Tài liệu giảng dạy CCNA - module 01 chapter 03 - Data Link Layer Fundamentals

1 Module 01 InterNetwork Overview Chapter 03 Data Link Layer Fundamentals: Ethernet LANs 2 Table of Content 1 Typical LAN Features for OSI Layer 1 2 Typical LAN Features for OSI Layer 2 3 Early Ethernet Standards 4 Recent Ethernet Standards 3 1. Typical LAN Features for OSI Layer 1  The OSI physical layer, or Layer 1, defines the details of how to move data from one device to another.  The OSI physical layer defines the standards used to send and receive bits across a physical network. 4 2. Typical LAN Features for OSI Layer 2 5 Data Link Function 1: Arbitration  The specifications for these data-link protocols define how to arbitrate the use of the physical medium to avoid collisions, or at least to recover from the collisions when they occur.  Ethernet uses the carrier sense multiple access with collision detection (CSMA/CD) algorithm for arbitration. 6 CSMA/CD  The CSMA/CD algorithm works like this:  1. A device with a frame to send listens until the Ethernet is not busy.  2. When the Ethernet is not busy, the sender begins sending the frame.  3. The sender listens to make sure that no collision occurred.  4. Once the senders hear the collision, they each send a jamming signal, to ensure that all stations recognize the collision.  5. After the jamming is complete, each sender randomizes a timer and waits that long.  6. When each timer expires, the process starts over with Step 1. 7 Data Link Function 2: Addressing  Every computer has a unique way of identifying itself : MAC address or physical address.  The physical address is located on the Network Interface Card (NIC).  MAC addresses have no structure, and are considered flat address spaces. MAC addresses are sometimes referred to as burned-in addresses (BIAs) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes.  0000.0c12.3456 or 00-00-0c-12-34-56. 8 MAC address format The first six hexadecimal digits, which are administered by the IEEE, identify the manufacturer or vendor. The remaining six hexadecimal digits comprise the interface serial number. 9 Using MAC addresses A DData A DData A DDataA DData Source Address Destination Address 1 0 Data Link Function 3: Error Detection  Most data-link protocols include a frame check sequence (FCS) or cyclical redundancy check (CRC) field in the data-link trailer. This field contains a value that is the result of a mathematical formula applied to the data in the frame.  Error detection does not imply recovery. The FCS allows the receiving device to notice that errors occurred and then discard the data frame. [...].. .Data Link Function 4: Identifying the Encapsulated Data 1 3 Early Ethernet Standards 1 10BASE2 and 10BASE5 Standard Topology Medium Maximum cable length Transport 10BASE5 Bus Thick coaxial cable 500m Half-duplex 10BASE2 Bus Thin coaxial 185m cable Half-duplex 1 A Repeater  Standards guarantee minimum bandwidth and operability... domains 1 10BASE-T Ethernet  Topology: star (hub)  Medium: CAT3 UTP  Maximum cable length: 100m  Transport: half-duplex 1 Ethernet 10BASE-T Cabling Pin 1 Pin 1 Pin 1 Pin 3 Pin 2 Pin 2 Pin 2 Pin 6 Pin 3 Pin 3 Pin 3 Pin 1 Pin 4 Pin 4 Pin 4 Pin 4 Pin 5 Pin 5 Pin 5 Pin 5 Pin 6 Pin 6 Pin 6 Pin 2 Pin 7 Pin 7 Pin 7 Pin 7 Pin 8 Pin 8 Pin 8 Pin 8 Straight-through cable Crossover cable 1 10BASE-T Hubs  The... Mbps, 100 Mbps, or 1000 Mbps  Gigabit Ethernet differs from the slower Ethernet specifications in how it encodes the signals onto the cable 2 Summary OSI Layer 2 Functions Ethernet Implementation Arbitration CSMA/CD algorithm Addressing 6-bytes-long MAC address Error detection FCS in Ethernet trailer Identifying the type of packet inside the frame Protocol Type (2 bytes)—DIX Ethernet DSAP (1 byte)—IEEE... allow the use of fullduplex operation 1 4 Recent Ethernet Standards 1 Fast Ethernet  Two of the key features of Fast Ethernet, as compared to 10-Mbps Ethernet, are higher bandwidth and autonegotiation  Medium: CAT5 UTP, fibre optic  Transport: half or full-duplex 2 Gigabit Ethernet  The most important similarity is that the same Ethernet headers and trailers are used, regardless of whether it’s 10 . 1 Module 01 InterNetwork Overview Chapter 03 Data Link Layer Fundamentals: Ethernet LANs 2 Table of Content 1 Typical LAN Features for OSI Layer 1 2 Typical LAN Features for OSI Layer 2 3. serial number. 9 Using MAC addresses A DData A DData A DDataA DData Source Address Destination Address 1 0 Data Link Function 3: Error Detection  Most data- link protocols include a frame check. burned-in addresses (BIAs) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes.  0000.0c12.3456 or 0 0-0 0-0 c-1 2-3 4-5 6. 8 MAC