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Estimating end-to-end performance in 3G Long-Term Evolution compared to HSDPA
Thesis work seminar presentation 18.10.2005
Mari-Jaana Pelkonen 51529B
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Acknowledgement
• Supervisor: Prof. Heikki Hämmäinen
• Instructor: Jani Kokkonen M.Sc
• Nokia Networks, System Technologies
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Agenda
• Thesis introduction
• HSDPA overview
• 3G LTE overview
• Estimation work
• Summary
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Thesis introduction
• 3G Long-Term Evolution standardization effort started in late 2004 in 3GPP
• 3G networks are implemented at very slow phase. One major reason for the operators low investment willingness is the low capacity it offers to the operator and to the customer.
• IEEE is standardizing mobile WiMAX => Threat for loosing competitive edge.
• In Japan the telecom technology is one step forward: DoCoMo is driving the standardization.
• Why not 4G? 4G will be a system that connects all the existing and future networks seamlessly together. The technology is not yet ready for that. 3G LTE is a evolution step towards the 4G, enabling the operators to use the existing infrastructure longer.
• Target to standardize simple, IP optimize network, offering mobile DSL type connections.
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Thesis introduction
• The scope of the thesis work was to prove that the performance in presented 3G LTE architecture is better than in the current available systems.
• 3G HSDPA was selected to the reference architecture.
• We were not only interested whether the new system is better, but why and why not.
• How much of the improvement could be achieved only improving capacity of the legacy systems?
• What is the impact of the new architecture solutions
• Different applications have different requirements for the network, performance is application specific. Therefore delay and throughput impact estimations were done for three applications: Web browsing, streaming video and VoIP.
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Thesis introduction
• This thesis work was written in 3G Long-Term Evolution architecture project
• One part was literature study about 3G HSDPA performance and performance in general.
• 3G LTE specific part is taken from the architecture project and standardization contributions. The 3G LTE architecture presented in this work is DRAFT architecture. It will not be standardized as presented here.
• The estimation work is done using a Service performance Excel tool created to calculate delays in 3G networks. The tool consists of signaling flows for different applications. For that work, the 3G LTE specific parts were added to the tool.
• Values used in the tool are for 3G networks measured or estimated. To get 3G LTE values, I consulted several experts working with that area. Some of the values are targets, other derived from 3G values and the rest are educated guesses.
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HSDPA
• High-Speed Downlink Packet Access is 3G performance enhancement technology. It does not change the core network, but only the radio interface in the downlink direction.
• HSDPA offers theoretical DL bit rates up to 14.4 Mbps.
• Only test networks implemented, not yet in commercial use. The effective bit rate offered to users is assumed to be around 800 kbps.
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HSDPA: 3G architecture
UE
Node
B
Node
B
RNC
SGSN GGSN
UTRAN
CN PS domain
HLRAuC EIR
Registers
CNUu
Iu
RNS
Iub
Iub
Gn
Gi
UE = User Equipment
Node B = base station
RNC = Radio Network Controller
RNS = Radio Network System
CN = Core Network
UTRAN = Universal Terrestrial Radio Access Network
SGSN = Service Gateway Supporting Node
GGSN = Gateway GGSN Supporting Node
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HSDPA: 3G QoS bearer architecture
End-to-end Service
Local Bearer Service
Backbone Bearer Service
CN Bearer Service
External Bearer Service
Iu Bearer Service
Radio Bearer Service
UTRA ServicePhysical
Bearer Service
UMTS Bearer Service
Radio Access Bearer Service
TE MT UTRAN CN Iu edge
CN Gateway
TE
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HSDPA: Protocol stack (user plane)
GGSN3G-SGSNRNCUE Server
HLR
BSBS
MAC-hsMAC-hs
HS-HS-DSCH DSCH
FPFP
L2L2
L1L1Radio Radio L1L1
Radio Radio L1L1
MACMAC
PDCPDCPP
IPv6/v4u
ApplicatioApplicationnTCP/UDP
RLC-RLC-UU
IPIP
UDPUDP
GTP-GTP-UU
L2L2
L1L1L1L1
L2L2
HS-HS-DSCH DSCH
FPFP
MAC-MAC-DD
RLC-RLC-UU
PDCPDCPP
L1L1
L2L2
IPv6/v4
IPIP
UDPUDP
GTP-GTP-UU
L2L2
L1L1
IPIP
UDPUDP
GTP-GTP-UU
L2L2
L1L1
IPIP
UDPUDP
GTP-GTP-UU
L2L2
L1L1
IPv6/v4
TCP/UDPApplication
L1L1
L2L2
L1L1
L2L2
UU IubIub IuPIuPss
GnGn GrGr
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HSDPA: WCDMA RRC and PMM states
CELL_PCHCELL_PCH CELL_FACHCELL_FACH CELL_DCHCELL_DCH
RRC state changeRRC state change DCH channel DCH channel allocation allocation timetime
2-5 s timer2-5 s timer 2-5 s timer2-5 s timer
If DL If DL activated, activated, paging paging causes delaycauses delay
IDLEIDLE
PMM DetachedPMM Detached
PMM PMM ConnectedConnected
RRC Connection establishment timeRRC Connection establishment timeGPRS GPRS AttachAttach
Mobile is allowed to send data in CELL_FACH and CELL_DCH states. DCH channel is dedicated channel for end user data.
