Re: [rtcweb] LTE using AM_RLC or UM_RLC mode for UDP?

On Jul 19, 2012 4:41 AM, "Göran Eriksson AP" <goran.ap.eriksson@ericsson.com>
wrote:
>
>
> ________________________________________
> Från: rtcweb-bounces@ietf.org [rtcweb-bounces@ietf.org] f&#246;r Harald
Alvestrand [harald@alvestrand.no]
> Skickat: den 19 juli 2012 12:07
> Till: rtcweb@ietf.org
> Ämne: [rtcweb] LTE using AM_RLC or UM_RLC mode for UDP?
>
> Branching off a discussion because we seem to have two people saying
> contradictory things about something that may actually have a clear
answer:
>
> When sending an UDP packet over a random port pair across an LTE
> network, is it transferred in acknowledged mode (with L2-level
> retransmissions) or in unacknowledged mode (without retransmissions)?
>
> The possible answers seem to be (if I understand the statements
correctly):
>
> - Acknowledged (Cameron)

Works in mobile network

> - Unacknowledged (Fabio)
> - "It depends"
>
>     As far as I know, both AM and UM can be used in a "radio bearer" in
LTE. Whether to use AM/UM when realizing/configuring
>     a "radio bearer"  depends partly on the requirements on delay, packet
loss, etc for the "radio bearer".
>

It is a radio bearer parameter controlled by the qos profile on a per
bearer basis. It has nothing to do with dscp, udp, or the application you
are using.... It has do more with the user profile and apn in use.... More
like layer 1 setup than layer markings or layer 7 apps

>    AM introduces delay but how much differs of course from 2G, 3G, LTE
(4G). For this reason UM has been preferred.
>    With LTE however- since the retransmission- things may be different
and AM *may* be useful even for RTC radio bearers.
>

All theoretically correct so far, i am not sure how much UM exists in the
real world

>    I guess it also depends on the characteristics of the specific radio
network in question.
>

Actually, it depends on implementation. UM is generally not implemented
afaik. A MAJOR radio manufacturer confirmed they have no support for UM in
practical LTE deployments, only AM.  At the network i work at, there is no
plan for UM support in any scenario, which is pretty much the default
setting and radio vendor recommentation. I tried to push UM on them after
our discussion on list, but no luck.

CB
>   In the end, I am not sure exactly how it is of relevance for this WG
but that may in itself be worth while discussing and both
>   Cullens DSCP draft and Markus Mobile draft is a first step.
>
>
> Unlike some other arguments in the parent thread, this one seems to be
> amenable to source citations.
>
> On 06/27/2012 11:11 PM, Fabio Pietrosanti (naif) wrote:
> > On 6/27/12 10:54 PM, Cameron Byrne wrote:
> >>> You are saying that in EDGE, UMTS, HSDPA when an IP stack send an UDP
> >>> packet, it will handled from L2 like in the old age of GSM CSD and be
> >>> automatically retransmitted?
> >>>
> >> Yes. LTE too.
> > I read (by googling cause i don't have LTE access) that also LTE uses
> > for IPTV and all other IP streaming applications the UM_RLC
> > (unacknowledged mode).
> >
> > So also LTE should not do retransmission, unless being set in AM_RLC
> > (acknowledged mode).
> >
> > Fabio
> > _______________________________________________
> > rtcweb mailing list
> > rtcweb@ietf.org
> > https://www.ietf.org/mailman/listinfo/rtcweb
>
>
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