Friday, December 23, 2016

Mobile Terminated Call in GSM

Mobile Terminated Call


        •The calling party dials the MSISDN for the mobile subscriber.
The PSTN identifies the network (PLMN) that the dialed MSISDN belongs to and will locate a GMSC for that network.
        •The PSTN sends an Initial Address message to the GMSC.
•The GMSC forwards the MSISDN to the HLR and requests routing information for it.
The HLR looks up the MSISDN and determines the IMSI and the SS7 address for the MSC/VLR that is servicing the MS.
•The HLR then contacts the servicing MSC/VLR and asks it to assign a Mobile Station Routing Number (MSRN) to the call. (a MSRN is assigned to the call not to the MS itself. )
The MSC/VLR allocates the MSRN and forwards it to the HLR.

 
Mobile Terminated Call in GSM
Mobile Terminated Call in GSM 

Route Establishment: 
       •The HLR forwards the MSRN as well as routing
information for the servicing MSC/VLR to the GMSC.

         •The GMSC sends an Initial Addressing message to the           servicing MSC/VLR and uses the MSRN to route the call to the      MSC/VLR.


The HLR forwards the MSRN as well as routing
information for the servicing MSC/VLR to the GMSC.
The GMSC sends an Initial Addressing message to the servicing MSC/VLR and uses the MSRN to route the call to the MSC/VLR.
Once the servicing MSC/VLR receives the call, the MSRN can be released and may be made available for reassignment.

•             Once the servicing MSC/VLR receives the call, the MSRN can be released and may be made available for reassignment.


Paging the Mobile Station:
•             The MSC/VLR then orders all of its BSCs and BTSs to page the MS.
•             Since the MSC/VLR does not know exactly which BSC and BTS the MS is monitoring, the page will be sent out across the entire Location Area.


Initial Setup:
•              The MS receives the Page Request (PAG_REQ) on the PCH. The MS recognizes that the page is intended for it, based on a TMSI
•              The MS sends a Channel Request (CHAN_REQ) message
on the RACH.
•              The BSS responds on the AGCH by sending an Immediate Assignment (IMM ASS) message which assigns an SDCCH to the MS.
•              At this point, the network does not know that the MS is the one that it is paging, it only knows that this MS wants access to the network.
•              The MS immediately switches to the assigned SDCCH and sends a Paging Response (PAG_RES) message on the SDCCH. This lets the network know that the MS is responding to its page.


 Authentication:
•              Before the network will provide any services to the MS, the network will require the MS to authenticate itself.
•              The BSS sends an Authentication Request (AUTH_REQ) message to the MS. The RAND serves as the "challenge" for authentication.
•              The MS calulates the proper SRES based on the RAND that was given and sends the SRES to the BSS in an Authentication Response (AUTH_RESP) message.
•              The BSS verifies the SRES. If the SRES is correct then the MS is authenticated and allowed access to the network.
•              Once the MSC/VLR has authenticated the MS, it will order the BSS and MS to switch to cipher mode using the CIPH_MOD_CMD message. Once the MS in in encryption mode, the VLR will normally assign a new TMSI to the MS.


 Establishing a  Channel:

•             Once the MS is authenticated and in encryption
mode, The MSC sends a Setup Message to the BSS.
•             BSS forwards the SETUP message to the MS on the assigned SDCCH.
•             The SETUP message may include the Calling Line Identification Presentation (CLIP), which is essentially caller ID.
•             The MS responds by sending a Call Confirmed (CALL_CON) message; which indicates that the MS is able to establish the requested connection. The BSS relays the message up to the MSC.


 Call Setup
•             The BSS then sends an Assignment Command (ASS_CMD) message to the MS on the assigned SDCCH. The ASS_CMD message assigns a Traffic Channel (TCH) to the MS.
•             The MS immediately switches to the TCH and responds with an Assignment Complete (ASS_COM) message on the FACCH. The MS begins ringing once it has established the TCH.
•             The MS sends an ALERT message to the MSC on the FACCH. The BSS forwards the ALERT message through the PSTN to the calling party and the caller hears the line ringing.


 Establishing the  Call
•             Once the user answers the call (by pressing the send button), the MS will send a Connect CON message to the MSC. The Connect message is forwarded back to the caller's switch to activate the call.
•             The MSC sends a Connect Acknowledge CON_ACK
message to the MS and the call is established.


