Network Technologies DVB-ASI to IP - Manual (Page 92)

ASI-IP-GTW User's Manual
Page 92
12 Appendix F: Quality of service – Setting
Packet priority
Normal IP routing is by best effort. This does not work well for
broadcast television as the video and audio components needs to be
transport as a continuous flow of packets without inference caused by
other traffic over the internet. There are different techniques to secure a
high quality of service. The main ones are:
o
MPLS (Multi Protocol Label Switching)
o
Layer 3 routing priority
o
Layer 2 routing priority
12.1 MPLS
In networks running MPLS, the packets are forwarded along a
predefined path from an ingress router to an egress router. Packet
switching is then done according to the label and packets will be
switched expediently. The MPLS label is added to the IP packet by the
ingress router and removed on the egress router. The labelling is done
on the basis of packet classification.
12.2 Layer 3 Routing
An alternative technique to get QoS is to use layer 3 routing and give
video content packets higher priority than other data. IP packets are
put into queues according to their priority. Packets with high priority
are forwarded expediently and have a lower probability to being
discarded due to buffer overflow.
There are two ways prioritize IP packets called Differentiated services
(Diff-serve) or by the precedence bits (TOS). Both these method use
the same bits in the IP header and both of them are in common use.
IP precedence values range from 0 to 7.
DSCP values range from 0 to 63.
Figure 43 Differentiated services (Diff-serve) or by the precedence bits (TOS )
Layer 3 prioritisation may also be combined with MPLS where layer 3
routing is used in the aggregation network and MPLS in the core
network. The DSCP priority setting may be used for MPLS tagging.