Abstract:
In a third generation telecommunications network, quality of service can be provided to a mobile in a foreign network by providing a quality of service session divided into a first section from the correspondent node ( 24 ) to the home network ( 50 ) and a second section from the home network ( 50 ) to the mobile node ( 28 ); a quality of service enquiry message is sent through both sections, but a quality of service response message is not returned in the first section until the response message from the second section has been received by the home network ( 50 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims priority of Great Britain Patent Application No. 0020581.5, which was filed on Aug. 21, 2000.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to an improved method of operating a mobile telecommunications network, especially a method of addressing packets destined for a mobile terminal in a foreign network.  
           [0004]    2. Description of Related Art  
           [0005]    In third generation telecommunications networks such as GPRS (General Packet Radio Service) and EDGE (Enhanced Data-rate for GSM Evolution), when a mobile terminal moves into a foreign network, network connectivity is optionally maintained by the use of Mobile Internet Protocol (Mobile IP). In the home network, a Home Agent (HA) is set up which maintains the location information of the mobile by use of Binding Updates, i.e., registration of information sent to the HA by the mobile node.  
           [0006]    Mobile IP has two working modes. The first is illustrated in FIG. 1; a mobile terminal is currently attached as Mobile Node (MN)  14  in a network different from its home network. The MN  14  is communicating with a Correspondent Node (CN)  12 . A Home Agent  16  is set up in the home network by the CN  12 , and a Foreign Agent (FA)  18  is set up in the foreign network. The FA  18  allocates a unique IP address for the visiting mobile, a Care of Address (COA) and this address is sent to the HA  16  in a Binding Update.  
           [0007]    Packets for the mobile are encapsulated by the HA  16  and tunnelled along tunnel  20  to the FA  18  for transmission to MN  14 . In such encapsulation, an extra IP header is added to each packet, including the COA of the MN  14 . This is known as FA-COA working mode.  
           [0008]    In the second working mode (not illustrated) there is no FA, the MN  14  is allocated a unique COA and encapsulated packets are tunnelled by HA  16  directly to MN  14 ; this is known as Colocated Care of Address mode of working (CO-COA).  
           [0009]    In both FA-COA and CO-COA modes of working, the encapsulation generates extra headers, and possibly only small payloads can be used, which results in inefficient transmission and inefficient use of expensive system and network resources, such as radio links. Further, encapsulation hides the flow identification, and the differentiation of classes of services is thus also disabled, so that Quality of Service (QoS) provision mechanisms, such as RSVP (Resource reSerVation Protocol) Int Serve, must be changed.  
           [0010]    The disadvantages of encapsulation can be avoided by the use of Non Encapsulation Mobile IP technique, as set out in the applicant&#39;s co-pending patent application “Non-encapsulation Mobile IP” filed on Feb. 26, 1999 as no. 99301437.2. In this technique, the current COA of the mobile node is used as the destination address, and the original source address, i.e. the CN address, is maintained. For FA-COA working, this deletes a header of length at least 20 bytes and introduces a header of only 2 bytes; for CO-COA mode of working no header is introduced. However a disadvantage is that any firewall or egress filtering in the home network may reject such packets, because they have a source address different from the home network address.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the invention to provide a method of packet addressing which overcomes the disadvantages set out above, and allows QoS to be provided.  
           [0012]    According to the invention, a method of providing quality of service in a third generation mobile telecommunications system, in which packets are addressed to a mobile node which has a correspondent node in a home network and which is currently associated with a foreign network characterized by the steps of :-  
           [0013]    sending a quality of service enquiry message from the correspondent node to the home network;  
           [0014]    sending said quality of service enquiry message from the home network to the mobile node;  
           [0015]    sending a quality of service response message from the mobile node to the home network by the same route as the enquiry message;  
           [0016]    and sending a quality of service response message from the home network to the correspondent node only after receipt of the quality of service response message from the mobile node. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will be described by way of example only with reference to FIGS.  2  to  4  in which:  
         [0018]    [0018]FIG. 2 a  illustrates the invention operating in FA COA mode;  
         [0019]    [0019]FIG. 2 b  illustrates the invention operating in COCOA mode;  
         [0020]    [0020]FIG. 3 a  illustrates a prior art packet header format;  
         [0021]    [0021]FIG. 3 b  illustrates a packet header format according to the invention; and  
         [0022]    [0022]FIG. 4 illustrates a RSVP session. 
     
    
     DETAILED DESCRIPTION  
       [0023]    In FIG. 2 a , which is similar to FIG. 1, a mobile terminal MN  28  has a FA  30 . CN  24  has a HA  26 ; the figure illustrates FA COA mode. In FIG. 2 b , the mode is CO-COA, therefore there is no FA and packets pass directly to MN  28 .  
         [0024]    It will be seen that, in comparison with FIG. 1, FIGS. 2 a  and  2   b  do not have a tunnel from HA  26  towards either FA  30  or MN  28 . This is because in the inventive arrangement the packets are not encapsulated and therefore no tunnel is needed. A suitable name and acronym for the inventive technique is Non-Encapsulation Mobile Internet Protocol, NEMIP.  
         [0025]    In FIG. 3 a , a packet  30  conventionally addressed to a mobile in a foreign network has as source address  32  the IP address of CN  24 ; and as destination address  34  the home address of MN  28 ; FIG. 3 a  also illustrates payload  38  and other fields  36 .  
