When designing a wide area network (WAN), one of the most difficult problems is choosing the appropriate connection type. You have to take several factors into account before starting the implementation, and a solid understanding of all the connection types is essential to make the right choice.
Most carriers offer three types of connection:
- Circuit-switched connections
- Packet-switched or cell-switched connections
- Dedicated connections
Each type of connection has its advantages and disadvantages. This article summarizes what each type of connection has to offer, taking into account bandwidth, availability, cost and ease of management.
Note: The best-known carriers in Europe are Orange (formerly France Télécom), Deutsche Telekom (DT), BT (British Telecom), Telefónica, AT&T, COLT, SFR, Belgacom (now Proximus) and many others.
Circuit-switched connections
Circuit-switched connections are currently the most popular type of WAN connection. Circuit switching transmits data streams and datagrams over dedicated physical circuits. To provide asynchronous dial-up and ISDN services, telephone companies use circuit switching.
Asynchronous dial-up
The public switched telephone network (PSTN) uses circuit-switched technology to provide asynchronous services (which do not go at the same speed). Asynchronous dial-up connections offer a low-bandwidth solution, easy to manage and cost-effective, available almost everywhere in the world.
ISDN
ISDN, Integrated Services Digital Network (in French Réseau Numérique à Intégration de Services) is a digital circuit-switching technology used for carrying voice, data or even video. ISDN is a low- to medium-bandwidth solution with a relatively low cost. However, availability is somewhat limited and configuration and support are more difficult than for asynchronous communication.
ISDN (integrated services digital network) connections have the disadvantage of being billed by the call.
Both of these types of connection can use the protocols SLIP (obsolete), HDLC (little used) or PPP (the most common).
Packet-switched or cell-switched connections
Packet-switched and cell-switched networks are point-to-point connections that pass through the network of a public carrier.
Although these types of connections are more expensive than asynchronous dial-up and ISDN connections, packet-switched and cell-switched services can provide very high-bandwidth solutions at a lower cost than dedicated connections. Examples of packet-switched and cell-switched networks include Frame Relay (packet-switched), X.25 (packet-switched) and asynchronous transfer mode or ATM (cell-switched).
Frame Relay
Frame Relay is one of the most popular methods of packet-switched networks. With support for a variety of network protocols, Frame Relay can provide flexible high-bandwidth solutions for most networks. Frame Relay service charges are generally based on the committed information rate (CIR). The CIR is the amount of bandwidth guaranteed by the service provider. The larger the CIR, the more expensive the Frame Relay solution. In addition, designing and supporting Frame Relay networks can be a nightmare. Consequently, a highly qualified network professional is needed to install and troubleshoot Frame Relay networks.
X.25
X.25 is an old packet-switched data-link layer protocol designed in the 1970s. X.25 was designed to operate over loaded analog lines and, consequently, has built-in error-checking mechanisms. The overhead required to perform error checking makes X.25 a low-bandwidth solution by current standards. However, if you have to deploy a WAN in an environment that contains loaded lines and legacy network equipment, X.25 remains a viable solution.
ATM
Asynchronous Transfer Mode (in French Mode de transfert asynchrone or ATM) is quickly becoming the connection method of choice for high-speed communications.
ATM is a cell-switched network protocol of the network layer of the OSI model. It uses a multiplexing technology; it concentrates different data streams onto the same physical link using a TDM or MRT (time-division multiplexing) technique.
ATM supports speeds up to OC-192 (i.e. 10 Gbit/s), making ATM the solution for high-speed networks supporting voice, video and data.
Of course, all these features come at a price.
Dedicated connections
Dedicated connections are point-to-point serial connections that offer fixed and permanent connections to remote networks. Dedicated links can provide speeds up to T3 (44,736 Mbps) over the network of a public carrier. Since dedicated connections are fixed and permanent connections, there is less overhead required to establish communication between two sites. And since dedicated connections offer low overhead and high-speed transmissions, they are excellent solutions for companies that need high-bandwidth WAN connections 24/7.
However, the charges and support costs for dedicated connections are high.
