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C H A P T E R
4
F E A T U R E S
Notice that all RTs are accessed over the primary route 0:1. This is because in our example, Port 1 of the
chassis is used as the aggregate port in SCADA mode and is connected to the local RT unit. All other units
must be programmed in a similar way (they will of course contain a route to Node 0, our local node) and
then voice calls may be made between any stations.
As with the standard fixed-link mode of operation, destination channels for voice calls may be either
entered as specific channel numbers for hotline operation or left in "AUTO" mode, when the V100
destination channel number is dialled on the telephone. Thus, to place a telephone call to voice channel 3
in Option Card 1 of Node 2 from anywhere in the network, pick up the receiver and dial "213". The routing
menu tells the unit how to reach Node 2 and which destination RT number to transmit to the local RT to
establish the link. Once the link is established, the rest of the dialled number tells the receiving unit which
channel to route the call to.
During placement of the call it is normal to hear a succession of rapid beeps denoting establishment of the
link. This will then be followed by a ringing tone when the connection is made. If the link cannot be
established due to network congestion, the user will hear the normal "busy" tone in the handset.
All of the normal V100 voice channel facilities are still available in SCADA mode and so for example may
be used to connect to PABX extension ports in FXO mode or between PABXs over the 4-wire Tie-line
interface. Group III FAX machines or modems may also be used.
To prevent any unintended call or bandwidth charges, Voice Activation may be utilised.
4.12.2.1
Spanning Tree Protocol
The spanning tree protocol is an implementation of IEEE802.1d. The protocol may be enabled on
individual bridge ports by changing the Bridge mode in the networks menu (see section 3.4.9.2). The
spanning tree protocol is used to detect and prevent loops in bridged networks. If the V100 is bridging in
a network topology that contains loops then the Bridge mode should be set to STP on each port that
makes up part of the looped network - the port takes part in the spanning tree protocol and forwards
bridged traffic when the spanning tree protocol determines the port is in a forwarding state. If the V100 is
bridging in a network topology that does not contain loops then the Bridge mode should be set to On –
the port does not take part in the spanning tree protocol and forwards bridged packets.
The spanning tree protocol operates between the bridges in a looped network, and produces a tree
structure of bridge ports. Ports that would complete network loops are put in a blocking mode and do not
actively forward bridged packets. The tree topology is determined by the relative priority of each bridge in
the network and the relative path cost assigned to bridge hops. The V100 bridge priority can be
configured here in the GENERAL menu. The port priority is set to a default of 128 and cannot be altered.
The relative path cost assigned to each bridge port is calculated as 19 for the Ethernet port and
(1000000000/assigned dba rate) for V100 tributary ports. Note that the spanning tree protocol relies on
the periodic sending of "hello" bridge protocol data packets. When the V100 is determined to be the root
bridge in the spanning tree network, the period of sending these "hello" packets is set to the HELLO TIME
V100 Versatile Multiplexer Technical Manual Version 2.2
Page 169 of 231
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