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(E)GPRS Signaling Flow & Test
ZTE university
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Course Objectives
To be familiar with common (E)GPRS signaling flow
To be familiar with (E)GPRS test content
To master (E)GPRS test techniques
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Contents
A Brief Introduction to (E)GPRS Signaling
Main (E)GPRS Signaling Flows
(E)GPRS Field Test
Main (E)GPRS Test Signaling Flow
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A Brief Introduction to (E)GPRS Signaling
(E)GPRS Signaling Protocol Stack
Relay
Network
Service
GTP
Application
IP/X.25
SNDCP
LLC
RLC
MAC
GSMRF
SNDCP
LLC
BSSGP
L1bisGSMRF
BSSGP
L1bis
Relay
L2
L1
IP
L2
L1
IP
GTP
IP/X.25
Um Gb Gn i
Network
Service
UDP/
TCP
UDP/
TCP
RLC
MACNetwork
Service
L1bis
MS BSS SGSN GGSN
GPRS Protocol Stack of Data
Transmission Platform
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A Brief Introduction to (E)GPRS Signaling
( (E)GPRS Signaling Protocol Stack
GPRS Protocol Stack of
Control Platform
Um GbMS BSS SGSN
GMM/SM
LLC
RLC
MAC
GSM RF
Relay
RLC
MAC
GSM RF
BSSGP
NetworkService
L1
LLC
BSSGP
NetworkService
L1bis
GMM/SM
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A Brief Introduction to (E)GPRS Signaling
GSM RF Protocol Physical layer can be divided into two sub-layers by
function—physical RF sub-layer and physical link sub-layer:
Physical RF sub-layer is used to modulate the bitstream sent from upper physical sub-layer and todemodulate the waveform coming from peer layer;
Physical link sub-layer provides information
transmission on the physical channel between MSand network, including: data delimitation, coding,error detection and correction, on physicalmedium.
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A Brief Introduction to (E)GPRS Signaling
RLC/MAC Protocol
RLC/MAC layer is a lower-layer data link layer. The functions for RLC/MAC
layer are as follows:
MAC
1. Provide effective multiplexing of UL/DL data and control signaling.
2. Provide contention solution, including conflict detection & recovery, for channel access initiated by MS.
3. Provide access scheduling, including the PS queuing, for the channel accessterminated by MS.
4. Priority processing.
RLC1. Provide interface primitives for transmitting LLC-PDU between LLC and MAC.
2. Segment LLC-PDU and reorganize it into RLC data block.
3. The reverse error correction process for the selective retransmission of incorrect data.
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A Brief Introduction to (E)GPRS Signaling
LLC ProtocolLLC layer, i.e. Logical Link Control (LLC) layer, is used to transmit
packet data between MS and SGSN.
Functions of LLC:
1. Provide one or more logical link connections through DLCI.
2. Sequence control, guaranteeing the sequence of frames on logicallink.
3. Check transmission, format and operation errors on logicalchannels.
4. Recover errors detected.5. Notification of unrecoverable errors.
6. Flow control.
7. Encryption
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A Brief Introduction to (E)GPRS Signaling
SNDCP (Sub-Network Dependent Convergence Protocol )Functions of SNDCP:
1. Multiplex many PDPs;
2. Compress/extract user data and protocol control information;
3. Segment N-PDU into LL-PDU or desegment LL-PDU intoN-PDU
Relay
The Relay in BSS is used to relay the LLC PDU between Um
interface and Gb interface. The Relay in SGSN is used to relay the
PDP PDU between Gb interface and Gn interface.
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A Brief Introduction to (E)GPRS Signaling
BSSGP (Base Station System GPRS Protocol )This layer transmits routing-related and QoS-related information
between BSS and SGSN, and does not perform error correction. In
BSS, this layer likes the interface between LLC and RLC/MAC.
NS (Network Service Layer)
Functions of NS:
1. Provide NS SDU transmission
2. Provide network congestion indication
3. Provide status indication, e.g. changes of usable transmissioncapacity
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A Brief Introduction to (E)GPRS Signaling
Different Parts of NS Protocol
NSCtrl (Functions of NS Control layer)
1. Provide NS SDU transmission
2. Load splitting
3. NSVC management, including block, unblock, reset, and test.
Functions of SNS (Functions of Sub-network Service)
1. Provide the access to intermediate transmission network, i.e. NSVL
2. Transmit data sequentially on NS-VC
3. Detect and report errors in protocol, and errors such as failure of
intermediate transmission network, equipment fault, and link failure,etc.
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A Brief Introduction to (E)GPRS Signaling
GTP (GPRS Tunneling Protocol)
This protocol supports data and signaling transmission between the supporting
nodes of GPRS backbone network. All PTP PDU PDP need be encapsulated
by GTP.
UDP/TCP
TCP carries the GTP PDU that need be supported by reliable data link (e.g.
