Live data from Hacker News

Ask HN: Why isn't VoIP better?

news.ycombinator.com

81–90 of 141 posts

Re: Ask HN: Why isn't VoIP better?

#82
post #66

I'm surprised that no one has mentioned bufferbloat yet. In most home routers, people can see seconds of delay when there's significant other traffic on the link. (And remember, "other traffic" can be ordinary web browsing, where pages average 2 mbytes these days...) The latency (and jitter) caused by bufferbloat has been a solved problem for almost five years: fq_codel, and the newer cake qdisc's are are in the Linu…

Bufferbloat is a side affect of congestion or microbursts, and not the primary cause of poor voice calls. Either packets get dropped (shallow buffer) or queued (enough buffer), and in both cases the quality of the call will suffer. Mitigation: Don't congest. If you need to, mark VOIP traffic with a DSCP value that has queues that are serviced prior to all others (e.g., EF, DSCP46).

Yes. I'm a Republic Wireless (WiFi VoIP phone) customer. They mark their RTP packets with DSCP 48 (CS6 / ToS 192) and their SIP packets with DSCP 56 (CS7 / ToS 224). I limit ingress & egress bandwidth on my home router (a Mikrotik), and prioritize flows with those DSCPs above all other traffic.

The result is that even when my pipe is completely full, VoIP packet latency is practically unaffected. Compare to ~3 s latencies I would incur by Comcast's awful traffic shaping.

Re: Ask HN: Why isn't VoIP better?

#83
post #66

Earlier quoted context omitted.

Bufferbloat is a side affect of congestion or microbursts, and not the primary cause of poor voice calls. Either packets get dropped (shallow buffer) or queued (enough buffer), and in both cases the quality of the call will suffer. Mitigation: Don't congest. If you need to, mark VOIP traffic with a DSCP value that has queues that are serviced prior to all others (e.g., EF, DSCP46).

Applications do it already, but edge routers are adept at ignoring these flags or applying them only to their own service. So that you use it and not competition. Net neutrality would be the antidote.

You're correct, most applications do.

QoS/CoS services are best when clearly spelled out in service agreements. Providers may clear markings, but likely because either they don't want to have a free for all when it comes to their queues, or because they didn't purchase the gear that offers the rich queuing needed.

Re: Ask HN: Why isn't VoIP better?

#84
post #66

I'm surprised that no one has mentioned bufferbloat yet. In most home routers, people can see seconds of delay when there's significant other traffic on the link. (And remember, "other traffic" can be ordinary web browsing, where pages average 2 mbytes these days...) The latency (and jitter) caused by bufferbloat has been a solved problem for almost five years: fq_codel, and the newer cake qdisc's are are in the Linu…

Bufferbloat is a side affect of congestion or microbursts, and not the primary cause of poor voice calls. Either packets get dropped (shallow buffer) or queued (enough buffer), and in both cases the quality of the call will suffer. Mitigation: Don't congest. If you need to, mark VOIP traffic with a DSCP value that has queues that are serviced prior to all others (e.g., EF, DSCP46).

I have almost no bufferbloat when downloading (about 1ms) but about 300ms when uploading.

What does this mean?

Re: Ask HN: Why isn't VoIP better?

#85
Ive seen some enterprise level voip providers in the UK not only provide clients with VOIP systems either on site or a cloud PBX, but also a dedicated leased ADSL line. Usually 2mbps both up / down (They say this is good for about 20 concurrent users). They also connect the the line directly to their voip server, so it dosnt have to make multiple hops.

Never tried one in practice though. We run our voip over our main 200mbps down, 15 up fibre connection. Have QOS and VOIP prioritisation setup on the router, SIP ALG off etc. Seems pretty good, but as you said, if you know what to look for you can always tell your on a voip call.

Re: Ask HN: Why isn't VoIP better?

#87
post #84
post #66

Earlier quoted context omitted.

Bufferbloat is a side affect of congestion or microbursts, and not the primary cause of poor voice calls. Either packets get dropped (shallow buffer) or queued (enough buffer), and in both cases the quality of the call will suffer. Mitigation: Don't congest. If you need to, mark VOIP traffic with a DSCP value that has queues that are serviced prior to all others (e.g., EF, DSCP46).

I have almost no bufferbloat when downloading (about 1ms) but about 300ms when uploading. What does this mean?

I didn't look at that tool, but just reading this suggests that you're being shaped/policed more aggressively on egress (in the direction of your provider) than you are on ingress. Shaping and policing (typically) both use the same mechanisms as interface buffers to temporarily store packets in order to prevent congestion/discards. The distinction between them is that shaping actively buffers packets, where policing will more aggressively drop them (and aim to trigger a TCP congestion event) - in most cases, policing will involve a burst bucket that is somewhat similar to a shallow queue.

This would make sense if you have a higher bit rate from your provider for down vs up.

Re: Ask HN: Why isn't VoIP better?

#88
post #79

First, as others pointed out, you will need a decent internet connection, with minimized packet loss and jitter. Most metro area data connections and quality WiFi access points will be sufficient. However, the wifi router that comes from your provider and stuffed away on the other side of the house might not work very well. Secondly, good codecs make a world of difference. This is where I'll add the disclaimer that I…

Does it automatically report your political and religious affiliation to chinese ministry of public security? Lol, zing.

Re: Ask HN: Why isn't VoIP better?

#89
post #60

Earlier quoted context omitted.

just want to point out: vast knowledge of telephony/VOIP is not something every sysadmin should be expected to know. If you don't have telephony expertise on staff I hesitate to suggest someone build out a VOIP infrastructure on their own. It can be extremely time consuming to learn and it is definitely painful to troubleshoot.

Shouldn't it be possible for me to get some IP phones in my office and tunnel through my router to a competent online voice provider? If so, can you recommend such a provider?

Yes, that is exactly what we do at work. We have ~20 IP phones in the office plus a few in remote locations. A few of us also use softphones (X-Lite or Zoiper) & USB headsets.

Our pbx is hosted by http://sipworxx.com/ and it works great.

Re: Ask HN: Why isn't VoIP better?

#90
post #88
post #79

First, as others pointed out, you will need a decent internet connection, with minimized packet loss and jitter. Most metro area data connections and quality WiFi access points will be sufficient. However, the wifi router that comes from your provider and stuffed away on the other side of the house might not work very well. Secondly, good codecs make a world of difference. This is where I'll add the disclaimer that I…

Does it automatically report your political and religious affiliation to chinese ministry of public security? Lol, zing.

It's end-to-end encryption. For large sites, customer owns the encryption keys on their hardware so we can't intercept/decrypt even if we're ordered to.
Post reply on HN