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USSD Workflow & Benefits
Hi Friends, Here are some more details about USSD Workflow & Benefits,
Working Principle:- USSD Originated at Network Side
1. USSD Originated by HLR – In HLR, application is there from where it originates a session with MSC/VLR, sends a USSD_REQUEST or USSD_NOTIFY messages to MSC/VLR & waits for the response. As the response received by MSC/VLR, HLR releases the session or sends another USSD_REQUEST or USSD_NOTIFY messages on the same session. After receiving the USSD messages from the HLR, if the MS is reachable, the MSC/VLR originates a session to the MS and transparently transmits the received USSD messages and the subsequent messages between the MS and HLR. If one of the sessions (the session between the HLR and MSC/VLR and that between the MSC/VLR and MS) is released, the MSC/VLR releases another session.
2. USSD Originated by MSC/VLR - In MSC/VLR, application is there from where it originates USSD_REQUEST or USSD_NOTIFY messages, if the MS is reachable, the MSC/VLR originates a session to the MS, sends an USSD_REQUEST or USSD_NOTIFY message to the MS, and then waits for the response. MSC/VLR controls the session. After receiving the response from the MS, the MSC/VLR can release the session or sends another USSD_REQUEST or USSD_NOTIFY message on the same session. In certain cases, such as application timeout in the MSC/VLR, the MSC/VLR can release the session before receiving the response from the MS.
3. USSD Originated by External Nodes - The external nodes, such as the USSD center and SCP (Service Control Point/IN), can originate USSD, Based on the routing mode of the short message center in sending short messages, the external node sends a message to the home HLR of the subscriber. If the MS is reachable, the HLR sends the address of the MSC/VLR that serves the MS to the external node. After obtaining the address, the external node directly sends an USSD_REQUEST or USSD_NOTIFY message to the MSC/VLR. The MSC/VLR then transparently transmits the message to the MS. The subsequent messages between the external node and the MS are also transparently transmitted by the MSC/VLR.
4. Processing of MS for USSD Operation Originated by Network - The MS may receive, at any time, the USSD operation originated by the network. If the MS
has an on-going USSD operation or a supplementary service that is unrelated with calls, the MS rejects the USSD operation originated by the network. If the MMI (Man-Machine Interface) does not meet the requirement of USSD, the MS also rejects the USSD operation originated by the network. If the MS does not support the characters of the USSD operation, the MS sends a message to inform the network.
USSD Originated by MS (Mobile Station)
1. Processing of MS – Before originating USSD, the MS sets up the CM connection with the network. After the CM connection is set up, the MS sends the USSD request to the MSC and waits for the response. After receiving the response from the network, the MS displays the received information for the subscriber. When the MS waits for the response, the MS may receive a USSD_REQUEST or USSD_NOTIFY message sent by the network. Upon receiving the message, the MS processes accordingly and then continues to wait for the response to the initial USSD request.
2. Processing of MSC/VLR - After receiving the USSD message sent by the MS, the MSC/VLR processes the message based on the SC (Service Code) in the message. Depending on SC, MSC/VLR processes the USSD operation in the local office or with HLR, if the MSC/VLR does not support the characters in the USSD message or if the session cannot be set-up with HLR, the MSC/VLR returns an error to the MS.
3. Processing of HLR - After receiving the USSD message, the HLR processes the message. If the HLR does not support the characters in the USSD message, the HLR informs the MS and releases the session.
USSD Benefits:- For Carriers - Many Real-Time value-added services can be provided, such as those
providing stock, lottery, weather forecast, and airline information. These services can attract subscribers.
For Mobile Subscribers - Subscribers' requirements in many fields can be fulfilled, such as querying lottery information and stock information.
Applicable-to Network – It’s applicable to all the GSM/UMTS networks, There is no special requirement for software/hardware, but USSD center is required.
Flow details will be coming soooon...
Keep checking for new posts till then HaPPy Reading.
ChEEeeerSTelecom Tigers Team
[email protected]://homepageforu.webs.com/
Posted by Tel Tig at 1:07 PM 0 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Tuesday, September 20, 2011Difference between USSD & SMS Messages
Hi All,
Greetings from TT Team,
SMS & USSD both are GSM Services, On one hand both appear similar technically and functionally, but there are considerable and significant differences in their technologies and features.
