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Public Switched Telephone Network : 

Public Switched Telephone Network (PSTN)

::AIM OF PRESENTATION:: : 

::AIM OF PRESENTATION:: Basic operations PSTN. Telephony switching hierarchy. Signaling SS7 network

What Is A Network ? : 

What Is A Network ? Switching Office CPE CPE Transmission Facilities Switching Office

Slide 4: 

Figure 5.19 Modulation/demodulation

Slide 5: 

Figure 5.18 Telephone line bandwidth

Slide 6: 

(a) A binary signal (b) AM (c) FM (d) PM

Slide 7: 

Fig b uses 2 values : 0 amplitude to represent 0 and non-zero amp. To rep. 1 Fig c uses 2 values : f1 to rep. 0 and f2 to rep. 1 Fig d uses phase : phase shift represents change in value and no phase shift rep. No change in value

Common Channel Signaling (CCS) : 

Common Channel Signaling (CCS) Common Channel Signaling (CCS) is a signaling method that uses a separate dedicated channel to send and receive signaling information for a group of trunks or facilities by means of labeled messages.

Signaling System 7 (SS7) LINKS : 

Signaling System 7 (SS7) LINKS A A A A CO CO CO C C STP STP STP STP SCP SCP

Limitations of ASK and FSK : 

Limitations of ASK and FSK Limitations of ASK ; very much susceptible to noise Limitations of FSK ; bandwidth requirement For detailed study : refer to Forouzan.

Modems (2) : 

Modems (2) (a) QPSK. (b) QAM-16. (c) QAM-64.

Trellis Coded Modulation : 

Trellis Coded Modulation With a dense constellation diagram, a small amount of noise in amplitude or phase can result in an error. To reduce the chance of an error, higher speed modems do error correction by adding extra bit(/s) to each sample. This scheme is called TCM.

Few terms : 

Few terms Bit rate : number of bits transmitted per second. Baud rate : number of signal units (or samples) transmitted per second. Bit rate = Baud rate x number of data bits per sample.

Some traditional modem standards : 

Some traditional modem standards Earlier modems used the QAM schemes. For QAM schemes the baud rate is equal to the bandwidth (to be shown by …or refer to Forouzan pg117 to 126). Hence for a telephone line of 2400 Hz bw, baud rate of 2400 was used. V.32 : 4 data bits + 1 error bit : 2400 x 4 = 9600 bps V.32bis : 6 data bits + 1 error bit : 2400 x 6 = 14,400 bps V.34 : 12 data bits : 2400 x 12 = 28,800 bps V.34bis : 14 data bits : 2400 x 14 = 33,600 bps

Limitations of traditional modems : 

Limitations of traditional modems When the analog signal is digitized at the telephone company switching station (using codecs) noise is introduced in the signal. Hence the data rate is limited according to the Shannon’s capacity. In traditional modems, data exchange is between two computers A and B,( thru the digital telephone network.), Hence this sampling exists in both the directions. Thus the maximum data rate is 33.6 kbps in either direction.

PSTN contd… : 

PSTN contd… Can be viewed to have two types of componenets: External (communication medium…last mile, long haul trunks etc) and, Internal (Switching Offices)

Switching Offices : 

Switching Offices Two types of switching is used: Circuit Switching (PSTN) Packet Switching (Internet)

Circuit Switching : 

Circuit Switching (a) Circuit switching. (b) Packet switching.

Message Switching : 

Message Switching (a) Circuit switching (b) Message switching (c) Packet switching

Topics for presentation : 

Topics for presentation Satellite Networks (2 people) : Explain user to user, where and how they are used etc. Mobile Networks (3-5 people), take book from me for reference, rest from net, talk about GSM, GPRS, EDGE, CDMA, their 2nd gen, 3rd gen etc, difference between “use of data card to connect to internet wirelessly anywhere anytime” and GPRS/EDGE enabled mobile phone etc. Cover in detail: which frequency range, call setup, their switching offices etc, technology used etc

Packet Switching : 

Packet Switching A comparison of circuit switched and packet-switched networks.

I Acknowledge : 

I Acknowledge Help from the following site http://www.cs.vu.nl/~ast/ In preparing this lecture.