nho cac bac dich giup em bai nay sang tieng viet

Data Link Layer Fundamentals © 2004 - iPMAC Informatics Technology J.S.C Cisco Icons and Symbols IPMAC Networking Academy Overview Different Layer features Ethernet and the LAN standards today Operation of hubs and switchs Ethernet family and its Future IPMAC Networking Academy Typical LAN Features for OSI Layer The physical layer defines the standards used to send and receive bits across a physical network The physical layer defines the details of cabling: The maximum length allowed for each type of cable The number of wires inside the cable The shape of the connector on the end of the cable… Most cable include several conductors (wires) inside the cable The endpoint of these wires are called pins, which end inside the connector The physical layer also must define the purpose of each pin IPMAC Networking Academy CAT5 Cable with RJ-45 Connector RJ-45 is a typical connector used with Ethernet cabling today One pair of wires is used for transmitting data, using pins and One pair of wires is used for receiving data, using pins and pins IPMAC Networking Academy Typical LAN Features for OSI Layer The data link layer defines the standards and protocols used to control the transmission of data across a physical network Each data link protocol “controls” a particular type of physical layer network, the details of how a data link protocol functions must include some consideration of the physical network Most of data link protocols perform the following functions: Arbitration Addressing Error detection Identification of the encapsulated data IPMAC Networking Academy Data Link Function 1: Arbitration With some type of physical networks, data frames can collide if devices can send any time they want When frames collide in a LAN, the data in each frame is corrupted and the LAN is unusable for a brief moment The specifications for these data-link protocols define how to arbitrate the use of the physical medium to avoid collisions, ar at least to recover from the colisions when they occur Ethernet uses the carrier sense multiple access with collision detection (CSMA/CD) algorithm for arbitration IPMAC Networking Academy Data Link Function 2: Addressing Many physical networks allow more than two devices attached to the same physical network Data-link protocols define addresses to make sure that the correct device listens and receives the data that is sent By putting the correct address in the data-link header, the sender of the frame can be relatively sure that the correct receiver will get the data Each data-link protocol defines its own unique addressing structure Ethernet uses Media Access Control (MAC) Frame Relay uses data-link connection identifier (DLCI) IPMAC Networking Academy Data Link Function 3: Error Detection Error detection discovers whether bit errors occurred during the transmission of the frame Most data-link protocols include a frame check sequence (FCS) or cyclical redundancy check (CRC) field in the datalink trailer This field contains a value that is the result of a mathematical formula applied to the data in the frame If the FCS sent by the sender matches the FCS calculated by the receiver, the frame did not have any errors Error detection does not imply recovery The FCS allows the receiving device to notice that errors accurred and then discard the data frame IPMAC Networking Academy Data Link Function 4: Identifying the Encapsulated Data This function identifies the contents of the Data field in the frame Each data-link header has a Type field to identify the type of protocol that sits inside the frame’s data field IEEE Ethernet 802.2 Logical Link Control (LLC) uses a field in its header to identify the type of data in the Data field Coming up … Ethernet Standard IPMAC Networking Academy 10BASE-T Hub operation NIC sends a frame NIC loops the frame back Hub receives the frame Hub sends it to all ports, except the received port Hub sends the frame out If two PCs sent a frame at the same time, a collision would occur IPMAC Networking Academy Collisions and Duplex Settings 10BASE2, 10BASE5, and 10BASE-T Ethernet would not work without CSMA/CD With CSMA/CD algorithm, Ethernet becomes more inefficient under higher loads In the next section, you will read about two things that have improved network performance, both relating to the reduction or even elimination of collisions: LAN Switching Full-Duplex Ethernet IPMAC Networking Academy Reducing Collisions - LAN Switching LAN switches overcome the problems created by collisions and the CSMA/CD algorithm by removing the possibility of a collision Switches not create a single shared bus, they treat each individual port as a separate bus Switches use memory buffers to hold incoming frame Switch performs OSI Layer functions by interpreting Ethernet header information to make forwarding decisions IPMAC Networking Academy Full-Duplex Ethernet The original Ethernet specifications used a shared