Layer 1, 2 LAN (Ethernet)

Layer 1, 2 LAN (Ethernet)
Outline
o Ethernet (LAN link)
Layer 1, 2
Wired Ethernet
Wireless
o WAN Link
HDLC / PPP / Frame Relay
Broadband ADSL
Physical and Data link Layer
2
Outline
o Ethernet
LAN (Ethernet)
History
Architecture
Media
CSMA/CD
o Wireless LAN
4
History
o 1976: Ethernet developed by Xerox Palo Alto Research
Ethernet
o
อีเทอร์ เน็ต
o
o
o
o
Center, including Bob Metcalfe (who later founded 3Com)
1980: 10Mbps Ethernet specification by DEC, Intel, and
Xerox
1985: becomes IEEE 802.3 standard (already widely used
before this time)
1995: 100Mbps “Fast Ethernet” standardized in IEEE
802.3u (already widely used before this time)
1998: 1Gbps “Gigabit Ethernet” IEEE standard issued
1999: 10Gbps Ethernet under development
6
History
Architecture
Bus to Star Topology
o Metcalfe’s first design (~197x)
o bus topology popular through mid 90s
all nodes in same collision domain (can collide with
each other)
o today: star topology prevails
“Hub” from 90’s , cheaper and extended range
2000’s active switch in center
each “spoke” runs a (separate) Ethernet protocol
(nodes do not collide with each other)
7
8
Architecture
Architecture
Frame Format
Bus to Star Topology (cont.)
IEEE 802.3
7
1
6
6
2
PA
SFD
DA
SA
LEN
46 – 1500
LLC PDU
4
FCS
Calculate FCS
64 – 1518 bytes
Ethernet
“STAR”
9
6
6
2
PA
DA
SA
Type
46 – 1500
Data
4
CRC
PA : Preamble - 10101010s for synchronization
SFD : Start of Frame delimiter -- 10101011 to start frame
DA : Destination Address -- MAC address
SA : Source Address -- MAC address
LEN : Length -- Number of data bytes
Type: identify the higher -level protocol
LLC PDU+pad : -- minimum 46 bytes, maximum 1500
FCS : Frame Check Sequence -- CRC-32
switch
“BUS”
8
10
Architecture
Architecture
Ethernet MAC address
Signal Encoding : Manchester (reversed for 802.3)
• 0 : high to low
• 1 : low to high
I/G =0 Individual address
I/G =1 Group address
U/L=0 Global administered address
U/L=1 Local administered address
Unicast : define a single destination
Broadcast : FFFFFFFF each station on the network receive and
accept frames
Multicast : a group address defines multiple recipient
11
12
Architecture
Architecture
Ethernet Architecture
Ethernet Architecture
100 BASE TX
Trans Mission Rate
13
Base band /
Broad band
Media
14
Media
Media
Media Type
15
16
Media
Media
o 10 BASE 5
17
18
Media
Media
o 10 BASE 2
19
20
Media
Media
100 BASE : 100 Mbps base band (Fast Ethernet)
o Copper
• 100 Base TX – Twisted Pair distance ~ 100m
o Fiber
• 100 BASE-FX – 400m to 2 km multi mode / single mode
, NIR wave length
• 100 BASE-SX – 300m , short wavelength, lower cost
• 100 BASE-BX – FX + Multiplexer on single mode
21
22
Media
Media
1000 BASE : 1000 Mbps (Gigabits Ethernet)
o Copper
o Gigabit
• 1000 Base T – Twisted Pair distance ~ 100m (cat5e,
cat6,..)
