GB2462939A

GB2462939A - Email communications system having a secondary wireless link with static IP addresses

Info

Publication number: GB2462939A
Application number: GB0915155A
Authority: GB
Inventors: David Richard Gardner
Original assignee: Datel Solutions Ltd
Current assignee: Datel Solutions Ltd
Priority date: 2008-09-01
Filing date: 2009-09-01
Publication date: 2010-03-03
Anticipated expiration: 2029-09-01
Also published as: GB2462939B; GB0915155D0; WO2010023330A1; GB2463047A; GB0815777D0

Abstract

Networks having an internal email server (33) commonly have a secondary wireless connection (39) to the internet in case the primary connection (36), e.g. ADSL, fails. However, emails cannot be sent to the email server through the wireless connection from emails servers (33A) outside the network because the wireless connection is not associated with a public routable static IP address which can be given to the domain name system (38). The present invention provides the wireless link (39) to the access point (APN, 41) with a private static IP address (IP7), the static IP address being associated with a public static IP address (IP7P), and configures the APN to route data received through the public static IP address to the private static IP address and visa-versa.

Description

An Email Communications System The following invention is of particular relevance to local networks which use an internal mail server.

Fig 1 illustrates a schematic representation of a prior art email communication system having a local network 1 comprising a number of personal computers 2 and an internal email server (mail transfer agent) 3 linked through a computer networking device 4.

Commonly networks like that shown at 1 are connected to the internet to allow access to the worldwide web and enable emails to be sent and received to/from computers located outside the local network.

Connection to the internet may be provided via a wired link such as a Digital Subscriber Line (DSL and typically an Asymmetric DSL) 6 to an internet service provider (ISP) 7. Data is sent from and received by the network 1 through a DSL transceiver 5. Connection 6 is assigned a unique routable static IP address by ISP 7.

By virtue of this, email server 3 has a corresponding IP address. A domain name server DNS 8, holds a number of records associated with the domain name including, a record of the domain name of the network 1 and the associated lIP address of the email server 3 (Address A' Record), and a second record comprising the domain name of the network and the host name of the email server 3 (MX record). Each MX record also contains an indication of the priority of the server relative to any other servers which receive mail for the domain. Commonly a domain name is served by multiple mail servers, the additional servers acting as backups in case the primary server fails. Where there are multiple servers, the DNS keeps an A' record and a MX record for each server. The DNS 8 may be held by the ISP 7 or by a 3' party.

Emails received from a PC 2 which are addressed to another PC 2 in the same network 1 can be handled internally within the network 1 by the internal email server 3. When the server 3 receives an email from a PC 2 addressed to a domain which is not served by the internal email server 3, e.g. to a computer 2A outside of the network 1, the server 3 needs to obtain the IP address used to reach the email server 3A which will accept emails for that specific domain. To achieve this, the email server 3 queries the local domain name server 8. The DNS 8 subsequently returns (usually after querying through the domain name system other local and higher DNS5) the IP address (from the A record) and the host name (from the MX record) of the email server 3A which will accept emails for the specific domain. Using this information the email server 3 then tries to establish a connection with the mail server 3A and, if successful, sends the email using simple mail transfer protocol (SMTP).

In order for the internal email server 3 to be able to receive emails sent from outside the network 1, it is generally necessary for the IP address of the network's transceiver 5 to the internet to be static. By static it is meant that the transceiver 5 is assigned the same address each time it is initiated. It is also necessary that the local DNS 8 holds the MX record and A' record for the email server 3 (and any additional servers) so that queries for the IP address of domain's email server 3 can be resolved.

As a safeguard against the sending of unsolicited mail, the DNS 8 will often conduct a procedure referred to as a reverse DNS lookup'. For each email sever 3, the DNS 8 also holds a third record (pointer record; PTR) which holds an P address and a corresponding domain name (similar to the A' record but in reverse). When a reverse DNS lookup is performed, the DNS 8 obtains the IP address of the connection from which the query was made and the domain name from which the query purports to come, retrieves the appropriate PTR record and checks the domain name in the record against the domain from which the query is purported to come. A match indicates that the query is from a genuine source and the DNS 8 will answer the query.

