Introduction
In this lesson you will learn about Wide-Area Network (WAN) technology, digital vs. analog signal transmission, circuit-switched and packet-switched networks. You will also be introduced to multiprotocol label switching and its application in a networked environment.
Lesson Objectives
By the end of this lesson, you will be able to:
- Categorize WAN technology and properties.
- Explain digital vs. analog signal transmission.
- Explain the difference between circuit –switched and packet – switched networks.
- Describe Multiprotocol Label Switching and where it is used in a networked environment.
What is a WAN?
A Wide Area Network (WAN) is used to describe the connection between two distant geographical locations, where the distance limitations of fiber, wireless (RF) and copper wire are exceeded.
A WAN link speed is typically slower than the internal Local Area Network (LAN) speeds. WAN communication happens over a Telecom or ISP network. Data is sent over pre-existing copper and fiber media.
Analog vs. Digital
Data can be transmitted via Analog or Digital signals. Analog is a copy of a frequency. Analog does not provide high bandwidth for data traffic. Digital technology (use of 0’s and 1’s) is used currently for transmitting data.
When using 56k modems, the analog signal is converted into a digital one so the computer can process it. When sending from a modem the digital signal is converted into analog to be placed on Public Switched Telephone Network (PSTN).
Communication Circuits
Different WAN solutions employ different methods to access and send data across a WAN link.
- Circuit switching is a WAN connection that is initiated by dialing in for access and closes once transfer is complete.
- Packet switching is a WAN connection that is always connected. This type of circuit breaks data into packets and sends them to their destination in a random order.
Examples of circuit switching include Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN). Examples of packet switching include X.25, Frame Relay, and Asynchronous Transfer Mode (ATM). There are various types of circuit switch technologies in use today. Review the following to learn more.
Public Switched Telephone Network (PSTN) requires a modem to convert digital signal to analog and vice versa. Data is sent through the PSTN or Plain Old Telephone System (POTS) to the one’s ISP, such as NetZero. The speeds on a PSTN can reach up to 56kbps (kilobits per second).
Integrated Services Digital Network (ISDN) sends and receives data digitally and does not use a modem. Data is still sent over the POTS copper wire infrastructure and equipment that is non-digital requires the use of a Terminal adaptor (TA). The ISDN is made up of 2 B channels (64kbps) and one D channel (16kbps) which is referred to as (2B + D).
Speeds of channels can be bonded and can reach 128kbps (Basic access Rate). The D channel is responsible for handling the signal so the other 16kbps are not available. The ISDN also has a Primary access Rate which allows for speeds up to 1.544 Mbps.
The Primary access Rate in Europe has speeds up to 2Mbps. ISDN’s are usually used as backups if the primary WAN connection, using faster technology, fails.
Digital Subscriber Line (DSL) digitally transmits data. Data is still sent over the POTS copper wire infrastructure using Point–to–point (PTP) technology which experiences little to no congestion. DSL provides for better bandwidth than ISDN.
| xDSL | Data Speed | Distance |
| ADSL | 1.5 – 8 Mbps downstream
Up to 1.544 upstream |
18,000 ft. |
| VDSL | 13 – 52 Mbps downstream
1.5 – 2.3 Mbps upstream |
1,000 – 4,500 ft. |
Satellites are used to send and receive Data via radio waves. Modems and dish antenna (VSAT) with transceiver are required for this type of communication which can reach speeds up to 18Mbps. Satellite WAN links are not widely used due to line of sight and environmental issues.
Packet Switch Technology
Packet switching is a method of digital network communication that groups data that is being transmitted into sizable pieces in a variable-bit rate data stream composed of a sequence of packets. Packet switching involves x.25, Frame Relay, and Asynchronous Transfer Mode.
1. X.25: X.25 is a connection oriented analog packet switching protocol that reaches speeds up to 2 Mbps. X.25 operates on Layers 1 -3 of OSI Model.
2. Frame Relay: Frame Relay is the updated, digital version of the X.25 protocol. It requires no error checking or flow control and reaches speeds up to 50 Mbps. Data packets are multiplexed and travel over high quality data lines. Frame Relay operates on Layers one and two of the OSI Model and combines packets to maximize bandwidth.
3. Asynchronous Transfer Mode (ATM): ATM is a connection oriented protocol that breaks data into small packets (53 bytes). The packets are then sent to switching centers and directed to the network with optimal delivery time with speeds up to155 Mbps. ATM is the latest in packet switching technology.
‘Always On’ WAN Circuits
Cable modems supply always-on 24/7 network service by using cable television lines. Cable modems offer two-way channels which allow users to send and receive data on a scalable, high bandwidth network, with speeds ranging from 6-27 Mbps (megabits per second).
Plain Old Telephone Service (POTS) Leased Lines
Digital Signal (DS) lines provide fixed bandwidth between sites and data is multiplexed. The designation E1 is used for leased lines in Europe.
- T1/E1 lines carry 24 DS channels at 64 Kbps
- T3/E3 lines carry 672 DS channels at 64 Kbps
American Standard
| Carrier | Data Rate |
| T1 (DS-1) | 1.544 Mbps |
| T3 (DS-3) | 44.736 Mbps |
| T4 (DS-4) | 274.176 Mbps |
European Standard
| Carrier | Data Rate |
| E – 1 | 2.048 Mbps |
| E – 3 | 34.368 Mbps |
Channel Service Unit and Data Service Unit
Channel Service Unit (CSU) acts like an LAN interface. Data Service Unit (DSU) is the interface for the circuit.
Features and Purpose:
- The CSU/DSU is used to connect to the circuit.
- CSU/DSU has colored alarms.
- Blue indicates there is an incoming signal loss.
- Yellow indicates link failure.
- Red indicates a corrupt incoming signal.
Optical
WAN uses optical networking which has a set standard for North American and International users. Review the following terms to become familiar with the features of optical networking.
- Synchronous Optical Network (SONET) is the North American standard for WAN data transmission over optical fiber.
- Synchronous Digital Hierarchy (SDH) is the International standard equivalent of SONET.
- OCx describes the optical carrier data rates.
- Fiber Optic Backbone Networks are the destination of many of the previous WAN technologies (Note: For additional details regarding optical carriers and data rate go here.)
- Dense Wavelength Division Multiplexing (DWDM) is used to amplify multiplexed optical signal.
- Passive Optical Network (PON) allows service providers to run point to multi – point fiber to multiple POP locations.
Wireless WAN
It is also possible to provide WAN communications over national mobile wireless networks using various technologies as indicated below.
Cellular: Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), Cellular Digital Packet Data (CDPD)
- Speeds up to 1 Mbps
- Range = 18 miles
High Speed Packet Access (HSPA+)
- Speeds up to 168 Mbps
- Range = 124 miles
Long Term Evolution (LTE) – Note: Upgrade to GSM and HSPA networks.
- Speeds up to 300 Mbps
- Range = 30 miles
Worldwide Interoperability for Microwave Access (WiMAX) – Note: Microwave links which can span cities.
- Speeds up to 1 Gbps
- Range = 4 miles
Multiprotocol Label Switching
Multiprotocol Label Switching (MPLS) directs data from one node to another based on a label it attaches to the data packet. This technology is protocol agnostic and can encapsulate packets using ATM, frame relay, DSL, and other WAN technologies. Multiprotocol label switching takes place on layer two of the OSI model and speeds data transmission between network nodes.
Summary
In this lesson you learned about WAN technologies along with their standards and descriptions as well as the importance of MPLS which is a technology used to increase performance across WAN links.
