WIRELESS COMMUNICATION AND NETWORKS ECE,B.TECH IV, II SEM UNIT VII MOBILE DATA NETWORKS ( REF BOOK:PRINCIPLES OF WIRELESS NETWORKS BY KAVEH PAHLAVAN CHAPTER.

WIRELESS COMMUNICATION AND NETWORKSECE,B.TECH IV , II SEM

UNIT VII

MOBILE DATA NETWORKS

(REF BOOK:PRINCIPLES OF WIRELESS NETWORKS BY KAVEH PAHLAVAN CHAPTER 9)

UNIT VII Syllabus

• Introduction

• Data oriented CDPD Network,

• GPRS and higher data rates

• Short messaging services in GSM

• Mobile Application Protocol

INTRODUCTION

• of Mobile Data Networks or wireless wide area networks refers to lower speed wide area wireless data services.

• Wireless data networks are becoming increasingly important in the light of wireless access to the Internet, development of wireless oriented consumer products, and wireless home networking.

• As compared to voice oriented services, shift towards data services is fueled by new content based services, SMS, advertisements, E-commerce, M-commerce etc.

• Mobile data Industry started with ARDIS (in 1983) as a pvt. Network for IBM

WHAT IS MOBILE DATA• The mobile data networks refers to those services,

technologies, and standards that are related to data services over wide area coverage i.e. areas spanning more than the local area or campus..

• SMS services are embedded in digital cellular systems such as GSM.• These services use 10 digit keypad of the mobile terminal or computer

keyboards to type and display a message and use the digital cellular network facilities to deliver the message.

• Mobile Data Networks are part of WLAN. These are classified as below.

INDEPENDENT MOBILE DATA• Independent networks have their own spectrum that are not

coordinated with any other service and their own infrastructure that is not shared with any other service.

• These Networks are divided into two groups according to the status of their operating frequency band.

• The FIRST GROUP uses independent spectrum in licensed bands. Example: ARDIS Network and Mobitex Network.

• These Networks were not Economically successful.

• The SECOND GROUP is independent mobile data networks making use of un-licensed spectrum that is shared among a variety of applications and users.

• Example: Metricom’s Ricochet service, which used the 915 MHz unlicensed band. This service was deployed in airports and some Metropolitan area for Wireless Internet access.

SHARED MOBILE DATA• These networks share the spectrum and part of the infrastructure with

an already existing voice-oriented analog services• The service uses the same Radio channel used for analog voice, but

they have their own air-interface and MAC protocol.• In addition to dedicated channels for data, these mobile data services

can also use the available unused voice channels.• These systems share an existing system infrastructure, therefore the

initial investment is not huge ,and it could be made as gradually as possible.

• Example: CDPD service which shares spectrum and part of the infrastructure with AMPS, is an example of such networks.

• CDPD does not have an independent air-interface and MAC layer, along with additional infrastructure required for operation of data services.

• For long time CDPD user base did not grow as expected. However, It improved with the availability of MODEMS for palm computing devices

OVERLAY MOBILE DATA

• The last group of mobile data networks is an OVERLAY on existing networks and services. This means that the data service will not only make use of the spectrum allocated for another service but also the MAC frames and air-interface of an existing voice oriented digital cellular system.

• Example: GPRS and GSM’s SMS services • They make use of free time slots available within the traffic channels

and signaling channels in GSM.• The requirement of additional infrastructure is reduced to minimum.• Most of the extra components required are implemented in software,

making it inexpensive and easy to deploy.

• GPRS type of services uses computer keyboard to communicate longer messages, and SMS use the cellular phone dialing keypad to communicate short message.

THE DATA ORIENTED CDPD NETWORK• CDPD has been one of the longest surviving wide area mobile data

technologies worldwide.

• It is a shared mobile data network that shares part of the infrastructure and the entire system with AMPS in USA.

• It is an open standard making its implementation easier and more widespread.

• Specifications of CDPD are based on an open architecture, and the mobility management technique closely follows and is a precursor of the mobile-IP standard.

• The CDPD standard came out in 1995 though it was in deployment since 1992 in BAY area.

DEDIGN OBJECTIVES OF CDPD• Open Architecture. Minimum invention.• Reusing as much of the existing RF infrastructure as

possible.• Location independence • Independence from Service provider so that coverage

could be maximized• Application transparency• Multi-protocol support,• Interoperability between products from multiple vendors,

• Optimal use of RF where air-interface efficiency is given priority over other resources.

• Design to be evolutionary and based on OSI model with support for native IP, so that if transport layer or application layer protocols were implemented, there was no need for changes.

DEDIGN FEATURES OF CDPD • CDPD used primitive RF technology for cost reasons • Modulation scheme GMSK• Raw signaling rate 19.2 Kbps.• With Reed-Solomon coding the effective data rate is14.4 Kbps full

duplex before control overhead.

• The prominent feature of CDPD has been its openness and freedom from all proprietary technology, support for multi-vendor interoperability, and simplicity in design.

• CDPD works on shared mobile data networks where AMPS is having priority over usage of spectrum.

• CDPD employs a technique called “RF SNIFFING” to detect whether an AMPS call is trying to access a frequency chl. and hopping to move from such a band to another to give the voice call priority.

• About 20% of AMPS channels that can be used for CDPD are idle at a given time.

CDPD SERVICES 1:NETWORK SERVICES are the basic form of services

offered by CDPD like:• Transfer of Data from one location to another via popular

or standard network layer protocol-CLNP ( connectionless network protocol) and in that sense acts simply as a wireless extension to the Internet.

2: NETWORK SUPPORT SERVICES are services necessary to maintain the operation of the mobile data network such as management, accounting, security ETC.

• These services include mobility and Radio resource management and usually transparent to the user.

• Such services add intelligence to the network.

3: NETWORK APPLICATION SERVICES: These are value added services.

REFERENCE ARCHITECTURE IN CDPD• There are 3 Key CDPD interfaces that form logical boundaries for a

CDPD service provider’s network.• They are essential for proper operation of CDPD.• There are some interfaces internal to the “cloud”.• Such interfaces are only recommended, and service provider can

implement them differently.• Each interface specifies a protocol stack corresponding to the OSI

model and primitives are defined at each layer that can request and obtain services from the layer below

INTERFACE DETAILS There are 3 Key CDPD interfaces that form logical

boundaries for a CDPD service provider’s network

1:The “A-Interface” is the air link interface.

2: The “E-Interface” is the external interface, and it is the means by which CDPD operates with the rest of data network.

• Over this interface IP and CLNP ( connection less network protocol) are supported and IPv6 will be supported as it becomes deployed.

• Other protocols are supported by encapsulation because they are outside the CDPD Specs.

• Mobility is transparent to the network beyond the E-interface.

INTERFACE DETAILS (cont..)3: The “I-interface” is the inter-service provider interface.

When networks are partitioned in multiple service providers, the I-interface enables seamless nationwide service.

• It supports all of the E-interface protocols Plus two CDPD specific protocols- “ The Mobile Network Location

Protocol” (MNLP) which is the protocol by which users from one system are supported by another system and is the Key piece of CDPD mobility management scheme.

• Network management and accounting protocols are also defined at the I-interface

• All the protocols are based on CLNP ( except reverse channel IP packet).

PHYSICAL ARCHITECTURE 1:M-ES Mobile –end system (are telemetery devices, laptops, vending

m/c, hand set etc) is ultimate source and destination of protocol control data units (PDUs).

• M-ES protocols are specified up to layer 3.• The subscriber unit establishes and maintains data communication,

executes CDPD air-interface protocols, and includes administrative and management layers.

2: MDBS is the system end( network side) of the MAC sub-layer over the air-interface.

• MDBS is equivalent to BSS of GSM system and is pretty much the BS electronics foe CDPD.

• It is also like an ETHERNET Hub and acts as a link layer or bridge.• It communicates with M-ES through the A-interface and performs the

modulation of data bits and demodulates the RF signal• It actively participates in Digital Sense Multiple Access (DSMA).• It is Layer 3 addressable for network management

PHYSICAL ARCHITECTURE (Cont…)

.

3: The MD-IS is the focal point od CDPD mobility management and packet forwarding.

• It has a mobile serving function (MSF) that serves as the foundation for registration of a mobile and mobile home function (MHF) and serves as an anchor point for locating a mobile.

4: The fixed end system (F-ES) is a conventional network node that includes most PC work stations, and so on that are transport layer peers of the M-Es.

• It usually operates functionally in the role of administrative servers and value-added servers.

