Components of DATA and INTERNET NETWORKING MODULE
(MSc EEM.din & Linked UG EE4.din)
LANs, High Speed LANs and
LAN Interconnections
Dr Zhili SUN
University of Surrey
Guildford
Surrey
GU2 7XH
Tel: 01483 68 9493
Fax: 01483 68 6011
Email: Z.Sun@eim.surrey.ac.uk
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Sections
Œ
1. Local Area Networks (LANs):
IEEE 802 standard LANs: Ethernet (803.3), Token Ring (802.5), Token
Bus (802.4), MAC sublayer, LLC sublayer.
Œ
2. High Speed LANs (HSLANs):
Fast Ethernet (IEEE802.3u), Hub, Switched Ethernet, gigabit Ethernet
(IEEE802.3z), FDDI,
Œ
3. Wireless Networks
Wireless LAN (IEEE803.11a, 11b & 11g), Broadband Wireless
(IEEE802.16), Bluetooth (IEEE802.15)
Œ
4. LAN interconnection:
Repeaters; Bridges - Transparent and Source Routing; Spanning Tree
Algorithm, internetworking different LAN types, VLAN (IEEE802.1Q)
Œ
Recommended text books
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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1. Local Area Networks (LANs)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Introduction
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LAN classification
IEEE 802 standard LANs:
• Ethernet (802.3)
• Token Ring (802.5)
• Token Bus (802.4)
Medium Access Control (MAC) sublayer
Logical Link Control (LLC) sublayer
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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LAN Classification
Classifications are based on:
ΠPhysical Transmission Medium: Shielded/Unshield
Twisted Pair (STP/UTP) 10baseT, Co-axial Cable
(10base2 thin 0.25 and 10base5 thick 0.5 inch diameter),
optical Fibre 10baseF, wireless,
Œ
Œ
Topology: Bus, Ring, Tree/Hub, Star
Media Access Control: CSMA/CD, control token, fixed
slots
Œ
Standards bodies: IEEE, ISO
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Standards - IEEE 802.x (ISO 8802.x)
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At start of LAN development many incompatible
networks were developed
In the early 1980’s an IEEE committee examined the
various types, classified them and proposed standards
to remove much of the incompatibility.
LAN types thus became known by the IEEE 802
classification e.g. 802.3, 802.4, 802.5 ...
ISO adopted IEEE 802 as ISO 8802
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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The framework of IEEE 802 Standards
802.1
Architecture, Management & Internetwork
802.7
Broadband
LANs
802.3
802.4
802.5
802.6
802.9
CSMA/CD
Token Bus
Token Ring
MANs
Integrated
voice/data
802.2
Link Services
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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802.8
FDDI
802.10
Secure LANs
IEEE 802 relevant to LANs
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802.1 — High layer LAN Protocol: Overview & architecture, bridging, VLAN
802.2 — Logical Link Control services Working Group (WG) (inactive)
802.3 — Ethernet (CSMA/CD) WG: access method & physical signalling
802.4 — Token Bus WG: access method & physical signalling (inactive)
802.5 — Token Ring WG: access method & physical signalling
802.6 — Metropolitan Area Network - MAN (DQDB): WG (inactive)
802.7 — Broadband Technical Advisory Group (TAG) (inactive)
802.8 — Fiber-Optic Technical Advisory Group (FDDI-II):
802.9 — Isochronous LAN WG: Integrated Service LAN
802.10 — LAN Security Architecture WG: for all IEEE 802 at various level
802.11 — Wireless LAN (HiperLAN in ETSI): access method & physical signalling
802.12 — Demand priority WG.
802.13: not used.
802.14 — Cable modem WG.
802.15 — Wireless personal area network WG.
802.16 — Broadband wireless access Study Group (SG)
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QoS / Flow control study group
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LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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LAN Protocol and OSI reference model
Application
Presentation
Session
Service Access Points
Transport
Network
Data Link
Logical Link Control
Physical
Medium Access Control
Physical
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Functions of LLC, MAC and PHY layers
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Logic Link Control (LLC) - Provide one or more Service
Access Points (logical interfaces between adjacent
layers)
Media Access Control (MAC) - On transmission
assemble data into frames with address and CRC; On
reception disassemble frame and perform address
recognition and CRC validation; and Manage
communication over link
Physical layer - Encoding/decoding of signals; Preamble
generation/removal (for synchronization); and bit
transmission/reception.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Topologies
Bus
Ring
Hub/Switc
h
Tree
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Medium access control (MAC) techniques
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Round robin: With round robin, each station in turn is
given the opportunity to transmit. During that opportunity,
the station may decline to transmit or may transmit subject
to a specified upper bound (maximum amount of data or
time)
Reservation: For stream traffic, reservation techniques
are well suited.
