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Chapter07 -- wa ns and remote connectivity


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Basic Networking Guide

Basic Networking Guide

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  • 1. Chapter 7: WANs and Remote Connectivity Network+ Guide to Networks
  • 2. Objectives
    • Identify network applications that require WAN technology
    • Explain various WAN topologies, including their advantages and disadvantages
    • Describe a variety of WAN transmission and connection methods, including PSTN, ISDN, T-carriers, DSL, broadband cable, and SONET
  • 3. Objectives (continued)
    • Assess WAN implementation options based on speed, security, and reliability
    • Understand the hardware and software requirements for remotely connecting to a network
  • 4. WANs and Remote Connectivity
      • A WAN is a network that connects two or more geographically distinct LANs
      • Remote connectivity and WANs are significant concerns for organizations attempting to meet the needs of telecommuting workers, global business partners, and Internet-based commerce
  • 5. WAN Essentials
      • A WAN is a network that traverses some distance and usually connects LANs, whether across the city or across the nation
      • The internet is the largest WAN in existence today7
      • LANs use a building’s internal cabling, such as twisted-pair, that runs from work area to the wall, through plenum areas and to a telecommunications closet
  • 6. WAN Essentials (continued)
      • WANs typically send data over publicly available communications networks, which are owned by local and long-distance telecommunications carriers
        • Such carriers, which are privately owned corporations, are also known as network service providers (NSPs)
  • 7. WAN Essentials (continued)
      • For better throughput, an organization might lease a dedicated line, or a continuously available communications channel, from a telecommunications provider, such as a local telephone company or ISP
      • A WAN link is a connection between one WAN site (or point) and another site (or point)
  • 8. WAN Topologies
    • Bus
      • A WAN in which each site is directly connected to no more than two other sites in a serial fashion is known as a bus topology WAN
        • A bus topology WAN is similar to a bus topology LAN in that each site depends on every other site in the network to transmit and receive its traffic
        • The WAN bus topology uses different locations, each one connected to another one through point-to-point links
  • 9. WAN Topologies (continued)
        • A bus topology WAN is often the best option for organizations with only a few sites and the capability to use dedicated circuits
        • Bus WAN topologies are suitable for only small WANs
        • A single failure on a bus topology WAN can take down communications between all sites
  • 10. WAN Topologies (continued)
    • Ring
      • In a ring topology WAN, each site is connected to two other sites so that the entire WAN forms a ring pattern
      • This architecture is similar to the simple ring topology used on a LAN, except that a WAN ring topology connects locations rather than local nodes and in most WANs, a ring topology uses two parallel paths for data
  • 11. WAN Topologies (continued)
      • A ring topology WAN cannot not be taken down by the loss of one site; instead, if one site fails, data can be rerouted around the WAN in a different direction
      • WANs that use the ring topology are only practical for connecting fewer than four or five locations
  • 12. WAN Topologies (continued)
    • Star
      • The star topology WAN mimics the arrangement of a star topology LAN
      • A single site acts as the central connection point for several other points
  • 13. WAN Topologies (continued)
      • If a single connection fails, only one location loses WAN access
      • When all of its dedicated circuits are functioning, a star WAN provides shorter data paths between any two sites
  • 14. WAN Topologies (continued)
    • Mesh
      • A mesh topology WAN incorporates many directly interconnected sites
      • Because every site is interconnected, data can travel directly from its origin to its destination
      • Mesh WANs are the most fault-tolerant type of WAN because they provide multiple routes for data to follow between any two points
  • 15. WAN Topologies (continued)
      • The type of mesh topology in which every WAN site is directly connected to every other site is called a full mesh WAN
      • Partial mesh WAN are used when only critical WAN sites are directly interconnected and secondary sites are connected through star or ring topologies
      • Partial mesh WANs are more common in today’s business world than full mesh WANs because they are more economical
  • 16. WAN Topologies (continued)
    • Tiered
      • In a tiered topology WAN, sites connected in star or ring formations are interconnected at different levels, with the interconnection points being organized into layers to form hierarchical groupings
  • 17. WAN Topologies (continued)
      • Tiered systems allow for easy expansion and inclusion of redundant links to support growth
      • Their enormous flexibility means that creation of tiered WANs requires careful consideration of geography, usage patterns, and growth potential
  • 18. PSTN
      • Stands for Public Switched Telephone Network
