Advanced EPC MBB enabling services and improving user experience
Advanced EPC MBB enabling services and improving user experience 1 Introduction ........................................................................................................................1 2 EPC standards timeline ........................................................................................................2 3 Challenges and opportunities for the Advanced EPC ............................................................3 4 Advanced EPC Key Features ................................................................................................4 4.1 Signaling congestion control ............................................................................................4 4.2 User plane congestion control ..........................................................................................4 4.3 Carried grade WiFi integration .........................................................................................5 4.4 Voice service for LTE users ...............................................................................................6 4.5 Video enhancement .........................................................................................................7 4.6 Proximity based services ..................................................................................................8 4.7 Group communication system enabler .............................................................................9 4.8 Machine type communications ........................................................................................9 4.9 Architecture enhancement for application interworking ................................................11 4.10 XML based access to PCRF .............................................................................................12 4.11 SGi traffic steering .........................................................................................................12 5 Conclusions .......................................................................................................................14 6 Annex: Abbreviation ..........................................................................................................15
1 Introduction 3GPP’ s 4G mobile system LTE/EPC has been developed by the mobile industry in the last few years during 3GPP releases 8 and release 9 to meet the continuously growing service requirements of MBB. The overall system consists of the radio system LTE and the Evolved Packet Core (EPC). A further evolution of the LTE radio system has been done in the time frame of 3GPP release 10 and is called LTE-Advanced. The corresponding overall system has been selected as an ITU 4G technology option. It should be noted that LTE denotes the radio system, but is also the official terminology for marketing the overall mobile system of LTE and EPC. During the following 3GPP releases on the network side the further evolution of the EPC is targeting at enabling of more profitable services and improving user experience, both bringing added value for the whole mobile market. Service enabling has thus become an important topic after basic EPC features have been specified during initial 3GPP releases. In this whitepaper it focuses on the current phase of EPC, which is denoted as Advanced EPC. It takes advantage of the excellent radio capability of LTE and LTEAdvanced. The current phase of the Advanced EPC is facing the following challenges: ・High penetration of smart phones with a variety of applications causing traffic of virtually any pattern and volume. ・Fast traffic growth with growth of revenues not keeping pace. ・Increasing diversity of service types and their related Quality of Experience. To address those challenges, the following areas of improvement have been identified: ・Enhancements that mitigate or prevent system overload. ・Capacity boosting by WiFi integration and offloading. ・Enhancements for enabling key services and other new business opportunities. ・Introduction of new service enablers. In this whitepaper it provides an overview on how the EPC timeline developed, considers the specific challenges and opportunities for the Advanced EPC and describes the different key features of the Advanced EPC that are intended to address the challenges and opportunities.
1
2 EPC standards timeline The initial activities on the LTE/EPC system started already in 2004. The radio access system and the related core network have been designed to provide a new mobile system targeting at higher spectral efficiency, higher peak data rates, shorter round trip times and frequency flexibility. This radio access system is called Evolved UTRAN (E-UTRAN), and the core network is the Evolved Packet Core (EPC). Both together form the Evolved Packet System (EPS). EPC is designed by 3GPP not only as the core network for the LTE/EUTRAN radio access system but as well for its predecessors GERAN and UTRAN. The EPC is thus an evolution of the packet core that was designed for GERAN/UTRAN. Main differences to the earlier packet core are the new access interface adjusting for the specifics of the E-UTRAN/LTE radio access, a simplified bearer management scheme solely relying on network controlled bearer services and a split into control and user plane network entities. EPC also contains capabilities for using Non-3GPP access technologies (e.g. WiFi) as access systems. EPS is a pure packet system and, besides SMS, it does not provide any telecom services for end users like circuit switched telephony. A separate IP Multimedia Subsystem using the bearer services of the EPS provides multimedia telephony for the end user. To enable initial EPS deployments without an IP Multimedia Subsystem (IMS), 3GPP defined the “Circuit Switched Fallback” feature (CSFB), which transfers the device from LTE to GERAN or UTRAN for performing circuit switched calls, but enjoying for IP based services the high bandwidth and low latency of E-UTRAN/LTE. For deployments with EPS and IP Multimedia Subsystem 3GPP defined the “Single Radio Voice Call Continuity” features (SRVCC) to enable a stepwise rollout of E-UTRAN/LTE coverage by continuing IP Multimedia Subsystem provided services as Circuit Switched services via GERAN/UTRAN when a user leaves E-UTRAN/LTE coverage.
