CompTIA® Network+ : Wan Technology , Wireless Standards , Network Topologies

3.4 Categorize WAN technology types and properties.

• 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

• OC stands for Optical Carrier and is used to specify the speed of fiber optic networks conforming to the SONET standard. 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

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

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

• 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.

  ISDN specifies two standard access methods:

  1. BRI (Basic Rate Interface): Consists of two B channels (64Kbps) and one D channel (16Kbps).

  1. The B channels can be used for digitized speech transmission or for relatively high-speed data transport.

  2. The D channel carries signaling information (call setup) to control calls on B channels at the UNI (User-Network Interface)

  2. PRI (Primary Rate Interface): Consists of 23 B channels and one D channel with a bandwidth of 1.544Mbps. PRI uses a DSU/CSU for a T1 connection. B stands for Bearer Channel.

• WiMAX is a short name for Worldwide Interoperability of Microwave Access. WiMAX is described in IEEE 802.16 Wireless Metropolitan Area Network (MAN) standard. It is expected that WiMAX compliant systems will provide fixed wireless alternative to conventional DSL and Cable Internet. Typically, a WiMAX system consists of two parts:

  1. 1. A WiMAX Base Station:Base station consists of indoor electronics and a WiMAX tower. Typically, a base station can cover up to 10 km radius (Theoretically, a base station can cover up to 50 kilo meter radius or 30 miles, however practical considerations limit it to about 10 km or 6 miles). Any wireless node within the coverage area would be able to access the Internet.

  2. 2. A WiMAX Receiver- The receiver and antenna could be a stand-alone box or a PCMCIA card that sits in your laptop or computer. Access to WiMAX base station is similar to accessing a Wireless Access Point in a WiFi network, but the coverage is more.

• LTE, or long-term evolution, is a type of mobile broadband that rivals WiMAX. Both services are IP-based and use a technology called orthogonal frequency-division multiplexing (OFDM) access. They also use a type of wireless technology that lets people get high-speed Internet across coverage areas that span miles. The standard is maintained as a project of the 3rd Generation Partnership Project (3GPP), operating under a name trademarked by one of the associations within the partnership, the European Telecommunications Standards Institute (ETSI).

• The goal of LTE is to increase the capacity and speed of wireless data networks utilizing cutting-edge hardware and DSP techniques that have recently been developed. Its wireless interface is incompatible with 2G and 3G networks, and so it must be operated on separate wireless spectrum.

• Features of LTE include an all-IP flat network architecture, end-to-end QoS including provisions for low-latency communications, peak download rates nearing 300 mbps and upload rates of 75 mbps, capacity exceeding 200 active users per cell, the ability to manage fast-moving mobiles, and support for multi-cast and broadcast streams.

3.5 Describe different network topologies.

A topology is physical and logical network layout. Physical layout include actual layout of cables and other network devices where as Logical layout include the way in which the network appears to the devices that use it.

Mesh : In this topology each computer is connected to every other. This topology is rarely used.

Ring :In this topology each network computer and device are connected to each other forming a large circle (or similar shape). Each packet is sent around the ring until it reaches its final destination. Typically FDDI, SONET or Token Ring technology are used to implement a ring network.

BUS : Bus networks use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Star: In Star topology, all the components of network are connected to the central device called "hub" which may be a hub, a router or a switch. All the data on the star topology passes through the central device before reaching the intended destination. Hub acts as a junction to connect different nodes present in Star Network, and at the same time it manages and controls whole of the network. Depending on which central device is used, "hub" can act as repeater or signal booster. Central device can also communicate with other hubs of different network. Unshielded Twisted Pair (UTP) Ethernet cable is used to connect workstations to central node.

Hybrid:It is an integration of two or more different topologies to form a resultant topology. This combination of topologies is done according to the requirement of the organization.

For example an office can use a star topology in each of its department and ring topology to connect these departments.