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LTP-8X optical line terminal
Chapter 19.
Service Models
This Chapter considers main terms and classification of service models.
Introduction
In general, a service model is based on a method which describes how the services are provided: "VLAN
for Subscriber" or "VLAN for Service". The "VLAN for Service" architecture means that a service VLAN (S-
VLAN) is used to provide all users with a certain service. The "VLAN for Subscriber" architecture, in its
turn, implies that a client VLAN (C-VLAN) is used to provide a user with multiple services. These methods
are often combined in practice and form a hybrid model which uses S-VLAN and C-VLAN simultaneously.
"VLAN for Subscriber" Architecture
A separate VLAN is used for each subscriber in the C-VLAN model. A dedicated C-VLAN is used to provide
services to each user between OLT and service routers. Service GEM ports are created for every OLT
service between ONT and OLT. When a service request is generated upstream, records are added to the
MAC table in OLT according to C-VLAN. In case of downstream traffic, a corresponding GEM port is
determined for a definite service according to the MAC table in OLT.
If destination address of downstream transmission is not known (broadcast or unknown unicast), i. e.
the GEM port can not be determined, two options are available:
— transmission through a dedicated broadcast GEM port;
— transmission to all GEM ports which correspond to the services provided to the subscriber.
The destination address, in case it is unknown (broadcast or unknown unicast), will be determined
based on the method implemented in a definite service model.
The architecture of this service model is shown in Fig. 19.1.
