User guide

EDA System Services
54 1/1551-HSC 901 35/3 Uen C 2005-12-02
6.2.3 QoS Implementaion
The Quality of Service functions (mapping and queuing, scheduling) are
implemented in different places in the EDA network in different ways. The
implementation in the aggregation part of the network (switches and
routers) is less demanding since it is expected that the ratio of available
bandwidth compared with the traffic is greater than in the Access nodes
(DSL lines).
In the Access Domain Ethernet the QoS functions are implemented as
described in this section. On the DSL lines, the QoS functions are
implemented based on the ATM native PVCs, or Ethernet like mechanism
in a single PVC, or a combination of both. These mechanisms are further
explained in section 6.3 on page 56.
6.2.4 QoS in IP Based Network Sections
Within routed parts of the network, that is, when EDA traverses an IP
network in order to reach a remote Service Provider’s PoP, differentiated
services is used on the IP level. The principle of the forwarding process of a
router is similar to the process in an Ethernet switch.
Within IP networks various standards for priority tag indication exist, using
DiffServ Code Point (DSCP) fields within the IP header. The tags used to
indicate specific services within these fields also differ from network to
network. Therefore mapping must be performed within the edge nodes in
order to adapt to the priority tags used in the specific network.
6.2.5 Delay Imposed on Telephony over IP
There are two contributors to the delay imposed on voice packets:
• The interacting functions (decoding and encoding of analog
information).
• The network itself, queues in network devices and physical distance (no
matter how fast the connection is, one bit of information has a definite
speed).
Figure 40 on page 55 illustrates the definition of the delays.