Unit-3 Wireless Data Services

Unit-3 Wireless Data Services

CPDP(Cellular Digital Packet Data) CPDP technology is used by telecommunication carriers to transfer data to users via unused analog cellular networks. It uses the entire 30KHz channel of AMPS on shared basis. No extra bandwidth required as it overlays itself on AMPS radio channels. Inexpensive and easy to construct. CPDP doesn t use MSC for routing, rather it has its own traffic routing capabilities. CPDP radio channel varies with time.

CPDP(Cellular Digital Packet Data) Every CPDP channel is duplex in nature with conventional first generation AMPS.

CDPD Infrastructure

CDPD - Layering Application Transport Network Data link Physical Network layer IP/CLNP RRMP MDLP MAC Physical CDPD Layer Connectionless Network Protocol Radio Resource Management Protocol Mobile Data Link Protocol Media Access Control Physical

CDPD Physical Layer 30KHz BW channels, shared with AMPS Separate forward and reverse channels Forward channel is continuous Reverse channel is multiple access. Gaussian Minimum-Shift Keying-GMSK GMSK compromises between channel bandwidth and decoder complexity. 19.2kbps per channel. IP/CLNP RRMP MDLP MAC Physical

CPDP Data Link Layer-MDLP Provides logical data link connections on a radio channel by using the address contained in each packet frame. Takes care of the packet sequence control. Error detection and flow control of the packets.

CPDP-Layer 3-RRMP Manages radio channel resources of a CPDP system and enables M-ES to find the radio channel without interfering with the AMPS communication. Handles BS identification and configuration messages for all M-ES stations. Handles channel hopping commands, cell handoffs and M-ES change of power commands.

AMPS and CDPD CDPD runs alongside AMPS AMPS system is unaware of CDPD system CDPD system watches AMPS behavior AMPS generally has unused channels. Blocked calls when all channels are allocated. 1% block probability => all channels used only 1% of the time. Every time MSC chooses a channel for the BS, 30% of channel time is unused, which is exploited by the CPDP network.

Effects of CDPD on AMPS CDPD logically transparent to AMPS Can reduce AMPS service quality More channel usage by CDPD => increased interference.

Problems with CDPD Limited bandwidth 19.2kbps shared per channel Modern applications demand more bandwidth. Security Man in the middle identity theft attack IP network attacks Denial of Service attacks easy.

Potential Improvements Multichannel / multicarrier transmission Would allow faster rates with AMPS compatibility. Security Improvements Secure against man-in-the-middle attacks. Switch to CDMA/GSM. Digital cellular services are more able to accommodate data services.

ARDIS(Advanced Radio Data Information Systems) Channel Characteristics of ARDIS Type of Message Retry Rate Packet Overhead Short ARDIS message Long ARDIS message Low High High Spread over the lgt. Of the packet

RAM Mobile Data (RMD) named MOBITEX

Common channel signaling CCS is a digital communication technique that provides simultaneous transmission of User Data and signaling data and other control information. Some common signaling functions in Telephone circuits are: Dial tone Transmission of digits Ringing Busy tone; etc. Signaling can be classified into two groups In channel signaling: Signaling is a part of data/voice channel itself Inband Out of band 18

Areas of Signaling There are mainly three areas of signaling during a telephone call between subscribers and exchanges. within exchanges. between exchanges. between exchanges Exchange A Exchange B within exchange between Subscriber and exchange

In - Band Signaling Signaling path = voice path Voice path clogged with signaling Busy calls, congestion, and ring-no-answers result in 20-35% of incomplete calls Slower call setup due to channel sharing

Signaling Techniques In-channel signaling In-band

Out - of - Band Signaling Signaling path done on a separate channel Voice path dedicated only to voice Much faster call setup and knockdown Led to SS7 and Advance Intelligent Network(AIN) Can be operated in connectionless fashion as the signaling traffic is bursty and is of short duration, efficiently utilizing the packet data transfer techniques. Packet sizes are variable in length.

