Users15&Name=GSM Call Flows

GSM Call Flows Aniket Parab TAC - RAN

GSM Channel Structure

Location Update MS

BTS

BSC

MSC

Chan Request (RACH)

RAC H

Chan Required Chan Act Chan Act ACK  Imm Ass Cmd (Imm Ass)

AGCH

Imm Ass (AGCH) SABM (Loc Update Req)

LAPD

UA(Loc Update Req)

Est Ind (Loc Update Req) CR (Loc Update Req) CC

Layer 2

Location Update Accept BSSMAP (Clear Cmd) SDCCH

Chan Release DISC

Data Req (Chan Release) Deact SDCCH Release Ind RF Chan Release RF Chan Release ACK 

BSSMAP (Clear Cmp) RLSD RLC

IMSI Detachment – Mobile Power Off  BTS

MS

BSC

MSC

Chan Request

RAC

Chan Required

H

Chan Act Chan Act ACK  AGCH

Imm Ass SABM(IMSI Detach Ind)

LAPD Layer 2

Est Ind (IMSI Detach Ind)

UA(IMSI Detach Ind) Chan Rel

SDCCH

Imm Ass Cmd(Imm Ass)

DISC UA

DR (Chan Rel) Deact SACCH Release Ind RF Chan Rel RF Chan Rel ACK 

CR(IMSI Detach Ind) CREF RLSD RLC

Originating Call M

S

B

C

RAC

h

a n

R

e q

u

e s t

T

S

( R

A

B

C

H h

H C

AGCH S

LAPD – Layer 2

a

n

C

I m A

B

U

m

A

h

h

R

e

a n

a

m

( C

M

( C

M

S

A

S

e r

e r

R

R e

q E)

e q ) s t I n

SDCCH

d

M e a l l

C C A B

s s i g

n m

e n

h

h

t

C

M

m

( C

M

s s i g

n

m

e

n

t

C

R

FACCH

R

S

e

t P

U p r o c e

r

A

C C

a n

c

e

m

r

R

A

s s )

e

q

A

) R

( C

M

S

C

C

A s s e q o n f  

R

e

q

A

s s i g

n

m

e

C

K

e r

R

e q

t

i n g

o n t e x t o n t e x t

R C

u

e s t

c t

c

t

A

o

m

m

a n

d

s t

c e p

e d

A

m

e a

c

F

I n

C

K

d

F

I S

C

e

l e

a

e

D

s e

R

F

a

n

R

e

R

C

C

m

p

e

l e

a s e

I n d A

g t A

o

e

c

o

m

n

n t

H

e l e a s e

n

a

h

c t

C a

n

S

C

C

h

h

a n

R

A

e l e a s e F

C

n e c e c t

s e

( C

R R

C

K t

e l e a s e

l e

R D

A

a n

i s c R

R

a

o n n n

o D

n

t e

l e r t i n

C

R

l e S

h

h

C

FACCH

t

C C

TCH

p

e l e a s e A

D

K ( I m

S

n

o

R

a

d

C d

a

E

D

h

C

A A

C

i r e

A

C

P h y s i c a l P h y s i c a l

A

S

t

C

C

U

u c

c t

s s

S

S

q

A

n

A

C

LAPD – Layer 2

M

s s

M

A

C

)

C

I m

S

a n

e

C

l e

l e

C

t e C

a s e )

H

e l e

e l e

l e a r

l e a r C o R L S D R L C

C

K

a s e

a s e

A

C

C

I n d R

R

p

m

d

m

p

l e

t e

)

Terminating Call M S

B S C

B T S

M S C

P P P

PCH C

RAC

a h

g

i n

a n

g R

R

e

q

e q

u

e s t

a

C

h

H

a

C C I m

AGCH

g i n

I m

m

S

B

A

A

s s i g

M

LAPD – Layer 2

U

( P

n

a g

m

e n

R

e s p

n h

h

m

A

g

C

R

e

a n

q

A

m

d

u

i r e

a g i n g

d

c t

a n A c t s s C m

A d

c k ( I m

m

A

s s )

t )

E

s t

I n d

( P

a g

R

e s p )

A

C

R

( P C

S e t u p a l l C o

C P

h y

s i c a l

C

o

P

h y s i c a l

C

o n

C

S

LAPD – Layer 2

A U

B

A M

s s i g

n

m

e n

C C

t

h

a n

A

n t e x t

R

e q

s t

R

e s p

)

t e x t

C

o n

s s i g

n

m

n

t

R

e

C

o

m

m

a n

e

q

f  

c t

h a n A c t A o m m a n d E

g

n f i r m A

SDCCH

a

C

I n

c k

d

A A

s s i g

n

m

e

n

t

C

o

m

p

l e

t e A

A

FACCH C

l e r t i n

s s i g

n

m

e

n

t

p

g

C

o

n

n

e c t

o

n

n

e

c t

A

c

k

TCH D

i s c o n n e c t e l e a s e

R R

FACCH

D C

h a n D

n e l I S

R

e l e a s e R

e l e a s e

( C

D

C

a

n

n

e a c t

S

A

R R

R F

h

C

e l e a s e

F C

C h

h a

a n n

R

o m e

l

p l e t e R

e

C

C

H

I n

d

R e

l e

a s e

e l e a s e l e a s e A

)

C

l e a r

C

o

C

l e a r

C

o m

R

L R

c

k

S L

D C

m

p l e t e

d

l e

t e

PSTN

1

GMSC

2

6

5

MSC/VLR  4 3

HLR 

1.MSISDN

2. MSISDN 3. IMSI 4. MSRN

5. MSRN

6. MSRN

MS

Intra-cell Handover M

B

S M

SACCH

e

a

s

R

T

e

B

S

M

e

s s i g S

LAPD – Layer 2 FACCH

A U

n B

C

o

a

s

R

e

M

S

r f o

r m

s

P

h

y

C

o

n

t e

x

P

h

y

C

o

n

t e

s t

A

c

C A

C

p

C

FACCH

S

m

h m

h

a

a

n

a

M

n

E

n A

c

I n

d

t

R

e

C

q

o

n

f

 

t

t

A

C

K

d

s t

A A

s s i g D

e

R R

F F

a

n

c

t

C C

C S

h h

m

A

a a

o

n n

p l e H o C H

C R R

e e

l e l

a A

t e P

e

s e C

K

C

Inter-cell handover M

S M

SACCH

e

a

B

T

S

s

R

e

B

1 p

T

M

e

S

a

2

s

R

C

h

C

FACCH

H

O

C

M

H P

LAPD – Layer 2

FACCH

O

h

y

A U

H

A s i c

S

D

D c a M

C

o

t a

e

s s

I n

f o

c

l

B

a

e

a

R

e

H

O

p

l e D

R R

F

s t

C C

h h

a a

H

n

I n

S

C

K

C c

M

D

t

d

I n

d

( H

n

R

He

R

C

O

D e t e t i o n

t e a t a

F

c t c t A

A (

a

E m

A

n

M

C

l t

n

q

r m

S

s u

a

h

A O

B

e

l O l A

O

C

o

P C

e K

m r f o

SABM & UA Constituents of LAPD (Link Access Protocol – Channel D)– layer 2 Constituents 1. SABM - Set Async Balance Mode. 2. UA - Un-numbered Ack. 

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