Figure 2 shows how broadband connectivity is extended from the core infrastructure to end users' devices such as PCs, personal digital assistants (PDAs), telephones, television sets, and digital cameras. Infrastructure gateway equipment provides broadband access to the packet-based infrastructure. Customer premises equipment (CPE) access gateways extend broadband access connectivity to end-user devices via one or more home networking technologies.

Figure 2: Broadband Connectivity

Broadband Access Technologies
There are many competing broadband access technologies being brought to bear to address last-mile connectivity, including the following:

• Cable modem
• Digital subscriber line (DSL)
• Fiber
• 2.5G and 3G cellular wireless
• Wireless Ethernet

Cable
As an alternative to existing copper phone wires, cable companies have been providing broadband access by upgrading their cable plant to carry data and voice services in addition to traditional video services. A cable-modem termination system (CMTS) communicates with cable modems located at the customer premises to provide broadband access services. The cable modem typically provides an Ethernet interface to a PC or to a small router when multiple PCs are connected. Today's cable networks generally deliver data with download speeds roughly between 500 kbps and 2 Mbps and upstream speeds of 128 kbps. Newer-generation cable-modem technologies will significantly increase the available bandwidth to further enable interactive applications such as videoconferencing and high-end on-line video.

Internet protocol (IP) telephony is one of the services that can be delivered over coaxial cable. For the cable operators, IP telephony enables them to offer voice services that, to date, have been the domain of the telephone companies.

DSL
DSL technology is a copper-loop transmission technology for transmitting high-speed data over ordinary telephone wires. A DSL modem is installed at the customer premises and at the central office (CO). Different variants of DSL exist to address different technology trade-offs that can be made regarding different network environments and applications. One of the key trade-offs is distance (referred to as reach) from the CO and data rate. Asymmetrical DSL, or ADSL, is primarily used for residential services. ADSL takes advantage of the fact that there is more crosstalk interference at the CO end of a copper pair than at the subscriber end due to the large bundles of cabling entering the CO. ADSL can provide data rates up to 8 Mbps from the network to the subscriber direction, and up to 1 Mbps from the subscriber to the network direction. The asymmetry of ADSL works well for today's home applications where the majority of bandwidth is consumed in the network to user direction.

Symmetrical DSL, or SDSL, is a cost-effective solution for small and medium enterprises, offering a competitive alternative to T1 and E1 lines. The International Telecommunication Union-Telecommunications Standardization Sector (ITU-T) standard G.991.2, also known as G.shdsl, is a replacement standard for proprietary SDSL. G.shdsl offers data rates from 192 kbps to 2.3 Mbps while providing a 30% longer reach than SDSL.

Very-high-data-rate DSL, or VDSL, can support symmetrical or asymmetrical services. Asymmetrical VDSL is capable of providing data rates to the user of up to 52 Mbps, making it suitable for transporting high-speed applications such as real-time video streaming. The trade-off for this high speed is restricted reach. This requires that the customer be located close to the CO or that the infrastructure access gateway resides outside the CO (and closer to the customers) in a remote terminal (RT).

Fiber
For new infrastructure buildout, where copper wires are not currently present, the installation of fiber is being employed. Fiber-optic technology, through local access network architectures such as fiber-to-the-home/building (FTTH/B), fiber-to-the-cabinet (FTTCab), and fiber-to-the-curb (FTTC) offers a mechanism to enable sufficient network bandwidth for the delivery of new services and applications. A fiber-optic cable is run from the CO to the neighborhood. Passive optical splitters are used to provide point-to-multipoint connectivity. This is referred to as a passive optical network or PON. In the case of FTTCab or FTTC architectures, the signal is converted to provide connectivity to the subscribers via copper-pair wires. Since these cabinets are collocated in a neighborhood, the copper-pair run is typically less than 3,000 feet; thus enabling high-performance xDSL access to be achieved.

