close

Вход

Забыли?

вход по аккаунту

?

IAEAC.2017.8054144

код для вставкиСкачать
Research of ROHC for PoC Service Based on 3G
Cellular Network
Li Li-fu1, Li Hai-wen1,2, Li Hong-liang1, Gu Yong-jun1
1. Chongqing Communication Institute,Chongqing, China
2. Zhengzhou Information Science and Technology Institute,Henan, China
[email protected], [email protected], [email protected], [email protected]
AbstractPoC is a group communication service using VoIP
technology based on 3G cellular network packet domain carrier.
ROHC can complete the header compression in PS domain of
3G network, which can improve the efficiency of wireless transmission. This paper analyzes the working principle and the operation modes of ROHC, designs the processing of the compressor and decompressor. Simultaneity an improved algorithm applied to the U mode is presented against PoC service features,
with great benefits on cost and quality of service (QoS).
KeywordsPoC; VoIP; ROHC; compressor; decompressor
I. INTRODUCTION
PoC is a group communication service using VoIP technology based on mobile cellular network, PoC can provide
users with these functions, such as a single call, group call,
group management, user classification, state real-time presence etc[1].
Fig. 1. PoC system network architecture
The PoC system include UE with the PoC Client software,
Radio Access Network (RAN), Core Network (CN) and PoC
Server platform. The PoC client accesses the PoC service
platform via the PS domain of 3G networks, The PoC Server
platform which fulfills the dispatch and unified access of the
correlative message for PoC service is made up of the service
access module, service function module and service supporting module.
PoC is achieved through the VoIP technology, i.e. Using
RTP/UDP/IPv4 as the form of transmission data packets, the
total packet headers are 40 bytes. If using gsm encoding, the
voice payload is 33bytes, the packet headers possess 55% of
the entire length. Using RTP/UDP/IPv6 as the form of transmission data packets, the total packet headers are 60 bytes,
the packet headers possess 65% of the entire length. Obviously, the transmission useful information is very small, the effective utilization of the link is very low, which is difficult to
guarantee the QoS of the PoC. So the 3GPP finally choose the
PDCP sublayer to solve the header compression [2].
III. ROHC COMPRESSION PRINCIPLE
The ROHC compression principle of RTP/UDP/IP is
shown in Fig.2. The main reason why header compression
can be done at all is the fact that there is significant redundancy between header fields, within the same packet header and
in particular between consecutive packets belonging to the
same packet stream.
The early header compression schemes were primarily designed for the wired link, such as VJHC/IPHC/CRTP[3-4].
ROHC is designed against the wireless environment with the
high delay and high error rate, the header compression
scheme has the better robustness and the higher compression
efficiency.
The ROHC compressor creates four profiles[6]: RTP,
UDP, ESP and UNCOMPRESSED. The compression profiles
establish an appropriate context for every stream belonging to
themselves. Similarly, so does the decompressor. The relevant
information from past packets is maintained in the context.
The context information is used to compress and decompress
subsequent packets. The compressor and decompressor constantly update their contexts upon certain events. Impairment
events may lead to inconsistencies between the contexts of
the compressor and decompressor, which in turn may cause
incorrect decompression. So ROHC adopts CRC in the compressed packet, and utilizes the feedback information to ensure that the decompressor correctly updates the context in
time.
II. POC SYSTEM ARCHITECTURE
The PoC system network structure on 3G cellular network
is shown in Fig.1. A PoC server platform and a set of user database are set in the whole country, the PoC service platform
is a core equipment for the PoC system[5].
978-1-4673-8979-2/17/$31.00 ©2017 IEEE
900
The U-mode is without a feedback channel, in order to ensure the timely update of the context, the compressor need to
periodically transfer to the low state; the O-mode and R-mode
have the feedback channel.
IV. ROHC IMPLEMENTATION PROCESS
A. Implementation of Compressor
The operation state of the compressor will determine the
compression efficiency. In the U-mode, to ensure the compression efficiency, improving the compression state and updating the context duly are very important; in the O-mode and
R-mode, it is necessary to adjust the compression state according to the feedback to ensure the correctness of ROHC
compressed packet chose.
Fig. 2. ROHC compression principle
1) Implementation process of compressor
A. ROHC Operation States
The compressor and the decompressor each has three
states.
PoC is achieved via VoIP, so the main tasks of the compressor are:
For compressor, the three states are: the Initialization and
Refresh(IR), First Order(FO), and Second Order(SO) states.
a)only compressing the received RTP/UDP/IP packets and
generating the context and CID in order to ensure the decompressor can correctly decompress;
b) to receive and process the feedback from the decompressor;
c) completing the transfer of the three states, and optimizing the compression efficiency and robustness etc;
The specific process of the compressor is shown in Fig.6.
Fig. 3. The compressor state transition
2) Implementation process of the feedback
After some conditions are met, the above three states can
transfer shown in Fig.3, but the compression is always started
from the IR state.
The processing module of the feedback information in the
compressor will deal with the feedback information from the
decompressor, identify the type of the feedback, update the
context of the compressor, and determine the mode conversion and the state transition according to the feedback, Fig.7
shows the operation process of the feedback.
The decompressor also exists in three states: No Context
state; Static Context state; Full Context state. The state transitions among the three states are shown in Fig.4.
B. Implementation of Decompressor
