WO2010145685A1

WO2010145685A1 - Flat architecture in geran

Info

Publication number: WO2010145685A1
Application number: PCT/EP2009/057363
Authority: WO
Inventors: Sergio Parolari; Giovanna De Zen
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-06-15
Filing date: 2009-06-15
Publication date: 2010-12-23
Also published as: EP2443906A1

Abstract

A method and a device for data processing in a mobile communications network are provided, wherein a local link control layer is terminated at a base station. Furthermore, a communication system is suggested comprising said device.

Description

FLAT ARCHITECTURE IN GERAN

The invention relates to a method and to a device for data processing in a mobile communications network.

GERAN (GSM EDGE Radio Access Network) is a key part of GSM and also of combined UMTS/GSM networks. GERAN is the radio part of GSM/EDGE together with the network that joins the base stations (comprising Ater and Abis interfaces) and the base station controllers.

The current GERAN architecture has a hierarchical structure, i.e. a number of base stations (BS), also referred to as base transceiver stations (BTSs) , are connected to a base station controller (BSC) , which is in turn connected to a core network (CN) . This applies for the circuit switched (CS) domain as well as for the packet switched (PS) domain and for control plane (C-Plane) traffic as well as for user plane (U- Plane) traffic. Hence, U-Plane traffic cannot directly be transferred between the CN and the BTSs, but has to pass and to be processed at the BSC.

Fig.l shows a protocol diagram visualizing as how GPRS U- Plane traffic is conveyed between a mobile station (MS) and a core network via a radio access network (RAN) . The RAN comprises a BSC and a BS summarized as base station subsystem (BSS) in Fig.l. The core network comprises a Serving GPRS

Support Node (SGSN) and a Gateway GPRS Support Node (GGSN) . An interface between the MS and the BSS is referred to as Um- interface and an interface between the BSS and the core network is referred to as a Gb-interface .

The BSS provides a protocol conversion between the MS and the SGSN. Fig.2 shows a protocol diagram visualizing GPRS C-Plane traffic between the MS and the SGSN via the BSS. The BSS converts protocol layers of the MS and the SGSN to serve the Um interface and the Gb interface.

It is noted that in Fig.l as well as in Fig.2, a logical link control (LLC) layer is present at the SGSN regarding the U- Plane traffic as well as the C-Plane traffic. The LLC is used to establish a secure link layer connection between the MS and the SGSN to exchange ciphered C-plane and U-plane traffic, said traffic being multiplexed at the LLC layer. Hence, a direct tunnel in Gb mode cannot be established between the MS and the SGSN. In other words, the LLC layer of the SGSN merges said U-Plane traffic and C-Plane traffic thereby pre- venting a flat architecture.

Hence, it is a disadvantage that U-Plane traffic and C-Plane traffic cannot be separated in GERAN.

The problem to be solved is to overcome the disadvantages mentioned above and in particular to provide an efficient solution for separating U-Plane traffic and C-Plane traffic in a GERAN, in particular with regard to a PS domain.

This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims .

In order to overcome this problem, a method for data process- ing in a mobile communications network is provided, wherein a local link control layer is terminated at a base station.

It is noted that the base station may be any base station subsystem or radio access network comprising a interface to- wards a mobile station and an interface towards a core network . An existing base station may be modified to comprise an extended packet control unit function that provides the service of LLC layer termination. Such extended packet control function may be utilized to access a base transceiver station, in particular a radio interface for conveying C-Plane traffic and U-Plane traffic to/from the mobile station.

It is further noted that mobile station as referred to herein may be any device with a radio interface capable of process- ing data according to any wireless communication technique, in particular according to 2G, 2.5G, 3G, LTE, WiMAX, WLAN, etc. The device can be a cellular phone, a user equipment (UE) , a personal digital assistant (PDA) , a laptop computer, a personal computer or the like.

The approach provided enables a flat architecture in GERAN.

