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TECHNICAL REPORT
LTE;
Study on Context Aware Service Delivery in RAN for LTE
(3GPP TR 36.933 version 15.0.0 Release 15)
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3GPP TR 36.933 version 15.0.0 Release 15 1 ETSI TR 136 933 V15.0.0 (2018-07)
Reference
RTR/TSGR-0336933vf00
Keywords
LTE
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3GPP TR 36.933 version 15.0.0 Release 15 2 ETSI TR 136 933 V15.0.0 (2018-07)
Intellectual Property Rights
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Foreword
This Technical Report (TR) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
.
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
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Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 4
Introduction . 4
1 Scope . 5
2 References . 5
3 Definitions, symbols and abbreviations . 5
3.1 Definitions . 5
3.2 Abbreviations . 6
4 Definitions and problems description . 6
4.1 Issue 1: Backhaul long latency . 6
4.2 Issue 2: TCP E2E delay with throughput decreasing . 6
4.3 Issue 3: Video transmission issue cases . 6
4.4 Issue 4: UL Video transmission critical data discard . 7
5 Solutions . 7
5.1 General Principles . 7
5.2 Solutions for issue 1 . 7
5.2.1 Solution 1: UE assisted local cache solution . 7
5.2.2 Conclusion for Issue 1 . 9
5.3 Solutions for issue 2 . 9
5.3.1 TCP Performance Enhancing Proxy (TCP PEP) . 9
5.3.2 Network based Radio-Aware TCP . 9
5.3.3 UE Based Radio-Aware TCP Solution . 10
5.3.4 eNB generates TCP ACK on behalf of the UE . 10
5.3.5 Conclusion for Issue 2 . 11
5.4 Solutions for issue 3 . 11
5.4.1 Solutions for case 1 . 11
5.4.1.1 Solution 1: UE request a higher QoS profile . 11
5.4.1.2 Solution 2: Video Context Aware Solution . 11
5.4.2 Solutions for case 2 . 12
5.4.2.1 Solution 1: PCC-based Solution . 12
5.4.2.2 Solution 2: Solution of DASH optimi satio n . 13
5.4.2.3 Solution 3: Solution of DASH optimisation via local breakout . 14
5.4.3 Solutions for case 3 . 15
5.4.3.1 Solution 1 . 15
5.4.4 Conclusion for Issue 3 . 16
5.5 Solutions for issue 4 . 16
5.5.1 Solution 1: Dynamic adaptation of LTE radio resource allocation during the call . 16
5.5.2 Solution 2: Static acceptance or rejection of adaptation of LTE radio resource allocation for the call . 16
Annex A (informative): Video playout buffer aware scheduling . 17
Annex B (informative): Change history . 18
History . 19
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Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
Introduction
Voice was the major service and 3GPP defined voice specific cross-layer optimizations for 3G and 4G. Web based
streaming video and Apps are expected to take majority of 4G/5G bandwidth, and are key source to further increase the
ARPU for operators. MPEG and 3GPP SA4 have been considering cross-layer optimizations by RAN and App mutual
aware, e.g. network assisted DASH, video-aware scheduling. It is worthwhile and right time to study whether deep
cross-layer optimizations for Web based streaming video and Apps can deliver the desired benefits. It is also
worthwhile to take into account the related work in other SDOs/Working groups, e.g. ETSI MEC work on mobile video
delivery optimization and local content caching. It is also beneficial to study and analyse the potential impact to
architecture, protocol, and signalling to support RAN based local cached delivery, local breakout; and support RAN
optimizations based on context awareness.
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1 Scope
The present document provides descriptions and possible solutions of use cases for the Context Aware Service Delivery
in RAN for LTE, and also provides analysis of these solutions. Considerations with regards to requested functionality in
scope of other 3GPP groups, if any, may be captured in this document as well.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] IETF RFC3135, Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations
[3] X. Xu, Y. Jiang, T. Flach, E. Katz-Bassett, D. Choffnes, and R. Govindan, “Investigating
performance enhancing proxies in cellular networks,” in AIMS: 6th Workshop on Active Internet
Measurements, Mar. 2014.
