Data Communications Systems : Internet

The Internet is a public data network that interconnects private and government computers. The Internet transfers data from point-to-point by packets that use Internet protocol (IP). Each transmitted packet in the Internet finds its way through the network switching through nodes (computers). Each node in the Internet forwards received packets to another location (another node) that is closer to its destination. Each node contains routing tables that provide packet-forwarding information. The Internet was designed to allow continuous data communication in the event some parts of the network were disabled. The world wide web (WWW) is an application on the Internet that allows users to graphically navigate through computers that are connected to the Internet.

The Internet is a network of networks. Although these networks communicate with each other using many different languages (protocols), they all agree to transport data within their network according to a common Internet communication language called transmission control protocol/Internet protocol (TCP/IP). TCP/IP is a set of protocols developed by the U.S. Department of Defense (US DOC) that facilitate the interconnection of dissimilar computer systems across networks. The TCP protocol coordinates the overall flow of data during a data communication session between points (nodes) in the Internet.

IP is an addressing structure that allows packets of data to be routed (re-directed) as they migrate through different networks to reach their ultimate destination. Each network receives packets of data in a format that is compatible with the Internet (IP address followed by control and data information) and they encapsulate (place the whole Internet data message into their own data packet format (including the IP address and control information). This allows IP data packets (called “datagrams”) to be sent through the network regardless of their actual length or format.

Figure 1 shows that the Internet is the network of networks and it communicates using the universal protocol language TCP/IP. This diagram shows a user who is sending email through the Internet. In this diagram, the application is email. The data from the email is divided into packets and given sequence number by TCP protocol. The destination address is appended to each packet by the IP layer. The IP packets are then sent through an Ethernet LAN by encapsulating the IP datagram within the Ethernet data packet. When the data packet is extracted from the Ethernet, it is placed on the E1 transmission line. When the IP data packet reaches the ATM network, it is subdivided into very small 53 byte data packets that travel through the ATM network. When the ATM packets reach their destination in the ATM network, the original IP datagram is recreated and transferred via the T1 communication line. The T1 communication line interfaces to another Ethernet data network. This Ethernet data network encapsulates the IP datagram and forwards it on to the NIC of the receiving computer. The NIC of the receiving computer removes the IP address and reassembles the IP data packets to form the original email message.


Figure 1: Internet Data Routing

Telephone and Device Numbering

Each device within a network must have its own unique address. Some of the different types of addresses that are available include telephone numbers and data network addresses.

International Numbering Plan (ITU)
The International Telecommunications Union (ITU), a division of the United Nations, has defined a world numbering plan recommendation, “E.164.” The E.164 numbering plan defines the use of a country code (CC), national destination code (NDC), and subscriber number (SN) for telephone numbering. The CC consists of one, two or three digits. The first digit identifies the world zone. The number of digits used for telephone numbers throughout the world varies. However, no portion of a telephone number can exceed 15 digits. There are several “E” series of ITU numbering recommendations that assist in providing unique identifying numbers for telephone devices around the world.

North American Numbering Plan (NANP)
An 11 digit-dialing plan is used within North America. It contains 5 parts: international code, optional intersystem code (1 +), geographic numbering plan area (NPA), central office code (NXX), and station number (XXXX). The NPA code defines a geographic area for the serving telephone system (such as a city). The NXX defines a particular switch that is located within the telephone system. Finally, the station code identifies a particular line (station) that the switch provides service to. Figure below shows the telephone numbering systems.



Internet and Data Network Numbering
Most data network addresses are hierarchical where the beginning of the address identifies the entire network and each progressive address number (or group of numbers) identifies more specific parts within the network.

Data networks are usually composed of several interconnected links. These links can be of different technologies with each of their end points identified by a unique numbering system. Figure 1.14 shows how different types of data network addressing systems can co-exist. This diagram shows a data connection that is composed of several parts. An end-user is connected to an application server through a company Ethernet network. The computers network interface card (NIC) has an address unique to the Ethernet hub. The Internet address is included as part of the data message after the Ethernet address. The company’s network is connected to an ISP by a high-speed frame relay connection. The frame relay access device (FRAD) has a unique identifier to the ISP. The ISP connects the data connection via asynchronous transfer mode (ATM) to the ASP.



Number Portability
Number portability involves the ability for a telephone number to be transferred between different service providers. This allows customers to change service providers without having to change telephone numbers. Number portability involves three key elements: local number portability, service portability and geographic portability.

The first part of the telephone number (NPA-NXX) usually identifies a specific geographic area and specific switch where the customer subscribes to telephone service. If a telephone number is assigned to another system (different NXX) in the same geographic area (same NPA), the interconnecting carriers (IXCs) connecting to that system must know which local system to route the calls based on the selected local service providers. In this case, the IXC must look up the local telephone number in a database (called a database dip) prior to delivering the call to the end customer.

Figure below shows an example of local number portability (LNP). In this diagram, a caller in Los Angeles is calling to someone in Chicago. The call is routed through the LEC in Los Angeles and routed through a long distance provider who needs to connect the call into a local telephone company in Chicago. Because there are several local providers in Chicago, the IXC must look into a database to see if the number has been ported to a different service provider. This is the next to last switch before the call reaches the end office switch (called “N-1”). This switch uses the dialed digits to find which local carrier is providing service in the Chicago area. When the IXC finds which exchange is serving the number, the call is routed to the correct local switching office and the call is completed.


example of local number portability

Service portability allows a customer to take their telephone number to a different type of service provider. Service portability involves determination of the type of service provider (e.g., wireless or wired) who is responsible for completing the call using the area code and NXX. The interconnection and call processing for different types of service providers varies.

Geographic portability involves the transfer of telephone numbers outside the normal geographic boundaries of the service provider’s area. Geographic portability allows a customer to keep their same area code when they move to new cities or other distant geographic regions...