ATM Networks:
An Overview
Raj Jain
Professor of Computer and Information Sciences
The Ohio State University
Columbus, OH 43210-1277
http://www.cis.ohio-state.edu/~jain/CIS677-98/
Raj Jain
The Ohio State University
Overview
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ATM vs Phone Networks and Data Networks
ATM Protocol Layers
Cell Header Format, AALs
Physical Media
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ATM
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Asynchronous Transfer Mode
ATM Net = Data Net + Phone Net
Combination of Internet method of
communication (packet switching) and phone
companies method (circuit switching)
ATM
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ATM vs Phone Networks
125 s
Current phone networks are synchronous (periodic).
ATM = Asynchronous Transfer Mode
q Phone networks use circuit switching.
ATM networks use Packet Switching
q In phone networks, all rates are multiple of 8 kbps.
With ATM service, you can get any rate.
You can vary your rate with time.
q With current phone networks, all high speed circuits
are manually setup. ATM allows dialing any speed.
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ATM vs Data Networks
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Signaling: Internet Protocol (IP) is connectionless.
You cannot reserve bandwidth in advance.
ATM is connection-oriented.
You declare your needs before using the network.
PNNI: Path based on quality of service (QoS)
Switching: In IP, each packet is addressed and
processed individually.
Traffic Management: Loss based in IP.
ATM has 1996 traffic management technology.
Required for high-speed and variable demands.
Cells: Fixed size or small size is not important
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Old House vs New House
New needs:
Solution 1: Fix the old house (cheaper initially)
Solution 2: Buy a new house (pays off over a long run)
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ATM Interfaces
Private Private Public
Computer
UNI Switch UNI
Carriers
Private
Public
Public
Public
NNI
Private
Switch
Switch
Private
NNI
Computer
Switch
UNI
B-ICI
Digital
Router DXI Service
Unit
Carrier
Public
Switch
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ATM Interfaces
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User to Network Interface (UNI):
Public UNI, Private UNI
Network to Node Interface (NNI):
m Private NNI (P-NNI)
m Public NNI =Inter-Switching System Interface (ISSI)
Intra-LATA ISSI (Regional Bell Operating Co)
m Inter-LATA ISSI (Inter-exchange Carriers)
Broadband Inter-Carrier Interface (B-ICI)
Data Exchange Interface (DXI)
Between routers and ATM Digital Service Units (DSU)
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Protocol Layers
End System
End System
ATM
Adaptation
Layer
Switch
ATM
Adaptation
Layer
ATM
Layer
ATM
Layer
ATM
Layer
Physical
Layer
Physical
Layer
Physical
Layer
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Protocol Layers
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The ATM Adaptation Layer
m How to break messages to cells
The ATM Layer
m Transmission/Switching/Reception
m Congestion Control/Buffer management
m Cell header generation/removal at
source/destination
m Cell address translation
m Sequential delivery
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Virtual Circuit Switching
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4
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Circuit Switching: bits coming on wire 4 go on wire 2
Virtual Circuit Switching: Cells coming on VCI=4 go
on VCI=2
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Cell Header Format
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GFC = Generic Flow Control
m (Was used in UNI but not in NNI)
VPI/VCI = 0/0 Idle cell; 0/n Signaling
GFC/VPI
VPI
VPI
VCI
VCI
VCI
PTI
CLP
Header Error Check (HEC)
Payload
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Header Error Check (HEC)
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1 + x + x2 + x8
Protects header only
Optional Correction mode: Correct one bit errors if no
earlier errors
Discard cells with bad HEC
Recalculated on each hop
No Error
Correction
Mode
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No Error
Error
Correct if possible
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Error
Detection
Mode
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Payload Type Field Coding
000 User data cell, no congestion, AAU = 0
q 001 User data cell, no congestion, AAU = 1
q 010 User data cell, congestion, AAU = 0
q 011 User data cell, congestion, AAU = 1
q 100 Segment Operation and management (OAM) cell
q 101 End-to-end OAM cell
q 110 Resource management cell
q 111 Reserved
ATM-user-to-ATM-user (AAU) bit available for userto-user indication
q
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Path vs Channels
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24/28-bit connection identifier
First 8/12 bits: Virtual Path,
Last 16 bits: Virtual Circuit
VP service allows new VC's w/o orders to carriers
VP1
Link
VP2
VP3
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VC1
VC2
VC3
VC1
VC2
VC3
VC1
VC2
VC3
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VP/VC Assignment/Use
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Video Data
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56 2
Data Voice
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34 1
3
4
56
Switch 5
65
6
In
76
Out
Port VPI/VCI Port VPI/VCI
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1
1
2
2
3
4
5
6
0/37
0/34
0/33
0/56
16
1/35
0/56
0/65
4/76
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Original Classes of
Traffic
Class A
Time Sync Yes
Bit Rate
Constant
Connection Yes
-Oriented
Examples Circuit
Emulation
AAL
AAL1
Class B
Yes
Variable
Yes
Class C
No
Variable
Yes
Class D
No
Variable
No
Comp.
