Ethernet Standard

1
Unit 2 Switched and Shared Ethernet

• Ethernet Standard
• Physical Layer (encoding)
• CSMA/CD
• Ethernet Frame
• Ethernet, Fast Ethernet, and Gigabit Ethernet
• 10G Ethernet
• Structured Cabling Plant
• Switched and Full Duplex Ethernet

2
IEEE 802 Standards
3
Ethernet and ISO 7-layer Model
(802.3)
802.3 10Base-T
802.3u 100Base-T
802.3z 1000BaseX
802.3ab 1000Base-T
802.3ae 10G
802.3ak 10GBase-CX
802.3an 10GBase-T
work in progress
4
MAC and Physical Layer
5
Ethernet Physical Layer
6
Line and Block Encoding

• Line encoding the process of transforming binary
  information (bits) into a digital signal.
• Examples RZ, NRZ, NRZ-I, Manchester, MLT-3
• Block encoding
• The sequence of bits is divided into m-bit blocks
• Each m-bit block is mapped into an n-bit block
  where ngtm.
• Each n-bit block is line coded.
• Examples 4B/5B, 8B/10B, 64B/66B
• purpose ease of clock synchronization and error
  correction
• It is used in high data rate link

7
Ethernet Encoding Schemes

• Manchester (10BaseT)
• 0-bit voltage, - voltage
• 1-bit - voltage, voltage

8
NRZ-I Encoding (100Base-FX)
RZ
NRZ
9
MLT-3 Signal (100Base-TX)
1 gt 0 -1 gt 0 gt 1
10
Evolution of Ethernet Access Methods
MA Multiple Access CSMA Carrier Sense Multiple
Access CSMA/CD CSMA Collision Detection
(802.3) CSMA/CA Collision Avoidance (802.11)
11
Collision in CSMA
What is the problem if A receives the collision
signal after it completes sending the
frame? Requirement time to send a frame must be
longer than the round trip delay.
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CSMA/CD Procedure
Station is ready to send
try again
Wait (backoff strategy)
Sense Channel
channel busy
Send jam signal
Transmit data and sense channel
collision detected
successful transmission
13
CSMA with Collision Detection

• CSMA/CD can be in one of three states
  contention, transmission, or idle.

14
Backoff Algorithm
k gt 10
15
802.3 Parameters (Table 3.2)
Q Why do we need IFG? What is the problem of
not using IFG?
16
Backoff Example
A
B
1st collision
K K 1 1 P 2K 1 1 R random number 0
or 1 Backoff-time R ? slot-time
collision again
K K1 2 P 2K 1 3 R random 0, 1, 2,
3 Backoff-time R ? slot-time
3rd collision
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Example (cont.)

• If Station A and Station B try to transmit at the
  same time
• T0 collision (AB transmits at the same time)
• T0 ? 50 A transmits and 50 B transmits
• ? a very small interval gt retransmit
  immediately.
• T0 slotTime 50 A and 50 B
• Collision at the 2nd try 50
• If collision happens at the 2nd try, the
  probability of collision at the 3rd try is 25.
  (why?)

18
Ethernet Performance
Why do large frames have better performance?
19
802.3 MAC Frame
Preamble
2
Preamble for circuit synchronization SFD
Start of Frame Delimiter Frame Check Sequence
same as cyclic redundancy check (CRC)
20
Ethernet Address in Hexadecimal Notation
MAC Address Hardware Address
Q1 How do you find the MAC address of a Windows
workstation? Q2 How do you find the MAC address
of a Linux workstation?
21
Why 64 bytes?
2,500 m (specified, not derived)
Bit time time to transmit one bit (10M network
0.1 µs) Slot time time to transmit one frame
Requirements slot time gt round trip delay Frame
size 512 bit gt slot time 51.2 µs Round trip
delay transmission delay device delay
Signaling speed 2 108 m/sec Transmission
delay (one way) distance / speed 12.5 µs
Transmission delay (round trip) 25 µs Delay
in device (multiple boxes) transmission delay
25 µs Round trip delay 50 µs
22
Discussion

• Why is slot time gt round trip delay?
• What is the problem if slot time lt round trip
  delay?
• What is the problem if frame size lt 64 bytes?
• Why is the max frame size 1518 bytes?

