IEEE 802.1p/Q Utilization Within Cisco TelePresence Networks

When a TelePresence endpoint is configured to utilize a Voice VLAN (VVLAN) (consistent with current best practice recommendations for IP telephony deployments), the switch port to which the endpoint is connected effectively operates as a VLAN trunk. All traffic (voice, video, signaling, and management) received from the primary codec of the TelePresence endpoint includes an IEEE 802.1Q header with the VLAN tag corresponding to the VVLAN number. Likewise, all traffic sent to the primary codec from the Cisco Catalyst access edge switch also includes a VLAN tag corresponding to the VVLAN number. VLAN tagging is also extended to all traffic to and from the associated IP Phone attached to the primary codec of a CTS endpoint. Figure 1 shows an example of this.

 
Figure 1: Voice VLAN tagging of TelePresence traffic

The implementation of the Voice VLAN that includes TelePresence traffic and traditional VoIP traffic can be used to both isolate access to devices on the Voice VLAN and to provide a separate and consistent quality of service (QoS) for all traffic corresponding to the VVLAN across the network infrastructure. Traffic isolation can be accomplished by access control lists (ACL) defined on network infrastructure devices, which restrict access to the VVLAN only to those devices that require such access. Consistent QoS can be provided by trusting the CoS value of ingress frames from the VVVLAN and mapping CoS values to ingress or egress queues for prioritization. CoS values can also be mapped to DSCP values to provide a consistent QoS and prioritization as the TelePresence traffic flows across Layer 3 uplinks that do not use VLAN trunking.

The implementation of a VVLAN for TelePresence deployments is optional. If a VVLAN is not defined on the Cisco Catalyst access edge switch, all traffic to and from the TelePresence endpoint is sent without any IEEE 802.1Q VLAN tags. In such cases, the switch can be configured to trust the DSCP value within the Layer 3 IP header of the TelePresence traffic and then map the DSCP values into appropriate ingress or egress queues for prioritization across the network infrastructure.