      • Refers to the network of typical telephone lines and carrier equipment that service most homes
      • PSTN may also be called plain old telephone service (POTS)
      • The PSTN comprises the entire telephone system, from the lines that connect homes and businesses to the network centers that connect different regions of a country
  • 19. PSTN (continued)
      • The PSTN is often used by individuals connecting to a WAN (such as the Internet) via a dial-up connection
      • A dial-up connection is one in which a user connects, via a modem, to a distant network from a computer and stays connected for a finite period of time
  • 20. PSTN (continued)
      • A central office is the place where a telephone company terminates lines and switches calls between different locations
      • The portion of the PSTN that connects your house to the nearest central office is known as the local loop, or the last mile
  • 21. X.25
      • X.25 is an analog, packet-switched technology designed for long-distance data transmission
      • The X.25 standard specifies protocols at the Physical, Data Link, and Network layers of the OSI Model
      • The X.25 provides excellent flow control and ensures data reliability over long distances by verifying the transmission at every node
      • X.25 checks for errors and, in the case of an error, either corrects the damaged data or retransmits the original data
  • 22. Frame Relay
      • An updated, digital version of X.25 that also relies on packet switching
      • Frame Relay protocols operate at the Data Link layer of the OSI Model and can support multiple different Network and Transport layer protocols
      • The name is derived from the fact that data is separated into frames, which are then relayed from one node to another without any verification or processing
      • Frame Relay does not guarantee reliable delivery of data
  • 23. X.25 and Frame Relay
      • Both X.25 and Frame Relay may be configured as switched virtual circuits (SVCs) or permanent virtual circuits (PVCs)
      • SVCs are connections that are established when parties need to transmit, then terminated once the transmission is complete
      • PVCs are connections that are established before data needs to be transmitted and maintained after the transmission is complete and they are not dedicated, individual links
      • The service provider guarantees a minimum amount of bandwidth, called the committed information rate (CIR)
  • 24. ISDN
      • Integrated Services Digital Network is an international standard for transmitting digital data over the PSTN
      • ISDN specifies protocols at the Physical, Data Link, and Transport layers of the OSI Model
      • ISDN relies on the PSTN for its transmission medium
      • ISDN is distinguished because it can simultaneously carry as many as two voice calls and one data connection on a single line
  • 25. ISDN (continued)
      • All ISDN connections are based on two types of channels: B channels and D channels
      • The B channel is the “bearer” channel, employing circuit-switching techniques to carry voice, video, audio, and other types of data over the ISDN connection
      • The D channel is the “data” channel, employing packet-switching techniques to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals
  • 26. ISDN (continued)
      • In North America, two types of ISDN connections are commonly used: Basic Rate Interface (BRI) and Primary Rate Interface (PRI)
      • BRI (Basic Rate Interface) uses two B channels and one D channel
      • In a process called bonding, these two 64-Kbps B channels can be combined to achieve an effective throughput of 128 Kbps
  • 27. ISDN (continued)
      • PRI (Primary Rate Interface) uses 23 B channels and one 64-Kbps D channel
      • PRI is less commonly used by individual subscribers than BRI is, but it may be selected by businesses and other organizations that need more throughput
      • PRI link can carry voice and data, independently of each other or bonded together
  • 28. T-Carriers
      • T-carrier standards specify a method of signaling, which means they belong to the Physical layer of the OSI Model
      • A T-carrier uses time division multiplexing (TDM) over two wire pairs (one for transmitting and one for receiving) to divide a single channel into multiple channels
      • Each channel may carry data, voice, or video signals
      • The medium used for T-carrier signaling can be ordinary telephone wire, fiber-optic cable, or wireless links
  • 29. T-Carriers (continued)
    • Types of T-Carriers
      • T1 circuit can carry the equivalent of 24 voice or data channels, giving a maximum data throughput of 1.544 Mbps
      • A T3 circuit can carry the equivalent of 672 voice or data channels, giving a maximum data throughput of 44.736 Mbps
  • 30. T-Carriers (continued)
      • A fractional T1 lease allows organizations to use only some of the channels on a T1 line and be charged according to the number of channels they use
      • The signal level refers to the T-carrier’s Physical layer electrical signaling characteristics
      • DS0 (digital signal, level 0) is the equivalent of one data or voice channel
  • 31. T-Carriers (continued)
    • T-Carrier Connectivity
      • Every T-carrier line requires connectivity hardware at both the customer site and the local telecommunications provider’s switching facility
      • T-carrier lines require specialized connectivity hardware that cannot be used with other WAN transmission methods
