Chapter Questions
Give a simple definition of time-division switching. Compare space-division switching with time-division switching.
Give at least five advantages of time-division switching compared to spacedivision switching.
Give two technical issues relating to time-division switching and digital networks. (Hint: These may be listed as disadvantages in relation to question 2.)
What are the two principal functional elements of digital switching? These elements carry out the actual switching of digital connections (e.g., not control).
Define the terms read and write as used in this chapter. Differentiate between sequential read-random write and random read-sequential write.
What are the three basic building blocks of a time switch?
What are the limitations of a time (T) switch? How are these solved by the addition of space (S) switching capability?
A space array has $M$ horizontals and $N$ verticals in its matrix. Relate $M$ to $N$ for nonblocking tandem switching, for local switch expansion, and for local switch concentration.
We have a $30 \times 30$ space array with a time-slot interchange (TSI) at each input. The TSI is designed for DS1 operation. How many total time slots can the array handle?
Why is a TST switch more desirable than an STS switch? Where would an STS switch have application?
How can blocking probability be reduced in a TST switch?
What is the function of "junctors" in a switch (e.g., a DMS-100)?
Internal bit rates of switches differ from the external interface of 8-bit time slots. Northern Telecom DMS-100 maps the 8-bit PCM "word" into a -bit time slot. What is/are the function(s) of the extra two bits?
To make a switch "universal"- that is, easy to change over from DS1 format to El format and vice versa-often internal bit rates were also based on an $X / Y$ ratio between DS1 and E1. What are the values of $X$ and $Y$ ?
The AT\&T 5ESS has 100,000-line capacity. How does it accomplish this capacity with only a TST architecture (i.e., only one space stage)?
Suppose a digital switch were based solely on a time stage consisting of an E3 format. How many lines could it handle?
Why would fiber-optic transmission links find application internally to these third-generation PCM switches?
Give at least two applications of remote switching, particularly in light of Chapter 2.
What are the two principal factors that change network structure?
In your opinion, what is delaying "fiber to the home"?
What is the effect on the subscriber when his/her telephone subset operates without sidetone?
What is the meaning of each letter in BORSCHT?
Of what use to the telecommunication system engineer is a hypothetical reference circuit or hypothetical reference connection?
In the digital network, digital bit streams require synchronization at three levels. What are they?
Why is it imperative that every outgoing bit stream from a digital switch have its bit rate very close to the nominal? If not, what impairment results?
What is the cause of slips?
Which type of user of the digital network suffers the most when a slip occurs?
What is the most common boundary for a controlled slip? Why there?
The velocity of propagation for optical fiber is $2 \times 10^8 \mathrm{~m} / \mathrm{s}$. A data source is transmitting at $1000 \mathrm{Mbits} / \mathrm{s}$. How many bits will there be on $1000 \mathrm{~km}$ of fiber-optic cable?
Six methods of synchronizing a digital network were given in the text. Name four of them.
Give a value of frequency stability when we mean high stability regarding synchronization of the digital network.
What is the most common way for a digital network to disseminate timing?
We commonly meet what is termed the "two-clock problem." An international switch is an example, where it is more of a multiclock problem. How can a switch handle such a problem?
Define plesiochronous operation.
What is a unit interval (UI)? Define it.
What is the end-to-end BER specified by CCITT for an ISDN?
Why did CCITT come up with a new way of specifying error performance on the digital network?
What is the basic performance measure of a digital network?
What primary performance parameter does timing jitter affect?
If network synchronization is working properly, what slip rate can be expected?
What is the most common method of converting $A$-law to $\mu$-law and vice versa? (We face this when E1 interfaces with DS1 and vice versa.)
To control echo, we can insert loss in a voice channel. How can loss be inserted on the digital side?