Ch'12 Local Area Networks

1
Ch.12 Local Area Networks

• Lecturer Tae-Hyong Kim (B201-4)
• thkim_at_cespc1.kumoh.ac.kr

2
Contents

• Introduction
• Project 802
• Ethernet
• Other Ethernet Networks
• Token Bus
• Token Ring
• FDDI
• Comparison

3
Introduction

• LAN Allows devices to communicate directly with
  each other in a limited geographic area
• Dominant architectures
• Ethernet
• Token bus IEEE(project 802)
• Token ring
• FDDI (Fiber Distributed Data Interface) - ANSI
• DLC portion of the LAN protocols are all based on
  HDLC.

4
12.1 Project 802

• In 1985, the Computer Society of the IEEE
  developed Project 802.
• Covers the first two layers of the OSI model and
  part of the third layer
• LAN Compared with the OSI Model

• LLC sublayer non-architecture specific, same
  for all IEEE-defined LANs
• MAC sublayer contains a number of distinct
  modules specific to the LAN product

5
Project 802 (cont.)
MAC sublayer protocols
6
Project 802 (cont.)

• IEEE 802.1 Internetworking
• assures the compatibility of different LANs and
  MANs
• allows data to be exchanged across incompatible
  networks
• not yet complete
• IEEE 802.2 LLC protocol
• handles the end-user portions of the HDLC frame
• the logical addresses, control information, and
  data
• common to all LAN protcols
• MAC sublayer protocols
• resolves the contention for shared media, and
  handles
• the synchronization, flag, flow and error control
  specifications
• the physical address of the next station

7
Project 802 (cont.)

• PDU (Protocol Data Unit) The data unit in a
  protocol level
• PDU Format
• SAP (Service Access Point)
• a port (logical link) to the upper layer protocol
• ensures that the same upper layer protocol at the
  Source talks to the same upper layer protocol at
  the Destination
• i.e. LLC SAP TCP/IP talks to TCP/IP and Netbios
  talks to Netbios

8
Project 802 (cont.)

• LLC Service

9
Project 802 (cont.)

• Control Field in a PDU
• no flag fields, no CRC, no station address
• These fields are added in the MAC sublayer

10
12.2 Ethernet

• IEEE 802.3

10Base5 Thick Ethernet 10Base2 Thin
Ethernet 10Base-T Twisted-pair Ethernet 1Base5
Star LAN
11
Ethernet (cont.)

• Access Method CSMA/CD

• ??? ??? station? listen (voltage check)
• medium? idle (no voltage)?? ????
• medium? busy? channel? idle ? ??? listen ????
• collision (extremely high voltage)? ???? ?? frame
  ??? ???? random? ???? ???? ?? ???

12
Ethernet (cont.)

• Collision in CSMA/CD

13
Ethernet (cont.)

• jamming sequence 32bits
• - to make sure collision

14
Ethernet (cont.)

• Addressing
• Each station on an Ethernet network has its own
  NIC (Network Interface Card) provides a 6 byte
  physical address
• IEEE 802.3 MAC Frame
• Preamble
• for synchronization of receivers H/W with the
  incoming signal
• bit pattern 10101010..
• Preamble SFD ? flag in HDLC

15
Ethernet (cont.)

• IEEE 802.3 MAC Frame (cont.)
• Destination/Source address
• serial number on the NIC (unique)
• Broadcast address (only for DA) all 6 bytes set
  to 1
• Data 0-1500 bytes
• Generated by LLC
• Pad 0-46 bytes
• inserted when data portion is less than 46 bytes

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Ethernet (cont.)

• 10BASE5 Thick Ethernet
• Bus topology

?? ??? repeater? bridge? ???? ????
RG-8 cable
transceiver tap (vampire tap)
17
Ethernet (cont.)
18
Ethernet (cont.)

• 10BASE5 Thick Ethernet
• Ethernet Segments (max 2500 meters 5 segments)

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Ethernet (cont.)

