The following is a basic QoS Policy for a branch office router to prioritize voice traffic . The assumption made is that the voice traffic is marked at source (i.e. ip phones). This is an example of a LLQ (Low Latency Queue) in which voice traffic is placed in a priority queue and all other traffic is placed in a WFQ (Weighted Fair Queue). DMVPN is being used for connectivity back to the main office so we have to use the qos pre-classify command to ensure QoS is applied before data is encrypted and markings on the tunneled packets are preserved. Congestion management and avoidance is implement using a WFQ (Weighted Fair Queue) and WRED (Weighted Random Early Discard) for all non voice traffic.

class-map match-all VOICE
  match ip dscp ef
class-map match-any CALL-SIGNALING
  match ip dscp cs3
class-map match-any CRITICAL-DATA
  match ip dscp cs6
  match ip dscp af21 af22
  match ip dscp cs2

  priority 256
class CALL-SIGNALING
  bandwidth 32
class CRITICAL-DATA
  bandwidth 64
class class-default
  fair-queue
interface Dailer0
bandwidth 1500
service-policy output WAN-EDGE