• Leaky Bucket: Analogy
  • Leaky Bucket: Doesn’t allow bursty transmissions
  • Token Bucket
    		•

    Resource Reservation (cont’d)




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    Resource Reservation (cont’d)

    • Once a connection is accepted, the host must use only the amount of resources reserved. It may not use more than that.
    • What if the host is malicious and attempts to use more network resources than it reserved?

    Leaky Bucket

    • Used in conjunction with resource reservation to police the host’s reservation
    • At the host-network interface, allow packets into the network at a constant rate
    • Packets may be generated in a bursty manner, but after they pass through the leaky bucket, they enter the network evenly spaced

    Leaky Bucket: Analogy

    • Leaky
    • Bucket
    • Network
    • Packets from host

    Leaky Bucket (cont’d)

    • The leaky bucket is a “traffic shaper”: It changes the characteristics of packet stream
    • Traffic shaping makes more manageable and more predictable
    • Usually the network tells the leaky bucket the rate at which it may send packets when the connection begins
    • Polices the average rate

    Leaky Bucket: Doesn’t allow bursty transmissions

    • In some cases, we may want to allow short bursts of packets to enter the network without smoothing them out
    • For this purpose we use a token bucket, which is a modified leaky bucket

    Token Bucket

    • The bucket holds tokens instead of packets
    • Tokens are generated and placed into the token bucket at a constant rate
    • When a packet arrives at the token bucket, it is transmitted if there is a token available. Otherwise it is buffered until a token becomes available.
    • The token bucket has a fixed size, so when it becomes full, subsequently generated tokens are discarded

    Token Bucket

    • Network
    • Packets from host
    • Token Generator
    • (Generates a token
    • once every T seconds)

    Token Bucket vs. Leaky Bucket

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    • Arrival time at bucket
    • Departure time from a leaky bucket
    • Leaky bucket rate = 1 packet / 2 time units
    • Leaky bucket size = 4 packets
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