DT Etherlink IV
User Manual
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Table 3.5 Line settings per SHDSL interface, multipair mode.
The next figure shows an example of an Etherlink_IV device working in four-pair operation mode
(the <MULTIPAIR> command is used to configure multipair operation mode). Four SHDSL channels
are combined into one group. Through this multipair channel one E1 stream and Ethernet packets
are transmitted. This mode allows increasing the transmission range, compared to the use of only
one single SHDSL channel, because the data rate of each SHDSL channel is lower (the advantage
in the transmission range will depend on the cable parameters and noise immunity).
SA-RC-ETHERLINK_II_4DSL-4E1-4ETH
G. 703 (E1-1)
G. 703 (E1-1)
ATS
Customer Premises Equipment
Central Office
ETH1
Ethernet
Network
S-Access
Etherlink_II
LTU
ETH1
Ethernet
Network
DSL2
DSL1
ATS
DSL4
DSL3
SA-RC-ETHERLINK_II_4DSL-4E1-4ETH
S-Access
Etherlink_II
LTU
Figure 3.4 Example of four-pair multipair data transmission
3.2.2.1.3 Reservation Mode
Reservation is provisioned for 2- and 4-channel S-Access Etherlink_IV devices. The main task of
reservation is to transmit the most important data even in the case of the failure of one or several
SHDSL connections. Reservation also takes care about an efficient bandwidth usage over all
SHDSL channels like the normal transmission modes.
Reservation will not guarantee a continuous transmission of important data in the case of a failure.
When one or several DSL connections fail, a short-term loss of Ethernet packet and E1 data can
occur.
SHDSL channels with successive numbers (example: DSL-1, DSL-2 or DSL-2, DSL-3, DSL-4) are
merged into a group of channels with reservation. For these merged channels, the traffic in the
SHDSL channels with the lowest numbers has higher priority than the traffic with higher numbers.
For example, DSL-1 has a higher priority than DSL-2, and DSL-2 has a higher priority than DSL-3. If
the communication in one or several SHDSL channels inside the reservation group is broken,
remaining working channels transmit the data of the failed high-priority channels. At any failure the
system always operates as if the low-priority channels failed.
Consider the reservation with two channels: DSL-1 and DSL-2 (DSL-1 has a higher priority
compared to DSL-2). If the DSL-2 channel fails, the DSL-1 channel continues to operate without any
changes. If the DSL-1 channel fails, the DSL- 2 channel transmits the data of the DSL- 1 channel.
Hence, the DSL-1 channel should transmit the high-priority data.
If the substitute channel has a lower transmission capacity than the main channel, the transmitted
data will be decreased. First, the volume of WAN data will be decreased up to 1 timeslot (TS,
64kbit/s), and then, the number of transmitted E1 timeslots will be decreased. If multiple E1 streams
are transmitted, the streams at the end of the list will be decreased (if E1-1, E1-2 are in the list, the
E1-2 stream will be deleted). First, timeslots with large numbers are deleted. However, there is an
exception for TS 16, which, if transmitted, will be deleted before or after TS 0.
