[PPT] - Computer Networks I Data Link Layer Local Area Network (LAN) Prof. PowerPoint Presentation

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Data Link Layer – LAN

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l2lan.ppt

Prof. Dr.-Ing. Lars Wolf

IBR, TU Braunschweig Mühlenpfordtstr. 23, D-38106 Braunschweig, Germany, Email: wolf@ibr.cs.tu-bs.de

Computer Networks I

Data Link Layer – Local Area Network (LAN)

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Scope

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Overview

1 What are Local Area Networks (LANs)? 2 Medium Access Control (MAC) 3 Dynamic Channel Allocation: Contention Free 3.1 Polling 3.2 TDMA (Time Division Multiple Access) 3.3 Token – Procedure 4 Dynamic Channel Allocation: with Contention 4.1 ALOHA 4.2 CSMA (Carrier Sense Multiple Access) 4.3 Comparing ALOHA, CSMA.., CSMA CD 5 Reference Model and Logical Link Control

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Overview

6 IEEE 802.3: CSMA / CD 6.1 802.3: Configurations 6.2 Maximum Distance between Two Stations 6.3 802.3: Frame Format 6.4 802.3: Frame Format – Details on Minimum Length 6.5 802.3: Control Flow 6.6 802.3: Behavior When Colliding 6.7 Switched 802.3 LANs 6.8 802.3: Conclusion CSMA / CD 7 IEEE 802.5: Token Ring 7.1 802.5: Ring Topology 7.2 802.5: MAC Protocol 7.3 802.5: Physical Layer 7.4 802.5: Calculations, also Ring Bit Number 7.5 802.5: MAC Frame Formats 7.6 802.5: Summary Token Ring 8 Other LANs and a Comparison 8.1 IEEE 802.4: Token Bus 8.2 Comparison of 802.3 and 802.5 9 Faster IEEE 802.3 Variants 9.1 IEEE 802.3u: Fast Ethernet 9.2 IEEE 802.3z: Gigabit Ethernet 9.3 IEEE 802.3ae: 10 Gigabit Ethernet

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What are Local Area Networks (LANs)?

A LAN (Local Area Network) is

a network for the bit-serial transmission of information between

components that are

independent and
connected to each other
legally it is controlled by the user
its range is usually limited to the area within the property boundaries

Source: ISO TC 97 (International Standardization Organization - Technical Committee 97)

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... ... ... campus 1 km building 100 m LAN room 10 m ... ... ... Example CPUs are in a common .. Processor Distance

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What are Local Area Networks (LANs)?

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Features of Local Area Networks

relatively high speed (>1 Mbps)
easy / reasonably priced connection
no telecommunication regulations
distance limited to a few kilometers
transmission of varying types of information
texts, general data
images, animated images
audio, video
connecting different devices
computers
terminals / printers
storage units
...

Common aspects of LANs:

several senders/sources share a channel/medium

MEDIUM ACCESS CONTROL

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Medium Access Control (MAC)

Reasons for the need of MAC

if

several persons (senders/sources) share a channel/medium

then

it is very likely that two or more will start communicating at the same time

schemes needed to avoid chaos Important sublayer of L2

especially for LANs
technically lower part of L2

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Channel Allocation Problem

Static Channel Allocation in LANs and MANs

using schemes such as FDM or TDM
simple
does not work well with bursty traffic
inefficient and with poor performance

Dynamic Channel Allocation in LANs and MANs needed

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Dynamic Channel Allocation Schemes

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Dynamic Channel Allocation – Terms / Assumptions

1. Station Model
N independent stations (computers, ...) generating frames for transmission
station blocks until frame has been successfully transmitted
2. Single Channel Assumption
single channel for all communication (all can send / receive)
3. Collision Assumption
2 frames transmitted simultaneously overlap signal is garbled

collision

stations can detect collisions
4. (a) Continuous Time
frame transmission can begin at any instant; no master clock

(b) Slotted Time

time is divided into discrete intervals (slots)
frame transmission always begins at start of slot
slot may contain 0, 1, 2, ... frames (idle, successful transmission, collision)
5. (a) Carrier Sense
stations know whether channel is in use or not before trying to use it
if channel sensed as busy, no station will attempt to transmit until it goes

idle (b) No Carrier Sense

stations cannot sense channel before trying to use it

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Dynamic Channel Allocation: Contention Free