CELL_PCH and URA_PCH (not shown in the figure) are used for paging.
In idle mode mobile has no radio connection.
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3G LTE
• IP optimized network architecture
• Target is to solve the performance problems that current 3G architecture has and offer DSL type mobile internet connection.
• Simple architecture
• Short user plane RTT
• Cell capacity up to 100 Mbps
• In between 3G and 4G, interworking with existing and future network technologies inbuilt in the architecture.
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3G LTE: Goodbye circuit switched voice!
• The evolution of packet switched network technology has made possible to transmit voice over IP network with acceptable end-user performance.
• The SKYPE is one of the most popular example of that.
• Current 3G and 2G networks are optimized for circuit switched voice, that makes them complex and not best possible for data traffic.
• Operators need to invest in and maintain two parallel networks: CS and PS.
• The all-IP architecture will be simple and cheap!
• Of course operators are not willing to cannibalize their CS voice business by offering VoIP. The success of SKYPE shows, that former or later customers are changing to the VoIP. To ensure not to loose the future profit, operators need to be inside the VoIP business.
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3G LTE reference architecture
UE = User Equipment
BS = Base Station
SN-C = Serving Node (Control plane)
SN-U = Serving Node (User plane)
SGW = Service Gateway
Access Network
BS
BS
Serving Node - C
Serving Node - U
ServiceGateway
Subscription
Operatorservicenetwork
AAA Registers
Internet
Inter -connection
HA
RNC functionalities moved in the base station.
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3G LTE: QoS bearer architecture
BS SN
User -IPTunneling or forwarding
TransportRadio
UE
Transport
Note: this is called bearerless compared to current 3G bearer architecture. Air interface connection establishment and modification is simplified by reducing the number of air-interface bearers.
Instead of four radio bearers, only one radio bearer has to be established. This leads to the significantly reduced radio connection setup time.
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3G LTE: Mobility Management States
Idle Active Associate RLID
Release RLID
Detached
Connection Failure , UE local release
Assign UE_LLA, Associate RLID
Release UE_LLA & RLID
Idle Active Associate RLID
Release RLID
Detached
Connection Failure , UE local release
Assign UE_LLA, Associate RLID
Release UE_LLA & RLID
Idle Active Associate RLID
Release RLID
Detached
Connection Failure , UE local release
Assign UE_LLA, Associate RLID
Release UE_LLA & RLID
The number of channels reduced. Only one channel for user data. That channel is associated, if UE is in Active state.
That allows to reduce the number of states to three. If user is connected to the network, it is Idle or Active, whether it has data to send or receive.
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3G LTE: Protocol stack (User plane)
All-IP protocol architecture, one continuous IP layer through all the network elements.
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Estimation work
• Throughputs, link utilizations and transfer delays for TCP is estimated for different file sizes.
• Studied applications were VoIP, web browsing and streaming.
• For VoIP call, the most critical Key Performance Identifiers are session setup delay, end-to-end delay and delay variation. Session setup delay and end-to-end delay were estimated.
• For web browsing, the KPI studied is the click-to-content time, i.e. the time that takes after user selects page until it is loaded to his computer.
• KPIs for streaming are session setup delay and the throughput. Because throughput is studied separately, only session setup delay is estimated.
