tailieunhanh - Lecture Business data communications: Chapter 5 - Behrouz A. Forouzan

Chapter 5 - Data link layer. After reading this chapter, the reader should be able to: Understand the functions of the data link layer, understand the concept of hop-to-hop delivery compared to host-to-host delivery and application-to-application delivery, understand the concept of access method and define different access methods used in LANs and WANs. | Chapter 5 Data Link Layer Understand the functions of the data link layer. Understand the concept of the hop-to-hop delivery compared to host-to-host delivery and application-to-application delivery. Understand the concept of access method and define different access methods used in LANs and WANs . After reading this chapter, the reader should be able to: OBJECTIVES Understand the addressing mechanism used in the data link layer and how network layer addresses are mapped to data layer addresses. Understand how error control is handled at the data link layer. DUTIES OF THE DATA LINK LAYER Figure 5-1 Data link layer in the Internet model Figure 5-2 Data-link layer duties HOP-TO-HOP DELIVERY Figure 5-3 Hop-to-hop delivery PACKETIZING ADDRESSING Technical Focus: Addresses in Local Area Networks The physical address for most computers on local area networks is imprinted on the network card that is installed in the computer. If the user or network manager changes the . | Chapter 5 Data Link Layer Understand the functions of the data link layer. Understand the concept of the hop-to-hop delivery compared to host-to-host delivery and application-to-application delivery. Understand the concept of access method and define different access methods used in LANs and WANs . After reading this chapter, the reader should be able to: OBJECTIVES Understand the addressing mechanism used in the data link layer and how network layer addresses are mapped to data layer addresses. Understand how error control is handled at the data link layer. DUTIES OF THE DATA LINK LAYER Figure 5-1 Data link layer in the Internet model Figure 5-2 Data-link layer duties HOP-TO-HOP DELIVERY Figure 5-3 Hop-to-hop delivery PACKETIZING ADDRESSING Technical Focus: Addresses in Local Area Networks The physical address for most computers on local area networks is imprinted on the network card that is installed in the computer. If the user or network manager changes the network card (because of a failure, for example), the physical address of the computer is changed. In most cases, changing the network card requires reconfiguration of the computer. Figure 5-4 ARP operation ERROR CONTROL Data can be corrupted during transmission. For reliable communication, errors must be prevented, or detected and corrected. Note: In a single-bit error, only 1 bit in the data unit has changed. Note: Figure 5-5 Single-bit error A burst error means that two or more bits in the data unit have changed. Note: Figure 5-6 Burst error of length five Error detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. Note: Figure 5-7 Redundancy Figure 5-8 Detection methods In vertical redundancy check (VRC), a parity bit is added to every data unit so that the total number of 1s becomes even. Note: Figure 5-9 Even parity VRC concept Figure 5-10 LRC In longitudinal redundancy check (LRC), a block of bits is divided into rows .