      • T-carrier lines require different media depending on their throughput
      • Wiring
        • T1 technology can use unshielded or shielded twisted-pair (UTP or STP) copper wiring
        • STP is preferable to UTP
  • 32. T-Carriers (continued)
    • CSU/DSU (Channel Service Unit/Data Service Unit)
      • The CSU/DSU is the connection point for a T1 line at the customer’s site
      • The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring
      • The DSU converts the T-carrier frames into frames the LAN can interpret and vice versa
      • After being demultiplexed, an incoming T-carrier signal passes on to devices collectively known as terminal equipment
  • 33. T-Carriers (continued)
    • Terminal Equipment
      • On a typical T1-connected data network, the terminal equipment will consist of switches, routers, or bridges
      • Usually, a router or Layer 3 or higher switch is the best option, because these devices can translate between different Layer 3 protocols that might be used on the WAN and LAN
      • On some implementations, the CSU/DSU is not a separate device, but is integrated with the router or switch as an expansion card
  • 34. DSL
      • Digital subscriber line (DSL) is a WAN connection method introduced by researchers at Bell Laboratories in the mid-1990s
      • DSL can span only limited distances without the help of repeaters and is therefore best suited to the local loop portion of a WAN link
      • DSL can support multiple data and voice channels over a single line
      • DSL uses advanced data modulation techniques
  • 35. DSL (continued)
    • Types of DSL
      • The term xDSL refers to all DSL varieties, of which at least eight currently exist
      • DSL types can be divided into two categories: asymmetrical and symmetrical
      • The term downstream refers to data traveling from the carrier’s switching facility to the customer
      • Upstream refers to data traveling from the customer to the carrier’s switching facility
  • 36. DSL (continued)
      • A technology that offers more throughput in one direction than in the other is considered asymmetrical
        • In asymmetrical communications, downstream throughput is higher than upstream throughput
      • Symmetrical technology provides equal capacity for data traveling both upstream and downstream
        • Symmetrical transmission is suited to users who both upload and download significant amounts of data
  • 37. DSL (continued)
    • DSL Connectivity
    • A DSL modem is a device that modulates outgoing signals and demodulates incoming DSL signals
      • The DSL modem may be external to the computer and connect to a computer’s Ethernet NIC via an RJ-45,USB, or wireless interface
      • DSL access multiplexer (DSLAM) aggregates multiple DSL subscriber lines and connects them to a larger carrier or to the Internet backbone
      • DSL is not available in all areas of the United States
  • 38. Cable
      • Cable connections require that the customer use a special cable modem, a device that modulates and demodulates signals for transmission and reception via cable wiring
      • Cable modems operate at the Physical and Data Link layer of the OSI Model, and therefore do not manipulate higher-layer protocols such as IP or IPX
      • To provide Internet access through its network, the cable company must upgrade its existing equipment to support bidirectional, digital communications
      • The cable company’s network wiring must be replaced with hybrid fiber-coax (HFC), an expensive fiber-optic link that can support high frequencies
  • 39. Cable (continued)
        • Either fiber-optic or coaxial cable may connect the node to the customer’s business or residence via a connection known as a cable drop
        • These nodes then connect to the cable company’s central office, which is known as its head-end
  • 40. SONET
      • SONET (Synchronous Optical Network) is a high-bandwidth WAN signaling technique
      • SONET specifies framing and multiplexing techniques at the Physical layer of the OSI Model
  • 41. SONET (continued)
      • Its four key strengths are that it: can integrate many other WAN technologies; offers fast data transfer rates; allows for simple link additions and removals; and provides a high degree of fault tolerance
      • The word synchronous means that data being transmitted and received by nodes must conform to a timing scheme
  • 42. SONET (continued)
      • SONET provides interoperability
      • SONET is often used to aggregate multiple T1s, T3s, or ISDN lines
      • SONET is also used as the underlying technology for ATM transmission
      • Internationally, SONET is known as SDH (Synchronous Digital Hierarchy)
      • SONET’s extraordinary fault tolerance results from its use of a double-ring topology over fiber-optic cable
      • Self-healing is a characteristic of dual-ring topologies that allows them to automatically reroute traffic along the backup ring if the primary ring becomes severed
  • 43. SONET (continued)
      • Most SONET multiplexers allow for easy additions or removals of connections to the SONET ring, which makes this technology easily adaptable to growing and changing networks
      • The data rate of a particular SONET ring is indicated by its Optical Carrier (OC) level
  • 44. WAN Implementation
    • Reliability
    • A WAN’s reliability depends partly on the transmission medium it uses and partly on its topology and transmission methods
