Acer ISDN 128 Surf USB Bedienungsanleitung Seite 7

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3 Quality of Service (QoS)
We said many times that VoIP applications require a real-time data streaming cause we
expect an interactive data voice exchange. Unfortunately, TCP/IP cannot guarantee this kind of
purpose, it just make a "best effort" to do it. So we need to introduce tricks and policies that
could manage the packet flow in EVERY router we cross. So here are:
TOS field in IP protocol [3] to describe type of service: high values indicate low
urgency while more and more low values bring us more and more real-time urgency
Queuing packets methods:
o FIFO (First in First Out), the more stupid method that allows passing
packets in arrive order.
o WFQ (Weighted Fair Queuing), consisting in a fair passing of packets (for
example, FTP cannot consume all available bandwidth), depending on kind
of data flow, typically one packet for UDP and one for TCP in a fair fashion.
o CQ (Custom Queuing), users can decide priority.
o PQ (Priority Queuing), there is a number (typically 4) of queues with a
priority level each one: first, packets in the first queue are sent, then (when
first queue is empty) starts sending from the second one and so on.
o CB-WFQ (Class Based Weighted Fair Queuing), like WFQ but, in addition,
we have classes concept (up to 64) and the bandwidth value associated for
each one.
Shaping capability, that allows to limit the source to a fixed bandwidth in:
o download
o upload
Congestion Avoidance, like RED (Random Early Detection).
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