mobile originating & terminating

7/23/2019 Mobile Originating & Terminating

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The below Description is a mobile-originated call that terminates outside the PLMN .

Request Access

The MS sends a Channel Request (CHAN_REQ) essa!e on the RACH.The "SS responds with a radio reso#rce assi!nent ($MM_ASS_CMD) on the A%CH.

The MS sends a Service Request (CM_SER&_REQ) essa!e to the "SS on the SDCCH.

Authentication"e'ore the networ will proide an* serices to the MS+ the networ will re,#ire the MS to

a#thenticate itsel'. The "SS sends an Authentication Request (A-TH_REQ) essa!e to the MS.

The RAND seres as the challen!e 'or a#thentication.

The MS calc#lates the proper SRES based on the RAND that was !ien and sends the SRES to

the "SS in an Authentication Response (A-TH_RES/) essa!e.

The "SS eri'ies the SRES. $' the SRES is correct then the MS is a#thenticated and allowed

access to the networ. The "SS will send a Service Accept (CM_SER&_ACC) essa!e lettin!the MS now that the serice re,#est was receied and processed.

0nce a#thenticated+ the "SS orders the MS to switch to cipher ode with the

C$/H_M0D_CMD essa!e.

Initial Call SetupThe MS will iediatel* switch to cipher ode and send a Cipher Mode Coplete

(C$/H_M0D_C0M) essa!e.

The MS then sends a Call Set#p (SET-/) essa!e to the "SS. The essa!e incl#des the addressin'oration (MS$SDN) o' the called part*.

The "SS assi!ns a TCH to the MS b* sendin! an Assi!nent Coand (ASS_CMD) essa!e.

This essa!e incl#des which Transceier (TR1) and which Tie Slot (TS) to #se.

The "SS does not act#all* assi!n a TCH to the MS #ntil the MSC sends a Call /roceedin!

(CA22_/R0C) essa!e to the "SS indicatin! that the $AM has been sent.

The MS iediatel* switches to the assi!ned TCH. The MS sends an Assi!nent Coplete

(ASS_C0M) essa!e bac to the "TS on the 3ACCH.

Remember that a FACCH is not a separate channel; it is simply a stolen time slot from the TCH that is used for signaling datainstead of voice traffic.

Call SetupThe MSC sends an $nitial Address Messa!e ($AM) to the %MSC. The $AM contains the

MS$SDN o' the called part* as the MS dialed it.



The MSC will also send a Call /roceedin! (CA22_/R0C) essa!e down to the "SS and this is

when the "SS wo#ld assi!n a TCH to the MS+ as described in step 45 aboe.

"ased on the dialed n#ber+ the %MSC decides where to ro#te the $AM within the /STN.

The /STN will contin#e to ro#te the $AM #ntil it reaches the correct Switchin! Center and the

call ro#tin! is coplete. The /STN will then establish the call circ#it and send an AddressCoplete Messa!e (ACM) bac to the %MSC.

The %MSC then 'orwards the ACM bac to the responsible MSC indicatin! that the call circ#it

has been established

Call Establishment0nce the MSC receies the ACM+ it sends an A2ERT essa!e to the MS indicatin! that the call

is !oin! thro#!h. The "SS sends the A2ERT essa!e on the 3ACCH. 0nce the MS receies the

A2ERT+ it will !enerate the rin!in! so#nd in the earpiece. The "SS sends an alertin! essa!ethe s#bscriber will hear the line rin!in!.

0nce the called part* answers the phone+ the /STN will send an Answer essa!e to the MSC.The MSC 'orwards this to the MS in a Connection (C0N) essa!e.

0nce the MS receies the C0N essa!e+ it switches oer to oice and be!ins the call. All oicetra''ic occ#rs on the assi!ned TCH.

Call Termination6hen either the caller or the called part* han!s #p+ the call will be disconnected. Either part* can

initiate the disconnect. $n this e7aple+ the MS initiates the disconnect. The MS sends aDisconnect (D$SC) essa!e to the "TS on the 3ACCH.

The "SS 'orwards the D$SC to the MSC. 0nce the MSC receies the D$SC essa!e+ it sends a

Release (RE2) essa!e thro#!h the %MSC to the /STN as well as down thro#!h the "SS to the

MS.

The MS responds b* sendin! a Release Coplete (RE2_C0M) essa!e to the "SS on the

3ACCH. The "SS 'orwards the RE2_C0M essa!e #p to the MSC. 0nce the MSC receies theRE2_C0M essa!e the call is considered ended 'ro the call control perspectie.

Altho#!h the call has ended+ the "SS still has a TCH allocated to the MS. The MSC sends aChannel Release (CHAN_RE2) essa!e to the "SS. The "SS 'orwards the CHAN_RE2

essa!e to the MS.

The MS responds with a D$SC (2A/D) essa!e and ret#rns to an idle ode. The "SSreallocates the channel 'or other call or releases the TR1.



Mobile Terminated Call

In this example, the call is originating from outside the PM!"

Route Establishment to find the MSC#$R The callin! part* dials the MS$SDN 'or the obile s#bscriber. The /STN identi'ies the networ(/2MN) that the dialed MS$SDN belon!s to and will locate a %MSC 'or that networ. The

/STN sends an nitial Address essa!e to the %MSC.

