Definitions and Concepts

  • Definitions and Concepts

    Access line speed – refers to the maximum achievable download speed over the physical communications line into a house. Access line speed is not the same as broadband speed; which refers to the speed of the broadband service delivered over the physical access line into a house.

    Busy hours – typically 7.00 pm to 11.00 pm

    Buffers are primarily used for very temporary storage of data in transit between other media. Buffers in video clients are designed to be long enough (e.g. minutes) to hold enough data to allow smooth playout of the video without interruptions.

    Congestion occurs when total data traffic demands on a network link exceed its capacity. Initially that results in queueing delay, and sometimes packet loss. End to end internet protocols such as TCP respond to the extra queueing delay or packet loss by reducing the speed of the data connections sharing that link so that their total speed can be carried within the available capacity.

    Contention – Contention occurs when more than one user has data queued for transmission across a shared network element.

    Intermediate network links are shared transmission lines that connect two or more routers. The link capacity must be adequate to carry the total downloads required by all users with acceptable slowing in the busy hours (ie 7.00 to 10.00 pm).

    Latency refers to delays incurred in the processing of network data, or how long it takes for a packet of data to travel across a network. There is a difference between the inherent latency in the end to end path and the latency that is caused by the internet protocols under packet loss or congestion. The underlying latency is generally not high enough to slow data throughput from local servers, and the measured latency under congestion is the result of the internet protocol’s response to congestion.

    For example, the inherent transmission latency involved in accessing a site in the USA will always have some impact on your internet download speed.

    nbn: nbn co ltd. is the corporation building and operating the nbn™ network, which is the network itself.

    Packet loss occurs when some packets never make it to the receiver. If the lost packets cannot be retransmitted in time by internet protocols, packet loss can cause missing sounds, syllables, words or phrases in voice or streaming video services. Packet loss is normally low on most services except ADSL and VDSL (which is the technology underlying FTTN); for those services short, sudden episodes of interference causes line errors that result in dropped packets.  Packet loss can also increase under network congestion as the latency of packets increases and buffers reach capacity. Those packet losses are a signal to the end-to-end internet TCP protocol to slow down further so that all flows match the available capacity.

    Real-time protocols like VoIP are more susceptible to packet loss than traditional network data applications, due to the inability to wait for retransmission of missing data.   Streaming video services such as Netflix are designed to cope with packet loss, by using TCP retransmissions and using very large receiver buffers (e.g. 1 minute) to allow plenty of time to wait for retransmissions of lost packets and to smooth out some fluctuations in available speed.

    TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP. The TCP part controls packet loss by ordering retransmissions of lost packets and controls transmission speed by slowing flows when packets are delayed or lost in transit.