In order to provide a continued internet connection during a disruption of the DSL line 6, it is possible to provide a second, wireless connection 9. To effect this the network 1 is provided with a wireless transceiver 10 which communicates via a base station through wireless operator 11 to an access point (APN) 1 1A which provides access to the internet. The APN 1 1A is usually provided by the network operator 11.

Both the DSL and wireless transceivers 5, 10 may be contained within a single unit and are commonly sold commercially incorporated with other hardware/software such as firewalls as ADSL/3G routers. Suitable routers are available under names "Billion," a trade mark of Billion Electric Co., Ltd and "Draytek," a registered trade mark of DrayTek Corp..

The wireless connection 9 between the wireless transceiver 10 and the network operator 11 is assigned by the operator 11 a dynamic IP address (IP1). By dynamic it is meant that a new (and usually different) IP address is assigned to the connection 9 each time it is initiated. A dynamic address may also change at intervals when the connection is refreshed. IP 1 is a private address meaning that it is only recognised within the operator's 11 network. When a computer 2 wishes to access information from the internet, e.g. a webpage, a query to the webpage address is sent through connection 9 to the APN 1 1A who relays the request through a gateway IP address 1P2 to the webpage address. 1P2 is a public address. The gateway address IP2is associated with the IP address IP 1 of connection 9 by the APN upon establishment of connection 9 with the APN 1 1A. Because the APN 1 1A is usually shared by many connections 9, the gateway address 1P2 is assigned dynamically and it is common for multiple connections 9 to share the same gateway address TP2. APN 1 1A acts to route the request to the appropriate websever via the gateway connection address 1P2. The response, e.g. a webpage document, is received back by the APN 1 1A about the gateway address 1P2 and is routed on via connection 9. In order to ensure data received through gateway address 1P2 is correctly directed to transceiver 10, the APN 1 1A has a register holding a record for each connection 9 made to it. This record associates the IP address (IP1) of connection 9 with the assigned gateway IP address (1P2). A record is generated each time connection 9 is established. The record will usually also hold additional information e.g. port number which allows effective routing where multiple connections share the same gateway address.

A mechanism may also be put in place to automatically initiate the wireless connection 9 on sensing that the DSL connection 6 has failed.

The above described system, however, does not allow the effective sending and receiving of emails when the network's connection to the internet is via the wireless link9.

When, through connection 9, the email server 3 makes a query to the DNS 8 for the relevant information of an email server for a domain, a reverse DNS lookup will indicate that the IP address from which the query has come is not the same as that held its PTR record, and will therefore refuse to provide the necessary MX' or A' records preventing the email from being sent.

It is not possible for the appropriate TP address(es) to be given to the DNS 8 or for an email server 3A to communicate with email server 3 via connection 9 through the gateway IP for multiple reasons, including that: the gateway IP address is unlikely to be known and is likely to change, the ANP 11 is likely to use the same gateway address for multiple connections, connection 9 has a private address and so will be known and is also dynamic so will change each time a connection is established.

Certain wireless internet providers provide SIMs having mobile subscriber identities which are recognised by the network as being associated with a specific private static IP address. These are typically used for making machine to machine connections via virtual private networks (VPNs). Though any \/PN created will still need to be initiated by the device having the private static address as the address is not routable.

An example in which a device having private static IP has been made routable is illustrated schematically in Fig 2. A series of closed circuit cameras 20A, 20B, 20C are adapted to communicate wirelessly via a 3G/GPRS network and the internet to a control centre 22. The cameras 20A, 20B, 20C communicate to an APN 21 through connections 23, 24, 25, each connection being assigned a static private IP address 1P3, 1P4, 1P5 by virtue of the transceiver associated with each camera being provided with a STM of the type mentioned above. The APN 21 is configured to associate with each connection 23, 24, 25 a unique public static IP address (gateway address) IP3P, IP4P, TP5P each time the relevant connection 23, 24, 25 is established. These associations are held in a register 21A. When control 22 wishes to instruct a specific camera, say camera 20A, it sends a request (which may a request to set up a vpn or the instructions themselves) to the appropriate gateway IP address in this case IP3P, the request is directed to the APN 21 which uses the register 21 A to obtain the relevant private IP address, in this case 1P3, and routes the request via connection 23 to camera 20A.