The %MSC 'orwards the MS$SDN to the H2R and re,#ests ro#tin! in'oration 'or it. The H2R

loos #p the MS$SDN and deterines the $MS$ and the SS! address 'or the MSC8&2R that issericin! the MS.

The H2R then contacts the sericin! MSC8&2R and ass it to assi!n a Mobile Station Ro#tin!

N#ber (MSRN) to the call.

The MSC8&2R allocates the MSRN and 'orwards it to the H2R. "ote# t is important to remember that the $SC%&'R assigns a $SR" to the call not to the $S itself.

The H2R 'orwards the MSRN as well as ro#tin! in'oration 'or the sericin! MSC8&2R to the

%MSC.

The %MSC sends an $nitial Addressin! essa!e to the sericin! MSC8&2R and #ses the MSRN

to ro#te the call to the MSC8&2R. 0nce the sericin! MSC8&2R receies the call+ the MSRNcan be released and a* be ade aailable 'or reassi!nent.

Paging the Mobile StationThe MSC8&2R then orders all o' its "SCs and "TSs to pa!e the MS. Since the MSC8&2R doesnot now e7actl* which "SC and "TS the MS is onitorin!+ the pa!e will be sent o#t across the

entire 2ocation Area.

Initial SetupThe MS receies the (age Request (/A%_REQ) on the /CH. The MS reco!ni9es that the pa!e is

intended 'or it+ based on a TMS$ or an $MS$.

The MS sends a Channel Request (CHAN_REQ) essa!e on the RACH.

The "SS responds on the A%CH b* sendin! an mmediate Assignment ($MM ASS) essa!e

which assi!ns an SDCCH to the MS. At this point+ the networ does not now that the MS is theone that it is pa!in!+ it onl* nows that this MS wants access to the networ.

The MS iediatel* switches to the assi!ned SDCCH and sends a (aging Response

(/A%_RES) essa!e on the SDCCH. This lets the networ now that the MS is respondin! to its pa!e.

Authentication



"e'ore the networ will proide an* serices to the MS+ the networ will re,#ire the MS to

a#thenticate itsel'. The "SS sends an Authentication Request (A-TH_REQ) essa!e to the MS.

The RAND seres as the challen!e 'or a#thentication.

The MS calc#lates the proper SRES based on the RAND that was !ien and sends the SRES to

the "SS in an Authentication Response (A-TH_RES/) essa!e.

The "SS eri'ies the SRES. $' the SRES is correct then the MS is a#thenticated and allowed

access to the networ.

0nce the MSC8&2R has a#thenticated the MS+ it will order the "SS and MS to switch to cipherode #sin! the C$/H_M0D_CMD essa!e. 0nce the MS in encr*ption ode+ the &2R will

norall* assi!n a new TMS$ to the MS.

Establishing a Channel0nce the MS is a#thenticated and in encr*ption ode+ The MSC sends a Set#p Messa!e to the

"SS+ the "SS 'orwards the SET-/ essa!e to the MS on the assi!ned SDCCH.the assi!nedSDCCH. The SET-/ essa!e a* incl#de the Calling 'ine dentification (resentation (C2$/)+

which is essentiall* caller $D.

The MS responds b* sendin! a Call Confirmed (CA22_C0N) essa!e: which indicates that the

MS is able to establish the re,#ested connection. The "SS rela*s the essa!e #p to the MSC.

Call SetupThe "SS then sends an Assignment Command (ASS_CMD) essa!e to the MS on the assi!ned

SDCCH. The ASS_CMD essa!e assi!ns a Tra''ic Channel (TCH) to the MS.

The MS iediatel* switches to the TCH and responds with an Assignment Complete (ASS_C0M) essa!e on the 3ACCH. The MS be!ins rin!in! once it has established the TCH.

Remember that all signaling that occurs on the traffic channel actually occurs on a FACCH) *hich is a time slot that is stolen

from the TCH and used for signaling.

The MS sends an A2ERT essa!e to the MSC on the 3ACCH. The "SS 'orwards the A2ERTessa!e thro#!h the /STN to the callin! part* and the caller hears the line rin!in!.

Call Establishment0nce the #ser answers the call (b* pressin! the send b#tton)+ the MS will send a Connect C0Nessa!e to the MSC. The Connect essa!e is 'orwarded bac to the caller;s switch to actiate

the call.

The MSC sends a Connect Ac+no*ledge C0N_AC< essa!e to the MS and the call isestablished.

Call %isconnect



Disconnect happens the sae wa* as 'or an* other call. $n this e7aple+ the callin! part* initiates

the disconnect.

6hen the callin! part* han!s #p+ the callin! part*;s switch initiates a Release (RE2) essa!e.The essa!e is 'orwarded to the serin! MSC+ which is then 'orwarded to the "SS.

The "SS will send a ,isconnect (D$SC) essa!e to the MS on the 3ACCH.

The MS con'irs release o' the call b* sendin! a Release (RE2) essa!e on the 3ACCH+ which

is 'orwarded to the MSC.

The MSC sends e Release Complete (RE2_C0M) essa!e thro#!h the "SS to the MS. As 'ar ascall control (CC) is concerned+ the connection has been terinated.

The MS still has a TCH assi!ned to it+ so the "SS sends a Channel Release (CHAN_RE2)

essa!e to the MS. This releases the radio reso#rce on the Air $nter'ace.

The MS responds be sendin! a 'inal ,isconnect essa!e and ret#rns to idle.

mobile originating & terminating

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