Voice Desk Port Audit — TechKnowSurge

About this interactive

A desk with a Cisco IP phone and a PC needs one wall jack and one switch port: the PC plugs into the phone, which is a small switch. That port is an access port in the data VLAN with a voice VLAN added. The switch tells the phone the voice VLAN over CDP, and the phone tags its own frames with it; the PC's frames pass through untagged and land in the data VLAN. Voice gets its own VLAN so calls, which break up past about 150 ms of delay, can be prioritized: at Layer 2 by the class of service (CoS), 3 bits in the 802.1Q tag, and at Layer 3 by the DSCP value in the IP header. This audit gives you a technician's write-up of one such desk to check line by line: the desk, the switch port and the priority marks. Some lines are wrong; find each one. Lines that look odd may still be right, so check every one. After you submit, every wrong line is shown with what is wrong and the fix.

What you'll learn

Check a desk port that serves an IP phone with a PC behind it: one wall jack and one access port per desk, the PC's untagged frames in the data VLAN and the phone's tagged frames in the voice VLAN
Find the faults in such a write-up: a port count, a port role, the VLAN a frame lands in, or a priority mark put at the wrong layer

Aligned to

Cisco CCNA

2.1 Configure and verify VLANs (normal range) spanning multiple switches

4.7 Explain the forwarding per-hop behavior (PHB) for QoS

Key terms

Voice VLAN: A VLAN dedicated to IP telephony traffic, configured on an access port alongside a data VLAN. The switch instructs the attached IP phone via CDP or LLDP-MED to tag its voice frames with the voice VLAN ID, while an attached PC's untagged frames remain in the data VLAN.
Access Port: A switch port that belongs to a single data VLAN and sends and receives untagged frames, used for connecting end devices such as PCs and printers. An access port may additionally carry a tagged voice VLAN for an IP phone without becoming a trunk.
Trunk Port: A switch port that carries traffic for multiple VLANs over a single link by tagging frames with their VLAN ID, used between switches or between a switch and a router. All VLANs are tagged except the native VLAN.
Cisco Discovery Protocol: A Cisco proprietary Layer 2 protocol that allows Cisco devices to discover and share information about directly connected Cisco neighbors, including device type, IP address, and interface details. CDP operates independently of Layer 3 protocols and is used for network topology mapping and troubleshooting.
Class of Service: A Layer 2 QoS mechanism that uses the 3-bit Priority Code Point field in an IEEE 802.1Q VLAN tag to classify and prioritize network traffic into up to eight service classes. CoS markings are used by switches to apply differential queuing and forwarding treatment.
Differentiated Services Code Point: A 6-bit value in the IP header's Type of Service field used to mark packets for differentiated forwarding treatment in a DiffServ network. Routers read the DSCP marking to apply the appropriate queuing, scheduling, and drop policy.

Topics

Voice Vlan Access Port Ip Phones Class Of Service Interactive Spot The Error

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