The present invention was devised with the intention to enable email to be sent and received when the primary connection is disrupted or cut off According to the invention there is provided An email communications system comprising a network having a domain name, an email server and a first and a second connection to the internet, the first and second connections having respective first and second public routable static IP addresses; the email communications system comprising a domain name server which can be queried by the email server via either first or second connections to the internet, the domain name server holding the addresses of the two connections, and an indication of the priority for each of the connections; and that the domain name server is such that, upon being queried for an address for use to send an email to the email server, it selects and returns the first and/or second routable static IP addresses; characterised in that the second connection is formed at least in part by a wireless link between the network and an APN the wireless link being assigned a private static IP address; and that the APN is adapted to route an email sent to the second public routable IP address to the email server via the wireless connection.

By assigning the email server with two public routable static IP addresses through either the first connection or second wireless connection, emails can be still be sent to the email server in the advent that one of the connections is interrupted or fails.

By holding an indication of the priority, it enables emails to be preferably directed through the first connection unless it becomes interrupted, whereby emails will then be sent via the second connection.

Additionally the system may also comprise a router which switches between connections in response to a loss of one connection.

The invention will now be described by way of example with reference to Figure 3.

Figure 3 illustrates a local network 31 having a number of personal computer 32 and an email server 33 linked through networking device 34. The email server 33 is adapted to receive and send emails to and from a domain having a registered domain name. The network 31 is connected to the internet via TSP 37 through an ADSL connection 36 by transceiver 35. The ADSL connection 36 is provided with a first public routable static IP address 1P6.

A second auxiliary connection 39 is provided through a wireless, e.g. GPRS or 3G, network (though not necessarily with handover capabilities) via router/wireless transceiver 40. The wireless transceiver 40 is provided with a SIM holding a mobile subscriber identity recognised by the network infrastructure as being associated with a specific static IP address 1P7. Examples of such SIMs can be obtained from Vodafone� of Vodafone House, The Connection, Newbury, Berkshire, RG14 2FN, England (other providers are available) and are compatible with most wireless routers, including 3G routers. Using firmware held on the SIM/transceiver 40 the transceiver 40 is configured to communicate through the GPRS/3G network to an APN41.

The APN 41 is configured to associate IP address 1P7 of connection 39 with a unique gateway address IP7P. This gateway address is a public static address. The APN 41 is configured to assign the same gateway address to connection 39 each time connection 39 is established. The APN 41 acts as a network address translator (NAT) between 1P7 and IP7P, i.e. routes any information sent to it from connection 9 having IP address TP7 to/towards its final destination through gateway address IP7P and similarly route any information received through IP7P to the wireless link having IP7P i.e. transceiver about connection 9.

A DNS 38 holds two A' records, a first of the hostname of email server 31 and IP address of connection 36, a second A' record holding an alternative hostname of email server 33 and IP address IP7P. The DNS 38 also holds two MX records, each holding a hostname for the email server 33 associated with each of the A' records, and a priority indication. The priorities are chosen such that the DNS 38 will preferentially provide information for connection 36 over 39. The DNS 38 also holds two PTR records corresponding to the two A' records.

When email server 33 wishes to send an email to an email server 33A outside of network 31, the email server 33 queries DNS 38 via either connection 36 or 39.

When queried through connection 39, the query passes to APN 41 which, noting that that the query derives from address 1P7, routes the query to the DNS 38 from the gateway address IP7P. Because DNS 8 holds a PTR naming IP7P it will serve the query. The DNS 38 sends the A and MX records back to IP7P. The APN 41 identifies that the records are addressed to IP7P and from register 41 A identifies the corresponding address as 1P7 and routes the records via connection 39.

When connection 36 is unavailable and email server 33A (on behalf of personal computer 32A) wishes to send an email to email server 33, the local DNS 38 returns the A' and MX' records associated with gateway IP address TP7P. Email server 3A sends an email to address IP7P, the email is received by the APN 41 which routes the email through connection 39 to the transceiver 40.

With the above example it is necessary to reserve a gateway address for connection 39 even when the connection is not active. This may be a problem when the number of gateway addresses is limited. A solution to this is to provide connection 39 with a dynamic gateway address and to use a dynamic DNS. Upon the establishment of connection 39 and assignment of a dynamic gateway address, the APN 41 notifies the dynamic DNS which updates its A', MX' and PTR' accordingly with the new gateway address.

