Routing – mtr output with high packet loss on one hop

One way to do this is ICMP Timestamp, which is milliseconds from midnight UTC. It has the added benefit that you don't necessarily need to control both ends, as long as the far-end is not firewalled, there is good chance it'll work.

However, to have reliable one-way measurements, you need reliably same time in both ends. As ICMP timestamp only have precision of 1ms (which is not nearly enough for many applications, but sufficient for this) it's reasonably easy to find even non-cooperating hosts where ICMP timestamp will provide useful data.

If you control both ends, be sure that you are synchronizing NTP to only 1 server and same server. The absolute clock is not very important, it's just important that you experience as closely same time as possible.

If ICMP timestamp is not sufficient, it's very easy to write 10 lines of ruby/perl/python or even C to do measurements when you control both ends.

I can't really suggest software for doing ICMP timestamp measurements unidirectionally, hping2 supports sending ICMP timestamp but for some reason does not output unidirectional values. I wrote patch for hping2 to display one way latencies.

(Fun fact: I used to work with the guy that originally wrote mtr in '97)

If you check out the source on github, specifically in net.c, there's this tidbit:

  int jinta;        /* estimated variance,? rfc1889's "Interarrival Jitter" */

RFC 1889 is the RFC for RTP, later superseded by RFC 3550. Here's the excerpt detailing how interarrival jitter is calculated (taken from RFC 3550):

An estimate of the statistical variance of the RTP data packet interarrival time, measured in timestamp units and expressed as an unsigned integer. The interarrival jitter J is defined to be the mean deviation (smoothed absolute value) of the difference D in packet spacing at the receiver compared to the sender for a pair of packets.

As shown in the equation below, this is equivalent to the difference in the "relative transit time" for the two packets; the relative transit time is the difference between a packet's RTP timestamp and the receiver's clock at the time of arrival, measured in the same units.

If Si is the RTP timestamp from packet i, and Ri is the time of arrival in RTP timestamp units for packet i, then for two packets i and j, D may be expressed as

D(i,j) = (Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si)

The interarrival jitter SHOULD be calculated continuously as each data packet i is received from source SSRC_n, using this difference D for that packet and the previous packet i-1 in order of arrival (not necessarily in sequence), according to the formula

J(i) = J(i-1) + (|D(i-1,i)| - J(i-1))/16

Whenever a reception report is issued, the current value of J is sampled.

The jitter calculation MUST conform to the formula specified here in order to allow profile-independent monitors to make valid interpretations of reports coming from different implementations. This algorithm is the optimal first-order estimator and the gain parameter 1/16 gives a good noise reduction ratio while maintaining a reasonable rate of convergence [22]. A sample implementation is shown in Appendix A.8. See Section 6.4.4 for a discussion of the effects of varying packet duration and delay before transmission.