The basic difference between the two technologies is,
USSD (Unstructured Supplementary Service Data) is session-based, SMS (Short Message Service) uses the store-and-forward approach.
Below are some more differences :-
Message Flow details will be coming soooon...
Keep checking for new posts till then HaPPy Reading.
ChEEeeerSTelecom Tigers Team
[email protected]://homepageforu.webs.com/
Posted by Tel Tig at 11:31 AM 0 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Saturday, July 16, 20113G ChannelsHi All,
Here is the list of different channels used in 3G network for transporting information at much faster speed.
These are divided into Logical, Transport & Physical.
UTRA Channels
UTRA FDD radio interface has logical channels, which are mapped to transport channels, which are again mapped to physical channels. Logical to Transport channel conversion happens in Medium Access Control (MAC) layer, which is a lower sublayer in Data Link Layer (Layer 2).
Logical Channels:
Broadcast Control Channel (BCCH), Downlink (DL). Paging Control Channel (PCCH), DL Dedicated Control Channel (DCCH), UL/DL Common Control Channel (CCCH), UL/DL Dedicated Traffic Channel (DTCH), UL/DL Common Traffic Channel (CTCH), Unidirectional (one to many)
Transport Channels:
Dedicated Transport Channel (DCH), UL/DL, mapped to DCCH and DTCH
Broadcast Channel (BCH), DL, mapped to BCCH Forward Access Channel (FACH), DL, mapped to BCCH, CCCH, CTCH,
DCCH and DTCH Paging Channel (PCH), DL, mapped to PCCH Random Access Channel (RACH), UL, mapped to CCCH, DCCH and
DTCH Uplink Common Packet Channel (CPCH), UL, mapped to DCCH and
DTCH Downlink Shared Channel (DSCH), DL, mapped to DCCH and DTCH
Physical Channels:
Primary Common Control Physical Channel (PCCPCH), mapped to BCH Secondary Common Control Physical Channel (SCCPCH), mapped to
FACH, PCH Physical Random Access Channel (PRACH), mapped to RACH Dedicated Physical Data Channel (DPDCH), mapped to DCH
Dedicated Physical Control Channel (DPCCH), mapped to DCH Physical Downlink Shared Channel (PDSCH), mapped to DSCH Physical Common Packet Channel (PCPCH), mapped to CPCH Synchronisation Channel (SCH) Common Pilot Channel (CPICH) Acquisition Indicator Channel (AICH) Paging Indication Channel (PICH) CPCH Status Indication Channel (CSICH) Collision Detection/Channel Assignment Indication Channel (CD/CA-
ICH)
Keep checking for new posts till then Happy Reading.
ChEEeeRrS
Telecom Tigers [email protected]://homepageforu.webs.com/Posted by Tel Tig at 5:20 PM 0 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Saturday, June 4, 2011
Mobile Location Update
Hi Friends,
Lets discuss something about Location Update Procedure, because of which a mobile user can move freely.
As a mobile user, a person can be anywhere but a network has to keep track of user, in-case if somebody wants to call him, so the transaction that keeps network updated about the subscriber present location is termed as location update.
A mobile phone constantly receives information sent by the network, which includes ID of the VLR area in which mobile is currently located & mobile stores that ID.
Every time the network broadcasts the ID of the area, the mobile compares this information to the area ID stored in its memory. When the two IDs are no longer the same, the mobile sends the network a request, i.e. a registration inquiry to the area it has just entered. The network receives the request and registers the mobile in the new VLR area. Simultaneously, the subscriber’s HLR is informed about the new VLR location and the data concerning the subscriber is cleared from the previous VLR.
There are 3 different kinds of location update procedure like,
Location Registration (power on). Generic. Periodic
Location Registration (power on) - Whenever mobile turns ON, location registration takes place, which is also termed as IMSI attach, because as soon as the mobile station is switched on, it informs the VLR that it is now back in service and is able to receive calls, as a result of a successful registration, the network sends the mobile station two numbers that are stored in the SIM (Subscriber Identity Module) card of the mobile station.
1. Location Area Identity (LAI) – it’s a globally unique number.2. Temporary Mobile Subscriber Identity (TMSI) - is used for security
purposes, so that the IMSI of a subscriber does not have to be
transmitted over the air interface. It’s a temporary identity, which regularly gets changed.
