CompTIA® Network+ Exam Notes : Comparing Different Wan Technologies

2. Infrastructure

2.5 Compare different WAN technologies

WAN technologies: It is commonly used with dedicated leased lines include digital circuits, such as T1, E1, T3, and E3. These circuits can use multiplexing technology to simultaneously carry multiple conversations in different 64-Kbps channels. A single 64-Kbps channel is called a Digital Signal 0 (DS0). When one of these circuits comes into your location, it terminates on a device called a channel service unit/data service unit (CSU/DSU).

WAN (Wide Area Network) devices extend the reach of LAN (Local Area Network) devices. WANs typically span over a wide area, such over multiple cities / countries. WANs are connected over serial lines that typically operate at lower speeds than LANs.

Some of the WAN devices are:

1. Routers: Routers are responsible for routing the packets in an internetwork.

2. Modems: Modems connect to public telephone circuits through dial-up.

3. CSU/DSU: Stands for Channel Service Unit / Data Service Unit. CSU/DSUs are used for connecting to Central Office of a Telephone switching company and provides serial WAN connections.

4. Communication Servers: These are used for dial in/out to remote users. Provides RAS (Remote Access Server) functionality.

5. Multiplexers (mux): Multiplexers combine two or more signals before transmitting on a single channel. Multiplexing can be done by sharing "time" or "frequency"

1. Analog modem: Analog modem uses the telecom company's copper wire to connect to the exchange, and most widely used.

2. DSL: DSL uses existing copper telephone lines. DSL technologies typically provide speeds up to 1.544 Mbps.

3. Cable modem: Cable modem uses the same line as cable TV. Possible bandwidth for Internet access reaches up to 27 Mbps.

4. ISDN: ISDN comes in two flavors- BRI and PRI. The most commonly used is BRI, Basic Rate Interface. BRI is composed of two 64-Kbps B (bearer) channels and one 16 Kbps D (delta) channel. ISDN supports both voice and video.


In the figure shown, two LANs are connected together using a Wide Area Network (WAN). If the LANs are in the same building, there is no need to use a WAN link. Therefore, they are geographically separate locations. The routers A and B may use either static routes or dynamic routes to communicate within the WAN. It is not necessary that all hosts on LAN "A" communicate with all the hosts on LAN "B"

Service type:

A CSU/DSU (Channel Service Unit/Data Service Unit): It is a hardware device that converts a digital data frame used on a local area network (LAN) into a frame appropriate to a wide-area network (WAN) and vice versa. For example, if you have a leased digital line (perhaps a T-1 or fractional T-1 line) to a phone company or a gateway at an Internet service provider, you have a CSU/DSU at your end and the phone company or gateway host has a CSU/DSU at its end.

ISDN: The basic rate ISDN has two B channels at 64 Kbps and one D channel at 16Kbps. B channels carry the user data, whereas the D channel is used for out of band signaling

Dial up access means to connect to the Internet or a remote network through telephone line and modem. Since the same line used for a household phone is used for dialup access, it is called the POTS (plain old telephone system) method of access.

PSTN and ISDN require dialup connections to establish communication sessions.

ISDN has two defined interface standards:

  • Basic Rate Interface (BRI)
  • and Primary Rate Interface (PRI).

BRI ISDN uses three separate channels; two bearer (B) channels of 64Kbps each and a delta channel of 16Kbps. B channels can be divided into four D channels, which enable businesses to have eight simultaneous Internet connections. The B channels carry the voice or data, and the D channels are used for signalling.

PRI is a form of ISDN that generally is carried over a T1 line and can provide transmission rates of up to 1.544 Mbps. PRI is composed of 23 B channels, each providing 64Kbps for data/voice capacity, and one 64 Kbps D channel, which is used for signaling.

Speed 128Kbps 1.544 Mbps
Channels 2B+D 23B+D
Transmission Carrier ISDN T1


The transmission speed of a T1 circuit (Used mainly in North America) is 1.544Mbps

The transmission speed of an E1 circuit (Used mainly in Europe) is 2.048Mbps.

The transmission speed of a T3 circuit (Used mainly in North America) is 44.736 Mbps

OC3-OC192: OC stands for Optical Carrier and is used to specify the speed of fiber optic networks conforming to the SONET standard. Basic OC-1 supports 51.84 Mbps. OC-x have a speed of 51.84 multiplied by x. For example, OC-3 will have a bandwidth of 51.84 multiplied by 3 or 155.52 Mbps.

Below are the speeds for some common OC levels.

OC level Speed
OC-1 51.85 Mbps
OC-3 155.52 Mbps
OC-12 622.08 Mbps
OC-24 1.244 Gbps
OC-48 2.488 Gbps
OC-192 9.952 Gbps

Transmission rates supported by leased lines are

T1 - 1.544 Mbps

T3 - 44.736 Mbps

E1 - 2.048 Mbps

E3 - 34.368 Mbps

OC3 - 155.52 Mbps

OC12 - 622.08 Mbps

Characteristics of service:

Point-to-Point Protocol (PPP) is a data link protocol used to establish a direct connection between two nodes. It can provide connection authentication, transmission encryption , and compression.

A common Layer 2 protocol used on dedicated leased lines is Point-to-Point Protocol (PPP).

A less common protocol used on dedicated leased lines (as compared to PPP) is High-Level Data Link Control (HDLC). HDLC lacks many of the features of PPP, and in its standards-based implementation, it can only support a single Layer 3 protocol on a circuit.

Frame Relay: Frame Relay is a "Packet Switched" WAN technology.

Access Rate (AR) -The maximum data rate of the user access channel. The speed of the access channel determines how rapidly (the maximum rate) that the end user can transmit data into a Frame Relay network.

Committed Information Rate (CIR) -This is the rate at which a Frame Relay network provider agrees to transfer information under normal conditions. CIR, measured in bits per second (bps), is one of the key negotiated tariff metrics.

Data-Link Connection Identifier (DLCI) -A Frame Relay service provider typically assigns DLCI values, which are used on Frame Relay interfaces to distinguish between different virtual circuits.

Switched Virtual Circuit (SVC) - A virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic.

DMVPN: A dynamic multipoint virtual private network (DMVPN) is a secure network that exchanges data between sites without needing to pass traffic through an organization's headquarter virtual private network (VPN) server or router.

The benefits to DMVPNs are as follows:

  • Traffic between remote sites does not need to go through the hub, thus saving resources such as bandwidth and computing resources at the hub.
  • They eliminate additional network delays as the traffic can go directly from spoke to spoke.
  • Costs for VPN circuits are lower as DMVPN is typically deployed over the Internet.
  • They provide a backup mechanism to private networks.

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