• 10BASE2 Thin Ethernet
• Bus topology
• reduced cost, easy installation
• shorter range (185m), smaller capacity (fewer
  stations)

RG-58 cable
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12.2 Ethernet

• 10BASE-T Twisted-Pair Ethernet
• Topology physically star, logically bus
• maximum length 100m (hub to station)
• the most popular

CAT3/CAT5 cable
balanced mode tx rx
21
Ethernet (cont.)

• Ethernet Wiring Scheme
• Type of connection between
• a NIC and a network
• Thick Ethernet wiring (10 base 5)
• Thin Ethernet wiring (10 base 2)
• Twisted pair Ethernet (10 base-T)

22
Ethernet (cont.)

• 1Base5 StarLAN (ATT)
• uses twisted-pair cable
• but allows as many as 10 stations to be linked
• infrequently used due to slow speed

23
12.3 Other Ethernet Networks

• Switched Ethernet
• A switch is used instead of a hub
• Fast Ethernet
• 100Base-TX
• 100Base-FX
• 100Base-T4
• Gigabit Ethernet
• 1000Base-LX/SX/CX/T

24
Other Ethernet Networks (cont.)

• An Ethernet Network Using A Hub (10Base-T)
• Topology physically star, logically bus

25
Other Ethernet Networks (cont.)

• Switched Ethernet
• An Ethernet Network Using a Switch

frames are routed (no collision)
The performance (network capacity) can be
theoretically improved N times (when N devices)
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Other Ethernet Networks (cont.)

• Fast Ethernet
• Concept How to increase data transmission rate?
• Collision domain
• the maximum distance data travels between two
  stations
• Ethernet 2500m for 10Mbps under CSMA/CD Method
• a station should be able to sense the collision
  before the whole frame is sent on the
  transmission media
• Before the last bit is sent, the first bit must
  have reached the end of domain for collision
  detection
• The minimum size of Ethernet frame 72 bytes
  (576 bits)
• The minimum transmission time 57.6 msec
• the collision must be detected during 57.6 msec
• The round trip time (RTT) 5000m/prop. speed lt
  57.6 msec
• prop. speed gt 86800 km/s sufficient
  (gt150000km/s)
• To increase the data rate (transmission time?),
  we have to decrease RTT
• For 100Mbps, RTT should be reduced to 5.76 msec
• Collision domain must be decreased to 250m

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Other Ethernet Networks (cont.)

• Fast Ethernet (cont.)
• Properties
• Transmission speed 100Mbps
• Collision domain 250m
• Star topology
• no change in the MAC frame format and access
  method

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12.3 Other Ethernet Networks

• 100Base-TX

covered by general LAN cable (4P UTP)

• usually used with NRZ-I signaling
• every 4 bits of actual data are encoded in a
  5-bit code (Table 12.3)
• in order to break up long sequence of 0s and 1s
• Every 5bit code has no more than one leading 0
  and
• no more than two trailing 0s
• no pair of 5 bit cods results in more than three
  consecutive 0s
• The resulting 5 bit codes are then transmitted
  using NRZ-I

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12.3 Other Ethernet Networks

• 100Base-FX

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12.3 Other Ethernet Networks
edited

• 100Base-T4

the existing telephone lines can be used
similar to 4B/5B, for smaller baud rate
33.66Mbps each
31
12.3 Other Ethernet Networks
edited

• Gigabit Ethernet
• The same MAC layer and access scheme
• Reduced collision domain
• Change in physical layer mainly use optical
  fiber
• Usage backbone to connect Fast Ethernet
  networks
• Encoding 8B/10B
• Now 10 Gigabit Ethernet is under standardization

32
12.4 Token Bus

• IEEE 820.4
• Combines the features of Ethernet and Token Ring
• Physically Bus Topology
• Logically Ring Topology (Token Ring)
• Stations are logically organized into a ring
• Collision-free
• The throughput may be varied according to the
  construction of the logical ring
• limited to factory automation and process control
• no commercial application in data communication