2007
2008
Release 8
2009
Release 9
LTE
EPC: basic
2010
Release 10
2011
2012
Release 11
LTE-Advanced
2013
2014
Release 12
2015
2016
2017
Release 13 and later on
Further LTE evolution on LTE-B/C
Advanced EPC: Service Enabling for MBB
Further EPC evolution
Figure 2a. EPC standards timeline
2
After the basic EPC features, i.e. providing high performance IP bearer services for MBB, had been completed within 3GPP release 8 and release 9, work started on enabling voice, multimedia and machine type communications services, like emergency call, CSFB/SRVCC enhancements, M2M related features. The currently ongoing phase of advancing the EPC targets at improving or creating business opportunities for operators by enhancing existing or developing new EPC services and features. The timeline of the Advanced EPC is shown in the figure 2a.
3
Challenges and opportunities for the Advanced EPC
In the last few years the Telco industry experienced significant changes. One significant trend is the move of Internet services from personal computers to mobile devices. This trend got accelerated especially with the explosive penetration of smart phone. Another trend is that in many developed markets the penetration rate of mobile subscribers is reaching some saturation. This increases the interest of looking for new revenue opportunities and extending mobile services to other potential markets (Enterprise, government, machine communications, etc). The whole mobile industry eco-system started to change when smart phone begun to dominate the terminal market. One significant change is that traditional telecom services like voice and message get more and more challenged by the so-called Over-The-Top (OTT) applications using the mobile system as a transparent bit-pipe. However, there is more and more interest in offering better services to the users by making the mobile system application-aware and providing added value, like QoS, for OTT applications. The following activities have been identified for Advanced EPC to proactively cope with the above trends and challenges: ・Make the mobile system more robust and efficient, in order to manage the increasing amount of connected devices, but also the increasing variance of connection types, e.g. from M2M, and save OPEX and CAPEX. ・Enlarging the system capacity, in order to meet the requirements from huge traffic volume, which is still in a process of growing fast. ・Support new services and further improve the Quality of Experience for key services like voice and video. ・Offer network capabilities to applications for better supporting the diversity of Internet services and facilitating an expansion of the mobile ecosystem towards including applications. 3
4 Advanced EPC Key Features 4.1 Signaling congestion control The origin of the investigation on signaling overload in the core network was a specific case of a Radio Network Controller (RNC) restart leading to a flood of UE registering with the network in a short time period. The affected HLR could not answer all the requests, which made the situation even worse since UEs retried the registration. Similar issues were identified for other scenarios and other network entities. 3GPP has thus started to look at these issues with the setup of a study item on Core Network Overload (CNO). One of the issues being studied was the load handling for Diameter applications. Comparable to SS7, a new logical function is introduced, the Diameter Load Manager. It influences the route selection when a congested node is detected. Another investigated issue is about the optimization for the reporting of user location information. The basic idea of avoiding too much location report traffic in the network is to adjust the granularity of the location reporting according to the needs, e.g. by defining a specific area for which a report is wanted. A third issue is on the overload control for GTP-C interfaces. Different approaches are evaluated for reducing the traffic towards loaded nodes caused by too many GTP-C requests.
