lecture7

Boyce

Download

Post to :

URL :

Related Presentations :

Add to Flag Embed

Uploaded from authorPOINTLite

Views: 164

Category: Entertainment

Presentation Description

No description available.

Comments

By: lalipruthi (15 month(s) ago) Private Comment

good presentation

Presentation Transcript

CMPE 150 Fall 2005Lecture 7:

CMPE 150 Fall 2005 Lecture 7 Introduction to Networks and the Internet

Announcements:

Announcements Labs: Tue 6-8pm. W 4-6pm. First lab is next week. TA office hours: T 6-7pm and Th 1-2pm in BME 314. My office hours will be posted this weekend, Please e-mail me if you need to meet. Homework 1 due on Monday. Homework 2 will be posted between today and Monday.

Reading Assignment:

Reading Assignment Tanenbaum Chapter 2.

Last Class:

Last Class PHY (Cont’d). Guided media. The PSTN.

Today:

Today PHY (cont’d).

Public Switched Telephone System:

Public Switched Telephone System Structure of the Telephone System. The Local Loop: Modems, ADSL and Wireless. Trunks and Multiplexing. Switching.

Structure of the Telephone System:

Structure of the Telephone System (a) Fully-interconnected network. (b) Centralized switch. (c) Two-level hierarchy.

Structure of the Telephone System (2):

Structure of the Telephone System (2) A typical circuit route for a medium-distance call.

Major Components of the Telephone System:

Major Components of the Telephone System Local loops Analog twisted pairs going to houses and businesses Trunks Digital fiber optics connecting the switching offices Switching offices Where calls are moved from one trunk to another

PSTN:

PSTN

Local Loop:

Local Loop “Last mile”. End office-subscriber connection. Analog, twisted pair. Traditionally, voice but it has been changing: data transmission. To transmit data, conversion digital to analog: modem. At phone office, data usually converted back to digital for long-distance transmission over trunks.

Transmission Impairments:

Transmission Impairments Problems that happen with signal as it propagates. Attenuation: loss of energy as signal propagates. Different frequencies suffer different attenuation. Different Fourier components attenuated by different amount. Distortion: different Fourier components shifted in time. Noise: unwanted energy from other sources. E.g., thermal noise: unavoidable random motion of electrons in wire.

Modulation:

Modulation Signal with wide range of frequencies is undesirable. Square waves exhibit wide frequency range. To avoid that, AC signaling is used. Sine wave “carrier” to carry information. Modulation: Information is encoded in the carrier by varying either amplitude, frequency, or phase.

Modulation: Examples :

Modulation: Examples Binary signal Amplitude modulation Frequency modulation Phase modulation

Modem:

Modem Modulator-demodulator. Modulates digital signal at the source and demodulates received signal at the destination. How to transmit faster? Nyquist says that capacity is achieved at 2*H*log2V. So there is no point sampling faster than 2*H. But, can try to send more bits per sample.

Baud Rate:

Baud Rate Baud rate = symbols/sec. Data rate = bits/sec. If 2 voltage levels are used, then 1 symbol=1bit. Baud rate = bit rate. But, if can encode more than 1 bit in a symbol… E.g., if voltages 0, 1, 2, and 3, every symbol consists of 2 bits. Thus, 2400 baud line corresponds to 4800 bps. The same thing for 4 different frequencies: QPSK.

Bandwidth, Baud- and Bit Rates:

Bandwidth, Baud- and Bit Rates Bandwidth: physical property of medium. Range of frequencies transmitted with adequate quality. Measured in Hz. Baud rate is number of samples/sec or symbols/sec. Modulation technique determines number of bits/symbol: symbols/sec * bits/symbol. Modern modems transmit several bits/symbol frequently combining multiple modulation schemes.

Quadrature Modulation:

Quadrature Modulation (a) QPSK. (b) QAM-16. (c) QAM-64.

Trellis Coded Modulation:

Trellis Coded Modulation (a) V.32 for 9600 bps. (b) V32 bis for 14,400 bps. (b) 128 points: 6 data and 1 parity 32 points: 4data bits + 1 parity Constellation Diagrams TCM includes error detection!

Full Duplex, Half Duplex, Simplex:

Full Duplex, Half Duplex, Simplex Full duplex: traffic in both directions simultaneously. Half duplex: traffic in both directions but 1 direction at a time. Simplex: traffic allowed only one way. Examples?

What’s next?:

What’s next? Modems were getting faster, e.g., 56Kbps. But, demand for faster access was growing! CATV and satellite as competitors. Phone company’s response: DSL. “Broadband” access. ADSL: asymmetric digital subscriber line. When you subscribe to DSL service, you are connected to the local office without the filter to frequencies below 300Hz and above 3400Hz. Physical limitation still exists and depends on thickness, length, etc.

Digital Subscriber Lines:

Digital Subscriber Lines Bandwidth versus distanced over category 3 UTP for DSL.

Digital Subscriber Lines (2):

Digital Subscriber Lines (2) Operation of ADSL using discrete multitone modulation. Available 1.1MHz local loop spectrum divided into 256 channels (4.3KHz each).

ADSL:

ADSL Typically, 32 channels for upstream and the rest for downstream traffic. Usually, 512 Kbps downstream and 64 Kbps upstream (standard) and 1 Mbps downstream and 256 Kbps upstream (premium). Within each channel, modulation scheme is used (sampling at 4000 baud).

Typical ADSL Setup:

Typical ADSL Setup A typical ADSL equipment configuration.

Wireless Local Loop:

Wireless Local Loop Last mile is wireless. Why? Historically: local telcos had monopoly for local telephone service. In the mid 1990’s market open to competition, e.g., long distance carriers. Cheaper alternative to stringing cables to customers is using a wireless local loop. Mobile telephony? “Fixed” wireless.