o Fiber
• 1000 BASE-SX – Single mode 65.2/125 µm or 50/125
µm , 500 m, Multi mode 300 m
• 1000 BASE-LX – Single mode 9 µm 5 km
• 1000 BASE-LH – Over 10 km
23
24
Media
Media
o Fiber optics - Multi mode
o Single mode
26
25
Media
Media
o Gigabit Ethernet Media Type
name
Balanced copper cabling
1000BASE-SX
Multi-mode fiber
25 meters
220 to 550 meters
dependent on fiber
diameter and
bandwidth
1000BASE-LX
Multi-mode fiber
550 meters
1000BASE-LX
Single-mode fiber
Single-mode fiber using 1310 nm
wavelength
5 km
1000BASE-ZX
28
specified
distance
medium
1000BASE-CX
1000BASE-LX10
27
(gigabit)
10 km
1000BASE-BX10
Single-mode fiber at 1550 nm wavelength
Single-mode fiber, over single-strand fiber:
1490 nm downstream 1310 nm
upstream
~ 70 km
10 km
1000BASE-T
Twisted-pair cabling (CAT-5, CAT-5e, CAT6, or CAT-7)
100 meters
1000BASE-TX
Twisted-pair cabling (CAT-6, CAT-7)
100 meters
Media
Media (10/40/100 GB)
10 GB / 40 GB / 100 GB
First 10 GB since 2002
Copper : standard 10GBASE T (100m)
40GBASE-CR4 100GBASE-CR10
Fiber : various standard
• 10GBASE (R, SR, LR, LRM, ER, ZR, LR4, ..)
• 40GBASE (SR4, LR4)
• 100GBASE (SR10, LR4, ER4)
Backplane / LAN / WAN
29
30
CSMA/CD
CSMA/CD
o CSMA : Carrier Sense Multiple Access
31
o CD : Collision Detection
32
CSMA/CD
CSMA/CD
o Detect Collision
o CSMA / CD Algorithm
34
33
CSMA/CD
CSMA/CD
o Worse Case Collision Timing
o Collision Detection Rules
35
1. NIC receives datagram 4. If NIC detects another
transmission while
from network layer,
transmitting, aborts and
creates frame
sends jam signal (48 bits)
2. If NIC senses channel
5. After aborting, NIC enters
idle, starts frame
exponential
backoff: after
transmission If NIC
th
m collision, NIC chooses
senses channel busy,
K at random
from
waits until channel idle,
{0,1,2,…,2m-1}. NIC waits
then transmits
K·512 bit times, returns to
3. If NIC transmits entire
Step
2
frame without detecting
another transmission, NIC
is done with frame !
36
CSMA/CD
CSMA/CD
o Minimum Frame Size
o Worse Case Collision Timing (cont.)
37
38
CSMA/CD
CSMA/CD
o Late Collision
39
o Interframe Gap
40
CSMA/CD
Fast Ethernet
o Ethernet Speed and Collision Detection
o 100 Mbps transmission rate
o same frame format, media access, and collision detection
o
o
o
o
o
o
41
rules as 10 Mbps ethernet
can combine 10 Mbps ethernet and fast ethernet on same
network using a switch, or combined hub+switch
64 byte minimum frame ==> 5.12 microsecond xmit time
96 bit interframe gap ==> 0.96 microsecond
network diameter must be smaller than 10 Mbps ethernet
media: twisted pair or fiber optic cable (no coax)
42
Gigabit
o same frame format, media access, and collision detection
o
o
o
o
43
rules as previous ethernet generations
same 64 byte minimum frame and 96 bit interframe gap
can combine 10 Mbps, 100 Mbps, and gigabit ethernet on
same network (but not on same cable) using a switch
200 meter network diameter (using UTP) requires a
minimum transmission time of 512 bytes on shared media
several media types:
• UTP, shielded copper
• short-wave fiber optics
• long-wave fiber optics
Wireless
Outline
Elements of a wireless network
o Wireless links, characteristics
wireless hosts
o laptop, PDA, IP phone
o run applications
o may be stationary (nonmobile) or mobile
CDMA
o IEEE 802.XX wireless
802.11 WLAN
802.15 PAN (Bluetooth)
802.16 WiMAX
network
infrastructure
wireless does not
always mean mobility
o Cellular Internet Access
architecture
standards (e.g., GSM)
45
46
Elements of a wireless network
Elements of a wireless network
base station
wireless link
o typically connected to
network
infrastructure
47
o typically used to
wired network
o relay - responsible for
sending packets
between wired network
and wireless host(s) in
its “area”
network
infrastructure
e.g., cell towers,
802.11 access
points
48
connect mobile(s) to
base station
o also used as backbone
link
o multiple access
protocol coordinates
link access
o various data rates,
transmission distance
Elements of a wireless network
Characteristics of selected wireless link
standards
infrastructure mode
o base station connects
Data rate (Mbps)
200
54
5-11
802.11n
802.11a,g
802.11b
4
1
802.11a,g point-to-point
data
802.16 (WiMAX)
UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO
network
infrastructure
3G cellular
enhanced
mobiles into wired
network
o handoff: mobile
changes base station
providing connection
into wired network
802.15
.384
UMTS/WCDMA, CDMA2000
.056
3G
2G
IS-95, CDMA, GSM
Indoor
Outdoor
10-30m
50-200m
Mid-range
outdoor
Long-range
outdoor
200m – 4 Km
5Km – 20 Km
49
50
Wireless network taxonomy
Elements of a wireless network
ad hoc mode
o no base stations
o nodes can only
single hop
transmit to other nodes
within link coverage
o nodes organize
themselves into a
network: route among
themselves
51
infrastructure
(e.g., APs)
no
infrastructure
52
host connects to
base station (WiFi,
WiMAX, cellular)
which connects to
larger Internet
no base station, no
connection to larger
Internet (Bluetooth,
ad hoc nets)
multiple hops
host may have to
relay through several
wireless nodes to
connect to larger
Internet: mesh net
no base station, no
connection to larger
Internet. May have to
relay to reach other
a given wireless node
MANET, VANET
Wireless Link Characteristics (1)
Wireless Link Characteristics (2)
Differences from wired link ….
