Teleworker ServicesAccessing the WAN – Chapter 6

Chia sẻ: Nguyễn Văn Chiến | Ngày: | Loại File: PDF | Số trang:63

Thêm vào BST

Báo xấu

64
lượt xem 8
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Tham khảo tài liệu 'teleworker servicesaccessing the wan – chapter 6', công nghệ thông tin, quản trị mạng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Teleworker ServicesAccessing the WAN – Chapter 6

Teleworker Services Accessing the WAN – Chapter 1 ITE I Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Objectives In this chapter, you will learn to: – Describe the enterprise requirements for providing teleworker services, including the differences between private and public network infrastructures. – Describe the teleworker requirements and recommended architecture for providing teleworking services. – Explain how broadband services extend enterprise networks using DSL, cable, and wireless technology. – Describe the importance of VPN technology, including its role and benefits for enterprises and teleworkers. – Describe how VPN technology can be used to provide secure teleworker services to an enterprise network. 2 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Business Requirement for Teleworker Services With advances in broadband and wireless technologies, working away from the office no longer presents the challenges it did in the past. – Organizations can cost-effectively distribute data, voice, video, and real-time applications, across their entire workforce no matter how remote and scattered they might be. On a broader scale, the ability of businesses to provide service across time zones and international boundaries is greatly enhanced using teleworkers. – Contracting and outsourcing solutions are easier to implement and manage. From a social perspective, teleworking options increase the employment opportunities for various groups, including parents with small children, the handicapped, and people living in remote areas. – Teleworkers enjoy more quality family time, less travel- related stress, and in general provide their employers with increased productivity, satisfaction, and retention. 3 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Teleworker Solution With the growing number of teleworkers, enterprises have an increasing need for secure, reliable, and cost-effective ways to connect to people working in small offices and home offices (SOHOs), and other remote locations, with resources on corporate sites. The figure displays 3 remote connection technologies available to organizations for supporting teleworker: 1. Traditional private WAN Layer 2 technologies, including Frame Relay, ATM, and leased lines, provide many remote connection solutions. 2. IPsec Virtual Private Networks (VPNs) offer flexible and scalable connectivity. • Site-to-site connections can provide a secure, fast, and reliable remote connection to teleworkers. • This is the most common option for teleworkers, combined with remote access over broadband, to establish a secure VPN over the public Internet. (A less reliable means of connectivity using the Internet is a dialup connection.) 4 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Teleworker Solution: Broadband Services 3. The term broadband refers to advanced communications systems capable of providing high- speed transmission of services, such as data, voice, and video, over the Internet and other networks. Transmission is provided by a wide range of technologies, including –digital subscriber line (DSL) –fiber-optic cable, –coaxial cable, –wireless technology, –satellite. The broadband service data transmission speeds typically exceed 200 kilobits per second (kb/s), or 200,000 bits per second, in at least one direction: –downstream (from the Internet to the user's computer) –upstream (from the user's computer to the Internet). 5 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Remote Connection Topologies for the Teleworker • Broadband vs. Baseband. – Baseband: only one In general, broadband refers to signal on the wire at telecommunication in which a wide band of once - time-division frequencies is available to transmit information. multiplexing: –Broadband is generally defined as any sustained • Ethernet networks. speed of 200K or more. – Broadband: multiple –Broadband options include signals - frequency •digital subscriber line (DSL), division multiplexing. •high-speed cable modems, •fast downstream data connections from direct broadcast satellite (DBS) •fixed wireless providers. •3G wireless –The most common problem with broadband access is lack of coverage area. 6 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Teleworker Solution To connect effectively to their organization's networks, teleworkers need two key sets of components: –Home Office Components - The required home office components are a laptop or desktop computer, broadband access (cable or DSL), and a VPN router or VPN client software installed on the computer. • When traveling, teleworkers need an Internet connection and a VPN client to connect to the corporate network over any available dialup, or broadband connection. –Corporate Components - Corporate components are VPN-capable routers, VPN concentrators, multifunction security appliances, authentication, and central management devices for resilient aggregation and termination of the VPN connections. 7 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Teleworker Solution Typically, providing support for VoIP requires upgrades to these components. –Routers need Quality of Service (QoS) functionality. –QoS refers to the capability of a network to provide better service to selected network traffic, as required by voice and video applications. The figure shows an encrypted VPN tunnel connect the teleworker to the corporate network. –This is the heart of secure and reliable teleworker connections. –A VPN is a private data network that uses the public telecommunication infrastructure. –VPN security maintains privacy using a tunneling protocol and security procedures. –This course presents the IPsec (IP Security) protocol as the favored approach to building secure VPN tunnels. 