reverse latency

hey, i've noticed recently using the thinkbb reverse trace tool that the latency on my llu connection jumps 5-6ms from the dslam to my router. is that normal / a technical limitation with the last mile telephone wire?

tested using a netgear dg834gt & speedtouch 516v6, fast path.

1 	adslguide-gw2.core-rs2.thdo.ncuk.net	15	15	0ms	0ms	0ms

2 	gi0-1-10-star1.bdr-rt1.thdo.ncuk.net	15	15	0ms	0ms	0ms

3 	gi4-15.telehouse-east2.core.enta.net	15	15	0ms	3ms	27ms

4 	te4-1.telehouse-north.core.enta.net	15	15	0ms	0ms	0ms

5 	te5-1.telehouse-north0.core.enta.net	15	15	0ms	1ms	17ms

8 	cr0.wwredr.uk.easynet.net		15	15	14ms	14ms	15ms

9 	bb-ip.ukonline.co.uk			15	15	19ms	19ms	20ms

Mine's interleaved and a lot worse so if you've got something to woory about I should be having a purple fit...

1 adslguide-gw2.core-rs2.thdo.ncuk.net 15 15 0ms 0ms 0ms
2 gi0-1-10-star1.bdr-rt1.thdo.ncuk.net 15 15 0ms 0ms 0ms
3 gi4-15.telehouse-east2.core.enta.net 15 15 0ms 0ms 0ms
4 te4-1.telehouse-north.core.enta.net 15 15 0ms 10ms 152ms
5 te5-1.telehouse-north0.core.enta.net 15 15 0ms 0ms 0ms
8 cr0.xxxxxx.uk.easynet.net 15 15 6ms 7ms 14ms
9 ip-87-82-nnn-nnn.easynet.co.uk 15 15 33ms 34ms 36ms

As my connection seems to be working perfectly I'm not concerned.

cheers, looks like it's normal for last mile to increase latency then.. was just wondering though, 15ms from london to my exchange (~250 miles) then 5ms from the exchange to my house.. atten of 17

the 5ms is as much the processing time in the DSLAM and in your router as the time of flight down the line.

The last hop isn't from the DSLAM to your router, it's from the ISP's router (wherever that is) to your house.
You can't see the DSLAM as a network hop as it's essentially a layer 2 device and so doesn't show as a IP (layer 3) hop.

Are you certain that is so for Easynet LLU (which by coincidence is what both of those tracerts show) The penultimate hop in both contains an exchange code (mine was edited out by me for reasons of paranoia). I think this is true for all Easynet LLU.

A normal tracert shows it followed by an easynet router


1 <1 ms <1 ms <1 ms 192.168.1.254
2 33 ms 63 ms 34 ms cr0.emchape.uk.easynet.net [87.87.250.200]
3 29 ms 28 ms 29 ms ip-87-87-146-97.easynet.co.uk [87.87.146.97]
4 33 ms 32 ms 32 ms 212.58.238.190
5 33 ms 32 ms 31 ms 212.58.238.189
6 32 ms 32 ms 32 ms 212.58.238.129
7 33 ms 32 ms 34 ms rdirwww-vip.thdo.bbc.co.uk [212.58.224.131]

I left in my exchange code this time around

Edited by kwikbreaks (Sat 12-Jul-08 14:05:40)

It's entirely possible the Easynet router is hosted in the exchange, but it remains that network hops only show Layer 3 devices, not layer 2, so you will not see the DSLAM as a separate hop.

The DSLAM would certainly contribute towards the latency of the last hop, as it forms part of the connection between the Easynet router and yours, but like an Ethernet switch (which is also a layer 2 device) it will not show as a network hop.

Hops are between routers, not switches, DSLAMS or other layer 2 devices.

It seems likely to me then that the EasyNet DSLAM also has a router in the same box and it still remains that the final mile or so including the DSLAM accounts for a large chunk of the oveall latency. Something I don't find especially surprising for my interleaved connection.