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Polling

Master Control Station LOOP FOR I = 1 TO N DO POLL StationI; /* Request Data / Give Permission To Send / WAIT for EOT from Station I; / End of Transmission*/ END; END; Follow-up (slave) Station X LOOP Wait for Poll for Station X; IF Data available to be send THEN Send Data; EOT to Master Control Station; END; Features:

simple and controlled but …
Master Control Station failure leads to complete outage
wasted capacity (polling unnecessary) if no data to be send

3.1

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TDMA (Time Division Multiple Access)

Station X Waiting for Start Pulse; I := 1; LOOP IF I = X THEN Send for the duration ∆T; I := (I MOD N) + 1; Wait for the next pulse; END; with I: slot number ∆T: slot duration Features:

poor channel utilization for stations with low transmission demands
fixed (and partially unused) channel capacity even when number of

stations varies

centralized pulse synchronization

3.2

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TDMA Collision-Free: Reservation

Principle:

transmission sequence among stations defined by PREVIOUSLY

distributed RESERVATION REQUESTS

alternating
distribution of reservation requests and
sending of reference data

Example: Basic bitmap protocol for 8 stations

contention slots: station j (j=0..7) announces that it has a frame to send
all stations get complete knowledge about which stations wish to

transmit Features:

Waiting time due to contention period
exact timing necessary
contention slots need some capacity too

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Token - based

stations form a virtual or a physical ring
a token (authorization to send) circulates on this ring
a station can send, if it has a token

Station X LOOP wait for Token; IF Data to Send THEN Send Message; Transmit Token to the Next Station; END; Features:

Waiting time (for Token)
deterministic scheme (fair)

3.3

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Dynamic Channel Allocation: with Contention

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(Pure) ALOHA

History

University of Hawaii, 1970
originally via radio station with 9.600 bps
413 MHz: centralized host (to everybody) on ground
407 MHz: all stations to host

Principle:

sending without any coordination whatsoever
sender listens at the (return-)channel (after sending)
host sends ACKs if data received successfully
in case of collision
retransmit after a random time interval

4.1

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ALOHA: Example of a Collision

t: time for sending a frame Collision

considering frame D, a collision occurs if
another frame has been generated between T0-t and T0 or

between T0 and T0+t

collision window:

Disadvantage:

large number of collisions

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Slotted ALOHA

History

University of Hawaii, 1972

Principle like Unslotted ALOHA, but discrete approach:

time divided into slots
start sending only at beginning of a slot
collision
if the beginning of a frame is between T0 and T0+t, i. e.

it cannot start at T0-t and last intoT0+t

the time pattern reduces the collision window by half (= t)
requires centralized synchronization

Disadvantage

still many collisions, but less than with Unslotted ALOHA

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ALOHA: Throughput

Assumptions here: a multitude of stations

t: time for sending a frame
S: AMOUNT OF NEW requests to send per frame sending time t

Poisson’s distribution

S > 1 more channel capacity required than available,
i. e. almost always collision
0 < S < 1

more sensible

G: ALL requests to send
(retransmissions added to new requests to send S) per frame time

Maximum channel usage

Unslotted ALOHA:

1/2e ≈ 0.184

Slotted ALOHA:

1/e ≈ 0.368

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CSMA (Carrier Sense Multiple Access)

ALOHA and Slotted ALOHA:

station sends (if request to send exists) and realizes
nly AFTERWARDS, if it was actually able to send

CSMA Principle

check the channel BEFORE sending
channel status
busy:
do not send but wait
keep checking continuously until channel is available

OR wait some time and re-check channel

idle:
transmit frame
possibility for collision still exists!
collision:
wait for a random time then start again with channel checking

4.2

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CSMA Variation 1-Persistent

Principle

Request to send check channel
channel status
busy:
continuous re-checking until channel becomes idle
idle:
send
i. e. send with probability 1
collision:
wait random time, then re-check channel

Properties

if channel is idle: send with probability 1 (thus 1-persistent)
MINIMIZING THE DELAY OF OWN STATION
but many collisions during higher load
low throughput

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CSMA Variation Non-Persistent

Principle

Request to send check channel
channel status
busy:
wait random time without checking the channel continuously,
channel RE-CHECK ONLY AFTER A RANDOM TIME INTERVAL
idle:
send
collision:
wait for a random time, then re-check channel

