CS610 Assignment No. 2 Solution
Wednesday, May 04, 2011 Posted In CS and IT Edit ThisAssignment Statements:
Q1. Leased line connections are mostly used in our homes and offices. Give a real time example of leased lines and also describe any four benefits of leased line.
(2+8 Marks)
Q2. How default routes are important in routing? In which type of network design default routes are more appropriate to implement. Support your answer with routing examples. (5+5 Marks)
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Solution:
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For Quesstion 1 helping material
A leased line is a service contract between a provider and a customer, whereby the provider agrees to deliver a symmetric telecommunications line connecting two or more locations in exchange for a monthly rent (hence the term lease). It is sometimes known as a 'Private Circuit' or 'Data Line' in the UK or as CDN (Circuito Diretto Numerico) in Italy. Unlike traditional PSTN lines it does not have a telephone number, each side of the line being permanently connected to the other. Leased lines can be used for telephone, data or Internet services. Some are ringdown services, and some connect two PBXes.
Typically, leased lines are used by businesses to connect geographically distant offices. Unlike dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection doesn't carry anybody else's communications, the carrier can assure a given level of quality.
An internet leased line is a premium internet connectivity product, delivered over fiber normally, which is dedicated and provides uncontended, symmetrical speeds, Full Duplex. It is also known as an ethernet leased line, DIA line, data circuit or private circuit.
For example, a T-1 channel can be leased, and provides a maximum transmission speed of 1.544 Mbit/s. The user can divide the connection into different lines for multiplexing data and voice communication, or use the channel for one high speed data circuit. Increasingly, leased lines are being used by companies, and even individuals, for Internet access because they afford faster data transfer rates and are cost-effective for heavy users of the Internet.
Contents [hide]
1 History
2 Applications
2.1 Site to site data connectivity
2.2 Site to site PBX connectivity
2.3 Site to network connectivity
2.4 International Private Lease Circuit
3 Availability
3.1 In the United Kingdom
3.2 In the United States
3.3 In Hong Kong
3.4 In India
3.5 In Italy
4 Leased line alternatives
5 See also
6 References
[edit]History
Leased lines services (or private line services) became digital in the 1970s with the conversion of the Bell backbone network from analog to digital circuits . This conversion allowed AT&T to offer Dataphone Digital Services (later re-branded digital data services) that started the deployment of ISDN and T1 lines to customer premises to connect.[1]
Leased lines were used to connect mainframe computers with terminals and remote sites, via IBM Systems Network Architecture (created in 1974) or DECnet (created in 1975).
With the extension of digital services in the 1980s leased lines were used to connect customer premises to Frame Relay or ATM networks. Access data rates increased from the original T1 option up to T3 circuits.
In the 1990s with the advances of the Internet, leased lines were also used to connect customer premises to ISP Point of Presence's whilst the following decade saw a convergence of the aforementioned services (frame relay, ATM, Internet for businesses) with the MPLS integrated offerings.
Access data rates also evolved dramatically to speeds of up to 10Gb/s in the early 21st century with the Internet boom and increased offering in long-haul optical networks or Metropolitan Area Networks .
[edit]Applications
Leased lines are used to build up private networks, private telephone networks (by interconnecting PBX's) or access the internet or a partner network (extranet).
Here's is a review of the leased line applications in Network designs over time:
[edit]Site to site data connectivity
Terminating a leased line with two routers can extend network capabilities across sites. Leased lines were first used in the 1970s by enterprise with proprietary protocols such as IBM System Network Architecture and Digital Equipment DECnet, and with TCP/IP in University and Research networks before the Internet became widely available. Note that other Layer 3 protocols were used such as Novell IPX on enterprise networks until TCP/IP became ubiquitous in the 2000s. Today, point to point data circuits are typically provisioned as either TDM, Ethernet, or Layer 3 MPLS.
[edit]Site to site PBX connectivity
Terminating a leased line with two PBX allowed customers to by-pass PSTN for inter-site telephony. This allowed the customers to manage their own dial plan (and to use short extensions for internal telephone number) as well as to make significant savings if enough voice traffic was carried across the line (specially when the savings on the telephone bill exceeded the fixed cost of the leased line).
[edit]Site to network connectivity
As demand grew on data network telcos started to build more advanced network using packet switching on top of their infrastructure. Thus number of telecommunication companies added ATM, Frame-relay or ISDN offerings to their services portfolio. Leased lines were used to connect the customer site to the telco network access point.
[edit]International Private Lease Circuit
An IPLC is an International Private Leased Circuit that functions as a point-to-point private line. IPLCs are usually Time-division multiplexing (TDM) circuits that utilize the same circuit amongst many customers. The nature of TDM requires the use of a CSU/DSU and a router. Usually the router will include the CSU/DSU.
Then came the Internet (in the mid-1990s) and since the most common application for leased line is to connect a customer to its ISP Point of presence. With the changes that Internet brought in the networking world other technologies were developed to propose alternative to Frame-relay or ATM networks such as VPN's (hardware and software) and MPLS networks (that are in effect an upgrade to TCP/IP of existing ATM/Frame-relay infrastructures). Usually, Time-division multiplexing (TDM) circuits that utilize the same circuit amongst many customers. The nature of TDM requires the use of a CSU/DSU and a router. Usually, the router will include the CSU/DSU. An IPLC is an International Private Leased Circuit that functions as a point-to-point private line. IPLCs are usually Time-division multiplexing (TDM) circuits that utilize the same circuit amongst many customers. The nature of TDM requires the use of a CSU/DSU and a router. Usually the router will include the CSU/DSU.
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For Question 1:
Definition: A leased line connects two locations for private voice and/or data telecommunication service. Not a dedicated cable, a leased line is actually a reserved circuit between two points. Leased lines can span short or long distances. They maintain a single open circuit at all times, as opposed to traditional telephone services that reuse the same lines for many different conversations through a process called "switching."
Leased lines most commonly are rented by businesses to connect branch offices, because these lines guarantee bandwidth for network traffic. So-called T1 leased lines are common and offer the same data rate as symmetric DSL (1.544 Mbps). Individuals can theoretically also rent leased lines for high-speed Internet access, but their high cost (often more than $1000 USD per month) deters most. Fractional T1 lines, starting at 128 Kbps, reduce this cost somewhat and can be found in some apartment buildings and hotels.
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