The Local Network (LAN): Types of LAN
Definition of LAN
A local area network (in English, Local Area Network or LAN, which is the term most commonly used by those skilled in the art) is a computer network on a relatively small geographic scale, typically a business location.
It allows to connect all the end devices of the company; It offers high speed to allow fast communication between devices.
It differs from WAN, which connects multiple LANs over long geographic distances, typically on the order of one country. The Internet is often referred to as the largest of the WANs. The speed of the WAN may vary depending on the connection option (DSL or fibre optic) but is generally slower than that of the LAN.
There are two technologies to build the local network of a company:
- Wired LAN based on Ethernet technology;
- Wireless LAN based on WiFi technology.
Ethernet Cabling Categories
The Ethernet standard defines several cabling categories corresponding to data transmission performance over the LAN, which are summarized in the following table.
To meet future requirements, we recommend network cabling at least Category 6 (certified at 1 Gbit / s over 100 m) or even 6A (certified at 10 Gbit / s over 100 m) for each new installation.
The structure of an Ethernet cable
An Ethernet cable consists of 4 pairs of electrical cables. Each pair is twisted on itself to maintain a space between cables and reduce interference problems between conductors (local crosstalk).
Conductors can be single or stranded. The monofilament for the connection cable between the junction boxes and the patch panel (in walls, cable ducts, etc.) should be used more strongly and with more flow and damping properties. Multi-wire cable for patch cords or patch cords is more flexible and easier to use.
To protect against external interference, the cable can have a more or less demanding shielding: shielding the individual sheath with a metal tape and braid; shielding each pair with a strip.
Here are two examples of Ethernet cable construction, the simpler (U / UTP) and the other much more efficient (S / FTP).
Network cabling - a professional matter
The implementation of local network cabling requires the Observance of many installation rules.
The components used (cables, connectors, panels, etc.) must be of high quality and meet the standards to ensure the reliability and performance of the local network: beware of unscrupulous operators who offer lower-cost installations by reducing quality from the local network.
The routing of the connecting cables must be checked so that the radii of curvature are not too small and a minimum distance is maintained from strong currents (power supply); The proximity of radiation interference (fluorescent ballast, etc.) is avoided. The length of a connection cable must not exceed 90 meters.
Cables must be pulled without excessive jerks and without twisting; the fixing of the cables must not force or tighten them (cable ties).
In a shielded installation, it is necessary to ensure the continuity of the shielding between all components (cable, connector, patch panel, conduit) for effective dissipation of interfering noises of external origin (alien crosstalk) and ground connection.
Once the local network is created, the installer must certify it.
This certification consists of carrying out a series of measures with a network certifier (Fluke DTX type) to ensure that the installation complies with the transmission capacities under the quality conditions established by the standard.
You can legitimately doubt the professionalism of a service provider that would not offer you the delivery of a recipe book with explanations of the certification measures.
Wireless Local Area Network (WIFI LAN)
The implementation of a WiFi LAN consists of the provision of access points (radio terminals), the number and properties of which are adequate for the desired coverage and speed objective.
This is a topic that is not trivial and deserves special development; that is why we have dedicated a separate article to it: see the WLAN tab in the workplace.
The Network Layer Model A little preamble is needed to understand the different types of switches.
Telecommunications standards are part of a layer model, of which a very brief description of the first 3 is included:
- The physical layer (level 1) ensures the transmission of bits in the form of an electrical, radioelectric or optical signal;
- The data link layer (layer 2) ensures the transfer of data blocks (frames) between two machines on the same local network. Each of the machines is identified by a unique identifier: the MAC address. Ethernet is the Layer 2 protocol over optical or copper media;
- The network layer (layer 3) specifies the mechanisms for routing (or routing) data traffic from one network to another; it is represented primarily by the Internet Protocol (IP).
- The basic functionality of any switch is to align data frames between connected peripheral devices. This is known as a Layer 2 circuit. This is also the namesake of this device (switching = toggle in English)
The device that performs inter-network routing at Layer 3 is the router.
The simplest switch offers little more functionality than Layer 2 switching.
Devices (desktops, servers, printers, etc.) are connected to the switch ports (connectors) to form the local network: the traffic directed to a specific device is sent in the correct direction, d to the port that corresponds to the recipient's MAC address.
The switch does this in a "self-learning" way: it gradually builds a mapping table between MAC addresses and port numbers. Use this table to determine how the frames are aligned between the ports.
So it doesn't require any configuration - just plug it in so it can detect all addresses on the network and forward the traffic. For this reason, we speak of an "unmanaged" switch.
The characteristics of an unmanaged switch are the number of ports (typically 5, 8, 16, and 24 ports) and the port speed: 100 Mbit / s (Fast Ethernet) or 1 Gbit / s (Gigabit Ethernet).
It can optionally offer a power-saving function.
A managed switch can go beyond simple Layer 2 switching.
Additional features can include many options, such as:
- Security features (enable/disable ports, only allow a MAC address on a port-specific, etc.);
- Management of virtual local area networks (VLAN);
- Quality of service (QoS) management;
In a hierarchical structure of several switches: link aggregation, layer 3 routings.
The following sections describe the two functionalities whose implementation is also more common for networks of "small" companies (a single switch): VLAN management and QoS management.
A VLAN (for Virtual LAN) is a virtual LAN: it is a logical grouping of machines that must form an independent network: only machines belonging to the same VLAN can communicate with each other.
There are several uses for implementing VLANs. One of the applications is when the network infrastructure is based on multiple switches. This makes it possible to configure a logical organization regardless of the physical fabric (the same VLAN can be implemented on any number of switches).
Other applications refer to the separation of data flows according to their typology, either for security reasons or to prioritize certain data flows.
First example: a company provides a WLAN network for its visitors. However, you want to prevent visitors from accessing your internal IT. In this case, we configure WLAN access on a dedicated VLAN so that the resulting network around the company IT is "waterproof".
Second figure: the installation of an IP telephony system & # 40; IP stations that are managed by a Centrex, for example, & # 41; VLANs may be required on the same LAN as the IT system - this enables correct routing of IT and telephony flows and QoS management.
If necessary, communication between VLANs is managed by the router with tightly controlled rules.
Quality of Service (QoS) management consists of managing the priorities in the flow transmissions.
To take the last example, QoS management prioritizes telephony flows (which require real-time transmission to maintain communication quality) from the central office over computer flows (which they can support) without causing any delay).