[4] M. Necker, M. Scharf, and A. Weber, “Performance of TCP and HTTP Proxies in UMTS
Networks,” in Wireless Conference 2005 - Next Generation Wireless and Mobile Communications
and Services (European Wireless), 11th European, April 2005, pp. 1–7.
[5] M. Meyer, J. Sachs, and M. Holzke, “Performance evaluation of a TCP proxy in WCDMA
networks,” Wireless Communications, IEEE, vol. 10, no. 5, pp. 70–79, Oct 2003.
[6] F. Ren, X. Huang, F. Liu, and C. Lin, “Improving TCP Throughput over HSDPA Networks,”
Wireless Communications, IEEE Transactions on, vol. 7, no. 6, pp. 1993–1998, June 2008.
[7] V. Farkas, B. Héder, and S. Nováczki, “A Split Connection TCP Proxy in LTE Networks,” in
Information and Communication Technologies. Springer Berlin Heidelberg, 2012, vol. 7479, pp.
263–274.
[8] S4-170238, Revised Work Item on “Server and Network Assisted DASH (SAND) for 3GPP
Multimedia Services”
[9] 3GPP TR 26.957: “Study on Server And Network-assisted Dynamic Adaptive Streaming over
HTTP (DASH) (SAND) for 3GPP multimedia services”
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in 3GPP TR 21.905 [1] and the following
apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP
TR 21.905 [1].
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3.2 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
3GPP TR 21.905 [1].
4 Definitions and problems description
4.1 Issue 1: Backhaul long latency
The issue may arise in cases where the distance between the RAN and the node hosting the application content is long
or the number of routers on this route is high. In these cases long transportation latency may be experienced.
Consequently certain kinds of service may be impacted significantly due to the long latency. For example, backhaul
delay increases the TCP RTT, therefore if TCP is configured in a way that it cannot cope with such delays, TCP
throughput can be affected.
4.2 Issue 2: TCP E2E delay with throughput decreasing
The behavior of TCP assumes that network congestion is the primary cause for packet loss and high delay. In cellular
networks the bandwidth available for each UE can vary by an order of magnitude on a TTI basis due to changes in the
underlying radio channel conditions. Such changes can be caused by the movement of devices or interference, as well
as changes in system load due to bursty traffic sources or when other UEs enter and leave the network. TCP has
difficulties adapting to these rapidly varying conditions.
If the E2E delay increases, the TCP RTT increases and the TCP throughput may decrease, which may impact the user
experience.
4.3 Issue 3: Video transmission issue cases
The Operator video is a video service under the LTE operator’s control. It is usually transmitted over a dedicated EPS
bearer or using a dedicated QCI. However, there might be cases where an operator decides not to apply any dedicated
QoS to a video service. These video services are named “Over-The-Top” (OTT) video and are video services that LTE
operators have no control on. Such service traffic is usually treated in the same way as normal internet traffic, e.g.
transmitted via default bearer, which may lead to poor QoE. Nevertheless, the QoS framework allows assignment of
dedicated QCI for video.
Dedicated bearer and QCI is helpful in lessening the video issues. Below are some of the issues that may occur when
operators decide to neither use dedicated bearers nor dedicated QCI for OTT video services.
Case 1: Empty buffer issue
The user is watching a streaming video. When the UE requests for some not yet buffered video segments e.g. by
dragging a play scroll bar or when playout buffer is exhausted due to link throughput fluctuation and if the scheduling
priority of the video content is not set accordingly, the video playing would probably stall depends on some condition,
e.g. eNB’s load and UE’s QoS profile.
Case 2: Inaccurate throughput prediction for DASH issue
DASH client requests video quality based on downlink throughput prediction. Throughput prediction is based on
implementation specific mechanisms. The accuracy of the prediction is dependent from the specific implementation.
However, one factor that may affect the prediction is that the DASH client may base the prediction on previous
downloads. The DASH client may not have an insight to whether the network conditions have changed, thus the current
available throughput may be difficult to predict. Conservative requesting low data rate video segment leads to low video
quality and aggressive requesting high data rate video segment leads to more video stalling.
