1) Three terminals A, B, and C are to be connected
to three computers D, E and F so that A is connected D, B to E
and C to F. All are in different cities. A and D are 1500 miles
apart as are B and E and C and F. The locations of the terminals
are 25 miles apart (i.e., A is 25 miles from B and C and B is
25 miles from C). The same is true for the locations of the computers
D, E and F.
If telephone lines cost $1 per mile, what is the line cost
for three independent lines?
A ---------------------------------------- D
B ---------------------------------------- E
C ---------------------------------------- F
$1 (Dollar per mile)x 1500 (miles per line) x 3(lines) = $4500
If a multiplexer/demultiplexer pair costs $2000, can you save
money by another arrangement of lines? If so, how much?
| $1x25miles + $1 x 1500 (line)------------------------------- |
B ---mux/demux-------------------------------mux/demux --------- E
| $1 x 25miles + $2000 (mux demux) ------------------------- |
C ------------------------------------------------------------ F
Total : ($1x25x2) x 2 + $2000 + $1x1500 = $3600
Therefore there a saving of $900.
(If someone uses $2000 x 2 for mux/demux pair then it is wrong since you need only one piece of equipment which has both the functions so only a pair would be needed for covering both the ends)
2) What is the switching technique used in the PSTN?
PSTN uses circuit switching for switching voice and data calls. The signaling for PSTN is carried on using a separate packet switching network discussed in the next answer.
3) What is common channel signalling? Name three services
that it enables on the PSTN?
CCS (Common Channel Signaling) is a separate signaling network connecting all the switches in the PSTN. It enables services like 800, 900 number calling, Call forwarding, caller_id, and all advanced intelligent services.
Answer the following questions after reading the Booz, Allen, Hamilton study on the telecommunications network for the State of Maryland.
4.1) How does the State of Maryland obtain voice services?
Is it a private network?
State of Maryland obtains its voice services from the local telephone companies and the long distance companies. It does not have a private network. The outward calling is enabled by AT&T software defined network and the inward 800 number facilities are provided by MCI.
For local loop, Maryland has an estimated combined total of 88,000
private branch exchange (PBX) and CENTREX lines. An agreement
with Bell Atlantic for services allows for the standardization
of switching services and reduces monthly costs. In addition,
PBXs will be replaced over the next 10 years using a contract
with GTE to install NEAX 2400 equipment. There are 60 PBXs throughout
the State, representing 15 different manufacturers and maintained
through multiple maintenance contracts.
Intra LATA voice calls in the State are normally routed over the public switched network (PSN). Some voice applications use the Digital Backbone Network (DBN), including access to the SCS Network. DGS bills approximately 20 percent of all telecommunications services used by the State government. Total DGS receipts amount to approximately $12 million annually. The remaining services are contracted and paid independently by agencies. Therefore it is a mixture of public and private network network (with more of the former than the latter).
(Although this is detailed answer, points will be given for basic understanding of the situation)
4.2) What does the study suggest with respect to implementation
of ISDN? What services is it expected to support. Be specific.
The study suggests that ISDN should be expanded to link multiple private branch exchange ( PBX) and CENTREX environments throughout the State and offer expanded data and video services. It should be used for VTC or tele-conferencing. As ISDN tariffs become more stable, ISDN should become the digital voice standard for the State. It offers the potential to improve voice quality among State agencies, network voice message systems, and expand video teleconferencing. (Expected services).
4.3) With respect to the decision to implement PBX
vs. Centrex, what is the State currently doing? Do you agree with
the implementation path the State is pursuing? Provide your rationale?
The State has begun to transition many of its local voice services to NEAX 2400 PBXs over the next 10 years. Right now it has 65 different PBX from variety of manufacturers. This arrangement can cause considerable pain in maintenance of the equipment and provide consistence service. If you suggest the PBX is better and that their rationale is OK you should write things like central PBXs may incorporate better standard of telecommunications. It will save money through economic of scale so that increase cost-effectiveness. It is better to reuse equipment and to maintain security.
If you suggest that the rationale is wrong and that you would recommend CENTREX services because the leased line cost associated with tying multiple locations served by a single PBX can be very high compared to CENTREX services. I would recommend CENTREX services because if the life cycle is less than 5 years since the lower cost.
4.4) Is there a role for ACD-based call centers in
Yes, Automatic call distributor can provide more rapid response to public by distributing the call to the target location.
5) What does the study propose with respect to implementation
of the recommended concepts for voice services over a 2 year,
5 year and 10 year horizon?
Two-Year Time Frame
In the 2-year time frame, the State of Maryland will be in the early stages of transitioning to private branch exchange (PBX) environment through its contract with GTE. During this time Maryland should begin to implement an expanded program similar to the Baltimore Master Plan to coincide with the PBX cutovers. The Baltimore Plan provided voice communications for targeted State agencies through remote modules. This approach would optimize the use of PBXs throughout the State by implementing remote modules, reducing the number of PBXs or remaining CENTREX switches. This process should be evaluated case-by-case based on the number of users supported by a switch. Agencies should also examine the need to develop additional citizen assistance programs. These programs could be developed using interactive voice response applications. For example, citizens would call either a local or toll free telephone number and gain access to a menu-driven service where they could get detailed recordings on how to fill out tax forms, or record their name and address to receive a brochure or report. These kinds of programs reduce the need to process incoming mail and the effort necessary for staff response to calls. For larger assistance programs, Maryland should deploy automatic call distribution (ACD) features to provide more rapid response to the citizens by distributing the call loads. Costs for interactive voice response (IVR) and ACD features are presented in Appendix C. During this time frame, Maryland should also begin transitioning to Centigram services statewide. This step will ensure common voice mail features and capabilities for State employees and citizens.
Five-Year Time Frame
During the 5-year time frame, the transition to the NEAX 2400 system should be approximately half complete. At that time, the State needs to reevaluate its voice grade requirements to determine if upgrading the PBXs to Integrated Services Digital Network (ISDN) is prudent. ISDN allows for inexpensive desktop video, Group 4 fax, and data connections to the network. The benefits of ISDN are fully accrued only if both the origination and destination points are ISDN compatible. In addition, transitioning to ISDN requires the purchase of ISDN handsets and equipment. The costs for ISDN are presented in Appendix C. Additionally, during this time frame, the State needs to evaluate the capabilities of new service providers. Competitive access providers (CAPs), who once were only allowed to provide transport, are now allowed to provide switched services. MFS of Maryland is an example of this trend. The availability of these services will depend on the Public Service Commission's and the legislature's activities. The State should evaluate the cost effectiveness of these alternative local services at least 1 year before the expiration of the Bell Atlantic CENTREX contracts.
Ten-Year Time Frame
In the 10-year time frame, Maryland will have completed the transition to a PBX environment. The traffic levels of traditional voice grade capabilities, such as fax, may have declined slightly due to the prevalence of data communications and applications such as electronic data interchange. At this point, it is possible that the telecommunications industry profile will have changed tremendously. Several CAPs may exist in the State, providing switched voice and data capabilities. In addition, the traditional local exchange and inter-exchange carriers' subsidiaries may have full entry into each other's markets. Maryland's information technology planners will be challenged to evaluate a plethora of available services and providers. Voice may be Asynchronous Transfer Mode (ATM)-switched with data and video over the digital public switched network (PSN). In addition, Maryland will need to evaluate the possibility of having one service provider of a seamless voice and data environment for both local and long distance traffic. Again, many of these services will depend on both State and Federal regulation and legislation.