CCNP Exam Prep Tips and Must Knows about Voice and Video in Campus Networks


What You Need to Know about Voice and Video in Campus Networks

Components of Unified Communications

  • IP phones
  • Call Agent: Provides call control for IP phones, CAC, bandwidth control and management, and address translation
  • Voice Gateways to PSTN: Provides translation between VoIP and non-VoIP networks
  • Application Server (voice mail)
  • Conference station (voice and video)
  • IP network (router and switches)

Characteristics of Voice and Data


  • Smooth
  • Benign
  • Drop sensitive
  • Delay sensitive
  • UDP priority


  • Smooth or bursty
  • Benign or greedy
  • Drop insensitive
  • Delay insensitive
  • TCP retransmits

 Video Applications

  • Cisco TelePresence
  • IP surveillance
  • Digital media systems

Characteristics of video applications

  • Most are interactive
  • Video contains voice as well
  • Requires a connection with little delay to prevent jitter
  • Requires a high-bandwidth connection depending on the video resolution
  • Peer-to-peer traffic
  • Video endpoints are connected to the access layer

Meeting the Requirements of Voice

  • Provisioning, management, and security – Voice VLAN and DHCP
  • Bandwidth, Delay/Jitter, and Packet Loss – QoS
  • Power – Power over Ethernet (PoE) and UPS
  • Availability – High availability and redundancy

Voice Implementation Steps
Voice VLAN

  • Configure voice VLANs on the access ports
  • Add voice VLANs to the trunks
  • Configure subnets for voice VLANs
  • Configure DHCP for voice subnets
  • Enable routing for voice VLANs


  • Provide PoE on access switches
  • Implement UPS


  • Implement auto QoS for VoIP

High Availability

  • Optimize the topology, routing, and redundancy

Voice VLAN Configuration

  • Switch(config)# interface fa0/4
  • Switch(config-if)# switchport mode access
  • Switch(config-if)# switchport access VLAN 10
  • Switch(config-if)# switchport voice VLAN 110
  • Switch(config-if)# spanning-tree PortFast
  • Switch(config-if)# spanning-tree bpduguard enable
  • Switch(config-if)# cdp enable

Power over Ethernet 802.3af
Two incompatible PoE detection methods

  • Cisco in-line power (2000)
  • IEEE 802.3af standard (2003)
  • TEC supports up to 15.4 W per port

New Cisco devices support both PoE methods

  • Cisco Aironet 1131AG and 1242AG access points
  • Cisco catalyst switches: 3560, 3750, 4500, and 6500 line cards okay
  • Routers with PoE: Cisco 1812 integrated services router, switch modules

Automatic detection is supported; no configuration is required

Test plan for IP phones

  • Does the IP phone receive an IP address?
  • Does the PC behind the IP phone receive an IP address?
  • Does the IP phone register with Cisco Unified Communications Manager or Cisco Unified Communications Manager Express?
  • Can you place a call to another IP phone?

High availability for VoIP and video

  • Traditional telephony networks claim 99.999% uptime
  • Real-time video applications are very sensitive to packet loss and delay
  • Data networks was considered reliability and availability requirements when incorporating voice and video
  • Methods to improve reliability and availability include:
    • Redundant hardware
    • Redundant links
    • UPS
    • Proactive network management

 Building voice, video, and data campus network

Access layer

  • Auto phone detection
  • Power over Ethernet
  • QoS: scheduling, trust boundary, and classification
  • Fast convergence

Distribution layer

  • High availability, redundancy, and fast convergence
  • Policy enforcement
  • QoS: scheduling, trust boundary, and classification


  • High availability, redundancy, and fast convergence
  • QoS: scheduling and trust boundary

 Recommended Practices: QoS

  • Deployed in an end-to-end configuration
  • Ensures mission-critical apps are not impacted by links or transmit queue congestion
  • Enforces QoS policies at aggregation and great transition points
  • Uses multiple queues with configurable admission criteria and scheduling

 Layer 2 Marking: 802.p, CoS

  • The IEEE 802.1P space User Priority Field is also called Class of Service (CoS)
  • Different types of traffic are assigned different CoS values
  • CoS 6 and 7 are reserved for network use

Layer 3 marking: IP Precedence, DSCP


  • The three most significant bits of the ToS byte are all IP precedence
  • Other gifts for unused


  • The six most significant bits of the ToS byte are called Diff Serv code point (DSCP)
  • DSCP is backward compatible with IP precedence
  • The remaining two bits are used for flow control

Voice VLAN configuration

  • Switch(config)# mls qos
  • Switch(config)# interface fastethernet 0/1
  • Switch(config-if)# switchport mode access
  • Switch(config-if)# switchport access vlan 10
  • Switch(config-if)# switchport voice vlan 110
  • Switch(config-if)#mls qos trust cos
  • Switch(config-if)# mls qos trust device cisco-phone

Make sure you can configure:

  • Voice VLAN
  • QoS for voice 

Make sure you are familiar with:

  • show power inline
  • show mls qos interface [fa0/1]
  • auto qos 


  • Trust boundaries for IP telephony
  • Voice implantation plan
  • Voice test plan
  • Voice campus network – implementations at Access, Distribution, and Core
  • Recommendations practices for QoS
  • High availability for voice and video
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