Transcript GSM Logical Channels, cont…

Southern Methodist University Fall 2003
EETS 8316/NTU CC745-N
Wireless Networks
Lecture 3: Mobility Management, Air Interface
Instructor: Jila Seraj
email: [email protected]
http://www.engr.smu.edu/~jseraj/
tel: 214-505-6303
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#1
Review
In the last meeting we discussed
Basic Structure of PSTN
SS7 as an application of OSI model and its
significance in PSTN
Basic structure of a wireless networks
Basic functionalities of wireless networks
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#2
Access Network
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#3
Access Network
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#4
Why SS7
SCP
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STP
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SS7
#5
OSI Model for SS7
Layer 4-7
MUP
TCAP
ISUP
MAP
INAP
OMAP
SCCP
Layer 3
Layer 1-2
MTP
Signaling link function, Signaling link physical requirement
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#6
TDMA Network Structure
PSTN
AUC
EIC
GMSC/MSC
/VLR
HLR
BSC
BSC
Base station controller
BSC
Base station
Base station
Air interface
Mobile
station
Base station
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#7
Basic Functions
Registration
— Power Up/Power Down Registration
— Location Area Update Registration
— Periodical Registration
Initiating a call
Receiving a call
— Paging is the process of searching for an MS in
the network. Location Areas are needed to make
paging efficient
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Location Area, MSC border
MSC-1
LA-1
MSC-1
LA-2
MSC-1
LA-3
MSC-2
LA-1
MSC-2
LA-2
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Handoff
Movement into a different cell requires
MTSO to automatically transfer call to
another base station without interruption
Hard handoff: “break before make”,
connection is broken then re-established
Soft handoff: temporarily connected to two
or more base stations simultaneously
before dropping all but one
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Handoff, (cont)
Initiation: Base station detects measured
signal strength drops below threshold (first
generation) or mobile station detects signal
from another base station is stronger than
current base station (second generation)
Resource reservation: frequencies are
reserved with new base station
Execution: actual handoff of connection
Completion: unneeded resources are
cleared
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Handoff Challenge
 Measured signal strength drop is caused by
momentary fading
 Handoff must be completed before signal strength
drops below a minimum acceptable level
 No channels are free at nearby base stations,
causing call connection problems, dropped calls.
 If mobile station moves to another cellular system
(controlled by different MTSO), an intersystem
handoff is required - more complicated
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Handoff, Cont.
There are three type of handoffs
— MS controlled handoff
— Network controlled handoff
— Mobile assisted handoff (MAHO)
D-AMPS and CDMA use MAHO, AMPS uses
network controlled handoff.
Capabilities required for the MS are taken
into account.
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Handoff, Cont.
BS
BS
PSTN
Target MSC #1
Serving MSC
BS
Target MSC #2
HANDMREQ
HANDMREQ
HANDMREQR
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Handoff, Cont.
BS
BS
PSTN
Target MSC #1
Serving MSC
FACDIR
FACDIRR
MSONCH
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Handoff, Cont.
• What happens if we go back to the anchor MSC?
• IS-41 has handoff back facility
• What if a third MSC gets involved?
• Path minimization process
BS
BS
PSTN
New Serving MSC
Anchor MSC
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#16
Path Optimization Process
6
BS
7
BS
BS
Serving MSC
PSTN
Anchor MSC
4
HANDTHIRD
2
Target MSC
1
FACDIR
FACDIRR
5
HANDTHIRDR
MSONCH
9
FACREL
FACRELR
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3
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Path Optimization Process, (cont)
BS
BS
BS
MSC
PSTN
Anchor MSC
New Serving MSC
Call Path after path minimization process
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#18
More On Roaming
Registration
—Power up/down
—periodical
—New system
—Call origination
MS Service Qualification
—validation information (billing)
—Service profile information, features, restrictions…
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More On Roaming, cont..
