Asymmetrical Hops; External Connection Speed And Radio Path Capacity - NEC IPASOLINK 400 Installation And Provisioning

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This solution uses a dual-polarized antenna with an integrated Orthomode Transducer (OMT). Four ODUs
can be attached directly to a single antenna without any cables or waveguides between the antenna and
the ODU.
The middle part of Figure 7 shows a 1+1 XPIC solution: it is protected against modem, cable and ODU faults.
A single fault will not affect the traffic capacity. This solution uses a hybrid connection between antenna
and the ODUs to connect two ODUs at a different frequency to the same antenna port.
The last solution with separate IDUs is the most complex but also best protected against equipment
failures. An external Ethernet switch is required at each end for traffic rerouting. Switching or load
balancing can be based on Link Loss Forwarding (LLF) or Link Aggregation Group (LAG). This solution
protects against practically all IDU failures.
XPIC requires the use of dual-polarized antennas. If an XPIC upgrade is anticipated, a dual-polarized
antenna with an integral OMT for two or four ODUs may be installed initially. The unused ports are
protected by blanking plates and gaskets and the empty fixing screw holes should be fitted with a screw,
washer and rubber washer in order to keep the OMT interface clean and ready for ODU and cable
installation later.

ASYMMETRICAL HOPS

Often the two ends of the hop are identical. But it is possible to use a different IDU (e.g. iPasolink 400 or
1000 in the aggregation node and iPasolink 200 or 100 in the remote end). The interface type can be
different (e.g. FE in the remote IDUs, optical GE in the aggregation IDU). Several Ethernet ports may be
used in one end and aggregated to a single port in the other end.
Similarly, it is possible to aggregate n x E1 interfaces of a long chain of links to a single STM-1 interface at
the trunk network node. In other words, the E1 channels of a modem can be cross-connected to the 16 x E1
connector of the main card, to another modem or to a time slot in the STM-1 connection.

EXTERNAL CONNECTION SPEED AND RADIO PATH CAPACITY

The total L1 capacity of the external Ethernet interfaces of an IDU may well exceed the available radio path
capacity. This is normal, of course. The type and speed of the external interface is selected based on the
external requirements. It is the sum of the L2 traffic carried by the interfaces at a given moment (plus the
available buffering capacity in iPasolink) that must fit in the radio channel. Note that iPasolink only
transmits the L2 bytes over the air. Constant L1 overhead bytes are removed and restored by the system
(L1 compression). For this reason the corresponding external L1 speed is always greater than the L2
capacity needed to transmit the information at the air interface (Figure 8).