Wcn Unit III- Wireless Data Services Dec-11

WIRELESS COMMUNICATION AND NETWORKSB.TECH IV , II SEM

UNIT IIIWRELESS DATA SERVICES

(REF. BOOK WIRELESS COMMUNICATIONBY RAPPAPORT-CHAP-10)

BYPROF. K.S. VERMA

2011-2012

UNIT III Syllabus

• CDPD• ARDIS• RMD• Common channel signaling• ISDN• BISDN and ATM• SS7• SS7 User part• Signaling traffic in ss7

WIRELESS DATA SERVICES

• Circuit switching is inefficient for dedicated mobile data services like: Fax, E-mail, SMS etc.

• 1G cellular systems that provide Data Communications using circuit switching had difficulty of passing modem signals through audio filters of receivers designed for analog FM common air interface.

• In 1993, US cellular Industry developed “cellular digital packet data (CDPD)” standard to coexist with the conventional voice only cellular system.

• In 1980s, two data only mobile servicesdata only mobile services called ARDIS and RAM Mobile Data (RMD). were developed to provide packet radio connectivity throughout the networks.

Cellular Digital Packet Data (CDPD)• CDPD is a data service for 1G and 2G cellular system using

30 KHz AMP Chls.( data rate 19.2Kbps) on a share basis.

• CDPD provides mobile Packet DATA connectivity to existing data networks and other cellular networks without any additional BW requirement.

• It uses unused airtime (estimated 30%) which occurs between successive RF Chl. Assignment by MSC.

• CDPD directly overlays with existing cellular infrastructure of Base stations.

• CDPD does not use the MSC but rather has its own traffic routing capabilities.

CDPD FEATURES (cont…) • CDPD chl. is duplex in nature having forward and reverse

chls.

• CDPD supports broadcast, dispatch, E-mail and field monitoring applications

• Modulation is GMSK BT= 0.5%

• CDPD transmissions are carried out using fixed-length blocks.

• User data is protected using a REED-Solomon(63,47) block code with 6 bits symbol.

• For each packet, 282 user bits are coded into 378 bit block, which provided correction for up to eight symbols

PROTOCOLS USED IN CDPD

• Lower two layers are used in CDPD.

• The Mobile Data Link Protocol ( MDLP) is used to convey information between data link layer entities across the CDPD air interface.

• MDLP provides sequence control to maintain sequential control and address in each packet.

• Radio resource management protocol (RRMP) is a higher, layer 3 protocol used to manage the radio channel resources of the CDPD.

• The RRMP handles base station identification and configuration for all M-ES station, and provides information that the M-ES can use to determine usable CDPD chls

• RRMP also handles chl hopping commands, cell handoffs, and M-ES change of power commands.

TYPICAL CDPD NETWORK

ADVANCED RADIO DATA INFORMATION SYSTEM (ARDIS)

• ARDIS is a private network service provided by Motorola and IBM. It is based on MDC4800 and RD-LAP (Radio data link access procedure) protocol developed at Motorola.

• ARDIS provides 800 MHz two way mobile data communication for short length radio messages in urban and in-building environment and users traveling at low speed.

• SHORT ARDIS MESSAGES: Have Low retry rates but high packet overhead.

• LONG ARDIS MESSAGES: Spread the overhead over the length of the packet but have higher retry rate.

• Table 10.3 lists some of the characteristics of ARDIS.

RAM MOBILE DATA (RMD)• RMD is a public, two way data service based upon the MOBITEX

protocol developed by Ericsson.

• RAM provides street level coverage for the short and long messages for user moving in an urban environment.

• RAM has capability for voice and data transmission, but designed primarily for data and fax.

• FAX messages are transmitted as normal text to a gateway processor, which then converts the radio message to an appropriate format.

• Thus the packet switched wireless transmission consists of a normal length message in stead of a much larger fax image, even though the end user receives what appears to be a standard fax.

COMMON CHANNEL SIGNALING

(IN TELEPHONE NETWORKS)

COMMON CHANNEL SIGNALING (IN TELEPHONE NETWORKS)

• A separate analogue voice channel is used for signaling.

