User's Manual

ALFOplus 24GHz (North America) - Release 01.05.0x - MN.00395.E - 004 59
ing from SIAE equipment and Hello-Packets’s loss (i.e. the high priority traffic is still transported while the
Best Effort traffic is cut). For this reason, the ACM functioning in presence of Ethernet ring protection could
generate disruptions into services because of the small amount of capacity passing across radio links af-
fected by propagation phenomena.
A key point to consider is the duration of an event that can result in a change of modulation: it ranges from
few minutes to tens of minutes. The effect of a single event lasting from milliseconds to few seconds (mul-
tipath phenomena) is already operated by the QoS management of the Microwave radio, in order to not
lose the priority traffic, while the slower phenomena must be handled by traffic re-routing.
The following therefore applies only to the phenomena longer than tens of seconds. In detail, consider the
following scenario:
Fig.25
In the network scenario shown above:
• in each site it has been connected a CISCO router to SIAE radio through LAN ports
• each microwave link is supposed to work with the ACM enabled: it’s worth to notice that the ACM
feature could be useful to optimise the antenna’s dimensioning by distinguishing between “High Pri-
ority Services” (i.e. the traffic to be guaranteed with an availability required by the customer) and
the “Best Effort Services” (i.e. the traffic to be discarded by the equipment in case of bad propaga-
tion conditions. The capacity reserved for these services depends on the maximum modulation
achievable by the equipment)
Basing on the above network scenario, on one branch, the cell sites A and B aren’t affected by atmospheric
phenomena and the mobile network operates at full services (from highest to lowest priority services). On
the other branch, for a given time interval, the radio link between the core network and the cell site C is
affected by heavy rain, resulting in capacity degradation. Since there is no balancing in the ring of traffic
priorities between branches, only the “surviving” mobile services are available in the affected branch.
The solution to this behaviour is the MW Adaptive Bandwidth (MAB) feature developed by SIAE and Cisco,
which allows for traffic forwarding on the Ethernet ring in accordance with the available bandwidth for each
priority in the two ring branches. In other words, using dynamic traffic engineering, you can optimize the
allocation of class of services in the whole ring. The feature is based on a protocol by which:
• the Microwave radio notifies the changes in link capacity to the Ethernet switch or router that it is
connected to, which in turn applies the relevant forwarding rules
• the notifications take place by means of OAM (Ethernet-Operations, Administration and Mainte-
nance) type messages which signal the changes in the band availability (BW-VSM messages)
• through the management (transmission and reception) of these messages and the proper configu-
ration of the forwarding rules, the ring will be able to change the traffic profile to take the degraded
path in consideration.
SIAE
radio
Cisco
ASR
SIAE
radio
SIAE
radio
Cisco
ASR
SIAE
radio
SIAE
radio
SIAE
radio
SIAE
radio
SIAE
radio
SIAE
radio
SIAE
radio
Cell site A
Cell site C
Cell site B
Core network
Ge Interface Radio link
Normal path
Degraded path
1