Traffic Shaping

This is a mechanism to control the amount and the rate of the traffic sent to the network.

Two techniques can shape traffic:

• Token Bucket
• Leaky Bucket

Leaky Bucket

Suppose we have a bucket in which we are pouring water in a random order but we have to get water in a fixed rate , for this we will make a hole at the bottom of the bucket. It will ensure that water coming out is in a fixed rate . And also if bucket is full we will stop pouring in it.

• If the bucket (buffer) overflows then packets are discarded.
• Input rate can vary but the output rate remains constant.

class LeakyBucketLimiter {
public:
    bool addDropToBucket(int timestamp) {
        if (timeOfLastLeak != -1) {
            int delta = timestamp - timeOfLastLeak;
            int numToLeak = delta * DROP_RATE;
            numOfDrops = max(0, numOfDrops - numToLeak);
            timeOfLastLeak = timestamp;
        }

        if (numOfDrops < BUCKET_SIZE) {
            numOfDrops++;
            return true; // drop added
        }

        return false; // overflow
    }
private:
    int numOfDrops = 0;
    int timeOfLastLeak = -1;
    int BUCKET_SIZE = 100;
    int DROP_RATE = 20;
};

Token Bucket

1. A token is added at every ∆t time.
2. The bucket can hold at most b-tokens. If a token arrive when bucket is full it is discarded, not the packet.
3. When a packet of m bytes arrived m tokens are removed from the bucket and the packet is sent to the network.
4. If less than n tokens are available no tokens are removed from the buckets and the packet may be enqueued for subsequent transmission when sufficient token have been accumulated in the bucket.

If C is the maximum capacity of bucket and ρ is the arrival rate and M is the maximum output rate then Burst Length S can be calculated as

Pros and Cons

Main advantage of token Bucket over leaky bucket

• If bucket is full in token Bucket , token are discard not packets. While in leaky bucket , packets are discarded.
• Token Bucket can send Large bursts can faster rate while leaky bucket always sends packets at constant rate.

file:///Users/xiaojiang/Downloads/trafficshapingpresentation-140126060026-phpapp01.pdf