8 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Options for Connecting the Teleworker Split tunneling: –Split tunneling is a computer networking concept which allows a VPN user to access a public network (e.g., the Internet) and a local LAN or WAN at the same time, •The remote user, for example, then downloads his email from the mail server at 10.10.0.5, and downloads a document from the Archive at 10.2.3.4. Next, without exiting the tunnel, the remote user can print the document through the PC's local network interface 192.19.2.32 to the printer at 192.19.2.33. –Advantages •An advantage of using split tunneling is that it alleviates bottlenecks and conserves bandwidth as Internet traffic does not have to pass through the VPN server. –Disadvantages •A disadvantage of this method is that it essentially renders the VPN vulnerable to attack as it is accessible through the public, non-secure network. 9 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Connecting Teleworker to the WAN Teleworkers typically use diverse applications (e-mail, web, voice, and videoconferencing) that require a high-bandwidth connection: –Dialup access - Dialup is the slowest option, and is typically used by mobile workers in areas where high speed connection are not available. –DSL - DSL also uses telephone lines. DSL uses a special modem that separates the DSL signal from the telephone signal and provides an Ethernet connection to a host computer or LAN. –Cable modem - The Internet signal is carried on the same coaxial cable that delivers cable TV. A special cable modem separates the Internet signal from the other signals and provides an Ethernet connection to a host computer or LAN. –Satellite - The computer connects to a satellite modem that transmits radio signals to the nearest point of presence within the satellite network. 10 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy What is a Cable System? John Walson the founder of the cable television. –He was the first cable operator to use microwave to import distant television stations, –He was the first to use coaxial cable to improve picture quality, and the distribute pay television programming. Cable television first began in Pennsylvania in 1948. John Walson, the owner of an appliance store in a small mountain town, needed to solve poor over-the-air reception problems experienced by customers trying to receive TV signals from Philadelphia through the mountains. –Walson erected an antenna on a utility pole on a local mountaintop that enabled him to demonstrate the televisions in his store with strong broadcasts coming from the three Philadelphia stations. –He connected the antenna to his appliance store via a cable and modified signal boosters. http://www.pcta.com/news/walson. –He then connected several of his customers who were php?PHPSESSID=bad26d0ac5fd located along the cable path. 8e02fb67d0d5045a6fab –This was the first community antenna television (CATV) system in the United States. 11 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy What is a Cable System? The “cable” in cable system refers to the coaxial cable that carries radio frequency (RF) signals across the network. Coaxial cable is the primary medium used to build cable TV systems. A typical cable operator now uses a satellite dish to gather TV signals. Early systems were one-way with cascading amplifiers placed in series along the network to compensate for signal loss. –Taps were used to couple video signals from the main trunks to subscriber homes via drop cables Modern cable systems provide two-way communication between subscribers and the cable operator. –Cable operators now offer customers advanced telecommunications services including high-speed Internet access, digital cable television, and residential telephone service. –(e.g. impulse-pay-per-view, home shopping, Internet access), 12 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy What is a Cable System? One Way Cable Modems –In this system, communications in the down 1-way vs. 2 way direction is by cable but the return path is by conventional telephone line and telephone modem (33 Kbps). •Some companies have a modem box which connects to both your telephone line and to the cable TV system. The box then connects to your computer via either a USB port or an Ethernet port. Two way Cable Modems –Two way cable systems transmit data in both directions via cable and therefore do not need a telephone line. Uplink speeds are typically higher than 56K modem but not as high as downlink speeds. –Cable modem service is always-on and so the http://www.azinet.com/a problems with busy signals, connect time, and rticles/cablemodem.htm disconnects are eliminated. –These systems generally permanently assign a dedicated internet address (IP number) to each user which allows the use of services where your friends need to know your Internet address such as ICQ or netphone. 13 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Cable Technology Terms The following terms describe key cable technologies: – Broadband: In cable systems, broadband refers to the frequency- division multiplexing (FDM) of many signals in a wide RF bandwidth over a hybrid fiber-coaxial (HFC) network. – Community antenna television (CATV): The term now widely refers to residential cable systems. Tap Amplifier – Coaxial cable: Coaxial cable transports RF signals and has certain physical properties that define the attenuation of the signal. These properties include cable diameter, dielectric construction, ambient temperature, and operating frequency. – Tap: A tap divides the input signal's RF power to support multiple outputs. Typically, the cable operators deploy taps with two, four, or eight ports called subscriber drop connections. --- (Passive) – Amplifier: An amplifier magnifies an input signal and produces a significantly larger output signal. ---- (Active) Figure: HFC Architecture – Hybrid fiber-coaxial (HFC): HFC is a mixed optical-coaxial network in which optical fiber replaces the lower bandwidth coaxial where useful in the traditional trunk portion of the cable network. – Downstream: This is the direction of an RF signal transmission (TV channels and data) from the source (headend) to the destination (subscribers). Transmission from source to destination