METROPOLITAN AREA NETWORKS (MAN’s)

Is the network with the size between LAN’s and WAN’s. It normally covers the area inside city and town only. It suitable to customers who needs high speed connection to internet

TECHNOLOGY USED IN IMPLEMENTING MAN’s

a) Using Microwave signal to establish communication link

In microwave link, there are two types of configuration that can be found here

1. Point to point MAN’s

This type of MAN uses line of sight for successful transferring of data

Wireless MAN was first developed　 as fixed wireless access

2. Point to Multi-point MAN’s

Today, it has been enhanced to be used as P-MP access

Can be used in Non Line of sight link

Frequency Band of operation is : < 11GHz (Licensed and Licence exempt)

b) Synchronous Digital Hierarchy (SDH)

The SDH is an international standard that is highly popular and used for its high speed data transfer of the telecommunication and digital signals

Is a standard technology for synchronous data transmission on optical media.

This technology provide faster and less expensive network ` interconnection

It is one of the technology used to interconnect different MAN’s

The basic transfer rate of the data is 2048 kilobits per second

For instance, in each speech transmission, the normal rate breaks into different thirty channels of 64 kilobits per second along with two different 64 kilobits per second in order to perform the tasks of synchronization and signalling..

SDH uses the following Synchronous Transport Modules (STM) and rates: STM-1 (155 megabits per second), STM-4 (622 Mbps), STM-16 (2.5 gigabits per second), and STM-64 (10 Gbps).

Advantages of SDH

High Transmission rates

Transmission rates of up to 10Gbps can be achieved in modern SDH systems making it the most suitable technology for backbones-the superhighways in today’s telecommunication networks

Provide built-in signal capacity for advanced network management and maintenance capabilities

Interconnection/Inter-operability of devices between different vendors1

c) Leased Lines(Dedicated link)

This is another technology used to interconnect MAN’s, there are usually referred to as a point to point or dedicated connection. It is the type of communication channels leased to a company for a privately use, and the company or organization will be required to pay for it basing on monthly or yearly according to the contract being signed between ISP and an organization

TECHNOLOGIES USED TO IMPLEMENT/ INTERCONNETC WAN’s

Basically there are two types of technology used to implement WAN’s

a) Frame Relay

b) ATM (Asynchronous Transfer Mode)

a) FRAME RELAY

Is a virtual circuit wide area network that was designed in response to a demand of new Type of WAN with ability to carry data at higher rate. It is designed for ordinary data application and transmits data frames with variable length .Provides data rate of up to 50 Mbps

BEFORE FRAME RELAY TECHNOLOGY

Before the invention of frame Relay Technology, Some organization used virtual circuit switching networks called X.25, that performed switching at the NETWORK LAYER, But this Switching technology (X.25), had some drawbacks over Frame Relay Technology

DISADVANTAGES OF X.25 OVER FRAME RELAY

i. X.25 had very low data rate of about 64kbps, that couldn’t meet people demand to transfer higher data rate

ii. X.25 has extensive flow and error control in both data link layer and network layer. This created large Overheads in the frames and packets, this results in slow transmission

iii. Due to its slow data rate, some organization were very disappointed with this technology and started to lease T-1 (1.544Mbps) or T-3 lines from public service providers. This approaches was very costly

Because if an Organization had n branches spread over an area (In mesh Topology). This needed total number of T1-lines or T3 lines given by the following formula

In response to the above drawbacks , frame relay was introduced because it had the following advantage s over X.25 technology

Advantages of Frame Relay Technology over X.25 (Old Technology)

i. Frame relay Operates at higher speed of up to 50 Mbps

ii. Frame relay operates on just Data link and physical layer, hence it can be used as the backbone network to provide services

iii. Frame Relay allows Busty data (Bandwidth on demand), rather than the old X.25 allows only Fixed data rate of about 1.544Mbps

Bursty data refers to the type of data which varies according to the requirements, and it is the demand for the today’s user. Example a user may want to send data at 6Mbps for 2 seconds, 0Mbps (nothing) for 7 seconds, and 3.44Mbps for 1 seconds

This type of demand is not suitable for the old technology X.25, becauseX.25 allows a user to send a constant data rate of 1.544Mbps only, while Frame relay allows this kind of demand (Bursty data or demand on demand)

iv. Frame relay allows large frame size (of bout 9000 bytes) to be propagated along the network

v. Frame Relay is less expensive compared to X.25

vi. Frame Relay has error Detection at the data link layer only. There are is no error control or flow control mechanisms. There is no even retransmission policy. If a frame is damaged, it is silently dropped

FRAME RELAY ARCHTECTURE

ii. ATM (Asynchronous Transfer Mode)

ATM is high performance; cell oriented switching and multiplexing Technology that utilizes fixed length packets to carry different types of data traffic.

ATM is a relay technology, which uses small fixed sized frames called CELLS

COMPOSITION OF CELLS

This CELL consists frame with a constant 53 octets in length

This CELL provides two services

• Variable bit rate (VBR) services that is optimum for data transmissions

• Constant bit rate (CBR) services that is optimum for voice and video application, CBR is not available in frame Relay Technology

Most of packet switched networks make use of variable sized packets, and this make results to significant variation in the arrival times of the packets of particular data streams

ATM is suited for carrying Bursty traffic data. ATM can allow communication between different devices operating at different speeds

CONCEPTS OF ATM

ATM is a connection oriented technology, where data traffic streams from the source to destination over a virtual circuit

The circuit (Virtual circuit), operates on the same concept as packet switching, but the routing of packets is specified before transmission

Data from different connections is distinguished by means of virtual path identifier (VPI) and virtual channel identifier (VCI)

By means of virtual circuit, cells in the same connection, reach the destination in the order they were sent

ADVANTAGES OF ATM SWITCHING

i. Delays in the network are much lower because of using a fixed sized frame

ii. The switching of cells are done in hardware rather than by software, This increases switching speed

iii. ATM provides both circuit switched and packet switched networks