4.2 User plane congestion control mobile network resources. Especially in RAN, user plane congestion occurs more frequently and becomes a serious problem to the operators. Mechanisms are wanted, which reduce the occurrence of congestion and alleviate congestion in a quick and smooth manner. 3GPP is studying this under User Plane CONgestion management (UPCON). Today application/user services with their different QoS needs can be identified and treated by using separate bearers. However in many deployed networks, services with different QoS requirements often share the same bearer, i.e. the default bearer. In this case the RAN has no information on differences among these services being conveyed in the shared bearer and transfers all IP packets in a uniform way according to the allocated bearer QoS. When congestion happens, RAN may need to decide on delaying or
4
discarding IP packets based on the bearer QoS. A shared bearer prevents the RAN from taking efficient approaches for avoiding/alleviating congestion specifically per application/user service. Marking the user data packets with an identifier for their priority during congestion (the so called Flow Priority Identifier,FPI ) is a solution that provides the RAN with extra information. The PGW/GGSN marks the data packets with the Flow Priority Identifier based on the subscription, application type and possibly other criteria. According to this information the RAN can shape or discard the data traffic specifically per priority of the application or user service. Another way of RAN node congestion mitigation is notifying affected applications, which may then try to adjust the service while maintaining the Quality of Experience as good as possible. For example, a video application could change its media codec or employ video compression. Other applications may trigger providing services based on load notifications, e.g. for delivering push data depending to the network traffic status.
4.3 Carried grade WiFi integration WiFi is more and more regarded as an important part of mobile operator networks. It can be connected to the EPC via S2a, S2b and S2c interfaces. But how to effectively utilize WLAN infrastructure using the so far standardized means is still a problem. In Advanced EPC, the S2a path with GTP will be enhanced to support UEs accessing EPC via WiFi with minimum changes for the UE IP stack. Further, concurrent multiple connections need to be supported for WiFi access and seamless handover between 3GPP and WiFi (considered under 3GPP release 12 work item SaMOG) to reduce efforts for implementing carrier grade WiFi support in UEs. A huge number of WLAN Access Points are deployed all over the world. From all those available WLAN Access Points most cannot be accessed by mobile subscribers. Often it is because many are just providing private services. As a consequence, useless access attempts consume large quantity of UE battery power and impact the user experience. An overall network discovery and selection mechanism considering PLMN selection and Hotspot 2.0 ANQP (Access Network Query Protocol) elements enables the UE to efficiently connect to the network via the most proper WLAN AP. A cellular assisted WLAN discovery and selection mechanism will improve the user experience when moving between 3GPP and WLAN without user perception. To decrease the time required for the mobility with WLAN, a new security architecture is designed to make the UE achieving substantially
5
faster access to WLAN. Network controlled IP flow mobility further enables the UE to route IP traffic simultaneously over 3GPP radio access and WLAN, and easily moving IP traffics between the radio access technologies smoothly based on operator’s policy.
4.4 Voice service for LTE users LTE/EPC is a mobile system for providing mainly IP bearer services. Voice services are however still important services and their support is considered a crucial factor for the success of LTE/EPC deployments. Voice services are provided either by deploying a subsystem for VoIP/VoIMS or by falling back to GERAN/UTRAN enabled Circuit Switched (CS) domain. CS Fallback (CSFB) and IMS/SRVCC (Signal Radio Voice Call Continuity) are the two key features for enabling voice services with the EPS. CSFB is considered the first step as it relies on fallback to legacy systems. It has been launched commercially with the early deployment of LTE/EPC and will continue to be supported in Advanced EPC at least for supporting roamers. To further improve the user experience Huawei developed “Ultra-Flash CSFB” (refer to figure 4a) as enhancements of the standardized CSFB. It optimizes the call-setup time for CS fallback, which is accomplished by the Advanced EPC network due to initiating call setup in parallel with the UE fall back to GERAN/UTRAN access network. With those optimizations, it provides an equivalent or even less call-setup time compared to a native 2G/3G CS call.
