Chapter 4 Troubleshooting and Diagnostics IPmux-1/1E Installation and Operation Manual
4-28 Frequently Asked Questions
Question: How can I ensure the IPmux TDMoIP traffic priority over an IP Ethernet
network?
Answer
The IPmux family is equipped with three different features that can be
implemented in order to give the IPmux TDMoIP traffic priority over an
IP/Ethernet network:
• VLAN ID (Layer 2)
• ToS field (Layer 3)
• UDP destination port (Layer 4)
Each QoS feature is based on a different OSI level and can be used individually in
order to ensure the TDMoIP traffic priority. When determining which feature to
use, it is important to verify that the different elements on the network, (Switches /
Routers / etc.), support the selected priority mechanism and are also configured to
give the highest priority to the labeled IPmux traffic.
Notice that the priority is given to the TDMoIP traffic by the network elements and
the IPmux is merely tagging the packets.
VLAN ID
The IPmux complies with standards IEEE 802.1p&q. This enables the user to set
both VLAN ID and VLAN Priority. It adds four bytes to the MAC layer (Layer 2) of
the Ethernet frame. These bytes contain information about the VLAN ID, and the
VLAN priority, which runs from 0-7. The IPmux only tags the packets, while the
Switches are responsible for giving the priority according to the VLAN info. Verify
that the IPmux traffic has the highest priority in the relevant Ethernet network.
ToS
There are several RFCs (RFC791, RFC1349, RFC2474) that define how the IP ToS
should be configured. The ToS is a byte located in the IP header (Layer 3).
In general the Type of Service octet, in most cases, consists of three fields:
The first field, labeled "PRECEDENCE", is intended to denote the importance or
priority of the datagram.
The second field, labeled "TOS", denotes how the network should make tradeoffs
between throughput, delay, reliability, and cost.
The last field, labeled "MBZ" (for "must be zero") above, is currently unused.
The IPmux enables configuring the whole IP ToS byte, and therefore it is adaptable
to each RFC in the market. The IP ToS parameter in the IPmux is user-configured
in terms of decimal value. However, on the frame itself it of course appears in
binary format. The decimal value varies between 0 and 255 (8 bits).
A configuration example:
Setting IP precedence of 101 and IP ToS of 1000 will give us the byte 10110000,
which means that the IPmux IP-ToS parameter should be configured to 176
decimals.
UDP Destination Port
The IPmux uses the UDP protocol (Layer 4) in order to transfer the TDMoIP traffic.
In the UDP protocol, the ¿Destination port¿ field is always set to the decimal value