Transcript pptx

Bandwidth estimation: metrics,
measurement techniques, and
tools
Presenter: Yuhang Wang
Content
• Three Bandwidth-related Metrics
• Different Techniques for accurate bandwidth estimation
• Taxonomy of Bandwidth Estimation Tools
Bandwidth-related Metric: Capacity
• Individual link Capacity
 Depending on the file size and the capacity of link layer
CL2: capacity of link layer
HL2: Link layer header
LL3: file size of network layer
• End-to-End Path Capacity
 the maximum IP layer rate that the path can transfer from source to sink
 The minimum link capacity in the path determines the end-to-end capacity
Bandwidth-related Metric: available
bandwidth
• The available bandwidth of a link relates to the unused, or “spare”,
capacity of the link during a certain time period.
• The average available bandwidth Ai of hop i is given by the unutilized
fraction of capacity Ai=(1-ui)Ci.
 where, ui is the average of instantaneous utilization over the time interval of
interest.
Bandwidth-related Metric: Bulk-TransferCapacity (BTC)
• Bulk-Transfer- Capacity (BTC) is maximum throughput obtainable by a
single TCP connection.
• Affecting factors:
 transfer size
 type of cross traffic (UDP or TCP)
 number of competing TCP connections
 TCP socket buffer sizes at both sender and receiver sides
 congestion along reverse (ACK) path
 size of router buffers and capacity
 load of each link
Techniques: Variable Packet Size (VPS) probing
• Aim: the capacity of each hop along a path
• Idea: measuring the RTT from the source to each hop of the path as a
function of the probing packet size.
• Methodology:
• Forcing probing packets to expire at a particular hop by manipulating Time-ToLive (TTL) field in IP header.
• Corresponding router discards the probing packets, returning ICMP “Timeexceeded” error messages to the source.
• The source uses the received ICMP packets to measure the RTT to that hop
Techniques: Variable Packet Size (VPS) probing
• Delay in the way:
 serialization delays –transmission delay
 propagation delays –time for a packet traverse the link
 queueing delays-time waiting in buffers of routers or switches
• Minimum RTT:
 VPS sends multiple probing packets of a given size
 VPS assumes that at least one will not encounter any queueing delays
 Minimum RTT:
Techniques: Variable Packet Size (VPS) probing
• Estimated Capacity at each hop i:
1
𝐶𝑖 =
𝛽𝑖 − 𝛽𝑖−1
• Drawback: significant capacity underestimation errors will occur if the
measured path includes store-and-forward layer-2 switches .
Techniques: Packet Pair/Train Dispersion (PPTD)
probing
• Packet pair probing is used to measure the end-to- end capacity of a
path.
Techniques: Packet Pair/Train Dispersion (PPTD)
probing
• The dispersion, between two packets, Δ𝑅 is:
,Where C is the capacity of the path.
• Drawback: The measurement is under the assumption that the path
is empty of any other traffic.
Techniques: Packet Pair/Train Dispersion (PPTD)
probing
• Packet train probing extends packet pair probing by using multiple
back-to-back packets
• Dispersion rate:
• Path capacity : C=E[D], with a large number of packets in the chain.
Techniques: Self-Loading Periodic Streams (SLoPS)
• SLoPS is a recent measurement methodology for measuring end-toend available bandwidth
• Methodology:
 Sending K(≈100) same-size packets
 monitoring variations in one way delays of the probing packets
 Following the an iterative algorithm similar to binary search
Techniques: Trains of Packet Pairs (TOPP)
• Trains of Packet Pairs to estimate the available bandwidth of a
network path.
• Methodology:
 sending many packet pairs at gradually increasing rates.
 Comparing the link rate at every hop.
 Measured rate at receiver:
Where RC=C-A, C is the capacity of end-to-end path, A is the available band-width.
Techniques: Other bandwidth estimation
methodologies
• Methodology estimates the utilization of a single bottleneck
• Methodology estimates available bandwidth using different packet
stream patterns from those of SLoPS and TOPP
• Methodology estimates the capacity of targeted subpaths in a path.
Taxonomy of Bandwidth Estimation Tools
Discussion
• Do you know some new techniques to measure bandwidth-related
metric?
• Is there any drawbacks in them?
Thank you for your attention!