Generic – It happens, if LAI present in mobile SIM & LAI received via control channels during network broadcast are different.
The mobile starts a Location Update process by accessing the MSC/VLR that sent the location data. A channel request message is sent that contains the subscriber identity (i.e. IMSI/TMSI) and the LAI stored in the SIM card.
When the target MSC/VLR receives the request, it reads the old LAI which identifies the MSC/VLR that has served the mobile phone up to this point. A signaling connection is established between the two MSC/VLRs and the subscriber’s IMSI is transferred from the old MSC to the new MSC. Using this IMSI, the new MSC requests the subscriber data from the HLR and then updates the VLR and HLR after successful authentication.
Periodic – It is carried when the network does not receive any location update request from the mobile in a specific time. A timer controls the periodic updates and the operator of the VLR sets the timer value.
The network broadcasts this timer value so that a mobile station knows the periodic location update timer values & when the set time is up, the mobile station initiates a registration process by sending a location update request signal.
The VLR receives the request and confirms the registration of the mobile in the same location area. If the mobile station does not follow this procedure, it could be that the batteries of the mobile are exhausted or the subscriber is in an area where there is no network coverage. In such a case, the VLR changes the location data of the mobile station to “unknown”.
Keep checking for new posts till then Happy Reading.
ChEEeeRrS
Telecom Tigers [email protected]://homepageforu.webs.comPosted by Tel Tig at 9:33 PM 3 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Sunday, March 13, 2011Difference between NGN & TDM NetworkHi,
In today's scenario, NGN is gradually replacing traditional TDM network,So below are the some differences / benefits of NGN system w.r.t. traditional TDM
Keep checking for new posts till then HaPPy Reading.
ChEEeeerSTelecom Tigers Team
[email protected]://homepageforu.webs.com/
Posted by Tel Tig at 9:21 PM 2 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Saturday, August 28, 2010Standard ISUP Release Causes
ISUP Release Cause Values and their meanings
REL Meaning
Cause Value
NORMAL EVENT CLASS1 Unallocated number2 No route to specified transit network3 No route to destination4 Send special information tone5 Misdialled trunk prefix6 Channel unacceptable7 Call awarded and being delivered in an established channel16 Normal call clearing17 User busy18 No user responding19 No answer from user (user alerted)20 Subscriber absent21 Call rejected22 Number changed26 Non selected user clearing27 Destination out of order28 Invalid format (address incomplete)29 Facility rejected30 Response to status enquiry31 Normal, unspecified
RESOURCE UNAVAILABLE CLASS34 No circuit/channel available38 Network out of order41 Temporary failure42 Switching equipment congestion43 Access information discarded44 Request circuit/channel not available47 Resource unavailable, unspecified
SERVICE/OPTION NOT AVAILABLE CLASS49 Quality of service unavailable50 Requested facility not subscribed55 Incoming calls barred within CUG57 Bearer capability not authorized58 Bearer capability not presently available63 Service or option not available, unspecified
SERVICE/OPTION NOT IMPLEMENTED CLASS
65 Bearer capability not implemented69 Requested facility not implemented
70Only restricted digital information bearer capability is available
79 Service or option not implemented, unspecified
INVALID MESSAGE CLASS81 Invalid call reference value82 Identified channel does not exist83 A suspend call existing but this call identity does not84 Call identity in use85 No call suspended86 Call having the requested call identity has been cleared87 User not member of CUG88 Incompatible destination91 Invalid transit network selection95 Invalid message, unspecified
PROTOCOL ERROR CLASS96 Mandatory information element is missing97 Message type non-existing or not implemented
98Message not compatible with call state or message type non-existing or not implemented
99 Information element non-existing or not implemented100 Invalid information element contents101 Message not compatible call state102 Recovery on timer expiry103 Parameter non-existent or not implemented109 Unrecognized message has been passed on110 Message with unrecognized parameter discarded111 Protocol error, unspecified
INTERWORK CLASS127 Interworking, unspecified
[email protected]://homepageforu.webs.com/Posted by Ashish Bhatia at 9:51 PM 1 comments
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Monday, January 25, 2010What is SigtranSIGTRAN (SIGnaling TRANsport) :- It is a set of protocols defined by IETF to transport SS7 messages over IP networks. It allows IP networks to inter-work with the Public Switched Telephone Network (PSTN) and vice versa. The telco switch sends SS7 signals to a signaling gateway (SG) that converts them into SIGTRAN packets, which travel over IP to the next signaling gateway or to a softswitch if the destination is not another PSTN. Sigtran Protocol Suite is made up of a new Transport Layer -- the Stream Control Transmission Protocol (SCTP) & a set of User Adaption (UA) layers, which mimic the services of lower layers of SS7 & ISDN.
