Roaming allows mobile subscribers to access voice and data services outside their home network coverage area by using a visited network. It requires roaming agreements between operators. There are several entities involved including home networks, visited networks, and clearing houses. Roaming can be national, international, or between different standards. Inbound roaming refers to customers of other operators using a home operator's network, while outbound refers to home customers using other networks. Roaming scenarios describe how calls are routed for subscribers roaming within and between networks. GSM technology benefits roaming by providing worldwide access across standards through a single number and device.

1. Telecom Roaming Overview
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2. Objective
 Roaming Overview
 Entities Related to Roaming Service
 Home Network & Visited Network
 National, International, Inter-standard Roaming
 Inbound & Outbound Roaming
 Roaming Scenario’s
 Benefit of GSM technology in Roaming
 Jargon

3. Roaming Overview
 Roaming is an ability to access mobile data and voice services even
if subscriber is outside the coverage area of HOME Network.
 It is possible via using VISITED Network services.
 To provide roaming facility to subscribers, operators should have
roaming agreement with the other operators in different places.

4. Roaming Overview …
City 1 (Home Area)
Subscriber’s own
area where they are
using its own
providers services
Home Operator Hutch Area
Visited Operator’s
Area (Roaming
Partner of Hutch)
City 2 (Visited Area)
Subscriber is on
Roaming.
Other operators
Network
Infrastructure
Hutch Network
Infrastructure
Hutch
Subscriber
MSC
MSC
Switch
Cell phone
Switch
Hutch Subscriber
but using other
operator services
for Roaming
purpose
Cell phone
Roaming
Agreement
Present between
Hutch and other
Operators

5. Entities Related to Roaming Service
 Home Network (HPMN) - Coverage area of subscribers own telecom
operator.
 Visited Network (VPMN) – Coverage area of another operator which is
providing telecom network access to home operator subscriber.
 Clearing House – Entity which is a mediator between home and visitor
operator to interchange their data in specified format.
 Roaming Agreement – To provide roaming facility both the operators
(Home and Visitor) should have agreement to use each others network
infrastructure.
 Data Clearing – Facility to validate, filter and clear the data from one
operator to another operator.

6. Home Network & Visited Network
Operator1 & Operator2 have
Roaming Aggrement
Roaming Data
from Operator2
for Operator1
Roaming Data
from Clearing
house to
Operator1
Operator1 suscriber in
Operator1 coverage area
Clearing House
Cell phone
City
NE
Cell phone
Visited Network
NE
Home Network
Operator1 suscriber in
Operator2 coverage area

7. National, International, Inter-standard
Roaming
 National Roaming – If visited Network is in the same country, it is
called National Roaming.
 International Roaming – If the visited Network is in the different
country, It is called international or Global Roaming.
 Inter-standard roaming - If the visited network operates on a different
technical standard than the home network, this is known as Interstandard roaming.

8. Inbound & Outbound Roaming
Assuming – Airtel as a home operator
 Inbound Roaming – Customers of other operator roaming in
Airtel area and using Airtel infrastructure then this activity is
called inbound roaming. Only those customers can roam in
Airtel network whose operator has Inbound Roaming
agreement with Airtel.
 Outbound Roaming – Outbound Roaming refers to Airtel
customers roaming in network of other operators area.
Customers of Airtel can roam in network of other operators
with whom Airtel has Outbound Roaming agreement.

9. Roaming Scenario’s
Scenario 1 - When Roamer receives calls while on roaming, all his calls will reach the MSC of his
Home Network in the first instance. He will be traced in his visited network and the calls are
therefore forwarded there.
City 1 (Home Area)
Subscriber’s own
area where they are
using its own
providers services
Home Operator Hutch Area
Hutch Network
Infrastructure
Visited Operator’s
Area (Roaming
Partner of Hutch)
City 2 (Visited Area)
Subscriber is on
Roaming.
Caller calling to
Hutch Roamer
MSC
HUTCH MSC
Other Operators NE
Hutch NE
Other operators
Network
Infrastructure
Caller
Roaming
Agreement
Present between
Hutch and other
Operators
Reciever
Hutch Subscriber
but using other
operator services
for Roaming
purpose