Properties

assumption that other stations want to send also,
therefore it is better to have the intervals for the re-checks randomly

determined

improved overall channel utilization (efficiency)
but longer delays for single stations

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CSMA Variation P-Persistent

wait random time, re-check channel

idle:

send with probability p, wait for next slot with probability 1-p, ...etc.

collision:

..etc

collision:
wait random time, re-check channel

Properties

compromise between delay and throughput
defined by parameter p

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CSMA Variation CD

Carrier Sense Multiple Access with Collision Detection

CSMA 1-persistent with CD

Principle:

sending stations abort transmissions as soon as they detect a

collision

saves time and bandwidth
frequently used (802.3, Ethernet)
algorithm
while sending a frame: station must detect collision (comparing received

with transmitted signal: signal encoding must allow collisions to be detection)

Contention period:

Extreme case: short frame, maximum distance between stations

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CSMA Variation CD: Contention Period

Extreme Case:

short frame, maximum distance between stations

collision window station can be certain only after 2τ

that it has occupied the channel with no collision
(1 km coax cable: τ ≈ 5 μs)

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Comparing ALOHA, CSMA.., CSMA CD 4.3

Terminates sending immediately, waits random time depending on procedure, (see above) 1-persistent is e.g. Ethernet X X

CSMA/CD

X sends with probability p, waits with probability 1-p (for next slot, then re-checks status) initially: continuous wait until chnl/slot idle (X) X p persist. continuous wait until channel is idle (X) X 1 persist. wait random time interval then re-check channel and send (if possible) (depending on algorithm “idle/ busy") sends immediately re-check channel only after random time interval (X) X nonpersist

CSMA

X X slotted re-transmit after random time interval sender does not know these conditions X pure

ALOHA

collision idle busy after during before Time slot behavior in case of desire to send and if one of the following states has been determined channel is checked (regarding decision to send, not with regard to collision)

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Throughput of e.g. Aloha

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.2 0.4 0.6 0.8 1

Normalized Channel Occupancy Normalized Throughput ~0.185 0.5

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Comparing Performance: CSMA, ALOHA

S channel usage / throughput per frame

i. e. new requests to send, per frame sending time t
note: possibly long delay

G load (attempts per frame-time)

i.e. all requests to send per frame time
re-transmissions added to new requests to send S

Normalized Throughput Normalized Channel Occupancy

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Reference Model and Logical Link Control

e. g.
IEEE 802.3 Ethernet (10 Mbit/s)
IEEE 802.3u Fast Ethernet (100 Mbit/s)
IEEE 802.3z / 802.3ab Gigabit Ethernet over fiber / twisted pair
IEEE 802.3ae 10 Gigabit Ethernet
IEEE 802.3..... .....

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802.2: Logical Link Control

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802.2: Logical Link Control (LLC)

Function

subset of HDLC
High Level Data Link Control HDLC
common interface
to L3 for all underlying LAN/MAN/WAN components

Services

unacknowledged connection-less (unreliable datagram)
upper layers ensure
that sequence is maintained, error correction, flow control
acknowledged connection-less (acknowledged datagram)
each datagram is followed by exactly one acknowledgement
connection-oriented
connect and disconnect
data transmission incl. acknowledgement, guaranteed delivery to

receiver

maintaining the sequence
flow control

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LLC Frame

Format

includes LLC Service Access Points SAPs for source and destination

Varying AC frames:

formats

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IEEE 802.3: CSMA / CD 6

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IEEE 802.3: CSMA / CD

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IEEE 802.3: CSMA / CD

History

1976
Ethernet by Xerox,

Robert Metcalf (2,94 Mbps)

1980
Ethernet industrial standard by

Xerox, Digital Equipment (today part of HP) and Intel (10 Mbps)

1985
IEEE 802.3 based on Ethernet

IEEE 802.3

specifies a family based on the 1-persistent CSMA/CD systems
(1 - ) 10, 100 Mbps, 1, 10, 100, … Gbps on different media
Ethernet is a protocol of this family

1-persistent CSMA / CD

L1:
Manchester Encoding
(on all cables except for 10BROAD36 broadband, here DPSK)

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IEEE 802.3: CSMA / CD

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802.3: Configurations

Rule (in general)