• Signaling in CCS is digital in nature and MODEMS are used for carrying digital data over analogue lines.

• A channel can carry signal information for a group of circuits. The group size is determined by the capacity of a signaling channel.•CCS Signaling is completely separate from switching and speech transmission.

• A 2.4 Kbps bit rate CCS signaling link can support up to 1500 – 2000 speech circuits.

CCS Signaling is done over a channel that is different from the one which carries the voice or data.Two signaling channels, one for each direction, are used in a dedicated manner to carry signaling information.

COMMON CHANNEL SIGNALLING (CCS) (WIRELESS NETWORKS)

• CCS is a digital communication technique that provide simultaneous transmission of user data, signal data and other related traffic throughout a network.

• This is accomplished by using OUT OF BAND SIGNALING channels which logically separate the network data from user information (voice and data) on the same channel.

• For 2nd generation wireless communication systems, CCS

is used to pass user data and control / supervisory signals between the subscriber and the base station, between base station and the MSC, and between MSCs.

• Even though the concept of CCS implies dedicated, parallel channels, it is implemented in a TDM format for serial data transmission.

COMMON CHANNEL SIGNALLING (CCS) CONT…

• CCS is an out of band signaling technique which allows faster communication between two nodes within PSTN.

• Because of out of band signaling, CCS supports signaling data rates from 56 Kbps to many Mbps.

• CCS provides substantial increase in the number of users which are served by trunked PSTN lines, but requires a dedicated portion of the trunk time to provide signaling channel used for network traffic.

• In first generation cellular systems, the SS7 family of protocols, as defined by the ISDN are used to provide CCS.

COMMON CHANNEL SIGNALLING (CCS) CONT…

• Since Network signaling traffic is bursty and of short duration, the signaling channel may be operated in a connection less fashion where packets data transfer techniques are efficiently used.

• CCS generally uses variable length packet sizes and a layered protocol structure.

• The expanse of a parallel signaling channel is minor compared to the capacity improvement offered by CCS, through out the PSTN, and often the same physical network connection( i.e. fiber optic cable) carries both the user traffic and the network signaling data.

THE DISTRIBUTED CENTRAL SWITCHING OFFICE FOR CCS

• As more users subscribe to wireless services, backbone network that links MSCs together

1: To provide end-to-end connectivity for each mobile user,

2: To maintain a robust network that can recover from failure

CCS, forms the foundation of network control and management function in 2nd and 3rd generation networks.

• Out-of-band signaling networks which connect MSCs through out the world enable

1: The entire wireless network to update and

2:Keep track of specific mobile user, wherever they happen to be.

THE DISTRIBUTED CENTRAL SWITCHING OFFICE FOR CCS

• The MSC provides subscriber access to PSTN via SEP.

• The SEP implements stored-program-controlled switching system known as service control point (SCP)

• SCP uses CCS to set up calls and to access the network database.

• The SCP instructs SEP for creating billing records.• The STP controls the switching of messages between

nodes in the CCS network.• The SMS contains all subscriber records, and also houses

toll free database which may be accessed by the subscribers.

SWITCHING TECHNIQUES

• Diverse characteristics of voice and Data traffic led to development different switching techniques other than the one used for voice communication.

• Two switching techniques are prevalent for data transmission.1: Circuit switching2:Store and forward (S&F) switching

• Circuit switching is entirely analogous to the telephonic switching.

• S&F switching is analogous to the postal or telegraph system.

CIRCUIT SWITCHING

• Electrical path is established between source and the destination before any data transfer takes place.

• It remains dedicated to the communication pair for the entire duration of the transmission irrespective of whether data is actually being transferred or not.

• The connection is released only when specifically signalled so by either of the communicating entities.

• Data transmission through PSTN connection is typical example of a circuit switched data transfer.

• There are three explicit phases involved in circuit switched data transfer.

1: Connection establishment

2: Data transmission.

3: Connection release.

DISADVANTAGES OF CIRCUIT SWSITCHING

• 1:Excessively long path set-up time, typically 20 to 30 s.• Excessive overhead for bursty computer traffic.