2 and 2.5 Generation (G) Cellular Wireless
Next-generation cellular is providing high-speed data capabilities in addition to traditional voice. Current 2G cellular services only offer data service rates on the order of 9.6 kbps. The emerging 2.5G services will boost available bandwidth to the user and facilitate always-on data services. For 2.5G networks, there are two primary technologies: general packet radio service (GPRS) and enhanced data rates for GSM and TDMA (IS-136) evolution (EDGE). Third-generation (3G) wireless communication technologies support even higher data rates. The packet switching is IP-based, making for efficient routing of data from the Internet through the carrier's gateway. The higher bandwidth should allow for better integration of voice, data, and video signals. Delivery of data services over cellular offers the promise of ubiquitous high-speed data access, including while in moving vehicles.

Wireless Ethernet
In addition to cellular-based wireless data services, wireless Ethernet, traditionally a home and enterprise networking technology (see next section), is being used for broadband access in public areas such as airports, hotels, sports arenas, convention centers, and coffee shops. This allows users to take their laptop and PDA devices with them and to use a common access technology to deliver high-speed Internet services in their office, home, and while on the road.

Home and Enterprise Networking Technologies While most corporations today have some form of wired Ethernet LANs to address their networking needs, most homes do not have any form of networking infrastructure. There are several competing home networking technologies, including the following:

• Ethernet
• HomePNA
• HomePlug
• Bluetooth®
• Wireless Ethernet

Ethernet is the most ubiquitous LAN technology and as such, very low-cost Ethernet adapters exist for PCs and other devices. However, installing Ethernet cabling in existing homes is expensive as it involves labor-intensive work to snake cables through existing walls, install outlets, and repair drywall. As such, installation of Ethernet cabling is typically relegated to new construction. As an alternative, technology has been developed to use existing phone wiring to run LAN traffic simultaneously with voice. The Home Phone Networking Alliance (HomePNA) defines standards for interoperability using this technology. Unfortunately, most homes have a limited number telephone jacks for access to the wires. Thus, the expense of adding new wires must still be tackled. Technology has been developed to use existing home AC wiring to run LAN traffic. As most rooms have multiple AC outlets, there is access to the LAN from practically anywhere. This still requires the device accessing the LAN to be tethered, as it must plug into the AC outlet.

As an alternate to wired networks, wireless standards exist, including Bluetooth and wireless Ethernet (wireless LAN or WLAN). Bluetooth was developed to replace the need for interconnect cabling between devices for short-range and relatively lower data rates. Wireless Ethernet is a standard developed by the Institute of Electrical and Electronics Engineers (IEEE) (802.11) that preserves Ethernet compatibility and data rates. It is gaining wide traction for home, enterprise, and public access networking.

The current standard for wireless Ethernet is 802.11b, and it offers 11 Mbps transmission rates using direct sequence spread spectrum (DSSS) technology. The standard, also known as Wi-Fi™, is widely used in offices, campuses, and homes. Radio transmission is in the 2.4-GHz band. The 802.11a variant of the standard operates in the 5-GHz frequency band and offers transmission rates up to 54 Mbps using orthogonal frequency division multiplexing (OFDM) technology in which the devices determine a set of noninterfering frequencies, multiplex these frequencies, and use them in parallel to achieve greater bandwidth. A recent addition to the 802.11 standard is 802.11g, which extends DSSS operation to 22 Mbps and also supports OFDM operation in the 2.4-GHz frequency band.

Wireless standards must address potential transmission interference with other devices, including microwaves, cordless telephones, and other wireless standards that operate at the same frequency. Also, since it is wireless, solid encryption is required for security purposes.

Networking Standard	Description	Type	Installation Requirements	Maximum Data Rate Mbps
802.3 Ethernet	Highest capacity; commodity hardware	Wired	New wires	10/100
802.11 Ethernet	Wireless Ethernet	Wireless	No wiring required	11/22/54
HPNA	Home networking using existing telephone wires	Wired	Some new wires	1/10/32
Bluetooth	Short range cable replacement	Wireless	No wiring required	1
HomePlug	Home networking using existing AC power	AC Wires	No new wires	10

Figure 3