BCENT - Basic Cisco Entry Networking Technician

Chapter 7

Introducing Wide-Area Networks

FOUNDATION TOPICS

•WAN Properties

•WAN Technologies

INTRODUCING WIDE-AREA NETWORKS

• What are the categories of WAN connections?

• How are data rates measured on various WAN technologies?

• Which types of media might be used in WAN connections?

• What are the characteristics of different WAN technologies?

INTRODUCING WIDE-AREA NETWORKS

• In the early 1990s, computer-networking design guides commonly invoked the Pareto Principle which stated that 80% of your traffic stays local while only 20% of your traffic leaves the local network. This was called the 80-20 rule.

• Today, network traffic patterns are more closely approximated with a 20-80 rule, meaning that most traffic leaves the LAN and travels across the WAN.

WAN CONNECTION TYPES

• There are three general categories of WAN connections:

Dedicated Leased Line

Circuit-switched connection

Packet-switched connection

DEDICATED LEASED LINE

CIRCUIT-SWITCHED CONNECTION

PACKET-SWITCHED CONNECTION

WAN DATA RATES

• WAN bandwidth can be measured in kbps, Mbps, and Gbps, just like LAN bandwidth. It can also be measured using optical carrier (OC) levels.

OC Level Bandwidth

OC-1 51.84 Mbps

OC-3 155.52 Mbps

WAN DATA RATES

WAN Technology Typical Available Bandwidth

Frame Relay 56 kbps – 1.544 Mbps

T1 1.544 Mbps

T3 44.736 Mbps

E1 2.048 Mbps

E3 34.4 Mbps

ATM 155 Mbps – 622 Mbps

SONET 51.84 Mbps (OC-1) –159.25 Gbps (OC-3072)

WAN MEDIA TYPES

• Physical Media

Unshielded twisted pair (UTP)

Coaxial Cable

Fiber-optic cable

Electric power lines

WAN MEDIA TYPES

• Wireless Media

Cellular phoneo Mobile hot spots

Satellite

WiMAX: Worldwide Interoperability for Microwave Access

HSPA+: Evolved High-Speed Packet Accesso Wireless broadband

Radio

WAN TECHNOLOGIES

• Dedicated Leased Line

Typically a point-to-point connection between two sites.

All the bandwidth on that line is available to those sites.

Common digital circuits are:o T1, E1, T3 and E3 circuits

• These digital circuits are usually measured in 64-kbps channels called Digital Signal 0 (DS0)

T-CARRIER SIGNAL LEVELS

Carrier Signal Level # of T1 signals # of Voice Channels

Speed

T1 DS1 1 24 1.544 Mbps

T1c DS1c 2 48 3.152 Mbps

T2 DS2 4 96 6.312 Mbps

T3 DS3 28 672 44.736 Mbps

T4 DS4 168 4032 274.760 Mbps

CHANNEL SERVICE UNIT / DATA SERVICE UNIT (CSU/DSU)

CSU/DSU Terminating a Synchronous Circuit

POINT-TO-POINT PROTOCOL (PPP)

• PPP is commonly used as a Layer 2 protocol on dedicated leased lines.

Simultaneously transmit multiple Layer 3 protocols.

Each Layer 3 Control Protocol runs an instance of PPP’s Link Control Protocol (LCP).

POINT-TO-POINT PROTOCOL (PPP)

• Four primary features of LCP:

Multilink interface (bonding/load balancing)

Looped link detection

Error detection

Authenticationo PAP (password in cleartext – bad)

o CHAP (password is hashed – better)

o MS-CHAP (Microsoft enhanced with additional features)

PAP

PAP Authentication

CHAP

CHAP Authentication

PPPOE

DIGITAL SUBSCRIBER LINE (DSL)

• DSL is common in many residential and small office/home office (SOHO) locations

• DSL provides high-speed data transmission over existing telephone wiring.

• DSL has several variants, which differ in data rate and distance limitations.

• Asymmetric DSL (ADSL)

• Symmetric DSL (SDSL)

• Very High Bit-Rate DSL (VDSL)

ADSL SAMPLE TOPOLOGY

CABLE MODEM

• Cable television infrastructure contains both coaxial and fiber-optic cabling, which is called a hybrid fiber-coax (HFC) distribution network.

• Specific frequency ranges are used for upstream and downstream data transmission.

• The device in the home or office that transmits and receives over those frequencies is a cable modem.

CABLE MODEM SAMPLE TOPOLOGY

SYNCHRONOUS OPTICAL NETWORK (SONET)

• SONET is a Layer 1 technology that uses fiber-optic cabling as its media. It can be used for different Layer 2 technologies like Asynchronous Transfer Mode (ATM).

• The physical topology can be linear (like a bus network), but it is typically configured in a ring topology.

SONET SAMPLE TOPOLOGY

SATELLITE

• In remote or rural locations, DSL and cable modem connections are not always available. In those cases a satellite WAN connection can be an option.

• Two potential design problems should be considered:

Delay

Weather Conditions

SATELLITE

PLAIN OLD TELEPHONE SERVICE (POTS)

• The Public Switched Telephone Network (PSTN) is comprised of multiple telephone carriers from around the world.

• Analog connections (voice and data) using the PSTN are called Plain Old Telephone Service (POTS) connections.

• Dial-up modems have a maximum bandwidth of 56-kbps because they can only access one 64-kbps channel.

DIAL-UP MODEM SAMPLE TOPOLOGY

INTEGRATED SERVICES DIGITAL NETWORK (ISDN)

• Integrated Services Digital Network (ISDN) supports multiple 64-kbps channels on a single connection.

• ISDN circuits are classified as either a basic rate interface (BRI) or primary rate interface (PRI)

BRI – Offers a 128-kbps data path

PRI – Offers a 1.472 Mbps data path

INTEGRATED SERVICES DIGITAL NETWORK (ISDN)

FRAME RELAY

• Frame Relay offers widespread availability and relatively low cost compared to leased lines.

• Frame Relay sites are connected via virtual circuits (VC).

• Virtual circuits can be point-to-point or point-to-multipoint connections.

FRAME RELAY SAMPLE TOPOLOGY

ASYNCHRONOUS TRANSFER MODE (ATM)

Asynchronous Transfer Mode (ATM) is a Layer 2 WAN technology that operates using the concept of PVCs and SVCs.

ATM uses fixed-length cells as its protocol data unit (PDU).

An ATM cell contains a 48-byte payload and a 5-byte header.

5-Byte Header

48-Byte Payload

ATM VIRTUAL CIRCUITS

ATM SAMPLE TOPOLOGY

MULTIPROTOCOL LABEL SWITCHING (MPLS)

• Multiprotocol Label Switching (MPLS) is a WAN technology used by service providers. MPLS is popular because it supports multiple protocols on the same network.

• MPLS can support both Frame Relay and ATM on the same MPLS backbone.

• MPLS also allows traffic to be dynamically routed based on load conditions and path availability.

MPLS SAMPLE TOPOLOGY

SUMMARY

•WAN Properties

•WAN Connection Types

Dedicated Leased line

Circuit-switched connection

Packet-switched connection

•WAN Media Types

Physical Media

Wireless Media

SUMMARY

•WAN Technologies

Dedicated Leased Line

DSL

Cable Modem

SONET

Satellite

POTS

ISDN

Frame Relay

ATM

MPLS