working of GPRS

• SGSN:

It manages to send and receive of packet data to and from MS. It is useful for keeping track of mobile devices within scope of service area. It works in mobility management subscribed user verification and provides data required for billing.

• GGSN:

It has vital role of routing information whichever is necessary for tunneling Protocol Data Unit (PDUs). To SGSN to Serve Distinct MS. It is on interface for external PDNs. i.e. public data units like internet and X.25.

Charging gateway

• It maintains log entries for activities like data being transfer, change in charging terms in peak/off to peak and vice-versa, end of session for GPRS etc.
• It has collection records related to GPRS, usage in buffering of data, storage, transfer of data.

GTP

GPRS tunneling protocol uses to encapsulate IP or X.25 packet which are transferred among SGSN and GGSN.

Q9) List the applications of GPRS?

Application of GPRS

GPRS provides many functions among several applications. These are listed below:

• Chat
• Information services as text or graphics.
• Still images.
• Moving images
• Web browsing
• Document sharing and remote collaborative working
• Audio reports
• Job dispatch
• Corporate email
• Vehicle positioning
• File transfer.

Q10) What is EDGE technology?

A10) Enhanced Data rates for Global Evolution (EDGE) introduces a new modulation technique, as well as protocol enhancements for transmitting packets over the radio.

The use of the new modulation and the protocol enhancements, result in dramatically increased throughput and capacity gains enabling 3G services in the existing GSM/GPRS networks. No changes are needed to the existing core network infrastructure to support EDGE. This emphasizes the fact that EDGE is only an “add-on” for BSS.

For EDGE, nine Modulation and Coding Schemes (MCS) are introduced (MCS1 to MCS9) and optimized for different radio environment. Four EDGE coding schemes are using GMSK and five are using 8 PSK Modulation.

Up gradation to EDGE

• Mobile Station (MS) − MS should be EDGE enabled.
• BTS − HW supplied is Edge enabled.
• BSC − Definitions for EDGE timeslots needs to be done in BSC.
• GPRS Support Nodes (GSNs) − Definitions for Edge need to be defined in GSNs.
• Databases (HLR, VLR, etc.) − No definition is required.

Benefits of EDGE

• Short-term benefits − Capacity and performance,
• Easy implementation on a GSM/GPRS network,
• Cost effective,
• Increases the capacity and triples the data rate of GPRS,
• Enables new multimedia services,
• Long-term benefit − Harmonization with WCDMA.

What EDGE Would Mean to Subscribers

• Streaming applications
• Very high speed downloads
• Corporate intranet connections
• Quicker MMS
• Video phone
• Vertical corporate applications - Video conference, Remote presentations.

Q11) Compare the 2.5G technologies?

A11)

Q12) Explain the concept of data communication in GPRS?

A12) GPRS architecture works on the same procedure like GSM network, but, has additional entities that allow packet data transmission. This data network overlaps a second-generation GSM network providing packet data transport at the rates from 9.6 to 171 kbps. Along with the packet data transport the GSM network accommodates multiple users to share the same air interface resources concurrently.

Following is the GPRS Architecture diagram:

Fig: GPRS Architecture

GPRS attempts to reuse the existing GSM network elements as much as possible, but to effectively build a packet-based mobile cellular network, some new network elements, interfaces, and protocols for handling packet traffic are required.

GPRS Mobile Stations

New Mobile Stations (MS) are required to use GPRS services because existing GSM phones do not handle the enhanced air interface or packet data. A variety of MS can exist, including a high-speed version of current phones to support high-speed data access, a new PDA device with an embedded GSM phone, and PC cards for laptop computers. These mobile stations are backward compatible for making voice calls using GSM.

GPRS Base Station Subsystem

Each BSC requires the installation of one or more Packet Control Units (PCUs) and a software upgrade. The PCU provides a physical and logical data interface to the Base Station Subsystem (BSS) for packet data traffic. The BTS can also require a software upgrade but typically does not require hardware enhancements.

When either voice or data traffic is originated at the subscriber mobile, it is transported over the air interface to the BTS, and from the BTS to the BSC in the same way as a standard GSM call. However, at the output of the BSC, the traffic is separated; voice is sent to the Mobile Switching Center (MSC) per standard GSM, and data is sent to a new device called the SGSN via the PCU over a Frame Relay interface.

GPRS Support Nodes

Following two new components, called Gateway GPRS Support Nodes (GSNs) and, Serving GPRS Support Node (SGSN) are added:

Gateway GPRS Support Node (GGSN)

The Gateway GPRS Support Node acts as an interface and a router to external networks. It contains routing information for GPRS mobiles, which is used to tunnel packets through the IP based internal backbone to the correct Serving GPRS Support Node. The GGSN also collects charging information connected to the use of the external data networks and can act as a packet filter for incoming traffic.

