Voice and Video Flashcards
source
http://www.coursehero.com/flashcards/430780/CCNP-SWITCH-642-813-Voice-and-Video/
What command will automatically trust QoS information received on a trunk?
mls qos trust cos.
How many ports on a Cisco IP phone’s internal switch?
3! Upload, PC, and phone!
Layer 2 devices can only utilize what one of the three basic QoS methods?
Best Effort Delivery.
When using the command “show inline power” a class of ‘n/a’ means what?
That the switch is providing power with ILP, and NOT 802.3af.
What is Differentiated Services Delivery?
Applying QoS on a per-flow and per-hop basis for all packets.
How does Cisco ILP detect if a device needs power?
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.
How much DC power is applied when using PoE?
48V DC
What is Integrated Services Delivery?
Establishing a dedicated path through the network before any data is sent. Think of this as circuit switching over a packet switched network.
How many classes of power are there in 802.3af? What is the default?
5 classes (0-4), default is 0 (15.4W)
When using dot1p to trunk a Cisco IP Phone, what VLAN is voice data sent on?
VLAN 0
What are the tree types of Auto-QoS options for voice?
Cisco-phone, Cisco-softphone, and trust (used for trunks/uplinks!)
Using the ‘mls qos trust’ command what are the tree things that can be trusted? what is generally used on IP phones?
cos, ip-precedence, or DSCP. cos is used for IP Phones.
If a port is not trusted in QoS, what happens to the voice packet QoS when they hit the switch?
They are overwritten by the switch! (bad!)
How does the command ‘mls qos’ affect the way a switch trusts QoS markers?
Without it, the switch trusts everything. With it, the switch trusts NOTHING!
Typically, when should an organization trust QoS parameters, and when should it NOT?
Trust when it is generated within your own network, and do NOT trust at the boundary with any external organization.
What is the best way that a switch can detect power requirements to a phone when running ILP?
By exchanging CDP information.
At what layer should Auto-QoS be used?
the access layer, or wherever you have more QoS leveraging services (like IP phones!)
What is a QoS trust boundary?
The perimeter formed by switches that do NOT trust incoming QoS.
What does ‘power inline never’ do?
Disables PoE on that port.
How many bits are used to classify layer 3 traffic when using ToS, and how many when using DSCP?
-ToS=3bits-DSCP=6bits
What pins get the power in PoE?
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)
What are the four trunking methods with a Cisco IP Phone?
VLAN-configured, dot1p, untagged, none.
What are the three levels of Drop Precedence in DSCP? Which one gives better service?
Low, Medium, High. Lower is better.
What are the two methods for providing PoE to connected devices?
Cisco Inline Power (ILP), and IEEE 802.3af
What are the three basic types of QoS?
Best Effort, Integrated services, and Differentiated services.
What is the only difference if trunking an IP phone with ‘untagged’ or ‘none’?
Untagged placed the voice/data information on the NATIVE VLAN. None placed the voice/data information on the Access VLAN.
How does 802.3af detect if a device needs power?
It sends a small voltage over the line, and measures the resistance to see if the device is drawing power.
QoS must be implemented where on the network to be totally effective?
on EVERY device that connects sender to receiver.
Define Delay, latency, jitter, and loss.
-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.
What is the range for IP precedence QoS values, what do they mean, and what is the default Class value?
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).
What is Best-Effort delivery?
First In First Out, packets are sent in the order that they are received.
How does a Cisco IP phone connect upstream?
via an 802.1Q trunk or a single VLAN access port
What are the 2 choices for VLANs with IPT?
they must be carried over a voice VLAN (VVID) or over a regular data VLAN (ie. The native VLAN or the PVID)
How is the IPT 802.1 trunk negotiated?