Case 3: Long video delay issue
In HTTP based streaming, client first buffers some content, i.e. initial buffering, before playout in order to absorb the
throughput and delay fluctuation. Assuming that scheduling priority is not appropriately set, a large buffer may cause
long delay, thus lead to bad user experience.
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4.4 Issue 4: UL Video transmission critical data discard
In conversational video (real-time streaming) the problem of PDCP discard of critical data in UL may occur. Critical
data include I-frames of an H.264 video sequence and RTCP feedbacks for lost RTP packets. Both types of data are
carried on the same bearer (dedicated, GBR, or non-GBR) and may be encapsulated in the same PDCP SDUs. Hence if
the video bearer queue is highly loaded (e.g. in case of UL congestion), both types of data may be discarded due to
expiry of the PDCP discard timer. Currently in AS, there are no means to prioritize I-frame data and RTCP feedback
packets over P-frame data because they are carried on the same bearer. If these critical data are lost because of internal
PDCP Discard on the sender device, the video stream may stop on the receiver side until these critical data are
successfully retransmitted or until a new I-frame is transmitted to allow resynchonizing the video codecs and restore the
video prediction chain. If forward error correction information is added to the H.264 payload the video may not be
subject to interruptions and it may result in lower video bitrate.
NOTE1: This issue case does not require any specific video codec awareness impact in RAN3.
5 Solutions
5.1 General Principles
Impacts to the following LTE/EPC functions and principles of operation should preferably be avoided in order to ensure
that the study can proceed within the RAN domain. Proposed solutions shall not be excluded solely on this basis, but
sufficient benefits must be demonstrated in order to justify such impacts.
- Security: current LTE security mechanism shall not be jeopardized, e.g. User identity and device confidentiality,
etc (TS 36.300, TS 33.401, TS 23.401).- Policy control: The Policy and Charging Enforcement Function shall
remain in the PGW (TS 36.300, TS 23.203, TS 23.401).
- Charging: it shall remain unchanged that the SGW/PGW is responsible for interfacing with the charging system,
and CDR generation (TS 36.300, TS 23.401).
- QoS: it shall follow current QoS control mechanism (TS 36.300, TS 23.203, TS 23.401).
- Mobility anchor: SGW is the local Mobility Anchor point for inter-eNodeB handover (TS 36.300, TS 23.401).
- UE IP address allocation: The UE’s IP address is assigned by PGW (or L-GW for local breakout) during the
default bearer activation, or after default bearer activation. The UE IP address allocation mechanism shall not be
changed. (TS 36.300, TS 23.401)
- Lawful Interception: The lawful interception mechanism shall not be changed (TS 36.300, TS 23.401).
5.2 Solutions for issue 1
5.2.1 Solution 1: UE assisted local cache solution
Local cache is a solution to solve the long backhaul latency issue.
An example of how local caching could be achieved is described as follows.
Step 1: UE initiates a content request, including indicator, e.g., based on service information list
Step 2: Network needs to check whether the UE is legal for the selective acceleration (cache) request from core
network.
During handover procedure, the eligibility check result may be transferred to the target eNB to avoid second eligibility
check. Meanwhile, the indicator in step 1 can also be transferred to the target eNB to assist the selective acceleration.
Step 3: If the UE is legal for the selective acceleration (cache) request, Network uses local path otherwise uses
traditional path
It needs to be noted that the exchange of information to RAN regarding the eligibility of UEs for local cache services
may be achieved in different alternative ways, e.g. at UE context setup. This solution can be applied to all the potential
deployment options regardless of where the cache is deployed. The possible local caching solutions are listed as below:
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Figure 5.2.1-1 cache server collocated in the eNB
Note: This solution may not require any changes to the standard, and can be considered as the eNB’s implementation
issue.
Figure 5.2.1-2 cache server after P-GW
Note: This solution may not require any changes to the standard, and can be considered as operator’s
deployment option.
Figure 5.2.1-3 cache server in the middle of S1-U
Figure 5.2.1-4 cache server off the S1-U path
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5.2.2 Conclusion for Issue 1
The local caching can be used to address the issue on backhaul long latency. The local caching is feasible, if CN
functionalities and principles when applied to local caching as defined in section 5.1 are respected. How to make it should
be considered in the normative work with respect existing architecture.