Serving GPRS Support Node (SGSN)

The Serving GPRS Support Node is responsible for authentication of GPRS mobiles, registration of mobiles in the network, mobility management, and collecting information on charging for the use of the air interface.

Internal Backbone

The internal backbone is an IP based network used to carry packets between different GSNs. Tunnelling is used between SGSNs and GGSNs, so the internal backbone does not need any information about domains outside the GPRS network. Signalling from a GSN to a MSC, HLR or EIR is done using SS7.

Routing Area

GPRS introduces the concept of a Routing Area. This concept is similar to Location Area in GSM, except that it generally contains fewer cells. Because routing areas are smaller than location areas, less radio resources are used While broadcasting a page message.

Q13) Compare GSM and GPRS?

A13)

Q14) How is data transferred though GPRS explain?

A14) Data routing or routing of data packets to and fro from a mobile user, is one of the pivot requisites in the GPRS network. The requirement can be divided into two areas:

• Data packet routing
• Mobility management.

Data Packet Routing

The important roles of GGSN involve synergy with the external data network. The GGSN updates the location directory using routing information supplied by the SGSNs about the location of an MS. It routes the external data network protocol packet encapsulated over the GPRS backbone to the SGSN currently serving the MS. It also decapsulates and forwards external data network packets to the appropriate data network and collects charging data that is forwarded to a charging gateway (CG).

There are three important routing schemes:

• Mobile-originated message - This path begins at the GPRS mobile device and ends at the host.
• Network-initiated message when the MS is in its home network - This path begins at the host and ends at the GPRS mobile device.
• Network-initiated message when the MS roams to another GPRS network - This path begins at the host of visited network and ends at the GPRS mobile device.

The GPRS network encapsulates all data network protocols into its own encapsulation protocol called the GPRS tunnelling protocol (GTP). The GTP ensures security in the backbone network and simplifies the routing mechanism and the delivery of data over the GPRS network.

Mobility Management

The operation of the GPRS is partly independent of the GSM network. However, some procedures share the network elements with current GSM functions to increase efficiency and to make optimum use of free GSM resources (such as unallocated time slots).

An MS can be in any of the following three states in the GPRS system. The three-state model is unique to packet radio. GSM uses a two-state model either idle or active.

Active State

Data is transmitted between an MS and the GPRS network only when the MS is in the active state. In the active state, the SGSN knows the cell location of the MS.

Packet transmission to an active MS is initiated by packet paging to notify the MS of an incoming data packet. The data transmission proceeds immediately after packet paging through the channel indicated by the paging message. The purpose of the paging message is to simplify the process of receiving packets. The MS listens to only the paging messages instead of to all the data packets in the downlink channels. This reduces battery usage significantly.

When an MS has a packet to transmit, it must access the uplink channel (i.e., the channel to the packet data network where services reside). The uplink channel is shared by a number of MSs, and its use is allocated by a BSS. The MS requests use of the channel in a random access message. The BSS allocates an unused channel to the MS and sends an access grant message in reply to the random access message.

Standby State

In the standby state, only the routing area of the MS is known. (The routing area can consist of one or more cells within a GSM location area).

When the SGSN sends a packet to an MS that is in the standby state, the MS must be paged. Because the SGSN knows the routing area of the MS, a packet paging message is sent to the routing area. On receiving the packet paging message, the MS relays its cell location to the SGSN to establish the active state.

Idle State

In the idle state, the MS does not have a logical GPRS context activated or any Packet-Switched Public Data Network (PSPDN) addresses allocated. In this state, the MS can receive only those multicast messages that can be received by any GPRS MS. Because the GPRS network infrastructure does not know the location of the MS, it is not possible to send messages to the MS from external data networks.

Routing Updates

When an MS that is in an active or a standby state moves from one routing area to another within the service area of one SGSN, it must perform a routing update. The routing area information in the SGSN is updated, and the success of the procedure is indicated in the response message.

A cell-based routing update procedure is invoked when an active MS enters a new cell. The MS sends a short message containing the identity of the MS and its new location through GPRS channels to its current SGSN. This procedure is used only when the MS is in the active state.

The inter-SGSN routing update is the most complicated routing update. The MS changes from one SGSN area to another, and it must establish a new connection to a new SGSN. This means creating a new logical link context between the MS and the new SGSN and informing the GGSN about the new location of the MS

Q15) Explain 4G technology?

A15)

• 4G takes on a number of equally true definitions, depending on whom you are talking to. In simplest terms, 4G is the next generation of wireless networks that will replace 3G networks sometimes in future.
• In another context, 4G is simply an initiative by academic R&D labs to move beyond the limitations and problems of 3G which is having trouble getting deployed

And meeting its promised performance and throughput.

