Routing area updating in packet radio network

Details Routing area updating in packet radio network Routing area updating in packet radio network

1999-07-08

2003-12-09

Vo, Nguyen T. (Department: 2681)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S328000, C370S341000

Reexamination Certificate

active

06661782

ABSTRACT:

This application is the national phase of international application PCT/FI98/00041 filed Jan. 19, 1998 which designated the U.S.
FIELD OF THE INVENTION
The invention relates to packet radio networks in general, and in particular to supporting mobility in packet radio networks.
BACKGROUND OF THE INVENTION
Mobile communication systems have been developed because it has been necessary to be able to reach people even when they are not close to a fixed telephone terminal. As the use of various data transmission services in offices has increased, different data services have also been introduced into mobile communication systems. Portable computers enable effective data processing wherever the user moves. Mobile communication networks in turn provide an effective access network to actual data networks for the user for mobile data transmission. To realize this, data services of new kind are designed for existing and future mobile communication networks. Mobile data transmission is supported particularly well by digital mobile communication systems, such as the pan-European mobile communication system GSM (Global System for Mobile Communication).
The general packet radio service GPRS is a new service in the GSM system, and is one of the objects of the standardization work of the GSM phase
2
+ at ETSI (European Telecommunication Standard Institute). The GPRS operational environment comprises one or more subnetwork service areas, which are interconnected by a GPRS backbone network. A subnetwork comprises a number of packet data service SN, which in this application will be referred to as serving support nodes SGSN, each of which is connected to the GSM mobile communication network (typically to base station systems) in such a way that it can provide a packet service for mobile data terminals via several base stations, i.e. cells. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile data terminals. Different subnetworks are in turn connected to an external data network, e.g. to a public switched data network PSPDN, via GPRS gateway support nodes GGSN. The GPRS service thus allows to provide packet data transmission between mobile data terminals and external data networks when the GSM network functions as an access network. The GPRS network architecture is illustrated in FIG.
1
.
In the GPRS system, layered protocol structures, known as a transmission level and a signalling level, have been defined for transmitting user information and signalling. A transmission level has a layered protocol structure providing transmission of user information together with control procedures of data transmission related to it (e.g. flow control, error detection, error correction and error recovery). A signalling level consists of protocols which are used for controlling and supporting the functions of the transmission level, such as controlling access to the GPRS network (Attach and Detach) and controlling the routing path of the established network connection in order to support the user's mobility.
FIG. 2
illustrates the signalling level of the GPRS system between an MS and an SGSN. The protocol layers of the transmission level are identical with those of
FIG. 2
up to protocol layer SNDCP, above which there is a protocol of the GPRS backbone network (e.g. Internet Protocol IP) between the MS and the GGSN (instead of protocol L3MM). The protocol layers illustrated in
FIG. 2
are:
Layer
3
Mobility Management (L3MM): This protocol supports the functionality of mobility management, e.g. GPRS Attach, GPRS Detach, security, routing update, location update, activation of a PDP context, and deactivation of a PDP context.
Subnetwork Dependent Convergence Protocol (SNDCP) supports transmission of protocol data units (N-PDU) of a network layer between an MS and an SGSN. The SNDCP layer, for example, manages ciphering and compression of N-PDUs.
Logical Link Control (LLC); this layer provides a very reliable logical link. The LLC is independent of the radio interface protocols mentioned below.
LLC Relay: This function relays LLC protocol data units (PDU) between an MS-BSS interface (Um) and a BSS-SGSN interface (Gb).
Base Station Subsystem GPRS Protocol (BSSSGP): This layer transmits routing information and information related to QoS between a BSS and an SGSS.
Frame Relay, which is used over the Gb interface. A semipermanent connection for which several subscribers' LLC PDUs are multiplexed is established between the SGSN and the BSS.
Radio Link Control (RLC): This layer provides a reliable link independent of radio solutions.
Medium Access Control (MAC): This one controls access signalling (request and grant) related to a radio channel and mapping of LLC frames onto a physical GSM channel.
With respect to the invention the most interesting protocol layers are the LCC and L3MM. The function of the LLC layer can be described as follows: the LLC layer functions above the RLC layer in the reference architecture and establishes a logical link between the MS and its serving SGSN. With respect to the function of the LCC the most important requirements are a reliable management of LCC frame relay and support for point-to point and point-to-multipoint addressing.
The service access point (SAP) of the logical link layer is a point where the LLC layer provides services for the protocols of layer
3
(SNDCP layer in FIG.
2
). The link of the LLC layer is identified with a data link connection identifier (DLCI), which is transmitted in the address field of each LLC frame. The DLCI consists of two elements: Service Access Point Identifier (SAPI) and Terminal End Point Identifier (TEI). The TEI identifies a GPRS subscriber and is usually a Temporary Logical Link Identity TLLI. The TEI can also be another subscriber identity, such as an international mobile subscriber identity IMSI, but usually transmission of the IMSI on the radio path is avoided.
When a user attaches to a GPRS network, a logical link is established between the MS and the SGSN. Thus it can be said that the MS has a call in progress. This logical link has a route between the MS and the SGSN, indicated with the TLLI identifier. Thus the TLLI is a temporary identifier, the SGSN of which allocates for a certain logical link and IMSI. The SGSN sends the TLLI to the MS in connection with the establishment of a logical link, and it is used as an identifier in later signalling and data transmission over this logical link.
Data transmission over a logical link is carried out as explained in the following. The data to be transmitted to or from an MS is processed with an SNDCP function and transmitted to the LLC layer. The LLC layer inserts the data in the information field of LLC frames. The address field of a frame includes e.g. a TLLI. The LLC layer relays the data to the RLC, which deletes unnecessary information and segments the data into a form compatible with the MAC. The MAC layer activates radio resource processes in order to obtain a radio traffic path for transmission. A corresponding MAC unit on the other side of the radio traffic path receives the data and relays it upwards to the LLC layer. Finally, the data is transmitted from the LLC layer to the SNDCP, where the user data is restored completely and relayed to the next protocol layer.
The LLC layer controls transmission and retransmission of LLC frames over a logical link. Several state variables are related to the controlling at both ends of the link. In multiframe transmission such state variables include e.g. a transmission state variable V(S), acknowledgement state variable V(A), transmission sequence number N(S), receiving state variable V(R), and receiving sequence number N(R). The V(S) indicates the number of the frame to be transmitted next. The V(A) indicates the number of the last frame the opposite end has acknowledged. The V(S) shall not exceed the V(A) by more than k frames, i.e. the size of the transmission window is k. The V(R) indicates the number of the next frame that is expected to be received.

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