Beyond Best Effort Technologies. Our primarily objective here is to understand more on QoS mechanisms so that you can make informed decision on opting for network devices and gadgets that support it. Chapter 6 of Kurose & Ross. QoS.
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Our primarily objective here is to understand more on QoS mechanisms so that you can make informed decision on opting for network devices and gadgets that support it.
Chapter 6 of Kurose & Ross
network provides application with level of performance needed for application to function.Multimedia, Quality of Service: What is it?
Multimedia applications: network audio and video
Protocols and Architectures
Beyond Best Effort
Scheduling and Policing Mechanisms
RSVP (covered earlier)
But loss tolerant: infrequent losses cause minor glitches
Antithesis of data, which are loss intolerant but delay tolerant.
Classes of MM applications:
1) Streaming stored audio and video
2) Streaming live audio and video
3) Real-time interactive audio and videoMM Networking Applications
instant messaging services are providing this
videoconference with Webcams
Going to now look at a PC-2-PC Internet phone example in detailReal-time interactive applications
Introduce Internet Phone by way of an example
Thus far: “making the best of best effort”
Future: next generation Internet with QoS guarantees
packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly
provide protection (isolation) for one class from others
While providing isolation, it is desirable to use
resources as efficiently as possible
Call Admission: flow declares its needs, network may
block call (e.g., busy signal) if it cannot meet needs
Let’s next look at mechanisms for achieving this ….
Priority scheduling: transmit highest priority queued packet
round robin scheduling:
Weighted Fair Queuing:
Goal: limit traffic to not exceed declared parameters
Three common-used criteria:
Token Bucket: limit input to specified Burst Size and Average Rate.
bucket size, b
D = b/R
maxPolicing Mechanisms (more)
Question: can newly arriving flow be admitted
with performance guarantees while not violating
QoS guarantees made to already admitted flows?
call setup, signaling (RSVP)
traffic, QoS declaration
per-element admission control
Arriving session must :
worst case traffic arrival: leaky-bucket-policed source
simple (mathematically provable) bound on delay [Parekh 1992, Cruz 1988]
token rate, r
bucket size, b
D = b/R
maxIntserv QoS: Service models [rfc2211, rfc 2212]
Controlled load service:
Concerns with Intserv:
- per-flow traffic management
- marks packets as in-profile and out-profile
- per class traffic management
- buffering and scheduling
based on marking at edge
- preference given to in-profile
- Assured Forwarding
Edge-router Packet Marking
Possible usage of marking:
may be desirable to limit traffic injection rate of some class:
PHBs being developed: