Arrangement, a system and a method relating to a packet data communication

#The present invention relates to an arrangement in a cellular communication system supporting packet data communication, a cellular communication system supporting packet data communication and a method of controlling the load distribution in an arrangement or in a node in a communication system supporting packet data communication.

#Cellular communication systems which, in addition to supporting communication of speech and circuit switched data, also support communication of packet data, are becoming more and more attractive. For example, for GSM (Global System for Mobile Communications) support for communication of packet data is developing through the general packet radio service (GPRS). Similarly the PDC system (Pacific Digital Communications) is provided with packet data communication support through the PPDC (Packet PDC). CDPD is another such packet data communication supporting service for the AMPS system.

#The general packet radio service (GPRS) of GSM uses a packet mode technique for the transfer of data as well as signalling and GPRS radio channels are defined the allocation of which is flexible and time slots in a TDMA frame (Time Division Multiple Access) are shared by the users that are active and uplink and downlink are allocated separately. In GPRS, as well as in other packet data communication supporting cellular systems, nodes are introduced for management of the packet data communication. Such nodes are here called packet data nodes. In GPRS the packet data node is called the serving GPRS support node (SGSN) which is at the same hierarchical level as an ordinary MSC (Mobile Switching Center) and it keeps track of the locations of individual mobile subscriber stations, performs security functions and access control. The SGSN is connected to the base station system with Frame Relay. GPRS also comprises another node, the gateway GSN (GGSN) providing interworking with external packet switched networks and it is connected with SGSN via an IP-based GPRS backbone network. Generally the amount of data packets sent from a mobile station through the data network via the packet data node is much lower than the traffic from the data network, via the packet data node, towards a mobile subscriber station. One reason therefore is that the mobile subscriber station, which for example may be connected to a small personal computer (PC) it reads E-mails from a mail server etc. Thus the subscriber station here for example only sends a short packet whereas it receives a large amount of packets or long messages. If for example connecting to Internet, the mobile subscriber station may for example just send a short message requesting a file whereupon it receives a large file. The problem is that the demands as to bandwidth are very asymmetrical in the packet data node handling mobile subscriber stations for all of which the situation may be similar, i.e. the load on the uplink is low whereas the load on the downlink is high. A packet data node may thus need several processors and it is a problem to handle the distribution of the load on the processors.

#The invention will in the following be further described in a non-limiting way and with reference to the accompanying drawings, in which:

#FIG. 1A is a simplified illustration of a communication system supporting packet data communication,

#FIG. 1B is a figure similar to FIG. 1A, as implemented to GSM GPRS,

#FIG. 1A shows an implementation of the invention in a mobile communication system supporting packet data communication. The communication system shows a number of base stations, in the following also denoted BS, 3A0, 3B0, 3C0, 3D0 communicating with a packet data node PDN 10 over a first communication protocol 110. Since the communication system also supports communication of speech and the circuit switched data it comprises a number of mobile switching centers MSC in a conventional manner and of which only one, MSC 50 is illustrated. For reasons of clarity is also only illustrated that MSC 50 communicates with BS:s 3C0, 3D0

#In FIG. 1A a mobile station MS 60 is illustrated which is connected to a digital terminal equipment DTE 70. MS 60 communicates via a radio link with BS 3A0. A second communication protocal 120 is illustrated for communication between PDN 10 and MS 60. Information on mobile subscriber stations is kept in the packet data node 10, which also provides for multiplexing, compression, access control etc. and the second communication protocol is virtual and “holds” packets together sent to/from the same destination. The packet data node 10 also communicates with an external data network such as Internet (IN) 80 via a third communication protocol 130.

#FIG. 1B is a figure similar to that of FIG. 1A relating to the general packet radio service GPRS of the GSM system. The packet data node here comprises a serving GRPS support node SGSN communicating with a number of base station controllers BSC 3A, 3B, 3C each of which in turn communicates with a number of base transceiver stations BTS 4A1, 4A2; 4B1, 4B2, 4B3; 4C1. The SGSN 1 communicates with the BSCs 3A, 3B, 3C via the first communication protocol 11 which here is the base station system GPRS protocol BSSGP. The SGSN is at the same hierarchical level as a mobile switching center MSC, here is only one MSC 5 illustrated, and it keeps track of the locations of individual MSs, performs security functions and access control. The SGSN 1 is connected to the base station system with frame relay. The SGSN 1 is connected to a network node gateway GSN, GGSN 2 which provides interworking with external packet switched networks and it is connected with SGSNs via an IP (Internet Protocol)-based GPRS backbone network. The second communication protocols are here LLC (Logical Link Control) and SNDCP (Subnetwork Dependent Convergence Protocol) 12. The functionalities of SGSN and GGSN may be combined in one and the same physical node or they may reside in different physical nodes as illustrated in FIG. 1B. GTP, the GPRS tunnelling protocol 13 is a protocol between GSN nodes in the GPRS backbone network and it includes both GTP signalling and data transfer procedures. The GTP protocol is described in GSM 09.60, Version 5.0.0, Draft TS 100 960 V 5.0.0 (1998-01) by ETSI (European Telecommunication Standards Institutes) and it is herewith incorporated herein by reference. The general packet radio service GPRS is further described in GSM 03.60, Version 5.2.0 (1997-12), by ETSI and it is also incorporated herein by reference. GSM 04.65, Version 5.1.0, GSM 04.64, Version 5.1.0 and TS GSM 08.18 Version 5.0.0 by ETSI are likewise incorporated herein by reference and among others describe the SNDCP protocol, the logical link control (LLC) layer and the BSSGP.