3271 chapter 5 & 6

Wide Area Networks (WANs)

• WANs are covered in chapter 5 of "Data Communications and Networking, With TCP/IP protocol suite, Sixth Edition" by Behrouz A. Forouzan.

Telephone Network

• The telephone network started in the late 1800s.
• The original telephone network used analog signals to transmit voice.
• It is now a mix of digital and analog technology.

Major Telephone Network Components

• Local loops, trunks, and switching offices are the three main components of the telephone network.
• End offices, tandem offices, and regional offices are several levels of switching offices.

Local Loop

• The local loop is a twisted-pair cable connecting a subscriber's telephone to the nearest end office or local central office.

Trunks

• Trunks handle communication between offices.
• A trunk manages hundreds or thousands of connections using multiplexing.
• Transmissions commonly occur through optical fibers or satellite links.

Switching Office

• Telephone companies use switching offices with switches to avert constant physical links between subscribers.
• A switch joins local loops or trunks, enabling connections between different subscribers.

LATAs

• After the 1984 divestiture, the United States was divided into over 200 local-access transport areas (LATAs).
• The number of LATAs has grown since 1984.
• A LATA's size can range from a small to a large metropolitan area.
• A small state might have one LATA, while a large state could have multiple.
• LATAs may overlap state boundaries.

Intra-LATA Service

• Intra-LATA services are the services offered by telephone companies within a LATA.
• A local exchange carrier (LEC) manages intra-LATA services.

Inter-LATA Service

• Interexchange carriers (IXCs) handle services between LATAs.
• IXCs long-distance companies provide communications between two customers in different LATAs.
• After 1996, any carrier, including those in intra-LATA services, can offer these services.

Points of Presence (POP)

• A point of presence (POP) is a switching office that allows interaction between carriers; intra-LATA services are offered by LECs and inter-LATA services are offered by IXCs.

Signaling

• The telephone network initially used a circuit-switched network with dedicated links.
• Human operators performed signaling tasks at first.
• Rotary telephones sent digital signals for multi-digit dialing.
• Telephone company switches employed digital signals to link callers and called parties.
• Both in-band and out-of-band signaling were implemented.

Data Transfer Network

• The data transfer network is a circuit-switched network that can carry multimedia, but can also be packet-switched.
• It follows the same protocols and concepts as other networks.

Signaling Network

• Signaling networks are packet-switched, using layers like the OSI or Internet model.
• Packet-switching is more appropriate because of the nature of signaling.

Signaling System Seven (SS7)

• Signaling System Seven (SS7) is the protocol for signaling networks.
• SS7 resembles the five-layer Internet model but with different layer names.

Services Provided by Telephone Companies

• Telephone companies provide both analog and digital services.

Analog Services

• Analog services consist of analog switched services or analog leased services.

Digital Services

• Digital services are less prone to noise and interference than analog ones.
• Switched/56 and digital data service (DDS) are two common digital services.

Dial-Up Service

• Traditional telephone lines transmit frequencies between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz.
• This range accommodates voice transmission, and interference and distortion is sometimes accepted.
• Data signals need high accuracy to ensure integrity.

56K Modems

• Traditional modems are limited to 33.6 kbps, according to Shannon's capacity.
• 56K modems are now available offering a bit rate of 56,000 bps.
• 56K modems can only be used if one party uses digital signaling.

Digital Subscriber Line (DSL)

• DSL was made to support higher-speed access to the Internet as traditional modems reached their peak data rate.
• DSL is a set of technologies each varying in the first letter: ADSL, VDSL, HDSL, and SDSL.

ADSL and Existing Local Loop

• ADSL uses existing local loop telephone lines.

Cable Network

• Initially, cable networks provided TV access to areas with natural obstructions like mountains.
• Later, cable networks gained further traction with the public for signal quality.
• Cable networks make connections to remote broadcasting stations possible using microwave connections.

Traditional Cable Network

• Cable TV started in the late 1940s to distribute broadcast video signals to locations with poor reception.
• It was initially called community antenna TV (CATV) since signals were received and distributed from a tall antenna using coaxial cables.

Hybrid Fiber-Coaxial (HFC) Network

• The second-generation cable networks are called hybrid fiber-coaxial (HFC) networks.
• HFC networks use a mix of fiber-optic and coaxial cables.
• The transmission medium from the cable TV office to the fiber node is optical fiber.
• Connection from the fiber node through the neighborhood and into the house uses coaxial cable.