Contention: For bursty traffic, contention techniques are
usually appropriate
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Standardised MAC techniques
Round
robin
Bus
technology
Ring
Switched
technology technology
Token bus (402.4)
Polling (802.11)
Token ring
(802.5, FDDI)
Request/priority
(802.12)
Reservation DQDB (802.6)
Contention
CSMA/CD (802.3)
CSMA (802.11)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
CSMA/CD (802.3)
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Aloha and Slotted Aloha
Contention system:
ŒTransmit whenever have data
ŒListen to the channel to see if the
frame is OK
ŒIf not, back-off and re-transmit
For slotted Aloha, transmit only at
beginning of the slot to improve
performance
Œ
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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The channel efficiency
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Throughput S = GP0
ΠPoisson distribution:
P[k] = Gk e-G / k!
In 2 frame interval, the number of
frames generated is 2G, thus P0 =
e -2G
=> S = G e -2G
ΠMax. throughput
S = 1/(2e), when G=1/2
ΠFor slotted Aloha
the vulnerable period is 1 frame period
(halved), thus P0 = e -G
=> S = G e -G
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Carrier Sense Multiple Access (CSMA)
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1-persistent: the station listens before sending.
If the channel is busy, it waits until it idle.
Transmit when the channel is idle. if collision,
the station waits a random amount of time and
start all over again
non-persistent: If busy, the station does not
continually sense. Instead, waiting for a random
period, then repeating the algorithm
p-persistent: It applies to slotted channel. If it is
idle, it transmits with probability of p.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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CSMA Persistence and Back-off
Constant or
Variable Delay
non-persistent:
transmit if idle, otherwise,
delay and try again
Channel Busy
Ready
Slot time
p-persistent: transmit as
soon as channel goes idle
1-persistent: transmit
as soon as channel goes idle. with a probability p, otherwise
delay one slot and repeat process
If collision, back-off and
try again.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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CSMA with Collision Detection (CD)
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Further improvement than persistent and nonpersistence over Aloha, by aborting transmission as soon
as stations detect a collision
Contention period is 2τ where τ is propagation delay
Example: for a 1 km cable, the τ is about 5 µs (microsecond)
Ethernet is one of this version
No MAC-sublayer protocol guarantees reliable delivery
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Ethernet System
Œ
The CSMA/CD system (as
defined by IEEE 802.3) is based
upon the original Ethernet
specification defined by Xerox.
The two are not identical.
Carrier
Sense
Multiple
Access
with
Collision
Detection
with network interface
card (LANCE)
PC
PC
Channel
CSMA/CD
Transceiver
Medium Access Unit (MAU)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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PC
Attachment Unit
Interface (AUI)
Ethernet Cabling
The most common kinds of Ethernet cabling.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Physical layer signal encoding
(a) Binary encoding, (b) Manchester encoding,
(c) Differential Manchester encoding.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Ethernet Frame Format
Bytes
7
1
Preamble
2 or 6
2 or 6
Destination
address
Source
address
Start of
frame
delimiter
2
46–1500
0–46
4
Data
Pad
Checksum
Length of LLC data field
or Ethernet type field
Preamble: Receiver synchronization (10101011)
Destination address: Identifies intended receiver
Source address: Hardware address of sender
Length/Type: Type of data carried in frame
Data: Frame payload
CRC: 32-bit CRC code
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Back-off algorithm & Operational Parameters
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Retransmission scheduling
uses the Truncated Binary
Exponential Back-off
algorithm
On the Nth retransmission
attempt the station chooses to
retransmit after waiting a
random integer number of
‘slot’ times, R, where:
0 <= R <= 2k
K = min(N, Back-off limit)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Bit rate
Slot time
Interframe gap
Attempt limit
Backoff limit
Jam size
Max frame size
Min frame size
10 Mbps
512 bit times
9.6 µs
16
10
32 bits
1518 octets
64 octets
CSMA/CD Operational Parameters
Wait for a frame to transmit.