• The entire line quality is affected if there is one bad link in the circuit.

• Speed of operation of the circuit the link is limited by the slower. This amounts to poor utilization of high quality high capacity links.

• The network provides no error control facilities which are to be handled by the end system.

• In circuit switched connections , the required Bandwidth is allocated statistically and the unused band width is wasted.

DRAW BACKS OF MESSAGE SWITCHING AND ADVANTAGES OF PACKET SWITCHING

MESSAGE SWITCHING• For long messages it becomes important to ensure that

there is adequate storage space on the receiving node before transmission is initiated.

• If error occurs during transmission, the entire message may have to be retransmitted.

• If an urgent short message is received during transmission of long message, it has to wait until transmission of long message is completed.

PACKET SWITCHING• In packet switching messages are split into a number of

packets (often of fixed sizes) at source and assembled back at the destination.

• Packets are transmitted in S&F fashion.• Each packet transmission is independent of others. They

may travel different path and arrive at destination with different delays.

PACKET FORMAT IN PACKET SWITCHING

• Every packet need to carry complete address information along with Actual data, viz

1:Destination Identifier

2: Source ID

3: Message ID

4: Packet ID

TYPES OF DATA PACKET SERVICES

• In order to be cost effective, packet networks offer two different forms of services.

1: DATAGRAM service

2: Virtual circuit service

In these services no resequencing is required to be done by the network.

• Datagram service is normally used for transmitting short messages of one or two packet lengths.

• In case of virtual circuit service, the route from the source to the destination is fixed for all packets of a message. Here packet sequencing is maintained. The circuit so chosen is not locked to one message only but each node can be fixed for other messages also simultaneously. Hence called virtual.

INTEGRATED SERVICES DIGITAL NETWORK (ISDN)

INTEGRATED SERVICES DIGITAL NETWORK (ISDN)

• ISDN is a complete network framework designed around the concept of common channel signaling.

• ISDN defines the dedicated signaling network that has been created to complement the PSTN for more flexible and efficient network access and signaling.

• ISDN may be thought of as a parallel world-wide network for signaling traffic that can be used to either route voice traffic on the PSTN

OR• Provide new data services between nodes and the new

end users.

ISDN SIGNALING TYPES• ISDN provides two distinct kinds of signaling components to

end users in a telecommunication network.

1: ACCESS SIGNALING: Supports traffic between the end user

and the network. Access signaling defines how end users

obtain access to the PSTN and ISDN for communication

services. It is governed by the suite of protocols known as

the Digital Subscriber Signaling System number1(DSS1)

2: NETWORK SIGNALING: Governed by SS7 protocol within

ISDN and providing backbone connectivity between MSCs

throughout the world , as they provide network interfaces for

common signaling traffic.

ISDN FEATURES• ISDN provides a complete digital interface between end users

over twisted pair telephone lines.• The ISDN interface is divided into three different types of

channels. 1: B CHANNELS: Information bearing channels called bearer

channels. These are exclusively used for end-user traffic ( Voice, Data, Video)

2: D CHANNELS: These are out of band signaling channels, called Data channels. These are used to send signaling and control information across the interface to end-users.

3: H CHANNELS: Are made up when several ISDN circuits are concatenated into high speed information channels. H chls are used by the ISDN backbone to provide efficient data transport of many users on a single physical connection,, and may also be used by PRI end-user to allocate higher transmission rates on demand.

H0:384Kbps, H11: 1536 Kbps and H12: 1920 Kbps

ISDN TRANSMISSION CHANNELS

• There are three types of fundamental channels in ISDN around which the entire information is organized. These are

• BASIC INFORMATION CHANNEL…………B CHANNEL, 64 Kbps.• SIGNALING CHANNEL…………… ………D CHANNEL, 16 or 64 Kbps.• HIGH SPEED CHANNEL…………………….H CHANNELS

H0 CHANNEL, 384Kbps H11 CHANNEL,

1536Kbps. H12 CHANNEL. 1920Kbps

• B and D channels are basically adopted from telephone digital networks with common channel signaling.

