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Basic network concepts (Part 5)

Basic network concepts (Part 5). Access Methods. Three major access methods: CSMA/CD CSMA/CA and Token passing. CSMA/CD. Carrier sense multiple access with collision detection (CSMA/CD ) is one of the most popular access methods in use today .

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Basic network concepts (Part 5)

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  1. Basic network concepts (Part 5)

  2. Access Methods • Three major access methods: • CSMA/CD • CSMA/CA and • Token passing

  3. CSMA/CD • Carrier sense multiple access with collision detection (CSMA/CD) • is one of the most popular access methods in use today. • Every host has equal access to the wire and can place data on the wire when the wire is free from traffic. • If a host wishes to place data on the wire, it will “sense” the wire and determine whether there is a signal already on the wire. • If there is, the host will wait to transmit the data; if the wire is free, the host will send the data

  4. CSMA/CD • Carrier sense multiple access with collision detection (CSMA/CD) • The problem with the process just described is that, if there are two systems on the wire that “sense” the wire at the same time to see if the wire is free, they will both send data out at the same time if the wire is free. • When the two pieces of data are sent out on the wire at the same time, they will collide with one another, and the data will be destroyed. • When a system determines that the data has collided and then retransmits the data, that is known as collision detection. • CSMA/CD provides that before a host sends data on the network, it will “sense” (CS) the wire to ensure that the wire is free of traffic. Multiple systems have equal access to the wire (MA), and if there is a collision, a host will detect that collision (CD) and retransmit the data.

  5. CSMA/CD

  6. CSMA/CA • Carrier sense multiple access with collision avoidance (CSMA/CA) • is not as popular as CSMA/CD and for good reason • With CSMA/CA, before a host sends data on the wire, it will “sense” the wire as well to see if the wire is free of signals. • If the wire is free, it will try to “avoid” a collision by sending a piece of “dummy” data on the wire first to see whether it collides with any other data. • If it does not collide, the host in effect assumes “If my dummy data did not collide, then the real data will not collide,” and it submits the real data on the wire.

  7. Token Passing • Token passing takes a totally different approach to deciding on how a system can place data on the wire. • With token passing, there is an empty packet running around on the wire—the “token.” • In order to place data on the wire, you need to wait for the token; once you have the token and it is free of data, you can place your data on the wire. Since there is only one token and a host needs to have the token to “talk,” it is impossible to have collisions in a token-passing environment. • All systems will look at the data, but they will not process it, since it is not destined for them. However, the system that is the intended destination will read the data and send the token back to the sender as a confirmation. Once the token has reached the original sender, the token is unflagged as being used and released as an empty token onto the network.

  8. Network Architectures • Broadband and Baseband • Baseband • Sends digital signals through the media as a single channel that uses the entire bandwidth of the media. • The signal is delivered as a pulse of electricity or light, depending on the type of cabling being used. • Baseband communication is also bidirectional, which means that the same channel can be used to send and receive signals.

  9. Network Architectures • Broadband and Baseband • Broadband • Sends information in the form of an analog signal, which flows as electromagnetic waves or optical waves. • Each transmission is assigned to a portion of the bandwidth, so unlike with baseband communication, it is possible to have multiple transmissions at the same time, with each transmission being assigned its own channel or frequency. • Broadband communication is unidirectional, so in order to send and receive, two pathways will need to be used.

  10. Network Architectures • Ethernet • Ethernet is defined as the IEEE 802.3 standard. •  is a family of frame-based computer networking technologies for local area networks (LANs).

  11. Ethernet • 10Base2 • The 10Base2 Ethernet architecture is a network that runs at 10 Mbps and uses baseband transmissions. 10Base2 typically is implemented as a bus topology, but it could be a mix of a bus and a star topology. • The 2 implies 200 meters. Now, what type of cable is limited to approximately 200 m? You got it; thinnet is limited to approximately 200 m (185 m, to be exact). • All Ethernet environments use CSMA/CD as a way to put data on the wire.

  12. Ethernet • 10Base2 • The following list summarizes features of 10Base2: • Baseband communication • 10 Mbps transfer rate • Maximum distance of 185 meters per network segment • 30 hosts per segment • 0.5 meters minimum distance between hosts

  13. Ethernet • 10Base5 • The 10Base5 Ethernet architecture runs at 10 Mbps and uses baseband transmission as well. It was also implemented as a bus topology. • The cable it uses is limited to approximately 500 meters, which is thicknet, and it uses CSMA/CD as the access method. • The thicker copper core in the wire allows the signal to travel farther than is possible with thinnet.

  14. Ethernet • 10Base5 • The following list summarizes features of 10Base5: • Baseband communication • 10 Mbps transfer rate • Maximum distance of 500 meters per network segment • 100 hosts per segment • 2.5 meter minimum distance between hosts

  15. Ethernet • 10BaseT • The 10BaseT Ethernet architecture runs at 10 Mbps and uses baseband transmission. • It uses a star topology with a hub or switch at the center, allowing all systems to connect to one another. • The cable it uses is CAT 3 UTP, which is the UTP cable type that runs at 10 Mbps. • Keep in mind that most cable types are backward compatible, so you could have CAT 5 UTP cabling in a 10BaseT environment.

