WANs and Remote Connectivity Chapter Seven WANs and Remote Connectivity

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

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

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)

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.

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

X.25 and Frame Relay X.25 Frame Relay Analog, packet-switched LAN technology optimized for long-distance data transmission Mid-70s 64Kbps – 1992 2.048 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

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

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

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

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

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

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 1.544 Mbps

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

T-Carriers Broadband T-carriers Group of network connection types or transmission technologies generally capable of reaching or exceeding 1.544 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 = 1.544 Mbps AT&T developed in 1957

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

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

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

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

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

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

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

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

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

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

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

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

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

Figure 7-12: Cable infrastructure

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

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

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

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

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

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

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

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

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

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

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