Format frame for transmission.
Incoming signal detected?
n
Carrier sense signal on?
y
y
n
Set carrier sense signal on.
Get bit sync and wait for SFD.
Receive frame.
Wait interframe gap time.
Start transmission.
n
Collision detected?
FCS and frame size OK?
y
n
y
Complete transmission and
set status as done.
Set status as attempt
limit exceeded.
Transmit jam sequence.
Increment attempts count.
y
Destination address matches
own or group address?
y
Attempt limit reached?
Pass frame to higher layer
for processing.
n
Transmit
Compute and wait
backoff time
Receive
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
n
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Discard
frame.
Token Ring
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The Token Ring is described
by the IEEE 802.5
specification. This is based
upon the original work by IBM
and now defines both 4Mbps
and 16 Mbps rings.
Suitable for real time
Delimiter, access control,
frame control
Sources, destination address,
and checksum are the same
as the IEEE 802.3
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PC
PC
Token
SD AC ED
PC
Token ring
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Token Ring Frame Formats
Bytes
1
1
1
SD AC ED
1
1
1
SD AC FC
Token Format
2 or 6
2 or 6
< 5000
DA
SA
DATA
4
1
1
FCS ED FS
Frame format
JK 0J K 00 0 Start delimiter (SD)
FF ZZZZZZ Frame Control (FC)
JK1JK1 I E
ACxx ACxx
End delimiter (ED)
PPPT MRRR Access Control
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
Frame Status (FS)
32-bit CRC: Frame Check Sequence (FCS)
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Token Ring Operation
Wait for a frame
to be received
Waiting for token to be received
Frame waiting to be
transmitted?
n
Forward token
with correct priority
y
Token?
Enter transmit
routine.
y
Token priority <=
frame priority?
n
n
Store frame contents and
repeat at ring interface
n
y
R bits < frame
priority?
Transmit waiting frame.
Remove frame after
circulating ring.
Pass A and C bits from tail
of frame to higher layer
y
n
Frame addressed to me?
Set R bits to frame priority
y
y
Token holding timer expired?
Set A and C bits at tail of frame.
Pass stored frame to higher layer.
Forward token
with correct priority
n
Receive
Transmit
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Discard
frame.
Ring Management
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In addition to tokens and data
frames the Token Ring
protocol employs a number of
special frame types to
facilitate ring management.
Ring management is required
for:
• Initialization
• Active monitoring
• Standby monitoring
• Fault diagnosis
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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The different ring management
frames include:
• Duplicate Address Test
(DAT)
• Active Monitor Present
(AMP)
• Standby Monitor Present
(SMP)
• Claim Token (CT)
• Purge (PRG)
• Beacon (BCN)
Token ring control frames
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Ring Fault Detection and Recovery
A
B
TCU
H
C
A
D
B
F
D
Standby ring
Failure
G
C
H
E
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G
F
E
Token bus
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Token bus frame
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Token bus control frames
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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IEEE 802.2 Logical link control
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LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Hide difference between the
various 802 networks by
providing a single format
and interface to the network
layer
Based on HDLC, provide 3
service options as the link
layer
Error control using
acknowledgement
Flow control using a slide
window
All 802 LANs and MAN offer
best-efforts service
Logical Link Control (LLC)
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The various IEEE 802 MAC
sublayers are all designed to work
with the 802.2 Logical Link Control
(LLC) sublayer
The LLC is based upon HDLC and
is thus similar to the LAPB protocol
used in X.25
The LLC sublayer can optionally
support three types of service:
• Type 1: Unacknowledged
connectionless
• Type 2: Connection-oriented
• Type 3: Acknowledged
connectionless
LLC frames are carried in the data
field of the MAC sublayer’s frame.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
Bytes:
1
1
1 or 2
>=0
DSAP
address
SSAP
address
Control
Information
LLC Frame format (LLC-PDU)
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LLC Control Field
N(S)
P/F
N(R)
Information frame
1 0
S
P/F
N(R)
Supervisory frame
1 1
M
P/F
M
0
Unnumbered frame
N(S),N(R) = send / receive sequence numbers (7 bits)
S = supervisory function bit
M = modifier function bit
p/f = poll/final bit
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Summary
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LANs