MS Location Update Process
— Location update at registration
— Location cancellation, AKA de-registration
• MSC triggered
•
– MSINACT with or without De-registration parameter
– Bulkdereg, remove all mobiles associated with the
MSC
HLR triggered
– Location update in another switch
– Administrative actions
– Data failure in HLR
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MS Location Management, Border Case
Multiple access problem
IS-41 revision C has a procedure for HLR to
determine the best serving system based
on the signal quality information received
from each system
MSC uses the signal quality information to
accept or deny registration cancellation.21
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Paging
Paging is used when there is a terminating
call to a mobile station.
Finding a mobile subscriber requires some
work, since its location is not known
The call towards the mobile subscriber is
routed towards gateway MSC.
Gateway MSC consults HLR to find the
mobiles location
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Paging, cont..
HLR looks up in its directory to find the
current MSC of the mobile
The address of the current MSC is sent
back to the gateway MSC.
Based on that information gateway MSC
routes the call to the visiting MSC.
Visiting MSC checks with VLR to find the
Location Area for the mobile. All cells in
that Location Area are pages
simultaneously.
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Paging, cont..
Mobile station hears the page and respond
to it.
Several base stations in the area might hear
the page response. They all report to MSC
that the mobile is in their coverage area
together with signal level data
MSC filters between these reports and
chooses the one that has the strongest
signal.
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Paging, cont..
MSC chooses an idle voice channel in the
chosen Base Station and prepares to set up
a voice channel connection.
MSC send a message to HLR informing that
the mobile is found together with other
useful information such as signal strength,
Location Area, etc.
HLR updates its database and forwards the
visiting MSC address to the gateway MSC.
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Paging, cont..
Gateway MSC has now sufficient
information to connect to the visiting MSC.
Gateway MSC send call set up request to
the visiting MSC, which sets up the call
What happens when more than one MSC
report to GMC that the mobile is its
coverage area?
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Paging, cont..
When HLR receives more than one
response, it chooses the MSC with
strongest signal.
It send the address of the chosen VMSC to
the gateway MSC and informs other MSC
that the call is off.
How does HLR know it has received
response from all MSCs? Internal timer
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Primer on RF
The radio frequencies are grouped into
bands.
Each set of bands are dedicated to different
purposes by FCC
Each frequency is logically divided into
time slots for communication between
mobile station and the base station.
Some time slots are reserved for user
traffic, such as voice and data and other for
signaling purposes.
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Cellular DCCH Structure
DCCH
Reverse
RACH
PCH
ARCH
EETS 8316/NTU TC 745, Fall 2003
Forward
SPACH
BCCH
SMSCH
FBCCH
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SCF
EBCCH
Reserved
SBCCH
#29
Cellular DCCH Structure, cont..
RACH = Random Access Channel
SPACH = SMS, Paging and Access
response Channel
PCH = Paging Channel
ARCH =Access Response Channel
SMSCH = SMS Channel
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Cellular DCCH Structure, cont..
BCCH= Broadcast Channel
F-BCCH = Fast Broadcast Control Channel
E-BCCH = Extended Broadcast Control
Channel
S-BCCH = SMS Broadcast Control Channel
SCF = Shared Channel Feedback
Reserved!
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Cellular DCCH Structure, cont..
DCCH Structure: sent on F-BCCH, indicates
the structure of DCCH
Access Parameters: sent on F-BCCH,
provides data necessary to access RACH.
Power level, maximum number of attempts,
authentication information
Control Channel Selection parameters: sent
on F-BCCH, provides channel reselection
parameters
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Cellular DCCH Structure, cont..
Registration Parameters: sent on F-BCCH,
indicates type of registration, power up,
power down, new system, location area,
forced and periodic. Also indicates options
for de-registration, foreign system
registration
System Identity: sent on F-BCCH, identity
and type of system (public, private,
residential), protocol version, mobile
country code. System identity is 15
characters long text.
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BCCH Message Set
Neighbor Cell: sent on E-BCCH. Included is
also reselection criteria for each neighbor
cell. Up to 24 neighbor cells can be defined
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SPACH Message Set
Analog voice channel designation: sent on
ARCH, contains channel number, power
level, SAT, and protocol version
Digital traffic channel designation: sent on
ARCH, contains DTC channel number, etc.