o SNR: signal-to-noise ratio
decreased signal strength: radio signal attenuates as
it propagates through matter (path loss)
interference from other sources: standardized wireless
network frequencies (e.g., 2.4 GHz) shared by other
devices (e.g., phone); devices (motors) interfere as
well
multipath propagation: radio signal reflects off objects
ground, arriving ad destination at slightly different
times
10-3
given physical layer:
increase power -> increase
SNR->decrease BER
given SNR: choose physical
layer that meets BER
requirement, giving highest
thruput
• SNR may change with
mobility: dynamically adapt
physical layer (modulation
technique, rate)
BER
10-4
10-5
10-6
10-7
10
20
30
40
SNR(dB)
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps)
54
Code Division Multiple Access (CDMA)
Wireless network characteristics
Multiple wireless senders and receivers create
additional problems (beyond multiple access):
B
A
o used in several wireless broadcast channels (cellular,
o
C
C
A
B
Hidden terminal problem
o B, A hear each other
o B, C hear each other
o A, C can not hear each other
means A, C unaware of their
interference at B
55
10-2
o SNR versus BER tradeoffs
…. make communication across (even a point to point) wireless
link much more “difficult”
53
10-1
larger SNR – easier to
extract signal from noise (a
“good thing”)
o
C’s signal
strength
A’s signal
strength
o
o
space
Signal attenuation:
o B, A hear each other
o B, C hear each other
o A, C can not hear each other
o
interfering at B
56
satellite, etc) standards
unique “code” assigned to each user; i.e., code set
partitioning
all users share same frequency, but each user has
own “chipping” sequence (i.e., code) to encode data
encoded signal = (original data) X (chipping sequence)
decoding: inner-product of encoded signal and chipping
sequence
allows multiple users to “coexist” and transmit
simultaneously with minimal interference (if codes are
“orthogonal”)
CDMA: two-sender interference
CDMA Encode/Decode
d0 = 1
data
bits
sender
code
Zi,m= di.cm
-1 -1 -1
1
-1
1 1 1
-1 -1 -1
slot 1
-1 -1 -1
slot 0
1
-1
-1
-1 -1 -1
slot 0
channel
output
slot 1
channel
output
1
-1
1 1 1 1 1 1
1
d1 = -1
1 1 1
channel output Zi,m
M
Di = Σ Zi,m.cm
m=1
received
input
code
receiver
1 1 1 1 1 1
1
-1 -1 -1
-1
1 1 1
1
-1
1 1 1
-1 -1 -1
slot 1
M
1
1
-1
d0 = 1
-1 -1 -1
-1
-1 -1 -1
slot 0
d1 = -1
slot 1
channel
output
slot 0
channel
output
57
58
IEEE 802.11 Wireless LAN
o 802.11b
802.11 LAN architecture
o 802.11a
o wireless host communicates
5-6 GHz range
2.4-5 GHz unlicensed
up to 54 Mbps
spectrum
o 802.11g
up to 11 Mbps
2.4-5 GHz range
direct sequence spread
up to 54 Mbps
spectrum (DSSS) in
o 802.11n: multiple
physical layer
antennae
• all hosts use same
2.4-5 GHz range
chipping code
up to 200 Mbps
with base station
Internet
base station = access
point (AP)
o Basic Service Set (BSS) (aka
AP
hub, switch
or router
“cell”) in infrastructure mode
contains:
wireless hosts
access point (AP): base
station
ad hoc mode: hosts only
BSS 1
AP
o all use CSMA/CA for multiple access
o all have base-station and ad-hoc network versions
59
BSS 2
60
802.11: Channels, association
802.11: passive/active scanning
o 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels
at different frequencies
BBS 1
AP admin chooses frequency for AP
interference possible: channel can be same as that
chosen by neighboring AP!