The term flat architecture allows for a direct transfer of the U-Plane traffic between the CN and the network node util- izing data transmission over a radio interface. Such flat architecture is available, e.g., in Internet-HSPA (I-HSPA) and LTE technologies.

A pre-requisite for enabling such flat architecture may com- prise an adoption of IP transport technologies.

It is an advantage of this approach that U-Plane traffic and C-Plane traffic can be handled separately in a GERAN, in particular with regard to PS services.

It is also an advantage of this approach that no extensive control functionality is required for processing U-Plane traffic in the RAN. Hence, no bulky equipment is needed. The routing capability supplied by the IP can be utilized for transport purposes instead.

In an embodiment, the mobile communications network is a GSM EDGE Radio Access Network (GERAN) . In another embodiment, said data processed are packet switched (PS) data.

In a further embodiment, control-plane traffic and user-plane traffic are being processed separately based on the termination of the logical link control layer at the base station.

The termination of the LLC layer allows for such separate handling of the U-Plane/C-Plane traffic. This advantageously enables direct tunneling between the CN and the BTS.

In a next embodiment, a modified Sl-interface is provided between the base station and the core network. In particular, the modified Sl-interface can be a modified Sl-MME interface.

It is also an embodiment that a Sl interface is utilized between the base station and the core network.

Pursuant to another embodiment, the core network is an LTE core network.

According to an embodiment, an adaptation layer is provided on top of the LLC layer to adjust control plane traffic at the base station.

According to another embodiment, a SGSN at the core network is modified to comprise an corresponding adaptation layer.

Said adaptation layer can be provided on top of a Sl-AP layer. This may apply for the base station side as well as for the SGSN at the core network.

In particular, an adaptation layer is still present at the BTS side.

In yet another embodiment, an SNDCP layer is terminated at the base station. Said SNDCP layer may be deployed on top of said LLC layer for U-Plane traffic. The U-Plane traffic may utilize an existing Sl-U interface between the base station and the core network.

According to a next embodiment, the base station utilizes a routing capability of the internet protocol.

The problem stated above is also solved by a device compris- ing and/or being associated with a processor unit and/or a hard-wired circuit and/or a logic device that is arranged such that the method as described herein is executable thereon .

According to an embodiment, said device is a communication device, in particular a or being associated with a network element, a base station, an access point, in particular a wireless access point.

The problem stated supra is further solved by a communication system comprising the device as described herein.

Embodiments of the invention are shown and illustrated in the following figures:

Fig.3 shows an exemplary block diagram comprising a RAN and a CN, wherein the RAN comprises a network element with a 2G BTS, an LTE BTS and a BTS with the PCU+ functionality;

Fig.4 shows a symbolic protocol diagram according to a first alternative comprising a PCU+ functionality providing a termination of the LLC layer thereby enabling a separation of C-Plane traffic and U-Plane traffic-

Fig.5 shows a symbolic protocol diagram according to a second alternative comprising a PCU+ functionality pro- viding a termination of the LLC layer thereby enabling a separation of C-Plane traffic and U-Plane traffic .

The approach provided may add a functionality to a packet control unit (PCU) function so that in particular an LLC layer and/or an SNDCP can be terminated at/in this PCU. Furthermore, another interface instead of the Gb-interface may be used towards the core network (CN) . Herein, such PCU with added functionality is referred to as "PCU+".

The added functionality with the PCU+ allows for a separation of U-Plane traffic and C-Plane traffic thereby establishing a basis for a flat architecture like LTE. Such flat architec- ture allows for a direct transfer of U-Plane traffic between the CN and the network element that is responsible for conveying data via a radio interface.

Hence, the flat architecture allows for a single RAN sce- nario, where several RATs may be supported at a BTS and traffic from those various RATs may converge towards the same CN, i.e. an evolved packet core (EPC) for PS services. In other words, the approach provided allows for an efficient modification of the BTS such that it is capable of coping with leg- acy wireless equipment (e.g., GSM mobile stations) and providing a transparent interface towards an LTE CN.

