Page 43 - ITU-T Focus Group Digital Financial Services – Consumer Experience and Protection

ITU-T Focus Group Digital Financial Services
Consumer Experience and Protection

Conversational class

The most well-known use of this scheme is telephony (e.g. over GSM). But with Internet and multimedia a
number of new applications will require this scheme, for example voice over IP and video conferencing tools.
Real time conversation is always performed between peers (or groups) of live (human) end-users. This is the
only scheme where the required characteristics are strictly given by human perception.

Real time conversation scheme is characterised by that the transfer time shall be low because of the
conversational nature of the scheme and at the same time that the time relation (variation) between information
entities of the stream shall be preserved in the same way as for real time streams. The maximum transfer delay
is given by the human perception of video and audio conversation. Therefore the limit for acceptable transfer
delay is very strict, as failure to provide low enough transfer delay will result in unacceptable lack of quality.
The transfer delay requirement is therefore both significantly lower and more stringent than the round trip
delay of the interactive traffic case.

Real time conversation - fundamental characteristics for QoS:

– preserve time relation (variation) between information entities of the stream;
– Conversational pattern (stringent and low delay).
Streaming class

When the user is looking at (listening to) real time video (audio) the scheme of real time streams applies. The
real time data flow is always aiming at a live (human) destination. It is a one way transport. This scheme is
characterised by the fact that the time relations (variation) between information entities (i.e. samples, packets)
within a flow shall be preserved, although it does not have any requirements on low transfer delay.
The delay variation of the end-to-end flow shall be limited, to preserve the time relation (variation) between
information entities of the stream. But as the stream normally is time aligned at the receiving end (in the user
equipment), the highest acceptable delay variation over the transmission media is given by the capability of
the time alignment function of the application. Acceptable delay variation is thus much greater than the delay
variation given by the limits of human perception.

Real time streams - fundamental characteristics for QoS:
– preserve time relation (variation) between information entities of the stream.

NOTE: This shall also be true for data communication even if not in the real time class. In packet data, higher
protocol levels (TCP and upwards) guarantees this time relation. Preservation of order is not directly linked
to low latency.
Interactive class

When the end-user, that is either a machine or a human, is on line requesting data from remote equipment
(e.g. a server), this scheme applies. Examples of human interaction with the remote equipment are: web
browsing, data base retrieval, server access. Examples of machines Interaction with remote equipment are:
polling for measurement records and automatic data base enquiries (tele-machines).

Interactive traffic is the other classical data communication scheme that on an overall level is characterised
by the request response pattern of the end-user. At the message destination there is an entity expecting the
message (response) within a certain time. Round trip delay time is therefore one of the key attributes. Another
characteristic is that the content of the packets shall be transparently transferred.
Interactive traffic - fundamental characteristics for QoS:

– request response pattern;
– preserve payload content.

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