Network Switching Sub System in Gsm Network

8/21/2019 Network Switching Sub System in Gsm Network

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Prepared By : Adhvaryu Akash D. (EC 02)



Contents

New Technologies:

SIGTRAN MULTI-HOMING and MPLS

ONE-NDS

MNP

Practical Work:

Health Check Up Acceptance Test Clear Codes Link Shifting



New

Technologies



SIGTRAN

SS7 Signalling over IP : Internet Protocol.

Between Signalling Gateway (SG), Media GatewayController (MGC) and IP enabled Signalling Point Code(IP-SPC).

SIGTRAN Layers



SCTP versus TCP

SCTP is designed to cope with time-sensitive SIGNALLING data whileremaining flexible enough for general use.

SCTP : Stream Control Transfer Protocol

SCTP has been designed to counter some features of TCP that makeit unsuitable for transporting real-time SIGNALLING data, such as:

TCP is byte-streamed. TCP timers are defined in terms of many seconds. There are no inherent security features in TCP itself.



On the other hand SCTP has :

It defines timers of much shorter duration than TCP. It supports multi-homing.

It supports bundling. It supports fragmentation. It is message-oriented, defining structured frames of data. It has a multi streaming capability.

Diagram illustrating the transport of three ISUP messages over a TCP link.



Diagram illustrating the delivery of ISUP messages over SCTP.

THE FOUR UA LAYERS

Diagram illustrating SIGTRAN's four UA layers



The M2UA Layer : M2UA is used to transfer MTP2 user data between the

MTP2 instance on a SG and the MTP3 instance on anMGC.

The M2PA Layer : M2PA is the peer-to-peer equivalent of M2UA. Ratherthan provide a link between remotely located MTP2

and MTP3 instances, it replaces an MTP2 link beneathMTP3.

The M3UA Layer : M3UA is similar to M2UA, in that it operates in a client-

server way to provide an upper layer SS7 with protocol

remote access to the lower layers. M3UA, however,operates between an SG and an MGC, providing anMTP3 service on the MGC.

The SUA Layer : SUA provides a means by which an application part (such

as transaction application capabilities part [TCAP]) on anIP-SCP may be reached via an SG. The network

architecture associated with SUA allows for multiple IP-SCPsto be reached via a single SG.



MULTI-HOMING and MPLS

MSSs without Multi-Homing

MULTI-HOMING :



Need: As shown in the schematic diagram 1, if the MGW 11 fails, theBSCs connected to it do not get the service regarding signalling andspeech data and so the costumers connected to those BSCs throughBTS do not get the service. Considering another scenario, if MSS 1fails, the MGWs, BSCs do not get any controlling information andhence the costumers in that MSS are not delivered service.

Solution: MULTI-HOMING

Multi-Homing architecture is as shown below. Firstly we create a pool ofMSS consisting of 2 or more MSS. Now the MGWs connected to this MSSsare connected to all other MSSs in the pool. Hence if MSS 1 fails, thetraffic is taken by MSS2 through MGW 11 and MGW 12. Similar is the case

with MSS 2.

Now lets discuss the case for the BSCs and the MGWs connectivity. Hereas we see, all the BSCs are connected to all other MGWs. So suppose ifMGW 11 fails, the traffic through BSCs connected to that MGW 11 ismigrated to MGW 12 and hence no interruption is recorded in this case.This is the case for all the BSCs shown in the Fig.



MSSs with Multi-Homing

Advantage: Costumers get UNINTERRUPTED Service. Disadvantages : Complexity of the network increases.



MPLS :



MPLS stands for Multi Protocol Label Switching.

In this technology, the different nodes are connected to each other

through the “ IP CLOUD”.

What IP CLOUD is basically a pre-defined network in which the connection

to all the nodes is made using routers.

Different layers of the TCP/IP or SIGTRAN send their own data to the

destination.

In the 1st step, Signalling is done and the path is getting decided. The

packet is transferred during the 2nd phase.

The home router detects the destination and the forwards the packet to

other router. This router do not have the capability to unwind the data in

the packet so it adds its “LABEL” to it indicating the destination of the next

router.

Now this packet is forwarded to the that router that comes in the way to

the destination.

This router accepts the packet and removes the previous LABEL and adds

the new LABEL to it that gives the location of the next router.

Following in this pattern, the packet reaches its destination. Also note thatthe LABEL is only locally defined.



ONE-NDS

ONE – NETWORK DIRECTORY SERVER

Connections between ONE-NDS and HLRs



The subscribers which are not latched to any VLR sincelong, in HLR, the DIRTY FLAGs are marked against theirdata.

When ONE-NDS is installed and ready to use, the copyof the HLRs’ data is copied to ONE-NDS’s database.

Then the DIRTY FLAGED subscribers are removed fromthe HLR but their copy is still there in ONE-NDS’s

database. If even after 10 days of DIRTY FLAG, the subscriber has

not performed any kind of operation from SIM, the dirtyflag is removed and they are moved to the CLEANEDdatabase.

After 30 days in CLEANED database if still no operationfrom the subscriber, the subscriber’s data ispermanently deleted and the number can be given tonew users.



Consider the case in which the SIM card is not directly usedas in the calls are forwarded to some other number from thisSIM card.

