I usually find that Gmail phone performs lot better then Skype for calls to PSTN. Usually latency on Skype is high as compared to Gmail phone in India (in US it was almost no difference).

I looked around today and here’s bit of test data I collected by calling couple of numbers from Skype & Gmail phone & monitored UDP traffic to collect information about destination servers which is very likely IP-PSTN gateway.

Phone calls made from Skype

US calls (outgoing): 216.49.203.243
US calls (incoming):  4.53.80.106
UK calls (outgoing): 213.244.170.88

While gateway IP for Gmail phone was same always and it was 209.85.175.126

As I experienced, latency was bit high on phone calls made from Skype, here’s a quick check to routing to these IP’s from my system on BSNL Network (AS9829) in India.

MTR to Skype US nodes:

HOST: anurag-laptop Loss% Snt Last Avg Best Wrst StDev
1.|– home-router 0.0% 10 1.7 3.6 1.5 11.5 3.5
2.|– 117.206.176.1 0.0% 10 23.1 23.8 22.8 30.8 2.5
3.|– 218.248.169.122 0.0% 10 28.7 29.8 28.6 34.9 2.1
4.|– 115.114.59.169.static-Mumbai.vsnl.net.in 0.0% 10 71.2 72.5 71.1 80.6 2.9
5.|– if-0-100.tcore1.MLV-Mumbai.as6453.net 0.0% 10 182.7 186.1 181.5 214.8 10.1
6.|– if-2-2.tcore2.MLV-Mumbai.as6453.net 0.0% 10 189.5 190.3 188.1 195.2 2.2
7.|– if-6-2.tcore1.L78-London.as6453.net 0.0% 10 209.4 209.5 193.1 221.5 10.2
8.|– Vlan704.icore1.LDN-London.as6453.net 60.0% 10 197.0 199.0 196.8 201.9 2.5
9.|– Vlan533.icore1.LDN-London.as6453.net 0.0% 10 189.5 190.9 188.4 201.1 3.7
10.|– ae-52-52.csw2.London1.Level3.net 0.0% 10 196.7 199.5 195.9 214.8 5.8
11.|– ae-58-223.ebr2.London1.Level3.net 0.0% 10 195.0 194.6 193.5 196.9 1.0
12.|– ae-41-41.ebr1.NewYork1.Level3.net 0.0% 10 288.7 274.7 271.9 288.7 4.9
13.|– ae-81-81.csw3.NewYork1.Level3.net 0.0% 10 281.8 276.6 270.3 283.1 5.1
14.|– ae-82-82.ebr2.NewYork1.Level3.net 0.0% 10 271.1 271.2 269.6 274.4 1.6
15.|– ae-2-2.ebr4.SanJose1.Level3.net 10.0% 10 340.9 341.7 340.5 343.2 0.9
16.|– ae-2-2.ebr3.LosAngeles1.Level3.net 10.0% 10 339.0 339.1 338.4 340.1 0.5
17.|– ae-73-73.csw2.LosAngeles1.Level3.net 10.0% 10 343.5 344.5 343.4 346.2 1.0
18.|– ae-22-70.car2.LosAngeles1.Level3.net 10.0% 10 339.2 339.8 337.9 347.9 3.1
19.|– unknown.Level3.net 10.0% 10 338.6 339.4 338.6 340.4 0.7
20.|– LAX-C10-C7613-1.ivanet.net 10.0% 10 344.4 346.6 344.3 357.0 4.0
21.|– LAX-H07-HP365-2.ivanet.net 10.0% 10 344.1 345.3 343.9 348.8 1.5

HOST: anurag-laptop Loss% Snt Last Avg Best Wrst StDev
1.|– home-router 0.0% 10 1.6 2.1 1.4 6.3 1.5
2.|– 117.206.176.1 0.0% 10 22.6 23.3 22.6 24.4 0.6
3.|– 218.248.169.122 20.0% 10 47.7 58.4 28.8 135.7 41.6
4.|– if-14-1.mcore4.NYY-NewYork.as6453.net 0.0% 10 387.5 370.5 303.5 453.8 49.9
5.|– if-8-0-2-28.tcore1.NYY-NewYork.as6453.net 0.0% 10 258.4 260.6 258.4 270.3 3.7
6.|– Vlan24.icore1.NTO-NewYork.as6453.net 0.0% 10 265.3 262.5 256.9 270.1 4.7
7.|– ae9.edge1.NewYork.Level3.net 0.0% 10 259.7 266.2 258.6 324.1 20.3
8.|– vlan51.ebr1.NewYork2.Level3.net 0.0% 10 258.9 260.6 258.3 272.6 4.2
9.|– ae-3-3.ebr2.Washington1.Level3.net 0.0% 10 262.3 262.8 261.8 264.2 0.6
10.|– ae-62-62.csw1.Washington1.Level3.net 10.0% 10 266.3 263.0 261.9 266.3 1.3
11.|– ae-11-60.car1.Washington1.Level3.net 10.0% 10 262.9 262.7 261.6 263.9 0.7
12.|– 4.53.80.106 10.0% 10 265.4 265.3 264.3 266.1 0.5

