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LAN ARCHITECTURE in computer networking.ppt
- 2. ETHERNET LAN ARCHITECTURE • Ethernet is a set of technologies and protocols that are used primarily in LANs. • It was first standardized in 1980s as IEEE 802.3 standard. • Ethernet is classified into two categories: classic Ethernet and switched Ethernet. • Classic Ethernet is the original form of Ethernet that provides data rates between 3 to 10 Mbps. • The varieties are commonly referred as 10BASE-X. Here, 10 is the maximum throughput, i.e. 10 Mbps, BASE denoted use of baseband transmission, and X is the type of medium used.
- 3. ETHERNET LAN ARCHITECTURE Architecture • Classic Ethernet is simplest form of Ethernet. It comprises of an Ethernet medium composed of a long piece of coaxial cable. • Stations can be connected to the coaxial cable using a card called the network interface (NI). • The NIs are responsible for receiving and transmitting data through the network. • Repeaters are used to make end-to-end joins between cable segments as well as re-generate the signals if they weaken. When a station is ready to transmit, it places its frame in the cable. This arrangement is called the broadcast bus.
- 4. ETHERNET LAN ARCHITECTURE The configuration is illustrated as follows −
- 5. ETHERNET LAN ARCHITECTURE Frame Format of Classic Ethernet The main fields of a frame of classic Ethernet are − Preamble: It is a 8 bytes starting field that provides alert and timing pulse for transmission. Destination Address: It is a 6 byte field containing physical address of destination stations. Source Address: It is a 6 byte field containing the physical address of the sending station. Type: It a 2 bytes field that instructs the receiver which process to give the frame to. Data: This is a variable sized field carries the data from the upper layers. The maximum size of data field is 1500 bytes. Padding: This is added to the data to bring its length to the minimum requirement of 46 bytes. CRC: CRC stands for cyclic redundancy check. It contains the error detection information.
- 6. TOKEN RING ARCHITECTURE Token Ring Network (IEEE Standard 802.5) in Computer Network. • In a token ring, a special bit pattern, known as a token, circulates around the ring when all the stations are idle. • Token Ring is formed by the nodes connected in ring format, as shown in the diagram below. • The principle used in the token ring network is that a token is circulating in the ring, and whichever node grabs that token will have the right to transmit the data. • Whenever a station wants to transmit a frame, it inverts a single bit of the 3-byte token, which instantaneously changes it into a normal data packet. • As there is only one token, there can be only one transmission at a time. • Since the token rotates in the ring, it is guaranteed that every node gets the token within some specified time. • So there is an upper bound on the time of waiting to grab the token so that starvation is avoided. • There is also an upper limit of 250 on the number of nodes in the network.
- 8. TOKEN RING ARCHITECTURE Modes of Operation • There are various modes of operations which are as follows • Listen Mode − In the listen mode, the incoming bits are simply transmitted to the output line with no further action taken. • Talk or Transmit Node − The ring interface is set to the talk or transmit node when the station connected to the ring interface has acquired a token. • The direct input to output connection through the single bit buffer is disconnected. • By-pass Mode − This mode reaches when the node is down. Any data is just bypassed. There is no one-bit delay in this mode.
- 9. TOKEN RING ARCHITECTURE Handling Breakage • The main problem with a ring network is that the network goes down when the ring cable breaks down or gets tempered. The solution to this problem is the use of a wire Centre • This wire center bypasses the terminals that have gone down from the ring. • This is done by connecting the bypass relay for that station. These relays are generally controlled by the software that operates automatically in case of station failure. • The use of a wire center improves the reliability and maintainability of the ring network. Priority and Reservation • In IEEE 802.5, each station has a priority code. As a token circulates on the ring, any station which wants to transmit the frame may reserve the token by entering its priority code in the Access Control (AC) field of the token frame or data frame.
- 10. TOKEN RING ARCHITECTURE Time Bounding • A station that is in possession of the token only can transmit his frames. It may transmit one or more data frames but before the expiry of Token Holding Time (THT). Typically, this time is 10 milliseconds. After the THT, the token frame must be handed over to some other station. The Monitor Station • The monitor station sets the timer on when each time the token passes. If the token does not regenerate in the allotted time, it is assumed to be lost, and then the monitor station generates a new token and sends it to the ring. If the monitor fails, a second station is designated as back- up.
- 11. FDDI ARCHITECTURE Fiber Distributed Data Interface (FDDI) Computer Network Computer Engineering MCA • Fiber Distributed Data Interface (FDDI) is a set of ANSI and ISO standards for transmission of data in local area network (LAN) over fiber optic cables. • It is applicable in large LANs that can extend up to 200 kilometers in diameter. Features • FDDI uses optical fiber as its physical medium. It operates in the physical and medium access control (MAC layer) of the Open Systems Interconnection (OSI) network model.
- 12. FDDI ARCHITECTURE • It provides high data rate of 100 Mbps and can support thousands of users. • It is used in LANs up to 200 kilometers for long distance voice and multimedia communication. • It uses ring based token passing mechanism and is derived from IEEE 802.4 token bus standard. • It contains two token rings, a primary ring for data and token transmission and a secondary ring that provides backup if the primary ring fails. • FDDI technology can also be used as a backbone for a wide area network (WAN).
- 13. FDDI ARCHITECTURE The following diagram shows FDDI –
- 14. FDDI ARCHITECTURE Frame Format The frame format of FDDI is similar to that of token bus as shown in the following diagram −
- 15. FDDI ARCHITECTURE The fields of an FDDI frame are − • Preamble: 1 byte for synchronization. • Start Delimiter: 1 byte that marks the beginning of the frame. • Frame Control: 1 byte that specifies whether this is a data frame or control frame. • Destination Address: 2-6 bytes that specifies address of destination station. • Source Address: 2-6 bytes that specifies address of source station. • Payload: A variable length field that carries the data from the network layer. • Checksum: 4 bytes frame check sequence for error detection. • End Delimiter: 1 byte that marks the end of the frame.