• In reality, as of first half of 2002, 4G is a conceptual framework for or a discussion point to address future needs of a universal high speed wireless network that will interface with wire line backbone network seamlessly.
• 4G is also represents the hope and ideas of a group of researchers in Motorola, Qualcomm, Nokia, Ericsson, Sun, HP, DoCoMo and other infrastructure vendors who must respond to the needs of MMS, multimedia and video applications if 3G never materializes in its full glory.

Motivation for 4G Research Before 3G Has Not Been Deployed?

• 3G performance may not be sufficient to meet needs of future high-performance applications like multi-media, full motion video, wireless teleconferencing. We need a network technology that extends 3G capacities by an order of magnitude.
• There are multiple standards for 3G making it difficult to roam and interoperate across networks. We need global mobility and service portability
• 3G is based on primarily a wide-area concept. We need hybrid networks that utilize both wireless LAN (hot spot) concept and cell or base-station wide area network design.
• We need wider bandwidth
• Researchers have come up with spectrally more efficient modulation schemes that cannot be retrofitted into 3G infrastructure
• We need all digital packet networks that utilize IP in its fullest form with converged voice and data capability.

Reasons to Have 4G

• Support interactive multimedia services: teleconferencing, wireless Internet, etc.
• Wider bandwidths, higher bit rates.
• Global mobility and service portability.
• Low cost.
• Scalability of mobile networks.

What's New in 4G?

Entirely packet-switched networks.

• All network elements are digital.
• Higher bandwidths to provide multimedia services at lower cost (up to 100Mbps).
• Tight network security.

Q16) Explain the need of 4G?

A16) Need of 4G:

• Firstly, 3G’s maximum data transfer rate of 384 kbps to 2 mbps is much slower than 20mbps to 100mbps of 4G.
• With its use of existing technologies & communication standards, 4G present a comparably inexpensive standard.
• 4G will utilize most of the existing wireless communication infrastructure

Q17) Explain the applications, advantage and disadvantages of 4G?

A17) Applications:

• 4G will provide for a vast no. Of presently nonexistent application for mobile devices.
• 4G device will differ from present day mobile device in that there will be navigation menus.
• 4G will provide a seamless network for users who travel & required uninterrupted voice/data communication.

Advantages and Disadvantages of 4G:

Advantages:

• Support for interactive multimedia voice, streaming video, internet & other broadband services.
• IP based mobile system.
• High speed, high capacity & low cost per bit.
• Global access, service portability & scalable mobile services.
• Better scheduling and call admission control technique.
• Ad-hoc & multi-hop network.
• Better spectral efficiency.
• Seamless network of multiple protocols & air interfaces.

Disadvantages:

• Expensive
• Battery uses are more hard to implement
• Need complicated hardware.

Q18) List all the designing goals which should be kept in mind for WLANs?

A18) The following are some of the goals which have to be achieved while designing WLANs:

• Operational simplicity: Design of wireless LANs must incorporate features to enable a mobile user to quickly set up and access network services in a simple and efficient manner.
• Power-efficient operation: The power-constrained nature of mobile computing devices such as laptops and PDAs necessitates the important requirement of WLANs operating with minimal power consumption. Therefore, the design of WLAN must incorporate power-saving features and use appropriate technologies and protocols to achieve this.
• License-free operation: One of the major factors that affects the cost of wireless access is the license fee for the spectrum in which a particular wireless access technology operates. Low cost of access is an important aspect for popularizing a WLAN technology. Hence the design of WLAN should consider the parts of the frequency spectrum (e.g., ISM band) for its operation which do not require an explicit licensing.
• Tolerance to interference: The proliferation of different wireless networking technologies both for civilian and military applications and the use of the microwave frequency spectrum for non-communication purposes(e.g., microwave ovens) have led to a significant increase in the interference level across the radio spectrum. The WLAN design should account for this and take appropriate measures by way of selecting technologies and protocols to operate in the presence of interference.
• Global usability: The design of the WLAN, the choice of technology, and the selection of the operating frequency spectrum should take into account the prevailing spectrum restrictions in countries across the world. This ensures the acceptability of the technology across the world.
• Security: The inherent broadcast nature of wireless medium adds to the requirement of security features to be included in the design of WLAN technology.
• Safety requirements: The design of WLAN technology should follow the safety requirements that can be classified into the following: (i) interference to medical and other instrumentation devices and (ii) increased power level of transmitters that can lead to health hazards. A well-designed WLAN should follow the power emission restrictions that are applicable in the given frequency spectrum.
• Quality of service requirements: Quality of service (QoS) refers to the provisioning of designated levels of performance for multimedia traffic. The design of WLAN should take into consideration the possibility of supporting a wide variety of traffic, including multimedia traffic.
• Compatibility with other technologies and applications: The interoperability among the different LANs (wired or wireless) is important for efficient communication between hosts operating with different LAN technologies. In addition to this, interoperability with existing WAN protocols such as TCP/IP of the Internet is essential to provide a seamless communication across the WANs. 1.2.2 Network Architecture This section lists the types of WLANs, the components of a typical WLAN, and the services offered by a WLAN. Infrastructure Based Versus Ad Hoc LANs WLANs can be broadly classified into two types, infrastructure networks and adhoc LANs, based on the underlying architecture. Infrastructure networks contain special nodes called access points (APs), which are connected via existing networks.
• APs are special in the sense that they can interact with wireless nodes as well as with the existing wired network. The other wireless nodes, also known as mobile stations, communicate via APs. The APs also act as bridges with other networks. Ad hoc LANs do not need any fixed infrastructure. These networks can be setup on the fly at any place. Nodes communicate directly with each other or forward messages through other nodes that are directly accessible.