Sv SGs MSC
MME
Ultra - Flash CSFB GERAN/UTRAN
LTE
Figure 4a: Ultra-Flash CSFB
IMS and SRVCC (including video SRVCC and its enhancements) are the long term voice solutions for voice over LTE/EPC and are supposed to support both voice (including HD voice) and video services in Advanced EPC. With CSFB and IMS deployed, two voice service options are available that may complement each other.
6
4.5 Video enhancement Video traffic has emerged as the dominant traffic in today's Internet (Per Huawei mLab report - H2 2012, streaming application will account for 40% to 60% of mobile usage in 2015, figure 4b). How to deliver such massive traffic with the required QoE becomes critical to operators. North America
West Europe 1.01%
0.96%
2.85%
4.36%
1.50%
2.08%
1.87%
13.31%
1.25%
18.77%
10.81%
58.20%
SouthEast Asia 0.34% 1.39%
8.44%
7.45%
0.92%
0.91%
Web browsing Streaming File transfer
9.06% 35.95%
47.83% 37.89%
55.62%
China 0.33%
0.19% 1.87%
1.73%
3.03% 27.66%
40.72%
1.71%
0.82% 0.60%
7.96%
4.07%
34.74%
4.67%
Latin America 2.22%
0.91%
IM SNS VOIP
43.97%
Email Gaming
Figure 4b. Mobile usage forecast of 2015
Progressive download has been a popular mechanism for video service in Internet. But it seems not working well in the cellular environment and proper architecture enhancements are needed in order to support mobile streaming services. In an industry-wide collaboration including multiple SDOs 3GPP and partners developed the method DASH (Dynamic Adaptive Streaming over HTTP). However, it is running on the application level and thus provides limited tooling for operator control. A network control enhancement to DASH [see figure 4c] is being discussed in 3GPP Release 12 to support more business scenarios like network aware adaptation, precise QoS control, etc. Server
Client 1
Client 2
Advertisement Client N
HTTP Adaptive Proxy （HTTP Cache）
High bit rate Medium bit rate Low bit rate
Figure 4c. DASH with network control
7
Another option is to take advantage of IP multicast technology which is supposed to be a cost effective way of delivering common content traffic to a group of users. The multicast technology can be applied to the cellular system with certain customization. MBMS (and eMBMS) is a cellular multicast technology for UMTS/LTE networks, which could be the base for further work. 3GPP has started to work on on-demand MBMS for this purpose. On-demand MBMS would allow operators to identify the common video traffic (carried over DASH) or deliver different video traffic with carrousel style, then shift the traffic from unicast mode to multicast mode. This transportation mode switch should of course consider information like user location, number of users accessing the same content, etc. to achieve reasonable gains.
4.6 Proximity based services Direct Device-to-Device discovery and data exchange services exist already for a long time. Bluetooth and WiFi Direct (802.11) provide examples of such service offerings. The 3GPP system introduces such functionality, named Proximity Services, within its release 12. The main driver for this is the interest to use the EPS for providing professional mobile radio services for public safety usage, like for police or ambulance. Some additionally considered usage scenarios are offering 3GPP proximity services for commercial or consumer applications, such as the discovery of other users belonging to the same application and who are in proximity or to enable direct LTE or WiFi communication between users or devices that are in proximity to each other. Proximity communications are also considered as an option for offloading traffic from the network and thus improving cost and resource efficiency. 3GPP proximity services include the discovery service and the communication service. Each may be used separately as an enabler for other, specifically application services. Proximity discovery and communication service will be available as functionality of the E-UTRAN/LTE access system. Public safety users or applications may use those services based on pre-configured permissions also when there is no coverage or connectivity with the mobile system. Consumer usage is only permitted with authorization by the mobile system on a per usage basis. Specifically for enabling Public Safety application services the 3GPP proximity services need to provide relay functionality for extending radio coverage in various scenarios.
