Questions and topics regarding GSM and SS7

ss7 role in gsm network

leekk8 said:

Sharing some info about SS7:

All the submodules in SS7 protocol stack:
- MTP1
- MTP2
- MTP3
- SCCP
- ISUP
- TUP
- SNM
- SNT
- MAP
- INAP/CAP
- TCAP

Added after 1 minutes:

Sharing info about GSM:

All the elements in GSM network:
- BTS
- BSC
- MSC
- VLR
- HLR
- AUC

Click to expand...

you forget the XCDR

Added after 19 minutes:

GSM Network Components




Now: GSM Terrestrial Interfaces


The terrestrial interfaces comprise all the connections between the GSM system entities, apart from the Um, or air interface. They are represented on the diagram opposite by the lines that connect the various entities together. The GSM terrestrial interfaces and message-transport mediums all conform to ITU-TSS
specifications widely used throughout the world. As we stated previously, it is from this use of standardized interfaces that the flexibility of GSM largely derives. The terrestrial interfaces transport the traffic across the system and allow the passage of the thousands of data messages necessary to make the system function. They transport the data for software downloads and uploads, the collection of statistical information and the implementation of operations and maintenance commands.
The standard interfaces used are as follows:
* 2 Mbit/s.
* Signalling System ITU-TSS #7 (“C7” or ‘‘SS#7”).
* X.25 (packet switched data); (LAPB).
* A bis using the LAPD protocol (Link Access Procedure “D”).
Whatever the interfaces and whatever their function, they will often share a common physical bearer (cable) between two points, for example, the MSC and a BSS.



ITU-TS Signalling System #7
The diagram opposite illustrates the use of C7 in the GSM system; carrying signalling and control information between most major entities, and to and from the PSTN. The following message protocols, which are part of C7, are used to communicate between the different GSM network entities:






* Interfacing the PSTN, the MSC performs call signalling functions using the
Telephone User Part (TUP), or interfacing the ISDN, the ISDN User Part (ISUP).
* Between the MSC and the BSC, the Base Station System Management
Application Part (BSSMAP) is used. The Direct Transfer Application Part (DTAP)
is used to send messages between the MSC and the mobile (MS). MAP is used
between the MSC and the VLR, EIR, and HLR.


Acronyms:

BSSAP Base Station System Application Part
BSSMAP Base Station System Management Application Part
DTAP Direct Transfer Application Part
ISUP ISDN User Part
MAP Mobile Application Part
SCCP Signalling Connection Control Part
TUP Telephone User Part
TCAP Transaction Capabilities Application Part


BSC Connections



Regards

difference dtap isdn

What you mean by XCDR?

Do you refer to xDR? As I know, xDR is a record of signaling message between all these interfaces...normally we have CDR, SDR and TDR.

difference between gsm ss7 and ss7 core

XCDR..the Transcoder
In GSM it is not called XCDR..it is called TRC - Transcoder Controller, an acronym used by Ericsson.
It is a functionality integrated in the BSC.

roaming gsm ss7

leekk8 said:

What you mean by XCDR?

Do you refer to xDR? As I know, xDR is a record of signaling message between all these interfaces...normally we have CDR, SDR and TDR.

Click to expand...

it is the transcoder, it is a cabinet installed in the MSC, it is one of Motorola's equipment for the GSM system, see this picture below for it



Transcoder (XCDR)
The Transcoder (XCDR) is required to convert the speech or data output from the MSC (64 kbit/s PCM), into the form specified by GSM specifications for transmission over the air interface, that is, between the BSS and MS (64 kbit/s to 16 kbit/s and vice versa) The 64 kbit/s Pulse Code Modulation (PCM) circuits from the MSC, if transmitted on the air interface without modification, would occupy an excessive amount of radio bandwidth. This would use the available radio spectrum inefficiently. The required bandwidth is therefore reduced by processing the 64 kbit/s circuits so that the amount of information required to transmit digitized voice falls to a gross rate of 16 kbit/s.

The transcoding function may be located at the MSC, BSC, or BTS. The content of the 16 kbit/s data depends on the coding algorithm used. There are two speech coding algorithms available and selecting which one to use depends on the
capabilities of the mobile equipment and the network configuration.