Automatically using DTP and CDP
How does IPT behave when the voice VLAN is in vlan-id mode?
data goes over native vlan, voice goes over specified VLAN, voice QOS is 802.1p
How does IPT behave when the voice VLAN is in dot1p mode?
data goes over native vlan, voice goes over VLAN0, voice QOS is 802.1p
How does IPT behave when the voice VLAN is in untagged mode?
data and voice over native vlan, no QOS but still uses 802.1p trunk
How does IPT behave when the voce VLAN is in the default none mode?
data and voice over native vlan no QOS and no 802.1p trunk
What is latency?
the total delay from start to finish
What is jitter?
variation in delay
What are the three basic types of QOS?
best effort delivery, integrated services model, and differentiated services model
What is best effort delivery QOS?
switches make an effort to move packets as quickly as possible
What is integrated services model QOS?
A path is pre-arranged for priority along the complete path from source to destination using the RSVP protocol.
What is differentiated services model QOS?
Each network device handles packets individually with no advance reservations
What method of QOS does voice traffic use most frequently?
differentiated services
How does an L2 switch do QOS?
an L2 switch can only forward frames best effort unless going across a trunk
How does 802.1q handle COS?
The frame tag includes a 3 bit COS value from 0 (low) to 7 (high). Native vlans are untagged so no COS
How does ISL handle COS?
The frame tag contains a 3 but portion tagged from 0 (low) to 7 (high)
How does L3 QOS classification happen?
The TOS field in the header is used. 2 methods 3 bits or 6 bits
What is DSCP?
Differentiated services code point
How does DSCP handle IP precedence?
5 classes with 3 drop precedences
What is DSCP codepoint EF(46)?
Critical…used most often for IPT
What is DSCP codepoint AF41(34)?
Flash override (class 4)
What is DSCP codepoint AF31(26)?
Flash (class 3)
What is DSCP codepoint AF21(18)?
immediate (class 2)
What is DSCP codepoint AF11(10)?
priority (class 1)
What is a QoS trust boundary?
The point at which a switch decides to trust incoming Qos. Usually at boundary with ISP
How is a QoS trust bondary configured?
Every switch and router in a network must be configured with appropriate QoS features and policies
Where is the QoS trust boundary usually configured on an IP phone?
Usually QoS from VOIP but not PC dataa
What are the 4 steps to extend QoS trust?
1- enable qos, 2-define qos parameters to be trusted, 3-make trust conditional, 4-instruct IP phone how to extnd boundary
For QoS, switch uplinks should always be considered as ____ _____?
trusted ports
How much BW does a PSTN connection use?
63 kbps
How much BW does a voip connection use?
12 kbps with headers and compression
How do Cisco IP phones communicate with the CCM?
with the skinny protocol
What does the skinny protocol do?
transmits keystrokes from phone and commands from CCM
How do IP phones communicate with each other?
Once the CCM gives them the parameters, they use RTP
What is RTP?
Real-time Transport Protocol
Which feature is automatically enabled when a voice VLAN is configured, but not automatically disabled when a voice VLAN is removed?
portfast
What is a *Voice VLAN*?
A Voice VLAN is a VLAN that segregates voice traffic from user data traffic in the same interface. Both the data and voice VLANs must be explicitly configured.
What are the two methods IP Phones can use to learn about the *Voice VLAN*?
IP Phones can use CDP if Cisco IP Phones or DHCP Option 156 for non-Cisco Phones to learn about the Voice VLAN.
What is usually implemented to provide better service for Voice?
QoS is usually implemented to prioritize voice traffic over data.
What configuration command sets up the Voice VLAN on a port?
Switch(config-if)# switchport voice vlan <vlan-id></vlan-id>
What issues does Voice QoS solve?
Voice QoS solves two major issues.
- Predictability for voice traffic
- Jitter and delay
What cannot be solved by *Voice QoS*?
Voice QoS cannot solve issues caused by chronic congestion, as that implies there is a design problem in the network.
What is *Expedited Forwarding*?
Expedited Forwarding is a QoS setting that matches against Voice traffic.
