There are 12 questions in this exam. The total number
of points is 175. Good luck.
1. Total:17.5 points
(5 points)
a. What is multiplexing?
Shared use of bandwidth by interleaving of signals.
Combining several low speed lines into a high speed medium.
(5 points)
b. Name at least three types of multiplexing. Give
an example of a commonly available service that make use of each
of the types of multiplexing.
Freq. Division Multiplexing - cable television
Synchronous TDM - Voice on PSTN
Statistical TDM - Packet switching/Data Services
Wave division Multiplexing - long distance telephony (optical fiber system)
(5 points)
c. leased lines are commonly used with multiplexers.
How are leased lines priced/ What about this pricing strategy
cost justifies investments in multiplexers?
Leased lines costs are bandwidth and distance
sensitive. The cost/kbps decreases more steeply as bandwidth and
distance increase. Thus cost/kbps of 56 kbps line is higher than
cost/kbps of T1 line as distance increases. This allows economies
of scale which cost justifies investment in multiplexing .
(2.5 points)
d. A few weeks ago, a new type of multiplexing technology
was introduced in the marketplace. What is its name? Where would
it find application?
Wave Division Multiplexing
It is used on Optical Fiber Systems.
(Total: 5 points)
2. What is inverse multiplexing? Give an example
of its use?
Inverse multiplexing is the use of several low speed circuits to transmit high speed data. For example, 128 kbps traffic can be inverse multiplexed on to two ISDN 64kbps.
of multiple T1 lines to simulate T3 speeds.
Total: 10 points
3. An organization would like to provide a range
of voice services (local and long distance) customized to the
needs of its personnel. It is considering a PBX-based solution
as well as a telephone company CO-based centrex solution.
(5 points)
a. State two conditions with a centrex solution would be preferred over a PBX-based solution.
(5 points)
b. State two conditions under with as PBX-based solution
would be preferred over a centrex solution.
Total: 15 points
4.
(5 points)
a. What is common channel signaling?
CCS is the use of a separate signaling to set
up long distance calls. This is a shared network by all the companies
in a TN.
(5 points)
b. What is computer telephony integration (CTI)?
CTI is the use of data supplied by CCS to offer
specific services such as routing to an appropriate agent or retrieval
of data from a database through use of caller entered digits or originating
telephone number.
c. Give an example of how CTI is used in organizations?
Retrieve customer profile/billing statements using
originating telephone number or caller entered digits and display
it with agent in a call center. Provides improved customer service.
Total: 15 points
5.
a. What is automatic call distribution (ACD)?
ACD is the routing of incoming calls to a call
center based on provider specified parameter such as customer
profile, time of day, day of week, etc.
(5 points)
b. Give an example of the use of ACD in conjunction
with 800/888 services?
ACD is used in airline reservation system and
mail order catalog companies to route calls to agents suited to
the customer needs or to route calls to different call centers
in different parts of the country to take advantage of time differences.
(5 points)
b. How is investment in an ACD-enabled application
cost justified? Use one of your examples above to provide context.
Cost justified either in terms of customer service
or saving in overtime.
Total: 15 points
6.
(5 points)
a. What is a software defined network?
An SDN is a bulk rate service offered on the PSTN.
The user makes calls as if on a private network (e.g., 5 digit
calls). These calls are processed using CCS and completed over
the PSTN.
(5 points)
b. Give two reasons why it might be preferred over
a private network?
(5 points)
c. State two conditions under which a private voice
network might be preferred over a software defined network.
Total: 25 points
7.
(5 points)
a. What is message switching? Give an example of
an application that used message switching.
Telex is an application. An entire message is
switched on its way from sending device to receiving device.
(5 points)
b. What is the disadvantage of message switching?
How is this disadvantage addressed by packet switching?
(5 points)
c. What is a fundamental difference between packet
switching and circuit switching?
(5 points)
Connection-oriented - all packets between a sending
and receiving device follow the same path through the network.
This path is set up when the virtual circuit is set up.
Connectionless - each packet is sorted over the
network and may follow a different path from sending device to
receiving device.
(5 points)
e. State the conditions under which each of these alternatives is the preferred alternative.
Connection oriented - overhead of call set up exists but is good for long and stable data transfer between locations.
Connectionless - no overhead of call set up. However
each packet needs to be routed individually. Good for short transfers.
Total: 20 points
8. Frame relay is a fast packet switching service. X.25 is the older packet switching service. These services can be provided over permanent virtual circuits or switched virtual circuits.