IEEE 802 standard LANs:
Ethernet (802.3)
Token Ring (802.5)
Token Bus (802.4)
MAC sublayer protocols
LLC sublayer
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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2. High Speed LANs
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Introduction
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Fast Ethernet (IEEE802.3u)
• Ethernet shared medium Hub
• Switched Ethernet
Gigabit Ethernet (IEEE802.3z)
FDDI
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Ethernet Shared Medium Hub
Hub
DTE
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
DTE
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DTE
Switched Ethernet
A simple example of switched Ethernet.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Switched Ethernet
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Add electronics to Hub so hub can recognise
(remember) the addresses of DTE connected to each
port thus only need to transmit frames intended for that
DTE (need FIFO to buffer until DA appears)
Arrange backplane with one line/port - steer frames to
specific line - several frames can be transit at same
time
Can have higher speed port to link to server DTE recipient of all unrecognised frames
Collision Detection only required when frame received
for a port already receiving a frame
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Fast Ethernet Specifications
IEEE 802.3
(100 Mbit/s)
100BASE-T4
100BASE-X
100BASE-TX
100BASE-FX
• 2 STP
• 2 Category 5 UTP
• 4 Category 3
• 2 Optical fibre
• 4 Category 5
IEEE 802.3 concise notation:
<rate in Mbit/s> <signalling method> <Max Length in 100m>
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15
Fast Ethernet: IEEE802.3u
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They must use hubs or switches
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Fast Ethernet 100base4T
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Main problem is to transmit 100Mb/s over Twisted pair!
The 100base4T scheme uses all 4 pairs in parallel
Uses 8B6T (8bits translated to 6 ternary symbols) to
reduce baud/pair to below 30Mbaud
(100 x (6/8))/3 = 25 MHz
Hub
DTE
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Fast Ethernet 100baseX
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100baseX uses single, higher specified twisted pair (or
optical fibre - hence X)
For FX - optical fibre cable,4B5B is used as used in FDDI.
For TX - Shielded twisted pair (STP), MTL-3 signalling
scheme is used.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Gigabit Ethernet – IEEE802.3z
(a)
(b)
A two-station Ethernet.
A multistation Ethernet.
The strategy for Gigabit Ethernet is the same as that for fast Ethernet:
ΠNew media and transmission specification
• Point to point
• Carrier extension
• Frame bursting
ΠThe same CSMA/CD protocols and Ethernet format and backward
compatible
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Gigabit Ethernet cabling
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1000BASE-SX: uses short-wavelength
1000BASE-LX: uses long-wavelength,
1000BASE-CX: use two pairs specialise shielded
twisted-pair (STP) cable
1000BASE-T: use four pair of Category 5 UTP
New encoding rules are used on fibres (10B/10B)
IEEE802.3ae is under studies for 100 gigabit Ethernet
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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Fibre distributed data interface (FDDI)
n
n
n
n
n
Modelled on IEEE 802.5
High speed LAN 100 Mbit/s
synchronised frame every 125 µs, support 96
PCM channels (4xT1 or 3xE1)
Bit error rate 2.5x10E-10
4B/5B encoding
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Fibre Distributed Data Interface (FDDI)
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ISO 9314, 100 Mbps,
200Km, 1000 nodes
Token passing
Dual ring structure
Intended primarily as a
means of interconnecting
LANs (via relays) but
individual nodes can be
attached.
Two station types:
SAS
inserted
bypassed
S
S
slave key
primary ring
M
M
master key
wiring
concentrator
A
B
inserted
bypassed
B
DAS
• Single Attach Station (SAS)
• Dual Attach Station (DAS)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
SAS
A
A
B
primary ring
51
DAS
secondary ring
optical
coupling
unit
FDDI frame formats
Frame check sequence coverage
Pre
SD
FC
DA
SA
>16
2
2
4 / 12
4 / 12
data
<=9000
symbols
Pre
SD
FC
ED
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token
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FCS
ED
FS
8
1/2
3
FDDI – Physical Layer Signalling
Data Symbols
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4-bit data
To enable clock synchronisation
0000
FDDI uses a 4 of 5 group code at
0001
0010
the physical layer.
0011
0100
0101
Symbols have at most 2
0110
0111
consecutive 0’s thus when using
1000
1001
NRZI (signal transition on each
1010
1011
‘1’) at most two bits between
1100
transitions.