bus, over which a single device could not be sending a frame and receiving a frame at the same time because it would mean that a collision was occurring That logic is called half-duplex logic Ethernet switches allow multiple frames to be sent over different ports at the same time If only one device is connected to a switch port, there is never a possibility that a collision could occur LAN switches with only one device cabled to each port of the switch can send and receive concurrently This is full-duplex operation IPMAC Networking Academy Ethernet Addressing Ethernet LAN addressing identifies either individual devices or groups of devices on a LAN Unicast Ethernet addresses identify a single LAN card Each address is bytes long, is usually written in hexadecimal, with periods separating each set of four hex digits For example, 0000.0C12.3456 is a valid Ethernet address Computers use these addresses to identify the sender and receiver of an Ethernet frame IEEE calls them MAC addresses IPMAC Networking Academy Unicast Ethernet Address The IEEE requires globally unique unicast MAC addresses on all LAN interface cards To ensure a unique MAC address, the Ethernet card manufacturers encode the MAC address onto the card, usually in a ROM chip Is is also called burned-in address (BIA) The first half of the address identifies the manufacturer of the card, is called the organizationally unique identifier (OUI) The second half of the address being assigned a number that this manufacturer has never used on another card IPMAC Networking Academy Group addresses Group addresses identify more than one LAN interface card The IEEE defines two general categories of group addresses for Ethernet: Broadcast addresses – the broadcast address, has a value of FFFF.FFFF.FFFF (hexadecimal notation) The broadcast address implies that all devices on the LAN should process the frame Multicast addresses – Multicast addresses are used to allow a subset of devices on a LAN to communicate Coming up … Ethernet family IPMAC Networking Academy Recent Ethernet Standards Fast Ethernet Gigabit Ethernet 10-Gigabit Ethernet IPMAC Networking Academy Fast Ethernet Fast Ethernet, as defined in IEEE 802.3u, is also known as 100Mbps Ethernet The two technologies that have become important are 100BASE-TX, which is a copper UTP medium and 100BASE-FX, which is a multimode optical fiber medium The CSMA/CD logic can be disabled for full-duplex point-topoint topologies The 802.3u specification calls for the use of the same old IEEE 802.3 MAC and 802.2 LLC framing for the LAN headers and trailers Both Fast Ethernet shared hubs and switches can be deployed IPMAC Networking Academy Fast Ethernet (cont) Fast Ethernet’s autonegotiation function allows an Ethernet card or switch to negotiate dynamically to discover whether it should use either 10 or 100 Mbps Many Ethernet cards and switch ports are called 10/100 cards or ports today because they can autonegotiate the speed The endpoints autonegotiate whether to use half duplex or full duplex as well If autonegotiation fails, it settles for half-duplex operation at 10 Mbps IPMAC Networking Academy Gigabit Ethernet The IEEE defines Gigabit Ethernet in standards 802.3z for optical cabling and 802.3ab for electrical cabling CSMA/CD still is used and can be disabled for full-duplex support The 802.3z and 802.3ab standards call for the use of the same old IEEE 802.3 MAC and 802.2 LLC framing for the LAN headers and trailers The most likely place to use Gigabit is between switches, between switches and a router, and between a switch and a server The same Ethernet headers and trailers are used, regardless of whether it’s 10 Mbps, 100 Mbps, or 1000 Mbps Gigabit Ethernet is obviously faster, at 1000 Mbps, or Gbps IPMAC Networking Academy 10- Gigabit Ethernet 10 Gig Ethernet, defined in IEEE 802.3ae, runs at 10 Gbps It uses the same 802.3 MAC and 802.2 LLC as the other types of Ethernet It have some differences with the other types: It allows only a point-to-point topology because it is intended for connectivity between switching devices It allows only full-duplex communication It specifies only optical fiber - no copper cabling (Support for copper wiring might be added later.) 10 Gig Ethernet using SM fiber for up to 40km IPMAC Networking Academy Future of Ethernet Ethernet has gone through an evolution from Legacy → Fast → Gigabit → MultiGigabit technologies The future of networking media is threefold: Copper (up to 1000 Mbps, perhaps more) Wireless (approaching 100 Mbps, perhaps more) Optical fiber (currently at 10,000 Mbps and soon to be more) Some discussions between IEEE members have begun that suggest the possibility of standards for 40-, 80-, and even 100-Gbps Ethernet IPMAC Networking Academy Summary The basics of Ethernet technology How Ethernet and the OSI model interact Ethernet frame field names and purposes 10Base2, 10Base5, 10BaseT The characteristics and function of CSMA/CD The backoff algorithm and time after a collision Ethernet errors and collisions Auto-negotiation in relation to speed and duplex Characteristics and varieties of 100-Mbps and 1000-Mbps Ethernet IPMAC Networking Academy Stop here! It’s time for questioning IPMAC Networking Academy [...]