ECS 152A

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ECS 152A

• 9. Local Area Networks

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LAN Applications (1)

• Personal computer LANs
• Low cost
• Limited data rate
• Back end networks
• Interconnecting large systems (mainframes and
  large storage devices)
• High data rate
• High speed interface
• Distributed access
• Limited distance
• Limited number of devices

3
LAN Applications (2)

• Storage Area Networks
• Separate network handling storage needs
• Detaches storage tasks from specific servers
• Shared storage facility across high-speed network
• Hard disks, tape libraries, CD arrays
• Improved client-server storage access
• Direct storage to storage communication for
  backup
• High speed office networks
• Desktop image processing
• High capacity local storage
• Backbone LANs
• Interconnect low speed local LANs
• Reliability
• Capacity
• Cost

4
Storage Area Networks
5
LAN Architecture

• Topologies
• Transmission medium
• Layout
• Medium access control

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Topologies

• Tree
• Bus
• Special case of tree
• One trunk, no branches
• Ring
• Star

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LAN Topologies
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Bus and Tree

• Multipoint medium
• Transmission propagates throughout medium
• Heard by all stations
• Need to identify target station
• Each station has unique address
• Full duplex connection between station and tap
• Allows for transmission and reception
• Need to regulate transmission
• To avoid collisions
• To avoid hogging
• Data in small blocks - frames
• Terminator absorbs frames at end of medium

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Frame Transmissionon Bus LAN
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Ring Topology

• Repeaters joined by point to point links in
  closed loop
• Receive data on one link and retransmit on
  another
• Links unidirectional
• Stations attach to repeaters
• Data in frames
• Circulate past all stations
• Destination recognizes address and copies frame
• Frame circulates back to source where it is
  removed
• Media access control determines when station can
  insert frame

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Frame TransmissionRing LAN
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Star Topology

• Each station connected directly to central node
• Usually via two point to point links
• Central node can broadcast
• Physical star, logical bus
• Only one station can transmit at a time
• Central node can act as frame switch

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Choice of Topology

• Reliability
• Expandability
• Performance
• Needs considering in context of
• Medium
• Wiring layout
• Access control

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Bus LAN Transmission Media (1)

• Twisted pair
• Early LANs used voice grade cable
• Didnt scale for fast LANs
• Not used in bus LANs now
• Baseband coaxial cable
• Uses digital signalling
• Original Ethernet

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Bus LAN Transmission Media (2)

• Broadband coaxial cable
• As in cable TV systems
• Analog signals at radio frequencies
• Expensive, hard to install and maintain
• No longer used in LANs
• Optical fiber
• Expensive taps
• Better alternatives available
• Not used in bus LANs
• All hard to work with compared with star topology
  twisted pair
• Coaxial baseband still used but not often in new
  installations

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Ring and Star Usage

• Ring
• Very high speed links over long distances
• Single link or repeater failure disables network
• Star
• Uses natural layout of wiring in building
• Best for short distances
• High data rates for small number of devices

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Choice of Medium

• Constrained by LAN topology
• Capacity
• Reliability
• Types of data supported
• Environmental scope

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Media Available (1)

• Voice grade unshielded twisted pair (UTP)
• Cat 3
• Cheap
• Well understood
• Use existing telephone wiring in office building
• Low data rates
• Shielded twisted pair and baseband coaxial
• More expensive than UTP but higher data rates
• Broadband cable
• Still more expensive and higher data rate

19
Media Available (2)

• High performance UTP
• Cat 5 and above
• High data rate for small number of devices
• Switched star topology for large installations
• Optical fiber
• Electromagnetic isolation
• High capacity
• Small size
• High cost of components
• High skill needed to install and maintain
• Prices are coming down as demand and product
  range increases

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Protocol Architecture

• Lower layers of OSI model
• IEEE 802 reference model
• Physical
• Logical link control (LLC)
• Media access control (MAC)

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IEEE 802 v OSI
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802 Layers - Physical

• Encoding/decoding
• Preamble generation/removal
• Bit transmission/reception
• Transmission medium and topology

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802 Layers -Logical Link Control

• Interface to higher levels
• Flow and error control

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Logical Link Control

• Transmission of link level PDUs between two
  stations
• Must support multiaccess, shared medium
• Relieved of some link access details by MAC layer
• Addressing involves specifying source and
  destination LLC users
• Referred to as service access points (SAP)
• Typically higher level protocol

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LLC Services

• Based on HDLC
• Unacknowledged connectionless service
• Connection mode service
• Acknowledged connectionless service

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LLC Protocol

• Modeled after HDLC
• Asynchronous balanced mode to support connection
  mode LLC service (type 2 operation)
• Unnumbered information PDUs to support
  Acknowledged connectionless service (type 1)
• Multiplexing using LSAPs

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Media Access Control

• Assembly of data into frame with address and
  error detection fields
• Disassembly of frame
• Address recognition
• Error detection
• Govern access to transmission medium
• Not found in traditional layer 2 data link
  control
• For the same LLC, several MAC options may be
  available

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LAN Protocols in Context
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Media Access Control

• Where
• Central
• Greater control
• Simple access logic at station
• Avoids problems of co-ordination
• Single point of failure
• Potential bottleneck
• Distributed
• How
• Synchronous
• Specific capacity dedicated to connection
• Asynchronous
• In response to demand

30
Asynchronous Systems

• Round robin
• Good if many stations have data to transmit over
  extended period
• Reservation
• Good for stream traffic
• Contention
• Good for bursty traffic
• All stations contend for time
• Distributed
• Simple to implement
• Efficient under moderate load
• Tend to collapse under heavy load

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MAC Frame Format

• MAC layer receives data from LLC layer
• MAC control
• Destination MAC address
• Source MAC address
• LLS
• CRC
• MAC layer detects errors and discards frames
• LLC optionally retransmits unsuccessful frames

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Generic MAC Frame Format
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Bridges

• Ability to expand beyond single LAN
• Provide interconnection to other LANs/WANs
• Use Bridge or router
• Bridge is simpler
• Connects similar LANs
• Identical protocols for physical and link layers
• Minimal processing
• Router more general purpose
• Interconnect various LANs and WANs
• see later

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Why Bridge?

• Reliability
• Performance
• Security
• Geography

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Functions of a Bridge

• Read all frames transmitted on one LAN and accept
  those address to any station on the other LAN
• Using MAC protocol for second LAN, retransmit
  each frame
• Do the same the other way round

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Bridge Operation
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Bridge Design Aspects

• No modification to content or format of frame
• No encapsulation
• Exact bitwise copy of frame
• Minimal buffering to meet peak demand
• Contains routing and address intelligence
• Must be able to tell which frames to pass
• May be more than one bridge to cross
• May connect more than two LANs
• Bridging is transparent to stations
• Appears to all stations on multiple LANs as if
  they are on one single LAN

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Bridge Protocol Architecture

• IEEE 802.1D
• MAC level
• Station address is at this level
• Bridge does not need LLC layer
• It is relaying MAC frames
• Can pass frame over external comms system
• e.g. WAN link
• Capture frame
• Encapsulate it
• Forward it across link
• Remove encapsulation and forward over LAN link

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Connection of Two LANs
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Fixed Routing

• Complex large LANs need alternative routes
• Load balancing
• Fault tolerance
• Bridge must decide whether to forward frame
• Bridge must decide which LAN to forward frame on
• Routing selected for each source-destination pair
  of LANs
• Done in configuration
• Usually least hop route
• Only changed when topology changes

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Bridges and LANs withAlternativeRoutes
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Spanning Tree

• Bridge automatically develops routing table
• Automatically update in response to changes
• Frame forwarding
• Address learning
• Loop resolution

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Frame forwarding

• Maintain forwarding database for each port
• List station addresses reached through each port
• For a frame arriving on port X
• Search forwarding database to see if MAC address
  is listed for any port except X
• If address not found, forward to all ports except
  X
• If address listed for port Y, check port Y for
  blocking or forwarding state
• Blocking prevents port from receiving or
  transmitting
• If not blocked, transmit frame through port Y

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Address Learning

• Can preload forwarding database
• Can be learned
• When frame arrives at port X, it has come form
  the LAN attached to port X
• Use the source address to update forwarding
  database for port X to include that address
• Timer on each entry in database
• Each time frame arrives, source address checked
  against forwarding database

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Spanning Tree Algorithm

• Address learning works for tree layout
• i.e. no closed loops
• For any connected graph there is a spanning tree
  that maintains connectivity but contains no
  closed loops
• Each bridge assigned unique identifier
• Exchange between bridges to establish spanning
  tree

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Loop of Bridges
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Layer 2 and Layer 3 Switches

• Now many types of devices for interconnecting
  LANs
• Beyond bridges and routers
• Layer 2 switches
• Layer 3 switches

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Hubs

• Active central element of star layout
• Each station connected to hub by two lines
• Transmit and receive
• Hub acts as a repeater
• When single station transmits, hub repeats signal
  on outgoing line to each station
• Line consists of two unshielded twisted pairs
• Limited to about 100 m
• High data rate and poor transmission qualities of
  UTP
• Optical fiber may be used
• Max about 500 m
• Physically star, logically bus
• Transmission from any station received by all
  other stations
• If two stations transmit at the same time,
  collision

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Hub Layouts

• Multiple levels of hubs cascaded
• Each hub may have a mixture of stations and other
  hubs attached to from below
• Fits well with building wiring practices
• Wiring closet on each floor
• Hub can be placed in each one
• Each hub services stations on its floor

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Two Level Star Topology
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Buses and Hubs

• Bus configuration
• All stations share capacity of bus (e.g. 10Mbps)
• Only one station transmitting at a time
• Hub uses star wiring to attach stations to hub
• Transmission from any station received by hub and
  retransmitted on all outgoing lines
• Only one station can transmit at a time
• Total capacity of LAN is 10 Mbps
• Improve performance with layer 2 switch

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Shared Medium Bus and Hub
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Shared Medium Hub andLayer 2 Switch
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Layer 2 Switches

• Central hub acts as switch
• Incoming frame from particular station switched
  to appropriate output line
• Unused lines can switch other traffic
• More than one station transmitting at a time
• Multiplying capacity of LAN

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Layer 2 Switch Benefits

• No change to attached devices to convert bus LAN
  or hub LAN to switched LAN
• For Ethernet LAN, each device uses Ethernet MAC
  protocol
• Device has dedicated capacity equal to original
  LAN
• Assuming switch has sufficient capacity to keep
  up with all devices
• For example if switch can sustain throughput of
  20 Mbps, each device appears to have dedicated
  capacity for either input or output of 10 Mbps
• Layer 2 switch scales easily
• Additional devices attached to switch by
  increasing capacity of layer 2

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Types of Layer 2 Switch

• Store-and-forward switch
• Accepts frame on input line
• Buffers it briefly,
• Then routes it to appropriate output line
• Delay between sender and receiver
• Boosts integrity of network
• Cut-through switch
• Takes advantage of destination address appearing
  at beginning of frame
• Switch begins repeating frame onto output line as
  soon as it recognizes destination address
• Highest possible throughput
• Risk of propagating bad frames
• Switch unable to check CRC prior to retransmission

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Layer 2 Switch v Bridge

• Layer 2 switch can be viewed as full-duplex hub
• Can incorporate logic to function as multiport
  bridge
• Bridge frame handling done in software
• Switch performs address recognition and frame
  forwarding in hardware
• Bridge only analyzes and forwards one frame at a
  time
• Switch has multiple parallel data paths
• Can handle multiple frames at a time
• Bridge uses store-and-forward operation
• Switch can have cut-through operation
• Bridge suffered commercially
• New installations typically include layer 2
  switches with bridge functionality rather than
  bridges

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Problems with Layer 2 Switches (1)

• As number of devices in building grows, layer 2
  switches reveal some inadequacies
• Broadcast overload
• Lack of multiple links
• Set of devices and LANs connected by layer 2
  switches have flat address space
• Allusers share common MAC broadcast address
• If any device issues broadcast frame, that frame
  is delivered to all devices attached to network
  connected by layer 2 switches and/or bridges
• In large network, broadcast frames can create big
  overhead
• Malfunctioning device can create broadcast storm
• Numerous broadcast frames clog network

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Problems with Layer 2 Switches (2)

• Current standards for bridge protocols dictate no
  closed loops
• Only one path between any two devices
• Impossible in standards-based implementation to
  provide multiple paths through multiple switches
  between devices
• Limits both performance and reliability.
• Solution break up network into subnetworks
  connected by routers
• MAC broadcast frame limited to devices and
  switches contained in single subnetwork
• IP-based routers employ sophisticated routing
  algorithms
• Allow use of multiple paths between subnetworks
  going through different routers

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Problems with Routers

• Routers do all IP-level processing in software
• High-speed LANs and high-performance layer 2
  switches pump millions of packets per second
• Software-based router only able to handle well
  under a million packets per second
• Solution layer 3 switches
• Implementpacket-forwarding logic of router in
  hardware
• Two categories
• Packet by packet
• Flow based

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Packet by Packet or Flow Based

• Operates insame way as traditional router
• Order of magnitude increase in performance
  compared to software-based router
• Flow-based switch tries to enhance performance by
  identifying flows of IP packets
• Same source and destination
• Done by observing ongoing traffic or using a
  special flow label in packet header (IPv6)
• Once flow is identified, predefined route can be
  established

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Typical Large LAN Organization

• Thousands to tens of thousands of devices
• Desktop systems links 10 Mbps to 100 Mbps
• Into layer 2 switch
• Wireless LAN connectivity available for mobile
  users
• Layer 3 switches at local network's core
• Form local backbone
• Interconnected at 1 Gbps
• Connect to layer 2 switches at 100 Mbps to 1 Gbps
• Servers connect directly to layer 2 or layer 3
  switches at 1 Gbps
• Lower-cost software-based router provides WAN
  connection
• Circles in diagram identify separate LAN
  subnetworks
• MAC broadcast frame limited to own subnetwork

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Typical Large LAN OrganizationDiagram
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High Speed LANs

• Range of technologies
• Fast and Gigabit Ethernet
• Fibre Channel
• High Speed Wireless LANs

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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
• Traffic patterns light
• Emphasis on file transfer and electronic mail
• Speed and power of PCs has risen
• Graphics-intensive applications and GUIs
• MIS organizations recognize LANs as essential
• Began with client/server computing
• Now dominant architecture in business environment
• Intranetworks
• Frequent transfer of large volumes of data 

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Applications Requiring High Speed LANs

• Centralized server farms
• User needs to draw huge amounts of data from
  multiple centralized servers
• E.g. Color publishing
• Servers contain tens of gigabytes of image data
• Downloaded to imaging workstations
• Power workgroups
• Small number of cooperating users
• Draw massive data files across network
• E.g. Software development group testing new
  software version or computer-aided design (CAD)
  running simulations
• High-speed local backbone
• Processing demand grows
• LANs proliferate at site
• High-speed interconnection is necessary

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Ethernet (CSMA/CD)

• Carriers Sense Multiple Access with Collision
  Detection
• Xerox - Ethernet
• IEEE 802.3

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IEEE802.3 Medium Access Control

• Random Access
• Stations access medium randomly
• Contention
• Stations content for time on medium

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ALOHA

• Packet Radio
• When station has frame, it sends
• Station listens (for max round trip time)plus
  small increment
• If ACK, fine. If not, retransmit
• If no ACK after repeated transmissions, give up
• 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 collision
• Max utilization 18

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Slotted ALOHA

• Time in uniform slots equal to frame transmission
  time
• Need central clock (or other sync mechanism)
• Transmission begins at slot boundary
• Frames either miss or overlap totally
• Max utilization 37

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CSMA

• Propagation time is much less than transmission
  time
• All stations know that a transmission has started
  almost immediately
• First listen for clear medium (carrier sense)
• If medium idle, transmit
• If two stations start at the same instant,
  collision
• Wait reasonable time (round trip plus ACK
  contention)
• No ACK then retransmit
• Max utilization depends on propagation time
  (medium length) and frame length
• Longer frame and shorter propagation gives better
  utilization

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Nonpersistent CSMA

• If medium is idle, transmit otherwise, go to 2
• 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

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1-persistent CSMA

• To avoid idle channel time, 1-persistent protocol
  used
• Station wishing to transmit listens and obeys
  following 
• If medium idle, transmit otherwise, go to step 2
• 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

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P-persistent CSMA

• Compromise that attempts to reduce collisions
• Like nonpersistent
• And reduce idle time
• Like1-persistent
• Rules
• If medium idle, transmit with probability p, and
  delay one time unit with probability (1 p)
• Time unit typically maximum propagation delay
• If medium busy, listen until idle and repeat step
  1
• If transmission is delayed one time unit, repeat
  step 1
• What is an effective value of p?

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Value of p?

• Avoid instability under heavy load
• n stations waiting to send
• End of transmission, expected number of stations
  attempting to transmit is number of stations
  ready times probability of transmitting
• np
• If np gt 1on average there will be a collision
• Repeated attempts to transmit almost guaranteeing
  more collisions
• Retries compete with new transmissions
• Eventually, all stations trying to send
• Continuous collisions zero throughput
• So np lt 1 for expected peaks of n
• If heavy load expected, p small
• However, as p made smaller, stations wait longer
• At low loads, this gives very long delays

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CSMA/CD

• With CSMA, collision occupies medium for duration
  of transmission
• Stations listen whilst transmitting
• If medium idle, transmit, otherwise, step 2
• If busy, listen for idle, then transmit
• If collision detected, jam then cease
  transmission
• After jam, wait random time then start from step 1

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CSMA/CDOperation
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Which Persistence Algorithm?

• IEEE 802.3 uses 1-persistent
• Both nonpersistent and p-persistent have
  performance problems
• 1-persistent (p 1) seems more unstable than
  p-persistent
• Greed of the stations
• But wasted time due to collisions is short (if
  frames long relative to propagation delay
• With random backoff, unlikely to collide on next
  tries
• To ensure backoff maintains stability, IEEE 802.3
  and Ethernet use binary exponential backoff

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Binary Exponential Backoff

• Attempt to transmit repeatedly if repeated
  collisions
• First 10 attempts, mean value of random delay
  doubled
• Value then remains same for 6 further attempts
• After 16 unsuccessful attempts, station gives up
  and reports error
• As congestion increases, stations back off by
  larger amounts to reduce the probability of
  collision.
• 1-persistent algorithm with binary exponential
  backoff efficient over wide range of loads
• Low loads, 1-persistence guarantees station can
  seize channel once idle
• High loads, at least as stable as other
  techniques
• Backoff algorithm gives last-in, first-out effect
• Stations with few collisions transmit first

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Collision Detection

• On baseband bus, collision produces much higher
  signal voltage than signal
• Collision detected if cable signal greater than
  single station signal
• Signal attenuated over distance
• Limit distance to 500m (10Base5) or 200m
  (10Base2)
• For twisted pair (star-topology) activity on more
  than one port is collision
• Special collision presence signal

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IEEE 802.3 Frame Format
82
10Mbps Specification (Ethernet)

• ltdata rategtltSignaling methodgtltMax segment lengthgt
• 10Base5 10Base2 10Base-T 10Base-F
• Medium Coaxial Coaxial UTP 850nm fiber
• Signaling Baseband Baseband Baseband Manchester
• Manchester Manchester Manchester On/Off
• Topology Bus Bus Star Star
• Nodes 100 30 - 33

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100Mbps Fast Ethernet

• Use IEEE 802.3 MAC protocol and frame format
• 100BASE-X use physical medium specifications from
  FDDI
• Two physical links between nodes
• Transmission and reception
• 100BASE-TX uses STP or Cat. 5 UTP
• May require new cable
• 100BASE-FX uses optical fiber
• 100BASE-T4 can use Cat. 3, voice-grade UTP
• Uses four twisted-pair lines between nodes
• Data transmission uses three pairs in one
  direction at a time
• Star-wire topology
• Similar to 10BASE-T

84
100Mbps (Fast Ethernet)

• 100Base-TX 100Base-FX 100Base-T4
• 2 pair, STP 2 pair, Cat 5 UTP 2 optical fiber 4
  pair, cat 3,4,5
• MLT-3 MLT-3 4B5B,NRZI 8B6T,NRZ

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100BASE-X Data Rate and Encoding

• Unidirectional data rate 100 Mbps over single
  link
• Single twisted pair, single optical fiber
• Encoding scheme same as FDDI
• 4B/5B-NRZI
• Modified for each option

86
100BASE-X Media

• Two physical medium specifications
• 100BASE-TX
• Two pairs of twisted-pair cable
• One pair for transmission and one for reception
• STP and Category 5 UTP allowed
• The MTL-3 signaling scheme is used
• 100BASE-FX
• Two optical fiber cables
• One for transmission and one for reception
• Intensity modulation used to convert 4B/5B-NRZI
  code group stream into optical signals
• 1 represented by pulse of light
• 0 by either absence of pulse or very low
  intensity pulse 

87
100BASE-T4

• 100-Mbps over lower-quality Cat 3 UTP
• Taking advantage of large installed base
• Cat 5 optional
• Does not transmit continuous signal between
  packets
• Useful in battery-powered applications
• Can not get 100 Mbps on single twisted pair
• Data stream split into three separate streams
• Each with an effective data rate of 33.33 Mbps
• Four twisted pairs used
• Data transmitted and received using three pairs
• Two pairs configured for bidirectional
  transmission
• NRZ encoding not used
• Would require signaling rate of 33 Mbps on each
  pair
• Does not provide synchronization
• Ternary signaling scheme (8B6T)

88
100BASE-T Options
89
Full Duplex Operation

• Traditional Ethernet half duplex
• Either transmit or receive but not both
  simultaneously
• With full-duplex, station can transmit and
  receive simultaneously
• 100-Mbps Ethernet in full-duplex mode,
  theoretical transfer rate 200 Mbps
• Attached stations must have full-duplex adapter
  cards
• Must use switching hub
• Each station constitutes separate collision
  domain
• In fact, no collisions
• CSMA/CD algorithm no longer needed
• 802.3 MAC frame format used
• Attached stations can continue CSMA/CD

90
Mixed Configurations

• Fast Ethernet supports mixture of existing
  10-Mbps LANs and newer 100-Mbps LANs
• E.g. 100-Mbps backbone LAN to support 10-Mbps
  hubs
• Stations attach to 10-Mbps hubs using 10BASE-T
• Hubs connected to switching hubs using 100BASE-T
• Support 10-Mbps and 100-Mbps
• High-capacity workstations and servers attach
  directly to 10/100 switches
• Switches connected to 100-Mbps hubs using
  100-Mbps links
• 100-Mbps hubs provide building backbone
• Connected to router providing connection to WAN

91
Gigabit Ethernet Configuration
92
Gigabit Ethernet - Differences

• Carrier extension
• At least 4096 bit-times long (512 for 10/100)
• Frame bursting

93
Gigabit Ethernet Physical

• 1000Base-SX
• Short wavelength, multimode fiber
• 1000Base-LX
• Long wavelength, Multi or single mode fiber
• 1000Base-CX
• Copper jumpers lt25m, shielded twisted pair
• 1000Base-T
• 4 pairs, cat 5 UTP
• Signaling - 8B/10B

94
Gbit Ethernet Medium Options(log scale)
95
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 WANs
• Connect geographically dispersed LANs between
  campuses or points of presence (PoPs)
• Ethernet competes with ATM and other WAN
  technologies
• 10-Gbps Ethernet provides substantial value over
  ATM

96
10Gbps Ethernet - Advantages

• No expensive, bandwidth-consuming conversion
  between Ethernet packets and ATM cells
• Network is Ethernet, end to end
• IP and Ethernet together offers QoS and traffic
  policing approach ATM
• Advanced traffic engineering technologies
  available to users and providers
• Variety of standard optical interfaces
  (wavelengths and link distances) specified for 10
  Gb Ethernet
• Optimizing operation and cost for LAN, MAN, or
  WAN 

97
10Gbps Ethernet - Advantages

• Maximum link distances cover 300 m to 40 km
• Full-duplex mode only
• 10GBASE-S (short)
• 850 nm on multimode fiber
• Up to 300 m
• 10GBASE-L (long)
• 1310 nm on single-mode fiber
• Up to 10 km
• 10GBASE-E (extended)
• 1550 nm on single-mode fiber
• Up to 40 km
• 10GBASE-LX4
• 1310 nm on single-mode or multimode fiber
• Up to 10 km
• Wavelength-division multiplexing (WDM) bit stream
  across four light waves

98
10Gbps Ethernet Distance Options (log scale)
99
Token Ring (802.5)

• Developed from IBM's commercial token ring
• Because of IBM's presence, token ring has gained
  broad acceptance
• Never achieved popularity of Ethernet
• Currently, large installed base of token ring
  products
• Market share likely to decline

100
Ring Operation

• Each repeater connects to two others via
  unidirectional transmission links
• Single closed path
• Data transferred bit by bit from one repeater to
  the next
• Repeater regenerates and retransmits each bit
• Repeater performs data insertion, data reception,
  data removal
• Repeater acts as attachment point
• Packet removed by transmitter after one trip
  round ring

101
Listen State Functions

• Scan passing bit stream for patterns
• Address of attached station
• Token permission to transmit
• Copy incoming bit and send to attached station
• Whilst forwarding each bit
• Modify bit as it passes
• e.g. to indicate a packet has been copied (ACK)

102
Transmit State Functions

• Station has data
• Repeater has permission
• May receive incoming bits
• If ring bit length shorter than packet
• Pass back to station for checking (ACK)
• May be more than one packet on ring
• Buffer for retransmission later

103
Bypass State

• Signals propagate past repeater with no delay
  (other than propagation delay)
• Partial solution to reliability problem (see
  later)
• Improved performance

104
Ring Repeater States
105
802.5 MAC Protocol

• Small frame (token) circulates when idle
• Station waits for token
• Changes one bit in token to make it SOF for data
  frame
• Append rest of data frame
• Frame makes round trip and is absorbed by
  transmitting station
• Station then inserts new token when transmission
  has finished and leading edge of returning frame
  arrives
• Under light loads, some inefficiency
• Under heavy loads, round robin

106
Token RingOperation
107
Dedicated Token Ring

• Central hub
• Acts as switch
• Full duplex point to point link
• Concentrator acts as frame level repeater
• No token passing

108
802.5 Physical Layer

• Data Rate 4 16 100
• Medium UTP,STP,Fiber
• Signaling Differential Manchester
• Max Frame 4550 18200 18200
• Access Control TP or DTR TP or DTR DTR
• Note 1Gbit specified in 2001
• Uses 802.3 physical layer specification

109
Fibre Channel - Background

• I/O channel
• Direct point to point or multipoint comms link
• Hardware based
• High Speed
• Very short distance
• User data moved from source buffer to destiation
  buffer
• Network connection
• Interconnected access points
• Software based protocol
• Flow control, error detection recovery
• End systems connections

110
Fibre Channel

• Best of both technologies
• Channel oriented
• Data type qualifiers for routing frame payload
• Link level constructs associated with I/O ops
• Protocol interface specifications to support
  existing I/O architectures
• e.g. SCSI
• Network oriented
• Full multiplexing between multiple destinations
• Peer to peer connectivity
• Internetworking to other connection technologies

111
Fibre Channel Requirements

• Full duplex links with two fibers per link
• 100 Mbps to 800 Mbps on single line
• Full duplex 200 Mbps to 1600 Mbps per link
• Up to 10 km
• Small connectors
• High-capacity utilization, distance insensitivity
• Greater connectivity than existing multidrop
  channels
• Broad availability
• i.e. standard components
• Multiple cost/performance levels
• Small systems to supercomputers
• Carry multiple existing interface command sets
  for existing channel and network protocols 
• Uses generic transport mechanism based on
  point-to-point links and a switching network
• Supports simple encoding and framing scheme
• In turn supports a variety of channel and network
  protocols

112
Fibre Channel Elements

• End systems - Nodes
• Switched elements - the network or fabric
• Communication across point to point links

113
Fibre Channel Network
114
Fibre Channel Protocol Architecture (1)

• FC-0 Physical Media
• Optical fiber for long distance
• coaxial cable for high speed short distance
• STP for lower speed short distance
• FC-1 Transmission Protocol
• 8B/10B signal encoding
• FC-2 Framing Protocol
• Topologies
• Framing formats
• Flow and error control
• Sequences and exchanges (logical grouping of
  frames)

115
Fibre Channel Protocol Architecture (2)

• FC-3 Common Services
• Including multicasting
• FC-4 Mapping
• Mapping of channel and network services onto
  fibre channel
• e.g. IEEE 802, ATM, IP, SCSI

116
Fibre Channel Physical Media

• Provides 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 Gbps
• Point-to-point from 33 m to 10 km

117
Fibre Channel Fabric

• General topology called fabric or switched
  topology
• Arbitrary topology includes at least one switch
  to interconnect number of end systems
• May also consist of switched network
• Some of these switches supporting end nodes
• Routing transparent to nodes
• Each port has unique address
• When data transmitted into fabric, edge switch to
  which node attached uses destination port address
  to determine location
• Either deliver frame to node attached to same
  switch or transfers frame to adjacent switch to
  begin routing to remote destination

118
Fabric Advantages

• Scalability of capacity
• As additional ports added, aggregate capacity of
  network increases
• Minimizes congestion and contention
• Increases throughput
• Protocol independent
• Distance insensitive
• Switch and transmission link technologies may
  change without affecting overall configuration
• Burden on nodes minimized
• Fibre Channel node responsible for managing
  point-to-point connection between itself and
  fabric
• Fabric responsible for routing and error detection

119
Alternative Topologies

• Point-to-point topology
• Only two ports
• Directly connected, with no intervening switches
• No routing
• Arbitrated loop topology
• Simple, low-cost topology
• Up to 126 nodes in loop
• Operates roughly equivalent to token ring
• Topologies, transmission media, and data rates
  may be combined

120
Five Applications of Fibre Channel
121
Fibre Channel Prospects

• Backed by Fibre Channel Association
• Interface cards for different applications
  available
• Most widely accepted as peripheral device
  interconnect
• To replace such schemes as SCSI
• Technically attractive to general high-speed LAN
  requirements
• Must compete with Ethernet and ATM LANs
• Cost and performance issues should dominate the
  consideration of these competing technologies