Abstract:
A method of routing a roaming cellular data terminal ( 12 ), for example an M2M device or telephone handset to an APN includes providing a DNS  20  in a roaming network  2  which resolves a FQDN to a local POP remote  22  from the home POP  18  in home network  6.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to British Patent Application No. 1410304.8, filed Jun. 10, 2014, which is hereby incorporated by reference in its entirety. 
     The invention relates to methods of operating a cellular or mobile device and apparatus for implementing the methods. 
     BACKGROUND ART 
     Conventionally, when a cellular modem wishes to access a packet session using for example GPRS, 3G or 4G technology the communication is to a specific network which has an access point, the name of the access point being known as an access point name, APN. This access point name is thus the name of an access point which connects to the packet network. Located at this access point is a Gateway GPRS Support Node, GGSN. 
     The mobile device reaches the appropriate GGSN through a Serving GPRS support node (SGSN) which is responsible for connecting to packet networks for mobile phones in a particular geographic location. 
     The protocols for the naming of these concepts, in particular the APN, are contained in the document 3GPP TS 23.003 V12.0.0 (2013-09). “Technical Specification 3rd Generation Partnership Project—Technical Specification Group Core Network and Terminals—Numbering, addressing and identification (Release 12)”, at www.3gpp.org, which teaches the definition and syntax of a number of concepts as used in such technology. 
     The format of the APN (the name of the network) is as follows. The APN is identified with an APN Operator Identifier, APN-OI, which may be derived from the IMSI as mncMNC.mccMCC.gprs, described by 3GPPTS23.003V12.0.0.0. In this format, “mnc” is a string and MNC is the numeric identifier of the network within a country. Similarly “mcc” is a string and MCC the numeric identifier of the country. An example of an APN OI is mnc058.mcc234.gprs, which is an identifier of the APN (in this case of Manx telecom). This default APN Operatorldentifier is used for roaming situations. 
     For example, using a general packet radio service, GPRS network, the user of the mobile device (or the software in the device) may select as the network the APN name “eseye.com”. This corresponds to a particular GGSN which represents the link to that network. 
     The GGSN is identified by a fully qualified domain name FQDN. The FQDN is made up of the APN name followed by the APN-OI so that the resulting FQDN would in the example be eseye.com.mnc058.mcc234.gprs. This FQDN is transmitted by the mobile device to the local SGSN which looks up “eseye.com.mnc058.mcc234.gprs in a local domain name server. The domain name server returns the IP address of the corresponding GGSN and the SGSN then communicates the relevant data with the required GGSN using the returned IP address. In this way, packets from the mobile phone are routed to the correct GGSN where they are connected onwards to a local network or the internet. 
     SUMMARY OF INVENTION 
     According to the invention, there is provided a method of mobile communication according to claim  1 . 
     By providing a local POP for the APN in some locations, DNS look up of the APN FQDN in domain name servers in those locations may be configured to point to a more local data POP. 
     This approach addresses three disadvantages of simply routing via the home network. When routing via the home network, the roaming partner network in general only has a billing relationship with the home network, so further bills must be generated against each session and issued to the home network. Further costs are incurred as the home network processes billing records to ascribe them to individual accounts. Further, where the devices are using local services, the transit costs can be significant to the local operator. This leads to rounding up of costs. 
     Such rounding can have a serious impact on some machine to machine, M2M, applications since tiny data packets are sent frequently, incurring significant costs. 
     By providing a local APN, billing can be dealt with more conveniently. 
     A bigger issue is the performance of an architecture which routes all data via the home network. Frequently, the data is generated and consumed in the same country, while a home network may be some distance away. If the home network is (for example) manx telecom, and the device is in use in South Africa, the data travels a 30 000 km round trip taking time, consuming network resources and risking data loss or complete failure. 
     By providing a local point of presence, POP, data routing is much less onerous 
     Some applications such as utility meter reading or healthcare applications may be subject to local regulations that do not permit the data to exit the country borders. Conventionally the advantages of a multi-network SIM card, can only be obtained by routing the data back from the network on which it is roaming, to the GGSN hosted by the Home Network. By providing a local point of presence, the data will remain in country and meet all legal requirements. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       Embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawing,  FIG. 1 , which illustrates a schematic of a number of networks according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A plurality of networks  2 ,  4 ,  6  are each provided in respective geographic areas  8  operated by respective network operators. 
     A mobile device  12  has a SIM card  14  provided by a respective network operator or other supplier with a mobile country code, MCC and a mobile network code, MNC. A home GGSN  16  is provided which connects to network  18 , which may in this instance be a private network, but may also be the public internet. The network  6  with the home GGSN is the home network  6 . The home network also contains an SGSN  20  and corresponding domain name server DNS  21 . 