• Having adopted 64Kbps rate, ISDN permits lower rate signals to be transmitted by using a RATE ADAPTATION.

• Alternatively, a number of low rate information channels may be multiplexed and sent on the B channel.

11.5 USER-NETWORK INTERFACE• Comprehensive user-network interface definitions are key to ensuring

world wide compatibility.• Two information rate access interfaces have been standardized for

ISDN

1: BASIC RATE ACCESS : Caters to low bit rate services.

2: PRIMARY RATE ACCESS: Caters to high bit rate services.

• In some sense they are analogous 5Amp and 15 Amp power sockets.

• The selection of user interface by ISDN is influenced by 1:Data rate of 64 Kbps of exiting digital switching and transmission system

2: matching with PCM encoded digitized voice

3: ISDN is supposed to support multiple services simultaneously.

4:One single B channel can not support multiple services

5:Rate chosen by the interface must be carried by wired PSTN

• Based on these factors BASIC RATE IS DEFINED AS

BASIC RATE ACCESS = 2B + D

BASIC RATE ACCESS CONSIDERATIONS

• Two B channels of 64 Kbps each and a signaling channel of 16Kbps make 144 Kbps. Taking data encoding, header and other overhead bits into account the actual rate works out to 192Kbps.

• This rate can be supported over most existing two wire loops.

• The basic access interface permits simultaneous use of voice, high speed data etc.

• It is possible to transmit speech at 32 Kbps using ADPCM, and remaining 32 Kbps in B channel may support wide variety of other applications.

PRIMARY RATE CONSIDERATIONS• PRIMARY RATE access interfaces cater to the high speed requirement .• The higher bit rates may stem from LAN or a PABX or from high speed

applications such as video and high speed facsimile.

• Keeping in mind existing PSTN structure, Two trans mission rates have been chosen for PRIMARY RATE ACCESS:1: 1544 Kbps ( T1 rate in USA ,CANADA and JAPAN)2: 2048 Kbps (E1 rate in Europe and India and other countries).

• Primary rate access are defined around B,H0, H11 and H12 channels.1544 Kbps 2048 Kbps23B+D 30B+D3H0+D 5H0+DH11 H12+D

• All signaling channels (D Channel) in above are 64 Kbps channel.

• H11 channel implies that signaling is being carried in a D channel associated with another interface structure such as 3H0+D or 23B+D.

BROADBAND ISDN AND ATM

• Resent work has defined ISDN interface standards that increase the end-user transmission bandwidth to several Mbps.

• The emerging networking technique is known as broadband ISDN (B-ISDN) and is based on (ATM) technology which allows packet switching rates up to 2.4 Gps and total switching capacities as high as 100Gps.

• ATM : it is a packet switching and multiplexing technique which has been specifically designed to handle both voice users and packet data users in a single physical channel.

• ATM data rates vary from 64 Kbps over twisted pair to over 100Mbps over fiber optic cable for high traffic rates between network nodes.

• ATM supports bidirectional transfer of data packets of fixed length between two end points, while preserving the order of transmission.

• ATM data units are called cells.• ATM cells are routed based on heather information in each unit

and is called LABLE that identifies the cell belonging to a spefic ATM virtual connection.

• ATM header also includes data for congestion control, priority information for queuing of packets.

• SIGNALING SYSTEM NO.7 (SS7)

SS7 SIGNALING FEATURES• SS7 has been designed to be an open ended CCS standard that can be used over a variety of digital circuit switched networks.

• While the network being controlled is circuit switched, the control signaling it self uses packet switching.

•The functions in SS7 are defined assuming packet switched operation, but the actual implementation can be in circuit switched nodes as additional functions.

•The internal control and network intelligence essential to an ISDN are provided by SS7.

• SS7 is suited for operation over analog chl. and at speeds< 64 Kbps.

• It is primarily optimized to work with digital SPC exchange.

• SS7 is suitable for operation over both terrestrial and satellite links.

