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

________________________________________
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)
- 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".

   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.

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

  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
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> rtcweb@ietf.org
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