"1 Introduction
Local IP access (LiPA) and selected IP traffic offload (sipto) technologies were originally proposed based on the home (enhanced) node B, H (E) NB) network. It means that the user's service flow data is directly accessed from the home base station without passing through the operator's core network, which is relative to the operator's core network.
IP is the abbreviation of Internet Protocol (protocol for interconnection between networks) in English and "network association" in Chinese, which is a protocol designed for communication between computer networks. In the Internet, it is a set of rules that enable all computer networks connected to the Internet to communicate with each other, and stipulates the rules that computers should abide by when communicating on the Internet. Any computer system produced by any manufacturer can be interconnected with the Internet as long as it complies with the IP protocol. IP addresses are unique and can be divided into five categories according to the nature of users. In addition, IP has the meaning of entry protection, intellectual property, pointer register, etc. How does IP realize network interconnection? The network systems and equipment produced by various manufacturers, such as Ethernet and packet switching network, cannot communicate with each other. The main reason for the failure is that the formats of the basic units (technically called "frames") of the data they transmit are different. IP protocol is actually a set of protocol software composed of software programs. It uniformly converts various "frames" into "IP packet" format. This conversion is one of the most important characteristics of the Internet, so that all kinds of computers can realize interoperability on the Internet, that is, it has the characteristics of "openness".
If h (E) NB is deployed in the communication system, users of H (E) NB can not only use public Internet services, but also contact other nodes in the home network to share resources in the home network and communicate with visiting users in the home network. If LiPA technology is introduced, the data transmission between users and other nodes in the home network can be realized directly through H (E) NB without transmitting to the core network nodes.
LiPA technology is an enhancement of H (E) NB function, allowing the terminal to access IP resources inside the home / enterprise through H (E) NB. This makes it possible for operators to develop more applications with family / enterprise characteristics based on H (E) NB. For terminals without Wi Fi capability, the effect similar to local Wi Fi access can be achieved.
With the development of wireless access technology, data transmission is transmitted at a higher rate. The increase of the number of users and the improvement of user data transmission rate put forward higher requirements for the network element performance of the core network. Radio interface technologies (RIT) radio access technology (also known as air interface) is the key problem of wireless communication. It refers to connecting the user terminal with the network node through wireless media to realize the information transmission between the user and the network. The signal transmitted by wireless channel should follow certain protocols, which constitute the main content of wireless access technology. An important difference between wireless access technology and wired access technology is that it can provide mobile access services to users. Wireless access network refers to an access technology that partially or completely uses radio waves as a transmission medium to connect users with the switching center. In the communication network, the positioning of wireless access system: it is a part of the local communication network and an extension, supplement and temporary emergency system of the local wired communication network. A typical wireless access system is mainly composed of controller, operation and maintenance center, base station, fixed user unit and mobile terminal.
Compared with that all IP packets are routed to relatively centralized core network nodes (such as centralized deployment of GGSN based on province), using sipto in macro network can allow gateway devices, such as GGSN, to be deployed in a distributed manner near users (such as cities, districts, etc.), so as to allow users' data to be routed from nodes closer to geography / logic.
2. Technical demand analysis
In the process of 3GPP standard formulation, the original H (E) NB requirements document (3GPP TS 22.220) only has the concept of LiPA. The application scenario is based on H (E) NB users, and its services can be home / enterprise network services or internet network services. However, the concept of sipto is put forward after the demand for shunting Internet services in macro network is clarified. The specific scenarios are as follows:
● LiPA for home / enterprise network service, the terminal can directly access the user's home network or other IP capable devices in the enterprise network through H (E) NB.
● for sipto in H (E) Nb, the terminal can directly access the Internet through H (E) NB.
● for sipto in macro network, the terminal can directly access the Internet through macro base station.
The classification can be understood from two aspects: first, from the form of service, LiPA is used for the service in H (E) Nb and sipto is used for the service in the public network; Secondly, in terms of network architecture, LiPA is used for H (E) Nb, while sipto can be used for H (E) Nb and macro network. The architecture of LiPA / sipto is shown in Figure 1 and Figure 2. Figure 1 describes the application scenario of H (E) Nb and Figure 2 describes the application scenario of 3G / LTE macro network.
Figure 1 LiPA / sipto for home base station
Figure 2 LiPA / sipto for macro network
Although LiPA and sipto have different application scenarios, the problems of LiPA / sipto are similar in terms of function and structure, and the network architecture is basically the same. Therefore, in order to maintain the consistency of solutions, 3GPP has conducted centralized analysis and Research on these two technologies in tr 23.829.
(1) LiPA technology requirements
● it shall be able to support UE access to the core network of mobile operators and access to home / Enterprise IP network through LiPA.
● LiPA is only used for service routing between UE, H (E) Nb and home / enterprise network.
● the UE using LiPA must also have legal signing data and pass the authentication of the operator's network.
● UE can use LiPA in the visiting network through roaming protocol.
● when UE roams to a specific VPLMN, HPLMN can turn off LiPA.
● the use of LiPA shall not affect other parallel services of UE.
● if the home / enterprise network can provide LiPA technology, it shall be able to notify the UE.
● when UE moves between H (E) Nb in the same home / enterprise network, it shall be able to maintain the IP connectivity from ue to home / enterprise network.
● the operator can turn off / on LiPA for H (E) Nb and UE.
● the use of LiPA cannot weaken the security of the operator's network.
(2) Sipto technical requirements for H (E) NB
● specific services can be shunted near the location where the UE is attached to the access network.