Such an interface between the BTS and the CN can be an Sl interface or a "Sl-like" interface, i.e. an interface that is similar to the Sl interface or a modified Sl interface. The PCU+ and the EPC can be connected via this Sl interface or the "Sl-like" interface.

Fig.3 shows an exemplary block diagram comprising a RAN 301 and a CN 302. The RAN 301 comprises a network element 303 (also possible to be provided as several network elements) with a 2G BTS 304, an LTE BTS 305 (e.g., a NodeB or an evolved NodeB) and a BTS 306 with the PCU+ 308 functionality. The network element 303 communicates with a MS 307 via a wireless interface.

The PCU+ 308 is connected via a packet switched network 309 to a network control server 310 (here: a mobility management entity) utilizing a Sl-MME interface or an interface based on such an Sl-MME interface for C-Plane traffic purposes. In addition, the PCU+ 308 is connected via said packet switched network 309 to a network gateway 311 (here: a S-GW) utilizing a GN/S1-U interface for U-Plane traffic purposes.

It is also indicated that the LTE BTS 305 is connected via a Sl-MME interface to the network control server 310 (for C- Plane traffic) and via a Sl-U interface to the network gate- way 311 (for U-Plane traffic) .

The PCU+ functionality can be implemented inside or it can be associated with the BTS. It may also be distributed among several network elements.

Advantageously, this approach allows serving legacy and upcoming MSs (mobile terminals of any kind or devices comprising a wireless interface), e.g., MSs according to GSM, GPRS and/or EDGE. These MSs are affected neither by the interface between the GERAN and the CN nor by any underlying EPC network elements.

Hence, the approach provides a PCU+, which comprises an extended PCU functionality that may implement a pure Sl inter- face or an interface that is similar to an existing Sl interface .

Exemplary Implementation (s) :

For example, the following implementations may be provided:

(a) A network control server may provide or implement an MME functionality, in particular a GMM/SM application on top of a protocol stack that corresponds or is similar to the Sl-MME interface. In this case, the PCU+ forwards and/or receives GMM/SM related messages to/from the network control server via the interface that is similar to the Sl-MME interface.

(b) The network control server may implement MME functions used for the EPC as well as for the GPRS MSs. In this case, the PCU+ maps GMM/SM information to EMM/ESM infor- mation and vice versa.

The scenario (a) is depicted in Fig.4, wherein an Sl-MME like interface 402 is provided between a PCU+ 404 and an EPC 403 (e.g., CN of LTE) . The PCU+ 404 is deployed, implemented or associated with a BTS unit 401 and provides a protocol stack 405 for processing U-Plane traffic and a protocol stack 406 for processing C-Plane traffic. Each such traffic can be separately processed to/from a MS 409 via RF interfaces 407, 408 utilizing, e.g., UDP/IP. It is noted that said RF inter- faces 407, 408 may provide BTS functionality conveying traffic to/from the MS 409. Advantageously, these RF interfaces 407, 408 do not have to provide any additional routing functionality, they may just process the UDP/IP traffic. This significantly reduces the efforts and costs spent on the BTS part of the network. In addition, the BTS unit 401 comprising the PCU+ 404 is of higher flexibility as it may serve legacy MSs and can be supplied by the EPC 403.

Fig.4 shows that the MS 409 has a protocol stack for U-Plane traffic comprising (in ascending order) a radio frequency

(RF) layer, a MAC layer, an RLC layer, an LLC layer, an SNDCP layer and an application (Appl) layer. The protocol stack for C-Plane traffic comprises (in ascending order) : A RF layer, a MAC layer, an RLC layer, an LLC layer and a GMM/SM layer.

In the BTS unit 401, the RF interface 407 for U-Plane traffic comprises a RF-layer towards the MS 409 and an Ethernet layer below an UDP/IP layer towards the PCU+ 404. This applies according for the RF interface 408.

