CS Voice Services over HSPA

3GPP is quite active in moving as many things as possible over to the HSPA high speed (packet based) shared channel on the UMTS air interface to save resources, increase capacity and to reduce mobile power consumption. An example I have reported on in the past is the Enhanced Cell-FACH feature. Looks like the traditional circuit switched voice service is now also set to migrate to HSPA with the CS (circuit switched) Voice Services over HSPA feature introduced in 3GPP Release 8.

This whitepaper from Qualcomm gives a good introduction. According to the paper, "all that is required" to put the circuit switched voice service on the packet switched high speed shared channel is a software upgrade in the radio network and the mobile. Like today, the MSC forwards the voice call to the Radio Network Controller (RNC) without any changes. On the RNC, the Adaptive Multi Rate (AMR) speech packets are then not put into a logical circuit switched bearer for a dedicated air interface channel but are instead put into PDCP packets which are then sent to the base station. The base station then schedules those AMR in PDCP packets on the high speed shared channel in the same way as IP in PDCP packets coming from the SGSN but gives them a higher priority.

On the mobile side a software enhancement is required to indicate to the network that CS voice over HSPA is supported. Further, the lower layer voice protocol stack needs to be enhanced to receive the AMR packets on the high speed shared channel instead of on a dedicated channel to the mobile.

As no IP layer is involved for transmitting the AMR speech packet in the radio network I would call this a Voice over Packet service. So be careful, this enhancement can't be counted as a wireless VoIP variant and is not related with the CS Voice over LTE proposal I reported on here, which is fully based on IP.

Will this feature make it into real networks? Time will tell. What do you think?

2 thoughts on “CS Voice Services over HSPA”

  1. Hi Hayo,

    Thanks for the link, saw it on LTE watch this morning as well. This one’s been long in the making (not as new as it looks like) and it has a twist to it 🙂

    Kind regards,

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