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Transcript DCN-9-Communication-Services

Communication Services

•Communication Services: –Problem: •

This chapter expands on topics introduced in earlier chapters related to long-distance communication services.

–Services offered by: •Long-distance carriers.


Circuit Switching


Packet Switching

Technology Infrastructure

Circuit Switching v/s Packet Switching

Circuit Switched Network

•Characteristics: –Data is sent through, •Pre-established dedicated channel.

–3 phases of data transfer: •Establish the connection by closing circuits.

•Transfer the data.

•Disconnect the call.

–For the transfer of the message, •A single connection is used which is, •Not used by any other network traffic at that point of time and hence, •Entire message follows the same path.

Circuit Switched Network

•Advantages: –No interference.

•Circuit is dedicated to the transfer. –Guaranteed full bandwidth for the entire call.

•No sharing of connection.

•Disadvantages: –Inefficient.

•Even if no data is being sent, the dedicated line still remains open.

–More susceptible to failure.

•During a crisis, it may become unstable / unavailable.

•Entire message needs to be retransmitted in case of failure.

Packet Switched Network

•Characteristics: –Message gets broken into, •Small data packets and each packet may, •Travel through a different route to the destination.

–Each packet has the following details: •A unique number to denote the position of packet in the entire message.

–Sequence number.

•Address of where it is supposed to reach.

–Destination IP address.

–At the receiver, •Packets may come out of order but are reassembled correctly using, –Sequence number.

Packet Switched Network

•Advantages: –Efficient: •Line is only occupied with data is actually being transferred.

•No need to wait for direct connection to be available.

–Resistant to failure.

•Not affected by a line failure.

•Only the lost packet needs to be retransmitted.

•Disadvantages: –Rules for reliable transfer.

•Protocols are needed for reliable transfer.

Intranets and Extranets


Intranets and Extranets

•Intranet: –Intranet is: •Interconnected network which uses, •TCP/IP protocol and, •Does not extend beyond the organization that created it.

–Mainly used to, •Distribute internal corporate information.

–Advantages: •Reduce software maintenance and update costs.

•Save time as distribution information on paper is slower and more expensive.

Intranets and Extranets


Intranets and Extranets

•Extranet: –Extended intranet which includes: •Entities outside the boundaries of the organization such as, –Business partners, Distributors, Remote employees etc.

–Can be setup through: •Private Network. •Public Network.

Intranets and Extranets

•Extranet on Private Network: –Private, leased-line connection for extranet.

–Advantages: •Security.

–Drawbacks: •Cost.

•Scaling Problem.

–As a result of major drawbacks, •It is not feasible to set up extranet using private networks.

Intranets and Extranets

•Extranet on Public Network: –A network that is available to public.

•Example: –Internet.

–Disadvantage: •High level of security risk for an Extranet.

Intranets and Extranets

•VPN: –Virtual Private Network is an, •Extranet that uses secure public networks to send information.

–Uses a technique called: •IP tunneling.

–Packet content is encrypted and placed in another packet.

•It is also called: –Encapsulation.

–It is called Virtual because: •Connection is actually temporary.

–Requirements to setup a VPN: •VPN software must be installed on the computers at both ends.

•Example: –Cisco VPN.

–Note: •Every VPN is an extranet but every extranet is NOT a VPN.

Intranets and Extranets

VPN (Virtual Private Network)


Demarcation Point (Demarc)


•Demarcation Point: –Point of connection between, •A customer’s telephone equipment and, •The common carrier (telecom carrier) network.

–Normally located on: •An outside wall of the customer’s home.

–Also known as: •NIU: Network Interface Unit.

–Uses: •Protects the customer’s equipment from, –Power spikes that may occur on the common carrier lines.

•Local loop testing can be performed by using the NIU, –Without requiring entrance into customer’s home.

•Used to determine if a problem with a telephone line exists, –Within a customer’s residence or, »In which case the customer pays for the repairs.

–Between the residence and central office.

»In which case the common carrier pays for the repairs.

Communication Services

Phone Service Could Transfer: Only voice Communication Type: Analog Requirement: Ability to transfer data (digital) and access Internet.

Communication Services

Dial-up Service Could Transfer: Voice & Data (Not both at the same time) Communication Type: Analog Speed: 56 Kbps Dial-up Modem Requirement:Ability to transfer both (Voice & Data) at the same time.

ISDN Modem

Communication Services

ISDN Service (Integrated Services Digital Network) Could Transfer: Voice & Data (At the same time) Communication Type: Digital Speed: 128 Kbps Requirement: Higher Speed

Communication Services

DSL Service (Digital Subscriber Line) Broadband Service Could Transfer: Voice & Data (At the same time) Communication Type: Digital Speed: 256 Kbps to 40 Mbps DSL Modem / Router

Communication Services

•ISDN: –Known as: •Integrated Services Digital Network.

–It uses, •Circuit Switched Telephone Network which also provides access to Packet Switched Networks and hence, –Can be used for simultaneous digital transmission of: »Voice, Data etc.

–Gives, •Circuit switched connections for, –Voice and, •Packet switched connections for –Data.

–Key feature is: •It integrates speech and data on the same lines at the same time which was not available in: –Dial-up connection

Communication Services

•ISDN: –Types of ISDN: •Narrowband ISDN (N-ISDN) –Basic Rate Interface (BRI) –Primary Rate Interface (PRI) •Broadband ISDN (BISDN)

Communication Services

•DSL: –Known as: •Digital Subscriber Line.

–Provide Internet access by, •Transmitting digital data over the wires of a local telephone network.

–Simultaneous transmission of voice and data is made possible because: •It uses different frequency bands for voice and data: –Lower frequency bands for voice and, –Higher frequency bands for data.

–On the customer’s premises (home), a special device called: •DSL filter (or splitter) is used.

Communication Services

•DSL: –Types of DSL: •SDSL: –Symmetric Digital Subscriber Line.

–Downstream (Download) and Upstream (Upload) speeds are equal.

–Normally used by, »Business users.

•ADSL: –Asymmetric Digital Subscriber Line.

–Downstream (Download) and Upstream (Upload) speeds are not equal.

»Download speed is normally higher than Upload speed.

–Normally used by, »Home users.

Communication Services

•SONET: –Service for connecting digital fiber-optic networks.

–Also called: •Synchronous Optical Network (SONET) –Was developed to, •Allow mixing and matching of optical equipments and, •Connect non-compatible (from different manufacturers) fiber-optic systems to one another because, •Before the development of SONET, –Optical transmission was done with proprietary formats set by the optical device manufacturers.

T1 Line 24 DS0 Lines 1.544 Mbps

Communication Services

Google Server DS0 Line 64 Kbps Protocols: Fast Packet Protocols DSL / ISDN Modem

Communication Services

•Fast Packet Services / Protocols: –X.25

–Frame Relay –ATM •Asynchronous Transfer Mode –SMDS •Switched Multimegabit Data Service –AIN •Advanced Intelligent Networks –MPLS •Multiprotocol Label Switching