User guide

EDA System Design
1/1551-HSC 901 35/3 Uen C 2005-12-02
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All VLANs solutions except for the three VLANs scenario (Management,
Data and Voice) have one drawback: each IP DSLAM and each top-level
switch must be configured manually. The PEM does not support automatic
configuration of VLANs, other than the three mentioned above, which are
the default for the IP DSLAMs. The top-level switches have to be
configured under all circumstances.
The various VLAN scenarios offer different levels of security. If VLANs are
used to separate different services or service providers it is natural to
define also a VLAN for management traffic. Still, the IP DSLAM filter must
be used if layer-2 separation is required.
Layer-2 separation is achieved automatically when VLANs are assigned to
individual subscribers, because traffic from one VLAN must pass an IP
router (the Edge Node) to reach another VLAN.
10.3.4 Service Selection by Using Domain Subnets
VLAN divides the Access Domain in separated layer-2 domains. It is
possible to associate a specific service or Service Provider with each layer-
2 domain. It is also possible to perform a layer-3 separation of the Access
Domain, and associate different Service Providers with each domain, by
splitting the Access Domain into different subnets. Each subnet has a
default gateway managed by a specific Access Provider. Different subnets
may use the same default gateway.
EDA subscribers are always assigned to a subnet (and a default gateway)
together with an IP address. Each EDA subnet may include one or more
subscribers, depending on its size. Assigning individual subnets per
subscriber is straightforward but can have some drawbacks regarding
efficient use of IP addresses. Consequently, a typical requirement to
address assignment is to have multiple subscribers share an IP subnet.
In order to provide layer-2 separation it is possible to use Forced
Forwarding in the IP DSLAM. This ensures that subscribers within the
same IP subnet cannot access each other directly on layer-2, but are
forced via the default gateway.
Forced forwarding requires the use of a single destination (the default
gateway) for upstream traffic. Thus, if Forced Forwarding is used together
with Telephony over IP, the voice traffic must go through IP router acting as
default gateway before it is passed on to the Voice Gateway.
10.3.5 Service Selection using LAN-to-LAN Transparency
LAN-to-LAN transparency enables the Service Broker to offer connections
by use of VLANs without any filtering in the IP DSLAM. The connection is