Internetworking | Research & Encyclopedia Articles

Internetworking

Internetworking refers to the science of connecting individual local-area networks (LANs) to create wide-area networks (WANs), and connecting WANs to form even larger WANs. An internetwork is therefore a collection of separate networks connected by intermediate networking devices (such as routers, bridges, and gateways) such that it functions as a single large network. Internetworking is complex because it has to take into consideration the fact that diverse networks use diverse network protocols. Communication needs to be supported across disparate technologies. Different networks could use different types of media or operate at varying speeds. Internetworks need to be able to offer seamless connectivity. Despite the challenges involved, internetworks are becoming increasingly used as they operate at very high speeds and offer broadband support of bandwidth-intensive applications such as voice and video-conferencing.

Internetworking evolved in response to several network problems, including that of isolated LANs, which secluded branch office communications and required the duplication of office and network resources. Hardware, software, and staff needs were frequently replayed at branch offices, while the payback--in terms of shared communications--was non-existent. Finally, no centralized method of managing and troubleshooting networks existed. Corporations with multiple LANs at different office sites ran high overheads to manage each separately. The need for communications via an internetwork was soon recognized as essential, along with the need for reliable service, centralized network support, centralized troubleshooting, and adaptability to change.

The largest example of an internetwork we have currently is the Internet. The Internet is a network created by the interconnection of tens of thousands of data networks worldwide. It grew out of an early internetwork, ARPAnet, created by the United States Defense Advanced Research Projects Agency (DARPA) in the 1960s. ARPAnet started as an internetwork between major universities and defense contractors, primarily for the purpose of research and communications. Fluency across network protocols was quickly recognized as being vital to internetworking. Foundational work in establishing ARPAnet resulted in the development of two fundamental protocols for the transmission of information: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), referred to collectively as TCP/IP.

To understand how protocols interact in a network, it is helpful to understand network communication layers. According to the Open Systems Interconnection (OSI) reference model, developed by the International Organization for Standardization (ISO) in 1984 and now the primary model for inter-computer communications, there are seven layers of network communication:

• Layer 7: Application layer
• Layer 6: Presentation layer
• Layer 5: Session layer
• Layer 4: Transport layer
• Layer 3: Network layer
• Layer 2: Data Link layer
• Layer 1: Physical layer

Communication at each OSI layer is made possible by using communication protocols, which offer rules and conventions for data exchange over a network. Network protocols are part of the suite of communications protocols.

The most fundamental network protocol is the "Internet Protocol" or IP, which defines how data is transmitted from one system to another, and how source and destination points are identified on the Internet. In a network of any kind, and particularly in an internetwork connecting not only computers but whole LANs or WANs, it is important to separately identify each computer by an address, so as to ensure clear transmission to the right destination. Every system on a network has an address. On the Internet, every system has a numeric IP address expressed in a four-number format separated by periods (for example, "132.134.331.1") which corresponds to a domain name such as printinfo.com or gwu.edu. Located at various points on the Internet are systems called Domain Name Servers (DNS) that translate Internet name addresses for hosts (meaning host computers) into the IP address numeric form. Because numeric IP addresses can change for a given location, it is more effective to use the Internet name address rather than the IP address, since name servers are generally kept updated.

IPng or IPv6, short for Internet Protocol Next Generation or Internet Protocol Version 6, is a new version of the Internet Protocol (IP); it was made an Internet Engineering Task Force (IETF) standard in August 1998. (The current version of IP is version 4, referred to as IPv4.) IPng is designed as an evolutionary upgrading of the Internet Protocol, and addresses some of the shortcomings of IP, including the finite addressing scheme. IPng will offer increased IP addresses and is targeted to support the growth of the Internet, both in terms of number of hosts connected and amount of data traffic transmitted.

TCP/IP is the suite of communications protocols used to connect hosts on the Internet, and uses several protocols, the two main ones being TCP and IP. Using IP, data is transmitted in chunks called packets. TCP provides a virtual connection between two systems connected physically, along with guarantees such as retransmission of dropped packets, sequential ordering of packets, and packet content integrity. TCP/IP is built into the UNIX operating system used by the Internet, making it the basic standard for transmitting data over networks.

An important TCP/IP protocol is ARP, short for Address Resolution Protocol. ARP is used to convert an IP address into a physical Data Link Control (DLC) address such as an Ethernet address. There is also Reverse ARP (RARP), which can be used by a computer to discover its own IP address. Basically, computers wishing to obtain a physical address for an IP address or vice versa can broadcast an ARP or RARP request as relevant onto the TCP/IP network. The host-owner of the IP address or an RARP server replies with the requisite physical or IP address.

Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP) are both protocols that allow IP data to be sent over dial-up lines, and they apply in cases where users connect to the Internet through an Internet Service Provider (ISP) by dialing up through a modem. PPP is newer and thought to be better than SLIP, although many Internet providers continue to support SLIP dial-up access. While connected to an ISP using SLIP or PPP, your system becomes one of the locations on the large internetwork of the Internet, with its own IP address.