lengths between stations can be anywhere from 2 kilometers (km) with multimode fiber, to 60 km with single-mode fiber.total ring length cannotexceed a maximum of 200km. FDDI was developed by the American National Standards Institute (ANSI) X3T9.5 standards committee in the mid-1980s.
Please do mention ->>FDDI uses counter-rotating primary and secondary rings.An FDDI concentrator (also called a dual-attachment concentrator [DAC]) is the building block of an FDDI network. It attaches directly to both the primary and secondary rings and ensures that the failure or power-down of any SAS does not bring down the ring. This is particularly useful when PCs, or similar devices that are frequently powered on and off, connect to the ring.
FDDI deﬁnes three type s of devices: single-attachment station (SAS), dual-attachment station (DAS), and a concentrator.An SAS attaches to only one ring (the primary) through a concentrator. One of the primary advantages of connecting devices with SAS attachments is that the devices will not have any effect on the FDDI ring if they are disconnected or powered off.Each FDDI DAS has two ports, designated A and B. These ports connect the DAS to the dual FDDI ring. Therefore, each port provides a connection for both the primary and the secondary ring.
Although not part of the FDDI standard, the Logical Link Control (LLC) is required by FDDI to assure transmission of user data.The PMD, SMF-PMD, and PHY are equivalent to the physical layer of the OSI model. The PLM defines the media requirements for multimode fiber, such as fiber optic cable, connecters and driver receiver operation for FDDI stations. SMD-PMD defines similar requirements for SMF optic media.PHY corresponds to the upper layer of the physical layer and defines the symbol set, link states and encoding/ decoding,clocking and framing.
Before FDDI <br />Groups that previously had no need for communication now want network connections.<br />Existing token ring and Ethernet backbones that are interconnected are now reaching their capacity.<br />Applications require increasing bandwidth, security, and fault tolerance.<br />
Introduction<br />What is FDDI?<br /> - speciﬁes a 100-Mbps token-passing<br /> - dual-ring LAN<br /> - using ﬁber-optic cable<br />Bandwidth Supported – 200Mbps<br />Coverage – 200 km <br /> - Multimode -> 2km<br /> - Single mode -> 60km<br />Developed by the American National Standards Institute (ANSI) X3T9.5 standards committee in the mid-1980s. <br />
Minimum Ethernet Frame Length issue<br />When link speed increases from 100 Mbps to 1000 Mbps, for half-duplex CSMA/CD to work well (to be able to detect collision<br />Reduce the network size by a factor of 10 to only 20 meter<br />Not acceptable<br />Or increase the minimum Ethernet frame length by a factor of 10<br />Network efficiency will decrease.<br />Higher layer protocols needs to be modified.<br />12- 18<br />
Carrier Extension<br />Gigabit Ethernet does not want to modify application programs. <br />We want application programs to still use 64 bytes as the minimum frame size. Ideally, they should not need to know whether they are using Ethernet, Fast Ethernet, or Gigabit Ethernet. <br />However, to be able to detect collision, the minimum frame size must be enlarged from 64 bytes to 512 bytes (4096 bits).<br />Carrier extension is introduced to insert padding at the MAC layer so that every transmitted frame is at least 512 bytes.<br />12- 19<br />
Frame Bursting<br />Although carrier extension solves the collision detection problem, the link utilization can be very low. <br />If every transmitted frame is a minimum-sized frame, because in every transmitted 512 bytes, there are only 64 useful bytes. The effective link utilization is only 64/512 = 12.5%<br />Frame bursting is introduced to improve link utilization.<br />12- 20<br />
Frame Bursting<br />If the source host has many small frames to send, it can send them in a burst after a MAC arbitration.<br />Except for the first frame, other frames sent in a burst need not be carrier-extended. <br />If the first frame is larger than 512 bytes, it need not be carrier-extended.<br />The burst can be as long as 8192 bytes.<br />12- 21<br />
Why Doing Carrier Extension for the First Frame in a Burst?<br />First, if there is no carrier extension, when collision happens, the sending host may have sent out many small frames. If the sending host resends all frames that have been sent, two problems may occur:<br />They may already be removed from the buffer.<br />The receiver may receive duplicate frames.<br />Second, if there is carrier extension and collision is detected in this period, the sending host knows that only the first frame should be retransmitted.<br />Third, if there is carrier extension and there is no collision detected in this period, the sending host can be assured that no collision will happen in the future. <br />12- 22<br />
Gigabit Ethernet over copper<br />Cable configuration – 1000BASE-T provides 1Gbps Ethernet signal transmission over four pairs of Category-5 UTP cable. 250Mbps per wire pair multiplied by 4 pairs = 1000Mbps<br />Distances – The copper standard covers cabling distances of up to 100 meters, or networks with a diameter of 200 meters (assumes 100 meters in two directions from a switch).<br />Half duplex and CSMA/CD – Although the standard includes half-duplex operation, few Gigabit products support half duplex to date. Full duplex is preferred to maximize performance. Gigabit Ethernet uses the CSMA/CD protocol only when running in half-duplex mode.<br />Full duplex and flow control – In full duplex, CSMA/CD collision detection is impractical. Instead, flow control methodology is used to avoid congestion and overloading.<br />The cost of a 1000BASE-T network adapter is much cheaper than that of a 1000BASE-X network adapter. <br />12- 23<br />
12- 24<br />Gigabit Ethernet Equipment<br />1000 Base X<br />1000 Base T<br />
Advantages<br />Increased bandwidth for higher performance and elimination of bottlenecks<br />Full-duplex capacity, allowing the effective bandwidth to be virtually doubled<br />Aggregating bandwidth to multi- Gigabit speeds using Gigabit server adapters and switches<br />Low cost of acquisition and ownership<br />Full compatibility with the large installed base of Ethernet and Fast Ethernet nodes<br />Transferring large amounts of data across a network quickly<br />12- 25<br />