Why SIGTRAN :
Ordered, Reliable Transfer. Redundancy in case of Link Failure. Low Loss & Delay.
The key components in the SIGTRAN architecture are :-
MGC–Media Gateway Controller, responsible for mediating call control (between the SG (Signaling Gateway) and MG (Media Gateway)) and controlling access from the IP world to/from the PSTN.
SG–Signaling Gateway, responsible for interfacing to the SS7 network and passing signaling messages to the IP nodes.
MG–Media Gateway, responsible for packetization of voice traffic and transmitting the traffic towards the destination.
IP SCP – an IP-enabled Service Control Point (SCP). This exists wholly within the IP network, but is addressable from the SS7 network.
IP Phone – generically referred to as a “terminal.”
SIGTRAN protocol stack consists of 3 components :
A standard IP layer. A common signaling transport protocol, Stream Control Transmission
Protocol (SCTP) An Adaptation layer, like - M2PA, M2UA, M3UA, and
SUA.
SCTP :- Stream Control Transmission Protocol SCTP is designed to transport SS7 signaling messages over IP networks. It operates directly on top of IP at the same level as TCP. SCTP's basic service is connection oriented reliable transfer of messages between peer SCTP users. Its aim of designing, is to address the Shortcomings of TCP. SCTP is a general purpose protocol, a replacement for TCP.
SCTP has the following set of features :-
It is a Unicast Protocol - data exchange is between two known endpoints.
It defines timers of much shorter duration than TCP. SCTP uses periodic heart-beat messages to confirm the status of each
end point. It provide reliable transport of data - detecting when data is corrupt or
out of sequence, and performing repair as necessary. It is Rate-Adaptive, responding to network congestion It support Multi-Homing - Each SCTP endpoint may be known by
multiple IP addresses. Routing to one address is independent of all others, & if one route fails, another will be used.
It uses an initialization process, based on cookies, to prevent denial-of-service attacks.
It supports Bundling, where a single SCTP message may carries multiple "Chunks" of data, each of which contains a whole signaling message.
It support fragmentation, where a single signaling message may be split into multiple SCTP messages in order to be accommodated within a underlying PDU.
It is message-oriented, defining structured frame of data, on the other hand, TCP imposes no structured on the transmitted stream of bytes.
It has a multi-streaming capacity, data is split into multiple streams, each with independent sequenced delivery, TCP has no such feature.
Sigtran Adaptation Layers serves common purposes like :-
To carry upper layer Signaling Protocol over a reliable IP-based transport.
To provide same class of services offered at the interface of PSTN equivalent.
Transparent. To remove as much need for the lower SS7 layers as possible.
Sigtran currently defines SIX adaption layers :-
1. M2UA :- It provides the services of MTP2 in a Client-Server Situation, such as SG to MGC. Its user would be MTP3.
2. M2PA :- It provides the services of MTP2 in a Peer-to-Peer Situation, such as SG to SG Connections. Its user would be MTP3.
3. M3UA :- It provides the services of MTP3 in both a Client-Server Situation (SG to MGC) & Peer-to-Peer Architecture, Its user would be SCCP and/or ISUP.
4. SUA :- It provides the services of SCCP in a Peer-to-Peer Situation, such as SG to IP SCP Connections. Its user would be TCAP.
5. IUA :- It provides the services of the ISDN Data Link Layer (LAPD), Its user would be an ISDN Layer 3 (Q.931) entity.
6. V5UA :- It provides the services of the V.5.2 Protocol.
More Information from Readers are Expected !!!
Thanks
[email protected]://homepageforu.webs.com/Posted by Ashish Bhatia at 10:46 PM 0 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Thursday, December 24, 2009NGN - Next Generation Network The general idea behind NGN is that one network transports all information and services (voice, data, and all sorts of media such as video) by encapsulating these into packets, like it is on the Internet. NGNs start making sense when voice, data, video are all in IP format.