Always EXACTLY ONE WAY between 2 stations in the Ethernet

Small configuration

6.1

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802.3: Configurations

Medium-sized configuration

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802.3: Configurations

Large configuration

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802.3: Hardware Components

Mainly used media/cables

used for higher speed best between buildings 1024 2000m Fiber optics 10Base-F most often used easy maintenance 1024 100m Twisted pair 10Base-T former cable cheapest system 30 200m Thin coax 10Base2 former cable (was) good for backbones 100 500m Thick coax 10Base5 Comment Advantages Nodes/ Segment Max. Segment Size Cable Name

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802.3: Hardware Components

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802.3: Hardware Components

Transceiver

connection to the Ethernet cable
electronics assembly for carrier and collision recognition

Ethernet cable

Thick/Thin Ethernet, Twisted Pair (single or double)

today usually UTP ("Unshielded Twisted Pair")

max. length: 500 m (or depend. on resp. cable type 500m/200m,

100m) Transceiver cable

connects transceiver and interface card, max. length: 50 m

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802.3: Hardware Components

Repeater

connects several cable segments
repeater connects over a distance of max. 100 m
because of 2 x connections to the transceiver at 50 m per 2 cable

segments

max. distance between 2 repeaters: 2.5 km
i. e. between the connections to the individual segments
max. 4 repeaters on one path between 2 (random) transceivers

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Maximum Distance between Two Stations

Example: Thick-Ethernet and fiber optic cable

6.2

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Maximum Distance between Two Stations

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802.3: Frame Format

Preamble:

always 7 times 01010101
allows synchronization of the receiver’s clock with sender’s clock

Start Frame Delimiter:

beginning of the frame (10101011)

6.3

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802.3: Frame Format

Destination Address and Source Address:

individually, group, all:
unicast

individual address

multicast

group address

broadcast

all address bits are "1"

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802.3: Frame Format

.. Destination Address and Source Address: (cont)

1. addressing in 16 bit/2 byte format

Group Address I/G = 1 Individual Address I/G = 0 15-Bit Address I/G

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802.3: Frame Format

.. Destination Address and Source Address: (cont)

…
addressing in 6 byte/48 bit format (COMMON PRACTICE)
common practice (e.g. with 10 Mbps only this format)
address assignment: ...
local address assignment
can be done on site by authorized entity
global address assignment
IEEE assigns worldwide unique 46 bit addresses
7,03E+13 (7,03 x 1013) potential addresses
L3 (network layer) has to locate address

Locally Administered Address U/L = 1 Globally Administered Address U/L = 0 Group Address I/G = 1 Individual Address I/G = 0 46-Bit Address U/L I/G

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802.3: Frame Format

Length:

number of bytes in LLC Data
encoded within 2 bytes

LLC Data:

0 - 1 500 bytes actual data

Frame Check Sum

CRC
to detect errors

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802.3: Frame Format

Pad:

min. frame length = 64 bytes (=6+6+2+46+4)
for collision detection (see below)
shorter frame length invalid frame

potentially padding bytes to achieve the minimum frame length

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802.3: Frame Format

Frame Length – Padding: Some Details

"IEEE 802.3 packets have minimum size restrictions

based on network bandwidth

When necessary, the data field should be padded

(with octets of zero)

to meet the 802.3 minimum frame size requirements.
This padding is
not part of the IP packet and is
not included in the total length field of the IP header."
see e.g.

www.zvon.org/tmRFC/RFC948/Output/chapter3.html

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802.3: Frame Format – Details on Minimum Length

Reason (for minimum length):

transceiver aborts frame transmission during collision
i. e. short invalid frames appear
algorithm
station should recognize during frame transmission whether a

collision occurred

extreme case:
short frame & stations at maximum distance

6.4

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802.3: Frame Format

collision window
802.3 Frame Format

Example: calculation with a length of 450 bit (>56 Byte)

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802.3: Frame Format

time to send 450 bits at 10 mbps :

collision window:
2τ , during this time 450 bits still have to exist at least on the

line of the length 2*dmax

with
resulting in

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802.3: Frame Format

comment:
the sample calculation above constitutes the calculation of the

theoretical maximum distance between two stations

behavior if parameterized differently:
with higher data rates

the minimum frame size must be larger

e. g. for 1 Gbps (expansion 2,5 km) 6400 bytes
or

data rate increased but frame size the same: shorter distance possible

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802.3: Control Flow

backoff = r • ∆t with ∆t = send time for 512 Bits (51,2 μs) 0 ≤ r < 2k with k = min (n, 10) n = number of unsuccessful attempts to send (1 ≤ n ≤ 16)

