ECE 3076 Summer 04 Professor Y' Wardi

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ECE 3076Summer 04Professor Y. Wardi

• Office hours (VL-478)
• Monday 1.10 - 2.40
• Wednesday 10.30 - 12.00
• GTA Taewon Hwang
• Office hours Tuesday 12-3, Wednesday 12-2
• Office Tutorial lab, C-448
• email gte921x_at_mail.gatech.edu
• Grading
• Quiz 1 20 (June 4)
• Quiz 2 20 (July 7)
• Homework 10
• Final exam 50

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Course contents Architectures and
protocols Data communications and the physical
layer Error detection and correction Data-link
layer protocols Network-layer issues LANs ATM
networks TCP/IP Web page
http//users.ece.gatech.edu/ywardi/ece3076/
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• Preliminaries
• WAN, LAN, MAN
• Circuit switching, packet switching
• Wireline vs. wireless
• Multiplexing
• Routing
• Network control

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Layered architectures
Layer 2
Layer 2
Layer 1
Layer 1
Layer 1 physical layer Top layer application
layer
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Protocol data unit (PDU), service data unit (SDU)
Header
Information
Trailer
SDU
PDU
Nth-layer PDU
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Encapsulation
H(N)
T(N)
H(N1)
T(N1)
N SDU
N PDU
N1 SDU
N1 PDU
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Protocol service structure
N1 layer
N1 layer
(N1)layer protocol
N SAP
N layer
N layer
N-layer protocol
SAP service access point
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• The main architectures
• OSI Reference Model (ISO)
• ATM (ATM Forum)
• LANs (IEEE 802)
• Internet (The Internet Engineering Task Force)

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The OSI Reference Model
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7
6
6
5
5
4
4
3
3
3
3
3
2
2
2
2
2
1
1
1
1
1
Subnet
Host
Node
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The 7 layers of the OSI model
7 Application layer
7
6 Presentation layer
6
5 Session layer
5
4 Transport layer
4
3 Network layer
3
3
2 Data-link layer
2
2
1 Physical layer
1
1
Host
Node
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Functions at the various layers
Physical-layer specifications - Mechanical -
Electrical - Functional - Procedural Data
link-layer functions - Framing - Error
control - Flow control
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Network-layer functions - Internal network
structure (virtual circuits, datagrams) -
Routing - Congestion control Transport-layer
functions - Flow control - Segmentation and
reassembly Session-layer functions - session
management Presentation-layer functions - Data
presentation, encryption
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Physical layer issues
Maximum data rate of a channel Nyquist sampling
theorem Let be a signal whose highest
frequency is H Hz. Suppose that the signal is
sampled at a rate of at least 2H samples per
second. Then, the signal can be
reconstructed exactly from its samples. Corollary
Given a channel whose cutoff frequency is H Hz.
Suppose you try to send through it a digital
signal having two symbols, one for 0 and one for
1. Then, the maximum data rate of the channel is
2H bits per second. Example on the 4-Khz line,
the maximum data rate is 8 Kbps.
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However, the Nyquist sampling theorem speaks of
samples/second, not bits/second. Therefore, the
maximum data rate on an H-Hz channel is 2H
signal-levels per second. Consequently, if we
have V signal levels, then each signal level
conveys bits, and hence,
For example, on a 4 Khz channel, the maximum
data rate is
To increase the bandwidth, increase V. How high
can you go?
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Shannons channel capacity
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• Line encoding
• Digital data, digital signals
• Unipolar NRZ
• Polar NRZ
• NRZ inverted
• Bipolar encoding
• Manchester
• Differential Manchester
• Digital data, analog signals
• Amplitude modulation
• Frequency modulation
• Phase modulation

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• Analog data, digital signals
• Pulse Code Modulation (PCM)
• Adaptive PCM
• Delta modulation

