User Manual NTU Orion 2
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Note: Stand Alone and MiniRack devices cannot use an external clock source.
E11, E12, E13 and E14 mean synchronization from one of the input E1 stream. If the stream,
which serves as a clock, is lost, the device switches to another clock according to the priority
level. These clocks should be listed as the second, third, fourth and fifth clocks in the priority list,
if the external clock generator is used. Otherwise, they will serve as primary clock sources and
be listed as the first, second, third, fourth and fifth ones, respectively, in the priority list, if the
external clock generator is absent.
INTERNAL means synchronization from an internal clock source. This clock source should be
the last one in the priority list (but in the absence of other clock sources, for example, when only
Ethernet data are transmitted, this source can be the primary and the only one).
Switching between clock sources occurs within 100 ms, after synchronization is lost.
3.3.2.3 Ethernet interface
FlexDSL Orion 2 devices have an IEEE 802.3 interface to connect local Ethernet networks.
The Ethernet networks use the method for access to the data transmission medium, which is
called carrier-sense-multiply-access with collision detection (CSMA/CD).
Modems and regenerators of the FlexDSL Orion 2 family supports the VLAN protocol (Virtual
Local Area Network – IEEE 802.1Q).
A virtual network represents a group of network nodes, whose traffic, including the broadcast
traffic, is completely isolated from other network nodes.
This means that the frame transmission between different virtual segments by using MAC
address is impossible independent of the type of the address, i.e., unique, group or broadcast
one. At the same time frames are transmitted within the virtual network by using the Ethernet
switching technique. By using the VLAN protocol one can unite the network users into separate
logic groups, for example, in order to decrease the traffic load in the network, to improve the
safety and to simplify management.
Organization of virtual networks allows one to decrease the load in the network, because the
broadcast traffic will be transmitted not to the entire network but to members of the VLAN
sender.
Due to the fact that the members of different VLANs can exchange information via a router,
which allows the traffic to be controlled rather simply, the use of VLANs provides a high level of
security.
In addition, introduction of changes in the network structure is simplified because one should
configure the modem port instead of configuring the work station to which the modem is
connected.
To construct VLAN networks and to provide the priority in the data transmission, an extended
Ethernet frame is used, which contains an additional VLAN tag of length of 2 bytes. The tag
includes the number of the VLAN to which the packet belongs and its priority level.
Some types of traffic should be sent via the network without any delays, for example, real-time
video at video conferences or IP traffic. To provide the necessary quality of this traffic, the
devices support the Ethernet traffic priority according to the IEEE 802.1P protocol, the so-called
QoS (Quality of Service) method. Analyzing the content of the header of the Ethernet frame, the
internal switch obtains information about the necessary priority of this application and places
data to the corresponding queue of the output port. The FlexDSL Orion 2 equipment supports
two priority queues when sending packets – a high priority queue and a low priority queue.
According to it, all Ethernet traffic can be divided into groups of high priority (for example, VoIP
traffic transmission, or control and management channel) and groups of low priority (for
example, LAN1 and LAN2).
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