The Full Rate speech algorithm is supported by all mobiles and networks. It produces 13 kbit/s of coded speech data plus 3 kbit/s of control data which is commonly referred to as TRAU data (Transcoder Rate Adaption Unit). The TRAU data on the downlink will be used by the BTS and therefore removed from the 13 k of speech data before transmission on the air interface. the 13 kbit/s of speech data is processed at the BTS to form a gross rate of 22.8 kbit/s on the air interface which includes forward error correction. In the uplink direction the BTS adds in TRAU data which will be used by the transcoder.

Enhanced Full Rate is an improved speech coding algorithm and is only supported by Phase 2+ mobiles and is optional in the Network. It produces 12.2 kbit/s from each 64 kbit/s PCM channel. The TRAU data in this case is made up to 3.8 kbit/s to keep the channel rate to and from the BTS at 16 kbit/s as for Full Rate. As with Full Rate the TRAU data is used at the BTS and Transcoder.

For data transmissions the data is not transcoded but data rate adapted from 9.6 kbit/s (4.8 kbit/s or 2.4 kbit/s may also be used) up to a gross rate of 16 kbit/s for transmission over the terrestrial interfaces, again this 16 kbit/s contains a 3 kbit/s TRAU. As can be seen from the diagram opposite, although the reason for transcoding was to reduce the data rate over the air interface, the number of terrestrial links is also reduced approximately on a 4:1 ratio.

lu message gsm

Ohh...it's actually transcoder...thanks for your detailed information.

where does ss7 reside in gsm network

Hi

I've have a qusetion about SS7 and GSM. I've started a topic:



Can anybody help me to understand next: The "Border Roaming Protocol" tools monitor LU requests towards HLR. They match the VLR in the LU request with the IMSI. If the VLR is different form home the LU is denied and SIM will try to make LU in another VLR.

I understand the principles of previous, but I don't understand the mechanism how that work. What exactly is happening?? Wich SS7 messages are beign monitored, and wich data in that messages?

Really need help about this one. Thanks.

what is the role of ss7 in gsm

rewind1990 said:

Hi

I've have a qusetion about SS7 and GSM. I've started a topic:



Can anybody help me to understand next: The "Border Roaming Protocol" tools monitor LU requests towards HLR. They match the VLR in the LU request with the IMSI. If the VLR is different form home the LU is denied and SIM will try to make LU in another VLR.

I understand the principles of previous, but I don't understand the mechanism how that work. What exactly is happening?? Wich SS7 messages are beign monitored, and wich data in that messages?

Really need help about this one. Thanks.

Click to expand...

Im not sure what's Border Roaming Protocol. From your explanation, this should involve the LU message only. Normally steered roaming is working like this, when you're attached to a VLR and trying to do LU, your HLR will examine the VLR. If the VLR is not the preferred network, it will reject the LU. Then your phone will not get location updated, and it will do LU again. Normally after few times still same VLR, HLR will accept the LU. So, in terms of signalling, the only messages involved is LU.

In LU message, data such as IMSI and VLR address are available.

1 ss7 link data rate

Border roaming protocol is a type of steered roaming. It simply deny access to visitor network when LU request come. It denies predefined number of times, and then allow mobile device to connect to visited network, because it is assumed that there is no home network coverage if mobile device is not able to connect to home network after predefined number of times.

Protocol is using SS7 network to intercept LU request from visited VLR to home network HLR.

By this, it is assured that there will be no accidental roaming for home users, except when there is really no home network coverage.

ericsson hlr commands

rewind1990,

then you already have the whole idea...what's your question here?

ss7 users gsm

leekk8 said:

rewind1990,

then you already have the whole idea...what's your question here?

Click to expand...

In the meantime I've found what I was looking for, so I just share knowledge.

Regards

gsm version of ss7

rewind1990 said:

leekk8 said:

rewind1990,

then you already have the whole idea...what's your question here?

Click to expand...

In the meantime I've found what I was looking for, so I just share knowledge.

Regards

Click to expand...

Ok, good...thanks for your sharing...if you have further information of this kind of protocol, share with us as well

vlr gt

Hi!
Which kind of SLAs or service Level Agreements should be present while signing an international SS7 trasit contract , e.g with France Telecom.
I will appreciate a your reply.

Re: GSM and SS7

Hello everyone,

I was wondering if the same kind of SS7 information available at the A-interface (between the MSC and BSS) can also be available at the HLR. I am particularly interested in probing/monitoring the SS7 network for certain events like call drops or busy tones as well as collecting information such as the IMEI.

Also, from reading the replies and schematics I understand that the MSC and HLR are in the same physical unit?? How many MSC-s does an average operator have anyway?

Many many thanks!!