23
5-4-3 Rule (10BaseX) 5 segments, 4 repeaters, 3
populated segments
hub/repeater
10Base2
24
Categories of 10-Mbps, Baseband Ethernet
25
Unshielded Twisted-Pair (UTP)

• To manage network cabling, it is necessary to be
  familiar with standards used on modern networks,
  particularly
• Category 3 (CAT3)
• Category 5 (CAT5
• Category 5e
• Category 6 (CAT6)

26
RJ-45 Connector
27
UTP Cable Type

• Straight-through cable
• Terminations at both ends are identical
• Crossover cable
• Terminations locations of transmit and receiver
  wires on one end of cable are reversed

Q give two examples that you will use crossover
cables
28
Fiber-Optic Cable

• Contains one or several glass fibers at its core
• Surrounding the fibers is a layer of glass called
  cladding

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Fiber-Optic Cable

• Single-mode fiber
• Carries light pulses along single path
• Multimode fiber
• Many pulses of light generated by LED travel at
  different angles

30
Fiber-Optic Cable Connector

• Two popular connectors used with fiber-optic
  cable
• ST connector (Straight Tip)
• SC connector (Simplex Connector)

Other Connector Types FC, MT-RJ, FDDI
http//www.jimhayes.com/content/FOcontent/term.htm
l
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Ethernet Evolution
802.3an(?)
802.3ak
802.3ae
802.3ab
802.3z
802.3u
802.3
32
Fast Ethernet Implementations
c.f. Fig. 7-16
Standard for 100BaseFX is 400m using MM.
33
Encoding and Decoding in 100BaseTX
Note that the encoding is no longer Manchester.
34
Encoding and Decoding in 100Base-FX
35
Using Four Wires in 100Base-T4 (a solution to a
non-existing problem)
Note there is also a standard 100Base-T2 using 2
pairs of Cat-3 cables. It is never supported and
deployed.
36
Two Approaches in Gigabit Ethernet Medium Access
37
Carrier Extension for 1000Base-T
38
Frame Bursting Approach
Multiple frames are sent in one burst. Filling
in IGG with padding data.
39
Gigabit Ethernet Implementations
802.3z
802.3ab
802.3ab
802.3z
40
Encoding in 1000Base-X
41
Encoding in 1000Base-T
42
10GbE (IEEE 802.3ae)

• Full-duplex only (no CSMA/CD)
• Fiber only (802.3ae)
• WAN (SONET-friendly) PHY
• Mapping to OC-192 carrier
• Rate adaptation to SONET payload capacity
• New line coding (64b/66b)
• New standard for copper 10GBase-CX (802.3ak)
• dual coax cable
• lt20m (for data center use only)
• Work-in-progress for 10GBase-T (802.3an)
• UTP cable (likely Cat-6)

43
1G to 10G
44
10GbE Specifications
45
10GbE Distance Support
46
Structured Cabling Plant
ANSI/TIA/EIA-569
CD Campus Distributor BD Building
Distributor FD Floor Distributor TO Telecom
Outlet
47
Evolution of New Technologies

• Auto Negotiation
• Bridged and Switched Ethernet
• Full Duplex Ethernet

48
Auto Negotiation

• Spec of most NICs and Ethernet device
  10/100BaseTX or 10/100/1000BaseT
• However, many old devices do not support auto
  negotiation.
• Automatically detect the operation mode and max
  speed, and use the max speed for data
  transmission.
• Important for network upgrade and backward
  compatibility

49
Bridge Connecting Layer-2 LAN
50
Bridged or Switched Ethernet

• Advantages
• Improve the network bandwidth
• Separate collision domains
• Bridge vs. Switch
• A bridge divides a collision domain into two
• A switch divides a collision domain into N.
• A switch is a multi-port bridge where each port
  defines a single collision domain.

51
Bridge vs. Ethernet Switch
Ethernet Switch
Bridge

• Software based
• Usually only two ports, but could be more
• Functionally, it is a two-port Ethernet switch.
• Referenced in books, papers, and standard
  documents.

• Hardware based (ASIC)
• More ports on a switch
• Functionally, it is a multi-port bridge.
• Referenced and used in the industry.