Signaling Techniques Common Channel Signaling (CCS) Signaling Network Dedicated data link between systems Out-band

Advantages of CCS One signaling path needed per trunk group Faster and simpler to transfer information between control processors No possibility of interference with speech path Signaling can t be accessed by customer

Advantages of CCS Value-added services of a signaling control point Shared processing for small offices Allows centralized decision making (flow mgmt) Permits Advanced Intelligent Network (AIN) services

Advantages of CCS Higher signaling capacity. More number of speech/data channels as there is only one signaling channel. Central offices can exchange information, not related to speech/data between themselves e.g. subscriber data. Various high end features like roaming are possible by using CCS7.

Trunk Group Disassociated CCS Signaling Switching Center Speech Paths CCS Data Link

Trunk Group Associated CCS DLC TR-303 Trunk Group CO Switch TR-303 Control Link

Trunk Group Associated CCS DLC TR-303 Trunk Group CO Switch TR-303 Control Link

Common Channel Signaling N/W Architecture Based on SS7 SEP s-switching End Points SS7-Signaling System No.7 STP s-signaling transfer Points SMS-Service Management System

CCS The MSC provides subscriber to access to the PSTN via SEP. SEP implements a stored-program-control switching system known as SCP (Service Control Point). SCP uses CCS to set-up calls and to access the network database. SCP instructs the SEP to create a billing record based on call information recorded by SCP.

The STP controls switching messages between nodes in the CCS network. For higher reliability of transmission SEP s are required to be connected to the SS7 network via atleast two STP s, which ensures the connection to the network even if one STP fails. The SMS contains all subscriber records which may be accessed by the subscribers. DBAS( Data Base Service Management System) is another managing service of the user database which helps in fraud detection.

ISDN Integrated Services Digital Network It is a switched digital telecommunication line that can be delivered over regular copper wires Possible to provide end-to-end digital communications Based on the concept of CCS Designed to ease the PSTN s working environment and increase the efficiency.

ISDN provides two distinct kinds of signaling components: üaccess Signaling: Supports traffic between end users and the network. Defines the users access to PSTN and ISDN for services and depends on DSS1 protocol. Digital Subscriber Signaling System No.1 ünetwork Signaling: Governed by SS7 suite of protocols. For wireless, the SS7 protocols within ISDN provide the backbone network connectivity between MSC s throughout the world., as they provide N/W interfaces for CCS traffic.

ISDN Two basic types of channels in ISDN: Bearer Channels(B Channels)-Exclusives for enduser traffic(voice, Data and Video) Data Channels(D Channels)-Out of band signaling channels, used to send signaling and control across the interfaces to end-users.

What Is ISDN?

ISDN Basic Characteristics B Channels 64 Kbps D Channel 16-64 Kbps Data Data Data Signaling

ISDN Benefits Carries a variety of user traffic, such as digital video, data, and telephone network services, using the normal phone circuit-switched network Offers much faster call setup than modems by using out-of-band signaling (D channel) Often less than one second Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel) Can combine multiple B channels to bandwidth of 128 kbps.

Bonding of B Channels or BOD (Bandwidth on Demand) Channel Bonded on Demand B (64 Kbps) 64-128 Kbps 64-128 Kbps B (64 Kbps) Inverse Multiplexers with Dynamic Bonding

ISDN ISDN users can select two different interfaces, Basic Rate Interface(BRI): Serves small capacity terminals(single phones) Primary Rate Interface(PRI):Serves large capacity terminals(pbx) B-Channel supports 64kbps data for both the BRI and PRI. D-Channel supports 64kbps data for PRI and 16kbps for PRI.

ISDN BRI Provides 2 X 64kbps bearer channels and 1 X 16kbps signaling channel(2b+d) PRI Provides 23X 64kbps bearer channels and 1 X 64kbps signaling channel(23b+d) (North America & Japan) Provides 30X 64kbps bearer channels and 1 X 64kbps signaling channel(23b+d) (Europe) For wireless subscribers, ISDN s BRI is provided same as for a fixed terminal. Extra control channels (c-channels) which replace D-channels are used. The wireless subscribers has 2B+C service.

Types of bearer services in ISDN Mode of Service Type of Service Transmission Speed Type of channel Circuit Mode services Unrestricted 64kbps,384kbps, 1.5 Mbps B,H0,H11 Circuit Mode services Packet Radio Services Speech 64kbps B Unrestricted Depending on throughput B,D(or C)

Broadband ISDN and ATM üincrease in bandwidth is the main criteria in the development of B-ISDN and ATM(Asynchronous Transfer Mode) technologies which depend on packet switching rates upto 2.4Gbps in comparison to 64 kbps provided by ISDN B-channel. üatm is a packet switching and multiplexing technique designed to handle both voice users and packet data users in a single physical channel. üdata Rates: 64kbps-twisted pair to 100Mbps over OF cables.