     When the mobile device  12  wishes to make a packet connection to a network it generates a fully qualified domain name, FQDN. The FQDN defines a specific combination of internet address and network operator code. In the particular embodiment, consider the example that the mobile device wishes to connect to the network eseye.com. The FQDN for that APN is made by combining the mobile country code, MCC and the mobile network code, MNC of the home network operator ( 6 ), i.e. the operator supplying the SIM card, for example 234 58 so that the resulting fully qualified domain name FQDN would in this example be eseye.com.mnc058.mcc234.gprs. This defines both “eseye.com” and the corresponding network operator code. As implied by the name FQDN, the FQDN is a domain name and to find out the corresponding IP address of the domain name the domain name is resolved in the DNS. 
     When in the home network, the mobile device simply communicates the FQDN to the local SGSN  20  in home network  6  which resolves the FQDN in its DNS server  21 , discovers the IP address of corresponding home GGSN and connects the mobile device to the GGSN  16 . The GGSN  16  in turn connects to network  18 . 
     Each network  2 ,  4 ,  6  has one or more SGSNs  20  each including a local DNS  21  which operate to look up DNS information for devices operating on the network. These servers may generally provided with conventional DNS information which may be obtained for example from DNS servers on the internet. 
     The embodiment as described to this point is conventional. However, conventionally DNS servers  21  will all resolve the same domain name to the same IP address. 
     In the present case, a GGSN  22  which may also be referred to as a point of presence  22  is provided in a first network  2  corresponding to a respective geographic region. The network  2  may be referred to as a roaming network, since it is not the home network  6  i.e. it is not the network operated by the network operator providing the SIM card  14 . 
     The DNS  21  on that network has a DNS table that is not a simple copy of the global DNS. Instead, the DNS table entry in that network  2  for the FQDN of the home network operator corresponding to the mobile device and APN, for example eseye.com.mnc234.mcc058.gprs, is keyed not to the network address of the home GGSN  16  as in the conventional approach but instead to the local GGSN or POP  22 . 
     It will be appreciated that this is not a normal DNS entry and accordingly the software in the DNS  21  must ensure that normal update rules for updating the DNS are not applied for the specific domain names concerned, i.e. for those domain names that are FQDNs corresponding to networks with a local POP  22 . 
     In this way, when the mobile device operating in network  2  seeks to access the network  18 , it communicates to local SGSN  20  the appropriate FQDN, for example eseye.com.mnc058.mcc234.gprs. The corresponding DNS  21  at network  2  provides the address of GGSN  22  in network  2  so communication is routed from SGSN  20  to the local GGSN  22  and not to the home GGSN  16 . 
     If the mobile device then leaves the geographic area of network  2  and enters the geographic area of network  4 , where there is no local POP for the relevant APN, then the DNS  21  in network  4  simply resolves the FQDN, for example eseye.com.mnc058.mcc234.gprs to the home GGSN  16 . 
     This approach has a number of advantages. 
     The invention proposes that a local GGSN  22  may be provided in some locations, and that the DNS lookup of the FQDN be configured to point to a more local data POP. 
     Consider first the example of a device roaming on a network  2  where the provider already has a POP  22  for a particular APN. A specific example would be a Manx SIM roaming on Safaricom in Kenya. Thus, in this case the home network  6  is the Manx network and the network  2  is the Safaricom network. In this case, an arrangement is made that the DNS lookup for eseye.com.mnc058.mcc234.gprs on DNS server  21  in network  2  does not return the GGSN that routes to the address of the APN in the Isle of Man, but returns a GGSN that routes to the GGSN  22  operated by Eseye in a data centre in Kenya. This has the advantage that the home network  6  is not required to transit the data, and is charging only for providing HLR services whilst the roaming network  2  can charge the APN service provider directly for the data that travels across their network. Thus the application gains the benefits of locally routed data direct data pricing. 
     However, there is a further benefit to the application. Should the device go out of coverage of the partner network  2  described, for example to alternative network  4 , a lookup for the APN in the DNS of network  4  will return the address of the instance of the APN routed via the home network infrastructure, i.e. the address of home GGSN  16 . Thus, in spite of the unusual and non-standard DNS entries, service may be maintained. 
     As a second example, consider a device roaming on a network  4  physically, i.e. geographically, closer to the network  2  where the APN service provider has an POP  22  than the Home Network  6 . In this alternative example, when the roaming Partner network  4  performs a DNS lookup of the FQDN of the APN, the DNS  21  in the SGSN in network  4  returns not the address of the home GGSN  16  in home network  6  which may be many thousand kilometres away, but returns instead the IP address of a more local instance in a nearby country, in the example GGSN  22  in network  2 . 
     A further benefit is that should a particular instance of the GGSN need to be shut down for maintenance, or become overloaded, or even fail, a simple DNS change will allow devices to continue to operate through an alternative instance of the GGSN.