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Estimation work: TCP throughputs
Average throughput in HSDPA and 3G LTE
0
1000
2000
3000
4000
5000
6000
7000
12 200 1000
Size of file (kB)
Av
era
ge
TC
P t
hro
ug
hp
ut
(kb
ps
)
HSDPA (800)
3G LTE (6000)
3G LTE (3000)
3G LTE (1500)
3G LTE (800)
TCP throughput for 3G LTE (800 kbps) is better with all file sizes than HSDPA
Due the TCP slow start effect, the TCP throughput is worse with small files than the large ones.
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Estimation work: TCP Link utilizations and delays
Link Utilization in HSDPA and 3G LTE
0
20
40
60
80
100
120
12 200 1000
Size of file (kB)
Link
util
izat
ion
(%) HSDPA (800)
3G LTE (6000)
3G LTE (3000)
3G LTE (1500)
3G LTE (800)
3G LTE link utilization with same bit rate is notable better.
TCP delay in HSDPA and 3G LTE
0
2
4
6
8
10
12
14
12 200 1000
Size of file (kB)
TCP
dela
y (s
)
HSDPA (800)
3G LTE (6000)
3G LTE (3000)
3G LTE (1500)
3G LTE (800)
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Estimation work: Streaming session setup timePhase 3G LTE delay (ms) HSDPA with always on
PDP context (ms)HSDPA delay (ms)
RTSP signaling 329 535 535
TCP connection establishment 77 156 156
Primary PDP context without RAB - - 769
RAB establishment 1408 1408
Secondary PDP context with RAB - 1975 1974
Delay before buffering 406 4073 4843
Buffering 5000 5000 5000
Total 5406 9073 9843
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Estimation work: VoIP call with Internet Multimedia Subsystem System SIP session setup delay
(ms)End-to-end delay
(ms) (for 210 bytes VoIP packet)
RTT UE1-UE2-UE1 (ms)
3G LTE 2385 34 68
HSDPA with always on PDP context
7894 97 194
Difference 5509 63 126
For 3G LTE the SIP session setup delay is less than the circuit switch PSTN call setup delay.
The difference ín session setup delay is 5.5 second. Most of the difference is caused by the secondary PDP context activation and RAB procedures.
End-to-end delay for 3G LTE 30 ms is not notable for user. HSDPA 71 ms end-to-end delay is not notable with echo cancellation.
-External network delay not calculated
- Both end-users are connected to their own
IMSs.
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Estimation work: VoIP End-toEnd Delay
RNC
3G-SGSN
GGSN
IP/MPLS/IPoATM-backbone
Node BUE IMS 1
3G
RNC
3G-SGSN
GGSN
IP/MPLS/IPoATM-backbone
Node BUE IMS 2
End-to-end delay consists of processing delays in UEs and in every network node in between them and transition delays between nodes.
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Estimation work: Web browsing
First Page Delay
0
2000
4000
6000
8000
10000
12000
40 300 600
Size of page and objects (kB)
To
tal d
elay
(m
s)
HSDPA (800/128)
HSDPA with always onPDP context
3G LTE (6000/2500)
3G LTE (3000/1500)
3G LTE (1500/512)
3G LTE (800/384)
3G LTE (512/2576)
Second page delay
0
2000
4000
6000
8000
10000
12000
40 300 600
Size of page and objects (kB)
To
tal d
elay
(m
s)
HSDPA (800/125)
3G LTE (6000/2500)
3G Lte (3000/1500)
3G LTE (1500/512)
3G LTE (800/368)
3G LTE (512/2576)
Estimation is done for HSDPA with and without always-on PDP context.
First page delay includes radio connection establishment, PDP context activation and DNS query
Second page delay consists only HTTP signaling.
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First page delay divided into parts
First page delay, page and objects total 40 kB
0
500
1000
1500
2000
2500
3000
3500
4000
HSDPA(800)
HSDPAwith
alwayson PDPcontext
3G LTE(6000)
3G LTE(3000)
3G LTE(1500)
3G LTE(800)
3G LTE(512)
tim
e (m
s)
DNS Query
RAB/Radio connection
PDP context
HTTP protocol
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Summary
• Performance advantage of presented 3G LTE is clear for investigated applications.
• The session setup delay (PDP context and radio connection establishment) in 3G affects worst in short living applications, or applications that transfers only small amount of data.
• Enhanced air- interface effect is notable only with applications that transmit large files
• The capacity increase or RTT decrease is not the only way to the better performance. The IP connectivity added with bearerless model presented here is needed to reduce the session setup latencies.