Lecture CCNA Exploration 4.0 (Kỳ 4) - Chapter 2: PPP

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This chapter describe the fundamental concepts of point-to-point serial communication including TDM, demarcation point, DTE-DCE functions, HDLC encapsulation, and serial interface troubleshooting; configure PPP on a serial interface including enabling PPP encapsulation.

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Nội dung Text: Lecture CCNA Exploration 4.0 (Kỳ 4) - Chapter 2: PPP

Chapter 2 – PPP CCNA Exploration 4.0 1
Introduction Học viện mạng Bach Khoa - Website: www.bkacad.com 2
Serial Point-to-Point Links Học viện mạng Bach Khoa - Website: www.bkacad.com 3
Introducing Serial Communications • Computers make use of relatively short parallel connections between interior components, but use a serial bus to convert signals for most external communications. Học viện mạng Bach Khoa - Website: www.bkacad.com 4
Introducing Serial Communications • In a parallel connection, it is wrong to assume that the 8 bits leaving the sender at the same time arrive at the receiver at the same time. Rather, some of the bits get there later than others. This is known as clock skew. Học viện mạng Bach Khoa - Website: www.bkacad.com 5
Introducing Serial Communications • Parallel wires are physically bundled in a parallel cable, and signals can imprint themselves on each other. The possibility of crosstalk across the wires requires more processing, especially at higher frequencies. Học viện mạng Bach Khoa - Website: www.bkacad.com 6
Introducing Serial Communications • Serial Communication Standards – All long-haul communications and most computer networks use serial connections, because the cost of cable and synchronization difficulties make parallel connections impractical. – The most significant advantage is simpler wiring. Also, serial cables can be longer than parallel cables, because there is much less interaction (crosstalk) among the conductors in the cable. Học viện mạng Bach Khoa - Website: www.bkacad.com 7
Introducing Serial Communications Học viện mạng Bach Khoa - Website: www.bkacad.com 8
TDM • Time Division Multiplexing – Bell Laboratories invented time-division multiplexing (TDM) to maximize the amount of voice traffic carried over a medium. – TDM divides the bandwidth of a single link into separate channels or time slots. – TDM transmits two or more channels over the same link by allocating a different time interval (time slot) for the transmission of each channel. Học viện mạng Bach Khoa - Website: www.bkacad.com 9
TDM • Statistical Time Division Multiplexing (STDM) – STDM uses a variable time slot length allowing channels to compete for any free slot space. It employs a buffer memory that temporarily stores the data during periods of peak traffic. – STDM does not waste high-speed line time with inactive channels using this scheme. Học viện mạng Bach Khoa - Website: www.bkacad.com 10
TDM Examples Học viện mạng Bach Khoa - Website: www.bkacad.com 11
TDM Examples Học viện mạng Bach Khoa - Website: www.bkacad.com 12
Demarcation Point Học viện mạng Bach Khoa - Website: www.bkacad.com 13
DTE-DCE • The CPE, which is generally a router, is the DTE. The DTE could also be a terminal, computer, printer, or fax machine if they connect directly to the service provider network. • The DCE, commonly a modem or CSU/DSU, is the device used to convert the user data from the DTE into a form acceptable to the WAN service provider transmission link. This signal is received at the remote DCE, which decodes the signal back into a sequence of bits. The remote DCE then signals this sequence to the remote DTE. Học viện mạng Bach Khoa - Website: www.bkacad.com 14
Cable Standards • The DTE/DCE interface for a particular standard defines the following specifications: – Mechanical/physical - Number of pins and connector type – Electrical - Defines voltage levels for 0 and 1 – Functional - Specifies the functions that are performed by assigning meanings to each of the signaling lines in the interface – Procedural - Specifies the sequence of events for transmitting data Học viện mạng Bach Khoa - Website: www.bkacad.com 15
Cable Standards Học viện mạng Bach Khoa - Website: www.bkacad.com 16
Cable Standards Học viện mạng Bach Khoa - Website: www.bkacad.com 17
Parallel to Serial Conversion • Your PC also has a Universal Asynchronous Receiver/Transmitter (UART) chip on the motherboard. Since the data in your PC flows along parallel circuits, the UART chip converts the groups of bits in parallel to a serial stream of bits. • To work faster, a UART chip has buffers so it can cache data coming from the system bus while it processes data going out the serial port. • The UART is the DTE agent of your PC and communicates with the modem or other serial device, which, in accordance with the RS-232C standard, has a complementary interface called the DCE interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 18
HDLC Encapsulation • HDLC - The default encapsulation type on point-to-point connections, dedicated links, and circuit-switched connections when the link uses two Cisco devices. HDLC is now the basis for synchronous PPP used by many servers to connect to a WAN, most commonly the Internet. Học viện mạng Bach Khoa - Website: www.bkacad.com 19
HDLC Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 20