Basically, the core network should have a common service delivery architecture, with any access network hanging off the core.Some important service characteristics for NGN would be real-time, multi-media communications, more personal intelligence, more network intelligence, more simplicity for users, personal service customization and management.
It will benefit from its advanced control, management, and signaling capabilities, enabling a much broader array of service types, such as
Specialized resource services (provision and management of transcoders, multimedia multipoint-conferencing bridges, processing and storage services),
Middleware services (brokering, security, licensing, transactions), Application-specific services (business applications, e-commerce
applications, supply-chain management applications, interactive video games),
Content-provision services (electronic training, information push services).
Next generation IP networks or NGN IP will be the key enabler of mobility and convergence. This would mean that convergence would not just be limited to wired networks. WLAN too can run voice, data, & video. NGN IP would help organizations achieve new levels of enhanced
productivity, reduced operational costs, increased operational efficiency and better overall profitability. NGN IP would also support new levels of personal mobility, allowing for seamless integration of fixed and mobile networks. And, for enterprises it helps to scale their network architecture and prioritize bandwidth usage, and reduce network management complexities. In an NGN environment, almost 60–70% bandwidth would be reserved for data, and as voice would be on the same pipe, it would come almost free. With no additional costs for using voice, the usage of voice services would increase. And it is voice over IP (VoIP) that would be the killer application for NGNs.
Fundamental to Next Generation Networking :-
Packet-Based Data Transfer. Separate control functions for bearer capabilities, calls/sessions and
applications/services. De-coupling of service provision from the network, and provision of
open interfaces. Support for a wide range of service applications and mechanisms
based on service building blocks (including real-time/streaming/non-real-time services and multi-media).
Broadband capabilities with end-to-end QoS and transparency. Interworking with legacy networks via open interfaces. Generalized mobility. Converged services between Fixed and Mobile networks.
Issues to be kept in mind while planning for NGN deployment :-
1. Latency (Delay)2. Jitter3. Bandwidth4. Packet Loss5. Reliability6. Security7. Inter-operability
NGN involves three main architectural changes that need to be looked at separately :-
In the Core Network, NGN implies a consolidation of several (dedicated or overlay) transport networks each historically built for a different
service into one core transport network (often based on IP and Ethernet). It implies amongst others the migration of voice from a circuit-switched architecture (PSTN) to VoIP, and also migration of legacy services such as X.25, Frame Relay (either commercial migration of the customer to a new service like IP VPN, or technical emigration by emulation of the "legacy service" on the NGN).
In the Wired Access Network, NGN implies the migration from the dual system of legacy voice next to xDSL setup in the local exchanges to a converged setup in which the DSLAMs integrate voice ports or VoIP, making it possible to remove the voice switching infrastructure from the exchange.
In Cable Access Network, NGN convergence implies migration of constant bit rate voice to PacketCable (CableLabs standards that provide VoIP and SIP services).
PacketCable Networks use the Internet Protocol (IP) to enable a wide range of multimedia services, such as Voice over IP (IP telephony), multimedia conferencing, interactive gaming, and general multimedia applications.
NGN Technology Components :-
NGNs are based on Internet technologies including Internet Protocol (IP) and Multiprotocol Label Switching (MPLS). At the application level, Session Initiation Protocol (SIP) seems to be taking over from ITU-T H.323.
For voice applications, one of the most important devices in NGN is a Softswitch - a programmable device that controls Voice over IP (VoIP) calls. It enables correct integration of different protocols within NGN. The most important function of the Softswitch is creating the interface to the existing telephone network, PSTN, through Signalling Gateways and Media Gateways.
Gatekeeper - This was originally a VoIP device, which converted (using gateways) voice and data from their analog or digital switched-circuit form (PSTN, SS7) to the packet-based one (IP). It controlled one or more gateways. As soon as this kind of device started using the Media Gateway Control Protocol, the name was changed to Media Gateway Controller (MGC).
IP Multimedia Subsystem (IMS) is a standardized NGN architecture for an Internet media-services capability.