X.25) in GPRS backbone network; UDP carries the GTP PDU that need not be
supported by reliable data link (e.g. IP). TCP provides flow control and protects
GTP PDU from being lost or damaged. UDP protects GTP PDU from being
damaged.
IP
It is a GPRS backbone network protocol applied to router user data and
control signaling. GPRS backbone network was based on IP version 4 protocol
initially, and will use version 6 finally.
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Main (E)GPRS Signaling Flows
One-phase Access onPBCCH
Contention Solution
After receiving UL assignment
message, MS must send three RLC blocks with TLLI. After receiving
the first RLC data block, network
will respond with PACKET
UPLINK ACK, in which “TLLI
received” should be set. If the TLLI
in the PACKET UPLINK ACK is
consistent with the one of MS, the
wireless resource for this message
is assigned to the MS. Otherwise,
MS should ignore the message.
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Main (E)GPRS Signaling Flows
Two-phase Access on CCCH
Contention Solution
After receiving the
second PACKET
UPLINK ASSIGN, MS
will compare the TLLI
contained in the message
with the one sent by
itself in PACKET
RESOURCE REQ. If the
two TLLIs are
consistent, the
contention solution is
successful.
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Main (E)GPRS Signaling Flows
Uplink TBF Establishment in PTM
MS Network
Packet Downlink Assignment
RLC/MAC BLOCK
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Main (E)GPRS Signaling Flows
Paging Flows
MS Network
Packet Channel Request
Packet Immediate Assignment
Packet Paging Response (LLC frame)
PRACH or RACH
PAGCH or AGCH
PACCH
PPCH or PCH Packet Paging Request
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Main (E)GPRS Signaling Flows
Uplink Data Transmission
Packet Uplink Ack/Nack
Data Block (CV=0)
Access and Assignment
MS BSS
PACCH
PDTCH
Packet Uplink Ack/Nack PACCH
PACCH
Data Block PDTCH
Data Block PDTCH
Data Block (last in send window)PDTCH
Data Block PDTCH
Data Block PDTCH
Data Block
final Packet Ack/Nack(FAI=1)PACCH
LLC PDU
SGSN
Packet Control Ack
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Main (E)GPRS Signaling Flows
Downlink Data Transmission
Packet Downlink Ack/Nack
MS Network
PACCH
Packet Downlink Assignment PACCH
PDTCH
PACCH final Packet Ack/Nack
Data Block PDTCH
Data Block PDTCH
Data Block (polling) PDTCH
PDTCH Data Block
PDTCH Data Block
Data Block
Data Block (last, polling) PACCH
Immediate Assignment AGCH
Packet Downlink Assignment
LLC PDU
SGSN
PACCH
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Main (E)GPRS Signaling Flows
Detach Signaling Flows
Upper left: Detach initiated by MSUpper right: Detach initiated by SGSN
Lower left: Detach initiated by MSC
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Main (E)GPRS Signaling Flows
Signaling Flow of Subscriber Authentication
1. SendAuthenticationInfo
1. SendAuthenticationInfo
2. AuthenticationandCipheringRequest
2. AuthenticationandCipheringResponse
MSBSS HLRSGSN
If SGSN did not sa
ve the authenticatio
n triple, it will send
HLR the “Send Authentication Info” m
essage, which conta
ins IMSI.
HLR responds with “
Send Authentication I
nfo Ack” that contains
authentication triple.Each authentication tr
iple contains RAND,
SRES and Kc.
SGSN sends MS
Authentication Re
quest (including R
AND, CKSN, and
encryption algorit
hm)
MS sends back Authentication Res
ponse (SRES) to f
inish authenticatio
n process
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Main (E)GPRS Signaling Flows
RAU intra SGSN
1. Routing Area Update Request
3. Routing Area Update Accept
2. Security Functions
MS BSS SGSN
4. Routing Area Update Complete
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Main (E)GPRS Signaling Flows
Cell Update (RAU intra RA)
BSC SGSN
1.1.
RA1
1. Send LLC PDU
Move from one
cell to anothercell within the
same RAC
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Main (E)GPRS Signaling Flows
PDP Deactivation Signaling FlowG
4. DeactivatePDPContext Accept
3. DeletePDPContext Resp
3. DeletePDPContext Requt
1. DeactivatePDPContext Request
SGSNMS
2. SecurityFunctions
1. DeletePDPContext
SGSN
1. DeletePDPContext
2. DeactivatePDPContext Accept
2. DeactivatePDPContext Request
MS
Initiated by Ms
Initiated by SGSN
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Contents
A Brief Introduction to (E)GPRS Signaling Main (E)GPRS Signaling Flows
(E)GPRS Field Test
Main (E)GPRS Test Signaling Flow
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(E)GPRS Field Test
Test Purpose To understand customers’ true feeling
To collect information unobtainable inOMCR, including:
service model specific to each region;
radio environment specific to each region;
service performance in moving state.