... cable problem affects only one device All devices are sharing a single bus, so we call this shared Ethernet IPMAC Networking Academy 10BASE-T Hub operation 1 NIC sends a frame 2 NIC loops the frame back 3 Hub receives the frame 4 Hub sends it to all ports, except the received port 5 Hub sends the frame out If two PCs sent a frame at the same time, a collision would occur IPMAC Networking Academy Collisions... collisions: LAN Switching Full-Duplex Ethernet IPMAC Networking Academy Reducing Collisions - LAN Switching LAN switches overcome the problems created by collisions and the CSMA/CD algorithm by removing the possibility of a collision Switches do not create a single shared bus, they treat each individual port as a separate bus Switches use memory buffers to hold incoming frame Switch performs OSI Layer 2... and waits that long (backoff algorithm) When each timer expires, the process stars over with step 1 IPMAC Networking Academy Repeaters 10BASE5 and 10BASE2 had limitations on the total length of cable The signal sent by one device could attenuate too much if the cable was longer than 500m or 185m Repeaters take an incoming signal, regenerate it and pass it on IPMAC Networking Academy 10BASE-T Ethernet... Networking Academy Introduction to Ethernet Most of the traffic on the Internet originates and ends with Ethernet connections The success of Ethernet is due to the following factors: Simplicity and ease of maintenance Ability to incorporate new technologies Reliability Low cost of installation and upgrade Bandwidth can be increased without changing underlying technology IPMAC Networking Academy Ethernet... Networking Academy 10BASE-T Ethernet 10BASE-T solved several problems with the early Ethernet specifications 10BASE-T allowed the use of telephone cabling that was already installed, or simply allowed the use of cheaper, easierto-install cabling when new cabling was required 10BASE-T networks make use of devices called hubs IPMAC Networking Academy Hubs The hubs are multiport repeaters The hub simply regenerates... control (LLC) – New L2 features Transitions up to the network layer IPMAC Networking Academy LLC sublayer Packet Packet LLC PDU Packet Frame LLC PDU includes: DSAP: Destination service access point SSAP: Source service access point Supports connection control methods specified by upper protocols IPMAC Networking Academy Original Ethernet Standard: 10BASE5 The original 1980 Ethernet product 10BASE5 transmitted... was length 10BASE5 systems also represent a single point of failure Each of the maximum five segments of thick coax may be up to 500 m (1640.4 ft) in length Because the medium is a single coaxial cable, only one station can transmit at a time or else a collision will occur 10BASE5 only runs in half-duplex resulting in a maximum of 10 Mbps of data transfer IPMAC Networking Academy Original Ethernet Standard:... each set of four hex digits For example, 0000.0C12.3456 is a valid Ethernet address Computers use these addresses to identify the sender and receiver of an Ethernet frame IEEE calls them MAC addresses IPMAC Networking Academy Unicast Ethernet Address The IEEE requires globally unique unicast MAC addresses on all LAN interface cards To ensure a unique MAC address, the Ethernet card manufacturers encode... Multicast addresses – Multicast addresses are used to allow a subset of devices on a LAN to communicate Coming up … Ethernet family IPMAC Networking Academy Recent Ethernet Standards Fast Ethernet Gigabit Ethernet 10-Gigabit Ethernet IPMAC Networking Academy Fast Ethernet Fast Ethernet, as defined in IEEE 802.3u, is also known as 100Mbps Ethernet The two technologies that have become important are 100BASE-TX,... up to 40km IPMAC Networking Academy Future of Ethernet Ethernet has gone through an evolution from Legacy → Fast → Gigabit → MultiGigabit technologies The future of networking media is threefold: Copper (up to 1000 Mbps, perhaps more) Wireless (approaching 100 Mbps, perhaps more) Optical fiber (currently at 10,000 Mbps and soon to be more) Some discussions between IEEE members have begun that suggest ... problem affects only one device All devices are sharing a single bus, so we call this shared Ethernet IPMAC Networking Academy 10BASE-T Hub operation NIC sends a frame NIC loops the frame back... Full-Duplex Ethernet IPMAC Networking Academy Reducing Collisions - LAN Switching LAN switches overcome the problems created by collisions and the CSMA/CD algorithm by removing the possibility of a collision... an incoming signal, regenerate it and pass it on IPMAC Networking Academy 10BASE-T Ethernet 10BASE-T solved several problems with the early Ethernet specifications 10BASE-T allowed the use of