The functions and configuration of the APN 41 as described above can be obtained using a combination of hardware and software using methods known to those skilled in the art.

The services provided by a dynamic DNS are obtainable through ZoneEdit � Inc., P.O.Box 821067, Vancouver, WA 98682 (owned by Dotstar Inc.).

The system could also contain other modifications, i.e. firewalls and mail relays.

The ADSL connection 36 may be replaced by any other type connection including other DSL connections, dial-up, cable, fibre optic or wireless.

Claims

Claims 1. An email communications system comprising a network having a domain name, an email server and a first and a second connection to the internet, the first and second connections having respective first and second public routable static IP addresses; the email communications system comprising a domain name server which can be queried by the email server via either first or second connections to the internet, the domain name server holding the addresses of the two connections, and an indication of the priority for each of the connections; and that the domain name server is such that, upon being queried for an address for use to send an email to the email server, it selects and returns the first and/or second routable static TP addresses; characterised in that the second connection is formed at least in part by a wireless link between the network and an APN the wireless link being assigned a private static IP address; and that the APN is adapted to route an email sent to the second public routable IP address to the email server via the wireless connection.
2. An email communications system according to claim 1 wherein the domain name server selects in preference the address corresponding to the first connection to the internet.
3. An email communications system according to any previous claim wherein the network comprises a router which switches between connections in response to a loss of one connection.
4. An email communications system substantially as described above or illustrated in Figure 3.
5. A network setup for use in a communication system according to Claim 1.

-10 -
6. An email communications system comprising a network having a domain name, an email exchange server and a first connection to the internet the communication being characterised by: a) a second, wireless connection to the internet, the first and second connections having respective first and second public static IP addresses; b) a register holding the addresses of the two connections for the domain name; and c) means for selecting one of the addresses and sending an email addressed to the exchange server via the selected address.
7. An email communications system comprising a network having a domain name, an email server and a first connection to the internet, the email communications system characterised by: a second, wireless connection to the internet, the first and second connections having respective first and second public routable static IP addresses; a domain name server which can communicate with the email server through either the first or second connections to the internet, the domain name server having a register holding the addresses of the two connections, and an indication of the priority for each of the connections; and the domain name server having means, upon being queried for an address for use to send an email to the email server, to select and return one of the addresses held in the register based on the indication of priority of the connections.Amendments to the claims have been filed as follows: 1. An email communications system comprising a network having a domain name, an email server and a first and a second connection to the internet, the first and second connections having respective first and second public routable static IP addresses; the email communications system comprising a domain name server which can be queried by the email server via either first or second connections to the internet, the domain name server holding the addresses of the two connections, and an indication of the priority for each of the connections; and the domain name server is such that, upon being queried for an address for use to send an email to the email server, it selects and returns the first and/or second routable static P addresses; characterised in that the second connection is formed at least in part by a wireless link between the network and an APN the wireless link being assigned a private static IP address and that the APN is adapted to route an email sent to the second public routable IP address to the email server Q via the wireless connection.2. An email communications system according to claim 1 wherein the domain name server selects in preference the address corresponding to the first connection to the internet.3. An email communications system according to any previous claim wherein the network comprises a router which switches between connections in response to a loss of one connection.4. An email communications system as hereinbefore described with reference to Figure 3.5. A network according to Claim 1.6. An email communications system comprising a network having a domain name, an email exchange server and a first connection to the internet the communication being characterised by: a) a second, wireless connection to the internet, the first and second connections having respective first and second public static IP addresses; b) a register holding the addresses of the two connections for the domain name; and c) means for selecting one of the addresses and sending an email addressed to the exchange server via the selected address.7. An email communications system comprising a network having a domain name, an email server and a first connection to the internet, the email communications system characterised by: a second, wireless connection to the internet, the first and second connections having respective first and second public routable static IP addresses; a domain name server which can communicate with the email server through either the first or second connections to the internet, the domain name server having a register holding the addresses of the two connections, and an indication of the priority for each of the connections; and the domain name server having means, upon being queried for an address for use to send an email to the email server, to select and return one of the addresses held in the register based on the indication of priority of the connections.