The decompressor re-generates the original data according
to its own context and the W-LSB information in the receiving ROHC compressed packets, and will determine whether
the generated data falls within a pre-set coding interval. If the
generated data do not fall on the set coding interval, then
move N coding intervals, if the data are not within the set
coding interval, then discard the packet; If the data fall on the
interval, the decompressor will restore the original
RTP/UDP/IP packets and transfer them to the upper.
Fig. 4. The decompressor State transition
B. ROHC Operation Modes
The ROHC scheme has three mode: Unidirectional(Umode), Bidirectional Optimistic(O-mode), and Bidirectional
Reliable(R-mode) mode. As is shown in Fig.5.
1) Implementation process of decompressor
The main tasks of the decompressor are to decompress the
ROHC packets, complete the conversion among the three
modes and among the three decompression states, send the
feedback to the compressor.
The process of the decompressor is shown in Fig.8.
When the decompressor receives the packet, the process is
as follows:
Fig. 5. the relation of operation modes and states transition
901
Step 1: First, to distinguish the type of the data packet that
a) if the type is RTCP/UDP/IP packets, without any treatment, directly transfer to the upper layer;
has already received:
an improved algorithm suitable for the U-mode is brought
forward, which can improve the robustness of the system and
the utilization rate of the wireless link.
b) if it is the feedback, which will be handed over to the
compressor, and continue to process in the light of step c);
ACKNOWLEDGMENT
This work was supported by Science and Technology Research Project of CQ CSTC (2012gg-yyjsB40005) and major
project of the ministry of industry and information technology
WG2013CX120006; 2013ZX03006003-006.
c) if it is ROHC compressed packet, to determine its legitimacy and the type of ROHC compressed packet.
Step 2: by reading the corresponding CID, to deal with the
different packets in the different way.
Step 3: discard those that do not pass the CRC check, if
the check passes, to decide whether it is need to update the
context of the decompressor. Last, the correctly decompressed RTP/UDP/IP packets should be transmitted to the upper.
REFERENCES
[1] OMA-RD-PoC-V1_0-20060609-A; Push to Talk over Cellular Requirements Approved Version 1.0[S]. 2006.
[2] 3GPP.TS 25.323 V8.3.0: Packet Data Convergence Protocol (PDCP)
specification [S].
2) improved algorithm of restoring compressed packets
[3] IETF RFC 2508.Compressing IP/UDP/RTP heads for low-speed serial
The PoC is a real-time service, so the Feedback as little as
possible, the best way is in the U-mode. The wireless link exists the possibility of a large number of packet loss and outof-order, which will likely cause the compressor and decompressor with the inconsistent coding intervals to lead to incorrect decompression. The decompressor can only wait for Umode to repair the context. This will affect the real-time seriously. Therefore, based on the traditional decompression
context algorithm [7], the paper proposes an improved algorithm of the rapid reduction packet shown in Fig.9, the algorithm can repair the large number of packet loss in time.
links[S].
[4] IETF RFC 2507. IP head compression[S].
[5] Haiwen Li, Wei Huang, Yu Wang, Lifu Li, Gang Yu, Research and
[6]
[7]
V. CONCLUSION
The wireless network has the characteristics of higher error rate and longer transmission delay, which will guarantee
the QoS for PoC difficultly. This article designs the implementation process of the corresponding modules according to
the fundamentals of the compressor and the decompressor, in
view of the strict delay requirements for PoC on 3G network,
902
Implementation of The PoC System over Heterogeneous Cellular Network, Tencon IEEE Region 10 Conference[J],Sep,2013.
IETF RFC 3095.RObust Header Compression(ROHC)Framework and
four profilesRTPUDPESP and un-compressed[S]. 2001.
Zhang Fengxiang, Hong Peilin, Li Jinsheng. The windows based LSB
codec correction algorithms used in ROHC mechanism [J]. Circuits and
Systems, 2004,01 .
Initialization
Receive a valid packet
RTP/UDP/IP packet
Feedback
RTCP/UDP/IP packet
Create context
Update the context
Not compress and
directly send
Create only CID
According to the feedback type
determine operation mode and
transfer state
R
U
ROHC operating mode
O
determine packet type to be sent
FAST/NORMAL way and
TIMEOUT process
Mode optimized
Yes
C-MODE=U?
No
Current ROHC state
SO
Send R/O-0/1
packet
FO
Transfer to R/O
mode
IR
Sent IR-DYN,
R/O-2 compressed packet
Send IR packet
Sent to the decompressor
Fig. 6. implementation process of the compressor
Initialization
U
current
operation
mode
O
R
current
operation
state
No
Meet the
optimized
conditions
Yes
Transfer to
the IR state
SO
FO
SO
current
operation
state
Receive feedback
IR
Meet the
optimized
conditions
Determine FEEDBACK-1
the type of
feedback
Meet the
optimized
conditions
FEEDBACK-2
FO
Meet the
optimized
conditions
IR
Meet the
optimized
conditions
No
Yes
Transfer to
the SO state
meet F_MAX_PERIOD
or F_MAX_TIME
setting conditions
IR timing
updating is
timeout
Transfer to
the FO state
Transfer to
the IR state
Yes
Transfer to
the SO state
NACK
Determine
FEEDBACK2 type
Transfer to the
SO state
ACK
STATIC_NACK
Transfer to
the FO state
Fig. 7. process of the feedback in compressor
903
Transfer to
the IR state
Transfer to
the SO state
Yes
Transfer to the
SO state
Yes
receive a valid packet
determine packet RTP/UDP/IP packet
types
ROHC packet
Full Context state
read CID state
No Context state
SC
handle all
compressed packets
process IR-DYN, R/O/U-2
compressed packet
only process IR packet
update the context
determine the
CRC is correct
restore RTP/UDP/IP
packet
send negative
feedback
According to each
mode, complete the
state transition
discard the
packet
Transmit the
feedback, if necessary,
transfer the restore
packet to the upper
Fig. 8.
Implementation process of decompressor
Fig. 9. improved algorithm of restoring compressed packets
904
Документ
Категория
Без категории
Просмотров
2
Размер файла
262 Кб
Теги
2017, 8054144, iaea
1/--страниц
Пожаловаться на содержимое документа