6.5

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802.3: Control Flow

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802.3: Collision Treatment

error message to L3 16th 0,..., 2k-1

k=min(n, 10)

nth ... 0, 1, 2, 3, 4, 5, 6 or 7 3rd 0, 1, 2 or 3 2nd 0 or 1 1st next attempt after a waiting ... frames ... collision after first request to send

Time is divided into discrete slots

slot length equal to worst case round-trip propagation

time (2t) Binary Exponential Backoff Algorithm Effects, behavior…

6.6

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802.3:Behavior When Colliding

Behavior

during increasing load

longer waiting periods

if more stations

lower utilization

if longer frames

higher utilization

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Switched 802.3 LANs

Problems with hubs (repeaters)

all stations within one collision domain

collision domain

individual connections combined to this
but no collisions with other domains

Increasing the throughput by

higher data rates than 10Base-T
100Base-T, …
but this requires new adapters
switching function in 802.3

6.7

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Switched 802.3 LANs

SWITCH (instead of HUBs) as relaying center

station sends frame
switch tries to locate
first:

the receiver within the "board"

and only if not located:

at a different location

but (typically) does not broadcast frame on all lines

(tries to avoid this)

hence: reduced collision domain

Twisted pair

Hub Switch

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802.3: Conclusion CSMA / CD

Properties + most widely spread + no network shutdown needed to connect new stations + practically no waiting time if utilization is low

analog components for collision detection
minimum frame size (64 bytes)
not deterministic (no maximum waiting period)
no prioritization
when load increases, probability for collisions also

increases poor throughput during high load periods

6.8

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IEEE 802.5: Token Ring 7

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IEEE 802.5: Token Ring

History

Z-Ring: prototype of a Token Ring (IBM Zurich)
IBM chooses Token Ring as the inhouse LAN standard
1985: IEEE 802.5
1986: IBM Token Ring product

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802.5: Ring Topology

Ring

not really a broadcast medium, but
a concatenation of point-to-point lines
station copies information bit by bit from one line to the next

(active station)

7.1

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802.5: MAC Protocol

Token Protocol Principle

token
frame with special bit pattern
ne token circulates on the ring
1. before station is permitted to send
it must own and remove the token from the ring
2. station may keep the token for a pre-defined time and may send

several frames

3. after sending
the station generates a new token

7.2

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802.5: MAC Protocol: Early Token Release

Token Ring behavior during increased data rate

until now (with lower rates) always data on the line, this means long bits
however, frames occupy only a minor part of the ring at higher speeds

(the remainder is lost) Principle

append token directly to the last data transmission, always only 1 token

in circulation

Sender A:

sends data appends free token to data

Sender B:

takes token appends its data to frame appends free token

Application

16 Mbps Token Ring and, in a modified variation, on FDDI

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802.5: Token and Frames

Typical (measured) values:

token circulates 20 times and
one frame circulates with e.g. 256 byte

Token

3 byte length

Frame AC contains TOKENBIT T T = 0: Token T = 1: Data

"Remove Token from Ring": T := 1

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802.5: Physical Layer

Parameter

medium:
twisted copper cable (Shielded Twisted Pair) or
coaxial conductor
digital transmission:
differential Manchester encoding
transmission rates:
(1 and) 4 Mbps
max. 250 stations

Extensions

coax, optic fiber (as FDDI)
increased transmission rates:
16 Mbps
(as Early Token Release, IBM product)

7.3

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802.5: Calculations, also Ring Bit Number

Additional condition:

token has to fit completely onto the network
otherwise the station sending the token might think that 2 tokens
ccupy the ring simultaneously
because it is receiving a token while it is still sending

Calculation V = signaling speed [approx. 200 m/µsec] L = full ring length K = transmission capacity [bit/sec] Ring circulation time U = L/V Ring bit number R = U • K (no. of bits on the ring) R = L • K/200 (m/µSec) Example: L = 1000 m; K = 4 Mbps: R = 20 bit 802.5 token(3byte) does not fit on ring Solution: artificial delay at each station...

