Tutorial: Mobile Operators, MVNOs and Roaming

Extracted from Chapter 9 of the Telecom 101 reference book.
Note: acronyms and abbreviations used below are explained in lessons leading up to this one.

9.7 Mobile Operators, MVNOs and Roaming

9.7.1 Mobile Network Operator

Mobile Network Operator (MNO) is the term usually used to refer to a facilities-based carrier, i.e. a company that owns base stations, a mobile switch, backhaul between them, and spectrum licenses, and sells services to the public… and to other carriers.

The MNO implements external links to other carriers for PSTN phone calls and for Internet traffic.

For PSTN phone calls, the MNO implements a fiber optic connection to a building traditionally called a Toll Center or Class 4 switching office. The termination of their fiber in that building is called a POP. It is their physical point of presence in the building.

Many other carriers have POPs in the building, including the ILEC, IXCs, CATV companies, other mobile carriers, and any other company that wants to connect phone calls to a phone on the MNO’s network.

The operator of the toll center, usually the ILEC, provides a switch in the Toll Center to switch phone calls from one carrier’s POP to a different carrier’s POP.

For Internet access, the MNO implements a fiber optic connection to one or more Internet Exchange buildings, where they pay the operator of the IX to route packets to other carriers with whom the MNO has established IP packet transit and peering arrangements.

9.7.2 Mobile Virtual Network Operator

Mobile Virtual Network Operator (MVNO) is the term used to refer to a non-facilities-based carrier… one that does not own the hardware or spectrum licenses or POPs.

Instead, the MVNO enters into a long-term contract with one or more facilities-based carriers to have them supply a “white label” service that the MVNO sells.

Typically the MVNO will develop a unique branding and sell smartphones and tablets to go along with its service.

When the MVNO deals exclusively with one carrier, the MVNO bill to the customer would be typically generated by the facilities-based carrier as a white-label service.

If the MVNO is very large and deals with multiple carriers, the MVNO may operate their own billing system, which is a significant investment.

The facilities-based carrier charges to the MVNO includes a volume-discount rate for IP addresses and Internet traffic, voice-minute airtime and switched access to the POP for PSTN phone calls.

The MVNO also has to pay for connectivity from the POP to other toll centers for “long-distance” connections, and the switched-access charge at the far end.

The rate plan the MVNO pays could be a mix of fixed-rate leases and usage-based billing.

Unless the MNO is obliged to sell capacity to MVNOs through regulations and tariffs, the nature of the plan is confidential business information.

9.7.3 Roaming

Roaming service is very similar to the service provided to MVNOs, in that it is the MNO that is providing the airlink, base stations, backhaul, mobile switch and connections to the PSTN and Internet.

In the case of roaming, the visitor uses their own phone, and billing is usage-based.

Roaming is an important feature for smaller players: they are facilities-based in selected cities, but to offer a national and international service to their customers, they must have roaming agreements in place with MNOs in other locations.

By denying roaming service to smaller or startup carriers, or charging an exorbitant price for roaming, an incumbent carrier can erect a barrier against competition.

In many countries, the right to roam and the wholesale cost of roaming is regulated to encourage competition.


These topics are covered in:

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Tutorial: Optical Ethernet

From the new textbook Telecom 101 Fifth Edition: 2020

SFP optical transceivers

Figure 111. SFP Optical Transceivers

10.5 Optical Ethernet

Optical Ethernet is signaling MAC frames (Section 4.4) from one device to another by flashing a light on and off; light on represents a 1 and light off represents a 0 in many systems.

The light, called a wavelength or lamda – λ in Greek – is as close to one single pure frequency as possible, in the infra-red, lower frequencies than what our eyes detect.

In sophisticated systems, the wavelength might be modulated with QAM (Section 3.4) to increase the bit rate.

Normally, Optical Ethernet is implemented as point-to-point connections: from a hardware port on one switch or router to a hardware port on another switch or router in a different building. This includes connections between core routers in cities, connections between routers and switches within a city, and connections from carriers to customers.

10.5.1 SFP Modules and Connectors

The light is generated by a laser controlled by pulses of electricity at the transmitter.  The intensity and sometimes phase of the light is modulated, i.e. changed in discrete steps, to represent bits optically based on the pulses of electricity. Up to 80 km (50 miles) away at the other end of a tube of glass thinner than one of your hairs, a photodetector at the receiver measures the received light and decides what bits are being represented, and transmits them onward as pulses of electricity.

As illustrated in Figure 111, most systems use two fibers, one for each direction. A device combining the transmitter and detector functions is called an optical transceiver.

This device has metal connectors on one side to plug into a slot on a router or switch, and optical connectors on the other side, either factory- or field-installed on the fibers plugged into the transceiver.

These transceivers are typically implemented as Small Form-factor Pluggable (SFP) modules, which are hot-swappable in the terminating equipment at each end.

100 Gb/s being communicated through this transceiver is the high end of commercially-deployed technology in 2020.

In some cases, the SFP modules are embedded in the terminating equipment, meaning the fibers are plugged into the terminating equipment. This allows re-use of existing fiber. In other cases, the SFP modules are attached to fiber cables by the fiber cable manufacturer, meaning the SFP module is plugged into the terminating equipment. This ensures the fiber and transceiver technology are matched and the optical connection is a high-quality “factory” connection.

The SFP module format is not the subject of a standard, but rather described in industry Multiple Sourcing Agreements (MSA).

10.5.3 IEEE Standards

There are many technologies for transceivers implemented in the SFP module. Some are proprietary; many are standardized by the IEEE. In practice, the same manufacturer’s product is used at both ends of the fiber to ensure compatibility. The table in Figure 112 lists current IEEE standards. More will be published in the future.

SFP optical transceivers

Figure 112. IEEE Optical Ethernet Standards

Most technologies use one fiber for each direction. Some, like for fiber to the home, use two wavelengths for two directions on one fiber. The bitrate of the standards beginning with 1000 is 1,000 Mb/s, or 1 Gb/s. A G at the beginning means Gigabits/second.  40 and 100 Gb/s technologies split the bitstream into subrates and transmit them in parallel on different wavelengths called paths or lanes.

The reach is the maximum length of fiber between devices.  Single-mode and multimode are designations for different qualities of fiber.  Most if not all builds today use single-mode fiber.

Source: Telecom 101 textbook / reference book, Fifth Edition: 2020 available in print and eBook.

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