VoIP question: Kbps combined or doubled for duplex?

[PliotronX]

Hey guys, experimenting in a VoIP class and wondering if say G.728 is quoted at 16Kbps, is that total for a single connection or is it 16K up/16K down = 32Kbps total? I just wanted to make sure because it appears from this table it would be 32Kbps total. The reason for my questions being that lines take so much bandwidth and my professor keeps expounding gigabit ethernet but for all intents and purposes I think 100Mbps FD is fine for VoIP and would support dozens of connections so I wanted an accurate figure to back me up. 32K would mean ethernet could support up to 63 lines (with some tweaked QoS) which is more than enough for 90% of businesses I deal with...

Anyone see a flaw in my thinking?

 

[drebo]

The voice payload is 16Kbps, but there are headers to consider as well. 32Kbps is a good estimate after headers are considered. If you're going over a GRE or IPsec tunnel, though, you have to add a good bit more.

That is for a single call leg (direction.)

In regards to 100mbps vs 1gbps, most phones only have 100mbps ports on them (though this is slowly changing.) That said, it's never a bad idea to think about growth. Gigabit to the desktop is pretty much the standard at this point.

That said, inter-site capacity planning is beyond the scope of any college course on networking, so whatever your professor says is probably wrong in that regard.

 

[PliotronX]

Ah, thank you those are great points! Yeah he is more business savvy than technically inclined but I enjoy the class and will earn a certification. I just think 100Mb is perfectly fine at the access layer. Gigabit or no it'll all be constrained by that T1 or DS3 because damn near all phone calls are to lines outside of the office/network. Just thinking around

 

[kevnich2]

Well it depends. End user connections, most of the time 100mb/s FE will be sufficient. If you're talking the uplink trunks between switches, 100mb/s FE won't cut it for alot of businesses. Business data and voice usage is increasing big time and the cost difference is negligible between FE and GE. But for switch uplinks and trunks, I wouldn't go anything below 1000mb/s As far as 16kb/s vs 32kb/s - it's 16kb/s symmetrical, meaning 16kb/s up and 16kb/s down. Just like FE is quoted as 100mb/s - but if it's full duplex that's 100mb/s up and 100mb/s down.

In network design, you always want to think forward as well. I would never stick 60 phones on a single 100mb/s FE connection as when you combine traffic from desktop's and other equipment and broadcast traffic, no.

As far as your last point being the T1 - T1's are very quickly becoming yesterday. As businesses move to VOIP, T1's are being replaced by faster and cheaper MetroE fiber lines and most calls on business phone systems are usually internal calls. I usually use a factor of 10/1 to allocate internal phones to how many outside voice channels I need to plan for, obviously taking the business itself into account.

 

[Mushkins]

As far as your last point being the T1 - T1's are very quickly becoming yesterday. As businesses move to VOIP, T1's are being replaced by faster and cheaper MetroE fiber lines and most calls on business phone systems are usually internal calls. I usually use a factor of 10/1 to allocate internal phones to how many outside voice channels I need to plan for, obviously taking the business itself into account.

It depends on where you are, honestly. We just put new circuits in a suburban office for our VoIP phones and got quotes on T1s and MetroE. MetroE to our building was somewhere to the tune of $1300/mo for their slowest offering whereas a T1 cost us less than half of that and still more than met our bandwidth needs as a strictly voice line. I'd imagine in a city, MetroE would be more competitive since it's probably already being run from the telco to somewhere reasonably close to your building.

 

[kevnich2]

It depends on where you are, honestly. We just put new circuits in a suburban office for our VoIP phones and got quotes on T1s and MetroE. MetroE to our building was somewhere to the tune of $1300/mo for their slowest offering whereas a T1 cost us less than half of that and still more than met our bandwidth needs as a strictly voice line. I'd imagine in a city, MetroE would be more competitive since it's probably already being run from the telco to somewhere reasonably close to your building.

It also depends on the carrier as well. Comcast and old telco's (verizon,att,etc) don't always price them competitively, to me they're trying to milk their copper infrastructure for all it's worth. We've had literally zero outages since switching all of our offices to fiber based MetroE from copper T1's 2 years ago. That to me is worth the price considering the latency and bandwidth fiber gives us between office locations.

 

[yinan]

100 Mb is no longer even close to sufficient for the desktop. You need 1 GB minimum.

 

[PliotronX]

Truly awesome posts guys, thank you so much! As it so happens I am also in my last semester of a Cisco course and this semester is about WAN tech and I have read of ethernet WAN, but how does it differ from MetroE? I'll have to keep that uptime of MetroE in mind as T1's in use at various remote locations of clients seem to go down usually for weather related reasons while the most recent was a mouse chewing through cabling into the demarc (they are not allowed to use rat poison for some reason!).

Another question, has anyone attempted to establish a SIP trunk between a Lync server and Asterisk call manager? Do you think trying to simulate a real-world setup like this is making it too complicated?