         [0026]    In FIG. 3 b , in a header according to the invention, the source address  32  is the address of HA  26  and the destination address  34  is the COA of MN  28 . The header contains two new fields,  40 ,  42 , containing respectively identifiers (ID) for CN  24  and MN  28 .  
         [0027]    When the network is operating in FA COA as illustrated in FIG. 2 a , the re-addressed packet is received by the FA  30  and the MN ID  42  is used by the FA to distinguish the different mobile nodes which are simultaneously using that FA, and the packet is routed to MN  28 .  
         [0028]    When the re-addressed packet is received by FA  30  (for FA COA mode), FIG. 2 a ) or by MN  28  (for CO-COA mode, FIG. 2 b ), the CNID  40  is used by the FA or the MN to recover the original source address, i.e. the address of the CN  24 ; the FA  30  or the MN  28  then re-calculates the checksum of the packet, and delivers it to an application.  
         [0029]    Considering now the CNID  40 , this unique identifier is allocated by HA  26  as soon as a packet addressed to the address of mobile is detected. The HA  26  adds an entry to an address mapping table of CNIDs and CNs, which is maintained by HA  26 . Then the HA  26  sends the CNID plus the IP address of the correspondent CN to FA  30  (FA COA mode) or to MN  28  (CO-COA mode); either a registration reply message, or a separate CNID notification message can be used.  
         [0030]    When the CNID is received by FA  30  or by MN  28 , an entry is added to a CNID-to-CN IP address mapping table which is maintained by the FA or MN.  
         [0031]    Information about MNs and MN IDs is similarly exchanged.  
         [0032]    As each packet destined for MN  28  arrives at HA  26 , the HA looks up the CNID and CN address mapping table to find the CNID corresponding to the source address on the packet; the HA then replaces the original source address with the HA address, and the destination address with the COA of MN  28 . The HA  26  adds a CNID field  40  and an MN ID field  42 , adjusts the packet checksum, and dispatches the packet.  
         [0033]    When the packet arrives at the FA  30  or MN  28 , the CNID-to-CN table is looked up and the source address of the HA  26  is replaced by the real address of CN  24 , and the destination address is replaced with the home address of the mobile. For FA COA mode, the MNID-to-MN table is looked up, as explained above. The checksum is adjusted and the packet is delivered to the MN  28  (for FA COA working) or to an application (for CO-COA mode).  
         [0034]    The CNID and MNID formats can be very short and simple, so that the additional fields do not substantially increase the header length.  
         [0035]    The method of packet heading according to the invention for a mobile in a foreign network retains the advantage of shorter headers, and higher payloads, in common with the invention set out in the copending patent application no. 99301437.2 referred to above. Since the HA address is used as the source address, the problems caused during egress filtering by using a source address different from the home network address can be avoided. Since the destination address is changed back before a packet is delivered, an application to which the packet is delivered does not need to be reconfigured, so irritating stops and re-starts of the application are avoided.  
         [0036]    A further advantage is that only the source and destination addresses of the header are changed; all other information is unchanged, including information identifying the traffic flows from the HA  26  to the current COA of MN  28 . It is therefore possible to adopt a standard QoS arrangement, such as RSVP, without modification to provide QoS services to the mobile.  
         [0037]    A QoS session will now be described using RSVP as an example.  
         [0038]    In FIG. 4, the CN  24  and HA  26  are associated with home network  50 , and the MN  28  and FA  30  are associated with a foreign network  52 . The RSVP session is set up as two parts, shown as Section  1  and Section  2  on the Figure; Section  1  operates between the CN  24  and the HA  26 , and Section  2  operates between the HA  26  and MN  28 .  
         [0039]    Section  1  is set up as a normal RSVP session in a non-mobile environment, with a path message sent from CN  24  to HA  26 ; the difference in the inventive arrangement is that the return RESV message from the HA  26  to CN  24  is not initiated until Section  2  has been completed.  
         [0040]    Section  2  covers the MN  28 , and is dynamically adapted as the mobile moves from one network to another.  
         [0041]    When HA  26  receives the PATH message from the CN  28 , with the source and destination address being the CN  24  and the home address of MN  28 , the HA  26  intercepts the packet and modifies or regenerates a PATH message via an RSVP proxy server by re-addressing the packet as described above. The packet passes through a number of nodes or network routers, and two routers,  54 ,  56  are illustrated. The PATH message is an end-to-end message. The proxy server can be attached to HA  26  or it can be a separate entity.  
         [0042]    In foreign network  52 , a foreign proxy server or its equivalent in the MN  28  or FA  30 , depending on the working mode, prepares a RESV message with the COA address of MN  28  as the source address and the HA&#39;s destination address; the message contains flow identification information such as protocol ID as well as source/destination port numbers, and is dispatched. The RESV message is routed hop-by-hop through the same servers  54 ,  56  as the PATH message, but in the reverse direction; the source and destination addresses for each hop are changed appropriately by the routers  54 ,  56 .  
         [0043]    When the RESV message is received by HA  26 , or an equivalent such as a home network proxy server, the RESV message is modified or re-generated with the home address of MN  28  as source address and the CN  24  as destination address; i.e. Section  2  is completed. The RESV message of Section  1  is now sent in conventional manner.  
         [0044]    When the CN  24  or the home network proxy server receives the RESV message, a RESV confirmation message can, if requested, be sent to confirm the whole RSVP session.  
         [0045]    When the mode of working is FA COA, to guarantee flow-specific identity, and this class of service differentiation, for Section  2  of the RSVP session, Port Clash avoidance control is necessary; this can be achieved by any conventional method.