MOBILITY SUPPORT IN CDPD• As in the case of most mobile networks, mechanism are in

place in CDPD to support the mobile environment. • We consider following aspects in CDPD:

1: Radio resources

2: Mobility management and

3 : Security

MOBILITY MANAGEMENT IN CDPD• HAND OFF in CDPD occurs when• i) An M-ES moves from one cell to another or• ii) If the CDPD chl. Quality deteriorates, • Iii) The current CDPD channel is requested by an AMP Voice call

(forced hop), or• iv) The load on the current CDPD chls. in the current cell is much more

than the load on the channels in an overlapping cell.

• PHYSICAL LAYER in CDPD provides • i) The ability to tune to a specific RF channel• ii) Ability to measure the received signal strength indication (RSSI)• Iii) Ability to set the power of the M-ES transmitted signal to specified

level and,• iv) Ability to suspend and resume monitoring of RF Chls in the M-ES.

MOBILITY MANAGEMENT IN CDPD (Cont…)• UPLINK AND DOWN LINK CHANNELS: • i) Both Channels atr slotted• ii) There is no contention in the DN-link, and MDBS will transmit link

layer frames sequentially.• iii) On UP-link, a DSMA/CD ( digital sense multiple-access with

collision detection) protocol is employed.• iv) Collision detection is at the BS and informed to the MHs on the DN-

link• v) On the DN-link, multiple cell configuration messages are broadcast,

including for the given cell and its neighbors,

1: The cell identifier

2: A reference channel.

3: The actual CDPD data channel

4: A RSS bias to compare the reference channels of a given cell and

adjacent cells.

5: a list of channels allocated to CDPD.• vi) RSS measurement is always done on the reference channel.

MOBILITY MANAGEMENT IN CDPD (Cont…)MOBILE HANDSET (MH) OPERATION

• Upon powering MH scans the air and locks to the strongest “acceptable” CDPD chl stream and register with the MD-IS that serves the base station.

• This is done via the Mobile Network Registration Protocol (MNRP) where by MH announces his presence and also authenticates itself.

• Registration protects against the Fraud and enables the CDPD network to know the mobile location, and update its mobility data base.

• The MH continues to listen to the CDPD channel unless it ( or the CDPD network) initiates a hand off.

• CDPD Mobile management is based on principles similar to MOBILE IP.

GPRS AND HIGHER DATA RATES• GPRS is an overlay on top of the GSM physical layer and

Network entities.

• It extends data capabilities of GSM and provides connections to external packet data network through the GSM infrastructure with short access time to the network for independent short packets(500-1000 bytes)

• There are no hardware changes to the BTS/BSC ( compared to CDPD

• easy to scale, • support for voice/data and data only terminals, • high throughput( up to 21.4 Kbps) and • user friend billing.

WHAT IS GPRS• GPRS is an enhancement of the GSM. It uses exactly the same

physical Radio as GSM channels.

• Allocation of these chls is flexible from one to eight radio interface timeslots can be allocated per TDMA frame.

• The active users share the time slots, and up-link and down-links are allocated separately.Physical channels are taken from the common pool of available chls in the cell.

• Allocation to circuit switched service and GPRS is done dynamically according to a “Capacity on Demand” principle. GPRS does not require permanently allocated physical chls.

• GPRS offers permanent connections to the INTERNET with volume based charging that enables a user to obtain a less expensive connection to the internet.

WHAT IS GPRS• The GPRS MSs are of three types.

1: Class A terminals operate GPRS and other GSM services simultaneously.

2: Class B terminals can monitor all services , but operate either GPRS or another service, such as GSM, one at a time.

3: Class C terminals operate only GPRS service .• This way there are options to have high-end or low-end terminal

LIMITATIONS OF GPRS• GPRS has some limitations in that there is only limited cell capacity for

all users and speeds much lower in reality.• There is no store and forward service in case the MS is not available.• The more popular short message service (SMS) provides this feature

ADAPTATION OF GPRS• The adaptation of GPRS to th IS-136 TDMA cellular

standard is called GPRS-136.

• It is very similar to GPRS except that it uses 30 KHz physical channels instead of 200KHz physical channels.

• There is no separate BSC

• It can use coherent 8-PSK in addition to π/4-DQPSK to increase the throughput over a limited area.

• ThesE concept is similar to the 2.5G data service called ENHANCED DATA RATE FOT GLOBAL EVOLUTION (EDGE)

GPRS NETWORK SERVICES 1:Point- to- Multipoint (PTM-M) service is a multicast service to all

subscribers in a given area,

2: Point-to- Multipoint (PTM-G) service is a multicast service to predetermined group that may be dispersed over a geographical area.

