Quality of Service (QoS) - Voice, Video, Data Traffic

Where we need Quality-of-Service(QoS) in a Network?

Ans: In Converged Architecture/Unified Communication network where Voice/Video/Data services are implemented.

Converged Architecture 

Converged Architecture - Combination of Multiple Services

Data:

Data Service is an Best Effort Services and it is Insensitive. It using CRC for data integrity check i.e. ACK, REQ, SYN, FIN etc.

Voice and Video:

Real time services, **remember - stored voice & video in computer is data. 

Most important thing for Voice and Video is Quality-of-Experience (QoE) which depends upon three things:

• Delay (Latency)
• Jitter (Inconsistent Delay)
• Drops

Voice

• Real time service, IP phone, analog is converted into digital form or packet form.
• Voice Packets are small (8 Kbytes - 64 kbytes)
• Voice Concealment Program is used
• Drop are allowed in Voice, 1 drop in 10000 voice packets (more than this is not very good QoS)
• Delay is not allowed in Voice, so called Delay Sensitive Communication/Low Latency communication.

Video

• Real time service, High definition (8.5 mb) and Standard Definition (2.5 mb)
• Packets are in form of frames.
• Need Consistency of Video frames
• Frames - I (Index), B (Actual Video) , P (Padding) - Blank screen means I frame is dropped, Glitch means B frame is dropped.
• Drop are not allowed in video, so called as Drop Sensitive Communication. 1 drop in 100000 video packets not more otherwise is not good.
• Delay is allowed, up to 200ms. 

*******IMPORTANT********

If there is a device with input DATA-700 MB, VOICE-64 kb, VIDEO-8 MB and device having 5 MB BW Output, so which packet will go first, then second and last?

ANS: 

1. VOICE because Delay not allowed.
2. VIDEO because Delay is allowed and data goes first then video will go into buffering and if it overload it will drop.
3. DATA because it is insensitive so last.

For this, devices should be capable of Classifying and Prioritization the packet which is called as QoS.

********IMPORTANT********* 

Configuration:

Coming up....

[http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91862-cat3750-qos-config.html

&

http://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/qos_solutions/QoSVoIP/QoSVoIP.html]

★CT21

Reference: https://rstforum.net/ (CCNA training)