Cisco QoS Exam 642-642 Study Guide Chapter 1
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- State the default bandwidth setting for serial interfaces on Cisco routers.
- On serial interfaces, the default bandwidth setting is T1 speed - regardless of the actual bandwidth.
- What are the default units when specifying the bandwidth of an interface?
-
Bandwidth is specified in kbps
ie: "bandwidth 1544" - State the QoS tools that affect Bandwidth directly.
- Compression, CAC (Call Admission Control) and Queuing
- State 8 types of "delay"
- Serialization, Propagation, Queuing, Forwarding / Processing, Shaping, Network, Codec, Compression
- Which types of delay are "fixed"?
- Serialization, Propogation, Codec
- Which types of delay are "variable"?
- Queuing, Forwarding / Processing, Shaping, Network, Compression
- Formula for serializaion delay?
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Serialization delay =
number of bits sent / link speed (in bits per second) - Formula for propagation delay?
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Propagation delay =
Length of Link (meters) / 3.0 x 10^8 meters/sec - Serialization delay is affected by what two variables?
- Link speed and the size of the packet.
- Which QoS tools affect delay?
- Queuing, LFI, Compression, Traffic Shaping
- Which QoS tools affect Jitter?
- Queuing, LFI, Compression, Traffic Shaping
- Which QoS tools affect Loss?
- Random Early Detection, Queuing
- What is the bit rate for voice payload using the G.711 PCM codec?
-
64 kbps
160 bytes payload per packet for 20ms of voice - Excluding layer 2 headers and trailers what is the bit rate for voice payload using the G.726 ADPCM codec?
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32 kbps
80 bytes payload per packet for 20ms of voice - What is the bit rate for voice payload using the G.729 codec?
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8 kbps
20 bytes payload per packet for 20 ms of voice - How to classify H.323/H.225 protocol
- TCP Port 1720
- How to classify H.323/H.245
- TCP port 1720 (Fast Connect)
- How to classify H.323/H.225 RAS
- TCP Port 1719
- How to classify "Skinny" protocol?
- TCP Ports 2000-2002
- How to classify Simple Gateway Control Protocol (SGCP)
- TCP Port 2000-2002
- How to classify Media Gateway Control Protocol (MGCP)
- UDP port 2427, TCP port 2428
- How to classify Intra-Cluster Communications Protocols (ICCP)
- TCP port 8001-8002
- How to classify Real Time Transport Protocol (RTP)
- UDP ports 16384-32767, even ports only
- How to classify Real Time Control Protocol (RTCP)
- UDP ports 16385-32767, odd ports only; uses RTP port + 1
- The actual bandwidth used for a voice payload call depends on what factors?
- Codec, Packet overhead (IP/UDP/RTP), Data-Link Framing, Compression
- ITU Acceptable range of one-way delay for voice?
- 150ms
- Cisco's acceptable range for one-way delay for voice?
- 200ms
- Identify three types of delay unique to voice traffic?
- Codec Delay, Packetization Delay, De-Jitter Buffer Delay
- What is the default initial playout delay in Cisco IOS Gateways?
- 40ms
- Real Time Streaming Protocol Ports
- TCP or UDP port 554
- Cisco recommend that no more than what percentage of a link be reserved for video traffic?
- 33%
- When configuring queuing tools for video you should allocate what percentage more than the average bandwidth to deal with the variability in video traffic flows?
- 20%
- What is the typical video delay budget for high quality video conferencing?
- 200ms
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True or False...
Using RED or video or voice traffic flows is good idea - False
- Three steps for planning and implementing QoS?
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1) Identify traffic
2) Divide traffic into classes
3) Define QoS policies for each class.