10 high speedla-ns
DESCRIPTION
TRANSCRIPT
High Speed LANs
Data and Computer Communications
IntroductionIEEE 802.3 standard (Ethernet) cover data rates
of:10 Mbps(Ethernet), 100 Mbps(Fast Ethernet)
CSMA/CD MAC protocol 1Gbps and 10 Gbps (Gigabit Ethernet)
switched technique
Range of technologiesFast and Gigabit Ethernet
Extention of 10 Mbps CSMA/CD to higher speedsFibre Channel switched technique
Provides a low-cost, easy approach to achieve very high data rates
High Speed Wireless LANs
(CSMA/CD : carrier sense multiple access with collision detection)
Why High Speed LANs?Office LANs used to provide basic connectivity
Connecting PCs and terminals to mainframes and midrange systems that ran corporate applications
Providing workgroup connectivity at departmental level
Emphasis on file transfer and electronic mailSpeed and power of PCs has risen
Graphics-intensive applications and GUIsMIS (Management information Systems)
organizations recognize LANs as essential Began with client/server computing
Now dominant architecture in business environment IntranetworksFrequent transfer of large volumes of data
'MIS' is a planned system of collecting, storing and disseminating data in the form of information needed to carry out the functions of management.
Applications Requiring High Speed LANsCentralized server farms
User needs to draw huge amounts of data from multiple centralized servers(servers farms)
E.g. Color publishing Servers contain tens of gigabytes of image data Downloaded to imaging workstations
Power workgroupsSmall number of cooperating usersDraw massive data files across networkE.g. Software development group testing new software
version or computer-aided design (CAD) running simulations
High-speed local backboneProcessing demand growsLANs grow at siteHigh-speed interconnection is necessary
IEEE802.3 Medium Access ControlCDMA/CD and its ancestor can be termed random access, or contention, techniques.
Random Access Stations access medium randomly
Contention (fight)Stations content for time on medium
Scheme from which CSMA/CD evolved ALOHA / pure ALOHASlotted ALOHACSMA algorithm used: nonpersistent CSMA,
1-persistent protocol, p-persistent
ALOHA / pure ALOHADeveloped for packet radio network
a station can transmit a frame at any timeWhen station has frame, it sends
Station listens (for max round trip time)plus small increment
If ACK, fine. If not, retransmitIf no ACK after repeated transmissions, give upReceiving station:Frame check sequence (as in HDLC)If frame OK and address matches receiver, send ACK
Frame may be damaged by noise or by another station transmitting at the same time (collision)
Any overlap of frames causes collisionIf frame received is determined to be invalid, receiving
station ignores itMax utilization 18%
(collision rises rapidly with increased load)
Slotted ALOHATo prove efficiency, time on the channel is
organized into uniform slots equal to frame transmission time
Need central clock (or other sync mechanism)
Transmission permitted only to begin at slot boundary
Frames either miss or overlap totallyMax utilization 37%
Pure ALOHA vs Slotted ALOHAIn pure Aloha, a user can transmit at any
time but risks collisions with other users' messages.
"Slotted Aloha" reduces the chance of collisions by dividing the channel into time slots and requiring that the user send only at the beginning of a time slot.
