Protected Microwave Links – White Paper

Traditional 1+1 radio protection

The basic radio protection scheme is the 1+1. Most radio units offer this option at the radio level. 1+1 in the radio world translates into radio redundancy: Two identical radio units, creating a single radio link with a single leased spectrum. The reason for that is in addition to the net time it takes to repair or replace the faulty unit, one needs to take into account travel time to the site with the correct spare parts and the time it takes a qualified technician to climb and perform the replacement at height. Hence, recovery time may be quite lengthy. In addition, legacy radios suffered from relatively low MTBF. In case of radio unit failure, the hot standby radio kicks in instantly and maintains the service to the site. This should happen within 50Msec to be as non service affecting, as possible. Switchover may also be managed remotely in case of suspected link malfunction, or for routine maintenance procedures. When climbing is logistically complex, costly or time limited, radio planners tend to choose an all-indoor 1+1 configuration to easily reach availability targets.

Ceragon approach for 1+1 radio protection

Traditional 1+1 radio configuration does not include equipment and facility protection, while Ceragon’s product line offers this component. Ceragon system-on-a-chip based radio units with no wire-bonding, enjoy excellent MTBF levels. This level of hardware reliability is comparable to the reliability of indoor units; therefore exceeding availability goals meaning operators can aim for complete indoor unit and line protection capabilities as well. The line protection is achieved by having two ports on two separate indoor units, located either in a single rack or on two different rack units.
To alleviate single point of failure at hubs or aggregation sites, the operators split the connection to the network elements, traditionally to an ADM (Add Drop Multiplexer) in TDM networks or to an Ethernet Bridge/switch/Router for packet networks. This is performed either by using a ‘Y’ cable to split the signal from a single port on the external network element towards the two ports on the indoor unit, or by applying a protection mechanism on the network element such as APS 1+1 or LAG. Thus two cables connect the two assigned ports on the indoor radio with the two assigned ports of the network element. Obviously this simplifies maintenance work allowing unit and cable replacements without affecting traffic.

Migration to Ethernet challenges

The shift from TDM to Ethernet at cell sites brings multiple Ethernet ports at a cell site or any other access nodes where microwave is used for the backhaul. Operators would like to use a simple and low cost Ethernet switch or cell site gateway for local traffic aggregation and service handover. This network element may also handle traffic arriving from other network nodes in a radio chain or ring. In these cases the Ethernet switch becomes a single point of failure. The alternative is to deploy a costly, fully protected Ethernet switch. Ethernet is also more vulnerable to network disruptions as some of the protocols require a relatively long time to converge thus increasing the need for protection. This is exactly where the FibeAir IP-10 integrated and protected networking functions become useful as its 1+1 configuration may also include a license for an integrated Ethernet service protection.

Download full article PDF: Ceragon-1-1-Resilient-Microwave-Links-Technical-Brief