Common Network Terms
Active Network Components
DIGITUS® Active Network Components –
Cableless with Wireless LAN Technology or conventially via Ethernet
Network topology is understood to be the manner in which individual network components are connected to each other. There many ways of constructing networks. The most frequent form is the star topology. In star topology, all the end devices are connected to a central station, such as a switch or a hub, for example. The cabling is done by making a point to point connection. Larger networks where several star topologies are networked with each other from a tree topology. Cell topology provides a connection without any cables and is used in radio link networks which continue to spread.
OSI Reference Model
The OSI Model, developed by the ISO consists of seven layers and is used as a basis for the understanding of network architectures. Each layer performs a specific task. In communication between two devices, information flows from the application layer accord•ing to each level until it meets the opposite side via the medium, a cable or by radio link, for example to pass though all the levels again until it has arrived at the application level to be processed.
A hub is a distributor in a star-shaped network. It connects the individual stations to each other. The pure relay function is a disadvantage of the hub. Information is always relayed to the stations so that the net load becomes greater and the hub only has a low efficiency.
A switch represents the further development of a hub. Switches distribute data in a network in a selective manner. The information packages are only relayed to the port which is connected to the target that is addressed in the package. The bandwidth of the network segment increases in this way and the package volume is reduced. Switches are categorized with the support of the individual OSI layers. The higher this level is located, the more intensive is the relay energy with the switch requiring more computing capacity. Professional versions offer a multiplicity of options for monitoring and guiding data flow.
Spanning Tree Protocol (STP)
The Spanning Tree Protocol (STP) is a very important function in switching. The network is an integral component in a company and is often secured with multiple connections between switches so create redundancies. Without the spanning tree protocol, these redundancies can cause duplicated data packages leading to faulty functions in the network. The STP provides a hierarchy in the network and automatically recognises redundant paths. Further developments of the protocol consist of the Rapid Spanning Tree Protocol which provides a clear increase in speed and the Multiple Spanning Tree Protocol which also includes virtual networks.
Virtual LAN (VLAN)
A VLAN is a separated, virtual network within a physical network or within the internet. A differentiation is made between port-based VLANs and newer package-based VLANs. They represent a considerable relief in the administration of a network. They also offer many safety aspects.
Quality of Service (QoS)
QoS is the sorting of data packages according to their importance. This technology allows trouble-free processing in a real time application, such as is the case in VoIP telephony, for example. Prioritisation is active if there is a bottleneck in the bandwidth. A guarantee can be made in this way that the quality of the connec•tion will not suffer. The bandwidth of the download is reduced if a download is running at the same time in order to provide sufficient bandwidth.
Simple Network Management Protocol (SNMP)
The SNMP Standard defines a uniform „language” for monitoring a network. An end device supported by SNMP provides information about its status when queried. The nature of this information can be found in a separate database, called the MIB which is delivered by the end device. A trap can also send a message to the monitoring station if a fault occurs.
Remote Monitoring (RMON)
The switch protocols different events, unlike the SNMP standard where only one snapshot of the status of a switch is made respectively. This function is of considerable use in the administration and analysis of a network.
A few professional switches master the technology of port switch•ing. The complete data traffic of a port is duplicated with this function and transmitted to another port where the data traffic is usually analysed. Network administrators value this feature which can be used for effective analysis without disturbing the data flow in a network.
The Store and Forward procedure describes fault control in a switch. An incoming information package is not relayed at the same moment. It is temporarily buffered and analysed. This repre•sents a time delay compared to immediate relay but is, however, a more effective method since faulty packages can be sorted out and directly queried again.
The switch buffer can overflow when there is a large data volume in a network. The flow control function, or also flow control has been developed for this case. A pause package us sent to the subscriber in the network if the buffer of a switch overflows and the data back log can be processed off. This function is used to prevent lost data packages.
Port Trunking describes the option of grouping bandwidths together. Switches with this function can gather several ports together. The connection behaves like a port with a double bandwidth, if two ports are grouped together.
Power over Ethernet (PoE)
This technology allows end devices, such as IP cameras, or VoIP telephones, for example to operated only via one network cable. Only four of the eight strands of a network cable are used during normal network operations in the 100Mbit mode. PoE uses thus state to guarantee energy supply to the individual end devices via the remaining four strands. Complicated and time consuming installations of power supply cables are not necessary. The current standard IEEE 802.3af differentiates between power suppliers (PSE) and end devices (PD). The integrated protection of end devices not supported by PoE is a special feature of this standard. If a short circuit normally showed that the end device is not PoE compatible, a PSE in accordance with the 802.3af standard auto•matically recognises if this is a PoE end device and supplies it with energy if necessary. There are special splitters which can be used for non PoE capable end devices and which separate data and energy supply from each other again in the network cable.