intro to wan

Intro to WAN

CNAP @ VCC

Semester 4, Chapter 2

Service providers

Central Office (CO): Each telephone connects to a single point called a CO.

Local Loop (LP): The line that connects the customer to the CO.

Local Exchange Carrier (LEC): The company that operates the local loop and owns the Co.

Local Access Transport Area (LATA): Limited Geographic areas served by LECs.

Service providers

Inter Exchange Carriers (IXC): Long distance carriers that connect COs.

Regional Bell Operating Companies (RBOC): Companies that served LECs such as Bell south, Bell Atlantic, and Southwestern Bell.

Competitive Local Exchange Carriers (CLECs)

http://www.learntcpip.com/InternetRuns/default.htm

WAN Connection Types

Asynchronous VS. Synchronous Transmission:Asynchronous means without respect to time.

No clock or timing source is needed to keep both the sender and receiver synchronized. Sender must signal the start and the stop of each character.

Synchronous: common timing signal is used between hosts.

WAN Connection Types

Dedicated Connectivity Circuit-Switched Networks Packet Switched Networks

Dedicated Connection

Continuously available point-to-point link between two sides.

Provides a single pre-established WAN path from the customer premises, through the carrier network to a remote network.

Offer high speed of up to 45 Mbps.

Ideal for high volume environment with steady-rate traffic patterns.

Very expensive: Includes a fixed fee for local-loop access for both locations and a distance fee for linking those two location.

Dedicated leased lines require synchronous serial connection


A CSU/DSU is classified as a data communication equipment (DCE) that provides signal timing and interfaces with the router or Data Terminal Equipment (DTE)

Fully meshed WAN is too costly to build using only dedicated lines

Typically connections on a dedicated network operates at the following speeds: 56Kbps 64kbps T1 (1.544 Mbps) T3 (44.736 Mbps)


A DTE such as the router connects to a DCE such as CSU/DSU using one of the following standards: EIA/TIA-232 EIA/TIA-449 V.35 X.21 EIA-530

When connecting a router to an analog modem, EIA/TIA-232 standards compliant cabling and asynchronous interfaces are used. When connecting the router to digital modem, V.35 standard compliant cabling and synchronous interfaces are used.

Circuit-Switched Connections

A dedicated physical circuit is temporarily established for each communication session.

Initial setup signal is used to establish the circuit, and a teardown signal brings the circuit down when transmission is complete.

Plain Old Telephone Service (POTS) is the most common circuit-switched technology. The temporary dedicated

circuit does not get established until you place a call.


Provide mobile and home users with access to a central site or to an ISP.

Normally circuit-switched connections are used as backup links, or to link branch offices with low vloume or periodic traffic to a company’s central office.


Circuit-switched connections can be costly if left continuously established. For that reason routers that are connected to a circuit-switched network use dial-on-demand routing.

With DDR, a router places a call only when it detects interesting traffic.

Typical Circuit-Switched connections include the following: Asynchronous Serial (POTS) ISDN Basic Rate Interface (BRI) ISDN Primary Rate Interface (PRI)

Asynchronous Serial Connections

Offer inexpensive WAN service through the existing telephone network.

Modem is required at each end of the connection

Provides a throughput of less than 56 kbps.

Used to connect home users or mobile users to corporate network

Asynchronous Serial Connections

Some routers are designed with dozens of asynchronous lines to support a large number of dial-in users

Routers that act as concentration points for dial-in and dial-out calls are called access servers.

To receive or place an asynchronous serial call, a router must have at least one asynchronous serial interface such as the auxiliary port.

ISDN Connections

Circuit-Switched Synchronous Connections Dial up connection that provide WAN access

when needed. Offers more bandwidth than asynchronous dial-

up connections. ISDN offers to levels of service: BRI, and PRI.

Packet-Switched Networks

Unlike leased lines and circuit-switched connections, packet switching does not rely on a dedicated point-to-point connection through the carrier network.

Allows service providers to support multiple customers over the same physical lines.

Typically, customers connect to the packet switched network through a leased line, such as a T1 or a fractional T1.

Frame Relay is the most common packet-switched WAN service in the United States.


In a packet-switched network, the provider configures its switching equipment to create virtual circuits that provide end-to-end connectivity.

VCs can be permanent or they could be established on demand.

A frame rely VC offers a speed of up to T3 line

Les control because the WAN facilities are shared, but also les cost


A single synchronous serial connections can support several logical VCs in a point to mulitipoint configuration.

Thus packet switching makes a full or partial mesh topology relatively affordable.

However frame relay does not offer the degree of reliability , flexibility and security afforded by dedicated lines

Therefore, dedicated lines are the preferred WAN service for mission critical traffic and continuous high volume exchanges.

WAN Encapsulation Protocols

Routers encapsulate packets with layer 2 frame before sending them across a WAN link.

The data link protocol that is used depends in part on what type of WAN connection is deployed.

WAN Connection

DATA Link Encapsulation

Dedicated PPP, HDLC, SLIP

Circuit-Switched

PPP, SLIP

Packet-Switched

X.25, Frame Relay, ATM

WAN layer 2 Protocols

Point-To-Point: Used for router-to-route and host-to network connections over synchronous and asynchronous circuits.

Serial Line Internet Protocol: forerunner to PPP.

HDLC: HDLC implementations are proprietary. When connecting routers from different vendors use PPP.

WAN layer 2 Protocols

X.25: Provides the standards that regulate how a DCE, and a DTE should communicate in a public data network. X.25 provides extensive error detection and windowing.

Frame Relay: High performance, packet switched WAN protocol that does not provide error detection.

ATM: Cell Relay in which multiple service types such as voice, video, or data are conveyed in fixed-length cells. +

Selecting Appropriate WAN Service

Leased Lines High speed, high cost, dedicated connectivity, Appropriate for mission critical applications and in situations where use is high and constant

Asynchronous Dial-up

Offers limited bandwidth over ordinary telephone line, but is highly available . Appropriate for home users and mobile users who need temporary connectivity for low-bandwidth application such as email

ISDN ISDN BRI offers a speed of 128 Kbps when both B channels are aggregated. Appropriate for telecommuters and small offices. Also used as a backup for other WAN connections

Frame Relay Offers speed at T1 or fractional T1 over shared WAN facilities. Permanent Virtual Circuits (PVCs) make frame relay appropriate for remote offices that require constant connectivity for bursty, intermittent traffic.

A worksite within a company can be categorized as: A central site A branch office Or a telecommuter site

LAB

Connecting a T1 line Routing over a T1 line. Configuring a CSU/DSU Connecting a DCE to a DTE

intro to wan

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