Chapter Seven

1. Chapter Seven WANs and Remote Connectivity

2. Objectives • Identify network applications that require WAN technology • Describe a variety of WAN transmission and connection methods • Identify criteria for selecting an appropriate WAN topology, transmission method, and operating system • Understand the hardware and software requirements for connecting to a network via modem • Install and configure simple remote connectivity for a telecommunicating client

3. WAN Essentials • WAN link • Connection between one WAN site and another site • A WAN link is typically described as point-to-point • Dedicated line • Continuously available link that is leased through another carrier

4. WAN Essentials Figure 7-1: Differences in LAN and WAN connectivity

5. PSTN • Public Switched Telephone Network • Refers to the network of typical telephone lines and carrier equipment that service most homes • Also called plain old telephone service (POTS)

6. PSTN • A dial-up connection uses a PSTN or other line to access remote servers via modems at both the source and destination • The Federal Communications Commission (FCC) sets standards and policy for telecommunications transmission equipment in the United States • The place where two telephone systems meet is the point of presence(POP)

7. PSTN Figure 7-2: A typical PSTN connection to the Internet

8. X.25 and Frame Relay • X.25 • Analog, packet-switched LAN technology optimized for long-distance data transmission • Frame Relay • Updated, digital version of X.25 that also relies on packet switching Figure 7-3: A WAN using frame relay

9. X.25 and Frame Relay • SVCs (switched virtual circuits) • Connections established when parties need to transmit, then dismantled once the transmission is complete • PVCs (private virtual circuits) • Connections established before data needs to be transmitted and maintained after transmission is complete • CIR (committed information rate) • Guaranteed minimum amount of bandwidth selected when leasing a frame relay circuit

10. ISDN (Integrated Services Digital Network) • International standard for transmitting data over digital lines • Established by the ITU • All ISDN connections are based on two types of channels: • The B channel is the “bearer” channel • The D channel is the “data” channel

11. BRI (Basic Rate Interface) • A variety of ISDN using two 64-Kbps bearer (B) channels and one 16-Kbps data (D) channel, as indicated by the following notation: • 2B+D • Through bonding, the two 64-Kbps channels can be combined to achieve an effective throughput of 128-Kbps

12. BRI (Basic Rate Interface) • The Network Termination 1 (NT1) device connects twisted-pair wiring at customer’s building with ISDN terminal equipment (TE) via RJ-11 or RJ-45 data jacks • A terminal adapter (TA) converts digital signals into analog signals for use with ISDN phones and other analog devices Figure 7-4: A BRI link

13. PRI (Primary Rate Interface) • A variety of ISDN using 23 B channels and one 64-Kbps D channel, as represented by the following notation: • 23B+D • PRI links use same kind of equipment as BRI links, but require the services of an extra network termination device—called a Network Termination 2 (NT2)—to handle multiple ISDN lines

14. PRI (Primary Rate Interface) • It is only feasible to use ISDN for the local loop portion of a WAN link Figure 7-5: A PRI link

15. T-Carriers • Broadband • Group of network connection types or transmission technologies generally capable of exceeding 1.544 Mbps throughput • T-carriers • Term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s

16. Types of T-Carriers • The most common T-carrier implementations are T1 and T3 • Signal level • ANSI standard for T-carrier technology that refers to its Physical layer electrical signaling characteristics • DSO (digital signal, level 0) • Equivalent of one data or voice channel • Fractional T1 • Arrangement allowing an organization to use only some channels on a T1 line, paying for what they use

17. Types of T-Carriers Figure 7-1: Carrier specifications

18. T-Carrier Connectivity • Wiring • Can use unshielded or shielded twisted-pair copper wiring • CSU/DSU (Channel Service Unit/Data Service Unit) • CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring • DSU converts the digital signal used by bridges, routers, and multiplexers into the digital signal sent via the cabling Figure 7-6: A CSU/DSU connecting a T1

19. T-Carrier Connectivity • Multiplexer • Device that combines multiple voice or data channels on one line Figure 7-7: Typical use of a multiplexer on a T1-connected data network

20. T-Carrier Connectivity • Routers and bridges • On a typical T1-connected data network, terminal equipment will consist of bridges, routers or a combination of the two Figure 7-8: A router on a T1-connected network

21. DSL • Digital Subscriber Lines • Uses advanced data modulation techniques to achieve extraordinary throughput over regular phone lines • Like ISDN, DSL can span only limited distances without the help of repeaters

22. Types of DSL • Term xDSL refers to all DSL varieties, of which at least eight currently exist • DSL types can be divided into two categories: • Asymmetrical • Symmetrical • To understand the difference between these two categories, you must understand the concept of downstream and upstream data transmission

