Project

General

Profile

Actions

HSL Femto » History » Revision 2

« Previous | Revision 2/9 (diff) | Next »
laforge, 02/19/2016 10:47 PM
add links to wireshark and openbsc branch


PageOutline = The HSL 2.75G Femtocell =

The HSL 2.75G Femtocell is a relatively recent product implementing a single-ARFCN BTS with 23dBm maximum output power.

Hardware

The hardware seems to be a much more software radio approach than the nanoBTS, which are
built from telephone baseband processors.

  • Ti DaVinci TMS320DM6443A (ARM9 CPU + DSP)
  • Xilinx Spartan-3A FPGA (XC3SD1800A)
  • 128 MByte DDR-2 RAM
  • 128 MByte NAND flash
  • Realtek RTL8201 Ethernet MAC
  • Dual 12-bit 65Ms/sec ADC (ADS5232)
  • Dual 14-bit 275Ms/sec DAC (DAC5672)

As you can see, the hardware is much more powerful than you would ever
need for a simple single-ARFCN femtocell. Using the high-speed DAC/ADC,
the combined power of the FPGA (with DSP slices) and DSP, you can probably
expect that they will at least want to do multi-ARFCN (if not 3G) on the
same hardware at some later point.

There's a dedicated [wiki:HSL_Femto/Hardware] page with more details.

Protocol
They use an odd down-sized minimalistic dialect of the ip.access Abis/IP.

=== ACS ===
Prior to connecting to the BSC, the cell downloads its current configuration
via https, using a HTTP POST of its serial number.

=== IPA layer ===
The IPA multiplex layer does not have PING/PONG keepalives, and it does
not do the ID_GET/ID_RESP/ID_CONF identification with the Unit ID.
Furthermore, both OML and RSL are encapsulated in the same TCP connection.

Stream identifier 0xDD is used for passing string debug messages from the
BTS to the BSC.

Neither OML nor RSL are implemented fully, as per 12.21 / 08.58

=== RSL ===
It seems to have a very 'creative' interpretation of the RSL specification. Some
examples: * use of SACCH INFO MODIFY instead of SACCH FILLING for default SI5/SI6 * it forgets to send RSL CHAN REL ACK on TS1...7 * it does not implement RSL CHAN MODIFY * it seems to be unable to run without DTX * it often detects RACH requests where there are none (!)

=== OML ===
OML is almost not present at all. Only software download and setting of
ARFCN + BSIC are supported. No managed objects, no state transitions, no
software activation procedures/events at all.

The configuration of each timeslot seems to happen 'on demand', i.e.
there are no OML commands to configure the timeslots, but it depends on your
RSL CHAN ACT whether a timeslot will become a TCH/H or TCH/F.

I have not managed to use a SDCCH/8 anywhere, just TCH/F and TCH/H as well as
SDCCH/4.

The BCCH claims to be a Combination 4, but in reality it is a Combination 5
(i.e. including the SDCCH/4)

=== GPRS ===
GPRS is quiite odd, too. The BSSGP is encapsulated in the RSL L3_INFO_IE,
this means we will have to run a NS link from the BSC to the SGSN, combining
all the BSSGP links from HSL Femtocells to the BSC.

Software support

=== wireshark ===

We have some wireshark patches for adding HSL RSL/OML support: * http://cgit.osmocom.org/cgit/openbsc/plain/wireshark/0005-rsl-hsl.patch * http://cgit.osmocom.org/cgit/openbsc/plain/wireshark/0006-abis_oml-hsl.patch

=== OpenBSC ==

OpenBSC support is being worked on in the {{{laforge/hsl}}} branch of openbsc.git: * http://cgit.osmocom.org/cgit/openbsc/log/?h=laforge/hsl

Files (0)

Updated by laforge about 8 years ago · 2 revisions

Add picture from clipboard (Maximum size: 48.8 MB)