BBS 1
BBS 2
BBS 2
AP 1
1
2
AP 1
AP 2
1
scans channels, listening for beacon frames containing
AP’s name (SSID) and MAC address
selects AP to associate with
may perform authentication [Chapter 8]
will typically run DHCP to get IP address in AP’s subnet
61
2
3
2
3
AP 2
4
H1
H1
o host: must associate with an AP
Passive Scanning:
Active Scanning:
(1) beacon frames sent from APs
(2) association Request frame sent:
H1 to selected AP
(3) association Response frame sent:
H1 to selected AP
(1) Probe Request frame broadcast
from H1
(2) Probes response frame sent from
APs
(3) Association Request frame sent:
H1 to selected AP
(4) Association Response frame
sent: H1 to selected AP
62
IEEE 802.11: multiple access
IEEE 802.11 MAC Protocol: CSMA/CA
o avoid collisions: 2+ nodes transmitting at same time
o 802.11: CSMA - sense before transmitting
802.11 sender
1 if sense channel idle for DIFS then
don’t collide with ongoing transmission by other node
transmit entire frame (no CD)
o 802.11: no collision detection!
2 if sense channel busy then
A
B
C
A
B
C
space
return ACK after SIFS (ACK needed due
to hidden terminal problem)
64
receiver
DIFS
802.11 receiver
- if frame received OK
C’s signal
strength
A’s signal
strength
sender
start random backoff time
timer counts down while channel idle
transmit when timer expires
if no ACK, increase random backoff
interval, repeat 2
difficult to receive (sense collisions) when transmitting due to
weak received signals (fading)
can’t sense all collisions in any case: hidden terminal, fading
goal: avoid collisions: CSMA/C(ollision)A(voidance)
63
1
data
SIFS
ACK
Avoiding collisions (more)
Collision Avoidance: RTS-CTS exchange
idea: allow sender to “reserve” channel rather than random
A
access of data frames: avoid collisions of long data frames
o sender first transmits small request-to-send (RTS) packets to
BS using CSMA
B
AP
reservation collision
RTSs may still collide with each other (but they’re short)
o BS broadcasts clear-to-send CTS in response to RTS
o RTS heard by all nodes
sender transmits data frame
other stations defer transmissions
DATA (A)
avoid data frame collisions completely
using small reservation packets!
defer
time
65
66
802.11 frame: addressing
2
2
6
6
6
frame
address address address
duration
control
1
2
3
2
6
seq address
4
control
802.11 frame: addressing
0 - 2312
4
payload
CRC
R1 router
H1
AP
Address 4: used only
in ad hoc mode
Address 1: MAC address
(Transmitter)
of wireless host or AP
Address 3: MAC address
to receive this frame
of router interface to
(Destination)
which AP is attached
Address 2: MAC address (BSSID)
of wireless host or AP
transmitting this frame
(Source)
R1 MAC addr AP MAC addr
dest. address
source address
802.3 frame
AP MAC addr H1 MAC addr R1 MAC addr
address 1
address 2
address 3
802.11 frame
67
Internet
68
802.11 frame: more
802.11: mobility within same subnet
frame seq #
(for reliable ARQ)
duration of reserved
transmission time (RTS/CTS)
2
2
6
6
6
2
frame
address address address
duration
control
1
2
3
2
Protocol
version
2
4
1
Type
Subtype
To
AP
6
seq address
4
control
1
1
From More
AP
frag
1
0 - 2312
4
payload
CRC
1
Retry
o H1 remains in same IP
1
Power More
mgt
data
subnet: IP address can
remain same
o switch: which AP is
associated with H1?