The PCU+ 404 has a protocol stack 405 (for the U-Plane traf- fie) comprising (in ascending order) : An Ethernet layer, an UDP/IP layer, a MAC layer, an RLC-layer, an LLC layer and an SNDCP layer towards the RF interface 407. Towards the EPC 403, this protocol stack 405 comprises (in ascending order) : A layer-1, a layer-2, an IP layer, an UDP layer and a GTP-U layer. This protocol stack 405 in particular provides ciphering, header compression and data compression and is connected over the Sl-U interface to a corresponding protocol stack 411 of the EPC 403, in particular of a S-GW or GGSN of the EPC 403.

This protocol stack 411 (for the U-Plane traffic) comprises (in ascending order) : A layer-1, a layer-2, an IP layer, an UDP layer and a GTP-U layer.

The PCU+ 404 has a protocol stack 406 (for the C-Plane traffic) comprising (in ascending order) : An Ethernet layer, an UDP/IP layer, a MAC layer, an RLC-layer, an LLC layer and an Adaptation layer 410 towards the RF interface 408. Towards the EPC 403, this protocol stack 406 comprises (in ascending order) : A layer-1, a layer-2, an IP layer, a transport layer (e.g., an SCTP layer), a Sl-AP layer and said Adaptation layer 410. The Adaptation layer 410 terminates the LLC layer and maps it to the layer utilizing the Sl-AP layer. This protocol stack 406 in particular provides ciphering and is connected over the Sl-MME like interface 402 to a corresponding protocol stack 412 of the EPC 403, in particular of a modified SGSN (also referred to as "SGSN+") or MME of the EPC 403.

This protocol stack 412 (for the C-Plane traffic) comprises (in ascending order) : A layer-1, a layer-2, an IP layer, an SCTP layer and an Sl-AP layer. On top of said Sl-AP layer there is either an Adaptation layer with a GSS/SM layer above or a EMM/ESM layer.

The PCU+ 404 allows for a separation of U-Plane traffic and C-Plane traffic. It terminates the LLC layer and adapts the C-Plane traffic in said protocol stack 406 by an adaptation layer 410 to correspond to the protocol stack handling said C-Plane traffic at the EPC 403, namely at the SGSN and/or the MME of the EPC.

The scenario (b) is depicted in Fig.5 utilizing the Sl interface between the PCU+ 404 and the EPC 403. In contrast to Fig.4, no adaptation layer is required at the EPC 403 as protocol stack 412 only comprises the EMM/ESM layer on top of the Sl-AP layer.

The PCU+ may in particular support the following functionalities :

- LLC layer information is ciphered and/or deciphered using a user's keys, which are provided by the MME and/or the SGSN+.

- The LLC protocol is terminated at the PCU+.

- Header information and/or data is compressed.

- The SNDCP is terminated at the PCU+. - The application protocol of the Sl interface (Sl-AP) is terminated at the PCU+.

- The user data of the GTP (GTP-U) is terminated at the PCU+.

- The U-Plane traffic is forwarded via a GTP-U tunnel to the S-GW or to the GGSN.

- A new adaptation function is provided by the PCU+.

According to scenario (a) , said new adaptation function provided by the PCU+ may adapt and/or map C-Plane signaling (GMM/SM procedures) so that it can be conveyed to a peer entity via the Sl-AP and vice versa. Pursuant to scenario (b) , the new adaptation function may map GMM/SM procedures to EMM/ESM procedures and vice versa.

Scenario (a) bears the advantage that the PCU+ may require information about a GPRS user that is stored on a HSS that is located in the CN. Hence, the modification provided to the CN allows conveying such information to the PCU+. In addition, a direct mapping from GMM/SM to EMM/ESM procedures would be more complex than the solution shown in Fig.4.

Further Advantages:

From an architectural perspective, the PCU+ allows

- extending the paradigm of the flat architecture to GPRS/EDGE data traffic enabling in particular a convergence to a CS CN and/or to an EPC;

- handling of existing GPRS MSs by the EPC;

- implementing a single RAN concept; and

- enabling a local breakout scenario for GPRS/EDGE traffic, i.e. Internet breakout and local data traffic breakout.