 Disconnecting the  Call
•             Assuming  the calling party initiates the disconnect, when the calling party hangs up, the calling party's switch initiates a Release (REL) message. The message is forwarded to the serving MSC, which is then forwarded to the BSS.
•             The BSS will send a Disconnect (DISC) message to the MS on the FACCH.
•             The MS confirms release of the call by sending a Release (REL) message on the FACCH, which is forwarded to the MSC.


 Disconnecting the  Call
•             The MSC sends Release Complete (REL_COM) message through the BSS to the MS. As far as call control (CC) is concerned, the connection has been terminated.
•             The MS still has a TCH assigned to it, so the BSS sends a Channel Release (CHAN_REL) message to the MS. This releases the radio resource on the Air Interface.
•             The MS responds be sending a final Disconnect message and returns to idle.




Video Tutorial for Mobile Terminated Call :





Read This:

Call Setup GSM Flow

Call Setup GSM Flow




GSM Call Flow (GSM Originating Call)

Call Setup GSM Flow
Call Setup GSM Flow


Call Setup GSM Flow:

•              The MSC sends an Initial Address Message (IAM) to the
GMSC. The IAM contains the MSISDN of the called party as
the MS dialed it.
•              The MSC will also send a Call Proceeding (CALL_PROC) message down to the BSS and this is when the BSS would assign a TCH to the MS, as described earlier
•              Based on the dialed number, the GMSC decides where to route the IAM within the PSTN.
•              The PSTN will continue to route the IAM until it reaches the correct Switching Center and the call routing is complete. The PSTN will then establish the call circuit and send an Address Complete Message (ACM) back to the GMSC.
•              The GMSC then forwards the ACM back to the responsible

MSC indicating that the call circuit has been established.


Call Establishment


             Once the MSC receives the ACM, it sends an ALERT message to the MS indicating that the call is going through. The BSS sends the ALERT message on the FACCH. Once the MS receives the ALERT, it will generate the ringing sound in the earpiece.
             Once the called party answers the phone, the PSTN will send an Answer message to the MSC. The MSC forwards this to the MS in a Connection (CON) message.

             Once the MS receives the CON message, it switches over to voice and begins the call. All voice traffic occurs on the assigned TCH.

Call Termination
              When either the caller or the called party hangs up, the call will be disconnected. Either party can initiate the disconnect.
              Assuming, the MS initiates the disconnect. The MS sends a Disconnect (DISC) message to the BTS on the FACCH.
              The BSS forwards the DISC to the MSC. Once the MSC receives the DISC message, it sends a Release (REL) message through the GMSC to the PSTN as well as down through the BSS to the MS.
              The MS responds by sending a Release Complete (REL_COM) message to the BSS on the FACCH. The BSS forwards the REL_COM message up to the MSC. Once the MSC receives the REL_COM message the call is considered ended from the call control perspective.

             Although the call has ended, the BSS still has a TCH allocated to the MS. The MSC sends a Channel Release (CHAN_REL) message to the BSS. The BSS forwards the CHAN_REL message to the MS.

             The MS responds with a DISC (LAPDm) message and returns to an idle mode. The BSS deallocates the channel and releases the TCH.



Video Tutorial for GSM Originating Call Flow :





Study PDF: GSM Originating Call Flow


Monday, September 12, 2016

What is Ray Model?

Introduction Ray Model


1. Optical fiber is basically a solid glass rod. The diameter of rod is so small that it looks like a
fiber.

2. Optical fiber is a dielectric waveguide. The light travels like an electromagnetic wave inside
the waveguide. The dielectric

waveguide is different from a metallic waveguide which is used at microwave and millimeter
wave frequencies.

3. In a metallic waveguide, there is a complete shielding of electromagnetic radiation but in an
optical fiber the electromagnetic radiation is not just confined inside the fiber but also extends outside the fiber.

4. The light gets guided inside the structure, through the basic phenomenon of total internal
reflection .

5. The optical fiber consists of two concentric cylinders; the inside solid cylinder is called the
core and the surrounding

6. For the light to propagate inside the fiber through total internal reflections at core-cladding
interface, the refractive index of the core must be greater than the refractive index of the cladding. That is .

