Tuesday, August 25, 2009


With some broadband systems, data signals travel from a computer to a satellite and are then beamed to the ISP where the request is processed. The main advantage of satellite broadband is that it is available to nearly anyone who has an unobstructed view of the southern sky, since satellites orbit the Earth near the Equator. Rural customers who may not have access to other broadband technology can usually receive service via satellite.

Satellite Satellite broadband has several limitations including upload and download delays, inclement weather disruptions, physical obstruction concerns, and costs to purchase, maintain and operate the necessary equipment. Due to the distance from the computer to the satellite, there is a delay of a half-second or more between information sent and data received. Inclement weather can increase the delay or disrupt satellite service altogether. Objects such as trees and buildings can severely restrict or prevent reception of satellite signals.

T Lines

T-1 Lines A T-1 line is a dedicated line supporting data rates up to 1.544 Mbps - using 24 individual channels with each supporting 64 Kbps. An individual channel can carry voice or data traffi c, while a customer switching unit/ digital switching unit (CSU/DSU) is necessary toconnect the channel to the four wires that carry the information. The CSU/DSU sends the data signal to
the router which connects it to a server that may send it to the Internet via other servers. Lines
Repeaters must be in place every 6,000 feet or less to help prevent data signal degeneration (as diagrammed below).

Telephone companies, in general, allow customers to buy individual channels in increments of 56 Kbps (8 Kbps per channel is used for data management). A full T-1 connection can theoretically accommodate 200+ users and other provider services.

T-1 lines use copper wire and offer a popular option to businesses and smaller Internet service providers (ISPs) wanting to connect to the Internet and the Internet backbone (such as faster T-3 connections). Because of costs, T-1 service is generally not considered an effective method for reaching most rural areas or residential customers.


Cable television companies (Comcast, Insight, Brighthouse, Time Warner, etc.) are now competing
with traditional telephone services by providing service over their own networks, usually Voice over Internet Protocol (VoIP). For more information on VoIP please refer to the OUCC’s VoIP fact sheet.

Coaxial Cable If a consumer uses a cable service for broadband access, a cable modem connects the user’s personal computer to a shared network, connecting the computer to the Internet via the cable company’s main offi ce (as shown below). Cable modems adhere to industry standards known as DOCSIS (Data Over Cable Service Interface Specifi cation). These standards allow them to interact with other DOCSIS-certifi ed equipment to ensure data privacy. Cable companies can install new service to customers very quickly and easily if those customers are already using cable TV. In general, cable companies offer faster download and upload speed than traditional DSL if the network is not congested. Cable modems can accommodate data speeds up to 27 Mbps downstream and 10 Mbps upstream, but typical speeds generally average 1 to 3 Mbps. Cable broadband speeds can be limited by congestion on the network, limiting providers’ ability to guarantee broadband speeds. The cost of deploying cable can hinder providers’ ability to extend service into low-density areas.


Digital Subscriber Line (DSL)

DSL Digital Subscriber Line (DSL) provides a dedicated digital circuit between a user’s premises and the Internet through the telephone company’s central offi ce via ordinary copper telephone wires. The two primary forms of DSL are Asymmetric Digital Subscriber Line (ADSL) and Symmetric Digital Subscriber Line (SDSL). ADSL has a higher download speed (1.544 to 6.1 Mbps downstream) and a lower upload speed (16 Kbps to 1.5 Mbps). SDSL’s download and upload speeds (1.544 Mbps) are equal. SDSL does not provide voice capabilities. ADSL – which is more widely used and available – must be within 18,000 feet of the central offi ce while SDSL users must be within 12,000 feet. Some companies, however, have begun to use new technologies such as fi ber lines and/or repeaters to extend DSL capabilities up to 25,000 feet.

An ADSL modem has a “plain old telephone service” POTS) splitter and a channel separator. The POTS splitter divides the phone line into two channels (voice and data) and the channel separator divides the data channel into two sections (downstream and upstream). Data are transported to another ADSL modem in the central offi ce. This modem sends the voice calls to the public switched telephone network (PSTN) and sends the data to the digital subscriber line access multiplexer DSLAM). The DSLAM connects many ADSL lines to a single asynchronus transfer mode (ATM) line or switch. This ATM line acts as both a traffi c aggregator and as a multiservice switch that is capable of forwarding traffi c in different ways, depending on needs. The ATM line then sends the data over the Internet.