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Physical layer examples RS-232 pp. 194-200 T1
Carrier 24 voice channels at 64 Kbps each.
Frame one byte from each source plus a sync
bit, for a total of 1.544 Mbps. The data-source
byte consists of 7-bit PCM plus one bit for
signaling. The sync bit has the pattern
10101010 What is the fundamental frequency of
the signal consisting of the sync bit?
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SONET Building block STS-1 (Synchronous
Transport Signal level 1), 51.84 Mbps STS-n
hierarchy, Interleaving bytes from the
lower-level signals Optical equivalent OC-n
(Optical Carrier level n) STM-n (Synchronous
Transfer Module n) signal Note STS-1
accommodates transmission rates in North America
STM-1 accommodates CCITT defined
signals
STS-OC-STM hierarchy STS OC bit rate
(Mbps) SDH STS-1 OC-1 51.84
STS-3 OC-3 155.52 STM-1 STS-9
OC-9 466.56 STM-3 STS-12 OC-12
622.08 STM-4 STS-18 OC-18 933.12
STM-6 STS-24 OC-24 1244.16 STM-8
STS-36 OC-36 1866.24 STM-12 STS-48
OC-48 2488.32 STM-16 STS-192 OC-192 9953.28
STM-64
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The SONET architecture
SONET terminal
MUX
Regenerator
Section
Section
Section
Section
Section
Section
Section
Line
Line
Line
Line
Path
Path
Line
Section
Optical
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STS-1 frame Frames are generated at the rate of
8,000 frames/sec
90
810 x 8 x 8000 51.84 Mbps
9
87
Section overhead
Path overhead
Line overhead
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87
Section overhead
Path overhead
Line overhead
Effective rate 9 x 87 x 8 x 8000 50.112 Mbps
Section overhead Framing, monitoring Line
overhead Synchronization, multiplexing, error
monitoring, etc. Path overhead path-layer (user)
information
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• Error detection
• Parity bit (even) append one bit so as to make
  the number of 1s even.
• Cyclic Redundancy Code (CRC) sender and receiver
  agree on a generating polynomial, G(x). Let
  ndeg(G).
• Let D(x) be the data polynomial.
• Sender Define
  Divide P(x)G(x), and add the remainder R(x)
  to P(x). Send P(x)R(x).
• Receiver Divide what you get by G(x). If there
  is a remainder, conclude that there was an error.
  If there is no remainder, delete the last n bits
  and consider the data as error free.
• Properties of the CRC
• If G(x) has an even number of 1 coefficients
  then the CRC will catch every error in
  an odd number of bits.
• If the least-significant bit of G(x) is 1, then
  the CRC will catch every error in a set of bits
  contained in a string of length n.

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Internet checksum algorithm Given 16-bit data
words. Sender appends one additional 16-bit word
as the checksum. Sender adds the numbers in the
data words mod Then it takes the 1
complement for the checksum word. Receiver sums
up all the numbers (including the checksum) and
concludes an error if the sum is not 0.
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• Data-link layer issues
• Framing
• Flow control
• Error control

Framing bit stuffing Encapsulate the frame by
flags at the start and end. The flag consists of
the bit pattern 01111110. The sender, when
detecting the pattern 011111 in the frame, stuffs
a 0. Receiver deletes the stuffed bits.
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• Flow control and error control Window flow
  control
• Stop-and-wait protocol
• Goback N
• Selective repeat

