Voice channels (FTTH, DOCSIS, VoLTE)

Mailman List Mirror (Read Only)
1

I need to verify some claims made by incumbents in Canada that VoLTE
data travels on a totally separate channel between the phone and the
antenna.

Does anyone have links to relevant VoLTE documentation that would
provide how VoLTE is provisioned ? I was under the impression that it
was more of an "app" on the phone that used the same IP address given
for access to Internet. Does the phone get a separate IP and possibly
separate VLAN with dedicated bandwidth to ensure voice call quality?

Or are all the performance tricks done on land beyond the antenna once
the packets are identified as VoLTE, but the phone itself just treats
them as a normal app ?

I know that for FTTH, there is a separate "channel" where the "POTS"
emulation can be provided with its own dedicated IP and bandwidth.

Would DOCSIS be the same as FTTH, with the cableco voice service riding
isnide the same DOCSIS bandwidth but with pre-allocated bandwidth, or do
they allocate separate NTSC channels with a totally separate data pipe ?

(in which case, in systems with only 42mhz of uplink frequencies, the
voice would have its own NTSC channel on uplink?

2

DOCSIS has a possibility to provision unidirectional data flows with
certain quality of service characteristics. A pair of these is usually
dedicated to a casual Internet connection, another one can be used for
layer 2 telephony service, etc. Allocating a whole TV channel frequency
would be a big waste. Not even sure it would be possible with standard
DOCSIS.

Marcin Cie�lak

3

Typically it travels on another "bearer" compared to Internet traffic.

http://blog.3g4g.co.uk/2013/08/volte-bearers.html

Think of bearers as "tunnels" between the mobile core network and the device. They have a lot in common with ATM PVCs in that they can have different QoS characteristics. So the VoLTE bearer can have scheduling priorities that means it'll always be low-latency and highest priority, meaning it might work well when the "Internet" bearer does not.

4

Many thanks for the pointer. The fact that VoLTE has its own dedicated
APN explains things.

I am however a bit confused on the "bearer" term.

Say a carrier has spectrum in 700Mhz bands A and B each 5mhz in each
direction, bonded together as a single 10mhz (each way) channel.

The docunment states:
"R.92 requires the use of a particular set of radio bearers"

Does this mean that a bearer is given specific spectrum within a block
(such as a dedicated colour on a fibre) or that it is just given
dedicated capacity on the single data channel formed by LTE compressing
all of the spectrum into one big channel ?

I though I understood the concept when the name "tunnel" had been
mentioned because I understand that a handset estabishes a "hopping"
tunnel with local IP which changes as you move from tower to tower, but
the tunnel itself maintains a permanent IP connection that remains
unchanged as you move from tower to tower. In such a concept, I could
understand each tunnel (one to the data APN, one to the IMS/VoLTE APN)
having bandwidth allocations.

But when the text brought up "radio bearer", I got confused again sicne
radio implies breaking the spectrum apart, which would reduce LTE
compression efficiency.

5

Typically it travels on another "bearer" compared to Internet traffic.

The 3G4G Blog: VoLTE Bearers

Think of bearers as "tunnels" between the mobile core network and the
device.

Many thanks for the pointer. The fact that VoLTE has its own dedicated
APN explains things.

I am however a bit confused on the "bearer" term.

Say a carrier has spectrum in 700Mhz bands A and B each 5mhz in each
direction, bonded together as a single 10mhz (each way) channel.

The docunment states:
"R.92 requires the use of a particular set of radio bearers"

the radio bearers described are are the signaling radio bearers. their
existence is independent of of the link/mac layer configuration. The mac
layer layer (e-utra) exists below the l2 bearers.

Does this mean that a bearer is given specific spectrum within a block
(such as a dedicated colour on a fibre) or that it is just given
dedicated capacity on the single data channel formed by LTE compressing
all of the spectrum into one big channel ?

I though I understood the concept when the name "tunnel" had been
mentioned because I understand that a handset estabishes a "hopping"
tunnel with local IP which changes as you move from tower to tower, but
the tunnel itself maintains a permanent IP connection that remains
unchanged as you move from tower to tower. In such a concept, I could
understand each tunnel (one to the data APN, one to the IMS/VoLTE APN)
having bandwidth allocations.

these are URBs they are terminated between the UE and the P-GW

But when the text brought up "radio bearer", I got confused again sicne
radio implies breaking the spectrum apart, which would reduce LTE
compression efficiency.

SRB and URB are the l2 presentation of the tunnels established for user
and signaling traffic.

6

SRB and URB are the l2 presentation of the tunnels established for user
and signaling traffic.

OK, so wth LTE, if carrier has 10mhz up and down, this represents a
single chunk of spectrum providing one pipe ? (in fibre terms: a single
light colour through one strand)

The "smoke and mirrors" is accomplished by having different tunnels
inside that one pipe, with some tunnels granted QoS or other
preferential treatment between the IMS/VoiP servers and the RAN ?

