This is just a proposal how a scalable cost-effective solution can look like. It is not implemented yet, but the goal is to work out a right approach. I developed quite similar things in 2003, when I interfaced ip.access BSC to S-12 and AXE-10. This is a piece of operator infrastructure, desired to be sold to MNO. In Russia it also assumes certification procedure, held by authorized center. On Mon, Mar 25, 2013 at 1:16 PM, John Wu <jwjohn0@gmail.com> wrote:

Hi Dmitri, Have you developed the solution connect private GSM network to operator core network? But this should be allowed by the local operator, right?

On Sat, Mar 23, 2013 at 5:09 PM, Dmitri Soloviev <dmi3sol@gmail.com>wrote:

...

Hi

we've got several requests to extend existing GSM networks with our radio equipment, where ip transport is appreciated.

Please take a look at my vision of interfacing A-over-ip to a legacy GSM A-interface.

Building blocks:

1. OpenBSC with ip.access-compatible A-over-ip interface

2. MGCP-controlled transcoder, built with Sangoma D-series cards. Can be assumed as a shared resource, available for several BSC instances. http://www.sangoma.com/assets/docs/datasheets/en/d500.pdf

3. TelscaleSS7card - a stand-alone signaling and media gateway, with 2 E1 and 2 Ethernet interfaces, running embedded linux on board. It converts A-over-ip to A-interface, acts as MGCP call agent for BTSs, transcoders and other telscaleSS7cards. A card is implemented in PCI form factor, but bus is used just to provide power supply. In other words, a card can act either as a combined SG+MG, converting A-over-ip into SS7 and RTP into E1 timeslot, or just a MG, converting RTP into E1, without any impact on the host system.

When a [signaling gateway + call agent] detects ASSIGNMENT_REQUEST or HANDOVER_REQUEST, it stores cic value. As soon as ASSIGNMENT_COMPLETE or HO_REQ_ACK is detected, it builds RTP chain that unites BTS<->transcoder<->media_gateway. The chain is broken after the call is finished.

Depending on the chosen cross plane, 4U 19" industrial PC can carry several BSC instances with transcoding, serving about 20 E1 interfaces (ea about 80 ARFCNs). Performance requirements for industrial PC cards are also negligible: computer will run OpenBSC and configure transcoder cards, being controlled by means of MGCP.

Best Regards, Dmitri