The Most Frequently Asked Questions About RoamFree® Interworking Gateway Products


1. What is RoamFree and why is it needed?
2. What is IS-41?
3. Why is RoamFree unique?
4. How can the interworking be accomplished without RoamFree?
5. Who are likely customers for RoamFree?
6. What is the purpose of interworking networks?
7. How do the systems communicate?
8. Will my current phone work with this new interworking network?
9. What services does RoamFree support?
10. How does RoamFree accomplish interworking?
11. Switch manufacturers tend to develop proprietary systems. Has RoamFree had any problem interfacing with the various switches?
12. Are there other versions of RoamFree?
13. Can RoamFree work with cellular other than AMPS?
14. What standards is RoamFree compatible with?

1. What is RoamFree and why is it needed?

RoamFree is a gateway that enables interworking between disparate wireless networks. For example, in the United States, there are two cellular networking standards: GSM and IS-41. Within each networking standard, messages are passed along from home location registers (HLRs) to visiting location registers (VLRs) with no problem. However, there is no communication between the networking standards without an interworking process.RoamFree allows the GSM carriers to quickly build out their service area by using the RoamFree gateway to interconnect GSM and IS-41 properties for seamless roaming.

2. What is IS-41?

IS-41 is the network standard used by carriers with AMPS, NAMPS, TDMA (DAMPS), and CDMA networks.

3. Why is RoamFree unique?

RoamFree accomplishes interworking with no impact to either the home or the visited systems. It communicates via the open interworking standards. RoamFree receives messages from the IS-41 side of the network as if it were an IS-41 HLR and receives messages from the GSM side of the network as if it were a GSM VLR. One RoamFree can support multiple switches/HLRs for the GSM carrier and it is within RoamFree that the message translation occurs.

4. How can the interworking be accomplished without RoamFree?

The other option for interworking is for carriers to install a dual mode HLR. The dual mode HLR would have to reside at each HLR. If course, this approach would tend to be more costly if a carrier has multiple HLRs.

5. Who are likely customers for RoamFree?

1. GSM operators in the United States who want to expand their footprint for coverage by interworking with the legacy cellular systems.

2. CDMA carriers in a predominant GSM country who want to provide coverage outside the CDMA serving areas.

3. International gateway operators.

4. Satellite-based systems.

5. GSM operators worldwide who want to expand their coverage footprint by interworking with North America CDMA systems

6. Anyone with different wireless network standards that needs to be able to interconnect them into one seamless network.

6. What is the purpose of interworking networks?

They are primarily used for roaming. When a subscriber registers on a system other than their home system, the visited system has to get all sorts of information from the home system. For example, billing authorization and special features such as call forwarding. In addition, when someone calls a subscriber, the call is routed to their home system. The home system must know where the subscriber is to the call can be routed. All of these features are supplied by MAP (Mobile Application Parts) protocols.

7. How do the systems communicate?

The networks use the SS7 protocol at the lower levels of the OSI stack. GSM MAP and IS-41 both run on top of SS7.

8. Will my current phone work with this new interworking network?

Phones that are designated as dual-mode phones are capable of working in dual, that is two, modes. One mode would be the mode of your home carrier, GSM, and the other mode would be AMPS or CDMA to support roaming into AMPS or CDMA areas.

9. Will my current phone work with this new interworking network?

Phones that are designated as dual-mode phones are capable of working in dual, that is two, modes. One mode would be the mode of your home carrier, GSM, and the other mode would be AMPS or CDMA to support roaming into AMPS or CDMA areas.

10. What services does RoamFree support?

RoamFree supports registration, location updates, call delivery, profile modification, voice mail notification and etc.

11. How does RoamFree accomplish interworking?

RoamFree interconnects with both the IS-41 network and the GSM network. In the version of RoamFree that supports GSM customers roaming onto IS-41 networks, RoamFree appears as an IS-41 HLR to the IS-41 network and a GSM VLR to the GSM network.

When a customer whose home network is on the GSM network roams into an IS-41 network, the IS-41 network sends a message to RoamFree. RoamFree looks like an IS-41 HLR, so the visited network communicates in a normal manner as it would with another IS-41 subscriber.

RoamFree then translates IS-41 messages that it receives as an HLR into GSM VLR messages. Thus, the GSM HLR receives messages from RoamFree that look like they are coming from a GSM VLR.

12. Switch manufacturers tend to develop proprietary systems. Has RoamFree had any problem interfacing with the various switches?

RoamFree has been able to work with a variety of switches. While it is true that switch manufacturers interpret the standards somewhat differently, Synacom has worked around that to ensure interoperability for the carriers.

13. Are there other versions of RoamFree?

Yes. RoamFree has several versions. The version described above supports PCS1900/GSM carriers who want to interwork with IS-41 networks.

Another version of RoamFree allows IS-41 carriers to deliver calls onto GSM networks.

Synacom has also examined interworking with PDC, the Japanese standard, and can develop that interworking capability as needed.

14. Can RoamFree work with cellular other than AMPS?

RoamFree can interwork with any IS-41 based technology, which includes AMPS, TDMA, and CDMA.

15. What standards is RoamFree compatible with?

IS-41 Revision A, B, & CGSM MAP, Phase 1 & 2IS-126 interworking standard