When a handset sends a VolTE packet to the "IMS" APN, is there any
preferential treatment given between the handset and the antenna ? Or
does preferential treatment begin at the RAN where the packet is
recognized as going to "IMS" APN and going on the fast track to it ?

or put another way. If everyone uploads a HD selfie movie at the same
time, are handset uploads slowled with normal TCP flow control (drop a
packet, no ack received, handset halves the TCP window size)?

In other words, some router near antenna, to prioriotize packets to the
IMS/VoLTE server, will flow control normal IP traffic to maintain
sufficient upload capacity for VolTE traffic ?

Or are the tunnels fixed in capacity such that unused capacity in one is
never used by the other ?

From a policy point of view, if I propose a net neutrality policy, I

have to make sure it doesn't prevent normal VoLTE functioning, while
preventing abuse of the ability for an incumbent to prioritize/zero-rate
its own services.

For instance:

AT&T in USA zero rates voice but not video calls over VoLTE.
Rogers in Canada zero rates both voice and video calls over VoLTE.

So if VoLTE video travels to the same IMS as voice, and not through the
normal IP APN, that means AT&T has to count the video traffic separately
and add it. But if Video goes through the normal IP traffic APN, it gets
counted fairly, like Skype packets, but Rogers then captures that
netflow and later deducts it from the total usage.

The issue here is that VoLTE is the new kid on the block with video
capability and incumbents can use their power to displace competitors
such as Skype/Facetime and that may constitute undue preference, unless
the standards are such that they have no choice because that it how it
has to work. (But AT&T shows that it can still count video and treat
video calls fairly compared o skype video calls).

7

SRB and URB are the l2 presentation of the tunnels established for user
and signaling traffic.

OK, so wth LTE, if carrier has 10mhz up and down, this represents a
single chunk of spectrum providing one pipe ? (in fibre terms: a single
light colour through one strand)

Not really the air interface uses OFDMA coding scheme, so it is both
divided into sub-carriers from 1.4 to 20mhz wide which are then also
scheduled accordingly.

The "smoke and mirrors" is accomplished by having different tunnels
inside that one pipe, with some tunnels granted QoS or other
preferential treatment between the IMS/VoiP servers and the RAN ?

you kinda want you qos policy to apply end-to-end in the carrier
network, not just on the ran.

When a handset sends a VolTE packet to the "IMS" APN, is there any
preferential treatment given between the handset and the antenna ?

sure, hence the qos policy template on the radio bearer.
differing numbers of subcarriers and slots can be assigned to UE based
on the services they are using.

Or
does preferential treatment begin at the RAN where the packet is
recognized as going to "IMS" APN and going on the fast track to it ?

or put another way. If everyone uploads a HD selfie movie at the same
time, are handset uploads slowled with normal TCP flow control (drop a
packet, no ack received, handset halves the TCP window size)?

Those flows going to have the best effort policy. but yes it is
reasonable to presume that in the event of congestion the best effort
queue will be preferentially dropped. likewise if you have voice and
data going at the same time they are not strictly speaking competing for
resources, because the volte radio bearer has a resource assigned to it
and the and the ip data bearer has a resource assigned to it.

8

Not really the air interface uses OFDMA coding scheme, so it is both
divided into sub-carriers from 1.4 to 20mhz wide which are then also
scheduled accordingly.

I have read in a number of places that 1 * 20mhz yields much more
capacity than 2 * 10mhz for LTE. but...

On the other hand, just read something on

https://www.nxp.com/files/wireless_comm/doc/white_paper/3GPPEVOLUTIONWP.pdf

and it states:

9

That is congruent with my understanding of how cableco voice is provisioned;
it has different rules WRT VoN -- specifically about 911 -- because the cable
company segregates it and handles it differently (your cablemodem is expected
to be tied to your service address -- or whatever terminal device does the
voice).

Cheers,
-- jra

10

With MGCP we're just using DSx Qos which is just services classification within the packet cable standard. Still runs over the same docsis network as all other traffic and not separated besides qos side of things.

We use a 64K reserved channel to set the call up, after that each call has its own service flow that is QOSed.

We also have reserved BW in the CMTS for 911 calls so that they always get through.

Where the modem resides in relation to 911 isn't really a factor as we go by services address for the account, a customer could moved the modem to another house across town and it will still work.

I know Time Warner has completely separate networks for voice and data, they didn't even reside on the same CMTS from what I understand. Don't know of anyone else doing it that way.

Luke

11

It's my jackleg appraisal -- I'm not an attorney much less an FCC specialist
attorney -- that that subjects your service to regulations and restrictions
that don't pertain to people who do it the other way; you are simply a VoN
carrier, competing with all the other VoN carriers like Vonage; if you *do*
give your own traffic priority, then you're violating... title II? Some
net neutrality provision that they don't cause they're not *moving the calls*
"over the Internet".

Cheers,
-- jra

12

​I've seen some telco types refer to this as VuIP i.e. "under IP" to
differentiate​ from VoIP such as Skype , Vonage, etc

Not sure if this applies to LTE.

j