10. Roaming Scenario’s
Scenario 2- When roamer makes calls to his Home Network (HPLMN), he obviously knows that he
is temporarily out of his home network and thus his calls are routed through his temporary
home network ie. visited network (VPLMN).
City 1 (Home Area)
Subscriber’s own
area where they are
using its own
providers services
Home Operator Hutch Area
Hutch Network
Infrastructure
Visited Operator’s
Area (Roaming
Partner of Hutch)
City 2 (Visited Area)
Subscriber is on
Roaming.
Hutch User
Receiving Hutch
Roamer Call
MSC
Other Operators NE
HUTCH MSC
Hutch NE
Other operators
Network
Infrastructure
Receiver of Hutch
Roaming
Agreement
Present between
Hutch and other
Operators
Caller - Hutch Roamer
Hutch Subscriber
but using other
operator services
for Roaming
purpose

11. Roaming Scenario’s
Scenario 3-When he makes calls within his visiting network which is his temporary home network,
his calls are routed within that without being routed through his home network (HPLMN).
City 1 (Home Area)
Subscriber’s own
area where they are
using its own
providers services
Home Operator Hutch Area
Hutch Network
Infrastructure
Visited Operator’s
Area (Roaming
Partner of Hutch)
City 2 (Visited Area)
Subscriber is on
Roaming.
Caller - Hutch Roamer
MSC
Other Operators NE
User Receiving
Hutch Roamer
Call
HUTCH MSC
Hutch NE
Other operators
Network
Infrastructure
Reciever
Roaming
Agreement
Present between
Hutch and other
Operators
Hutch Subscriber
but using other
operator services
for Roaming
purpose

12. Roaming Scenario’s
Scenario 4 - When he is making calls to networks other than his home network or the temporary
home network, his calls are routed through the temporary home network only.
City 1 (Home Area)
Subscriber’s own
area where they are
using its own
providers services
City 2 (Visited Area)
Subscriber is on
Roaming.
Hutch Network
Infrastructure
Home Operator Hutch Area
Visited Operator’s
Area (Roaming
Partner of Hutch)
City 3 (Receiver
Area)
City3 User
Receiving Hutch
Roamer Call
Caller - Hutch Roamer
Hutch Subscriber
but using other
operator services
for Roaming
purpose
HUTCH MSC
Reciever
MSC
Hutch NE
Other Operators NE
MSC
Other operators
Network
Infrastructure
Roaming Agreement
Present between
Hutch and other
Operators
City3 Operators NE
Roaming Agreement
Present between City2
& City3 Operators

13. Benefit of GSM technology in Roaming
 GSM Roaming, which involves roaming between GSM
networks, offers the convenience of a single number, a
single bill and a single phone with worldwide access to over
191 countries.
 The convenience of GSM Roaming has been a key driver
behind the global success of the GSM Platform.

14. Jargon
 PLMN - Public Land Mobile Network.
 HPLMN - Home Public Land Mobile Network (Home Network ie. say the state of West
Bengal)
 VPLMN - Visited Public Land Mobile Network (Visited Network - say the state where
roaming - outside West Bengal)
 Notional TAX - The Trunk Auto Exchange of a particular State (say for West Bengal it is
Asansol; for Orissa it is Cuttack and so on). Each state has a Level 1 TAX through which
the calls for & from other states pass.
 PSTN Phone - Public Switched Telephone Network ie. a Landline Phone.
 PSTN Charges - The fixed line phone charges either Local Call Charges or STD
Charges.
 Air Time - The duration of the call ie. during which time the call is there in the Air.
 POI - Point of Interconnect - This is where the mobile network is connected to the PSTN.
 SA - Service Area - The area served by a particular operator. Usual a state boundary.
 MSC - Mobile Switching Center ie. Mobile Exchange.
 BSC - Base Station Controller - It is an interface between the MSC on the one side and
the BTS on the other.
 BTS - Base Transceiver Stations (Towers)
 Billing and Accounting for Roaming Group (BARG) - A subgroup of the GSM
Association that focuses on the financial, administrative, and procedural issues related to
roaming (visiting) customers.

15. THANKS