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Network-layer issues Internal network structure
virtual circuits vs. datagrams Routing Congestion
control
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HDLC
Station types - Primary station - Secondary
station - Combined station Link
configurations - Unbalanced configuration -
Balanced configuration Data transfer modes -
Normal Response Mode (NRM) - Asynchronous
Balanced Mode (ABM) - Asynchronous Response Mode
(ARM)
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Frame format
8
8/16
16/32
01111110
01111110
Address
Control
Checksum
Data
Three types of control frames Information
frames Supervisory frames Unnumbered frames
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Control field
0
Sequence
Next
P/F
Information frame
0
1
Next
Type
P/F
Supervisory frame
1
1
Type
Modifier
P/F
Unnumbered frame
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Supervisory type frames 00 Receive Ready
(RR) 01 Receive not Ready (RNR) 10 Reject
(REJ) 11 Selective Reject (SREJ) Unnumbered
frames (partial list) Set normal
response/extended mode (SNRM/SNRME) Set
asynchronous response/extended mode
(SARM/SARME) Set asynchronous balanced/extended
mode (SABM/SABME) Set initialization mode
(SIM) Disconnect (DISC) Unnumbered
acknowledgement (UA) Unnumbered information
(UI) Reset (RSET) Test (TEST) Frame reject
(FRMR)
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X.25
Data packet
Q
D
Mod
Group
Channel
Ack
M
Seq
Ctr
Data
Control packet
Control types (partial) Call request Call
accepted Clear request Clear confirmation Interrup
t RR RNR REJ
0
0
0
1
Group
Channel
Type
Ctr
Additional information
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ATM Networks The BISDN cube
Management plane
Control plane
User plane
Higher layers
ATM adaptation layer (AAL)
ATM layer
Physical layer
Plane management
Layer management
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ATM cell format
GFC
VPI
VPI
VPI
VCI
VPI
VCI
VCI
VCI
PT
PT
CLP
CLP
VCI
VCI
HEC
HEC
Payload
Payload
UNI
NNI
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PT coding 000 user data cell congestion not
experienced SDU type 0 001 user data
cell congestion not experienced SDU type
1 010 user data cell congestion
experienced SDU type 0 011 user data
cell congestion experienced SDU type
1 100 OAM segment associated cell 101 OAM
end-to-end associated cell 110 RM
cell 111 Reserved for future use
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HEC operation at the receiver
Multibit error detected (cell discard)
Detection
Correction
No error detected
Error detected
mode
No error detected
mode
(cell discard)
Single bit-error detected (correction)
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• Transmission of ATM cells (I.432)
• ATM rates 25.6, 51.84, 155.52, 622.08 Mbps
• Cell-based physical layer
• SDH-based physical layer

Cell-based transmission
Hunt
Correct HEC
Incorrect HEC
Consecutive incorrect HEC
Presync
Consecutive correct HEC
Sync
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SDH-based transmission
155 Mbps
Path overhead
260 columns

H4
STS-3 envelope
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ATM service categories Real time Constant bit
rate (CBR) Real-time variable bit rate
(rt-VBR) Non-real time Non-real-time variable
bit rate (nrt-VBR) Unspecified bit rate
(UBR) Available bit rate (ABR) Guaranteed frame
rate (GFR)
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ATM adaptation layer (AAL)
AAL types AAL1 AAL2 AAL3/4 AAL5
The mapping of services to AAL types
Nrt-VBR
UBR
Rt-VBR
ABR
CBR
Circuit emulation, voice over ATM, ISDN
AAL1
Encoded video, VBR voice
AAL2
General data services
AAL3/4
LAN emulation (LANE)
Voice on demand, LANE
LANE, frame relay
LANE
IP over ATM
AAL5
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AAL architecture
Convergence sublayer (CS)
AAL
Service specific CS (SSCS)
Segmentation and reassembly (SAR)
CS
Common part CS (CPCS)
Higher layer
SSCS
CS
CPCS
AAL
SAR
ATM
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User data
CS PDU
SAR PDU
ATM cell
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AAl 1
AAL 1 pointer
CS PDU
1
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or
47
SAR PDU
CSI
SN
SNP
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1 bit
3 bits
4 bits
CSI even cells indicates the presence of a
CS-bublayer pointer.
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AAL 3/4
CPCS PDU
Btag
CPI
BA size
Pad
AL
Etag
Length
1
1
2
1-65,535
0-3
1
1
2
CPI (common part indicator) 0, AL(ingnment)0,
to make the trailer 4-byte long
SAR PDU
ST
SN
MID
LI
CRC
2
4
10
44
6
10
bits
bits
ST (segment type) COM, EOM, BOM, SSM
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AAL 5
Pad
UU
CPI
Length
CRC
CPCS PDU
0-47
1
1
2
4
0-65,535
UU transparent channel for user-to-user
information, CPI0
SAR PDU
48
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LAN
Topologies bus, ring, star
Bus ALOHA and slotted ALOHA CD CSMA
(nonpersistent, 1-persistent) Ring Token passing
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LAN architecture IEEE 802 reference model
Higher layers
LLC
MAC
Physical
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LLC
LLC services Unacknowledged connectionless Conn
ection-mode service (logical connection, flow and
error controls) Acknowledged connectionless
service (ack the datagrams) LLC protocols based
on HDLC Type 1, supports unacknowledged
connectionless service by using the unnumbered
information PDU Type 2, supports connection-mode
service by using the asynchronous balanced mode
(ABM) Type 3, supports an acknowledged
connectionless service by using two new
unnnumbered PDUs
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LLC PDU format
DSAP
SSAP
Control
1
1
2
variable
DSAP (destination SAP) first bit I/G
(individual/group), 7-bit addressing SSAP
(source SAP) first bit C/R (command/response),
7-bit addressing Control HDLC control with
extended 7-bit sequence numbers
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MAC
MAC PDU format
control
Dest. Addr.
Source addr.
LLC PDU
CRC
2 or 6
2 or6
4
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LAN interconnection

