DT Etherlink IV
User Manual
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3.2.2.3.2 Automatic V.54 Loops
The system supports only a local V.54 loop managed by the line 141. The support of the V.54 loops
is software programmable. You can use the command
AUTOLOOP
to adjust automatic loop
reaction: Lines 140 and 142 are not supported by the system.
3.2.2.4 Ethernet Interface
The Ethernet interfaces of all S-Access Etherlink_IV devices fulfil the standard IEEE 802.3 and
support the Port (PBVLAN command) and Tag (VLAN command) based 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. The
organization of virtual networks usually decreases 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 a
controlled traffic, the use of VLAN technology provides a high level of security. In addition, any
changes in the network structure are simplified because instead of configuring the work station to
which the modem is connected you only have to configure the modem port.
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 2 bytes length. The tag includes
the number of the VLAN to which the packet belongs and its priority level.
Some types of traffic (real-time video, voice or IP traffic) should be sent inside the network without
any delays. To provide the necessary quality of this traffic, the Etherlink_IV devices support Ethernet
traffic priority according to the standard protocol IEEE 802.1P (so-called QoS, Quality of Service). It
means to analyze the header content of each Ethernet frame to get information about the necessary
priority of this application. The internal switch places this data to the corresponding queue of the
output port. The Etherlink_IV equipment supports two priority queues when sending packets
– a
high and low priority queue. According to it, all Ethernet traffic can be divided into high priority
groups (for example VoIP traffic or control and management channels) and low priority groups (for
example LAN1 and LAN2).
The Ethernet traffic between all network interfaces of the device is distributed by the internal
Ethernet switch (see next figure). In Etherlink_IV devices four types of network interfaces exist:
Ethernet interfaces (external connector on the front panel, and back plane connector)
SHDSL interfaces (when the device is properly configured)
E1 interfaces (when the device is properly configured)
Virtual management port (Telnet session)
The number of E1 and SHDSL interfaces depends on the model of the Etherlink_IV family. The
choice of the interface (DSL or E1), which will be mapped to the corresponding WAN interface is
performed by the <PAYLOAD> and <WANTS> command.