1101
1110
1111
J and K symbols break 2 ‘0’s rule
Control Symbols
and are used as end-markers
IDLE
J
IDLE has all ‘1’s and thus max
K
clock transitions - used in
T
R
preamble
S
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QUIET
HALT
5-bit symbol
11110
01001
10100
10101
01010
01011
01110
01111
10010
10011
10110
10111
11010
11011
11100
11101
11111
11000
10001
01101
00111
11001
00000
00100
Latency
n
n
n
n
SD field of 2 symbols (5bits) requires a buffer at
receiver before SA known thus introduces
latency of 0.08µs
Generally rounded as 1µs / ring interface
Thus latency = propagation delay (5µs/km) +
N x Station latency (1µs)
20km ring with 200 stations = 300µs
or 30,000bits
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Timed Token Rotation Protocol
n
n
n
n
n
FDDI uses same approach as used in Token Ring
Preset parameter - Target Token Rotation Time
For each rotation of token station computes time since
last received token - TRT (Token Rotation Time)
TRT is a measure of loading on ring
The station computes THT = (TTRT-TRT)
this THT is Token Hold Time and determines
how long the station may hold the token and thus
continue to transmit frames
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Max Throughput or Untilisation
A
B
C
N stations
Τ = ring latency
i.e. time taken to pass token around loop
TTRT = Timed token rotation time
τ = time required to transmit token
Assume heavily loaded ring - all stations have frames to transmit
Consider B - when token first passed will not be able to transmit as
timed out - thus need complete token rotation (Τ)
On completion B transmits with holding time TTRT-Τ
It then has to transmit token time τ which takes Τ/n to reach C
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Max Utilization
TTRT-Τ
Umax =
TTRT >> τ
Umax =
(TTRT-Τ) + Τ + τ + Τ/n
thus
n(TTRT-Τ)
thus -> 1 as TTRT increases
nTTRT+Τ
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Maximum Access Delay
Have to wait for all other stations to transmit +
token rotation times
Amax = (n-1) (TTRT-Τ) + nΤ + Τ
= (n-1)TTRT + 2Τ
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Summary
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High speed LANs and technologies
Ethernet Hubs and Switches
Fast Ethernet
Gigabit Ethernet
FDDI
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun
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3. Wireless networks
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Outline
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Wireless LAN (IEEE802.11a, 11b & 11g)
• The 802.11 Protocol Stack
• The 802.11 Physical Layer, MAC Sublayer Protocol,
Frame Structure, and Services
Broadband Wireless (IEEE802.16)
• The 802.16 Protocol Stack
• The 802.16 Physical Layer, MAC Sublayer Protocol,
and Frame Structure
Bluetooth (IEEE802.15)
• Bluetooth Architecture
• Bluetooth Applications, Protocol Stack, Radio Layer,
Baseband Layer, L2CAP Layer and Frame Structure
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The 802.11 Protocol Stack
Part of the 802.11 protocol stack.
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The 802.11 MAC Sublayer Protocol
(a) The hidden station problem.
(b) The exposed station problem.
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The 802.11 MAC Sublayer Protocol (2)
The use of virtual channel sensing using CSMA/CA.
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The 802.11 MAC Sublayer Protocol (3)
A fragment burst.
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The 802.11 MAC Sublayer Protocol (4)
Interframe spacing in 802.11.
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The 802.11 Frame Structure
The 802.11 data frame.
Data,
Control,
management
RTS
CTS
ACK
More
fragments
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Power
Manage
67
More
frames
•WEP used &
•Order for processing
802.11 Services
Œ
Œ
Distribution services
• Association: connect mobile station to base stations
• Disassociation: release connection
• Reassociation: move rom one cell to another
• Distribution: route frame from the base station
• Integration: frame needs to be sent through non-802.11
Intracell services
• Authentication: authenticate the mobile station
• Deauthentication: the station leaves the network
• Privacy: Encryption using RC4
• Data delivery: data transmission
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Broadband wireless (IEEE802.16)
The 802.16 transmission environment.
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The 802.16 Protocol Stack
The 802.16 Protocol Stack.
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The Physical Layer and service classes
Frames and time slots for time division duplexing.
•
Service Classes
• Constant bit rate service
• Real-time variable bit rate service
• Non-real-time variable bit rate service
• Best efforts service
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The 802.16 Frame Structure
(a) A generic frame.
(b) A bandwidth request frame.