1
1
WEP
Rsvd
frame type
(RTS, CTS, ACK, data)
69
hub or
switch
BBS 1
AP 1
AP 2
H1
BBS 2
70
802.11: advanced capabilities
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps)
operating point
802.11: advanced capabilities
Power Management
10-1
10-2
o node-to-AP: “I am going to sleep until next beacon frame”
10-3
BER
Rate Adaptation
o base station, mobile
dynamically change
transmission rate (physical
layer modulation
technique) as mobile
moves, SNR varies
71
self-learning : switch
will see frame from
H1 and “remember”
which switch port can
be used to reach H1
router
10-4
AP knows not to transmit frames to this node
node wakes up before next beacon frame
o beacon frame: contains list of mobiles with AP-to-mobile
frames waiting to be sent
node will stay awake if AP-to-mobile frames to be
sent; otherwise sleep again until next beacon frame
10-5
10-6
10-7
10
20
30
SNR(dB)
40
1. SNR decreases, BER
increase as node moves
away from base station
2. When BER becomes too
high, switch to lower
transmission rate but with
lower BER
72
802.15: personal area network
802.16: WiMAX
station model
(mouse, keyboard,
headphones)
o ad hoc: no infrastructure
o master/slaves:
slaves request permission
to send (to master)
master grants requests
o 802.15: evolved from
radius of
coverage
M
P
S
P
2.4-2.5 GHz radio band
up to 721 kbps
range ~ 6 miles (“city
rather than coffee shop”)
~14 Mbps
P Parked device (inactive)
74
Components of cellular network architecture
802.16: WiMAX: downlink, uplink scheduling
o transmission frame
MSC
down-link subframe: base station to node
uplink subframe: node to base station
pream.
…
DL- ULMAP MAP
DL
burst 1
DL
burst 2
downlink subframe
…
cell
region
base station (BS)
analogous to 802.11 AP
mobile users attach
to network through BS
air-interface:
physical and link layer
protocol between
mobile and BS
…
DL
burst n
Initial request
SS #1 SS #2
maint. conn.
connects cells to wide area net
manages call setup
handles mobility
covers geographical
SS #k
…
uplink subframe
base station tells nodes who will get to receive (DL map)
and who will get to send (UL map), and when
o WiMAX standard provide mechanism for
Mobile
Switching
Center
Public telephone
network, and
Internet
Mobile
Switching
Center
wired network
scheduling, but not scheduling algorithm
75
point-to-multipoint
o unlike 802.11:
S Slave device
73
P
S
transmissions to/from
base station by hosts with
omnidirectional antenna
base station-to-base
station backhaul with
point-to-point antenna
P
S
M Master device
Bluetooth specification
point-to-point
o like 802.11 & cellular: base
o less than 10 m diameter
o replacement for cables
76
Cellular standards: brief survey
Cellular networks: the first hop
Two techniques for sharing
mobile-to-BS radio
spectrum
o combined FDMA/TDMA:
divide spectrum in
frequency channels, divide
each channel into time
slots
frequency
bands
o CDMA: code division
multiple access
2G systems: voice channels
o IS-136 TDMA: combined FDMA/TDMA (north
time slots
america)
o GSM (global system for mobile communications):
combined FDMA/TDMA
most widely deployed
o IS-95 CDMA: code division multiple access
GSM
78
77
Cellular standards: brief survey
Cellular standards: brief survey
2.5 G systems: voice and data channels
3G systems: voice/data
o Universal Mobile Telecommunications Service (UMTS)
o for those who can’t wait for 3G service: 2G extensions
o general packet radio service (GPRS)
data service: High Speed Uplink/Downlink packet
Access (HSDPA/HSUPA): 3 Mbps
o CDMA-2000: CDMA in TDMA slots
data service: 1xEvolution Data Optimized
(1xEVDO) up to 14 Mbps
evolved from GSM
data sent on multiple channels (if available)
o enhanced data rates for global evolution (EDGE)
also evolved from GSM, using enhanced modulation
data rates up to 384K
o CDMA-2000 (phase 1)
o ….. more (and more interesting) cellular topics due to mobility
data rates up to 144K
evolved from IS-95
79
Don’t drown in a bowl
of alphabet soup: use this
for reference only
(stay tuned for details)
80
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