2.  Inter exchange carrier networks  Local exchange carrier networks  Undersea networks  Enterprise links

3.  Inter-exchange carriers (IXCs) interconnect local systems with each other. IXCs are also known as long distance carriers.  Inter-exchange networks (IXCs) are telecommunications networks that connect local exchange carriers (LECs), competitive local exchange carriers (CLECs), local post, or telephone and telegraph (PTT) with each other.

4.  Among the different exchange carrier the major carriers is AT&T and sprint which is used in single mode fiber.In this WDM system is used on these routes  Another major carriers is MCI which has a number of links using dispersion shifted fiber which uses the high speed TDM system on these routes and WDM system on other route that uses single mode fiber  For inter-exchange connection, networks as a rule connect to long distance networks through a separate toll center (tandem switch). In the United States, this toll center is called a point of presence (POP) connection.

6.  An IXC carries traffic, usually voice traffic, between telephone exchanges. Telephone exchanges are usually identified in the United States by the three-digit area code (NPA) and the first three digits of the phone number (NPA-NXX).  Different exchanges are generally in different geographic locations, such as separate central offices (COs, also called "wire centers").

7.  IXCs used to carry voice traffic on analog lines, but these days, most voice traffic is digitized.  Therefore, voice traffic is more typically a data stream.  These voice data streams therefore can be intermixed with data traffic, too, such as uplinks for DSL.  Most commonly, links between an IXCs and COs are ATM links carried on optical fiber.

8.  For voice traffic transfer IXCs are using the Soft switches. The soft switching technology is solely based on the SIP, which is an abbreviation of Session Initiation Protocol, which assures that the communication will be free of any types of errors.  This seamless and flawless communication enables the ITSP’s to offer calls between Internet Protocol Phone to regular phone, computer to computer, computer to phone, and IP devices to other phone services.