I do not distinguish Ethernet switch and bridge
in this class.
52
Bridge a Layer-2 Device
Ethernet LAN (820.3)
Wireless LAN (820.11)
Application
Application
IP
IP
Bridge
802.11 (MAC)
802.3 (MAC)
802.3 M
802.11 M
802.11 (PHY)
802.3 (PHY)
802.3 P
802.11 P
53
Bridge Block Diagram
Learning Logic
Frame Buffer Memory
Frame Buffer Memory
MAC Address
Port
Age
MAC
MAC
Forwarding Logic
PHY
PHY
data
MAC Forwarding Table
data
Also referenced as Source Address Table (SAT)
54
How does a Bridge Work?
MAC Forwarding table
P1
P2
MAC11
MAC12
MAC21
MAC22
55
Bridge Flow Diagram
Receive/Store Frame on Port X
Read Source MAC Address (SA)
Is SA In SAT?
Source Address Table (SAT)
Y
Read Destination MAC Address (DA)
Yes ( Port Y)
N
Enter new SA Into SAT
Is DA FFF? (broadcast)
Is DA In SAT?
Is Port X Port Y?
N
N
Y
Y
N
Forward the frame to all ports
Discard the frame
Forward the frame to Port Y
56
How Bridges Learn Host Addresses and Locations?
MAC forwarding table
A
B
0260.8c01.1111
0260.8c01.3333
E0
E1
E2
E3
C
D
0260.8c01.2222
0260.8c01.4444

• Initial MAC forwarding table is empty

57
How Bridges Learn Host Addresses and Locations?
MAC forwarding table
E0 0260.8c01.1111
A
B
0260.8c01.1111
0260.8c01.3333
E0
E1
E2
E3
C
D
0260.8c01.2222
0260.8c01.4444

• Station A sends a frame to Station C
• Switch caches station A MAC address to port E0 by
  learning the source address of data frames
• The frame from station A to station C is flooded
  out to all ports except port E0 (unknown unicasts
  are flooded)

58
How Bridges Filter Frames?
MAC forwarding table
E0 0260.8c01.1111
E2 0260.8c01.2222
E1 0260.8c01.3333
A
B
E3 0260.8c01.4444
0260.8c01.1111
0260.8c01.3333
E0
E1
E2
E3
C
D
0260.8c01.2222
0260.8c01.4444

• Station A sends a frame to station C
• Destination is known, frame is not flooded

59
Broadcast Frames
E0 0260.8c01.1111
E2 0260.8c01.2222
A
B
E1 0260.8c01.3333
E3 0260.8c01.4444
0260.8c01.1111
0260.8c01.3333
E0
E1
E2
E3
D
C
0260.8c01.2222
0260.8c01.4444

• Station D sends a broadcast frame
• Broadcast frames are flooded to all ports other
  than the originating port

60
MAC Forwarding Table

• Unlike IP address, MAC address is local.
• MAC forwarding table is also local, within the
  single broadcast domain (which is an IP subnet).
• MAC address learning stops at the router, and a
  switch does not learn the MAC addresses at the
  other side of the router.
• The switch learns one MAC address of the router.

61
Full Duplex Ethernet

• One pair of UTP wire (or one fiber strand) is
  used exclusively for transmission, and another
  pair is for reception.
• No carrier-sense
• No collision detection
• New problem buffer overflow
• To be covered in 802.3x (flow control)

62
Full-Duplex Switched Ethernet
c.f. Fig 7-9
63
Lab Exercise

• If it is an Ethernet switch, it shall have a MAC
  forwarding table. However, you can see it only
  if it is manageable switch,
• Catalyst 2950 show mac-address-table vlan ltidgt
• Measure the delay and throughput on Ethernet
• Challenging question
• What is max throughput on 100BaseTX if the frame
  size is 64 bytes?
• What is the max throughput on 100BaseTX if the
  frame size is 1500 bytes?
• Explain the difference (show the details of your
  calculation)

64
Summary

• Encoding scheme line coding and block coding
• CSMA/CD and back-off algorithm
• Computation of network span, data throughput, and
  min frame size.
• Ethernet standard 10M, 100M, 1G, and 10G
• Auto negotiation
• Switched vs. shared Ethernet
• MAC forwarding table