VoIP calls over satellite links

VoIP services via high latency satellite links: overview

As we all know the VoIP market expanding rapidly over the past few years and SIP based services allows the voice communication over global Internet network, giving the customers great savings and more convenient service.  In the past with cooper wires you can do nothing about bad quality as in most cases the wires at your local site belongs to a single operator that you can’t change – only stay with bad service option or unsubscribe and have no service at all. Nowadays it’s much more easy to select the good service provider and change it if one day it became bad for you.

Voice communication is a real time event, thus VoIP traffic has a bit different nature. With web/http or e-mails one second delay is not an issue, but for VoIP the link latency is vital. VoIP real time flow works well over broadband connection such as cable or DSL.  However on high latency links, like Internet via satellite services, VoIP stream has a number of technical barriers.  So why quality VoIP calls via satellite links so difficult to accomplish?

For those who live (or temporary deployed) to/in a remote areas and cannot get access to a cable backbone or DSL service, Internet over satellite is their only choice to get an Internet connection.  I am sure many users that using satellite links would like to use VoIP services. As I’ve already mentioned the main problem that appears when you trying to send/receive VoIP stream over satellite link is the latency. Latency refers to the time that’s required for data to travel from the site up to the satellite and then go back to the ground facilities. The distance between a remote site and the satellite spacecraft (geostationary orbit) is approx 30,000 km above the Earth surface. As we know  radio signal can travel with the maximum speed of light, there’s going to be a delay up to 500 to 900 milliseconds (round trip).  For high quality VoIP service, the latency should not exceed 250 milliseconds, so we are on the edge.  A longer latency may cause very bad voice quality and a phone simply turns to a “walke-talke” radio.

Two other main factors that may affect on a service quality are jitter and packet loss.  Jitter is a variation of packet delays between a client and a server.  High jitter can make voice choppy and difficult to understand.  Packet loss may occur when your link is congested with a lot of traffic, so that caused dropped packets. So that’s why so important to setup QoS in a right way – to set a higher priority for SIP and UDP stream used by VoIP service.

Typical VoIP Problems like not proper codec, packet loss, jitter, not in order packets has been discussed in this article.

There are main problems reported by customers who are hooked to SIP service via satellite link:

• One way audio (you can hear other party, but they can’t hear you)
• Dropped calls (very bad stuff when you have a call with your wife and it’s disconnected on the middle)
• Calls not passing at all
• Poor call quality (like underwater sound)
• The voice is choppy

It will be great if you could find a satellite provider who has their own VoIP service, so they will be responsible for a turn-key solution as in most cases VoIP  providers saying that it’s not recommend to use  VoIP service over satellite links (thus they are not responsible for the quality). And some satellite providers can tell you that the satellite link itself is fine, but your VoIP service is bad. In this case it’s difficult to find our who is responsible for the problem, so buying VoIP service and satellite link from the same company will raise the chances of high quality service. But in most cases satellite providers simply don’t know how to configure VoIP it in a right way. Some of the systems don’t have enough CIR (dedicated bandwidth) allocated on the shared link they sell and even they do, QoS setup could be wrong.

For the remote areas where the satellite link is only way you can get Internet access, VoIP is your chance  to convenient and free get in touch with friends, family and colleagues. I am sure that VoIP is definitely “must have” service, especially on satellite links. In next  articles we will try to bring a short how-to on proper configuration for VoIP to be used over high latency links: how to select right harware/software to make/receive calls, how to configure it with with low bitrate codec, how to get an incoming number to receive calls.

Stay tuned!

Typical VoIP problems