ND SatCom SKYWAN IDU 7000, Руководство пользователя

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2010-10-26 Network Design and Engineering Guide 115
Data Networking
SkyWAN
®
Internet Protocol Features
4.2.5 Load Balancing for IP Unicast Traffic
The dynamic load balancing feature helps to equalize the utilization of multiple frequency chan-
nels of a
Sky WAN
®
network. Note that this feature is available for IP unicast only, dynamic load
balancing for IP multicast or frame relay services is not supported.
If an IP destination address is reachable via next hops to which satellite connections with dif-
ferent frequency channels exist, dynamic load balancing makes optimal use of available satel-
lite link capacity by selecting a connection with the least congested frequency channel.
There are two typical scenarios:
-
The next hop is a Sky WAN
®
IDU equipped with two demodulators: both home channels of
this station could be used to forward the packet.
- There are multiple possible routes to the destination with different Sky WAN
®
IDU next
hops, each of them using a different home channel. Also here multiple choices of frequency
channels for the packet forwarding are possible, depending on the selected next hop.
In the latter scenario, there are two possible modes which can be configured on the IDU:
- Equal Cost Multi-Path (ECMP) : Load balancing will only be performed over paths with
identical (minimal) path costs. This mode works for both static routing and OSPF .
- Non Equal Cost Multi-Path: Load balancing will be performed over all paths to a destina-
tion irrespective of the path cost. This mode only works for static routing .
Load balancing is only performed over the satellite link. If there are two alternative paths with
identical cost, one over the Ethernet interface and the other over the satellite interface, the path
over Ethernet will be preferred.
Load balancing is done on the basis of microflows (i.e. IP packet streams having the same IP
source and destination address as well as the same source and destination UDP/TCP port
number) or forwarding aggregates (cf. section IP QoS). Load balancing is supported for up to
64 microflows or forwarding aggregates.
For each new microflow the station will select one of the possible paths. Selection criteria are:
-
For real time IP flows: The channel with the largest amount of unassigned stream capacity
will be selected.
- For non real time IP flows: The channel with the lowest congestion level will be selected.
The congestion levels of each frequency channel are regularly signaled by the master to all
slave stations. Four congestion levels are defined:
-
Congestion level 1: Frame utilization < 50%
- Congestion level 2: Frame utilization 50 - 74%
- Congestion level 3: Frame utilization 75 - 89 %
- Congestion level 4: Frame utilization 90% and more
Since all packets within an IP microflow use the same path the packet sequence will be main-
tained.