SS7 PROTOCOL ARCHITECTURE THE PROTOCOL ARCHITECTURE OF SS7 HAS 4 LEVELS

THE LEVELS/LAYERS OF SS7 PROTOCOL ARCHITECTURE

1:NETWORK SERVICE PART (NSP): Which in turn is made up of three Message Transport Parts (MTPs) as follows i) MTP LEVEL1: Which provides interface for Signaling Data Link Functions ii) MTP LEVEL2 : Which provides reliability to Signaling link functions iii) MTP LEVEL3: which provides procedures for Signaling Network Functions

2:SIGNALING CONNECTION CONTROL PART(SCCP): Provides enhancement to addressing capabilities provided by MTP.

3: THE SS7 USER PART: Which in turn is made up of

i) ISDN User part (ISUP): Which Includes a) TELEPHONE USER PART(TUP) b) DATA USER PART (DUP)

ii) THE TRANSACTION CAPABILITIES APPLICATION PART (TCAP)

iii) OPERATION MAINTENANCE AND ADMINISTRATIONPART (OMAP)

iv) TELEPHONE USER PART(TUP)

• These Layers/Levels are explained in subsequent slides.

NETWORK SERVICES PART (NSP) OF SS7• The NSP provides ISDN modes with highly reliable and efficient

means of exchanging signaling traffic using connectionless services.

• The SCCP in SS7 actually supports packet data network interconnections as well as connection –oriented networking to virtual circuit networks

• The NCP allows network nodes to communicate throughout the world without concern for the application or context of the signaling traffic.

MESSAGE TRANSPORT PART (MTP) of SS7The function of the MTP is to ensure that signaling traffic can be transferred and delivered reliably between the end user and the network. MTP is provided at 3 levels.

MESSAGE TRANSFER PART (MTP) LEVEL 1

• Lower three levels referred to as MTP LAYERS provide a reliable service for routing messages through the SS7 network

Signaling Data Link Functions - MTP LEVEL1

• Provides an interface to the actual physical channel.

• Signaling data link, is concerned with physical and electrical characteristic of the signaling link between STPs and between STPs and SPs.

• All signaling data link in SS7 are full duplex links dedicated to SS7 traffic.

MESSAGE TRANSFER PART (MTP LAYER-2)

SIGNALING LINK FUNCTIONS CALLED - MTP LEVEL2• The main purpose of the 2nd layer viz signaling link, is to turn a

potentially unreliable physical link into a reliable data link.

• Variable length packet messages, called message signal units (MSUs) are defined in this layer.

• A single MSU cannot have a packet length which exceeds 272 octets, and a standard 16 bit CRC checksum is included in each MSU for error detection.

• The signaling link layer provides flow control and must ensure that.1. There are no losses or duplication of control message.

2. Messages are delivered in the same order in which they originate.

3. There is a match between the receiver capacity and the transmission rates.

MESSAGE TRANSFER PART (MTP LAYER 3)

SIGNALING NETWORK FUNCTION - MTP LEVEL 3• Provides

i) Signaling message handling :Providing

a) Routing,

b) Distribution and

c) Traffic discrimination

ii) Signaling network management : Allows the network

a) To reconfigure in case of node failure.

b) Has provision to allocate alternate routing facilities in

case of congestion or blockage in parts of the networks.

SCCP LAYERPROVIDES 4 CLASS OF SERVICES GIVEN BELOWTwo are connectionless and two are connection oriented. Thus SCCP has 4 function blocks

THE SS7 USER PART• Provides call control and management functions. • Provides call set up capabilities to the network.• ISDN User part (ISUP): provides in an ISDN environment,

1: Signaling function for carrier and

2: Supplementary services for voice, data, and ,video• ISUP message includes

i) A routing label that indicates the source and destination of

the message.

ii) A circuit identification code (CIC)

iii) A message code that serves to define the format and function of each message.

SIGNALING TRAFFIC IN SS 7• Call set ups, inter-MSC Hand-offs, and location updates are

main activities that generate the maximum signaling traffic in a network, and which are all handled under SS7.

END OF WSN UNIT 3