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2001: Homework assignment 9 model answer

Notice! The role of this model answer is instructional only. Everything that is asked in the assignment may not be covered in detail. The model answer gives you the content of the answer and an idea of what it should be. The things that are important in the grading of the homework have been emphasized. Please, inform the course staff if you think that there is a mistake in the model answer!

Assignment: Transmission in Telecom (total 25+3 points)

1. SDH (8 points total)

    1. The network will be synchronized by the uppermost SEC.
    2. Synchronisation through secondary synchronization chain still works and will be used.
    3. SECs on left will be synchronized via secondary chain, SECs on right by primary chain.
    4. That could cause a synchronization loop.

  2. Photonic layer: optical fiber
    Section layer: STE (Section Terminating Equipment) regenerator, repeater
    Line layer: DCS (Digital Cross-connect System), ADM (Add/Drop Multiplexer), LTE (Line Terminating Equipment)
    Path layer: PTE (Path Terminating Equipment), POH (Path Overhead)

ISDN (6 points):

  1. A channel: 4 kHz analog telephone channel
    B channel: bearer channel. 64-kbps digital PCM channel for voice or data.
    C channel: 8- or 16-kbps digital channel
    D channel: 16-kbps digital channel for out-of-band signaling
    E channel: 64-kbps digital channel for internal ISDN signaling
    H 384-, 1536- or 1920-kbps digital channel
    (Source: Tanenbaum 2.5.3.)
  2. Basic rate interface consists of two B channels and one 16-kpbs D channel. This is the basic home or small business ISDN intented to replace POTS. Primary rate interface, on the other hand, is intented for bigger businesses. It consists of 23 B and one 64-kbps D channel (being equivalent to T1) in U.S. and Japan, or 30 B and one D (equivalent to E1) in Europe.
  3. ISDN is available practically everywhere, DSL is not. ISDN is also cheaper if usage is small.

3. xDSL in theory and practise (4+3 points)

xDSL
 Speed
 Max. dist.
 Advantages
 Disadvantages
 Users
HDSL up to 2 Mbps,
symmetric only 		3,7 km old and tested,
symmetric 		no phone support,
requires 2 lines 		companies
ADSL 1.5-6.1 Mbps downstream,
up to 512 kbps upstream 		2.7-5.5 km phone support,
high downstream 		low upstream home users
VDSL 13-52 Mbps downstream asymmetric,
6-26 Mbps symmetric 		0.3-1.5 km high performance, symmetric short distance companies
SDSL 1.5-2 Mbps,
symmetric only 		3,7 km symmetric no phone support companies,
anyone who need symmetric
connection

DSL = Digital Subscriber Line

4. Get connected (6 point)

Any answer with justified opinions is right. This is just one example.

Tlarktown Interactive wants to run its own web, email etc. servers. They need reliable connection with both high upstream and downstream speed. SDSL connection or similar would probably be the best choice. WLAN is not very reliable, and cable modem has low upstream speed (especially if there are many users).

Tlarktown Shoeshop doesn't need Internet very much. They probably just want to pay their bills and perhaps maintain modest web pages (in provider's web hotel). Simple modem or ISDN connection is quite sufficient.

Tlarktown Soap Factory has 100 employees, but not many of them need Internet connection. Factory doesn't need own web or email server. Cable modem will probably be sufficient.

5. Feedback (1 point)

This page is maintained by the assistants of tlark , course newsgroup opinnot.tik.tlark
The page has last been updated 8.12.2001.
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