8
4.7 Group communication system enabler These enhancements are also driven by the interest of using the EPS for providing Professional Mobile Radio (PMR) services. The adoption of the 3GPP system as a common global mobile broadband system is caused specifcally by the interest in broadband features for group communications, which are not offered by current PMR systems, like ETSI TETRA or US P25. These current PMR systems provide group communications as narrow band services. The interest in using advanced features and services that require broadband support made 3GPP’ s EPS a good candidate for this. While proximity services cover mainly the service support under conditions without suitable radio coverage, the group communications system enablers consider all other aspects needed for operating PMR services via an EPS. It may be possible to use existing features, like EPS packet bearer services or roaming, without specific modifications. Special considerations are on efficient system resources usage. Especially for scenarios with many users in the same area multicast data delivery may be needed and therefore the usage of eMBMS or other enhancements need to be considered. Other challenges that may require specific systems enablers are the strict timing requirements from such mission critical services.
4.8 Machine type communications Machine to Machine (M2M) communication is identified as one of the most interesting chances for operators to generate new revenues specifically as this business is in addition to providing services for the human being population, whose growth already reached already saturation in some markets. A specific characteristics and therefore challenge of M2M is the often low ARPU per single device, which may be compensated by large device populations under the same contract, given that commissioning, operation and services can be managed in a cost efficient way. These are the areas where specific system features intend to enable or improve such business. Mobile M2M traffic worldwide is now doubling every year and the proportion of 3G and 4G M2M devices will increase continuously. M2M brings specific challenges to the network due to the potential massive number of devices to be supported and the fact that those may act in a coordinated manner. The basic capability for the mobile network is therefore to efficiently maintain and manage the connectivity for a huge number of M2M Devices. In addition, network robustness has to cope with situations
9
where a large number of M2M devices perform coordinated actions, e.g. transfer data at the same point in time or change the network when nodes of another network recover. Means for access control at different levels of the mobile system have been already specified to cope with such or other congestion situations to maintain normal service for other users. In addition, for efficient handling of large number of connections a special feature for device triggering was introduced by enhancing the existing SMS capability. For the current phase of the Advanced EPC, the focus is more on improved support for a large variety of M2M application scenarios. Specifically low cost, low power consumption and efficient handling of small data transfers have been identified as critical issues. Further 3GPP features and services will be provided and offered to applications or service platforms as enablers for the new emerging M2M business. Like the new future proof messaging service, which may be considered a more powerful SMS service, it transfers efficiently data units of up to 1kB size, independently from IP connectivity. Another example is the enhancement of 3GPP’ s discontinuous reception mechanisms that allow for frequent data transfers with less system processing and are also suited to reduce the device’ s battery power consumption. Further, a new device sleep state mechanism may enable devices with infrequent communications needs, e.g. tracking devices that report location every hour or day, to run years without replacing the battery. As soon as the work load situation allows for it, 3GPP may also continue to define a new monitoring framework to provide M2M and other service platforms with a comprehensive status overview about device, service and subscription conditions. This and other interworking with platform or service enablement layers is becoming more and more important for creating applications and services with added value.
10
4.9 Architecture enhancement for application interworking There is increasing interest in the mobile network to become aware of OTT applications. This awareness would facilitate the providing of network services in a more resource efficient way and also with better user experience. For instance, the network could optimize the radio resource scheduling for certain applications. For these requirements mechanisms already exist like SAPP (Service Awareness & Privacy Policy), SIRIG (Service Identification for improved Radio utilization In GERAN) or are under development like for User plane congestion control (UPCON) described above. Also letting applications being aware of the network status (e.g. congestion) may help to further improve the user experience. For example, a video server could proactively adapt the codec if it gets a congestion prenotification, thereby avoiding any annoying video interruption. Such awareness for applications should be addressed in a general way. A proposed framework is shown as below in figure 4d.
AIF: Application Interworking Functionality
Service Layer AS
AIF PCRF HSS MME UE
eNodeB
RAN
SGW/ PGW EPC
Figure 4d: Application Interworking Framework for Advanced EPC
A new function called AIF is introduced between the service layer and the mobile network to abstract the network capabilities in a systematic way and thus unifying and opening the network capabilities towards application service providers.