From a business perspective, PCU+ allows operators reducing CAPEX and/or OPEX based on the flat architecture described. In addition, operation of 2G SGSNs and 2G GGSNs can be suspended.

From a performance point of view, PS data performance for GPRS/EDGE users improves due to the PCU+ implemented at the BTS and due to the possibility to directly tunnel U-Plane traffic from the PCU+ to the S-GW and/or GGSN. Hence, a ping RTT may be reduced by at least 50%. List of Abbreviations

BS Base Station

BSC Base Station Controller BSS Base Station Subsystem

BSSGP Base Station System GPRS Protocol

BTS Base Transceiver Station

CN Core Network

C-Plane Control-Plane CS Circuit Switched

EDGE Enhanced Data Rates for GSM Evolution

EMM EPS Mobility Management

EPC Evolved Packet Core

EPS Evolved Packet System ESM EPS Session Management

GERAN GSM EDGE Radio Access Network

GGSN Gateway GPRS Support Node

GMM GPRS Mobility Management

GPRS General Packet Radio Service GSM Global System for Mobile Communications

GTP GPRS Tunneling Protocol

GW Gateway

HSPA High-Speed Packet Access

HSS Home Subscriber Server IP Internet Protocol

LAN Local Area Network

LLC Logical Link Control

LTE Long Term Evolution

MAC Media Access Control MM Mobility Management

MME Mobility Management Entity

MS Mobile Station (any device comprising a mobile interface)

PCU Packet Control Unit PDA Personal Digital Assistant

PDU Protocol Data Unit

PS Packet Switched

RAN Radio Access Network RAT Radio Access Technology

RF Radio Frequency

RLC Radio Link Control

RNC Radio Network Controller

RTT Round-Trip-Time

Sl-AP Si-Access Point

SAE System Architecture Evolution

SGSN Serving GPRS Support Node

S-GW Serving GW

SM Session Management

SNDCP Sub Network Dependent Convergence Protocol

UDP User Datagram Protocol

UE User Equipment

UMTS Universal Mobile Telecommunications System

U-Plane User-Plane

WiMAX Worldwide Interoperability for Microwave Access

WLAN Wireless LAN

Claims

Claims :

1. A method for data processing in a mobile communications network, wherein a local link control layer is terminated at a base station.

2. The method according to claim 1, wherein the mobile communications network is a GSM EDGE Radio Access Network.

3. The method according to any of the preceding claims, wherein said data processed are packet switched data.

4. The method according to any of the preceding claims, wherein control-plane traffic and user-plane traffic are being processed separately based on the termination of the logical link control layer at the base station.

5. The method according to any of the preceding claims, wherein a modified Sl-interface is provided between the base station and the core network.

6. The method according to claim 5, wherein the modified Sl-interface is a modified Sl-MME interface.

7. The method according to any of claims 1 to 4, wherein a Sl interface is utilized between the base station and the core network.

8. The method according to any of claims 5 to 7, wherein the core network is an LTE core network.

9. The method according to any of the preceding claims, wherein an adaptation layer is provided on top of the LLC layer to adjust control plane traffic at the base station .

10. The method according to claim 9, wherein a SGSN at the core network is modified to comprise an corresponding adaptation layer.

11. The method according to any of the preceding claims, wherein a SNDCP layer is terminated at the base station.

12. The method according to any of the preceding claims, wherein the base station utilizes a routing capability of the internet protocol.

13. A device comprising and/or being associated with a proc- essor unit and/or a hard-wired circuit and/or a logic device that is arranged such that the method according to any of the preceding claims is executable thereon.

14. The device according to claim 13, wherein said device is a communication device, in particular a or being associ- ated with a network element, a base station, an access point, in particular a wireless access point.

15. Communication system comprising the device according to any of claims 13 or 14.