1. Multi-Rate ETX: A Radio-Aware Routing metric for 802.11s Mesh Networks
Alok Nandan
Gautam Kulkarni
Daniela Maniezzo

2. Expected Transmission Count (ETX) (De Couto et al., Mobicom ’03)
Loss rate of broadcast packets between pairs of neighboring nodes
Probe every second
Nodes track the numbers of probes received and insert this information in the probe packet
Measurements of link quality
Probability that the data packet be successfully transmitted
ETX measured by tracking the number of probing packets received from each neighbor during a sliding window (10 seconds) and include this info in their probe packets.
11/24/2018
802.11s TG potential proposal

3. Expected Transmission Count (ETX)
p: loss probability of a packet; f: forward; r: reply
s(k): probability that packet be successfully delivered after k attempts
The equation of ETX assumes that the probability that a given packet is lost in transmission is independent of its size. It also assumes that the ETX metric is bidirectional.
ETX: Expected number of transmission required to successfully deliver a packet
11/24/2018
802.11s TG potential proposal

4. Why a new routing metric? (Draves et al., Mobicom ’04 paper)
ETX considers
only the loss rates but not their bandwidths
no preference to channel-diverse paths
11/24/2018
802.11s TG potential proposal

5. Weighted Cumulative Expected Transmission Time (WCETT)
Expected Transmission Time ETT
Bandwidth adjusted ETX
S: size of probe packet
B: bandwidth of the link (measured by packet-pair technique)
ETT takes both loss rate and bandwidth of a path into account.
ETT of a link as a “bandwidth-adjusted ETX”, bandwidth measured by sending packet-pair probe packets every minute.
No direct consideration of impact of contention due to traffic from nearby nodes, such as increase in packet loss rate due to contention and reduce in available bandwidth, but continuous measurement of ETX can reflect the contention from nearby nodes.
Round-trip latency should not be used because of self-interference. And such probing is of O(n2) and is not scalable.
More frequent broadcast probes to measure loss-rate, very infrequent unicast probes to measure the bandwidth to each neighbor.
It does not incorporate backoff time
11/24/2018
802.11s TG potential proposal

6. 802.11s TG potential proposal
WCETT
Xj: sum of transmission times of hope on channel j
Max Xj: bottleneck channel
Tradeoff between global good and selfishness
Tradeoff between delay and throughput
Adding one more hop should result in a non-decreasing effect on the metric, preferably an increase. It is because one more hop means more interference between paths and more resources consumed, more delay is also introduced.
Account explicitly for the deduction in throughput due to interference among links using the same channel.
The calculation of Xj implies hops that use the same channel always interfere with each other.
11/24/2018
802.11s TG potential proposal

7. ETX : Is it suitable for Multi-rate MACs?
Probing is done at fixed rate(1Mbps in the MOBICOM ’03 paper)
For a b network, this worked fine since the variation in DataRate (1Mbps -11Mbps) due to ARF algorithms was not significant. (Also noted in MOBICOM ’04 paper by Draves et al)
Conjecture: With the advent of a (upto 54Mbps) and n (>= 216Mbps) in the near future, vanilla ETX might not work.
11/24/2018
802.11s TG potential proposal

8. 802.11s TG potential proposal
Multi-Rate ETX
Simple Idea: Probe at multiple rates, not just one. Estimate loss rates (pf) and (pr) for different data rates. Hence evaluate ETXr for data rate r.
ETTr = ETXr / r for all r which are used for probing.
ETTlink = min( ETTr) over all probed datarates r
ETTpath = Sum ETTlink over all links
Rest of the WCETT calculations remain the same
Use CapProbe for Bandwidth Estimation instead of simple Packet-Pair as used in Draves et al.
11/24/2018
802.11s TG potential proposal

9. 802.11s TG potential proposal
References
Routing in Multi-Radio Multi-Hop Wireless Mesh Networks, Draves et al, MOBICOM 2004
High throughput Path Metric for multi-hop wireless networks, De Couto et al, MOBICOM 2003
11/24/2018
802.11s TG potential proposal