Directed retry, sent on ARCH, forces the
mobile to access another DCCH from its
neighbor list. Used when resources are not
available.
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SPACH Message Set, cont…
Message Waiting: sent on PCH, inform
mobile a message is waiting. The message
can be a voice message, SMS message or
fax message.
R-DATA: sent on SMSCH, conveys point-topoint teleservice layer message.
R-DATA Accept: sent on SMSCH to
acknowledge reception of R-DATA, may
include a delay data.
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SPACH Message Set, cont…
Registration Accept: sent on ARCH, informs
mobile that registration is complete, may
include paging frame class, current location
area, and other system related information.
SPACH Notification: Sent on PCH, informs
mobile that the network intends to deliver a
message to it on the ARCH or SMSCH and
what type of the information mobile should
expect.
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RACH Message Set
Capability Report: Informing the system of
mobile’s capability, protocol version, etc.
Origination: is sent when a mobile wants to
initiate a voice or data call. Includes calling
party number, type of service etc.
Page Response: is sent in response to
page, includes essentially the same
information as in origination message,
except for calling party number.
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RACH Message Set, cont..
R-DATA: is used to send point-to-point
teleservice layer messages
R-DATA Accept: is sent to acknowledge
reception of R-DATA
Registration: request registration with the
network
SPACH Confirmation: is sent to network to
confirm reception of SPACH notification
message.
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DTC Supervision
DTC has two associated control channels
for supervision of the DTC link on layer 3.
FACCH: Fast Associated Control Channel
SACCH: Slow Associated Control Channel
These associated control channels are
used in the connection phase to send and
receive information.
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FACCH Message Set, Forward
Alert with Info: sent on FACCH, causes
audible or visual signal, may include calling
name and number.
Base Station Ack: sent on FACCH.
Acknowledges the mobile that certain
message is received, such as connect,
release. In the case of release message,
DCCH information element might be sent to
mobile.
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#41
FACCH Message Set, Forward , cont..
Dedicated DTC Handoff: sent on FACCH,
order mobile to change from one DTC to
another DTC.
Flash with Info: sent of FACCH, used to
send message waiting information or
calling party number to mobile
Flash with Info Ack: sent on FACCH.
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FACCH Message Set, Forward , cont..
Handoff: sent on FACCH to order mobile
from one DTC to another DTC or AVC
Release: sent on FACCH
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FACCH & SACCH Message Set, Reverse
Capability Update Request: sent of FACCH
Capability Update Response: sent on
FACCH
Connect, sent on FACCH
Flash with info: sent on FACCH, indicates
that the user wishes to initiate a special
service.
Flash with Info Ack: sent of FACCH,
acknowledge receipt of Flash With Info
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FACCH & SACCH Message Set, Reverse
Mobile Ack: Can be sent on either channel
dependent on the type of message it
acknowledges. Is sent as response to Alert
with info, release, handoff, etc.
Release: sent of FACCH, may contain DCCH
information.
Service Request: sent of FACCH, is used
when mobile wished to change a service
during a call.
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Network Interfaces, TDMA
IS-41 is used for interface between MSCVLR, MSC-HLR, HLR-VLR, MSC-MSC, MSCPSTN, HLR-AC, MC-HLR and MC-MSC
IS-41 can be implemented on the top of
MTP, X.25, or IP protocols, though MTP is
the common one.
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IS-41 Protocol Stack
Application
Layer
Presentation
Layer
Session Layer
IS-41 MAP
TCAP
Null
Transport Layer
Null
Network Layer
SCCP
MTP Level 3
MTP Level 2
MTP Level 1
Data Link Layer
Physical Layer
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GSM Network Structure
PSTN
VLR
GSM Public
land mobile
network
(PLMN)
MSC
HLR
OMC
AUC
A
EIR
BSC
BSS
NMC
BSS
ADC
BTS
BTS
OSS
Um
MT
TE
MS
EETS 8316/NTU TC 745, Fall 2003
OSS: operation subsystem
BSS: base station subsystem
MS: mobile station
MS
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North American Numbering Plan
North American Numbering Plan consists of
10 digits, NPA-NXX-XXXX
All phone numbers follow the same
structure.
