Adressing scheme to be used in an IP-Based Radio Access Network, corresponding base station and radio network controller

The invention relates notably to an addressing scheme to be used in an IP-based Radio Access Network. According to the invention, the addressing scheme consists in that the radio channel type over which a base station communicates with an end-user radio terminal is univocally determined by a port number value mentioned in each TCP or UDP data packet exchanged over the Radio Access Network and belonging to a communication with the end-user radio terminal.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 has already been described in relation with the technical problem underlying the present invention. UDP will be preferred to TCP in the following as it better suits the delay requirements of a Radio Access Network than TCP. Unlike TCP, UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, UDP doesn't provide retransmission of packets. These specific TCP features badly influence the end-to-end delay in the Radio Access Network. However, the addressing scheme described above could also apply in an IP-based protocol stack using TCP since TCP as UDP use the concept of port numbers. FIG. 2 represents an IP packet exchanged in an IP-based Radio Access Network and illustrates the addressing scheme according to the invention. In the OSI communication model, the IP-based protocol stack relies on encapsulation of a communication unit belonging to a certain layer in a protocol unit belonging to the layer just beneath. IP packet 20 comprises an IP packet header 21 and an IP packet payload 22 . The IP packet payload 22 , in turn, encapsulates an UDP message consisting of an UDP header 23 and of a UDP payload 24 . UDP payload 24 encapsulates a radio part specific message. The header 25 of this message comprises inter alia the reference of the end-user radio terminal to which, respectively from which, this message is destined, respectively received, and the payload 26 of this message contains the end-user data. The reference of the end-user radio terminal consists preferably on an address referencing the end-user radio terminal. This address is unique in the area of the base station to which the end-user radio terminal is attached. The UPD header 23 is, as specified in the IETF standard, divided in four two bytes fields that specify following parameters: the port from which the UPD payload has been issued (source port number SPN); the port to which the UDP payload is destined (destination port number DPN); the UPD payload length L; and a UDP payload checksum CRC. The destination port number is used to demultiplex correctly the IP packet and forward each UPD payload to the application corresponding to the destination port. Usually, the source and destination port are only internally used in a host (e.g. base station or RNC). A pool of port numbers are reserved for concurrent applications performing in parallel an identical task. In usual use of the UDP protocol, the port numbers are thus either randomly allocated to an application when it is activated or according to a round-robin algorithm. This invention consists, contrary to the random port number allocation described above, in managing the pool of available port numbers in a way that each port number is no more only used for internal processing at the host but also conveys an indication regarding the radio channel type over which the data have to be transmitted, respectively the radio channel type from which the data were received. For this matter, the pool of port numbers is divided in several groups of port numbers, each group being exclusively used for processing data to be transmitted or received over one predefined type of radio channel. The pool of port number as well as the assignment of one group of port numbers to one channel type may preferably be the same for each host in the Radio Access Network. A first group of port number should be used for data to be transmitted over a first channel type after protocol translation at the base station. A second group is used for data to be transmitted over a second channel type and so on. Each group should at least comprise one port number. As already mentioned, the exact number of channel types have to be extracted from the radio interface specification of the considered radio communication network. The destination port number in the UDP header is used to make the association port number, channel type to be used on the radio interface. It could also be envisaged to use the source port number in the UDP header to make this association. A choice between the use of the one parameter or of the other parameter has to be made. The dimensioning of the different groups should be done in such a manner that it balances and optimizes the load on each available port number. The mapping between available port numbers and corresponding channel types on the radio interface may be a system parameter initialized at initialization of the Radio Access Network so that each base station or RNC is informed of it. This mapping may, in another embodiment, be dynamically updated according to the needs of the Radio Access Network and communicated to the base stations and the RNC once updated. An Operation and Management Center (OMC) part of the Radio Access Network may for example run statistics on the different traffic flows through the Radio Access Network and determine an optimal mapping between the port numbers and the radio channel types. This update may be done at constant time interval or according to any other update criterion known by a person skilled in the art. The correspondence between port numbers and channel types may be physically stored in a memory location or a database accessible for the base stations and the RNCs of the Radio Access Network. This memory location may be centrally located in the network or distributed in the different hosts. Except the base stations and the RNCs, the other elements of the Radio Access network (e.g. the edge and core routers) pass transparently the destination port number contained in the UDP header without modifying it. In the following, the use of this addressing scheme in an host of the Radio Access Network (base station or RNC) will be discussed in detail. A first part describes the use of the addressing scheme for data coming from the Radio Access Network at a base station and to be transmitted to a radio terminal over the radio interface. The base station identifies thanks to the UPD destination port number on which radio channel type the data have to be transmitted. A field in the UDP payload is also used to give the identifier of the end-user to which these data are destined. This identifier is unique for all end-user radio terminals belonging to one base station. The association of the end-user identifier and the UDP port determines univocally the destination of the message to be transmitted on the air interface. The RNC is also responsible for protocol translation. It receives usually a call identifier from the rest of the radio communication network and has to translate it in a format specific to the Radio Access Network. As a consequence, the call identifier is translated in a triplet comprising the IP address of the base station, the UDP destination port number and the end-user identifier. These parameters as well as the user data are then used to constitute an IP-packet to be sent over the Radio Access Network. A second part, describes the use of this addressing scheme for data received from a radio terminal at a base station and to be transmitted to the Radio Access Network. The base station detects the radio channel type on which these data have been received. It selects an available port number out of the memory location belonging to the group of port numbers assigned to the appropriate channel type. Then, the base station operates the protocol translation consisting in mapping the data format received from the radio channel to an IP packet. The destination port number field in the header of the encapsulated UDP packet is set to the value of the port number retrieved from the memory location. The radio part specific message encapsulated in the UDP packet contains in its header a field specifying an identifier of the end-user radio terminal at the origin of these data. This identifier in combination with the UDP port number is unique in the area of a given base station. At base station, besides the pure protocol translation, shaping and multiplexing of several data flow may be done. As a consequence, the UDP packet may not only encapsulate one radio part specific message but a plurality of multiplexed radio part specific messages belonging to different users but having been received, respectively to be transmitted, on radio channels having the same channel type. Several multiplexed radio part specific messages are called a container. The shaping consists in segmenting each radio part specific message according, for example, to different level of priority assigned to the radio part specific message.