The Internet protocol suite is a set of communication protocols that create the network architecture of the Internet. The Internet protocol suite consists of four abstraction layers, and the Internet layer is an intermediate layer; above it is the application and transport layers, and below it is the link layer. The primary responsibility of the Internet layer is providing a framework where data can be routed across interconnected networks; the internet layer is sometimes referred to, incorrectly, as the network layer. The following protocols are part of the Internet layer; although some are experimental protocols.
The core protocol of the Internet layer is the Internet Protocol (IP). The Internet Protocol (IP) provides a framework for assigning Internet devices with an address (number), and defines the structure of IP datagrams (packet) that enables the datagram to be routed from source to destination. The Internet layer includes two versions of the Internet Protocol (IP): IPv4 (version 4) and IPv6 (version 6). IPv4 defines a 32 bit number and IPv6 defines a 128 bit number; IPv6 was required because IPv4 ran out of numbers (roughly 4 billion), due to the number of host computers connecting to the Internet in the 1990's. The Internet Protocol (IP) Version 4 was designed in the 1970's as a part of the TCP/IP protocol set; as the popularity of TCP/IP grew, and the networks that used TCP/IP interconnected, the overall system of networks was eventually referred to as the Internet (Interconnected IP Networks), and TCP/IP was renamed to the Internet protocol suite.
IPv4 and IPv6 are 'best effort' datagram services, neither guarantees that their data payload will be delivered exactly how it was sent; Internet applications can use the TCP transport protocol, whose data segments are encased into IP datagrams, to reliable send data. The Internet protocol suite uses encapsulation between it's four layers (application > transport > internet > link) a process likened to a a letter envelope being placed into another envelope as it passes down the protocol stack: from application layer to link layer. When transport layer data segments are encapsulated into IP datagrams, IP adds it's own header with an IP address for the source and destination location; without this information the data could not be transported across networks. IP may fragment the datagram into smaller datagrams if the message is too large for the underlying network.
The link layer, situated below the internet layer, is the closest to the physically transmission of data and it's protocols interconnect network hosts and nodes. The Internet layer relies upon the link layer to interconnect hosts and the link layer encapsulates IP datagrams into a frame which is packaged and repackaged into a new frame for each network 'hop' as the IP datagrams weaves it's way from it's source address to it's destination address.