• Bridges
• Routers
• Hubs
• Switches (later-2 switches, layer-3 switches)

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Ethernet (802.3)
Frame format
preamble
SFD
SA
DA
L
LLC PDU
Pad
FCS
7
1
6
6
2
0-1,500
0-46
4
10 Mbps Ethernet CSMA/CD, binary backoff,
collision 16, minimum frame length 64
bytes Fast Ethernet (100 Mbps) hub-star
topology. CSMA/CD mode or switching
mode. Gbps Ethernet In CSMA/CD mode, minimum
frame length 512 bytes. Packet bursting
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Token ring
Frame format
SD
AC
FC
DA
FSC
ED
FS
SA
SD starting delimiter. JK0JK000 (J00 K11) AC
access control. PPPTMRRR. T token frame T0
token frame, T1 data frame. M monitor,
used by a monitor station to identify a bad token
and remove it. PPP priority levels. RRR
implement reservations. FC frame control.
FFZZZZZZ. FF01 data frame, ZZZZZZ is
irrelevant. FF00 control frame, ZZZZZZ
indicates the type of control. ED ending
delimiter. JK1JK1IE. E indicates error e.g.,
(line-code violation), I indicates the last one
in a sequence of frames. FS frame status.
ACXXACXX. A1 destination address was
recognized by the receiver, C1 the frame was
copies by the receiver. Thus, AC11 indicates an
ack.
MAN - FDDI
LC
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The Internet
Internetworking architecture
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IPv4
0
4
8
16
19
31
Version
IHL
Type of service
Total length
Identification
flags
Fragment offset
Time to live
Protocol
Header checksum
Source address
Destination address
Options and padding
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Version 4 IHL (Internet Header Length) in
32-bit words. Min IHL 5. TOS (Type of Service)
originally specified reliability, precedence,
delay, and throughput parameters. Currently,
first 6 bits specify differentiated services,
last 2 bits for ECN (explicit congestion
notification) Total length total datagram length
in bytes. Identification identifies the datagram
uniquely together with the source address,
destination address, and protocol. Flags 1.
More. 2. DF (dont fragment). 3.
Undefined. Fragment offset indicates the
position of the fragment in the original
datagram, in 64-bit units. This implies that,
other than the last fragment, all fragments must
have length that is multiple of 64 bits. TTL in
seconds. Every router must decrease by at least
1, so practically it is a hop count. Protocol
identifies the next higher-layer protocol. Header
checksum must be computed and checked at each
router. The 1-complement of all 16-bit
1-complement addition of all 16-bit words in the
header. Addresses network address end-system
address. Options Encodes the options requested
by the sending user. Padding Header must be a
multiple of 4 bytes. Date multiple of 8 bits in
length. Maximum datagram length 65,535 bytes.
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IP addresses
Global address, network identifier followed by a
host identifier. 32 bits.
Class A
0
Network (7 bits)
Host (24 bits)
Class B
1
0
Host (16 bits)
Network (14 bits)
Class C
Network (21 bits)
1
1
0
Host (8 bits)
Class D
1
1
1
0
Multicast
Class E
1
1
1
1
0
Future use
Addresses are often written in dotted decimal
notation, each byte written as a decimal e.g.,
192.15.16.60 1100000000001111000100000111100
Subnets and masks