      • Not very reliable, suited to individual or unimportant transmissions: PSTN dial-up
        • Sufficiently reliable, suited for day-to-day transmissions: ISDN,T1, fractional T1, T3, DSL, cable, X.25, and Frame Relay
        • Very reliable, suited to mission-critical applications: SONET
  • 45. WAN Implementation (continued)
    • Security
      • Fiber optic media are the most secure transmission media
      • WAN security depends in part on the encryption measures each carrier provides for its lines
      • Enforce password-based authorization for LAN and WAN access and teach users how to choose difficult-to-decrypt passwords
      • Take the time to develop, publish, and enforce a security policy for users in your organization
      • Maintain restricted access to network equipment rooms and data centers
  • 46. Remote Connectivity
    • As a remote user, you must connect to a LAN via remote access, which can be accomplished in one of several ways: dial-up networking, remote control, terminal services, Web portals, or a virtual private network (VPN)
  • 47. Remote Connectivity (continued)
    • Dial-up Networking
      • Dial-up networking refers to dialing into a private network’s or ISP’s remote access server to log on to a network
      • The remote access server (a server designed to accept incoming client connections) is attached to a group of modems, all of which are associated with one phone number
      • An advantage to using this remote access option are that the technology is well-understood and its software comes with virtually every operating system
      • Dialing into a remote access server can be slow because it relies on the PSTN
  • 48. Remote Connectivity (continued)
      • One well known program used to provide remote access is the Microsoft Routing and Remote Access Service (RRAS), which is available with the Windows Server 2003 network operating system
      • The Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP) are two protocols that enable a workstation to connect to another computer using a serial connection
  • 49. Remote Connectivity (continued)
    • Remote Control
      • Remote control allows the remote user to “take over” a computer that’s directly connected to the LAN
      • Remote control is not difficult to configure, but suffers from the same slow throughput as dialing into a remote access server
      • Another disadvantage to this solution is that it allows only one connection to the LAN at any given time
  • 50. Remote Connectivity (continued)
    • Terminal Services
      • In terminal services, multiple remote computers can connect to a terminal server on the LAN
      • A terminal server is a computer that runs specialized software that allows it to act as a host and supply applications and resource sharing to remote clients
  • 51. Remote Connectivity (continued)
      • Many companies have created software to supply terminal services
        • Microsoft’s version of this solution is called Terminal Services
        • Citrix System, Inc.’s version is Metaframe and remote workstations rely on software known as an ICA (Independent Computing Architecture) client
  • 52.
    • Web Portals
      • A Web portal is simply a secure, Web-based interface to an application
      • Any type of Internet connection is sufficient for using Web portals
      • On the host side, a Web server supplies the application to multiple users upon request
      • The use of Web portals calls for secure transmission protocols
    Remote Connectivity (continued)
  • 53.
      • Virtual private networks (VPNs) are wide area networks logically defined over public transmission systems
      • To allow access to only authorized users, traffic on a VPN is isolated from other traffic on the same public lines
      • The software required to establish VPNs is usually inexpensive, and in some cases is being included with other widely used software
      • RRAS allows you to create a simple VPN by turning a Windows server into an access server and allowing clients to dial into it
    Virtual Private Networks (VPN)
  • 54.
      • Two important considerations when designing a VPN are interoperability and security
      • To make sure a VPN can carry all types of data in a private manner over any kind of connection, special VPN protocols encapsulate higher-layer protocols in a process known as tunneling
      • A VPN tunneling protocol operates at the Data Link layer and encapsulates Network layer packets
    Virtual Private Networks (VPN) (continued)
  • 55.
      • Two major types of tunneling protocols are used on contemporary VPNs: PPTP or L2TP
      • PPTP (Point-to-Point Tunneling Protocol) is a protocol developed by Microsoft that expands on PPP by encapsulating it so that any type of PPP data can traverse the Internet masked as an IP or IPX transmission
      • Another VPN tunneling protocol is L2TP (Layer 2 Tunneling Protocol), based on technology developed by Cisco and standardized by the IETF
    Virtual Private Networks (VPN) (continued)
  • 56. Summary
    • Network applications that require WAN technology
    • WAN topologies, including their advantages and disadvantages
    • WAN transmission and connection methods, including PSTN, ISDN, T-carriers, DSL, broadband cable, and SONET
  • 57. Summary (continued)
    • WAN implementation options based on speed, security, and reliability
    • Hardware and software requirements for remotely connecting to a network