lect-17 - Resource Allocation & QoS (quality of...

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ECE/CS 438 1 Resource Allocation & QoS (quality of service) ECE/CS 438 Fall 2011 Slides mostly from Peterson & Davies
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Problem n We have seen enough layers of protocol hierarchy to understand how data can be transferred among processes across heterogeneous networks n Problem ¡ How to effectively and fairly allocate resources among a collection of competing users?
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Chapter Outline n Issues in Resource Allocation n Queuing Disciplines n TCP Congestion Control n Congestion Avoidance Mechanism n Quality of Service
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Congestion Control and Resource Allocation n Resources ¡ Bandwidth of the links ¡ Buffers at the routers and switches n Packets contend at a router for the use of a link, with each contending packet placed in a queue waiting for its turn to be transmitted over the link
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Congestion Control and Resource Allocation n When too many packets are contending for the same link ¡ The queue overflows ¡ Packets get dropped n Network is congested! n Network should provide a congestion control mechanism to deal with such a situation
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Congestion Control and Resource Allocation n Congestion control and Resource Allocation ¡ Two sides of the same coin n If the network takes active role in allocating resources ¡ The congestion may be avoided ¡ No need for congestion control
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Congestion Control and Resource Allocation n Allocating resources with any precision is difficult ¡ Resources are distributed throughout the network n On the other hand, we can always let the sources send as much data as they want ¡ Then recover from the congestion when it occurs ¡ Easier approach but it can be disruptive because many packets many be discarded by the network before congestions can be controlled
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Congestion Control and Resource Allocation n Congestion control and resource allocations involve both hosts and network elements such as routers n In network elements ¡ Various queuing disciplines can be used to control the order in which packets get transmitted and which packets get dropped n At the hosts end ¡ The congestion control mechanism paces how fast sources are allowed to send packets
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Issues in Resource Allocation n Network Model ¡ Packet Switched Network n We consider resource allocation in a packet-switched network (or internet) consisting of multiple links and switches (or routers). n In such an environment, a given source may have more than enough capacity on the immediate outgoing link to send a packet, but somewhere in the middle of a network, its packets encounter a link that is being used by many different traffic sources
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Issues in Resource Allocation n Network Model ¡ Packet Switched Network A potential bottleneck router.
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Issues in Resource Allocation n Network Model ¡ Connectionless Flows n For much of our discussion, we assume that the network is essentially connectionless, with any connection-oriented service implemented in the transport protocol that is running on the end hosts. ¡ We need to qualify the term
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lect-17 - Resource Allocation & QoS (quality of...

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