So we cannot delete the data of such SIM cards as they arestill in use.

So in ONE-NDS we have other database called CFdatabase.

It is CALL-FORWARDING database.

It keeps the record of such SIM cards from on which the call-forwarding service is activated.



MNP

MOBILE NUMBER PORTABILITY

The much awaited MNP (Mobile Number Portability) finally launched on 20th

Jan 2011 in India, empowering mobile phone consumers to change serviceprovider conveniently.

Mobile Number Portability (MNP) allows the mobile subscribers to retain the

existing mobile phone number when the subscriber switches from one

access service provider (Operator) to another irrespective of mobile

technology or from one technology to another of the same or any other

access service provider, in a licensed service area.



MNP PRINCIPLE IN INDIA

Applicable only for Mobile Numbers.

Applicable only in intra licensed area.

Applicable irrespective of Technology.

LRN based routing.

MNPDB query & Routing Method.



Central Side & Operator Side after MNP



Central Side – MNPO (Centralized Clearing House)

The central side is a MNPO, supposed to provide MNP Service in a particular zone. It

is also called MNP Clearing House (MCH).

MCH shall receive mobile number portability requests from the recipient operator;forward it to the donor operator for verification.

On getting clearance from donor operator MNP service provider shall control andcoordinate the mobile number portability process.

The MCH will send the details of the porting to the centralized Number PortabilityDatabase (NPDB) which in turn will update its own database by an appropriate routingnumber called Location Routing Number (LRN), a unique routing number assigned toeach operator in a service area by the DoT.

This updating will be communicated by the NPDB to all the service providers forupdating their respective local Number Portability database.



Operator Side – Service Providers

Service providers should connect their Local Number Portability

database to the both sites of MNPO.

Whenever any call is made to the ported mobile number, theoriginating network shall first query the number portability databaseto obtain LRN and then the call is routed directly to the destinationmobile network.

Service provider can directly connect its gateway to Central MNPDB.

Service Provider can deploy its separate Local MNPDB .

Service provider performs MNP query to its STP (which consist Local

MNPDB) to get appropriate LRN to route originating calls to subscription

network.



Call Flow after MNP



MNP Process Flow



Practical

Work



Health Check Up

Health Check-up is a daily activity where-in the current state of all the MSCs isobtained on an excel sheet through a series of command programmed through amacro.

ZAHO; : Shows the alarms currently ON.

ZAHP; : Prints alarm History from morning.

ZABO; : Blocked alarms.

ZUSI; : Status of Functional and Control Units.

ZISI:OMU,VPP:; : Checks the status of Virtual Printer Protocol (VPP).

ZISI:OMU,WDU:;: Status of Hard Disk.

ZIFI:CHU,0:GSMCHA:; : Shows amount of full files and currently opened

Disk File No.

ZUSI:;CLS; : Internal Clock.

ZNEL; : Status of Signalling Links. ZNHI; : Checks SCCP Status.

ZNRI; :Signalling Route Set Status.

ZAHP:NR=1001; : Shows the Restarted Units in the system.

ZMVI; : Shows Subscribers in VLR and Capacity of VLR.

ZDRI; : Synchronized Clock Status.



Acceptance Test

Signalling Link (SL), Signalling Group (SG) & Signalling Link Set



Signalling Route Set



Steps for Acceptance Test:

First of all we have to create Link, Link Set & Route Set inthe Media Gateway of both nodes.

After creating this in GCS (Gateway Control Server), wedefine Route Set, Route & CGR.

This definition is same from both nodes.

After CGR is created we add CIC into that for speechdata travelling.

Once all Links and Link Sets are created it is sending forR.A

After approval Link is live and 5 outgoing and incomingcalls are done for testing purpose. These calls are ofdifferent duration to check that whether the longduration calls are running properly or not.



Clear Codes

A clear code is the identifier code of the reason to clear a call.

A clear code may also act as control information in anexchange, ordering the exchange to handle a call in a certainway.

Main functions of clear codes:

To act as reportable information about the functions of a network.

To act as control information in handling a call.

A clear code can be generated in an exchange in two ways :



A clear code can be generated in an exchange in two ways :

An exchange receives a clearing message from the surrounding network,that is, from another exchange. The message identifies the clearing reason.When coming into an exchange, the clearing cause is converted into thecorresponding clear code.

An exchange discovers a reason to clear a call. It generates a clear codecorresponding to the clearing reason.

To be able to make use of clear code information, a network operator musthave:

Clear code information collected from network elements.

Information about the meanings of different clear codes.

Knowledge on situations in which calls can be cleared.

Knowledge on handling a call in a network.



Link Shifting

In above figure link (E1) is established between MSC-A & MSC-B.

Here we can note that link number may or may not be different onboth the side (MSCs.) but number of timeslot must be same on boththe side



Reasons for Shifting the Link :

Link is not used because of less traffic and at another MSC because of high trafficnew links (E1 & CGR) are needed.

If because of some reason, any link fails, shifting of the link is very necessary forpassing the successful signalling messages.

The Logical Steps followed in order to shift the link :

Inactivation of old link.

To deny the activation of old link.

Remove the link from the Link set.

Deletion of link.

Create the new link.

Activate the new link.

Documents

Network Switching Sub System in Gsm Network