Choosing the best WAN connection
Determining the best type of WAN connection for your company can be a difficult task. A correct analysis of WAN traffic patterns and requirements is the key to a successful deployment of WAN solutions. For complete information on selecting and configuring your WAN connections using Cisco equipment, see Cisco IOS 12.0 WAN solutions.
Hardware configuration on WANs
Wide area networks use several suitable devices. Some of the important hardware components are WAN switches, access servers, modems, routers, ISDN terminal adapters, ATM switches and multiplexers.
A brief description of each would help to understand the indispensable nature of these components. The multi-port internetwork device used in WAN carrier networks is the WAN switch. It is used for switching traffic such as in Frame Relay, X.25 and Switched Multi-megabit Data Services (SMDS). The access server is a server system through which ISPs allow users to connect to the Internet.
A modem is a device that allows a computer to transfer data over connection links such as telephone cable or WAN links. It modulates and demodulates analog signals to encode and decode digital information, respectively.
Routers are devices that forward data packets across the network. They are located at the connection point of two or more networks, that is to say they are the gateways. A router connection facilitates file sharing between several computer systems.
The digital interface device that facilitates the connection of the router to a digital circuit (T1, for example) is called a channel service unit/data service unit (CSU/DSU). For communication between the devices, the CSU/DSU provides signal timing.
An ISDN terminal adapter connects ISDN BRI (Basic Rate Interface) connections to the rest of a router's interfaces, such as EIA/TIA-232. Although it has a similarity to a modem, it does not perform the modulation/demodulation functions.
WAN hardware devices have specific functions that ultimately contribute to efficient WAN connections and therefore to business continuity for companies. Speed is an important factor underlying all this infrastructure. To achieve speed in connectivity, it is necessary to monitor network traffic and load balancing. WAN compression devices systematically reduce WAN traffic, increase WAN capacity and improve application performance and user response time.
WAN compression becomes effective when it is used selectively based on specific applications. Bandwidth is used to the maximum, reducing unnecessary and redundant data transmission. WAN compression devices systematically reduce WAN traffic, increase WAN capacity and improve application performance and user response time.
Telephone and cable WAN
The data transmission mode differs depending on the WAN configuration and the connection required by the user. The wide area network encompasses a vast geographical area and enables information sharing. This requires stable WAN hardware, WAN support devices and links.
The interconnection of networks to facilitate communication is made possible through different technologies. Cable WAN enables the connection and sharing of information over twisted-pair copper cable, coaxial cable and optical fiber. In local area networks (LANs), computers are connected via an Ethernet cable. Cable WAN enables a speed of network connectivity.
Voice-over-Internet Protocol (VoIP), the standard optimized for voice transmission over the Internet or packet-switched networks, is also known by several names such as IP telephony, WAN telephony, Internet telephony, broadband phone, WAN phone, etc. VoIP systems transmit telephony signals in the form of digital audio. Data compression techniques are used to reduce the data rate, which is then encapsulated in a stream of data packets and transmitted via the IP protocol.
WAN telephony is an excellent tool for voice transmission because it contains many enhanced features. A single high-speed connection can be used to transfer more than one telephone call. A WAN phone has features such as conference calling, call transfer, automatic redial and caller ID. Besides providing a secure telephone connection using encryption and authentication, the advanced features of WAN telephony include call routing, pop-ups and IVR implementations. These are cost-effective and easy to integrate.
While WANs must be configured for optimal data transmission, they must also be stable and have extreme availability. This aspect is the key to ensuring business continuity.
Relevance of business continuity and optimized solutions
Optimized network connectivity is an important element of business automation and of achieving an organization's business continuity objectives. Companies in today's competitive world have a definite need for technology solutions that guarantee a robust WAN to keep their activities on track.
The wide area network, as the main platform on which companies operate, requires features such as optimization, reliability, security and acceleration to deliver high application performance.
Advanced technology products are deployed in critical and highly secure WANs for redundant and fast Internet access. This is essential because optimized solutions help to meet service continuity standards.