EC: Encryption, type: packet or fragment, CI: present or not
of checksum, EK: encryption key used, length: frame length,
connection id: the packet belong to,
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Bluetooth Architecture (IEEE802.15)
Two piconets can be connected to form a scatternet.
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Bluetooth Applications
The Bluetooth profiles.
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The Bluetooth Protocol Stack
The 802.15 version of the Bluetooth protocol architecture.
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The Bluetooth Frame Structure
A typical Bluetooth data frame.
Identify the master
Identify
devices
Frame
types
F: flow control by slave
A: ack is used by piggyback
S: sequence to detect re-transmission
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Summary
Œ
Œ
Œ
Wireless LAN (IEEE802.11a, 11b & 11g)
Broadband Wireless (IEEE802.16)
Bluetooth (IEEE802.15)
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3. LAN interconnections
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Introduction
Œ
Œ
Œ
Œ
Œ
Œ
Œ
Repeaters
Bridges
Transparent Routing;
Spanning Tree Algorithm
Source Routing;
Internetworking different LAN types
VLAN
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Repeaters, Bridges & Routers and Gateways
(a) Which device is in which layer.
(b) Frames, packets, and headers.
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Hubs, Bridges and Switches
(a) A hub. (b) A bridge. (c) a switch.
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Repeater and Bridge functions
End Station
End Stat
End Station
End Stati
Bridge
Transport
Network
Transpor
Network
Transport
Network
LLC
MAC
Physical
LLC
MAC
Physical
LLC
MAC
Physical
Repeater
LAN Segment 1
LAN Segment 2
Relay
MAC
MAC
Physical Physical
LAN Segment 1
Repeater
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Transport
Network
Bridge
82
LLC
MAC
Physical
LAN Segment 2
Why Bridges ?
Œ
Œ
Œ
Œ
Œ
Œ
Removal of physical constraints such as length, number of
stations, segments, etc (geographical separated and
physical distance limit)
Buffering allows mix of LAN types (Different department
have different LANs initially)
Transparent to protocols above MAC
Easier management and security
Partitioning improves overall reliability
Accommodate the load
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Bridge Types
Œ
Œ
Transparent (or Spanning Tree)
• bridges make all routing decisions
• IEEE 802.1(D) standard
Source Routing
• end-stations make major routing decisions
• part of IEEE 802.5 - token ring - standard
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Transparent Bridges
•Bridge uses a
database so that frames
can be forwarded to
correct port
•Need someway for this
database to be
dynamically created and
maintained
Higher Layer Entities
(Bridge Protocol Entity, Bridge Management, etc.)
LLC Entities
LLC Entities
MAC Relay Entity
MAC Entity
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LAN 1
85
MAC Entity
LAN 2
Bridge Architecture
Forward
DataBase
Port
management
MAC
Station
address
Port
No.
Bridge
Protocol
Memory
LAN seg A
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MAC
LAN seg B
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Bridge Learning
Œ
Œ
If LAN segments + bridges arranged in a tree structure
(i.e. only 1 possible route from any station to any other
station) then possible for Bridge to learn station addresses
by monitoring traffic on each port. During this learning
phase frames are forwarded on all ports (‘flooding’)
By including an inactivity timer to limit remembrance of
address then DTE allowed to move around
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Multiple Paths
Œ
If however there are two paths between any segments
then the entry in the Forward DataBase will be continually
updated
1
receive
2
flood
flood
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1
2
Need to agree single path
Œ
Œ
Œ
Œ
Need to arrange single ‘logical’ path between any two
segments
Bridges regularly exchange special frames
Bridge Protocol Data Units
Each Bridge allocated priority value + unique identifier
Special Root Bridge dynamically chosen
(with highest priority and smallest id
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Spanning Tree Algorithm
Œ
Œ
Œ
Œ
The Spanning Tree Algorithm works
dynamically and in a distributed
fashion.
Bridges exchanging Bridge Protocol
Data Units (BPDUs) between
themselves.
All the bridges have a unique MAC
group address for exchanging BPDUs.
Each BPDU contains a number of
fields including:
• Bridge ID of the Root
• RPC to the root from the bridge
• ID of the bridge sending the BPDU
• ID of the port sending the BPDU
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Œ
Œ
Œ
Œ
Œ
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A single bridge is dynamically
chosen to be the Root Bridge.
Each bridge decides which of its
ports has the least Path Cost to the
Root (RPC). This port is treated as
the Root Port (RP).
