How do international carriers handle the routing of calls based on country codes?
Posted: Mon May 19, 2025 4:23 am
International carriers handle the routing of calls based on country codes by leveraging a standardized international numbering plan and a sophisticated signaling network. The key elements involved are the E.164 standard and the Signaling System No. 7 (SS7) network (or its modern IP-based equivalents). Here's a breakdown of the process:
1. The E.164 International Numbering Plan:
The International Telecommunication Union (ITU) developed the E.164 standard, which defines the format for international telephone numbers. This standard ensures that every phone number worldwide is uniquely identifiable.
An E.164 number has a maximum of 15 digits and typically includes:
Country Code (CC): A 1 to 3-digit prefix that uniquely identifies the country of the called party (e.g., +880 for Bangladesh, +1 for the USA, +44 for the UK).
National Destination Code (NDC): This can be an area code or a network operator code within the country. Its length varies.
Subscriber Number (SN): The unique number assigned to the individual subscriber or device within the NDC.
The '+' sign preceding the country code is a standard way to indicate an international number and instructs the originating network to use the appropriate international dialing prefix for the country from which the call is being made.
2. Call Initiation and the Role of the Originating Carrier:
When a caller dials an international afghanistan mobile phone number list number (e.g., from Dhaka to a number in the UK), their local carrier (e.g., a Bangladeshi mobile operator or BTCL) analyzes the dialed digits.
The carrier recognizes the country code (+44 for the UK) as indicating an international call.
3. Routing Through the Signaling Network (SS7 or IP-Based):
The originating carrier uses a signaling network, traditionally SS7 and increasingly IP-based signaling protocols like SIP (Session Initiation Protocol), to set up the call.
A crucial message, similar to the Initial Address Message (IAM) in SS7, is generated. This message contains the full E.164 dialed number, including the country code.
The signaling network routes this message through a series of interconnected switching centers and international gateways.
4. Utilizing Country Codes for International Gateway Selection:
International gateways are key nodes in the network that handle traffic exchange between different countries.
Based on the destination country code in the signaling message, the originating carrier's network (or transit carriers involved) determines the appropriate international gateway to route the call towards the destination country.
Routing tables within these gateways are configured to associate specific country codes with the network addresses (point codes in SS7 or IP addresses/ASNs in IP networks) of international carriers in the destination country.
5. Handover to the Destination Country's Carrier:
Once the call reaches an international gateway in or connected to the destination country (identified by the country code), it is handed over to a carrier within that country.
This incoming international carrier then analyzes the remaining digits (NDC and subscriber number) to route the call within its national network to the correct local exchange or mobile switching center serving the called party.
6. National Routing within the Destination Country:
The routing within the destination country proceeds using national numbering plans and signaling protocols to reach the specific subscriber number.
In essence, international carriers rely on the country code as the primary key for directing a call out of the originating country and into the network of the destination country. The E.164 standard ensures a consistent and unambiguous format for these country codes, allowing networks worldwide to correctly interpret and route international calls. The signaling network acts as the coordination mechanism, using the country code to select the appropriate pathways and interconnections between international carriers.
1. The E.164 International Numbering Plan:
The International Telecommunication Union (ITU) developed the E.164 standard, which defines the format for international telephone numbers. This standard ensures that every phone number worldwide is uniquely identifiable.
An E.164 number has a maximum of 15 digits and typically includes:
Country Code (CC): A 1 to 3-digit prefix that uniquely identifies the country of the called party (e.g., +880 for Bangladesh, +1 for the USA, +44 for the UK).
National Destination Code (NDC): This can be an area code or a network operator code within the country. Its length varies.
Subscriber Number (SN): The unique number assigned to the individual subscriber or device within the NDC.
The '+' sign preceding the country code is a standard way to indicate an international number and instructs the originating network to use the appropriate international dialing prefix for the country from which the call is being made.
2. Call Initiation and the Role of the Originating Carrier:
When a caller dials an international afghanistan mobile phone number list number (e.g., from Dhaka to a number in the UK), their local carrier (e.g., a Bangladeshi mobile operator or BTCL) analyzes the dialed digits.
The carrier recognizes the country code (+44 for the UK) as indicating an international call.
3. Routing Through the Signaling Network (SS7 or IP-Based):
The originating carrier uses a signaling network, traditionally SS7 and increasingly IP-based signaling protocols like SIP (Session Initiation Protocol), to set up the call.
A crucial message, similar to the Initial Address Message (IAM) in SS7, is generated. This message contains the full E.164 dialed number, including the country code.
The signaling network routes this message through a series of interconnected switching centers and international gateways.
4. Utilizing Country Codes for International Gateway Selection:
International gateways are key nodes in the network that handle traffic exchange between different countries.
Based on the destination country code in the signaling message, the originating carrier's network (or transit carriers involved) determines the appropriate international gateway to route the call towards the destination country.
Routing tables within these gateways are configured to associate specific country codes with the network addresses (point codes in SS7 or IP addresses/ASNs in IP networks) of international carriers in the destination country.
5. Handover to the Destination Country's Carrier:
Once the call reaches an international gateway in or connected to the destination country (identified by the country code), it is handed over to a carrier within that country.
This incoming international carrier then analyzes the remaining digits (NDC and subscriber number) to route the call within its national network to the correct local exchange or mobile switching center serving the called party.
6. National Routing within the Destination Country:
The routing within the destination country proceeds using national numbering plans and signaling protocols to reach the specific subscriber number.
In essence, international carriers rely on the country code as the primary key for directing a call out of the originating country and into the network of the destination country. The E.164 standard ensures a consistent and unambiguous format for these country codes, allowing networks worldwide to correctly interpret and route international calls. The signaling network acts as the coordination mechanism, using the country code to select the appropriate pathways and interconnections between international carriers.