3G history

First generation wireless, or 1G, refers to analogue networks introduced in the mid-1980s.
Examples include advanced mobile phone service (AMPS) used in North America and total access
communications system (TACS) used in the UK. In South Africa we had the C450 mobile system
run by Telkom which was relatively expensive and took ten years to achieve ten thousand subscribers. Most 1G technologies and systems were country or region-specifi c and thus offered
limited coverage.As mobile communications grew in popularity, networks often became
overloaded, resulting in busy signals and dropped calls. The solution was second-generation
wireless, or 2G, which emerged in the early 1990s. 2G technologies were digital and offered
the much-needed capacity that 1G analogue systems did not afford. Several technologies were
widely used:

• GSM was and still is popular in Europe and Asia Pacifi c, and Latin America
• TDMA was used in the Americas and is still used in Latin America
• CDMA IS-95 or cdmaOne was used primarily in the Americas and Asia Pacific

However, these 2G technologies are incompatible with each other. Thus, mobile service subscribers were still often limited to using their phones in a single country or region. In an effort to standardise future digital wireless communications and make global roaming with a single handset possible, the ITU established a single standard for wireless networks in 1999. Called IMT-2000, which is commonly referred to today as 3G, the initiative set forth the requirements (mentioned above) for the third generation of wireless networks.

3G standard

3G stands for third-generation wireless technology and networks. It is based on the International Telecommunication Union (ITU) initiative for a single global wireless standard called International Mobile Telecommunications-2000 (IMT-2000). This concept of a single standard evolved into a family of fi ve 3G wireless standards. Of those fi ve, the most widely accepted are CDMA2000, WCDMA (UMTS) and TD-SCDMA. According
to the ITU and IMT-2000, a wireless standard must meet minimum bit-rate requirements to be considered 3G:

• 2 Mbps in fixed or in-building environments
• 384 kbps in pedestrian or urbanenvironments
• 144 kbps in wide area mobileenvironments
• Variable data rates in large geographic areasystems (satellite)

In addition to providing faster bit rates and greater capacity over previous-generation technologies, 3G standards excel by effectively:

• Delivering mobile data
• Offering greater network capacity
• Operating with existing second-generation technologies
• Enabling rich data applications such as VoIP, video telephony, mobile multimedia,interactive gaming and more.


Assignment Lanka Tag Cloud
Computer Networks The History of Local Area Networks, LAN, The Topologies of a Networks, LANs describe different types of transmission Medias, Local Area Networks Access Methods, Carrier Sense Multiple Access with Collision Detect, Development of LAN Technologies. LAN -Token Ring, LAN Ethernet Digital, LAN - Ethernet Sun microsystems, LAN - Ethernet Mixed Environment, LAN - Token Ring was introduced by IBM LAN - IBM implementation of Token Ring, Token Ring Novell, LAN Token Ring - in a mixed environment, LAN - Fiber Distributed Data Interface, LAN - ATM, LAN Components, LAN Switching Methods, Virtual Local Area Network, Port based VLAN, Mac based VLAN, Protocol based VLAN, User Base VLAN, PC networks Components, PC networks Shared resources, PC Network operating systems, PC networks Novell Netware, PC networks Windows NT, PC networks IBM LAN Server Computer Programming Languages HTML Language, The Generations of Programming Languages, Different types of High Level Languages, Different types of High Level Languages Disadvantages
Computer Networks - IBM LAN Server, Windows NT Networks, Novell Netware, Network operating systems, Networks Shared, Networks Components, User Base, Protocol based, Mac based, Port based, VLAN, LAN Switching, LAN Components, ATM, Fiber Data, Token Ring, Token Ring Novell, IBM implementation, Ethernet, Sun microsystems, Ethernet Digital, Token passing, LAN Technologies, CSMA/CD, Access Methods, Transmission, Networks, The History of Local Area Networks, LAN