  16. Ethernet • 10BaseFL • The 10BaseFL Ethernet architecture allows for a 10 Mbps Ethernet environment that runs on fiber-optic cabling. • The purpose of the fiber-optic cabling is to use it as a backbone to allow the network to reach greater distances. • FL – Fiber Optic Link

  17. Ethernet • Fast Ethernet (100BaseTX and 100BaseFX) • These two standards are part of the 100BaseX family, which is known as fast Ethernet. • The different fast Ethernet flavors run at 100 Mbps, use a star topology, use CSMA/CD as an access method, but differ in the type of cabling used. • 100BaseTX uses two pairs (four wires) in the CAT 5 cabling, whereas 100BaseFX uses two strands of fiber instead of twisted-pair cabling.

  18. Ethernet • Gigabit Ethernet • Gigabit Ethernet is becoming the de facto standard for network architectures today. • With Gigabit Ethernet we can reach transfer rates of 1000 Mbps (1 Gbps), using traditional media such as coaxial, twisted-pair, and fiber-optic cabling. • There are two standards for Gigabit Ethernet: IEEE 802.3z and IEEE 802.3ab.

  19. Ethernet • IE 802.3z • The IEEE 802.3z standard defines Gigabit Ethernet that runs over fiber-optic cabling or coaxial cabling. • There are three types of Gigabit Ethernet that fall under this standard: • 1000BaseSX • The Gigabit Ethernet architecture that runs at 1000 Mbps over multimode fiber (MMF) optic cabling. This architecture is designed for short distances of up to 550 meters.

  20. Ethernet • IE 802.3z • 1000BaseLX • The Gigabit Ethernet architecture that runs at 1000 Mbps over single-mode fiber (SMF) optic cabling. This architecture supports distances up to 3 kilometers. • 1000BaseCX • The Gigabit Ethernet architecture that runs at 1000 Mbps over coaxial cable and supports distances of up to 25 meters.

  21. Ethernet • IE 802.3ab • The IEEE 802.3ab standard, known as 1000BaseTX, defines Gigabit Ethernet that runs over twisted-pair cabling and uses characteristics of 100BaseTX networking, including the use of RJ-45 connectors and the access method of CSMA/CD. Like 100BaseTX, 1000BaseTX uses CAT 5e or CAT 6 unshielded twisted-pair; the difference is that 100BaseTX runs over two pairs (four wires) while 1000BaseTX runs over four pairs (all eight wires)

  22. Ethernet • 10-Gigabit Ethernet • There are standards for 10-Gigabit Ethernet (10,000 Mbps) that have been developed that use fiber-optic cabling: • 10GBaseSR • Runs at 10 Gbps and uses “short-range” multimode fiber-optic cable, which has a maximum distance of 100 meters. • 10GBaseLR • Runs at 10 Gbps and uses “long-range” single-mode fiber-optic cable, which has a maximum distance of 10 kilometers. • 10GBaseER • Runs at 10 Gbps and uses “extra-long-range” single-mode fiber-optic cable, which has a maximum distance of 40 kilometers. • 10GBaseT • Runs at 10 Gbps using CAT 6 UTP cabling, which has a maximum distance of 100 meters.

  23. Ethernet • 10-Gigabit Ethernet • There are special WAN versions of 10-Gigabit Ethernet that use fiber-optic cabling to connect to a SONET network. • SONET - Synchronous Optical Networking • 10GBaseSW • The 10-Gigabit Ethernet standard for short-range, multimode fiber-optic cable, which has a maximum distance of 100 meters • 10GBaseLW • The 10-Gigabit Ethernet standard for long-range, singlemodefiber-optic cable, which has a maximum distance of 10 kilometers • 10GBaseEW • The 10-Gigabit Ethernet standard for extended-range, singlemodefiber-optic cable, which has a distance of up to 40 kilometers

  24. Network Architectures • Token Ring • A big competitor to Ethernet in the past was Token Ring, which runs at 4 Mbps or 16 Mbps. • Token Ring is a network architecture that uses a star ring topology (a hybrid, looking physically like a star but logically wired as a ring) and can use many forms of cables. • Token Ring is defined as the IEEE 802.5 standard. • IBM Token Ring has its own proprietary cable types, while more modern implementations of Token Ring can use CAT 3 or CAT 5 UTP cabling.

  25. Token Ring • Token Ring • Token Ring uses the token-passing access method. • The reason this network architecture appears to use a star topology is that all hosts are connected to a central device that looks similar to a hub, but with Token Ring, this device is called a multistation access unit (MAU or MSAU). • Token Ring uses token passing; it is impossible to have collisions in a tokenpassing environment, because the MAUs do not have collisions lights as an Ethernet hub does

  26. Token Ring

  27. Network Architectures • FDDI • Fiber distributed data interface (FDDI) is a network architecture that uses fiber-optic cabling, token passing, and a ring topology, but FDDI also uses two counter-rotating rings for fault tolerance on the network.

  28. Network Architectures

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