23. Types of DSL Table 7-2: Comparison of DSL types

24. DSL Connectivity • DSL connectivity, like ISDN, depends on the PSTN • Inside carrier’s POP, a device called a DSL access multiplexer (DSLAM) aggregates multiple DSL subscriber lines and connects them to a larger carrier or to the Internet backbone Figure 7-9: A DSL connection

25. DSL Connectivity • Once inside the customer’s home or office, the DSL line must pass through a DSL modem Figure 7-10: A DSL modem

26. 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 Figure 7-11: A cable modem

27. Cable • Hybrid fiber-coax (HFC) • Very expensive fiber-optic link that can support high frequencies • HFC upgrades to existing cable wiring are required before current TV cable systems can serve as WAN links • Cable drop • Fiber-optic or coaxial cable connecting a neighborhood cable node to a customer’s house • Head-end • Cable company’s central office, which connects cable wiring to many nodes before it reaches customers’ sites

28. Cable Figure 7-12: Cable infrastructure

29. SONET (Synchronous Optical Network) • Can provide data transfer rates from 64 Kbps to 39.8 Gbps using the same TDM technique used by T-carriers • Known internationally as SDH (Synchronous Digital Hierarchy) • SONET is self-healing Figure 7-13: SONET technology on a long-distance WAN

30. SONET (Synchronous Optical Network) Table 7-3: SONET OC levels

31. WAN Implementation:Speed Table 7-4a: A comparison of WAN technology transmission speeds

32. WAN Implementation:Speed Table 7-4b: A comparison of WAN technology transmission speeds

33. WAN Implementation:Reliability • WAN implementations can roughly be divided as follows: • 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

34. WAN Implementation:Security • Among other things, consider the following issues: • 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

35. WAN Implementation:Virtual Private Networks (VPNs) • VPNs are wide area networks logically defined over public transmission systems that serve an organization’s users, but isolate that organization’s traffic from other users on the same public lines Figure 7-14: An example of a VPN

36. Remote Connectivity • Remote access methods: • Direct dial to the LAN • The computer dialing into the LAN becomes a remote node on the network • Direct dial to a workstation • Software running on both remote user’s computer and LAN computer allows remote user to “take over” the LAN workstation, a solution known as remote control • Internet/Web interface • Through a browser, a user at home or on the road connects to a LAN whose files are made visible to the Web through Web server software

37. Remote Connectivity • ICA (Independent Computing Architecture) client • Remote access client developed by Citrix Systems, Inc. • Enables remote users to use virtually any LAN application over any type of connection, public or private • Remote Access Service (RAS) • One of the simplest dial-in servers • This software is included with Windows 2000 Server

38. Dial-Up Networking • Refers to the process of dialing into a LAN’s (private) access server or to an ISP’s (public) access server to log onto a network Figure 7-15: Choosing a network connection type

39. SLIP and PPP • Serial Line Internet Protocol (SLIP) • Communications protocol enabling a workstation to connect to a server using a serial connection • Can carry only IP packets • Supports only asynchronous transmission • Point-to-Point Protocol • Communications protocol enabling a workstation to connect to a server using a serial connection • Can carry many different types of Network layer packets • Supports both asynchronous and synchronous transmission

40. Chapter Summary • WANs are distinguished from LANs by the fact that the former networks traverse a wider geographical area • One WAN transmission method, PSTN, relies on the network of telephone lines that typically service homes • X.25 is an analog packet-switched technology optimized for long-distance data transmission • Frame Relay is an updated, digital version of X.25

41. Chapter Summary • Another WAN transmission method, ISDN, is an international standard established by the ITU for transmitting data over digital lines • Two types of ISDN connections are commonly used in North America are BRI and PRI • Another WAN transmission method is digital subscriber line (DSL) • Cable is another option for high bandwidth local loop WAN transmission

42. Chapter Summary • T-carrier technology uses time division multiplexing (TDM) to divide a single channel into multiple channels for carrying voice, data, video, or other signals • SONET can provide data transfer rates from 64 Kbps to 39.8 Gbps using the same TDM technique employed by T-carriers • When installing or upgrading a WAN, consider its ability to integrate with your present LAN or WAN equipment, transmission speed required, security needed, geographical distance the WAN must span, growth, and cost • VPNs represent one way to construct a WAN from existing public transmission systems

43. Chapter Summary • Three ways remote users connect to LANs: • Direct dial to the LAN • Direct dial to a workstation • An Internet connection with a Web interface • SLIP and PPP are communications protocols enabling a workstation to connect to a server using a serial connection