Q-Flex Satellite Modem Installation and Operating Handbook
6-62
When VLAN filtering is disabled, V
LAN tags are not generated or removed by the
modem. This means that no filtering of traffic based on VLAN ID takes place. Since each
remote modem receives the same broadcast traffic, a device such as a router must be
present to filter out any traffic that is intended only for the other remote modems.
When VLAN filtering is enabled, each remote modem can be assigned a VLAN id which
is used by the hub to tag each packet destined for any device attached to a network off
that particular remote modem. The tags
are added by the hub Tx modem and removed
by the remote modem. The remote modem uses the tag to filter out unwanted data that
has been broadcast indiscriminately to all remote modems.
Setting a value for the VLAN ID is required for remote modems only. Ass
ID to a hub modem has no effect. The VLAN ID should be used to uniquely identify each
remote modem. It is used to filter wanted from unwanted IP packets in point-to-
systems where there is a direct return path. The VLAN IDs of remot
automatically learnt by the hub Tx modem and all traffic destined for a particular remote
modem will be tagged at the hub. The VLAN tags are removed by the remote modems
prior to onward transmission.
6.2.3.6 Null Packet Insertion
Off When using the ASI or IP terrestrial interfaces with MPEG2
transport stream packets, any MPEG2 null packets within the
incoming terrestrial data stream will be left untouched (and will
therefore be transmitted over satellite) when null packet insertion
is set to Off.
On When null packet insertion is set to On, any MPEG2 null packets
within the data stream will be stripped out and discarded. Since
null packets contain no useful data then discarding them can save
bandwidth.
Strip & Insert The strip and insert option strips all MPEG2 null packets from the
incoming terrestrial data stream. It also inserts MPEG2 null
packets into the stream of packets transmitted to satellite in such a
way as to match exactly the required transmit symbol rate in the
event that there are less packets than required to fill the satellite
pipe.
Table 6-64 Null Packet Insertion
6.2.3.7 PCR Restamping
PCR restamping is an On/Off control that controls whether MPEG2 Program Clock
Reference (PCR) timestamps in received MPEG2 transport stream packets (via the ASI
or IP interfaces) are adjusted for any delay introduced by the modem. By adjusting the
To Next Page
Loading...