5.3 Solutions for issue 2
5.3.1 TCP Performance Enhancing Proxy (TCP PEP)
TCP PEP [2] has been widely discussed in IETF Performance Implications of Link Characteristics WG (PILC). A PEP
is used to improve the performance of the Internet protocols on network paths where native performance suffers due to
characteristics of a link or subnetwork on the path. Distinct standards track recommendations for the performance
mitigation of TCP over links with high error rates, links with low bandwidth, and so on, have been developed or are in
development by the Performance Implications of Link Characteristics WG (PILC). The TCP PEP is a transport layer PEP
implementations. The most common PEP variant is the split connection TCP Proxy, which intercepts the TCP handshake
(connection establishment) between the User Equipment (UE) and the server, becomes the TCP endpoint towards the UE
and establishes a TCP connection with the server on behalf of the UE. After the connection setup, the TCP Proxy operates
the separate server side (upstream) and UE side (downstream) connections asynchronously. The TCP Proxy has been
investigated in Wideband Code Division Multiple Access systems as well as in LTE [3][4][5][6][7].
There are two further options depend on where the TCP PEP is located.
- Option 1a: TCP PEP is deployed after P-GW/L-GW
Figure 5.3.1-1 example for TCP PEP after P-GW
This option is transparent to the UE. It does not require changes to standard. It can also use the Commercial-Off-The-
Shelf TCP PEP product.
- Option 1b: TCP PEP is collocated with the eNB
Figure 5.3.1-2 – example for TCP PEP collocated with the eNB
This option is transparent to the UE. This option can be considered as eNB’s implementation, and not require changes
to the standard.
5.3.2 Network based Radio-Aware TCP
Achievable data rate (ADR) could be used to improve the accuracy of TCP congestion control. In this solution, eNB
provides the ADR to server via CN.
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Figure 5.3.2-1: Network assisted radio-aware TCP solution
1. Upon decision to perform TCP optimisation, the CN will request eNB to report ADR, for this UE. In this step,
the CN may also configure the reporting criteria and other related information. During handover procedure, CN
may configure the target eNB to report optimization parameters by CN request or source eNB directly transfers
related ADR report configuration to target eNB.
2. According to the ADR assistance info report configuration, eNB reports the required ADR assistance info to CN.
This can be reported periodically or event triggered by CN configuration (e.g. ADR drops below a certain
threshold).
3. CN sends ADR assistance info to TCP server; then TCP server set/update its congestion window accordingly.
Eligibility check similar to that provided for solution 1 of issue 1 may be applied, in case TCP optimization is only applied
to some kind of user subscription, e.g. VIP users.
Potential impact:
1. CN sends ADR assistance information report configuration to eNB;
2. ADR report configuration transferred to the target eNB;
3. eNB sends required ADR assistance information to CN;
4. Eligibility check related impacts as already presented in solution 1 for issue 1.
5.3.3 UE Based Radio-Aware TCP Solution
In this solution, UE provides assistance information e.g. ADR to the server. The assistance information is derived by UE
with assistance from eNB.
5.3.4 eNB generates TCP ACK on behalf of the UE
In this option, the eNB monitors the DL TCP packet. After the eNB receives the RLC ACK from the UE, the eNB
generates the TCP ACK. To avoid the UE and eNB generates TCP ACK for a same TCP packet, the UE can request the
eNB to activate/deactivate this function. This option mainly reduces the period for the UE to send the TCP ACK.
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Figure 5.3.4-1: example for eNB generate TCP ACK on behalf of the UE
5.3.5 Conclusion for Issue 2
There is no consensus on whether TCP PEP is enough for LTE, or possibility if the TCP behavior needs to be changed.
5.4 Solutions for issue 3
RAN needs to check whether the UE is legal for the DASH optimisation from core network.
5.4.1 Solutions for case 1
5.4.1.1 Solution 1: UE request a higher QoS profile
Video transmission issues resulting from empty buffer can be mitigated by supplying UE’s higher QoS profile. If the
operator d
...