Glossary P, Q, R


Packets - A formatted unit of data carried over a network which contains both control information (such as error checking and destination address) and user data. 

PDU Power Distribution Unit - A device which distributes electrical power, these can be floor mounted on rack based. Both take high voltage electricity currents and reduce it into lower levels of voltage which have more usages.

PE Sheathed A Polyethylene outer sheath for copper cables meaning that the cables can be used outside as the sheath provides extra protection against outdoor elements as well as moisture and oil protection. 

Pigtail - A short fibre optical cable that has an optical connector on one end and exposed fibre on the other. These are commonly used to splice onto a single fibre in another multi fibre cable to breakout the cable into its fibre components for connection to end equipment. 

Plug and Play - A computing term describing a device which facilitates the discovery of a hardware component without the need for physical configuration or user intervention. 

PoE Power over Ethernet - a system whereby electrical power is passed safely over Ethernet cabling along with data. PoE provides 15.4w of DC power to each device. 

PoE+ - Like PoE but PoE+ provides 25.5w of power to each device. 

Port The exit and entrance point for information going our of and into a computer or other data communications device. 

Port Mirroring - Used on a network switch, Port Mirroring sends a copy of the network packets in use on one port to a network monitoring connection on another switch port. 

Port Trunking See Link Aggregation 

Priority Queues Data packets have differing priorities, in a Priority Queue there are four queues with different priorities levels assigned. Higher priority queues are served first and lower priority queues are only served if or when the high priority queues are empty.  

PSU - Power Supply Unit, the unit by which power is supplied to components. 

Q

Q in Q - An Ethernet networking standard which allows multiple VLAN headers to be inserted into a single frame, a must for metropolitan area networking. 

QoS Quality of Service - A range of resource control mechanisms that aim to guarantee a certain level of network performance or to provide different priorities to applications or users. 

QSFP Quad Small Form-factor Pluggable; a hot-swappable transceiver that supports 4 x GbE, 4GFC Fiberchannel or DDR InfiniBand.

QSFP+ An evoloution of the QSFP standard supporting 4 x 10GbE10GFC Fiberchannel or SDR InfiniBand.  The 4 channels can be combined to deliver 40GbE.

QSFP28 / QSFP100 / 100G QSFP Supports 100GbE and EDR InfiniBand.  Different venddors have abopted different terminology.  Can be broken out to 4x 25Gb ports with MPO/MTP Cable (QSFP28-4xSFP28)

R

RADIUS Server Remote Authentication Dial in User Service - a networking protocol that centralises authentication, authorisation and accounting management for PCs to connect and use a network service. 

Rate Limiting - This is a mechanism that controls the rate of traffic sent or received on a network, traffic that exceeds the set rate is then dropped or limited. 

Return Loss - Also known as reflection loss, meaning a loss of signal power due to a reflection caused by a discontinuity in an optical fibre - the discontinuity may arise from improper termination for example. 

RFI Radio Frequency Interference. See EMI 

RIP Routing Information Protocol - A protocol that automatically creates and maintains network routes, giving protection against failure. 

RIPng Routing Information Protocol Next Generation - RIP that supports IPv6. 

RPS Redundant Power Supply - In the event of main power supply failure to a network device, a redundant power supply is able to power the device thus improving network reliability by decreasing downtime. 

RSTP Rapid Spanning Tree Protocol - A supersession to Spanning Tree Protocol providing faster spanning tree convergences. RSTP has the ability to respond to failures in a few milliseconds or changes in around 6 seconds. 

Ruggedised or Ruggedized Flat Twin - A standard duplex patch cable that with an additional Low Smoke Zero Halogen sheath providing extra durability and stiffness to avoid kinking.

 
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