is called the forward path. – Upstream: This is the direction of an RF signal transmission opposite to downstream: from subscribers to the headend, or the return or reverse path. 14 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Cable Technology Terms Upstream vs. Downstream The following terms describe key cable technologies: – Value 768 kbps Upload Speed 256kbps – Basic 2.0 Mbps Upload Speed 384kbps – Advanced 4.0 Mbps Upload Speed 512kbps – Ultra 6.0 Mbps Upload Speed 512kbps. – Ultra Plus 6.0 Mbps Upload speed of 1Mbps. http://www1.wowway.com/internet/internet.aspx?ConIdent=1003&RCView=MAIN 15 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Cable System Components CATV distributes TV channels collected at a central location, called a headend, to subscribers over a branched network of optical fibers, coaxial cables, and broadband amplifiers. There are five major components of a cable system: Antenna site: The location of an antenna site is chosen for optimum reception of over-the-air, satellite signals. Headend: The headend is a master facility where signals are first received, processed, formatted, and then distributed downstream to the cable network. Transportation network: A transportation network links a remote antenna site to a headend. The transportation network can be microwave, coaxial, or fiber-optic. Distribution network: In a classic cable system called a tree-and-branch cable system, the distribution network consists of trunk and feeder cables. The trunk is the backbone that distributes signals throughout the community service area to the feeder. The feeder branches flow from a trunk and reach all of the subscribers in the service area. Subscriber drop: A subscriber drop connects the subscriber to the cable services. The subscriber drop is a connection between the feeder part of a distribution network and the subscriber terminal device (for example, TV set or cable modem). 16 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Cable System Benefits The cable system architecture provides a cost-effective solution for densely populated areas by cascading a broadcast architecture to the users. The development of cable systems made new services possible. –Cable systems support telephony and data services and analog and digital video services. Businesses that employ teleworkers can gain the following benefits from this widely available high-speed cable Internet access method: www.conniq.com/InternetAccess_cable.htm –VPN connectivity to corporate intranets –SOHO capabilities for work-at-home employees –Interactive television –Public switched telephone network (PSTN)- quality voice and fax calls over the managed IP networks 17 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Sending Digital Signals over Radio Waves When users tune a radio set across the RF spectrum to find different radio stations, they tune the radio to different electromagnetic frequencies across that RF spectrum. –The same principle applies to the cable system. The cable TV industry uses a portion of the RF electromagnetic spectrum. –At the subscriber end, equipment such as TVs, VCRs, and High Definition TV set-top boxes tune to certain frequencies that allow the user to view the TV channel or to receive high-speed Internet access. A cable network is capable of transmitting signals on the cable in either direction at the same time. 43–50 MHz: Cordless telephones, "49 MHz" FM walkie-talkies, and mixed 2-way mobile The following frequency scope is used: communication –Downstream: Transmitting the signals from the cable operator to the subscriber, the outgoing Downstream: Headend-to- frequencies are in the range of 50 to 860 MHz. subscriber has 810 MHz of –Upstream: Transmitting the signals in the reverse RF bandwidth. path from the subscriber to the cable operator, the Upstream: Subscriber-to- incoming frequencies are in the range of 5 to 42 headend has 37 MHz of RF MHz. bandwidth. 18 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy Sending Digital Signals over Radio Waves When a cable company offers Internet access over the cable, Internet use the same cables –the cable modem system puts downstream data -- data sent from the Internet to an individual computer -- into a 6-MHz channel. •On the cable, the data looks just like a TV channel. So Internet downstream data takes up the same amount of cable space as any single channel of programming. –Upstream data -- information sent from an individual back to the Internet -- requires even less of the cable's bandwidth, just 2 MHz, since the assumption is that most people download far more information than they upload. Putting both upstream and downstream data on the cable television system requires two types of equipment: a cable modem on the customer end and a cable modem termination system (CMTS) at the cable provider's end. http://computer.howstuffworks.com/cable-modem2.htm 19 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
Cisco Thai Nguyen Networking Academy The Data-over-Cable Service Interface Specification (DOCSIS) DOCSIS is an international standard developed by CableLabs, a nonprofit research and development consortium for cable-related technologies. – CableLabs tests and certifies cable equipment such as cable modem and cable modem termination systems. DOCSIS specifies the Open Systems Interconnection (OSI) Layers 1 and 2 requirements: – Physical layer: For data signals that the cable operator can use, DOCSIS specifies the channel widths (bandwidths of each channel) •DOCSIS 1.0: 200 kHz, 400 kHz, 800 kHz, 1.6 MHz, 3.2 MHz, •DOCSIS 2.0: 6.4 MHz. – MAC layer: Defines a deterministic access method (time- division multiple access [TDMA] or synchronous code division multiple access [S-CDMA]). DOCSIS currently uses two standards, and a third standard is under development: – DOCSIS 1.0 was the first standard issued in March 1997. – DOCSIS 2.0 was released in January 2002. •DOCSIS 2.0 enhanced upstream transmission speeds and QoS capabilities. – DOCSIS 3.0 is under development and expected to feature http://en.wikipedia.org/wiki/DOCSIS channel bonding, enabling the use of multiple downstream and upstream channels. 20 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public