Autor: Alexander Eichhorn

Networking Infrastructure

Computer networks consist of many interconnected devices (nodes).

They process, store and forward messages hop-by-hop. All networks have in common that they require some sort of physical medium for transmission, be it radio waves or laser light for wireless links, copper or fiber for wired links. By plugging together multiple such links a network can span longer distances and serve up to billions of devices connected through different physical media.

Network Equipment

Computers are equipped with a network interface card (NIC) to access network media. Typical NIC types are WiFi (wireless) and Ethernet (wired) with copper or optical connectors. Normal computers and servers often contain a single NIC although they may utilize more. Every NIC has a world-wide unique 48bit long address (MAC addresse) to identify itself during communication.

Modems are network elements that connect computer networks across physical media that was not designed for digital signals such as telephone or power lines. Modems convert digital signals to analog signals within a defined frequency spectrum of the carrier technoloy and vice versa. Because cable quality is typically very poor the available frequency spectrum is limited and the modulation must be adaptable.

Repeaters and hubs are network elements that filter and amplify electrical signals, reduce noise and relay signals for increased coverage of a network. Repeaters only work on the physical layer. They have mostly been replaced by active switches in wired networks, but wireless networks, in particular mobile wireless networks make heavy use of signal repeaters.

Switches are network devices that forward and filter link layer data packets based on MAC addresses. A switch is able to learn the addresses of connected NICs for each individual port and will forward only packets that are designated for a particular address. This increases the overall network capacity, hiding unrelated traffic from every other host. Enterprise-class switches can be managed and monitored, allowing for bettern quality of service control, security control and even for the definition of virtual overlay LANs (VLAN) without changing the physical topology of cables with is usually fixed in a building.

Routers are devices connecting multiple network segments and forwarding packets between them. For that purpose routers are equipped with at least one NIC per target network. Routers maintain a routing table that defines where packets with a certain destination address are sent. Small edge routers used at home or in small businesses usually support only 2 networks, an internal network and the ISP's upstream network. Core routers operating inside the Internet backbone are much more powerful, supporting 40 - 100 Gbit/s traffic and hundreds of destination networks.

Network Topologies

Local area networks (LAN) connect computers and other networked devices (e.g. printers) in a small geographical area, often a home, a laboratory or an office building. Zero-configuration protocols (DHCP, Bonjour, MDNS) allow connected computers to reach each other without the need for specialized networking equipment. LANs may contain any number of network switches and may use network bridges to attach segments with different link layers (e.g. a WiFi network to a wired Ethernet). LANs can be separated from each other by a router. Likewise, connecting a LAN to the Internet also requires a router.

A Backbone network is a dedicated high-performance network infrastructure that connects multiple LANs across buildings or wider geographical areas. It is typically used inside large organizations to connect departments in a single location or local branch offices across countries.

A wide area network (WAN) is a computer network covering large geographic areas such as cities, countries and continents. Network links in a WAN are typically fiber or optical links leased from large tier 1 or tier 2 carriers. The Internet core itself is a collection of many WANs, so called autonomous systems (AS) which are operated by different carriers such as Internet service providers (ISP) who service last-mile customers, content delivery network operators (CDN) and transit providers (who service only very large customers and ISPs). WANs or autonomous systems are interconnected at public internet exchange points (IPX), for example DE-CIX in Frankfurt (Germany), AMS-IX in Amsterdam, and NYIIX (New York City).

Author: Alexander Eichhorn

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