For each LAN segment a single
bridge port is selected for
forwarding frames. This is known
as the Designated Port (DP).
RPs cannot also be DPs.
Bridge ports which are neither RPs
nor DPs are ‘switched off’, i.e. a
port can either be in a forwarding
state or a blocking state.
Example of spanning tree bridges
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Source Routing Bridges
Œ
Œ
Œ
Œ
Œ
Œ
Can be used with any LAN type though primarily used with
Token Ring LANs
The end station perform the routing function. The routeing
information is inserted into the frame and is used by each
bridge.
Routeing information comprises of segment-bridge,
segment-bridge, ...., identifiers.
Each end station need to know the routeing information.
If a destination unknown, discovery frame is broadcasted to
find the routeing information
Spanning tree is used to avoid frame explosion.
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Token Ring Frame Format (Routing)
1
1
1
SD
AC
FC
2 or 6
2 or 6
Destination I Source
address
G address
variable
variable
4
1
1
Routing
information
Data
FCS
ED
FS
1= Routing information field present
0= No routing available
Routing
information
2
Routing
control
Frame
type
Maximum
frame size
2
2
2
Route
Route
designator 1 designator 2
Routing
field length
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Route
designator N
Segment
identifier
93
Bridge
identifier
Source Routing Frame Explosion
Bridge
Ring
A
••••
1 Frame
1
2
3 Frames
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B
N
3
N-1
Frames
Source Routing vs Transparent
Œ
Œ
Œ
Œ
Routing Philosophy
User chooses vs Bridge cooperation
Quality of Routes
Spanning tree avoid loops but doesn’t guarantee best;
with source routing can find all paths and choose best for
specific destination
Use of available bandwidth
source routing could load balance
Route forwarding overheads
Transparent bridge has to keep large route table slow search especially with high speed LANs
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Source Routing vs Transparent (cont.)
Œ
Œ
Route finding efficiency
Concerning with cost of determining route Transparent scheme needs 1 frame/branch of tree from a
bridge node; source routing although initial route frames
also follow tree subsequent all-routes broadcast frames
do not
Reliability
Transparent regularly check for bridge/link failures - in
source routing this task moved to stations which may not
have information
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Remote bridges
Œ
Œ
Œ
Œ
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It connect two or more distant
LANs
Put a bridge in each LAN and
connect the bridge pair-wise
with point to point lines (such
as leased telephone line)
Various protocols can be used
on the point to point lines (such
as data link protocol) putting
complete MAC frame in the
payload
Or strip off the MAC header
and tailor at the sources and
put it back at the destination
Mixed LAN Bridging
Unfortunately this is not as straight forward is it may at first
appear. Problems are caused by:
ΠDifferent frame formats: frames need reformatting - not too
much of problem
ΠDifferent data rates: bottlenecks fast->slow involves
queuing
ΠDifferent maximum frame sizes: potential problem as
different MACs have different sizes - segmentation not part
of 802.1(D) - get into Bridge-Routers
ΠPriorities
• Token Ring’s A and C bits
• Token Bus’s temporary token handoff feature
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IEEE 802 MAC Frame Formats (1/2)
Start
Access Frame
Preamble delimiter control control
DA, SA
Length
802.3
802.4
802.5
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Data
Pad
FCS
End
delimiter
Frame
status
IEEE 802 MAC Frame Formats (2/2)
The IEEE 802 frame formats. The drawing is not to scale.
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Virtual LANs (802.1Q)
(a) Four physical LANs organized into two VLANs, gray & white, by two bridges.
(b) The same 15 machines organized into two VLANs by switches.
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The IEEE 802.1Q Standard
Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded
symbols are VLAN aware. The empty ones are not.
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The IEEE 802.1Q frame
The 802.3 (legacy) and 802.1Q Ethernet frame formats.
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Summary
Œ
Œ
Œ
Œ
Œ
Œ
Œ
Repeaters;
Bridges
Transparent Routing;
Spanning Tree Algorithm
Source Routing;
Internetworking different LAN types
VLAN
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Recommended Books
Œ
Œ
Tanenbaum A., “Computer Networks - 4rd edition”,
Prentice Hall 1996, 0-13-066102-3.
Stalling W., “Data and Computer Communications - 6th
edition”, Prentice Hall 2000, 0-13-086388-2.
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