Cable TV for Data Transfer

• Cable companies compete with telephone companies for customers wanting high-speed data transfer.
• DSL technology offers high data rates over the local loop for residential subscribers.
• DSL uses unshielded twisted-pair cables which can be susceptible to interference.

Cable Data Bandwidth

• The upstream data bandwidth is 37 MHz.
• There are only six 6-MHz channels in the upstream direction for the CATV

Sharing Cable Channels

• Both upstream and downstream bands are shared by subscribers.
• 6 MHz channels are available in the upstream direction
• Time-sharing divides the band into channels, which are shared by subscribers in the same neighborhood.

Cable Modem (CM) and Cable Modem Transmission System (CMTS)

• Cable networks for data transmission will use: a cable modem (CM) and a cable modem transmission system (CMTS).
• The CM is installed at the subscriber's location.
• The CMTS is installed inside the cable company.
• The CMTS receives data from the Internet and sends it to the subscriber.
• The CMTS also receives data from the subscriber and then passes it to the Internet.

Cellular Telephony

• Cellular telephony offers communication between two moving units (mobile stations/MSs)
• Cellular telephony also offers communication between a mobile unit and a stationary unit (land unit).
• Providers locate, track callers, assign channels, and transfer channels between base stations to avoid dropped calls due to caller location.

Cellular Telephony Operation

• A service provider must locate/track the caller, assign a channel, and facilitate channel transfers from base station to base station when the caller moves.

Frequency-Reuse Principle

• Adjacent cells cannot use the same frequencies for communication.
• Limits affect users near cell boundaries due to potential interference.
• Frequency reuse becomes necessary because the set of frequencies available is limited.
• A frequency reuse pattern configures N cells, N being the reuse factor, which allows each cell uses a unique set of frequencies.
• Frequencies get reused when patterns repeat within the network

Transmitting (Cellular)

• To place a call, users enter a 7 or 10-digit code (phone number) and tap the send button on a station.
• The mobile station scans the band for a setup channel with a strong signal.
• Upon acquiring sufficient signal strength, station stations send data (phone number) to the nearest base station.
• The base station then sends this data to the MSC.
• The MSC then directs the data onward to the telephone central office.

Receiving (Cellular)

• Central office sends the number to the MSC when someone calls a cell phone.
• The MSC then determines station locations, sending query signals to cells (paging).
• The MSC then sends a ringing signal and links a voice channel when the mobile unit answers to begin the call.

Handoff (Cellular)

• Mobile stations may switch cells during conversations due to movement potentially weakening the signal.
• To counter drops, MSCs monitor levels of signals on the cellular network.
• The MSC seeks a better cell to continue conversations if a diminishing signal is detected.
• The MSC switches the channel to improve the connections.

Roaming

• Cellular telephony includes roaming, giving users access to communication within a coverage area.
• Service providers often have limited coverage.
• Neighboring service providers can extend coverage through roaming agreements.
• The roaming agreement is similar to snail mail contracts between countries.
• The sending/receiving service can bilaterally divide the charges for delivery.

First Generation (1G)

• Cellular telephony is in its fourth generation.
• 1G was for voice communication using analog signals.
• AMPS (Advanced Mobile Phone System) was a 1G mobile system used in North America.

Advanced Mobile Phone System (AMPS)

• The Advanced Mobile Phone System (AMPS) is an analog cellular system used in North America.
• AMPS uses FDMA to separate channels in a link.

Second Generation (2G)

• 2G cellular networks were developed for higher-quality (less noise-prone) mobile communications.
• 2G was geared towards digitized rather than analog voice.
• D-AMPS, GSM, and CDMA are three major systems that evolved in the second generation.

D-AMPS (Digital AMPS)

• Digital AMPS or D-AMPS evolved from the analog AMPS into a digital system.
• D-AMPS was designed to be backward-compatible with AMPS.
• Original deployment had the capability of one telephone using AMPS while another used D-AMPS.
• D-AMPS initially was defined by IS-54 (Interim Standard 54) and later revised by IS-136.

Global System for Mobile Communication (GSM)

• The Global System for Mobile Communication (GSM) is a European standard providing common 2G technology across Europe.
• The GSM was intended to replace an array of incompatible 1st-generation technologies.

