1. WANs and Remote Connectivity
Chapter Seven
WANs and Remote Connectivity

2. WAN Essentials Wide Area Network 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
Examples: p. 309

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

4. 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)

5. 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
Even with 56 Kbps modems, FCC limits PSTN lines to 53 Kbps to reduce crosstalk
The place where two telephone systems meet is the point of presence (POP)
LD to local, etc.

6. PSTN Figure 7-2: A typical PSTN connection to the Internet
Discussed on bottom of p. 311

7. X.25 and Frame Relay X.25 Frame Relay
Analog, packet-switched LAN technology optimized for long-distance data transmission
Mid-70s 64Kbps – Mbps
Developed as a more reliable connection for mainframes to remote terminals
Not widely accepted in U.S.
Frame Relay
Updated, digital version of X.25 that also relies on packet switching
Standardized in 1984
1.544 or 45 Mbps
Being replaced by newer, faster technologies
Depicted as clouds in diagrams

8. Figure 7-3: A WAN using frame relay
X.25 and Frame Relay
Contract with telecommunications company states:
Endpoints
Amount of bandwidth
Less expensive than a dedicated T1
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
Not dedicated like T-carrier services
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
Circuit-switching – max 64 Kbps, multiple channels
The D channel is the “data” channel
Packet-switching – max 16 or 64 Kbps, single channel
Two types of ISDN connection: BRI & PRI

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
Average monthly cost - $100-$250

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
Can achieve Mbps

14. PRI (Primary Rate Interface)
Figure 7-5: A PRI link
It is only feasible to use ISDN for the local loop (from customer to POP) portion of a WAN link due to 18,000 linear feet limitation

15. T-Carriers Broadband T-carriers
Group of network connection types or transmission technologies generally capable of reaching or exceeding Mbps throughput
Cable, DSL, & T-carriers
T-carriers
Term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s
T1 – 24 channels x 64 Kbps = Mbps
AT&T developed in 1957

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
International vs. NA standard - p. 318
Fractional T1
Arrangement allowing an organization to use only some channels on a T1 line, paying for what they use

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

18. T-Carrier Costs T1 Fractional T1 T3 $500-$2,000 installation
$500-$2,000 monthly access fees
Longer the distance, higher the access fees
Fractional T1
Only lease needed channels – in 64 Kbps increments T3
$3,000 installation
Monthly access fees based on usage
Full usage could max at $18,000/month

19. 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

20. 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

21. 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

22. 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
Costs
T-1 throughput - $100/month
Consumer-grade (1/2 bandwidth) - $20/month

23. 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 – different speed up & down stream
Symmetrical – same speed up & down stream
To understand the difference between these two categories, you must understand the concept of downstream and upstream data transmission
Downstream – Carrier’s POP to customer
Upstream – Customer to Carrier’s POP

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

25. 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

26. DSL Connectivity
Once inside the customer’s home or office, the DSL line must pass through a DSL modem
Voice signals use very small range of frequencies between 0 and 35 KHz
Figure 7-10: A DSL modem

27. 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
Not a true modem – p. 327
Figure 7-11: A cable modem

28. 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

29. Figure 7-12: Cable infrastructure

30. SONET (Synchronous Optical Network)
Developed in 1980s
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
Fiber-optics transmission media is used

31. SONET (Synchronous Optical Network)
Data rate indicated by Optical Carrier (OC) level
Table 7-3: SONET OC levels

32. WAN Implementation: Speed
Table 7-4a: 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 (RAS)
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
pcAnywhere, MS System Management Server (SMS)
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
Windows 2000 Terminal Services
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
Communications protocol enabling a workstation to connect to a server using a serial connection
Serial Line Internet Protocol (SLIP)
Can carry only IP packets
Supports only asynchronous transmission
Data transmitted/received doesn’t conform to timing scheme
Start and stop bits
Requires more configuration than PPP – rarely used

40. SLIP and PPP Point-to-Point Protocol (PPP)
Can carry many different types of Network layer packets
Supports both asynchronous and synchronous transmission
Synchronous – data transmitted/received must conform to timing scheme
Uses timing – not start and stop bits
Requires less configuration than SLIP