Q19) What are fundamentals on WLAN? What is the difference between wireless and wired transmission?

A19) The terms "node," "station," and "terminal" are used interchangeably. While both portable terminals and mobile terminals can move from one place to another, portable terminals are accessed only when they are stationary. Mobile terminals (MTs), on the other hand, are more powerful, and can be accessed when they are in motion. WLANs aim to support truly mobile work stations.

Differences Between Wireless and Wired Transmission

• Address is not equivalent to physical location: In a wireless network, address refers to a particular station and this station need not be stationary. Therefore, address may not always refer to a particular geographical location.
• Dynamic topology and restricted connectivity: The mobile nodes may often go out of reach of each other. This means that network connectivity is partial at times.
• Medium boundaries are not well-defined: The exact reach of wireless signals cannot be determined accurately. It depends on various factors such as signal strength and noise levels. This means that the precise boundaries of the medium cannot be determined easily.
• Error-prone medium: Transmissions by a node in the wireless channel are affected by simultaneous transmissions by neighboring nodes that are located within the direct transmission range of the transmitting node. This means that the error rates are significantly higher in the wireless medium. We need to build a reliable network on top of an inherently unreliable channel. This is realized in practice by having reliable protocols at the MAC layer, which hide the unreliability that is present in the physical layer. Uses of WLANs Wireless computer networks are capable of offering versatile functionalities. WLANs are very flexible and can be configured in a variety of topologies based on the application. Some possible uses of WLANs are mentioned below.
• Users would be able to surf the Internet, check e-mail, and receive Instant Messages on the move.
• In areas affected by earthquakes or other such disasters, no suitable infrastructure may be available on the site. WLANs are handy in such locations to set up networks on the fly.
• There are many historic buildings where there has been a need to set up computer networks. In such places, wiring may not be permitted or the building design may not be conducive to efficient wiring. WLANs are very good solutions in such places.

Q20) What are the qualities and services provided by 3G networks?

A20) Third generation (3G) is the generic term used for the next generation of mobile communications systems. These have been created to support the effective delivery of a range of multimedia services. In addition, they provide more efficient systems for the over-the-air transmission of existing services, such as voice, text and data that are available today.

3G wireless technology represents the convergence of various 2G wireless telecommunications systems into a single global system that includes both terrestrial and satellite components. One of the most important aspects of 3G wireless technology is its ability to unify existing cellular standards, such as CDMA, GSM, and TDMA, under one umbrella.

3G wireless networks consist of a Radio Access Network (RAN) and a core network. The core network consists of a packet-switched domain, which includes 3G SGSNs and GGSNs, which provide the same functionality that they provide in a GPRS system, and a circuit-switched domain, which includes 3G MSC for switching of voice calls.

3G: what's new?

A wide range of market-focused applications

 Long-term market-driven creativity, an innovative value chain and real user benefits, driving genuine market demand

 Advanced, lightweight, easy-to-use terminals with intuitive interfaces · Instant, real-time multimedia communications

 Global mobility and roaming

 A wide range of vendors and operators, offering choice, competition and affordability

High-speed e-mail and Internet access

3G enabled users to transmit voice, data, and even moving images. In order to realize these services, 3G improves the data transmission speed up to 144Kbps in a high-speed moving environment, 384Kbps in a low-speed moving environment, and 2Mbps in a stationary environment. 3G provides services like Internet connection, transmission of large-scale data and moving contents photographed by digital cameras and videos, and software downloading.

At present, maximum data transmission speed is 64Kbps offered in 3G services, and it was expected that by toward early 2001, 384Kbps would be possible. At the early stage of 3G services, a 144Kbps-transmission speed is expected. By around 2005 when 3G is in general use; a maximum speed of 2Mbps will be possible.