Communication Services Communication Services Problem This chapter expands
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.
Infrastructure Circuit Switching
Infrastructure 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 Intranet
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 Extranet
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)
Infrastructure Demarcation Point (Demarc)
Infrastructure • 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.
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 ISDN Modem
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.
Communication Services T 1 Line 24 DS 0 Lines 1. 544 Mbps Google Server DS 0 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
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