SoftSwitch :- It's a central device in a telecommunications network which connects calls from one phone line to another, entirely by means of software running on a computer system. This work was formerly carried out by hardware, with physical switchboards to route the calls. It is typically used to control connections at the junction point between circuit and packet networks. A single device containing both the switching logic and the switching fabric can be used for this purpose. however, modern technology has led to a preference for decomposing this device into a Call Agent and a Media Gateway. Call Agent takes care of functions like billing, call routing, signalling, call services and so on and is the 'brains' of the outfit. A Call Agent may control several different Media Gateways in geographically dispersed areas over a TCP/IP link. Media Gateway connects different types of digital media stream together to create an end-to-end path for the media (voice and data) in the call. It may have interfaces to connect to traditional PSTN networks like DS1 or DS3 ports (E1 or STM1), it may have interfaces to connect to ATM and IP networks and in the modern system will have Ethernet interfaces to connect VoIP calls. The call agent will instruct the media gateway to connect media streams between these interfaces to connect the call. In more recent times (i.e., in IP Multimedia Subsystem or IMS), the Softswitch element is represented by the Media Gateway Controller (MGC) element, and the term "Softswitch" is rarely used in the IMS context, but another word of AGCF(Access Gateway Control Function). Feature Server, often built into a call agent/softswitch, is the functional component that provides call-related features. Capabilities such as call forwarding, call waiting, and last call return, if implemented in the network, are implemented in the feature server. The feature server works closely with the call agent, and may call upon the media server to provide these services. These features do not require the subscriber to explicitly request them but tend to be triggered within the call handling logic.
More Information from Readers are Expected !!!
[email protected]://homepageforu.webs.com/Posted by Ashish Bhatia at 6:01 PM 1 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest
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Wednesday, December 16, 2009Location Update Procedure In order to make a mobile terminated call, The GSM network should know the location of the MS (Mobile Station), despite of its movement. For this purpose the MS periodically reports its location to the network using the Location Update procedure.
Location Area (LA) A GSM network is divided into cells. A group of cells is considered a location area. A mobile phone in motion keeps the network informed about changes in the location area. If the mobile moves from a cell in one location area to a cell in another location area, the mobile phone should perform a location area update to inform the network about the exact location of the mobile phone.
The Location Update procedure is performed:
When the MS has been switched off and wants to become active, or When it is active but not involved in a call, and it moves from one
location area to another, or After a regular time interval.
Location registration takes place when a mobile station is turned on. This is also known as IMSI Attach because as soon as the mobile station is
switched on it informs the Visitor Location Register (VLR) that it is now back in service and is able to receive calls. As a result of a successful registration, the network sends the mobile station two numbers that are stored in the SIM (Subscriber Identity Module) card of the mobile station.
These two numbers are :-
1. Location Area Identity (LAI) 2. Temporary Mobile Subscriber Identity (TMSI).
The network, via the control channels of the air interface, sends the LAI. The TMSI is used for security purposes, so that the IMSI of a subscriber does not have to be transmitted over the air interface. The TMSI is a temporary identity, which regularly gets changed.
A Location Area Identity (LAI) is a globally unique number. A Location Area Code (LAC) is only unique in a particular network.
Every time the mobile receives data through the control channels, it reads the LAI and compares it with the LAI stored in its SIM card. A generic location update is performed if they are different. The mobile starts a Location Update process by accessing the MSC/VLR that sent the location data.A channel request message is sent that contains the subscriber identity (i.e. IMSI/TMSI) and the LAI stored in the SIM card. When the target MSC/VLR receives the request, it reads the old LAI which identifiesthe MSC/VLR that has served the mobile phone up to this point. A signalling connection is established between the two MSC/VLRs and the subscriber’s IMSI is transferred from the old MSC to the new MSC. Using this IMSI, the new MSC requests the subscriber data from the HLR and then updates the VLR and HLR after successful authentication.
Periodic location update is carried out when the network does not receive any location update request from the mobile in a specified time. Such a situation is created when a mobile is switched on but no traffic is carried, in which case the mobile is only reading and measuring the information sent by the network. If the subscriber is moving within a single location area, there is no need to send a location update request.A timer controls the periodic updates and the operator of the VLR sets the timer value. The network broadcasts this timer value so that a mobile station knows the periodic location update timer values.
Therefore, when the set time is up, the mobile station initiates a registration process by sending a location update request signal. The VLR receives the request and confirms the registration of the mobile inthe same location area. If the mobile station does not follow this procedure, it could be that the batteries of the mobile are exhausted or the subscriber is in an area where there is no network coverage. In sucha case, the VLR changes the location data of the mobile station to “unknown”.