3: Point-to-point (PTP) service which is packet data transfer.

This PTP is of two type:

i) Connectionless based on IP and CLNP called PTP-CLNS and

ii) Connection-oriented based on X.25 (PTP-CONS).• GPRS also provides bearer service for GSM’s SMS .• There is also an anonymous access for MS at no charge (like 800nos

service.)

QOS AND RELIABILITY IN GPRS• GPRS has parameters that specify a QoS based on service

precedence, a priority of service in relation to another service( High, Normal, and Low) reliability and transmission characteristics required.

• Three reliability cases are defined and four delay classes. Here delay is defined on end to end basis, or between MS and the interface to the network external to GPRS.

• Transmission characteristics are specified by the maximum and mean bit rates. The max bit rate value can be between 8 kbps and 11 Mbps.

• The mean bit rate value is, 0.22Kbps to 111Kbps.

REFERENCE ARCHITECTURE IN GPRS• GPRS reuses the GSM Architecture to a very large extent.

• There are a few new network entities called GPRS Support nodes (GSN) that are responsible for delivery and routing of data packets between the mobile station and external packet network.

• There are two type of GSN

1: SGSN: The serving GPRS support node and

2: GGSN: The gateway GPRS support node.

• These are comparable to MD-IS

• There is also a new data base called the GPRS register (GR) that is co-located with the HLR. It stores routing information and maps the IMSI to a PDN address ( IP address for example).

• Fig 9.10 shows this reference Architecture.

LOCATION AND HAND OFF MANAGEMENT• These procedures in GPRS are based on keeping track of the MSs

location and having capability to rout packets to it.• The SGSN and GGSN play the role of foreign and HAs ( foreign and

home databases) in GPRS. • Location management depends on three states in which the MS Can

be.

LOCATION MANAGEMENT• In the IDLE state The MS is not reachable, and all PDP

contexts are deleted.

• In STANDBY state, movement across routing area is updated to the SGSN but not across cells. A STANDBY state focuses the area to the service area of the SGSN.

• In the REDDY state , every movement of the MS is indicated to the SGSN. The READY state pinpoints the area when the chances of packets reaching are high.

MOBILITY MANAGEMENT IN GPRS• Mobility management in GPRS starts at Hand off initiation.• The MS listens to BCCH (Broadcast control channel) and decides

which cell it has to select based on RSS measurement like in GSM.• Other than RSS hand off decisions can be based on path loss, cell

ranking etc. • The Hand off procedure is very similar to mobile IP.

POWER CONTROL AND SECURITY

• Power control and Security mechanisms are very similar to the way in which they are implemented in GSM.

• The CIPHERING ALGORITHM is used to provide confidentiality and integrity protection of GPRS user data used for PTP mobile originated and mobile- terminated data transmission and point to multi- group (PTM-G) mobile terminated data transmission.

• The algorithm is restricted to the MS-SGSN encryption.

PROTOCOL LAYERS IN GPRS

TRANSPORT LAYER• In order to transport different network layer packets, GPRS

specifies a protocol stack like CDPD and GSM. • This is transport plane ( where user data is transferred

over the GPRS/GSM infrastructure.

PROTOCOL LAYERS IN GPRS (Cont…)GPRS SIGNALING

• There is also GPRS signaling plane to enable signaling between various elements in the architecture ( like messaging between the SGSN and BSS etc.)

• GPRS employs out of band signaling in support of actual data transmission.

• Signaling between SGSN, HLR,VLR and EIR is similar to GSM and extends only the GPRS related functionality.

• It is based on SS-7

• Between the MS and sgsn, a GPRS mobility management and session management (GMM/SM) protocol is used for signaling purposes.

GPRS TRANSPORT PLANE LAYERS

• The GPRS transport plane has different layers in different elements.

PHYSICAL LAYER• The physical layers between the MS-BSS, BSS-SGSN and

SGSN-GGSN are shown in Fig 9.13

• Over the air , the physical layer is same as GSM.

• Its functionality include forward error correction and indication of uncorrectable code words, interleaving of radio “Blocks”, synchronization, Monitoring of radio link signal quality and so on.

• All other functions are similar to GSM.

GPRS TRANSPORT PLANE ALLOCATION OF RADIO RESOURCES

• Allocation of Radio resources is also slightly different compared with GSM.

• A cell may or may not support GPRS.• If it supports GPRS then radio resources are dynamically allocated

between GSM and GPRS services.• Channels nomenclature used for resource allocation.