33
Token Bus (cont.)

• Token Bus Logic

34
12.5 Token Ring

• IEEE 802.5
• Access method token passing
• Allows each station to send one frame per turn
• Resolves the uncertainty of collisions or delay
• The token is a series of bits, travels between
  the computers in a predetermined sequence
• Transmission in a Token Ring
• Sender look for free token
• When token is received, sender changes free token
  to busy token, appends data to the token, and
  then transmit them
• Receiver recognized that it is the destination of
  the frame
• Frame also returns to sender
• Sender generates free token when it is done
  transmitting

35
in Control field (LLC sublayer)
A,C bits (MAC sublayer)
36
Token Ring Algorithm (a) sending (b) receiving
37
Token Ring (cont.)

• Two modes of transmission
• token release after reception of data (free
  busy token)
• higher reliability
• 4Mbps
• C NTf/(NTf(N1)Tp)
• token release after transmission of data (free
  token only)
• higher throughput
• up to 16Mbps
• C NTf/(NTfTp)
• Electrical Spec. of Token Ring
• Differential Manchester encoding

38
Token Ring (cont.)

• Priority Reservation Another option
• each data and the token has its own priority (Pm
  and Pr)
• A station must wait for a free token with Pm Pr
  for transmission of data whose priority is Pm
• As a frame passes by, a station waiting to
  transmit can reserve the next open token
• by entering the priority of data (Pm) in the
  reservation area of AC (access control) field of
  the token or data frame
• A station with a higher priority data may remove
  a lower priority reservation and replace it with
  its own
• among equal-priority stations, FCFS
• Time Limit for detection of lost token or data
  frame
• SD field (the first field of token or data frame)
  must reach each station within this time
  usually 10ms

39
Token Ring (cont.)

• Token loss
• The token crashes before being transmitted - lost
  a free token
• A computer in the ring crashes - lost a busy
  token
• A token is always busy.
• A solution for the lost token problem
• Designate one computer to be the monitor station
  and another computer to be a backup monitor
  station.
• If no token circulated through the network for a
  certain length of time or if a busy token/data
  frame circulates too often (checked by monitor
  bit in AC field), the token monitor will create a
  new free token (and destroy the busy token if
  necessary.)

40
Token Ring (cont.)

• Token Ring Frame

• by Sender to stop its own transmission
• by Monitor to purge an old transmission
• from the line

41
Token Ring (cont.)

• SD/ED (Start/End Delimiter)
• equiv. to flag (for timing synchronization)
• J K violations by the physical layer for data
  transparency
• differential Manchester transition at the
  beginning the middle
• J violation both transitions are canceled
• K violation the middle transition is canceled
• AC (Access Control)
• priority the priority of the message (Pm) or
  the token (Pr)
• token bit token/abort(1) or data/command(0)
• FC (Frame Control)
• Type type of information control or data
• Special info Token Ring Logic (how to handle
  the AC field)
• FS (Frame Status)
• Contains address recognized bit (A) frame
  copied bit (C)
• Receiver sets A1 when frame arrives
• Receiver sets C1 when frame has been copied

42
12.5 Token Ring

• Data Frame Fields

43
12.5 Token Ring

• Token Ring Implementation Ring
• 150-ohm, STP
• Problem robustness
• Improving Reliability use a second ring

44
12.5 Token Ring

• Token Ring Implementation Switch
• listen state incoming bits are copied to output
  with 1-bit delay
• transmit state write data to the ring
• bypass state idle station does not incur
  bit-delay

Balanced mode
45
12.5 Token Ring

• Token Ring Implementation MAU (Multiple Access
  Unit)
• ??? hub look like a star but in fact a ring
• MAU ? 8 stations ?? ??

