Specifications

Installation Examples
301
Using Cisco Routers and Catalyst Switches
The Cisco 2600 series routers tested were running Software (C2691-JS-M), Version 12.3(9)
and the Catalyst C3550 Software (C3550-IfQ3L2-M), Version 12.0(20)EA1.
Basic Rules
• To segregate traffic, voice and data devices should be run on separate VLANs
• To transmit VLAN information and Ethernet priority between switches, the inter-switch con-
nections must be defined as VLAN Trunks. We recommend IEEE 802.1Q VLAN trunks.
• Separate VLANs means that voice and data will also be running on separate IP subnets.
• To communicate between two different subnets (and between VLANs) traffic must pass
through a router—same subnet communication does not and stays within its VLAN.
Basic IP Addressing Information
IP addresses can be written in several different ways; the two most common are:
• 192.168.100.1/24
• 192.168.100.1 255.255.255.0
To an end device these are the same - 255.255.255.0 is 24 binary 1s, therefore the /24. It is
binary mathematics on a combination of the IP addresses and subnet mask that defines whether
traffic being sent has to be directed to the router.
Basic Quality of Service (QoS)
In a VoIP network QoS exists at two layers:
1. Layer 2 – Ethernet priority information is used by switches to prioritize voice traffic over
data. It is set using 3 bits within the 802.1Q VLAN header called the 802.1p bits. We
recommend an 802.1p value of 6. However, an alternate value may be used provided that
it is consistent throughout the network and that QoS is set appropriately.
a. If a MiVoice IP Phone learns its VLAN information via CDP and no other priority infor-
mation is set (static or DHCP), then the 802.1p priority defaults to a value of 5.
b. When utilizing Cisco auto-qos, Cisco is expecting an 802.1p value of 5.
2. Layer 3 – IP priority is set using 6 bits within the IP header called Differentiated Services
Code Point (DSCP). DSCP is used by routers to prioritize traffic. The Mitel default value
was 44. This value is programmable to any value. Many IP networks expect a value of 46
- also called Expedited Forwarding (EF). On older ICP software loads the DSCP value may
need to be changed at the first router.
- When utilizing Cisco auto-qos, Cisco is expecting a DSCP value of 46.