These technologies are introduced in the following sections.

TDM (Leased Lines)

TDM is a type of digital multiplexing in which pulses representing bits from two or more channels are interleaved, on a time basis. Rather than using bandwidth only as required, TDM indefinitely reserves point-to-point connection bandwidth for transmissions.

ISDN

ISDN is a system of digital phone connections that has been available as a communications standard since 1984. This system allows voice and data to be transmitted simultaneously across the world using end-to-end digital connectivity. ISDN connectivity offers increased bandwidth, reduced call setup time, reduced latency, and lower signal-to-noise ratios, compared to analog dialup.

Frame Relay

Frame Relay is an example of a packet-switched technology for connecting devices on a WAN that has been deployed since the late 1980s. Frame Relay is an industry-standard networking protocol that handles multiple virtual circuits (VC) using a derivation of High-Level Data Link Control (HDLC) encapsulation between connected devices.

Frame Relay networks transfer data using one of two connection types:

■ PVCs, which are permanent connections.

■ SVCs, which are temporary connections created for each data transfer and then terminated when the data transfer is complete. SVCs are not widely used.

MPLS( Multiprotocol Label Switching)

MPLS is an Internet Engineering Task Force (IETF) standard architecture that combines the advantages of Layer 3 routing with the benefits of Layer 2 switching. With MPLS, short fixed-length labels are assigned to each packet at the edge of the network. Rather than examining the IP packet header information, MPLS nodes use this label to determine how to process the data.

MPLS Services

The following are some of the most common services provided by MPLS:

■ Traffic engineering: MPLS allows traffic to be directed through a specific path, which might be different from the least-cost path determined by the IP routing protocol. This ability to define routes and resource utilization is known as traffic engineering.

■ QoS support: MPLS creates a connection-oriented network for IP traffic, thereby providing the foundation for QoS traffic controls. For example, it might provide guaranteed bandwidth to specific traffic between two locations.

■ Fast reroute (FRR): Because FRR allows extremely quick recovery from node or link failure, it prevents applications from timing out and losing data.

■ MPLS VPNs: MPLS VPNs are much easier to deploy than traditional VPNs. They scale easily with increasing numbers of routes and customers and provide the same level of privacy as Layer 2 technologies. MPLS VPNs can also support nonunique IP addresses in various locations; for example, two organizations that use the 10.0.0.0 private address space can be supported simultaneously. MPLS VPNs are described in the later “Peer-to-Peer VPNs” section.

■ Multiprotocol support: MPLS can be used in an ATM network, a Frame Relay network, or a pure IP-based Internet. MPLS can be used to carry many kinds of traffic, including IP packets, and native ATM, SONET, and Ethernet frames.

Metro Ethernet

Metro Ethernet uses Ethernet technology to deliver cost-effective, high-speed connectivity for MAN and WAN applications. Service providers offer Metro Ethernet services to deliver converged voice, video, and data networking. Metro Ethernet provides a data-optimized connectivity solution for the MAN and WAN based on Ethernet technology widely deployed within the enterprise LAN. It also supports high-performance networks in the metropolitan area, meeting the increasing need for faster data speeds and more stringent QoS requirements.

DSL Technologies

DSL delivers high bandwidth over traditional telephone copper lines. It works by way of two modems at either end of the wire. Like dialup, cable, wireless, and T1, DSL is a transmission technology that enables SPs to deliver a wide variety of services to their customers. These can include premium, high-speed Internet and intranet access, voice, VPNs, videoconferencing, and video on demand.

Long Reach Ethernet Technology

Long Reach Ethernet (LRE) is Cisco-proprietary technology that allows greater distances than traditional Ethernet and is a WAN access technology. LRE technology enables the use of Ethernet over existing, unconditioned, telephone-grade wire (copper twisted pair) using DSL coding and digital modulation techniques.

Cable Technology

The cable technology for data transport uses coaxial cable media over cable distribution systems. The cable network is a high-speed copper platform that supports analog and digital video services over coaxial cables. This technology is a good option for environments where cable television is widely deployed. Cable service providers support both residential and commercial customers.

Wireless Technologies

With wireless technologies, networks do not have the limitations of wires or cables; instead, electromagnetic waves carry the RF signals.

wireless implementations include the following:

■ Bridged wireless: Designed to connect two or more networks, typically located in different buildings, at high data rates for data-intensive, line-of-sight applications. A series of wireless bridges or routers connect discrete, distant sites into a single LAN, interconnecting hard-towire sites, noncontiguous floors, satellite offices, school or corporate campus settings, temporary networks, and warehouses.

■ Mobile wireless: Includes cellular voice and data applications. Wireless technology usage increased with the introduction of digital services on wireless. Second- and third-generation mobile phones offer better connectivity and higher speeds. Mobile wireless technologies include the following:

• Global System for Mobile (GSM): GSM is a digital mobile radio standard that uses time division multiple access (TDMA) technology. It allows eight simultaneous calls on the same frequency, in three different bands: 900, 1800, and 1900 MHz. The transfer data rate is 9.6 kbps. One of the unique benefits of the GSM service is its international roaming capability, a result of roaming agreements established among the various operators.
• General Packet Radio Service (GPRS): GPRS extends the capability of GSM and supports intermittent and bursty data transfer. Speeds offered to the client are in the range of ISDN speeds (64 kbps to 128 kbps).
• Universal Mobile Telephone Service (UMTS): UTMS is a so-called thirdgeneration (3G) broadband, packet-based transmission of text, digitized voice, video, and multimedia at data rates up to 2 Mbps. UMTS offers a consistent set of services to mobile computer and phone users, regardless of their location in the world.
• Code Division Multiple Access (CDMA): CDMA is a spread-spectrum technology that assigns a code to each conversation; individual conversations are encoded in a pseudo-random digital sequence.

■ WLAN: Developed because of demand for LAN connections over the air and often used for intrabuilding communication. WLAN technology can replace a traditional wired network or extend its reach and capabilities. WLANs cover a growing range of applications, such as guest access and voice, and support services, such as advanced security and location of wireless