46
LAN Construction
47
Bridge and Repeater
repeater - ??? ??? ?? ????? ????? ? - ???
Segment? ??? ?? Segment? ?? - ??? ????
?? bridge - LAN segment? ??(same) - ?
segment? ?? frame? buffer? ????? ?? ??
??????? ?? ?? ??? ?? frame? ??? - ??
segment? ??? ??? ???? ?? frame ?? segment? ??
?? ???? load? ?? ?? - MAC sublayer?? ??
48
LAN Performance

• (a) 512 bit frame (b)
  12000 bit frame

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12.6 FDDI

• Fiber Distributed Data Interface
• ANSI ITU-T(ITU-TX.3) Standard
• FDDI is a 100Mbps token ring
• Dual redundant counter rotating ring topology
• Second ring adds a certain level of fault
  tolerance
• media fiber optics
• CDDI when using copper cable
• Max Frame Size 4500 bytes
• Allows up to 1000 connected stations
• Max ring circumference 200km

50
FDDI (cont.)

• Access Method in FDDI
• Token passing
• Support real-time data service
• Types of data frames
• Synchronous
• real-time data
• S-frame
• Asynchronous
• non-real-time data
• A-frame
• Token? ?? station? S-frame? ?? ??? ?? ???
  A-frame? ??

51
FDDI (cont.)

• FDDI Operation
• Timer Register to control circulation of the
  token and distribute link-access opportunities
  among the nodes equitably
• Synchronous allocation (SA)
• the time allowed for transmission of S-frame
• Different for each station
• Negotiated during initialization of the ring
• Target token rotation time (TTRT) mean time
• Absolute maximum time (AMT) 2 TTRT
• if TRTgtAMT, the ring must be reinitialized
• Timers
• Token rotation timer (TRT) count up here
• Token holding timer (THT)
• at a station for async. data transmission count
  down here

52
FDDI (cont.)

• An operation example
• When a token arrives, each station follows this
  procedure
• 1. THT is set to TTRT - TRT
• 2. TRT is reset to 0
• 3. The station sends its synchronous data
• 4. The station sends async. data as long as THT gt
  0
• assumptions
• TTRT 30Time unit, station? Token ?? 1 Time unit
• No of stations in a ring 4
• Each station sends 2 synchronous data per turn
• Each station has a lot of asynchronous data to
  send in its buffer

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1
1111
11111
26222
4
222
2
21822
22182
11111
3
11111
54
FDDI (cont.)

• Address 6 byte (on NIC Card)
• Electrical Specification
• Signaling (Physical layer)
• 4B/5B Encoding
• 5bit ???? ???? ?? 5bit code?? ????? ??
• NRZ-I Encoding
• Data rate 100Mbps?? ??

55
FDDI (cont.)

• FDDI Layers
• FDDI protocols
• PMD (Physical medium dependent)
• PHY (Physical)
• MAC (Media Access Control) similar to token
  ring
• LLC (Logical Link Control) similar to IEEE802.2
• Station Management ??? ????

56
FDDI (cont.)

• FDDI Frame types
• Each frame starts with 16 idle symbol (1111) 64
  bits
• to initialize clock synchronization with the
  receiver

57
FDDI (cont.)

• PMD Layer
• defines the required connections and electronic
  components
• Specification depends on the transmission medium
• Dual Ring
• Primary ring data transmission
• Secondary ring in case primary fails,
  self-healing

58
FDDI (cont.)

• FDDI Ring after a failure

59
FDDI (cont.)
DAS Dual attachment station SAS Single
attachment station DAC Dual attachment
concentrator MIC Media interface connector
Node connections
-DAS 2?? MIC ?? ?? ? ?? ?? ?? 1? ?? 2?
??? ???? fault ?? -SAS 1?? MIC??? ??? ?? ??
??, ?? ???? , ?? ??? ??? ?? fault ?
bypass ? -DAC DAS? SAS? ?? Fail ?? ???
?? ? ????
60
12.7 Comparison