Verklarende woordenlijst

Broadcasting - (het Engelse woord voor uitzenden) gebruikt om aan te geven dat een datapakket aan alle op het netwerk aangesloten apparaten beschikbaar wordt gemaakt.

Narrowcasting - "Narrowcasting is het leveren van informatie via een interactief netwerk zoals het Internet of Intranet gericht op een bepaald publiek, op een geselecteerde locatie en tijdstip via digitale schermen, op afstand aangestuurd met relevante visuele content". (Narrowcasting Rapport van MyRetail)

Unicasting - het verzenden van een pakket naar één begunstigde.

Multicasting - het verzenden van een pakket naar alle begunstigden die daar interesse voor getoond hebben.

Anycasting - het verzenden van een pakket naar een andere host van een bepaald type, waarbij het niet uitmaakt welke host specifiek de gegevens ontvangt.

IEEE 802 standaard - IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks. More specifically, the IEEE 802

standards are restricted to networks carrying variable-size packets. (By contrast, in cell-based networks data is transmitted in short, uniformly sized units called cells. Isochronous networks, where data is transmitted as a steady stream of octets, or groups of octets, at regular time intervals, are also out of the scope of this standard.) The number 802 was simply the next free number IEEE could assign, though "802" is sometimes associated with the date the first meeting was held - February 1980.The services and protocols specified in IEEE 802 map to the lower two layers (Data Link and Physical) of the seven-layer OSI networking reference model. In fact, IEEE 802 splits the OSI Data Link Layer into two sub-layers named Logical Link Control (LLC) and Media Access Control.

MAC-Adres - MAC staat voor "Media Access Control" en wordt ook wel hardware- adres genoemd. Vrijwel ieder netwerkapparaat heeft een vast, door de fabrikant bepaald MAC-adres.

Het MAC-adres wordt meestal in hexadecimale vorm aangeduid, bijvoorbeeld 00:0C:6E:D2:11:E6. In deze door de IEEE 802-standaard bepaalde nummering (MAC48) zijn er 281.474.976.710.656 (2566) unieke mogelijkheden. In principe dient elk apparaat een uniek MAC-adres te hebben en mogen er geen 2 dezelfde zijn in een netwerk. Dit wordt bereikt door aan elke fabrikant van netwerkapparatuur een verschillend bereik van adressen toe te kennen. De fabrikanten mogen elk adres maar eenmaal gebruiken. (Wikipedia)

Middleware - omvat de systeemsoftware die de informatie-uitwisseling regelt tussen de cliënt-software en de software die de bedrijfsgegevens beheert. De

middleware is een laag software en bevindt zich tussen de toepassingslaag en de communicatie- en besturingssoftware. toepassing

middleware

communicatie- en besturingssoftware

Slotted ALOHA -The Aloha protocol is an OSI layer 2 protocol for LAN networks with broadcast topology.

The first version of the protocol was basic:  If you have data to send, send the data

 If the message collides with another transmission, try resending later

Many people have made a study of the protocol. The critical aspect is the later concept. What is later? The quality of the backoff scheme chosen significantly influences the efficiency of the protocol and the predicatibility of its behavior.

The difference between Aloha and Ethernet on a shared medium is that Ethernet uses CSMA/CD: It uses a jamming signal to notify all computers connected to the channel that a collision occurred, forcing computers on the network to reject their current packet or frame.

Pure Aloha

Pure Aloha had a maximum throughput of about 18.4%. This means that about 81.6% of the total available bandwidth was essentially wasted due to losses from packet collisions. The basic throughput calculation involves the assumption that the aggregate arrival process follows

a Poisson distribution with an average number of arrivals of 2G arrivals per 2X seconds. Therefore, the lambda parameter in the Poisson distribution becomes 2G. The mentioned peak is reached for G = 0.5 resulting in a maximum throughput of 0.184, i.e. 18.4%.

Slotted Aloha

An improvement to the original Aloha protocol was Slotted Aloha, which introduced discrete timeslots and increased the maximum throughput to 36.8%. A station can send only at the beginning of a timeslot, and thus collisions are reduced. In this case, the average number of aggregate arrivals is G arrivals per 2X seconds. This leverages

the lambda parameter to be G. The maximum throughput is reached for G = 1. It should be noted that Aloha's characteristics are still not much different from those experienced today by Wi-Fi, and similar contention-based systems that have no carrier sense capability. There is a certain amount of inherent inefficiency in these systems. For instance 802.11b sees about a 2-4 Mbit/s real throughput with a few stations talking, versus its theoretical maximum of 11 Mbit/s. It is typical to see these types of networks' throughput break down significantly as the number of users and message burstiness increase. For these reasons, applications which need highly deterministic load behavior often use token-passing schemes (such as token ring) instead of contention systems. For instance ARCNET is very popular in embedded applications. Nonetheless, contention based systems also have significant advantages, including ease of management and speed in initial communication.

Because Listen before send (CSMA - Carrier Sense Multiple Access), as used in the Ethernet, works a lot better than Aloha for all cases where all the stations can hear each other, Slotted Aloha is used on low bandwidth tactical Satellite communications networks by the US Military, subscriber based Satellite communications networks, and contactless RFID technologies.