Contents

1 Definitions

A WAN is a datacommunications network that operates beyond the geographic scope of a LAN. WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.

When you build a WAN, regardless of the transport you choose, there is always a minimum of three basic components, or groups of components, connecting any two sites. Each site needs its own equipment (DTE) to access the telephone company’s CO serving the area (DCE). The third component sits in the middle, joining the two access points (for example, a Frame Relay backbone).

2 Telephone (Dial-Up) Access [3]

• History: First residential (last-mile) Internet access of the history. It started in the last-60’s.
• Hardware: Two copper wires and a two modems (bandwidth: $\left[300,4300\right]$ Hz in “analog” lines, the available (depending on the distance and the quality of the wire) in digital lines).
• Delay: Constant (the link is dedicated).
• Bit-rate:

3 Cable [3]

• History: In the 90’s, there is a large infrastructure of cable TV systems. Some channels are used to transmit data instead of TV signals to the home of the users (residential access).
• Hardware: Coaxial cable and a two cable modems. The backbone is optical fiber (HFC = Hybrid Fiber/Coaxial).
• Delay: Neighbors (typically from $500$ to $2,000$ active data subscribers are connected to a cable network segment) share upstream and downstream bandwidth. Because CDMA (Code Division Multiple Access) multiplexing is used (i.e., several transmissions can be done in the same instant without collisions), delay is constant although the bit-rate depends on the number of active users.
• Bit-rate: The actual bandwidth for Internet service over a cable line can be up to $27$ Mbps on the download path to the subscriber (downstream frequencies are in the range of $50$ to $860$ MHz, $6$ MHz/TV-channel) and about $2.5$ Mbps of bandwidth on the upload path (upstream frequencies are in the range of $5$ to $42$ MHz). QPSK (Quadrature Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) modulation is used.

4 Satellite [1]

• History: The first satellite to successfully reach a geostationary orbit was Syncom3, built by Hughes Aircraft for NASA and launched Aug. 19, 1963. The first Internet ready satellite for consumers was launched Sept. 27, 2003 by Eutelsat.
• Hardware: To access satellite Internet services, subscribers need a satellite dish, two modems (uplink and downlink), and coaxial cable between the dish and the modems.
• Delay: Although the channel is dedicated, i.e., the latency is constant, the distance between the satellite and the Earth is at least $35,786$ km. Therefore, the minimal latency is
  $$\frac{2\times 35,786\text{km}}{300,000\text{km/s}}=238\text{ms}.$$

• Bit-rate: Download: up to $15$ Mbps, upload: $1.5$ Mbps.

5 DSL (Digital Subscriber Line) [1]

• History: Bellcore (now Telcordia Technologies) developed ADSL (Asymmetric Digital Subscriber Line) and filled a patent in 1988. Now is the most used method for residential access.
• Hardware: Use the same line than the telephone, but the channel goes from $20$ kHz to $1$ MHz. The carrier is modulated using OFDM (Orthogonal Frequency-Division Multiplexing). A DSL modem is the device required to connect the computer or the network of the user to the telephone line.
• Delay: The link is dedicated and short (thousands of meters), so, the latency is very low and constant.
• Bit-rate: Bit-rates depends on the noise in the line. Theoretically:
  1. Download: up to $52$ Mbps.
  2. Upload: up to $16$ Mbps.

6 WiFi (Wireless Fidelity) [4]

• History: The first IEEE 802.11 device was debuted on the market, under the name of WaveLAN, in 1988. WiFi is an industry-driven interoperability certification promoted by the WiFi Alliance and based on a subset of the IEEE 802.11 standard.
• Hardware: At least two WiFi adapters and an electromagnetically permeable medium in the $2.4$ GHz ISM (Industrial, Scientific and Medical) band. Usually, communication is access point based, although peer to peer communication is also allowed.
• Delay: The medium is shared between all emitters and receivers (that must sends ACK packets). When carriers are modulated using OFDM (Orthogonal Frequency-Division Multiplexing) (802.11a and 802.11g) or MIMO (Multiple-Input and Multiple-Output)-OFDM (802.11n), the medium is multiplexed using CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance), i.e., the latency is variable (depends on the link load). When DSSS (Direct Sequence Spread Spectrum) (802.11b), several emitters can coexist without collide and the latency is constant (although the bit-rate is decreased when the number of emitters is increased).
• Bit-rate:

7 Bluetooth (IEEE 802.15.1) [4]

• History: Created by Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. Bluetooth links are also called WPANs (Wireless Personal Area Networks).
• Hardware: Bluetooth modems and a electromagnetically permeable medium in the $2.4$ GHz ISM (Industrial, Scientific and Medical) band. Peer to peer communication.
• Delay: Because in FHSS (Frequency-Hopping Spread Spectrum) devices frequency-hop every $400$ ms in a pseudo-random sequence around $79$ channels, when two (or more) devices transmit in same channel they collide, the packets have to be retransmitted and the delay in this case will be high. Otherwise the delay is almost constant and very small (notice that the devices are quite close).
• Bit-rate:

  Version	Bit-rate
  1.2	1 Mbps
  2.0	3 Mbps
  3.0	24 Mbps
  4.0	24 Mbps

8 ZigBee (IEEE 802.15.4) [4]

• History: ZigBee was conceived in 1998, standardized in 2003 and revised in 2006. It is used in applications that require a low data-rate and long battery life.
• Hardware: ZigBee modems and a electromagnetically permeable medium in the $2.4$ GHz ISM (Industrial, Scientific and Medical) band. Communication is always peer to peer.
• Delay: Medium is multiplexed with DSSS (Direct Sequence Spread Spectrum), therefore, the latency is constant but depends on the number of emitters.
• Bit-rate: Up to 250 Kbps.

9 Cellular [1]

• History: Cellular telephony born in the early 1980s. 1G (Generation) transmitted voice and was analog. The rest of technologies that have arrived later are fully digital.
• Hardware: A cellular (which obviously is basically a modem) and cellular radio tower (with an antenna), also known as a radio base station. Terminals always communicate with a station, never directly (no peer to peer). Stations can be closer if bandwidth per cell is higher (in the left example, the bandwidth/station is smaller). If he bandwidth is higher, the number of phones per cell can be higher.

• Delay: Most cellular technologies are TDM- or FDM-based. The bandwidth is reserved (we pay for that) and therefore, the latency is constant.
• Bit-rates:
  1. AMPS (Advanced Mobile Phone System) in US, TACS (Total Access Communications System) + NMT (Nordic Mobile Telephone) in Europe and NTT (Nippon Telegraph and Telephone) + JTACS (Japan Total Access Communications System) in Japan / 1G: Up to $14.4:-$ (download:upload) Kbps.
  2. GPRS (General Packet Radio Service): Used in GSM (Global System for Mobile)/2.5G. Up to $80:40$ Kbps.
  3. EDGE (Enhanced Data Rates for GSM Evolution): Used in GSM/2.75G. Up to $348:-$ Kbps.
  4. HSPA/HSPA+ (High-Speed Packet Access): Used in UMTS (Universal Mobile Telecommunications System)/3G. Up to $14,4:2$ Mbps (HSPA) $84:22$ Mbps (HSPA+).
  5. HSDPA (High-Speed Downlink Packet Access): Used in UMTS/3.5G. Up to $40:11$ Mbps.
  6. HSUPA (High-Speed Uplink Packet Access): Used in UTMS/3.75. Up to $5.76:-$ Mbps.
  7. IEEE 802.16 WiMAX (Worldwide Interoperability for Microwave Access): Used in UMTS/4G. Up to $1:-$ Gbps.
  8. LTE (Long Term Evolution): Used in UMTS/4G. Up to $326.5:86.5$ Mbps.

10 IEEE 802.3 Ethernet [1]

• History: Ethernet network was invented in mid 70s [2] and appeared commercially in 1980.
• Hardware: To connect two computers, you only need an Ethernet cable (4 twisted pairs or an optical fiber). However, in order to connect to a larger network, an Ethernet switch is needed, obtaining a star topology (switches can be connected together to expand the network). Links are full-duplex.
• Delay: Switched Ethernet use a TDM-FIFO strategy to transmit the frames. Therefore, the delay is variable although in general, the jitter is very small in non-congested networks.
• Capacity:
  1. 100Base-*: $100$ Mbps.
  2. 1000Base-*: $1$ Gbps.
  3. 10GBase-*: $10$ Gbps.

11 Frame Relay [1]

• History: Sprint International invented Frame Relay in the early 90s as a simpler version of the X.25 protocol to use across ISDN (Integrated Services Digital Network) interfaces. Frame Relay has become the most widely used WAN technology in the world.
• Hardware: Digital telephone lines and Frame-Relay switches.
• Delay: Links are under control, paid and dedicated. The delay is constant.
• Capacity: Typically (depends on the number of aggregated lines) up to $45$ Mbps. Full-duplex. Symmetrical bit-rate links.

12 ATM (Asynchronous Transfer Mode) [1]

• History: Developed by ANSI and ITU in the late 80s for carriage of a complete range of user traffic, including voice, data, and video signals. Now is used by telephone companies as a backbone network.
• Hardware: Digital telephone lines and ATM switches.
• Delay: Links are under control, paid and dedicated. The delay is constant.
• Capacity: Typically (depends on the number of aggregated lines) up to $622$ Mbps (OC-12).

13 Technologies summary

References