BROADBAND COMMUNICATION IMPORTANT QUESTIONS

BROADBAND COMMUNICATION QUESTION BANK


1.  (a)         
What are the advantages of optical fiber cables over the co-axial cables?    
(06)
(b)
Calculate NA, Acceptance angle and Angle of fiber with core and cladding refractive index values as n1=1.5 and n2=1.45 respectively.                                                                  
(06)
(c)
Explain the “mode theory” of optical fiber.   
(06)
2.  (a)         
What is meant by acceptance angle and acceptance cone for optical fiber? Show and explain it’s relationship to numerical aperture and refractive indices of core & cladding.
(06)
(b)
If a MMSI fiber of core radius 25 micrometer operating at 1300nm, has  core and cladding refractive index as 1.5 & 1.38 respectively; Calculate Numerical aperture, Normalized frequency, Solid acceptance angle and number of modes entering in the fiber
(06)
(c)
If the mean optical power in a 8 km long fiber at launching and output zone is 12 and 2 microwatt; determine (1) overall signal attenuation in dB and (2) when length is 10 km with the splices of 1dB attenuationeach at the interval of 1km.
(06)
3.  (a)         
What is dispersion in fiber? Explain intra-modal dispersion in details.
(08)
(b)
A SMSIfiber with core and cladding refractive indices as 1.447 and 1.442respectively is designed to operate at wavelength 1.3 micrometer. When core diameter is 7.2 micrometer; confirm that the fiber permits single mode transmission and estimate the range of wavelengths over which this will occur.           
(08)
4.  (a)         
Explain the “linear scattering losses” in fibers.
(08)
(b)
A MMSIF has NA as 0.3 and core refractive index as 1.45. The material dispersion parameter as 250 ps/nm.km makes it totally dominating intra-modular dispersion mechanism. Estimate (1) total pulse broadening/km when the fiber is used with the LED source of RMS spectral width of 50 nm, and (2) corresponding bandwidth-length product.
(08)
5.  (a)         
Explain the three transmissions windows of optical communication along with the attenuation curves for SMF.
(08)
(b)
Explain bending losses in fiber.         
(08)
6.  (a)         
Explain material absorption losses in silica fiber.
(08)

WIRELESS NETWORKS IMPORTANT QUESTIONS

WIRELESS NETWORKS QUESTION BANK


QUESTION BANK FOR WIRELESS NETWORKS :

Q.1.What are draw back of  2G  Services ? What are its silent features of 3G services that overcome the drawbacks of 2G services?
Q.2.Discuss the features of IMT2000 that have been adopted in UMTS/3G services.
Q.3.Explain the basic concept of WCDMA ?Which is a air interface of UMTS.
Q.4.Give the specification of WCDMA air interface .Also  explain how the information /message  is coded and scrambled in WCDMA
Q.5.Explain in brief the physical channels in WCDMA and the function performed by them
Q.6.Explain the transport channel in CDMA that are mapped on the physical channel.
Q.7.Draw the architecture of 3GPP RELEASE  4 distributed network architecture.
Q.8. .Draw the architecture of 3GPP RELEASE  5 All IP multimedia  network architecture.
Q.9.What is ALL IP network ? Explain its architecture  ? Explain its Advantages?
Q.10.What  is core network ?Explain its architecture ?
Q.13.Write a short note on TD-SCDMA and draw the system architecture of TD-SCDMA.

Q.14. Differentiate between the TD-SCDMA,WCDMA and CDMA 2000.

Friday, September 9, 2016

What is Satellite Communication?

Meaning of Satellite & Basic concepts:

Satellite:

"satellite is object which rotates around some body due to the effect of gravitational forces" .

OR

"A satellite is an object which has been placed into orbit by human endeavor" .


Wednesday, September 7, 2016

What is the meaning of Multiplexing ?

Multiplexing Definition and types:

Definition: Multi means 'Many', Plexing means 'having parts or units' combinely latin meaning suggest this but in reality this term is used for multiplexing of signals in telecommunications  "Multiplexing is the procedure in which numerous Data Streams, originating from diverse Sources, are joined and Transmitted over a Single Data Channel or Data Stream."

Wavelength division multiplexing (WDM)

Wavelength division multiplexing (WDM):


Wavelength division multiplexing (WDM)
Wavelength division multiplexing (WDM)

Definition: "Wavelength-division multiplexing (WDM) could be a technique of mixing multiple signals on optical device beams at varied infrared (IR) wavelengths for transmission on fiber optic media. every optical device is modulated by AN freelance set of signals. Wavelength-sensitive filters, the IR analog of visible-light color filters, square measure used at the receiving finish".

Saturday, September 3, 2016

IP Address Subnetting & CIDR


IP Address Subnetting & CIDR



IP Address Subnetting & CIDR

IP Address Subnetting & CIDR