11
4.10 XML based access to PCRF Nowadays mobile operators enable dedicated support for their own or 3rd party applications via the Rx interface, which is based on Diameter protocol. However, 3rd party application providers typically use XML based protocols more frequently. Changing those applications to support Diameter, if possible, would create additional efforts and is therefore no cost efficient option. In order to resolve this issue, an XML based access from the AF to the PCRF should be specified as a new XML based Rx variant or provided by a protocol converter (referring to figure 4e). Both options may be needed to support different deployment scenarios.
Diameter based Rx PCRF MME
eNodeB
Converter Gx (Diameter)
XML based Rx AF
SGW/PGW
Figure 4e. Options for XML based access to PCRF
4.11 SGi traffic steering Currently a range of Value Added Service (VAS) enablers are deployed between P-GW SGi interface and the edge router to the Internet Service Provider. These VAS enablers may include traffic compression, video optimization, web caching, HTTP header enrichment, Firewall, etc. These enablers are important for providing services in a cost efficient and stable way. Good VAS deployment will not only improve the user experience, but may also create additional revenue from enhancing or processing data in accordance with business relation. There is however a need for an efficient routing of user data traffic to avoid unnecessary traversing of individual VAS components, which are not needed according to the policy applicable to the specific user data traffic. Service Based Routing (SBR) has been added to the EPC by vendors to fulfill this requirement of steering user data traffic selectively through VAS
12
enabler components based on user identity, mobile network information, and service type. (Figure 4f)
VAS 1
VAS 2
VAS 3
SP Server MME UE
eNodeB
RAN
EPC
SGW/ PGW
SBR
Internet
Figure 4f: Basic SBR
In Advanced EPC, SBR can be further enhanced to provide dynamic chaining of VAS enabler components with better agility and optimization by adopting SDN based methods. In the SDN model, VAS enabler components will be concatenated by a programmable switch which is under the control of a centralized SDN controller (See figure 4g). The traffic routing policy is implemented by the interaction of SDN controller and programmable switch based on configuration or dynamic policy control.
VAS 1
VAS 2
SDN Controller
VAS 3
SP Server
MME UE
eNodeB
RAN
EPC
SGW/ PGW SBR
Switch
Internet
Figure 4g: SDN enabled SBR
13
5 Conclusions LTE/LTE-Advanced and the Advanced EPC are continuously developing for meeting new or extended challenges and expectations arising from the mobile system usage penetrating virtually any area of life and work. The Advanced EPC delivers new key features for enhancing efficiency and business for already deployed MBB services and applications. But the Advanced EPC is also opening for new usages by improving system efficiency and cost position for scenarios that are not typically broad band, e.g. massive usage of M2M with a small amount of data, or by offering specific features from the mobile system towards applications or service platforms for creation of a multitude of innovative services and applications. A main aim is always maintaining stability and robustness of the mobile system also with the growth of volume and variety of the traffic managed by the mobile system.
14
6 Annex: Abbreviation CNO
Core Network Overload
CSFB
CS Fallback
DASH
Dynamic Adaptive Streaming over HTTP
EPC
Evolved Packet Core
LTE
Long Term Evolution
M2M
Machine-to-Machine
MBMS
Multimedia Broadcast Multicast Service
M2M
Machine to Machine communication
SAPP
Service Awareness & Privacy Policy
SBR
Service Based Routing
SDN
Software Defined Network
SIRIG
Service Identification for improved Radio utilization In GERAN
SRVCC
Single Radio Voice Call Continuity
UPCON
User Plane CONgestion management
VAS
Value Added Server
XML
eXtensible Markup Language
15
Copyright©2013 Huawei Technologies Co., Ltd. All Rights Reserved. The information contained in this document is for reference purpose only, and is subject to change or withdrawal according to specific customer requirements and conditions.