PDCH: Packet data channel

PACCH: Packet associated control channel.

PDTCH: Packet data traffic channel.

PSCCH: Packet BCCH (Broadcast control channel)

PRACH: Packet RACH (Random access channel)

PAGCH: Packet AGCH (Access grant channel)

PTCCH: Packet timing-advance control channel• The process of Data Packets Negotiation used for resource allocation

in Up link and Down Link are shown in Fig 9.14 and 9.15 respectively

GPRS TRANSPORT PLANE ALLOCATION OF RADIO RESOURCES

• Up link and down link transmissions are independent The medium access protocol called “ Master-Slave Dynamic rate access” or MSDRA.

• Here the organization of time slot assignment is done centrally by the BSS.

• A “Master” PDCH includes common control channels that carry signaling information required to initiate the packet transfer.

• The “Slave” PDCH includes user data and dedicated signaling information for an MS.

• The Packet transfer on the uplink and down link are shown in fig 9.14 and 9.15. They are quite similar to the process in GSM.

GPRS NETWORK SUPPORTSNDCP PROTOCOL

• GPRS supports IP and X.25 packets at the network layer to be used by end-to-end application.

• The SNDCP ( Sub-Network dependent Convergence Protocol) supports a variety of network protocols( IP, X.25 , CLNP etc)

• ALL network layer packets share the same SNSCP.• It multiplexes and de-multiplexes the network layer payload and forms

the interface between link layer (LLC) and the network layer.

LLC LAYER• The LLC Layer forms the logical link between the MS and SGSN

(similar to CDPD’s MDLP).• Each MS has temporary logical link identity (TTLI) to identify itself in

the LLC header.• The LLC performs sequence control, error recovery, flow control, and

Encryption.• It has an acknowledged mode ( with retransmission for network layer

protocol) and an unacknowledged mode (for signaling and SMS)

Fig 9.16 shows how packets flow from higher layer, application. And signaling levels to the SNDCP and the LLC. The Packet transformation data flow is shown in fig 9.17

SHORT MESSAGING SERVICES IN GPRS

SHORT MESSAGING SERVICES (SMS) IN GPRS

• The proliferation of GSM enabled the introduction of the SMS.

• It is similar to peer –to-peer instant messaging service on the Internet.

• Users can Exchange alphanumeric message of up to 160

characters( mapped in to 140 bytes) within seconds of submission of message.

• The service is available wherever GSM exits.

• SMS was developed as part of GSM Phase 2 specification.

• It uses the same network entities ( with the addition of a SMS center-SMSC), the same physical layer, and intelligently reuses the logical channel of GSM system to transmit SMS message.

SMS SERVICE DESCRIPTION• Instant delivery service if MS is active or store and forward

if MS is inactive.

• Two type of services 1: CELL BROADCAST SERVICE: The message is

transmitted to all MSs that are active in a cell and subscribed to the service.

This is an unconfirmed one way service to send weather forecasts, stock quotes and so on.

2: PTP ( point-to-point service)

• A Short Message (SM) can have a specified priority level, future delivery time, expiration, or it might be one of the several short predefined messages.

• Sender may request acknowledge of receipt.

OVERVIEW OF SMS OPERATION• SMS makes use of the gsm infrastructure, protocols, and

physical layer to manage the delivery of message.• SMS service is of store forward nature.• SMSC sorts and routes the message appropriately.

OVERVIEW OF SMS OPERATION (CONT..)• There are two cases of short messages: a mobile origined

SM and a mobile terminated short message.

• A SM originating from MS first reached MSC for processing.

• A dedicated function in MSC called the “SMS-INTERNETWORKING” allows the forwarding of the SM to the SMSC using a global SMSC-ID.

• An SM that terminates at the MS is forwarded by the SMSC to the SMS gateway MSC function in MSC.

SMS LAYERS• There are four Layers in SMS-

1:The application layer (AL): The Al can generate and display the alphanumeric message

2: The transfer layer (TL):The SMS-TL services the SMS_AL to exchange SMs and receive confirmation of receipts

3: The relay Layer (RL): The RL relays the SMS PDUs through the LL

4: The link layer LL.

• There are 6 PDU’s type in SMS that convey the short message- from the SMSC to MS and vice-versa, convey a failure cause, and convey status reports and commends

END OF WCN UNIT VII

MOBILE DATA SERVICES