CSMA (carrier sense multiple access)A station wishing to transmit first listens to the
medium to determine if another transmission is in progress (carrier sense)
All stations know that a transmission has started almost immediatelyFirst listen for clear medium (carrier sense)If medium idle, transmit
If two stations start at the same instant, collisionWait reasonable time (round trip plus ACK
contention)No ACK then retransmit
No ACK = collision
CSMA (carrier sense multiple access)Max utilization depends on propagation time
(medium length) and frame lengthLonger frame and shorter propagation gives
better utilizationBetter than ALOHA and slotted ALOHA
With CSMA, an algorithm is needed to specify what a station should do if the medium is found busy.nonpersistent CSMA,1-persistent protocol p-persistent
Nonpersistent CSMA- attempts to reduce collision1. If medium is idle, transmit; otherwise, go to 22. If medium is busy, wait amount of time drawn
from probability distribution (retransmission delay) and repeat 1
Random delays reduces probability of collisions Consider two stations become ready to transmit at
same time While another transmission is in progress
If both stations delay same time before retrying, both will attempt to transmit at same time
Capacity is wasted because medium will remain idle following end of transmission Even if one or more stations waiting
Nonpersistent stations deferential
1-persistent CSMA-attempts to reduce idle time To avoid idle channel time, 1-persistent
protocol used Station wishing to transmit listens and
obeys following: 1. If medium idle, transmit; otherwise, go to
step 22. If medium busy, listen until idle; then
transmit immediately 1-persistent stations selfish If two or more
stations waiting, collision guaranteed Gets sorted out after collision
P-persistent CSMA Compromise that attempts to reduce collisions
Like nonpersistent And reduce idle time
Like1-persistent Rules:1. If medium idle, transmit with probability p, and
delay one time unit with probability (1 – p) Time unit typically maximum propagation delay
2. If medium busy, listen until idle and repeat step 1
3. If transmission is delayed one time unit, repeat step 1
CSMA/CD With CSMA, collision occupies medium for
duration of transmission Medium unusable waste
CSMA/CD :To reduce waste, stations listen whilst transmitting
1. If medium idle, transmit, otherwise, step 22. If busy, listen for idle, then transmit3. If collision detected, transmit a jamming signal then
cease transmission (backoff)4. After jam, wait random time then start from step
1IEEE 802.3 uses 1-persistent IEEE 802.3 uses 1-persistent algorithm
CSMA/CDOperation
IEEE 802.3 Frame Format
10Mbps Specification (Ethernet)In Ethernet, IEEE defines types of cable, connections, and signals used( physical layer standards)
<data rate><Signaling method><Max segment length>
10Base5 10Base2 10Base-T 10Base-F
Medium Coaxial Coaxial UTP 850nm fiberSignaling Baseband Baseband Baseband Manchester
Manchester Manchester ManchesterOn/Off
Max length500m 185m 100m 500mTopology Bus Bus Star StarNodes 100 30 - 33
100Mbps Fast EthernetUse IEEE 802.3 MAC protocol and frame
format100BASE-X use physical medium
specifications from FDDITwo physical links between nodes
Transmission and reception
Star-wire topologySimilar to 10BASE-T
100Mbps Specification (Ethernet)
In Ethernet, IEEE defines types of cable, connections, and signals used( physical layer standards)
<data rate><Signaling method><Max segment length>
100Base-TX 100Base-TX 100Base-FX 100Base-T4
Medium 2 pair, STP 2 pair, Cat 5 UTP 2 optical fiber 4 pair, cat 3,4,5
Signaling MLT-3 MLT-3 NRZI NRZ
Max length 100m 100m 100m 100m
Data rate 100Mbps 100Mbps 100Mbps 100Mbps
100BASE-T Options
Full Duplex OperationTraditional Ethernet half duplex
Either transmit or receive but not both simultaneouslyWith full-duplex, station can transmit and receive
simultaneously100-Mbps Ethernet in full-duplex mode, theoretical
transfer rate 200 MbpsAttached stations must have full-duplex adapter cards
(traditional Ethernet: half-duplex adapter cards)Must use switching hub (traditional Ethernet: multiport repeater /hub)
Each station constitutes separate collision domainIn fact, no collisionsCSMA/CD algorithm no longer needed802.3 MAC frame format usedAttached stations can continue CSMA/CD
Mixed ConfigurationsFast Ethernet supports mixture of existing 10-
Mbps LANs and newer 100-Mbps LANsE.g. 100-Mbps backbone LAN to support 10-
Mbps hubsStations attach to 10-Mbps hubs using 10BASE-T Hubs connected to switching hubs using 100BASE-T
Support 10-Mbps and 100-MbpsHigh-capacity workstations and servers attach directly
to 10/100 switchesSwitches connected to 100-Mbps hubs using 100-Mbps
links100-Mbps hubs provide building backbone
Connected to router providing connection to WAN
