Cisco 300-101 Pass4sure Questions

300-101 Question 4

Which three problems result from application mixing of UDP and TCP streams within a network with no QoS? (Choose three.)


A. starvation
B. jitter
C. latency
D. windowing
E. lower throughpu


Correct Answer: A,C,E
Explanation/Reference:
It is a general best practice not to mix TCP-based traffic with UDP-based traffic (especially streaming video) within a single  service provider class due to the behaviors of these protocols during periods of congestion. Specifically, TCP transmitters will throttle-back flows when drops h ave been detected. Although some UDP applications have application-level windowing, flow control, and retransmission capabilities, most UDP transmitters are com pletely oblivious to drops and thus never lower transmission rates due to dropping. When TCP flows are combined with UDP flows in a single service provider class a nd the class experiences congestion, then TCP flows will continually lower their rates, potentially giving up their bandwidth to drop-oblivious UDP flow s. This effect is called TCP-starvation/ UDP-dominance. This can increase latency and lower the overall throughput.
TCP-starvation/UDP-dominance likely occurs if (TCP-based) mission-critical data is assigned to the same service provider class  as (UDP-based) streaming video and the class experiences sustained congestion. Even if WRED is enabled on the service provider class, the same behavior would  be observed, as WRED (for the most part) only affects TCP-based flows. Granted, it is not always possible to separate TCP-based flows from UDP-based flows, b ut it is beneficial to be aware of this behavior when making such application-mixing decisions. Reference: http://www.cisco.com/warp/public/cc/so/neso/vpn/vpnsp/s pqsd_wp.htm