1. 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 Dedicated line
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. Figure 7-1: Differences in LAN and WAN connectivity
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 place where two telephone systems meet is the point of presence (POP)

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

8. 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

9. 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

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

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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. Cable Hybrid fiber-coax (HFC) Cable drop Head-end
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

22. Figure 7-12: Cable infrastructure

23. 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

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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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
Can carry many different types of Network layer packets
Supports both asynchronous and synchronous transmission

31. 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

32. 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

33. 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

34. 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