ECSE6660: Broadband Networks Exam 1

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ECSE-6660 Broadband Networks Exam 1

• Time 75 min (strictly enforced)
• Points 50
• YOUR NAME
• Be brief, but DO NOT omit necessary detail
• Note Simply copying text directly from the
  slides or notes will not earn (partial) credit.
  Brief, clear and consistent explanation will.

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• I. Quick True/False Questions (10 points)
• Tick True or False (1 pt each). Add a 1 line
  explanation JUSTIFYING your choice (1 pt each)
• T F
• ????Echo cancellors also manage the problem of
  side-tones
• F Balance circuits manage the problem
  of side-tones.
• ????Cable networks use twisted-pair cables in a
  switched network architecture
• F Cable networks use coaxial cables
  to provide broadcast services.
• ????The common carrier concept refers to the
  use of a common channel for signaling in
  telephony
• F Common carrier refers to the control
  of the conduit by a single controller.
• ????STS-Nc multiplexes STS-1 frames in a
  byte-interleaved manner
• F STS-Nc is the concatenated mode -- it DOES
  NOT byte-interleave STS-1s
• ???? TDMA and FDMA are examples of token-passing
  MAC approaches
• F TDMA/FDMA are channel partitioning methods,
  and they dont pass tokens.

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• II. Below, you are given a true or false
  statement and asked a follow up question.
• 1. 5 pts False statement Virtual Circuit is
  the same as Connectionless transmission
• Explain the differences between the notions of
  circuit, virtual circuit, connection-oriented
  and connectionless or datagram
• Circuit Refers to a physical connection between
  two endpoints along with resource reservation.
• Virtual Circuit A fixed path but no resource
  reservation.
• Connection-oriented Needs an explicit path
  set-up phase between the end points before actual
  data transfer.
• Connectionless/Datagram No session establishment
  is necessary, the packets take the path that is
  entirely dependent on the network. Multiple
  packets belonging to the same application/end-poin
  ts can take different paths.

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• 2. (11 pts) True statement SONET uses a pointer
  mechanism in addition to synchronous
  transmission.
• (3 pts) Discuss what was the fundamental problem
  that SONET pointers addresses?
• (2 pts) How was it addressed before in the
  T-carrier hierarchy?
• (3 pts) Why does this solution simplify
  multiplexing and allow high-speed communications?
• (3 pts) How is the virtual tributary mechanism
  different from the STS-N multiplexing mechanism?
• Sonet pointers address two main issues
• Multiplexing Data from various sources can be
  added to or dropped from the payload without
  resetting frame boundaries.
• Synchronization Bursty data can appear in a
  stream anytime. Pointers help create a floating
  payload that can be easily retrieved.
• T carriers used a combination of bit-stuffing
  coupled with TDM to address the problems of
  synchronization and multiplexing.
• The solution (Sonet pointers) helps multiplexing
  and synchronization by making the channel
  add/drop functionality more simple.

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We no longer need large multiplexer queues to add
or drop channels. The pointers using ADM can do
this in a mich flexible manner. (d) The Virtual
Tributary is the exact opposite of the STS-N. In
VT, lower bit rate streams are multiplexed. VTs
can exist even on a STS-1. STS-N multiplexing is
connection oriented. In case of STS, streams
having a higher bit rate are multiplexed. STS-N
multiplexes N STS frames into a STS-N frame.
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• II. 12 pts Telephony vs Data Networks vs Cable
  Networks
• Discuss
• (4 pts) WHY telephone networks opted for
  technologies like TDM/circuit-switching and the
  intelligent-core-dumb-phones architectural model,
• (4 pts) WHY data networks opted for technologies
  like statistical multiplexing/packet-switching
  and the end-to-end architectural model, and
• (4 pts) WHY cable networks opted for
  tree-and-branch, broadcast model of operation

Telephone networks deal with voice streams which
cannot tolerate high delays. Phone networks use
TDM and circuit switching since they provide
guaranteed delay and bandwidth. The network is
expected to do the call setup, routing etc. The
end systems were dumb terminals. The data
networks can afford loss of packets since
real-time access is not critical. . The model
chosen is cheaper than the telephone model since
the resources do not need to be dedicated for
each user. End to end model was used since
computing costs were reduced and hence the
intelligence can be pushed to the edge of the
network. Cable networks are half duplex
broadcast networks. The content is broadcasted to
hubs that distribute it to other hubs and to
users in a tree-and-branch like manner.
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• III. 12 pts Convergence Architectures
• Describe the key differences between the
  telephony-driven architectures SONET, X.25,
  Frame Relay, ISDN and ATM. (9 pts)
• How do they differ from Ethernet and Internet
  protocols ? (3 pts)
• This question is subjective and will be corrected
  based on individual responses.

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