(5 points)
a. What is a permanent virtual circuit? How does it differ from switched virtual circuits?
A PVC is a virtual circuit that is set up once
and is like a leased line offered over a network. A SVC holds
up in virtual circuit for the duration of data network.
(5 points)
b. What is committed information rate?
Committed information rate is the agreed upon
rate that the network guarantees to deliver. Any data above the
CIR is discard eligible and may not be delivered over the network.
(5 points)
c. In comparison to leased lies, frame relay is regarded as giving telecommunication managers more fine grained control in provisioning bandwidth. Say how. Be specific.
PVCS are not bought in 64 kbps chunks like leased
lines. CIR can be increases in 4 kbps chunks.
A network manager can tune the network to
meet the data communication requirements of the organization.
(2.5)
e. What are two popular applications of frame relay technology?
(2.5)
f. Despite its lower data rates, X.25 is preferred over frame relay under certain conditions. What is an example of an application where X.25 would be preferred over frame relay?
International applications
Total 12.5 points
9. SMDS (switched multi megabit data service) is a fast packet switching service.
(5 points)
a. State three ways in which SMDS differs from frame relay?
| Frame Relay | |
| Connectionless | Connection oriented |
| T3 access speed | T1 access speeds |
| Limited to metropolitan area | WAN service |
(5 points)
b. SMDS has been a technology generally implemented by competitive access providers and local exchange carriers. Why?
LEC's were limited to providing service within LATAs
SMDS with its geographical limitations is well
suited to deployment in a LATA.
(2.5 points)
c. Name a popular application of SMDS technology.
LAN interconnection in city
(15 points)
10. A bank has regional headquarters in Pittsburgh
and Philadelphia. The message traffic between these sites has
grown to 600,000 characters per day. Assume 23 days/month. Further
growth in traffic is expected. You have been retained to develop
a strategy to help the bank decide how it should use two alternative
solutions to its data communication needs, namely, leased lines
and a PDN.
The distance between Pittsburgh and Philadelphia
is 600 miles. Using the cost data shown below, answer the following
questions.
Leased line Rates:
First 200 miles $2.52 per mile (including monthly service charge fee).
Next 1000 miles $.94 per mile
PDN charges:
Connection charge per node $350 per month
packet charge $1.50 per 1000 packets
packet size 128 bytes
(5 points)
a. What is the cost of leasing a line between Pittsburgh and Philadelphia?
(200 x 2.52) + (400 x 94) = 880
(5 points)
b. What is the cost of using a PDN to provide connectivity
between Pittsburgh and Philadelphia given current needs?
( 350 x 2) + [ (600,000X23)/(128 x 1000)] x 1.50
= 861.718
(5 points)
c. What strategy would you recommend to the bank? now and in the future?
( 350 x 2) + [(X x 23)(1000 x 128)] x 1.50 = 200
x 2.52 + 400 x 0.94
This computation results in X = 667826 bytes/day
When traffic gtst to be greater than 667,826 bytes, switch
from PDN to leased lines.
Total: 15 points
11. Narrowband ISDN service is sold both at the basic
rate interface (BRI) and the primary rate interface (PRI).
(5 points)
a. BRI is billed as 2B+ D service. What does this denote? How much bandwidth is made available through this service?
2 Bearer channels - 2 x 64 kbps
1 data channel/signaling channel 16 kbps
(5 points)
b. What are the kinds of traffic usually carried on the B channel? on the D channel?
(5 points)
c. Name two applications whose requirements are well
suited to the capabilities of the ISDN BRI service.
(Total: 10 points)
12. The following are taken from the set of recommendations
in the Booz, Allen and Hamilton Report to the State of Maryland
regarding telecommunications services.
a. (5 points)
"It is recommended
that the State data systems (primarily the statewide wireline
and wireless backbones) be offered at no charge to the departments
and agencies. It is recommended that participation by State agencies
be voluntary." What was the rationale underlying these recommendations?
Provide incentive to use the State's backbone to
realize economies of scale. Voluntary use ("pull straegy") is
recommended to overcome resistance and allow certain departments that
have specialized individual needs the opportunity to explore their own
options.
b. (5 points)
The State is, in most cases, best served by leasing
rather than buying communications equipment and services. What
is the rationale underlying this recommendation? What, if any,
is the disadvantage of this approach?
This makes sense in a fast moving technology market.
No need to expose the State to getting locked into equipment
ownership and maintenance.
Disadvantage: