ND SatCom SKYWAN IDU 7000 Manual Download Page 121

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2010-10-26

Network Design and Engineering Guide

117

Data Networking

SkyWAN

Internet Protocol Features

4.2.7

IP Multicast Forwarding

Beside unicast traffic the

Sky

WAN

IDU supports IP multicast services, i.e. traffic flows going

to a group of recipients. The IP address range from 224.0.0.0 to 239.255.255.255 is reserved
for IP multicast services.

IP multicast services packet forwarding may be enabled on a

Sky

WAN

IDU by configuration:

the range from 224.0.0.0 to 224.0.0.255 is reserved for signaling purposes in the local net-
work, hence addresses in this range should not be used for user traffic.

For each multicast IP address which should be forwarded to the LAN interface or the sat-
ellite link an entry in the station’s IP multicast forwarding table must be present.

Up to 128 multicast addresses can be defined per station. For each entry the forwarding
direction has to be defined.

The following options are available:
-

Ethernet to Satellite Link

Satellite Link Demodulator 1 to Ethernet

Satellite Link Demodulator 2 to Ethernet

Bidirectional

For multicast addresses which shall be forwarded to the satellite link the frequency channels
must be defined on which this flow has to be forwarded. Using only one channel optimally ex-
ploits the inherent broadcast functionality of the satellite link. Using multiple channels means
also multiple consumption of capacity on the satellite link. It has to be ensured that the sending
station can allocate sufficient capacity on all channels to perform the packet forwarding on eve-
ry channel.

IGMP Querier Role

Sky

WAN

IDU supports the Internet Group Management Protocol (IGMP) version 2. This al-

lows hosts connected to the local LAN to register for specific multicast addresses. Forwarding
to ethernet can be made dependent on the existence of at least one host which is currently reg-
istered to this multicast address. If more than one IDU is connected to the same LAN, only one
IDU will have the IGMP querier role. Forwarding to the satellite link or the ethernet may be re-
stricted to the IDU having the querier role. Enabling this “querier dependency” prevents poten-
tial duplication of multicast flows, which may happen if more than one IDU would forward the
same multicast flow simultaneously to the same LAN network or satellite carrier.

Standard and FMCA Mode

There are two possible IP multicast operational modes which can be configured on every sta-
tion: “Standard” and “Flexible Multicast Channel Assignment (FMCA)” mode.
-

In standard mode, reception of IP multicast flows on the primary or secondary demodulator
is done on the configured frequency channels home channel One and home channel Two.

In FMCA mode the reception channel for the second demodulator is not fixed by configu-
ration but can be triggered by IGMP requests from hosts connected to the IDU’s LAN. The
following precondition must be fulfilled for FMCA mode:
-

Home channel Two tuning must be set to “automatic”.

Frequency channels used for reception on the secondary demodulator must be re-
served for IP multicast services, i.e. no mixing with IP unicast or frame relay traffic is