7.4

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802.5: Calculations, also Ring Bit Number

Solution: artificial delay at each station Calculation: D = delay / station [bit] N = number of connected stations Ring circulation time U = L/V + N • D/K Ring bit number R = U • K = L • K/V + N • D Example: L = 1 000 m; K = 4 Mbps; N = 50; D = 1 : R = 70 bit

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802.5: Maximum Waiting Period

What is the maximum waiting period for a station before it receives permission to send again?

i.e. all stations want to send with the max. amount of allowed time

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802.5: Maximum Waiting Period

What is the maximum waiting period for a station before it receives permission to send again? W = maximum waiting period: W = all others are sending + token rotates x-times = (N-1)(Pmax/K + U) + N(PT/K + U/N) = (N-1)(Pmax/K + U) + NPT/K + U = (N-1)(Pmax/K + U) + U Note: NPT/K = 0 for PT << Pmax

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802.5: MAC Frame Formats

Token Format Frame Format

7.5

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802.5: MAC Formats

Access Control (AC) T Token bit: token identifier M Monitor bit: recognizing orphaned messages Priority management

P . . . token priority
R . . . priority for reserving the next token
e. g. station wants to send frame containing priority N
but receives token only if P ≤ N
can reserve next token with priority N (R := N), if R ≤ N

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802.5: MAC Formats: Priorities

Priority classes: example: access by priority Station A:

sends data at low priority 0

Station B:

reserves priority token by setting access control field

Station A:

generates prioritized token

Station B:

gets prioritized token and
sends data with high priority

Station C = Receiver of Station B:

receives data and
releases token with previous priority

station management 7 reserved 5 - 6 bridges 4 available for data transfer 1 - 3 normal data transfer Use Priority

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Data Link Layer – LAN

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802.5: MAC Formats

Frame Status (FS) A = address-recognized bits C = frame-copied bits r = reserved bits RECEIVER RESETS BITS A=0 C=0: destination station does not exist A=1 C=0: destination exists, but frame is not accepted A=1 C=1: destination exists and frame is accepted Comments:

these bits (Frame Status) are not included in checksum, because
this field is set after whole frame has been received
duplicate included because of increased reliability

r r C A r r C A

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802.5 Management Tasks

Stations

detect monitor failure
determine another monitor (Claim Token procedure)

monitor recognizes and corrects errors, e. g.

orphaned frames
lost tokens

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802.5: Summary Token Ring

Properties + digital technology only + multitude of transmission media + wiring centers:

automatic recognition and repair of broken cable

+ deterministic behavior (max. waiting time) + priorities + random frame lengths + good throughput

even during increased utilization

central monitor
delays because of need to wait for token

7.6

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Data Link Layer – LAN

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Other LANs and a Comparison

8.1 IEEE 802.4: Token Bus 8.2 Comparison of 802.3 and 802.5

8

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Data Link Layer – LAN

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IEEE 802.4: Token Bus

HISTORY:

developed and recommended by General Motors in context with MAP

(Manufacturing Automation Protocol)

8.1

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Comparison of 802.3 and 802.5 8.2

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Data Link Layer – LAN

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High-Speed LANs, WANs and MANs

LAN development

towards
more speed
shared bandwidth
from conventional data towards
integrated data (conventional & audio/video)
sometimes also increasing extension (100 km)
i.e. High-Speed LAN also as MAN

WAN development

towards
more speed
bandwidth per connection
from audio (video) towards
integrated services (conventional & audio/video)
also decreasing extension (down to Desk Area range)
i. e. WAN also as MAN (and LAN)

9

SLIDE 87

Data Link Layer – LAN

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LAN, (MANs) and IEEE

802.1 Overview Document Containing the Reference

Model, Tutorial, and Glossary

802.1 b

Specification for LAN Traffic Prioritization

802.1 q

Virtual Bridged LANs

802.2 Logical Link Control
802.3 Contention Bus Standard 10 base 5 (Thick

Net)

802.3a Contention Bus Standard 10base 2 (Thin Net)
802.3b Broadband Contention Bus Standard 10 broad 36
802.3d Fiber-Optic InterRepeater Link (FOIRL)
802.3e Contention Bus Standard 1 base 5 (Starlan)
802.3i Twisted-Pair Standard 10base T
802.3j Contention Bus Standard for Fiber Optics 10base F
802.3u 100-Mb/s Contention Bus Standard 100base T
802.3x Full-Duplex Ethernet
802.3z Gigabit Ethernet
802.3ab

Gigabit Ethernet over Category 5 UTP

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Data Link Layer – LAN

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IEEE 802.3u: Fast Ethernet

History

High-Speed LAN COMPATIBLE to existing Ethernet
1992:
IEEE sets objective to improve existing systems
1995:
802.3u passed as an addendum to 802.3
(alternative solution containing new technology in 802.12)

