3 ms·

I don't want an emergency call failing due to a DNS timeout, for one

by ketralnis 9y ago

Rjevski 9y ago
Your DNS lookup is 10x more reliable than the telco infrastructure.
- recursive 9y ago
  However, the failure of the two is independent.
  - Rjevski 9y ago
    Not really, most of today's SS7 traffic goes over IP, so if IP is somehow flawed you'll be in trouble in either case. Luckily IP links are pretty reliable so that's not an issue - VoIP also allows for more resiliency, for example my phone has two independent network connections, mobile and Wi-Fi, and my VoIP provider has two servers (advertised via DNS SRV records). So my VoIP app can try each server over each connection to make a call. A conventional landline or mobile on the other hand has a single link to the telco, so if that's down you're in trouble.
    - Aloha 9y ago
      IP != Internet Yes, much traffic does traverse on IP now - but its private tightly controlled networks.
      - tatersolid 9y ago
        Not "private" as in "dedicated to voice traffic". Almost all modern telcos route their PSTN as packets on the same MPLS/IP or pure-IP network as internet traffic. This network is usually "privately owned" by the telco in the USA, but is publicly owned or subsidized in many parts of the world. But there is in general no "separate" PSTN other than last-mile copper in most of the world.
  - thaumasiotes 9y ago
    If this is true, you'd want your emergency calls to be going over the more reliable service, not the less reliable one. Independent failures are only relevant if you use both networks redundantly.
    - Rjevski 9y ago
      Well my SIP client app manages the loss of Wi-Fi or mobile connectivity pretty well - I loose audio for a second while it renegotiates the path through the other network link but after that it's business as usual. On a conventional call when I loose cell coverage the call is dropped, so SIP is a winner for me. On the server side you can do amazing things with high availability like floating/virtual IPs (the IP of the SIP server is actually shared between multiple machines, and if the primary machine goes down the secondary takes over its IP and as far as the client is concerned nothing happened).
- Aloha 9y ago
  Got a source to back up this assertion? My experience tells me otherwise.
  - Rjevski 9y ago
    A DNS lookup can be answered by any DNS server in the world, so even if that goes down you can retry with another one. If the equipment responsible from taking calls from your phone is down there often isn't a second one it can automatically fail over to.
    - Aloha 9y ago
      Thats comparing two vastly different parts of their respective networks though - its a bit like comparing Apples and Volkswagens. No ONE DNS server is as reliable as a Class 5 Telephone Switch. The telephone network is on whole more reliable than any single component of the internet - and its certainly more reliable that the internet on whole. The internet however is more survivable - much more, because there are less common choke points to fail. In a way you are correct though - nearly every component required for internet access is unreliable (because you can substitute another one with ease) whereas every network element in a phone call is much more reliable (because beyond a certain point, you cannot).

I don't want an emergency call failing due to a DNS timeout, for one

Rjevski 9y ago

Your DNS lookup is 10x more reliable than the telco infrastructure.

recursive 9y ago
However, the failure of the two is independent.
- Rjevski 9y ago
  Not really, most of today's SS7 traffic goes over IP, so if IP is somehow flawed you'll be in trouble in either case. Luckily IP links are pretty reliable so that's not an issue - VoIP also allows for more resiliency, for example my phone has two independent network connections, mobile and Wi-Fi, and my VoIP provider has two servers (advertised via DNS SRV records). So my VoIP app can try each server over each connection to make a call. A conventional landline or mobile on the other hand has a single link to the telco, so if that's down you're in trouble.
  - Aloha 9y ago
    IP != Internet Yes, much traffic does traverse on IP now - but its private tightly controlled networks.
    - tatersolid 9y ago
      Not "private" as in "dedicated to voice traffic". Almost all modern telcos route their PSTN as packets on the same MPLS/IP or pure-IP network as internet traffic. This network is usually "privately owned" by the telco in the USA, but is publicly owned or subsidized in many parts of the world. But there is in general no "separate" PSTN other than last-mile copper in most of the world.
- thaumasiotes 9y ago
  If this is true, you'd want your emergency calls to be going over the more reliable service, not the less reliable one. Independent failures are only relevant if you use both networks redundantly.
  - Rjevski 9y ago
    Well my SIP client app manages the loss of Wi-Fi or mobile connectivity pretty well - I loose audio for a second while it renegotiates the path through the other network link but after that it's business as usual. On a conventional call when I loose cell coverage the call is dropped, so SIP is a winner for me. On the server side you can do amazing things with high availability like floating/virtual IPs (the IP of the SIP server is actually shared between multiple machines, and if the primary machine goes down the secondary takes over its IP and as far as the client is concerned nothing happened).
Aloha 9y ago
Got a source to back up this assertion? My experience tells me otherwise.
- Rjevski 9y ago
  A DNS lookup can be answered by any DNS server in the world, so even if that goes down you can retry with another one. If the equipment responsible from taking calls from your phone is down there often isn't a second one it can automatically fail over to.
  - Aloha 9y ago
    Thats comparing two vastly different parts of their respective networks though - its a bit like comparing Apples and Volkswagens. No ONE DNS server is as reliable as a Class 5 Telephone Switch. The telephone network is on whole more reliable than any single component of the internet - and its certainly more reliable that the internet on whole. The internet however is more survivable - much more, because there are less common choke points to fail. In a way you are correct though - nearly every component required for internet access is unreliable (because you can substitute another one with ease) whereas every network element in a phone call is much more reliable (because beyond a certain point, you cannot).