Cirrus Logic Bundle Assignments in CobraNet Systems - Manual (Page 2)

On a switched network, there is no fixed maximum number of Bundles possible. The number will be
determined by the network design. Again, Bundles from 1 to 255 are Multicast Bundles and, since they are
multicast, will usually be sent to every port in the network. It is not suggested to use more than 4 multicast
Bundles in a switched CobraNet
TM network. There are special cases where more could be used, which we
will go into later.
Bundles from 256 to 65,279 are called Unicast Bundles. These are addressed to a single destination unit
and are sent Unicast. A switch will send these channels only out the ports leading to the CobraNet
TM device
they are addressed to. Unlike Multicast Bundles, Unicast Bundles will not be transmitted unless a receiver
is requesting that channel. This allows destination controlled routing, where the receiver selects one of
several possible transmitters to receive, and only the selected transmitter is activated.
It is possible to have far more than 8 total Bundles active on a switched network if most of those channels
are sent unicast using Unicast Bundles. A given port on a Fast Ethernet switch can only send 8 Bundles out
without running out of bandwidth. Those Bundles will consist of every Multicast Bundle on the network,
plus any Unicast Bundle addressed to a CobraNet
TM device connected either directly or through other
switch(s) to this port on the switch.
Some switches have Gigabit Ethernet ports in addition to the Fast Ethernet ports. The Gigabit ports can be
used to transfer data between switches with 10 times the bandwidth of a Fast Ethernet port and can carry
ten times as many Bundles as Fast Ethernet can.
CobraNet
TM over a switched network allows coexistence with ordinary computer data on the same network,
as there are few or no collisions possible. There is the possibility that CobraNet TM traffic on the network
will cause problems for 10 Mbit Network Interface Cards (NICs) used for computer data traffic. Recall that
Multicast Bundles are sent to all nodes in the same network. Since 8 Bundles will fill a Fast Ethernet (100
Mbits) switch port, if that port is connected to a 10 Mbit NIC (most Fast Ethernet switch ports are dual
speed 10/100 ports) then it is easy to see that multicast data from CobraNet
TM can saturate the 10 Mbit NIC
and cause it to drop packets.
There are several possible solutions:
• Use a 100 Mbit NIC. The 100 MBit interface standard is both faster and operates in full duplex
mode.
• Use few, if any, Multicast Bundles.
• Use a Managed Switch. Most managed switches have multicast filtering features. These allow you
to exclude multicast traffic from a specified port. If your data is carried by the Internet protocol
(IP), it is usually safe to filter all multicast traffic except the FF:FF:FF:FF:FF:FF destination
address used by the address resolution protocol (ARP) associated with IP.
• Use separate physical networks for audio and data.
• Uses VLANs. VLANs are supported by most managed switches and allow the creation of
logically separated networks. This provides the benefit of separate networks while using the same
network infrastructure. All traffic in a given VLAN, even multicast traffic, is isolated to only those
ports which are part of the VLAN. You can typically partition multiple VLANs and assign ports to
them as needed. In addition, uplink ports used to connect multiple switches can typically be
configured to route VLAN traffic between switches allowing creation of a VLAN that can span
multiple switches.
• VLANs can also be used in some cases when you need to use more Multicast Bundles than is
allowable on a given CobraNet TM network. By splitting the network into two virtual networks you
have the ability to run twice as many Multicast Bundles.
• Use multi-unicast bundles. Another solution that can be used with some CobraNet TM devices, is
transmitting the same audio information on two, three, or four Unicast Bundles to specific
destinations instead of a single Multicast Bundle. Please note that legacy CobraNet
TM devices may
not have this capability. Some devices can only transmit 2 Bundles, while others can transmit 4.
Bundle Assignments Ap Note Rev. 1.0 ©Copyright 2004 Cirrus Logic, Inc
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