APN (Access Point Name) is a gateway between a GSM, GPRS, 3G or 4G mobile networks and another computer network, frequently the public Internet. APN is used to find the right IP address that the device should be identified with in the network, determine if a private network is needed, and chooses the correct security settings that should be used. Mobile device making a data connection must be configured with an APN to present to the carrier. Carrier then will examine this identifier to determine what type of network connection should be created.
How APN works:
The APN identifies the packet data network (PDN) that a mobile data user wants to communicate with. To identifying a PDN, an APN may also be used to define the type of service that is provided by the PDN. Eg: connection to Wireless Application Protocol (WAP) server, multimedia messaging service (MMS). APN is used in 3GPP data access network such as general packet radio service (GPRS), evolved packet core (EPC).
Structure of an APN:
It consist two parts: Network Identifier and Operator Identifier.
Network Identifier: Defines the external network to which the Gateway GPRS Support Node is connected. It may also include the service requested by the user. This part of APN is mandatory.
Operator identifier: Defines the specific operator's packet domain network in which the GGSN is located. This part of APN is optional.
IPv4 and IPv6 are APN protocol and APN roaming protocol. IPv4 is required to access much of the internet, and should not be disabled. If IPv6 is supported by user's device, then both can be enabled. IPv6 support will be more useful in the future if and when more sites or other services begin to adopt it.
IPv4 allows sending packets (short pieces of information) from one machine to another over a global network using a unique numerical address given to every machine on the network. The length of an address in IPv4 allows for around 4 billion unique addresses, which are assigned by the Internet Assigned Numbers Authority (IANA) to ISPs in various countries. Length of address is 32 bits.
IPv6 was created as a new Internet protocol to address the limits imposed by IPv4. It uses 128 bits long unique address. It is separate and incomplete protocol than IPv4 and allows the possible addresses worldwide from around 4 billion to way more than the numbers of atoms in the human body.
The Different APN Settings:
2) APN Types are generic, supl, mms and wap.
3) MMSC (Multimedia Messaging Service) is needed in case of MMS service.
4) Proxy - This is used to set up a proxy between the network and the internet.
Typically, APN is auto-configured or auto-detected for your phone or tablet. Wireless carriers have different pricing for different APNs. Switching from one to another can change data plan.