NPA is the area code
NXX is the switch identifier
XXXX indicates the subscriber in the switch
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North American Numbering Plan, cont…
Due to this structure, there is no way for a
switch to identify that a number belongs to
a mobile subscriber, nor can it identify the
network provider.
Mobile network provider “buy” a certain
number series in each area for their users.
Therefore we can not bill a caller to a
mobile user for the air usage. They do it in
other countries!
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GSM Logical Channel Structure
TCH/F
TCH/H
BCH
FCCH SCH
CBCH
CCH
TCH
CCCH
BCCH
DCCH
PCH AGCH RACH
SACCH
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ACCH
SDCCH
FACCH
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GSM Logical Channels
3 groups of logical control channels
—BCH (broadcast channel): point-tomultipoint downlink only
• BCCH (broadcast control channel): send
cell identities, organization info about
common control channels, cell service
available, etc
• FCCH (frequency correction channel):
send a frequency correction data burst
containing all zeros to effect a constant
frequency shift of RF carrier
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GSM Logical Channels, cont…
• SCH (synchronization channel): send
TDMA frame number and base station
identity code to synchronize MSs
—CCCH (common control channel): for
paging and access
• PCH (paging channel): to page MSs
• AGCH (access grant channel): to assign
MSs to stand-alone dedicated control
channels for initial assignment
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GSM Logical Channels, cont…
—RACH (random access channel): for MS to
send requests for dedicated connections
— DCCH (dedicated control channel): bi-directional
point-to-point -- main signaling channels
• SDCCH (stand-alone dedicated control
channel): for service request, subscriber
authentication, equipment validation,
assignment to a traffic channel
• SACCH (slow associated control channel): for
out-of-band signaling associated with a traffic
channel, eg, signal strength measurements
• FACCH (fast associated control channel): for
preemptive signaling on a traffic channel, eg, for
handoff messages
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GSM Logical Channels, cont…
• FACCH (fast associated control channel):
for preemptive signaling on a traffic
channel, eg, for handoff messages
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GSM Numbers
International mobile station equipment
identity (IMEI). IMEI= TAC + FAC + SNR + SP
— TAC = Type Approval Code, 6 decimals
— FAC = Final Assembly Code, 6 decimals,
assigned by manufacturer
— SNR = Serial Number, 6 decimals, assigned by
manufacturer
— SP = Spare, 1 decimal place
EIR has while, black and optionally grey list
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GSM Numbers, cont…
International mobile Subscriber Identity
(IMSI). Stored on the SIM (Subscriber
Identity Module) card. IMSI is obtained at
the time of subscription. IMSI is not made
public.
IMSI = MCC + MNC + MSIN
MCC = Mobile Country Code, 3 decimals
MNC = Mobile Network Code, 2 decimals
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GSM Numbers, cont…
MSIN = Mobile Subscriber Identification
Number, maximum 10 decimal digits
Mobile Station ISDN number (MSISDN), is
the real phone number of the subscriber.
Stored in HLR and on SIM card
MSISDN = CC + NDC + SN
CC = Country Code, up to 3 decimals
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GSM Numbers, cont…
NDC = National Destination Code, typically
2-3 decimals
SN = Subscriber Number, maximum 10
decimals.
Mobile Station Roaming Number (MSRN),
same format as MSISDN. A temporary
location dependent ISDN number.
Is assigned in two cases, at registration or
at call set up.
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GSM Numbers, cont…
Location Area Identity (LAI). Regularly sent
on BCCH LAI = CC + MNC + LAC,
LAC = Location Area Code, max 5 decimals
(<FFFFhex).
Temporary Mobile Subscriber Identity
(TMSI). Stored only in the VLR and SIM
card. Consists of 4*8 bits excluding value
FFFF FFFFhex
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GSM Numbers, cont…
TMSI has only local meaning and can be
defines according to operator’s
specifications.
LAI + TMSI uniquely identifies the user, I.e.
IMSI is no longer needed for ongoing
communication
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