Video
AAL2
Frame
Relay
AAL3
SMDS
AAL4
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AAL 5
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Designed for data traffic
Less overhead bits than AAL 3/4
Simple and Efficient AAL (SEAL)
No per cell length field, No per cell CRC
User
PAD Control Length CRC-32
Payload
0-64kB 0-47
2
2
4
0
PTI bit indicates last cell
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1
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AAL2
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Ideal for low bit rate voice
Variable/constant rate voice
Multiple users per VC
Compression and Silence suppression
Idle channel suppression
Payload 1
Payload 2
Payload 3
Pkt
Pkt
Pkt
Payload 1
Payload 2
Payload 3
Hdr
Hdr
Hdr
Cell
Cell
Header
Header
Pkt
Pkt
Pkt
Payload 1
Payload 2
Payload 3
Hdr
Hdr
Hdr
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Cell-Stream Phy
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Cell
Continuous stream of cells. No framing.
Hunt bit-by-bit for correct header.
Look for correct headers before entering synch state
incorrect headers resynchronize
and are parameters.
Correct HEC
Correct HECs
Hunt
Sync
Incorrect HEC Presync
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Incorrect HEC
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SONET
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Synchronous optical network
Standard for digital optical transmission
(bit pipe)
Developed originally by Bellcore.
Standardized by ANSI T1X1
Standardized by CCITT
Synchronous Digital Hierarchy (SDH)
You can lease a SONET connection from carriers
Carriers
City A
City B
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Signal Hierarchy
Synchronous Transport Signal Level n = STS-n = n 51.84 Mbps
STM=Synchronous Transport Module, OC=Optical Carrier level
ANSI
Optical CCITT
Data Rate Payload Rate
Designation Signal Designation
(Mbps)
(Mbps)
STS-1
OC-1
51.84
50.112
STS-3
OC-3
STM-1
155.52
150.336
STS-9
OC-9
STM-3
466.56
451.008
STS-12
OC-12 STM-4
622.08
601.344
STS-18
OC-18 STM-6
933.12
902.016
STS-24
OC-24 STM-8
1244.16
1202.688
STS-36
OC-36 STM-12
1866.24
1804.032
STS-48
OC-48 STM-16
2488.32
2405.376
STS-96
OC-96 STM-32
4976.64
4810.176
STS-192
OC-192 STM-64
9953.28
9620.928
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STS-3c Frame Format
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STS-3c is similar to STM-1
125 s = 2430 bytes at 155.54 Mbps
270 Columns
Overhead
Payload
9 Columns 261 Columns
9 Rows
Path Overhead
Note: All sizes are multiples of 3
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SONET/SDH Phy
260 Columns
...
Cell
9 Rows
J1
B3
C2
G1
F2
H4
Z3
Z4
Z5
...
...
9 Columns
Path Overhead
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The Ohio State University
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SONET STS-3c
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Payload rate = 9 260 8/125 = 149.76 Mbps
Cell payload rate = 135.63 Mbps
Cell delineation using HEC.
m Look for 5-byte blocks with HEC separated by 48
bytes
Cells are packed one after another One can send
127 bits matching the scrambling sequence resulting
in all 1s or 0s.
Scramble by dividing by 1 + x43.
Only one in 243 patterns will cause all 1s or 0s.
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Physical Media
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Multimode Fiber: 100 Mbps using 4b/5b,
155 Mbps SONET STS-3c, 155 Mbps 8b/10b
Single-mode Fiber: 155 Mbps STS-3c, 622 Mbps
Plastic Optical Fiber: 155 Mbps
Shielded Twisted Pair (STP): 155 Mbps 8b/10b
Coax: 45 Mbps, DS3, 155 Mbps
Unshielded Twisted Pair (UTP)
m UTP-3 (phone wire) at 25.6, 51.84, 155 Mbps
m UTP-5 (Data grade UTP) at 155 Mbps
DS1, DS3, STS-3c, STM-1, E1, E3, J2, n T1
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Summary
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ATM Overview: History, Why and What
Protocol Layers: AAL, ATM, Physical layers, Cell
format
Interfaces: PNNI, NNI, B-ICI, DXI
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Homework
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Read Sections 11.1-11.5 of Stallings
Submit answers to Exercise 11.4
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