IS-95

• Interim Standard 95 (IS-95) is a 2G standard in North America.
• IS-95 is based on CDMA and DSSS.

Third Generation (3G)

• 3G includes technologies delivering both digital data and voice communication.
• 3G networks facilitate voice communications with other world users while using a portable device with quality similar to fixed telephony.

Fourth Generation (4G)

• The fourth generation of cellular telephony is expected to evolve how cellular communications are handled.

Access Schemes (4G)

• New access techniques are evolving to improve capacity and scalability of 4G networks.
• Orthogonal FDMA (OFDMA) and interleaved FDMA (IFDMA) are being looked at to upgrade downlink and uplink transmissions on upcoming UMTS (Universal Mobile Telecommunications System) networks.
• IEEE 802.20 is evaluating implementing MC-CDMA (multi-carrier code division multiple access).

Modulation (4G)

• More efficient quadrature amplitude modulation (64-QAM) is being proposed with Long-Term Evolution (LTE) standards.

Radio System (4G)

• 4G employs a Software Defined Radio (SDR) system.
• SDR systems use adaptable software instead of the inflexible hardware found in common radio.
• SDR units have the ability to change their program by shifting frequencies to resolve disturbances.

Antenna (4G)

• Multiple-input multiple-output (MIMO) and multi-user MIMO (MU-MIMO) antenna systems, a type of intelligent antenna, are now evolving.
• Modern antenna designs for fourth-generation environments use a unified antenna system and improved multiplexing to stream data, boosting throughput exponentially.
• MIMO shifts transmitter-receiver parameters to avoid interference.

Satellite Networks

• Satellite networks are a combination of nodes including satellites to support communications from one point to another on Earth.
• Nodes in a satellite network include satellites, ground stations, and end-user devices or telephones.

Satellite Network Operation

• One discussion is geared toward general issues relating to satellites.

Satellite Orbits

• Artificial satellites requires an orbit, a defined path rotating around the Earth.
• Orbits are defined as equatorial, inclined and polar.

Orbital Period Example

• Kepler provides us period calculation guidelines such as one example in which: Period = (1/100)*(384,000+6378)^1.5 = 2,439,090 s = 1 month

Satellites Located About Earth Example

• Consider the solution for which: Period = (1/100)*(35,786+6378)^1.5 = 86,579 s = 24 hours, shows that a satellite will have a 24 hour orbital period at 35785km above Earth.

Footprint Definition (Satellite)

• Satellites are equipped with bidirectional antennas (line-of-sight) to facilitate processing with microwaves.
• A focused footprint target specific area of signal.
• A point with maximum signal power is at the center of the satellite's footprint.
• Power is reduced as the distance from the central footprint point increases.
• The defined level where predefined measurements are collected becomes is the established boundary of a "footprint".

Satellite Communications Frequency Bands

• Microwave frequencies in the gigahertz (GHz) range are booked in for satellite transmissions.
• Satellites send and receive over two different bands.
• Transmission from the ground to the satellite refers to Uplink connections.
• Downlink refers to the return transmissions from the satellite to the ground.

Categories of Satellites

• Satellites orbits may divide into geostationary Earth orbit (GEO), low-Earth-orbit (LEO), and medium-Earth-orbit (MEO).

GEO Satellite

• GEO satellites require line-of-sight propagation necessitating the presence of sending and receiving antennas that are locked onto the other's location.
• Satellites moving faster or slower will have short usage parameters relative to the needs for constant Earth rotation.
• Satellites sustain consistent Earth rotations to appear anchored on the ground with constant communication, known as geostationary.

MEO Satellite

• Medium-Earth-orbit (MEO) satellites are positioned between the two Van Allen belts.
• It takes a satellite approximately 6 to 8 hours to circle the Earth in this orbit.

GPS

• The Global Positioning System (GPS) is an example of MEO.
• GPS is contracted, monitored, and run by the U.S. Department of Defense orbiting at 18,000 km (11,000 mi) above the Earth.

LEO Satellite

• Low-Earth-orbit (LEO) satellites have polar orbits.
• LEOs' altitude is between 500 and 2000 km, with rotation periods of 90 - 120min.
• Satellites fly has a speed of 20,000 to 25,000 km/h.
• LEO usually follows a cellular type access format, similar to the cellular telephony system.
• A LEO footprint has a standard diameter of 8000km.