ATM Preserves the order transmission of packets of fixed length between two end users. Fixed length packets have been chosen for packets to arrive synchronously at the switch. 5 bytes 48 bytes Header Data Cell Format of ATM ATM data units are called CELLS.

ATM Cells are routed based on header information based on each unit(called label), which identifies the cell as belonging to a specific ATM virtual connection. Once the label is determined i.e., a user is chosen the connection remains till the end of the virtual connection. ATM header also includes data for congestion control, priority information for queuing of packets, and priority indicating the drop of packets in case of congestion in N/W.

Signaling through SS7 network SS7 was first standardized by CCITT for ISDN in 1980 with revisions in 1984 and 1988. Control messages flowing through the network are in packets. However, it controls the circuit switched network. Transmission rate up to 64 Kbps in 1G. The purpose of SS7 is to provide an internationally standardized general-purpose common channel signaling system. Management functions performed by SS7 are: Call setup Maintenance of call and Call termination 47

Signaling through SS7 network Salient characteristics of SS7 are: High availability/high reliability; Low transit delay; Traffic management and fault isolation; Automatic congestion detection SS7 is highly reliable because it has at least one alternate path around any network node. For achieving low transmission delay, the network works at relatively high speeds of 56 Kbps & 64 Kbps.

SS7-Signaling System Number 7 NSP-N/W Service Part-Provides highly reliable means of exchanging signaling traffic using connectionless services. NSP also allows world wide communication without the concern of the application and signaling traffic. SCCP- Support packet data as well as connection oriented networking. MTP- Ensures that the signaling traffic can be transferred and delivered reliably between end users and the network.

SS7 Signaling data link functions: MTP Level 1- Provides interface to actual physical channel over which communications take place. CCITT-MTP-1 uses 64 kbps. ANSI-MTP1 uses 56kbps. Signaling link functions : MTP Level 2- Correspond to second layer in OSI. Provides reliable link to transfer of traffic between two directly connected signaling points. MSU s are defined here which are variable packet units(max-272 octets & 16 bit CRC)

SS7 MTP2 also provides flow control b/w two signaling points. Signaling Network Functions-MTP-3: They provide procedures that transfer msgs b/w signaling nodes. Two functions(isdn) - Signaling Handling Functions-For routing, distribution and traffic discrimination. - Signaling function Management-Allows to reconfigure the network in case of node failures providing alternate routes to navigate the packet.

SS7 User Part: Provides call control & management functions and call set-up capabilities to the network. They use the transport facilities provided by MTP and the SCCP. SS7 user part: - ISDN User Part(ISUP) 1.Telephone User Part(TUP) 2.Data User Part(DUP) - Transaction Capabilities Application Part(TCAP) - Operations maintenance & Administration Part(OMAP)

ISUP: Provides signaling functions for carrier and supplementary services for voice, data and video in an ISDN environment. ISUP uses MTP for transfer of messages between different exchanges. User-to-User signaling, closed user groups, calling line identification, and call forward are also provided. TCAP: Refer to application layer in OSI, which invokes the services of the SCCP and the MTP in a hierarchical format. It is concerned with remote operations.

SS7 User Part OMAP: Includes monitoring, coordination, and control functions to ensure that trouble free communications are possible. Signaling traffic under SS7: Call set-ups, Inter MSC handoff s and Location updates

A Typical SS7 Network

Message Types: SS7 network Two types of messages flow through the network: Circuit related Database related Circuit-related messages are used to set up and tear down a call between two switches or signaling points; STP transfers these messages from the originating signaling point to the terminating signaling point. Database access messages are used to access information stored in the SCP. A query message is sent from the SSP, via the STP, to the SCP requesting that required data be sent to the requesting SSP. The SCP returns the data in a response message over SS7 network, back to the originating signaling point. In the case of a cellular signaling network, the SSP includes the functions of the mobile switching center (MSC). 59