Major technical support in specific areas(e.g. large gathering, sports events)
To handle customers’ complaints
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(E)GPRS Field Test
Test ItemsCategories Test Items Relevant NEs
CQT
ATTACH SGSN
PDP GSN
WAP login WAP gateway
WAP refresh WAP gateway
WAP picture & ringtonedownload WAP gateway
PING INTERNET gateway
FTP download INTERNET gateway
Email upload/download INTERNET gateway
KJAVA download WAP gateway
DT
WAP login WAP gateway
WAP refresh WAP gatewayWAP picture & ringtone
downloadWAP gateway
FTP download INTERNET gateway
EGPRS coverage rate CELL
GPRS coverage rate CELL
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(E)GPRS Field Test
Points for Attention before Test Test time: As PS service is influenced a lot by the number of users,
different test should be conducted at different time.
Cell reselection: As a result of the inherent defects in GSM system,cell reselection will inevitably lead to TBF interruption; in CQT,there should be no more than 4 cell reselections according toCMCC test protocol, otherwise, the tests for this cell will be invalid.
Traveling speed for the test: CMCC requires that DT should notexceed 40km/h in urban districts, and should not exceed 70km/hon expressway. In network optimization, the same traveling speedshould be adopted in the comparative tests before and after theoptimization.
Test level: PS service needs high C/I value, taking MCS9 as an
example, to reach an ideal rate, C/I should be above 20, and thelevel should be above -70dBm.
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(E)GPRS Field Test
Points for Attention about Test Equipment Except test software, all software that may occupy
bandwidth in the test PC should be disabled;
Change the connection rate of testing handset to
115200 and disable the MMS Auto Extract
function; choose version R97 for GPRS test, and
versions above R97 for EGPRS test;
Points for attention about Modem setting:
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(E)GPRS Field Test
Points for Attention about Test Equipment Setting of network connection;
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(E)GPRS Field Test
Points for Attention in TestLevel: The mean RxLev in CQT should be above -70dBm, the mea
n RxLev in DT should be above -80dBm, and should not be lower t
han -90dBm.
Maximum TxPower: In PS service, MS does not perform power co
ntrol; during the test process, the maximum TxPower should be 33for GSM network and 30 for GSM1800 network.
BEP value: BEP value is specific to EGPRS. These two values are u
sed to decide which coding rate should be adopted, the maximum v
alue for CV_BEP and MEAN_BEP is 7/31 respectively, the average
value should be above 6.5/27.
Whether to enable frequency-hopping: It is not recommended to en
able frequency-hopping in PS service, and it is recommended to ad
opt BCCH frequency in RF frequency-hopping cells.
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(E)GPRS Field Test
Points for Attention in TestNumber of channels & coding scheme: In a test, uplink should occ
upy a certain number of channels, e.g. CMCC protocol requires t
hat downlink should occupy 4 channels, and uplink should occupy
1 channel; the higher level the encoding mode, the better, and MC
S9 encoding mode should be over 90% during EGPRS test.
Block error rate: Occasional block error occurring under high-level
encoding mode is normal, but if there are continuous block errors,
it needs to pay attention to wireless quality and hardware.
Throughput: PS service test involves mainly RLC layer throughput
and APP throughput. RLC layer throughput is the actual throughp
ut on the Um interface, while APP throughput is the user data thro
ughput.
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(E)GPRS Field Test
Points for Attention in Test
C1/C2: At present, PS servic
e shares the same C1/C2 al
gorithm as CS service. A co
mparison between C2 and R
xLev can display those cellswith unreasonable reselectio
n parameters. Conflicts betw
een CS service and PS servi
ce should be avoided during
the adjustment to unreasona
ble parameters.
CRH: In PS service,
CRH in GMM STAND
BY state works only
when an MS is crossing routing area and l
ocation area; while C
RH in GMM READY
state works all the ti
me.
CRO: This parameter
affects both CS servi
ce and PS service gr
eatly. As adjustment t
o this parameter tends to cause changes t
o cell load and hence
generate side effect, t
he adjustment should
be avoided as much
as possible.
PT & PO: These two
parameters can avoid
too fast the GPRS re
selection, but the ste
p size is too large, e.g. the step size is 10
dBm for PT, and 20s
for TO, which should
be paid close attentio
n to during adjustmen
t.
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Contents
A Brief Introduction to (E)GPRS Signaling Main (E)GPRS Signaling Flows
(E)GPRS Field Test
Main (E)GPRS Test Signaling Flow
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(E)GPRS Field Test
Attach &Detach
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(E)GPRS Field Test
PDP active & deactive
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(E)GPRS Field Test
RAU
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(E)GPRS Field Test
FTP & Ping
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