Principle

retain all procedures, format, protocols
bit duration
reduced from100 ns to 10 ns

Properties: CSMA/CD at 100 Mbps

cost efficient extension of 802.3
very limited network extension
sender has to be able to recognize collision during simultaneous

sending

network extension must not exceed the size of the minimum frame
frame at least 64 byte, i.e. 5 µs at 100 Mbps per bit
i.e. extension only a few 100 meters

"collision domain diameter" = 412 m (instead of 3000m)

many collisions (lower utilization)

9.1

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IEEE 802.3u: Fast Ethernet

Use of 10Base-T (UTP) wiring style: no 10Base-2 / 10Base-5 Medium 100Base-F (fiber optics):

maximum segment length of 2000 m too long for collision recognition

may be used only in context with buffered hub ports collisions impossible

usually improved procedure required

for 100 Mbps and more to transmit data in real time

Full duplex at 100Mbps

two multimode fiber (one per direction)

2000m Fiber optics 100Base-F Full duplex at 100Mbps (Cat 5 UTP)

better cable quality
uses 2 twisted pairs (one each to/from hub)
4B/5B encoding

(16 out of 32 bit combinations)

100m Twisted pair 100Base-TX Uses category 3UTP

cables can’t handle 100 Mbps Manchester

signalling speed: 25 MHz

needs 4 twisted pairs

(1+1+2: to/from hub, switchable)

no Manchester but ternary encoding (8B/6T)

100m Twisted pair 100Base-T4 Characteristics Max. segment Cable Name

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IEEE 802.3z: Gigabit Ethernet

History

IF POSSIBLE,
High-Speed LAN compatible with existing Ethernet
1998: 802.3z passed as an Addendum to 802.3

Desirable principle

if 100% compatible
retain all procedures, formats, protocols
bit duration reduced from 100 ns over 10 ns to 1 ns
but, then
maximum extension would also be
1/100 of the 10 Mbit/s Ethernet,
i. e. (depending on the type of cable) approx. 30 m

9.2

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IEEE 802.3z: Gigabit Ethernet

Principle for

A. point-to-point links
full duplex mode
no change of packet size
interconnected by switch function
with 1 Gbps in both directions
B. shared broadcast mode
half duplex mode
CSMA/CD
interconnected by hub function
tradeoff between distance and efficiency
i.e. see the following details

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IEEE 802.3z: Gigabit Ethernet:Shared Broadcast Mode

Principle:

maintain (as far as possible)
CSMA-CD with 64 byte minimum length
introducing two features
carrier extension
frame bursting

Carrier extension

from 512 bit (64 byte) length, previously
to

512 byte length

i. e. by attaching a new extension field
following the FCS field (Frame Check Sum)
to achieve the length of 512 byte
Approach:
added by sending hardware and
removed by receiving hardware
software doesn’t notice this
low efficiency
transmit 46 byte user data using 512 byte: 9%

Frame bursting

allow sender to transmit CONCATENATED SEQUENCE OF MULTIPLE

FRAMES in single transmission

needs frames waiting for transmission
better efficiency

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IEEE 802.3z: Gigabit Ethernet:Shared Broadcast Mode

Maximum extension of a segment (i.e. of a Collision Domain)

5 UTP

100 m

coax

25 m

multimode fiber

550 m

single mode fiber

5 km Possible uses

preferably

in the "Backbone- Network" Sources of information

IEEE
http://grouper.ieee.org/groups/802/3/z/index.html
Gigabit Ethernet Alliance
http://www.gigabit-ethernet.org

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IEEE 802.3ae: 10Gbit Ethernet

History:

1999: IEEE 802.3ae task force founded
2002: approval as a standard

Objectives

to preserve 802.3 frame format
incl. minimal and maximal frame sizes
to support full duplex operation only

no CSMA/CD required Type of media used

works over optical fiber only, no UTP or coax

Sources of information

IEEE
http://grouper.ieee.org/groups/802/3/ae/index.html
further
10 Gigabit Ethernet Alliance (10GEA) and others
http://www.10gea.org
http://www.10gigabit-ethernet.com/

9.3

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IEEE 802.3ae: 10Gbit Ethernet

Supported distances:

850nm: 300 m