The Location Update process consists of the following phases
Request for service; the MS detects that it has entered a new Location Area and requests to update its location. The new MSC/VLR identifies the MS.
Authentication - The new MSC/VLR requests to the AUC for authentication parameters (SRES, Kc, RAND). Using these parameters the MS is authenticated.
Ciphering - Using the parameters which were made available earlier during the authentication the uplink and the downlink are ciphered.
Update HLR/VLR - The new MSC/VLR requests to update the MS location in the HLR. The MS is de-registered in the old VLR.
TMSI re-allocation - The MS is assigned a new TMSI.
1. The MS detects that it has entered a new Location Area and transmits a Channel Request message over the Random Access Channel (RACH).
2. Once the BSS receives the Channel Request message, it allocates a Stand-alone Dedicated Control Channel (SDCCH) and forwards this channel assignment information to the MS over the Access Grant Channel (AGCH). It is over the SDCCH that the MS will communicate with the BSS and MSC.
3. The MS transmits a location update request message to the BSS over the SDCCH. Included in this message are the MS Temporary Mobile Subscriber Identity (TMSI) and the old Location Area Identification (oldLAI). The MS can identify itself either with its IMSI or TMSI. The BSS forwards the location update request message to the MSC.
4. The VLR analyzes the LAI supplied in the message and determines that the TMSI received is associated with a different VLR (old VLR). In order to proceed with the registration, the IMSI of the MS must be determined. The new VLR derives the identity of the old VLR by using the received LAI, supplied in the location update request message. It also requests the old VLR to supply the IMSI for a particular TMSI.
5. The new VLR sends a request to the HLR/AUC (Authentication Center) requesting the “authentication triplets” (RAND, SRES, and Kc) available for the specified IMSI.
6. The AUC, using the IMSI, extracts the subscriber's authentication key (Ki). The AUC then generates a random number (RAND), applies the Ki and RAND to both the authentication algorithm (A3) and the cipher key generation algorithm (A8) to produce an authentication Signed Response (SRES) and a Cipher Key (Kc). The AUC then returns to the new VLR an authentication triplet: RAND, SRES, and Kc.
7. The MSC/VLR keeps the two parameters Kc and SRES for later use and then sends a message to the MS. The MS reads its Authentication key (Ki) from the SIM, applies the received random number (RAND) and Ki to both its Authentication Algorithm (A3) and Cipher key generation Algorithm (A8) to produce an authentication Signed Response (SRES) and Cipher Key (Kc). The MS saves Kc for later, and will use Kc when it receives command to cipher the channel.
8. The MS returns the generated SRES to the MSC/VLR. The VLR compares the SRES returned from the MS with the expected SRES received earlier from the AUC. If equal, the mobile passes authentication. If unequal, all signaling activities will be aborted.
9. The new MSC/VLR requests the BSS to cipher the radio channel. Included in this message is the Cipher Key (Kc), which was made available earlier during the authentication.
10. The BSS retrieves the cipher key, Kc, from the message and then transmits a request to the MS requesting it to begin ciphering the uplink channel.
11. The MS uses the cipher key generated previously when it was authenticated to cipher the uplink channel, and transmits a confirmation over the ciphered channel to the BSS.
12. The BSS upon ciphering the downlink channel sends a cipher complete message to the MSC. At this point, we are ready to inform the HLR that the MS is under control of a new VLR and that the MS can be de-registered from the old VLR.
13. The new VLR sends a message to the HLR informing it that the given IMSI has changed locations and can be reached by routing all incoming calls to the VLR address included in the message.
14. The HLR requests the old VLR to remove the subscriber record associated with the given IMSI. The request is acknowledged.
15. The HLR updates the new VLR with subscriber data (mobiles subscriber’s customer profile).
16. The MSC forwards the location update accept message to the MS. This message includes the new TMSI.
17. The MS retrieves the new TMSI value from the message and updates its SIM with this new value. The mobile sends then an update complete message back to the MSC.
18. The MSC requests from the BSS that the signaling connection be released between the MSC and the MS.
19. The MSC releases its portion of the signaling connection when it receives the clear complete message from the BSS.
20. The BSS sends a "radio resource" channel release message to the MS and then frees up the Stand-alone Dedicated Control Channel (SDCCH) that was allocated previously. The BSS then informs the MSC that the signaling connections has been cleared.
