Term
| How much DC power is applied when using PoE? |
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Definition
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Term
| What are the two methods for providing PoE to connected devices? |
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Definition
| Cisco Inline Power (ILP), and IEEE 802.3af |
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Term
| How does 802.3af detect if a device needs power? |
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Definition
| It sends a small voltage over the line, and measures the resistance to see if the device is drawing power. |
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Term
| How many classes of power are there in 802.3af? What is the default? |
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Definition
| 5 classes (0-4), default is 0 (15.4W) |
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Term
| How does Cisco ILP detect if a device needs power? |
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Definition
| The switch sends a tone along the line, and since Cisco IP Phones auto-loopback their interfaces when powered off, the switch will 'hear' the tone when it is sent back. |
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Term
| What pins get the power in PoE? |
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Definition
| Both methods send power over pairs 2 and 3 (pins 1,2 and 3,6) but 802.3af can also send on the other pairs (pins 4,5 and 7,8) |
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Term
| What is the best way that a switch can detect power requirements to a phone when running ILP? |
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Definition
| By exchanging CDP information. |
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Term
| When using the command "show inline power" a class of 'n/a' means what? |
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Definition
| That the switch is providing power with ILP, and NOT 802.3af. |
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Term
| What does 'power inline never' do? |
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Definition
| Disables PoE on that port. |
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Term
| How many ports on a Cisco IP phone's internal switch? |
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Definition
| 3! Upload, PC, and phone! |
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Term
| What are the four trunking methods with a Cisco IP Phone? |
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Definition
| VLAN-configured, dot1p, untagged, none. |
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Term
| When using dot1p to trunk a Cisco IP Phone, what VLAN is voice data sent on? |
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Definition
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Term
| What is the only difference if trunking an IP phone with 'untagged' or 'none'? |
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Definition
| Untagged placed the voice/data information on the NATIVE VLAN. None placed the voice/data information on the Access VLAN. |
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Term
| Define Delay, latency, jitter, and loss. |
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Definition
-Delay is the time it takes a device to process data.
-Latency is the total end-to-end delay time.
-Jitter is the variance in end-to-end delay.
-loss is the measure of packets that were not delivered to the destination. |
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Term
| What are the three basic types of QoS? |
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Definition
| Best Effort, Integrated services, and Differentiated services. |
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Term
| QoS must be implemented where on the network to be totally effective? |
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Definition
| on EVERY device that connects sender to receiver. |
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Term
| What is Best-Effort delivery? |
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Definition
| First In First Out, packets are sent in the order that they are received. |
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Term
| What is Integrated Services Delivery? |
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Definition
| Establishing a dedicated path through the network before any data is sent. Think of this as circuit switching over a packet switched network. |
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Term
| What is Differentiated Services Delivery? |
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Definition
| Applying QoS on a per-flow and per-hop basis for all packets. |
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Term
| Layer 2 devices can only utilize what one of the three basic QoS methods? |
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Definition
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Term
| How many bits are used to classify layer 3 traffic when using ToS, and how many when using DSCP? |
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Definition
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Term
| What is the range for IP precedence QoS values, what do they mean, and what is the default Class value? |
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Definition
| 0-7, default is 0 (best effort), 1-4 are Assured Forwarding (AF), 5 is Express Forwarding (EF), and 6-7 are for network information (routing protocols and STP). |
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Term
| What are the three levels of Drop Precedence in DSCP? Which one gives better service? |
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Definition
| Low, Medium, High. Lower is better. |
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Term
| Typically, when should an organization trust QoS parameters, and when should it NOT? |
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Definition
| Trust when it is generated within your own network, and do NOT trust at the boundary with any external organization. |
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Term
| What is a QoS trust boundary? |
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Definition
| The perimeter formed by switches that do NOT trust incoming QoS. |
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Term
| How does the command 'mls qos' affect the way a switch trusts QoS markers? |
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Definition
| Without it, the switch trusts everything. With it, the switch trusts NOTHING! |
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Term
| Using the 'mls qos trust' command what are the tree things that can be trusted? what is generally used on IP phones? |
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Definition
| cos, ip-precedence, or DSCP. cos is used for IP Phones. |
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Term
| At what layer should Auto-QoS be used? |
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Definition
| the access layer, or wherever you have more QoS leveraging services (like IP phones!) |
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Term
| What command will automatically trust QoS information received on a trunk? |
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Definition
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Term
| What are the tree types of Auto-QoS options for voice? |
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Definition
| Cisco-phone, Cisco-softphone, and trust (used for trunks/uplinks!) |
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Term
| If a port is not trusted in QoS, what happens to the voice packet QoS when they hit the switch? |
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Definition
| They are overwritten by the switch! (bad!) |
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