Types of WAN Technologies

Wide Area Networks (WANs) are used to interconnect networks that are not physically close to each other, might be physically separated across the cities, across regions, or even across geography. Currently there are many WAN technologies available. Primary different between WAN technology and LAN technology is about the distance that separates the interconnected networks. WANs use different transmission media, hardware, and protocols. Data transfer rates are typically much lower for WAN communication when compared to LAN rates. WAN Communication WAN technologies rely on other party such as Telco carries company which provides long distance connectivity.

Unlike LAN where the data are transmitted from one digital device / computer to another computer through direct physical line connection, WAN technology uses combination of analog signal and digital signal in transmitting the data. The following WAN diagramdescribes each of WAN elements and functions in the WAN technologies concept.

1. DTE (Data terminal equipment) is a device on the side of WAN link (resides on the subscribers premises) that sends and receives data. DTE (which is usually a network router, or a computer, or a multiplexer) is a mark point between the LAN and the WAN. DTE is a device that communicates with the DCE at the other end.
2. Demarcation points (Demarc) is the points as the network interface or point of presence where the telephone wiring company connects to the clients.
3. Local loops is the cable that extends from the demarc to the CO (central office) which is maintained by the Telco. It can be UTP, fiber optic, or combination of both and other media.
4. DCE (data circuit terminating equipment) is a device (which is typically a router at the ISP) that communicates with both DTE and WAN clouds. DCE is a device that supplies clocking signals to DTEs. A modem or CSU/DSU at the customer site can be classified as DCE. DTE and DCE can be similar device / router but with different role and function.
5. WAN Cloud, the hierarchy of trunks, switches, and CO – central office, that makes up a network telephone lines. Physical structure varies, and different networks with common connection points may overlap, so that’s way it is represented as a Cloud. The important part is that data goes in, travels through the line, and arrives at the destination.
6. PSE (packet switching exchange) is a switch on a carrier’s packet switched network. PSEs are the intermediary points in the WAN cloud.

Messages travel from point to point differently depending on the physical connections and the protocols used that can be one of the following WAN connection types:

1. Dedicated connections
2. Circuit-switched networks
3. Packet-switched networks

Dedicated and switched networks have an always available connection to the network but circuit switched networks need to establish connection first via a dial-up mechanism between devices. In a dial-on-demand routing the routers open connections automatically when the data needs to be sent, and will close automatically when the line is idle.

Dedicated wan connection or leased line

Leased-line-diagram

A dedicated WAN connection or leased line connection is a permanent, dedicated point-to-point connection between one device and another with the following characteristics:

1. Dedicated point-to-point – synchronous serial
2. Permanent connection, such as T1, T3
3. High availability
4. Lines are usually leased from a WAN service provider
5. Lease line is more expensive than other WAN solutions
6. Use separate WAN connections between each point

When should we use this type of WAN connection? We can use this dedicated leased line WAN connection when you:

1. Have a high data traffic over the WAN connection
2. Need constant connectivity between sites
3. Have few interconnected sites

See also Point-to-point protocol – one of WAN protocol that use this type of WAN connection

Circuit switched networks

circuit-switched-diagram-1

This circuit switched WAN connection type gives you an alternative to leased lines, letting you use shared lines. This WAN connection type works both ways, allowing both dial-in and dial-up WAN connections. When you use this circuit switched WAN connection:

1. The sending computer dials-in to the line and the WAN connection is set up.
2. The receiving computer sends acknowledgement and locks the line.
3. The sending computer transmit the data over this WAN connection
4. After the transmission is complete, the connection is released for other users.

A circuit switched network uses switched virtual circuit (SVCs). A dedicated data transmission path is established before communication begins by throwing electrical switches. The path remains until the communication ended.

Packet switched networks

Packet switched Diagram

Packet switched networks do not require a dedicated or temporary reserved line. Instead, a message’s path is dynamically set as the data flows through the network. This WAN connection type has the following characteristics:

1. Messages are divided into packets.
2. Packets travel independently through the internetwork (i.e. take different paths)
3. Packets are reassembled into the correct order at the receiving end
4. Sending and receiving devices assume an ‘always on’ connection (no dials-up needed)

This wan connection type – packet switched networks use permanent virtual circuits (PVCs). Although a PVC looks like a direct, dedicated WAN connection, the path each packet can take through the internetwork can vary. Dedicated and switched networks have an always available connection to the network but circuit switched networks need to establish connection first via a dial-up mechanism between devices. In a dial-on-demand routing the routers open connections automatically when the data needs to be sent, and will close automatically when the line is idle.

WAN Services
Many types of WAN technologies exist and served by the WAN service providers today:
PSTN
PSTN is the Public switched telephone network is the oldest and widely used worldwide for WAN communication. PSTN is one of WAN technologies in circuit-switched network. This is a dial-up basis or leased line (always-on) using telephone line where data from digital (at the computer) is converted to analog using the modem, and the data travel with the speeds limited to 56 Kbps.
Leased lines
Leased line is a dedicated type of WAN technologies using a permanent – direct connection between devices and provides a constant connection of connection line quality. It is more expensive off course compared to PSTN on demand.
X.25
X.25 is specified by ITU-T – a packet switching WAN technology over PSTN. X.25 is built refers to Data Link and Physical Layers in the OSI model. Originally X.25 used analog lines to create a packet-switched network, although X.25 can also be built on digital network. X.25 protocols define how connection between DTEs and DCEs are set up and maintained in Public Data Network (PDN). See also ATM WAN – best practices.

• You need to subscribe for X.25 services which can use dedicated line to the PDN to make WAN connection
• X.25 can operate at up to 64 Kbps on analog lines.
• X.25 uses frame as a variable packet size
• Error detection and correction is included assuring the reliably over lower quality analog lines

Frame relay Frame relay is discussed more detail in separate articles including the frame relay network and connection. Frame relay is one of WAN technologies in packet switching WAN communication over high quality digital lines.

ISDN 
ISDN is not discussed here, complete discussion is on separate ISDN technology. ISDN (Integrated services digital network) defines standards for using analog telephone lines for both analog and digital transmission.

ATM
Asynchronous Transfer Mode (ATM) is a high-speed connection using one of WAN technologies packet switched system with the speed from 155 Mbps to 622 Mbps. It can transmit data simultaneously with digitized voice, and digitized video over both LANs and WANs.

• ATM uses small fixed-sized dells (53-byte) which are easier to process than X.25 or Frame Relay variable-length cells
• Transfer rate can be as high as 1.2 Gigabits
• It’s a high quality and low noise digital lines and eliminate error checking
• Can use many types of transmission media from coaxial, twisted pair, or fiber optic.
• Can transmit any types of data simultaneously

WAN technologies have been changing radically in recent years. Small businesses today do not use T1 or frame relay for their WAN connection. Several new solutions have emerged that offer considerable cost savings and ease of use over standard WAN solutions including the following:

• Digital Subscriber Line (DSL):
DSL uses existing Telco copper local loop at the speeds of T1 lines but much cheaper than T1 lines. Home users today welcome this technology for their home Internet connection.

• Virtual private network (VPN):
VPN becomes an easy affordable solution for connecting different locations using private Internet Protocol (IP) traffic. VPN can use any carriers including dial-up, DSL, and T1. The advantage here is that data can be carried long distances without any added cost since a public network carries the traffic instead of a carrier’s private network.