Gigabit Ethernet Configuration
Gigabit Ethernet – PhysicalIn Ethernet, IEEE defines types of cable,
connections, and signals used( physical standards)
1000Base-SXShort wavelength, multimode fiber
1000Base-LXLong wavelength, Multi or single mode fiber
1000Base-CXCopper jumpers <25m, shielded twisted pair
1000Base-T4 pairs, cat 5 UTP
Signaling (encoding scheme) - 8B/10B
Gbit Ethernet Medium Options(log scale)
10Gbps Ethernet - Uses High-speed, local backbone interconnection between
large-capacity switches Server farm Campus wide connectivity Enables Internet service providers (ISPs) and network
service providers (NSPs) to create very high-speed links at very low cost
Allows construction of (MANs) and WANsConnect geographically dispersed LANs between campuses
or points of presence (PoPs) Ethernet competes with ATM and other WAN
technologies 10-Gbps Ethernet provides considerable value over ATM
10Gbps Ethernet - Physical Maximum link distances cover 300 m to 40 km Full-duplex mode only 10GBASE-S (short):
850 nm on multimode fiberUp to 300 m
10GBASE-L (long)1310 nm on single-mode fiberUp to 10 km
10GBASE-E (extended)1550 nm on single-mode fiberUp to 40 km
10GBASE-LX4:1310 nm on single-mode or multimode fiberUp to 10 kmWavelength-division multiplexing (WDM) bit stream across four
light waves
10Gbps Ethernet Distance Options (log scale)
Token Ring (802.5)Developed from IBM's commercial token
ringBecause of IBM's presence, token ring has
gained broad acceptanceNever achieved popularity of EthernetCurrently, large installed base of token ring
products
Ring OperationEach repeater connects to two others via
unidirectional transmission linksSingle closed pathData transferred bit by bit from one repeater to
the nextRepeater regenerates and retransmits each bitRepeater performs data insertion, data
reception, data removalRepeater acts as attachment pointPacket removed by transmitter after one trip
round ring
802.5 MAC ProtocolSmall frame (token) circulates when idleStation waits for tokenChanges one bit in token to make it SOF (start of
frame) for data frameAttach rest of data frameFrame makes round trip and is absorbed by
transmitting stationStation then inserts new token when transmission
has finished and leading edge of returning frame arrives
Under light loads, some inefficiencyUnder heavy loads, round robin
Token RingOperation
Fibre Channel - BackgroundData comms with processor:I/O channel
Direct point to point or multipoint comms linkHardware basedHigh SpeedVery short distanceUser data moved from source buffer to destination
bufferNetwork connection
Interconnected access pointsSoftware based protocolFlow control, error detection &recoveryEnd systems connections
Fibre ChannelBest of both technologiesChannel oriented
Simplicity and speedNetwork oriented
Flexibility and interconnectivity
Fibre Channel RequirementsFull duplex links with two fibers per link100 Mbps to 800 Mbps on single line
Full duplex 200 Mbps to 1600 Mbps per linkUp to 10 kmSupports simple encoding and framing schemeIn turn supports a variety of channel and
network protocols
Fibre Channel ElementsEnd systems - NodesSwitched elements - the network or fabricCommunication across point to point links
Fibre Channel Network
Fibre Channel Protocol Architecture (1)Fibre Channel standard is organized into five levels:FC-0 Physical Media
Optical fiber for long distancecoaxial cable for high speed short distanceSTP for lower speed short distance
FC-1 Transmission Protocol8B/10B signal encoding
FC-2 Framing ProtocolTopologiesFraming formatsFlow and error controlSequences and exchanges (logical grouping of frames)
FC-3 Common ServicesIncluding multicasting
FC-4 MappingMapping of channel and network services onto fibre channel
e.g. IEEE 802, ATM, IP, SCSI
Fibre Channel Physical MediaProvides range of options for physical
medium, the data rate on medium, and topology of network
Shielded twisted pair, video coaxial cable, and optical fiber
Data rates 100 Mbps to 3.2 GbpsPoint-to-point from 33 m to 10 km
Fabric AdvantagesScalability of capacity
As additional ports added, aggregate capacity of network increases
Minimizes congestion and contentionIncreases throughput
Protocol independentDistance insensitiveSwitch and transmission link technologies may
change without affecting overall configurationBurden on nodes minimized
Fibre Channel node responsible for managing point-to-point connection between itself and fabric
Fabric responsible for routing and error detection
Alternative TopologiesPoint-to-point topology
Only two portsDirectly connected, with no intervening
switchesNo routing
Arbitrated loop topologySimple, low-cost topologyUp to 126 nodes in loopOperates roughly equivalent to token ring
Topologies, transmission media, and data rates may be combined
Five Applications of Fibre Channel
END!!