And latency with Europe based node

HOST: anurag-laptop Loss% Snt Last Avg Best Wrst StDev
1.|– home-router 0.0% 10 1.5 1.8 1.5 3.6 0.7
2.|– 117.206.176.1 0.0% 10 22.6 22.7 22.0 23.5 0.5
3.|– 218.248.169.122 10.0% 10 28.5 34.8 28.5 67.9 13.0
4.|– if-14-1.mcore4.NYY-NewYork.as6453.net 0.0% 10 342.1 300.9 255.6 360.4 46.7
5.|– if-8-0-2-28.tcore1.NYY-NewYork.as6453.net 0.0% 10 283.3 262.3 257.7 283.3 7.8
6.|– Vlan24.icore1.NTO-NewYork.as6453.net 10.0% 10 265.3 262.0 257.1 269.9 5.0
7.|– ae9.edge1.NewYork.Level3.net 0.0% 10 260.1 264.0 258.8 275.9 6.8
8.|– vlan51.ebr1.NewYork2.Level3.net 10.0% 10 259.7 259.6 258.7 260.7 0.7
9.|– ae-4-4.ebr1.NewYork1.Level3.net 0.0% 10 259.7 260.8 259.7 263.7 1.2
10.|– ae-42-42.ebr2.London1.Level3.net 0.0% 10 248.5 247.3 246.3 248.5 0.7
11.|– ae-48-48.ebr2.Amsterdam1.Level3.net 0.0% 10 256.7 257.2 256.1 257.9 0.5
12.|– ae-59-224.csw2.Amsterdam1.Level3.net 10.0% 10 257.6 257.4 256.7 258.3 0.5
13.|– ae-2-52.edge4.Amsterdam1.Level3.net 10.0% 10 273.8 264.2 257.6 294.3 12.4
14.|– 213.244.170.88 10.0% 10 257.9 257.8 257.0 258.5 0.5

When I tested on Gmail phone, IP address was always: 209.85.175.126

This IP address belongs to Google’s ASN 15169 and covers in two block announcements by Google:

209.85.128.0/17 & 209.85.174.0/23

Quick traceroute to IP

HOST: anurag-laptop Loss% Snt Last Avg Best Wrst StDev
1.|– home-router 0.0% 10 1.7 1.8 1.5 2.5 0.3
2.|– 117.206.176.1 0.0% 10 23.6 23.1 22.6 24.0 0.4
3.|– 218.248.169.122 10.0% 10 30.4 34.5 27.9 76.8 15.9
4.|– 115.114.59.169.static-Mumbai.vsnl.net.in 0.0% 10 72.0 72.1 70.9 75.9 1.5
5.|– 121.240.1.38 0.0% 10 71.8 73.5 71.0 85.2 4.3
6.|– 209.85.241.52 0.0% 10 69.6 69.8 68.8 72.6 1.1
7.|– 209.85.251.95 0.0% 10 126.3 100.5 96.7 126.3 9.1
8.|– 66.249.94.38 0.0% 10 132.1 133.5 129.7 157.7 8.5
9.|– 209.85.242.125 0.0% 10 135.3 134.6 130.8 137.5 1.7
| |-- 209.85.241.173
10.|-- 66.249.94.126 0.0% 10 138.2 136.8 130.8 142.7 4.1
| |– 66.249.94.158
11.|– nx-in-f126.1e100.net 10.0% 10 135.8 137.1 135.8 138.3 0.9

137ms latency – very likely Singapore. Infact it’s confirmed also from my tests from various looking glasses.

Summary of results

1. Skype seems using multiple gateways for PSTN calls and most of them are located in US and Europe. 
2. Latency with these Skype gateways & Indian ISP networks varies from 250-350ms.
3. Gmail seems using Singapore gateway for Indian users and latency is just 135ms.
4. Latency & performance is very for Google since they have their own PoP in India and they carry International traffic themselves rather then replying on Public Internet infrastructure or upstream ISP’s.
5. Calls beyond these gateways have usually very low latency as they reply on dedicated circuits & route over circuit switched network.