User guide

Telephony and Multimedia Services
78 1/1551-HSC 901 35/3 Uen C 2005-12-02
8.4 Telephony Deployment in EDA
Whether base band POTS or Telephony over IP should be used to provide
telephony services depends on the specific EDA deployment scenario.
Both applications are capable of providing first line telephony, that is, they
can provide reliable telephony with the range of services supplied by
existing POTS telephony implementations.
Telephony over IP provides a number of independent phone lines on a
single local loop, emulated on the ADSL link in order to provide derived
telephony services. Telephony over IP may consequently be used to supply
additional lines to customers, either alone or in combination with base band
POTS. In the latter case more lines per subscriber can be supported, one
as base band POTS more as Telephony over IP, (the number depends on
the IAD used).
8.5 Broadcast Handling
Within the Ethernet parts of the EDA network special attention must be paid
to the amount of broadcast traffic generated.
Basically, Ethernets are broadcast networks. In principle, a frame
transmitted from one unit may reach the ports of all other units. The
learning switches used in EDA limits the amount of broadcast traffic.
However, broadcast traffic cannot be totally prevented.
Especially in networks with links of different capacity there is a risk of
overloading the low capacity links. What appears to be just a few percent of
overhead on a Gigabit Ethernet link may impose a heavy load on a link with
less bandwidth.
In EDA, the IP DSLAMs act as ARP proxies and as filters, thereby
preventing broadcast traffic originated in the Central Office parts of the
Ethernet Access Domain from reaching the ADSL line. Only traffic destined
for known addresses is allowed.
EDA also provides an opportunity to divide the physical Ethernet into virtual
sections distinguished by VLAN ID’s. Thereby the broadcast traffic can be
isolated and limited to the amount of traffic generated within each VLAN.