User's Manual

Doc. No.
Rev.
Date
DRAFT
1.01
2012-01-27
Damm Cellular Systems A/S, Denmark
TetraFlex
®
7.5 Manual - IP Backbone network layout and
configuration
TetraFlex® 7.5 Manual 2-157
Activity in the TetraFlex
®
nodes may induce traffic load on the connecting IP backbone
network. This load varies, depending on the type of activity.
2.16.5.1 Group call:
The communication scheme in use for group calls is point to multipoint. As the call type by
nature is one too many – this is comparable to point to multipoint. The BSC with PTT’ing
terminal will generate a stream of data packets.
All nodes with members of the same group as the PTT radio will receive the data stream and
present it on their air interface. The CMoIP stream will be at approximately 12 Kbit/s on the
LAN port of the SB421. After having passed the router the resulting bandwidth will be 22
Kbit/s. The difference is relating to the fact that IPSec and GRE both will add protocol
overhead to the stream.
At the rendezvous point – the data stream will be replicated as applicable – resulting in one
or more data streams leaving the rendezvous router (RP). Amount of outgoing streams from
RP is decided through the IGMP mechanism.
To summarize: at the RP router – there will be one incoming voice stream with bandwidth 22
Kbit/s per active group call (from the PTT BSC). The amount of outgoing bandwidth is
decided through IGMP and is 22 Kbit/s per receiving BSC. The incoming/outgoing pattern will
change according to which node has the PTT activity
2.16.5.2 Full duplex:
Full duplex call is point to point. In TetraFlex
®
it is still transported as multicast. The full
duplex call will generate a bidirectional voice packet stream. So at each BSC relating to the
call there will be 12 Kbit/s outgoing and ingoing. Thus a full duplex call will load the RP with
2*22 Kbit/s in both ingoing and outgoing direction.
2.16.5.3 Half duplex:
Half duplex call is point to point. In TetraFlex
®
it is still transported as multicast. Half duplex
call will generate a voice packet stream where the direction of packets is decided by the PTT
BSC. So a half duplex call will load the RP with 22 Kbit/s ingoing and outgoing.
2.16.5.4 Replication:
The replication of subscribers is done via the signaling group and the replication group. All
active BSCs are listening to the signaling group. When a master register decides to replicate
because of checksum errors or a forced download of subscriber details is initiated through
TetraOM, it results in a data stream from the BSC with the master register to the RP and
outgoing stream from the RP as many as there are BSC’s with faulty slave registers. The
replication is done at a rate of 130 Kbit/s on the LAN – resulting in 158 Kbit/s on the “outside”
port of router. So in a scenario with 10 nodes (1 master register and 9 slaves) this will result
in RP load of 1*158 Kbit/s incoming and 1*158 Kbit/s outgoing if 1 slave register is faulty. If 2
slave registers are faulty the resulting load on RP is 1 ingoing and 2 outgoing streams.
2.16.5.5 Control packets: