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Semester 1Semester 1

CHAPTER 7CHAPTER 7

Wael YousifWael YousifConnecting The Internet Generation

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ContentContent

• Token-ring.

• FDDI LAN.

• Ethernet and IEEE 802.3.

• Layer 2 devices and effects on data flow.

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BASIC OF TOKEN-RINGBASIC OF TOKEN-RING

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VariantsVariants

IBM developed the first IBM developed the first Token Ring network in Token Ring network in

the 1970s. It is still the 1970s. It is still IBM's primary LAN IBM's primary LAN technology, and is technology, and is

second only to Ethernet second only to Ethernet (IEEE 802.3) in terms of (IEEE 802.3) in terms of

LAN implementation. LAN implementation.

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Ring topologyRing topology

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Data passingData passing

• When a station has information to transmit, it seizes the token and sends data frame to the next station.

• When frame reaches the destination station, the data is copied for processing.

• Frame continues to circle the ring until it returns to the sending station.

• Sending station removes the frame from the ring, verifies receipt, and releases the token.

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Token-Ring frame formatToken-Ring frame format

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Start delimiter and End delimiterStart delimiter and End delimiter

• Start delimiter.

– Alert for the arrival of a token.

• End Delimiter

– Completes the token or data/command frame.

– Contains damage indicator.

– Last of logical sequence.

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Access controlAccess control

• P: Priority bits

• T: Token bit

• M: Monitor bit

• R: Reservation bits

PP PP PP TT MM RR RR RR

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Priority and reservation bitsPriority and reservation bits

• B'000' Normal User Priority

• B'001' Normal User Priority

• B'010' Normal User Priority

• B'011' Normal User priority

• B'100' Bridge/Router

• B'101' Reserved IBM

• B'110' Reserved IBM

• B'111' Station Management

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Priority managementPriority management

• Using the priority field and the reservation field.

• Stations with a higher priority can reserve the token for the next network pass.

• Stations that raise a token's priority level must reinstate the previous priority after their transmission has been completed.

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Frame controlFrame control

• Only present in data/command frames.• Indicates whether frame contains data

or control information.• If control, this byte specifies type of

control information.

• Only present in data/command frames.• Indicates whether frame contains data

or control information.• If control, this byte specifies type of

control information.

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Destination and Source addressesDestination and Source addresses

• Universal Address.• Local Administered Address.• Broadcast Address• Functional Address (0x0C0000 00XXXX)

• Universal Address.• Local Administered Address.• Broadcast Address• Functional Address (0x0C0000 00XXXX)

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DataData

• Length limited by the maximum time a station may hold the token.

• Length limited by the maximum time a station may hold the token.

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Frame checksumFrame checksum

• Frame Check Sequence.• Source fills field with calculated

value dependent on frame contents.• Destination recalculates to check

data integrity.• Frame is discarded if damaged.

• Frame Check Sequence.• Source fills field with calculated

value dependent on frame contents.• Destination recalculates to check

data integrity.• Frame is discarded if damaged.

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Frame statusFrame status

• Address recognized / frame copied indicator.• Address recognized / frame copied indicator.

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Management mechanismsManagement mechanisms

• Active Monitor

– One station acts as centralized source of timing information for other stations.

– Removes continuously circulating frames by set monitor bit to 1.

– Start a token, when token have been lost.

• Beaconing– Detects and repairs network faults.

– Initiates auto-reconfiguration.

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Physical topologyPhysical topology

• Physical topology : Star.

• Logical topology : Ring.

• IBM Token Ring network stations are connected to MSAU (Multi-Station Access Unit).

• Many MSAU can be wired together to form one large ring.

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Multi-MSAUMulti-MSAU

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Physical connectionPhysical connection

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BASIC OF FDDIBASIC OF FDDI

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CharacteristicsCharacteristics

• Fiber Distributed Data Interface.

• FDDI is popular as a campus backbone technology.

100 Mbps

Token passing

Dual-ring

Fiber Optic Cable

Total fiber length of 200Km

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FDDI dual-ring (PR and SR)FDDI dual-ring (PR and SR)

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Fiber-optic modesFiber-optic modes

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FDDI ConnectionsFDDI Connections

• Class A: connect directly with PR – SR.

– DAC: Dual Attachment Concentrator

– DAS: Dual Attachment Station

• Class B: connect via FDDI concentrator.

– SAS: Single Attachment Station

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Operation mechanismsOperation mechanisms

• Connection Establishment– Station connect to neighbors to form the ring.

– Negotiate the length of the link.

• Ring Initialization– Station claim the right to generate a token.

• Steady-state Operation– Token passing

• Ring Maintenance– Detects and repairs token or network faults.

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FDDI topologyFDDI topology

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ETHERNET AND IEEE 802.3ETHERNET AND IEEE 802.3

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Ethernet introductionEthernet introduction

• Ethernet is the most widely used local area network (LAN) technology.

• Ethernet was designed to carry data at high speeds for very limited distances.

• Ethernet is well suited to applications where a local communication medium must carry sporadic, occasionally heavy traffic at high peak data rates.

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Datalink and Physical layersDatalink and Physical layers

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Comparing Ethernet and IEEE 802.3Comparing Ethernet and IEEE 802.3

• Specify similar technologies.

• Broadcast network.

• Using CSMA/CD algorithm.

• Hardware implementation.

• Differences:– Ethernet provides services corresponding to

physical and datalink layer.

– IEEE 802.3 specifies the physical layer and the channel-access portion of the data link layer but does not define a LLC protocol.

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Ethernet family: Ethernet family: 1000Base-SX-LX1000Base-SX-LX

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Ethernet family: Ethernet family: 1000Base-T1000Base-T

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Ethernet family: Ethernet family: 100Base-TX100Base-TX

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Ethernet family: Ethernet family: 10Base-T10Base-T

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Ethernet familyEthernet family

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Ethernet frame formatEthernet frame format

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PreamblePreamble

• Note that a frame is Ethernet or IEEE 802.3.

• Note that a frame is Ethernet or IEEE 802.3.

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Start of frame delimiter (SOF)Start of frame delimiter (SOF)

• The IEEE 802.3: synchronize the frame-reception portions of all stations on the LAN.

• Be explicitly specified in Ethernet.

• The IEEE 802.3: synchronize the frame-reception portions of all stations on the LAN.

• Be explicitly specified in Ethernet.

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Source and destination addressesSource and destination addresses

• MAC addresses.• Unicast.• Multicast (D)• Broadcast (D)

• MAC addresses.• Unicast.• Multicast (D)• Broadcast (D)

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TypeType (Ethernet) (Ethernet)

• Specifies the upper-layer protocol to receive the data after Ethernet processing is completed

• Specifies the upper-layer protocol to receive the data after Ethernet processing is completed

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Length Length (IEEE 802.3)(IEEE 802.3)

• The length indicates the number of bytes of data that follows this field

• The length indicates the number of bytes of data that follows this field

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DataData (Ethernet) (Ethernet)

• the data contained in the frame is sent to an upper-layer protocol

• the data contained in the frame is sent to an upper-layer protocol

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DataData (IEEE 802.3) (IEEE 802.3)

• Data send to LLC layer, including LLC header and upper-layer data

• Data send to LLC layer, including LLC header and upper-layer data

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Frame check sequenceFrame check sequence (FCS) (FCS)

• This sequence contains a 4 byte CRC value that is created by the sender and is recalculated by the receiver to check for damaged frames

• This sequence contains a 4 byte CRC value that is created by the sender and is recalculated by the receiver to check for damaged frames

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Media Access Control (MAC)Media Access Control (MAC)

• Shared-media broadcast technology.

• Ethernet’s MAC performs three functions:

1. transmitting and receiving data packets

2. decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model

3. detecting errors within data packets or on the network

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Broadcast technologyBroadcast technology

MAC

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Broadcast addressBroadcast address

FF-FF-FF-FF-FF-FF

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CSMA/CDCSMA/CD

• When a station wishes to transmit, it checks the network to determine whether another station is transmitting.

• If network is free, the station proceeds with the transmission.

• While sending, the station monitors the network to ensure that no other station is transmitting.

• If a transmitting node recognizes a collision, it transmits a jam signal so that all other nodes recognize collision.

• All transmitting nodes then stop sending for a backoff time (randomly 0 .. 2n - 1 of 51.2s).

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CSMA/CD (cont.)CSMA/CD (cont.)

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CSMA/CD AlgorithmCSMA/CD Algorithm

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Ethernet star topologyEthernet star topology

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Ethernet star topology (cont.)Ethernet star topology (cont.)

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TIA/EIA-568-A HC StandardTIA/EIA-568-A HC Standard

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TIA/EIA-568-A:TIA/EIA-568-A: Distance limit Distance limit

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LAYER 2 DEVICESLAYER 2 DEVICES

ANDAND

EFFECTS ON DATAFLOWEFFECTS ON DATAFLOW

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Layer 2 DevicesLayer 2 Devices

• NIC (Network Interface Card)

– Connect your computer with network.

– Provide MAC addresses to each connection.

– Implement CSMA/CD algorithm.

• Bridge

– Forward or filter frame by MAC address.

• Switch

– Multi-port bridge.

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NICNIC

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NIC (cont.)NIC (cont.)

• Provides ports for network connection.

• When selecting a network card, consider:1. Type of network:

• Ethernet• Token Ring• FDDI

2. Type of media • Twisted-pair• Coaxial• Fiber-optic

3. Type of system bus• PCI• ISA

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NIC: NIC: Layer 2 functionsLayer 2 functions

• Logical link control (LLC): communicates with upper layers in the computer

• Naming: provides a unique MAC address identifier

• Framing: part of the encapsulation process, packaging the bits for transport

• Media Access Control (MAC): provides structured access to shared access media

• Signaling: creates signals and interface with the media

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BridgeBridge

• Connects network segments.

• Make intelligent decisions about whether to pass signals on to the next segment.

• Improve network performance by eliminating unnecessary traffic and minimizing the chances of collisions.

• Divides traffic into segments and filters traffic based on MAC address.

• Often pass frames b/w networks operating under different Layer 2 protocols.

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Bridge (cont.)Bridge (cont.)

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Bridge (cont.):Bridge (cont.): Filter Filter

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Bridge (cont.):Bridge (cont.): Forward Forward

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LAN SwitchLAN Switch

• Switches connect LAN segments.

• LAN switches are considered multi-port bridges with no collision domain.

• Use a MAC table to determine the segment on which a frame needs to be transmitted.

• Switches often replace shared hubs and work with existing cable infrastructures.

• Higher speeds than bridges.

• Support new functionality, such as VLAN.

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LAN Switch (cont.)LAN Switch (cont.)

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LAN Switch:LAN Switch: MAC table MAC table

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LAN Switch:LAN Switch: Micro-segmentation Micro-segmentation

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Benefits of LAN SwitchBenefits of LAN Switch

• No collision domain, because of micro-segmentation.

• Low latency levels and a high rate of speed for frame forwarding

• Increases the bandwidth available on a network

• Is performed in hardware instead of in software, it is significantly faster.

• BUT: All hosts connected to the switch are still in the same broadcast domain.

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Why segment LANs?Why segment LANs?

• Isolate traffic between segments.

• Achieve more bandwidth per user by creating smaller collision domains.

• LANs are segmented by devices like bridges, switches, and routers.

• Extend the effective length of a LAN, permitting the attachment of distant stations.

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Segmentation with bridgesSegmentation with bridges

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Segmentation with bridges (cont.)Segmentation with bridges (cont.)

• Bridges increase the latency (delay) in a network by 10-30%.

• A bridge is considered a store-and-forward device because it must receive the entire frame and compute the cyclic redundancy check (CRC) before forwarding can take place.

• The time it takes to perform these tasks can slow network transmissions, thus causing delay.

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Segmentation with switchesSegmentation with switches

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Segmentation with switches (cont.)Segmentation with switches (cont.)

• Allows a LAN topology to work faster and more efficiently.

• Uses bandwidth so efficiently, the available bandwidth can reach to 100%.

• Ease bandwidth shortages and network bottlenecks (such as client-server).

• A computer connected directly to an Ethernet switch is its own collision domain and accesses the full 10Mbps.

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Segmentation with routersSegmentation with routers

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Segmentation with routers (cont.)Segmentation with routers (cont.)

• Routers operates at the network layer

• Routers bases all of its forwarding decisions on the Layer 3 protocol address.

• Routers ability to make exact determinations of where to send the data packet.

• Router operate with a higher rate of latency.

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Teaching topologyTeaching topology

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Basic 10BaseT troubleshootingBasic 10BaseT troubleshooting

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