More Information from Readers are Expected !!!
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Posted by Ashish Bhatia at 6:12 PM 36 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Sunday, November 8, 2009STP (Signaling Transfer Point)
Hi,
There are different types of signaling points in SS7 Standards, likeService Switching Point (SSP) - like MSC, Tandem Switch, etc.Service Control Points (SCP) - like HLR, etc.Signaling Transfer Point (STP).
These Signaling points provide access to the SS7 network, databases, & transfer messages to other signaling points.
STP :- It is a vital element in SS7 network serving as a Signaling hub for the transfer of digital data packets between network nodes. It routes messages throughout the network using, call information & network addressing structured within SS7 data packets.
It serves as dynamic router, controlling traffic flow & access to variety of SS7 nodes & network.
Functions of STP :-
1. Receives the MSU's & direct them to appropriate destination.2. Network Management.3. (ANSI to ITU) or (ITU to ANSI) protocol conversion.4. Global Title Translation (GTT).5. Measurement of Data.6. Gateway Function.7. Gateway Screening (GWS)8. Local Number Portability (LNP).
Different Links used with STP :-
A-Link - It provide STP/SSP or STP/SCP connectivity. Maximum of 16 links can be there in a link set or maximum of 32 links in combined set.
B-Link - It connects one STP to other STP of same hierarchical level. Maximum of 8 links in quad configuration of link set.
C-Link - Maximum of 16 links in a link set. D-Link - Maximumof 8 links in a link set.
E Links - It connects a STP to other STP other then its Home STP & provides an alternate route for SS7 messages if congestion occurs at home STP.
F Links - It provides SSP to SSP connectivity. It provides only Call Setup/TearDown capability & it should be adjacent.
Why STP ???
It provides Centralized Network Management, facilitating the delivery of Intelligent Services throughout the network.
Reduction in Signaling Terminal Hardware in SSPs / SCPs. (like MSC, IN, HLR, etc.)
Central Database for GTT at STP, Minimizes Errors. Efficient Routing of Messages. Flexible SS7 Network Management. Fast Integeration of New Nodes in the network. Easy Migration to Next Generation Networks like VOIP, Soft Switch, etc.
Expecting More Information from Readers.
Thanks & [email protected]://homepageforu.webs.com/Posted by Ashish Bhatia at 6:15 PM 4 comments Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest Links to this postLabels: Telecom Terms
Thursday, November 5, 2009What is E1 / T1
The PDH (plesiochronous Digital Hierarchy) has 2 primary communication systems as its foundation.
These are,T1 system based on 1544kbit/s that is recommended by ANSI &E1 system based on 2048kbit/s that is recommended by ITU-T.
Common Characteristics :-
1. Both are having Same Sampling Frequency i.e. 8kHz.2. In both (E1 & T1) Number of samples/telephone signal = 8000/sec.3. In both (E1 & T1) Length of PCM Frame = 1/8000s = 125µs.4. In both (E1 & T1) Number of Bits in each code word = 8.5. In both (E1 & T1) Telephone Channel Bit Rate = 8000/s x 8 Bit = 64
kbit/s.
Differing Characteristics :-
1. In E1 Encoding/Decoding is followed by A-Law while in T1 Encoding/Decoding is followed by µ-Law.
2. In E1 - 13 Number of Segments in Characteristics while in T1 - 15 Number of Segments in Characteristics.
3. In E1 - 32 Number of Timeslots / PCM Frame while in T1 - 24 Number of Timeslots / PCM Frame.
4. In E1 - 8 x 32 = 256 number of bits / PCM Frame while in T1 - 8 x 24 + 1* = 193 number of bits / PCM Frame. (* Signifies an additional bit).
5. In E1 - (125µs x 8)/256 = approx 3.9µs is the length of an 8-bit Timeslot while in T1 - (125µs x 8)/193 = approx 5.2µs is the length of an 8-bit Timeslot.
6. In E1 - 8000/s x 256 bits = 2048kbit/s is the Bit Rate of Time-Division Multiplexed Signal while in T1 - 8000/s x 193 bits = 1544kbit/s is the Bit Rate of Time-Division Multiplexed Signal.
Read more at http://telecomtigers.blogspot.com/search/label/Telecom%20Terms#U7xiUXt0slQveGIR.99