● operators can turn on / off sipto technology for users, for example, based on user fees or signing information.
● for multiple services performed by the same UE, only part of the services can be shunted without affecting the use of other services.
● the use of sipto shall not weaken the security of mobile operators.
● sipto can be executed without user participation.
● sipto shall support mobility in macro network, mobility between home base station and macro network and mobility between home base stations.
● HPLMN can provide VPLMN with user's sipto information, such as whether sipto is allowed in the visiting network and which networks can be sipto.
(3) Sipto technical requirements for macro networks
● operators can turn on / off sipto in specific areas of the network.
● sipto cannot weaken the integrity and confidentiality of the diverted services.
(4) Key problems to be solved in LiPA / sipto Technology
● where is the service diversion point or service interruption point, and which network element determines the service interruption?
● based on what principles are businesses diverted, that is, what businesses need to be diverted?
● how to realize billing for shunted services? How to report billing information? Which ne reports it?
● is it necessary to support legal monitoring? If yes, where is the legal listening point?
● when implementing LiPA / sipto, since the home base station has no GX interface, can QoS control only be based on static policies?
● when implementing LiPA / sipto, can the operator dynamically change based on the system configuration and load? Or does it happen statically based on configuration data?
In the process of discussing and studying the solution of LiPA / sipto technology, the basic principles of network architecture to be followed are:
——For services to pass through the operator's core network, the S-GW / SGSN user plane function is in the operator's core network.
——Mobility management signaling is handled by the operator's core network.
——During LiPA / sipto, its session management signaling and services to be transmitted through the core network are terminated in the core network.
——The service diversion point should be as close to the user as possible. This diversion point can be reselected in the mobility program in idle mode.
3 solution
For the above key problems and basic architecture principles, 3GPP puts forward six solutions. These six schemes are briefly described below.
(1) Option 1
The scheme is applicable to the service diversion of H (E) NB. The principle of the scheme is that the local gateway (l-gw) is set together with H (E) Nb, and a dedicated APN is used to identify the PDN requiring service diversion. The services in the operator's core network are transmitted with PDN connections different from the PDN. The locations of l-pgw (local p-gw) and l-ggsn (local GGSN) are in the home / enterprise network, such as H (E) NB.
The scheme can be implemented based on S5 interface, that is, the downlink packet data in idle state is stored in S-GW and forwarded through S5 interface between S-GW and l-gw; It can also be implemented based on S4 / S11 interface. At this time, there will be S11 / S4 interface between l-gw and Mme / SGSN. Its function is a subset of S11 / S4 interface function, which mainly completes the session management of LiPA service.
(2) Option 2
This scheme can be used in H (E) Nb, but not in macro networks. The idea is to realize LIAP / sipto through NAT in H (E) Nb, split and insert the service flow according to the operator's strategy, and route the service flow through NAT in H (E) NB subsystem. The terminal uses only one PDN connection, and adds the functions of NAT and routing strategy in the home base station subsystem to realize data diversion.
(3) Option 3
The scheme can be used in 3G network. The principle is that the local gateway is deployed on the wireless base station, and the network element on the wireless side reports the local gateway address suitable for shunting; The core network judges whether to allow sipto to establish and select the local gateway through the user's signing; SGSN needs to establish a direct tunnel for LiPA / sipto connection. Based on the operator's strategy, SGSN can select the appropriate GGSN for service grooming or diversion according to the location of diversion points.
(4) Option 4
This scheme is only applicable to 3G networks. The principle of the scheme is to implement service diversion in IU PS based on NAT. A new network element, trafficoffload function, is added to the architecture. TOF is located at IU PS interface and can be set independently or in combination with RNC / hnbgw. TOF can determine the diversion strategy, divert and insert services, provide standard IU PS interfaces to RNC and SGSN, and provide operators with different levels of sipto applications through NAT and SPI / DPI functions based on operator policies.
(5) Option 5
This scheme is suitable for shunting Internet services, but not for services in home base stations. The scheme is based on local p-gw selection to realize service diversion. When selecting GW, Mme / SGSN should consider the user's location and select a gateway close to the user. The gateway selection can be performed based on DNS mechanism. In addition, the scheme moves the user plane ne down to the wireless side. For the GPRS system, the local GGSN is deployed on or near the RNC, using a direct tunnel; EPS is the abbreviation of electric power steering, namely electric power steering system. Electric power steering system is the development direction of automobile steering system. The system directly provides steering power by the electric power assisted machine, which eliminates the power steering oil pump, hose, hydraulic oil, conveyor belt and pulley installed on the engine necessary for the hydraulic power steering system, which not only saves energy, but also protects the environment. In addition, it also has the characteristics of simple adjustment, flexible assembly and providing steering power under various conditions. With these advantages, as a new steering technology, electric power steering system will challenge the well-known hydraulic steering system with a history of more than 50 years.
(6) Option 6
This scheme is applicable to all scenarios of business diversion. The scheme is to realize service diversion based on the architecture of local gateway, add l-gw to support LiPA / sipto, and configure a direct expansion tunnel between l-gw and p-gw / GGSN to facilitate user's LiPA / sipto downlink data transmission in idle state and data forwarding in connected state. The function of l-gw can be on the wireless side or the core network side. L-gw does not migrate p-gw / GGSN functions to ENB / e-utran, but only includes a few of them.
4 Conclusion
The SA2 working group of 3GPP is currently working on stage R10
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