Joseph D. Robinson is an Advisory Marketing Support Representative at the IBM Network Computing Systems Center in Cary, North Carolina. He has implemented both Classic IP and ATM LAN Emulation products for the past 4 years, including various IBM ATM switches, routers, and bridges. The document is a tutorial that provides an overview of basic ATM concepts such as the layered model, addressing, permanent and switched virtual circuits, quality of service, and connection types.

1. Tutorial
T4: ATM Basics
Joseph D. Robinson
Advisory Networking Specialist
Network Computing Systems Center
International Business Machines Corporation
1001 Winstead Drive
Cary, NC 27513
919-301-3882
Fax: 919-301-3794
Internet: joerobin@vnet.ibm.com

2. Joseph D. Robinson is an Advisory Marketing Support
Representative at the IBM Network Computing Systems Center in
Cary , North Carolina. He works with IBM Networking Services
Specialists and IBM Customers planning and implementing Campus
ATM Networks. Joe has implemented both Classic IP and ATM LAN
Emulation products for the past 4.0 years. These products include
the 8260 ATM Switch, 8210 Multiprotocol Switch Server (MSS), the
827X LAN Switches, the 8285 Workgroup Switch, the 8281 ATM
LAN Bridge, ATM Campus Manager, Classic/IP for the RS/6000 and
LAN Emulation for Netware, DOS, and Windows.
Prior to his work at the Network Computing Systems Center Joe
was a Networking Systems Engineer for 7 years in Tampa, Florida.
Biography

3. What is switching? Why cell switching? What is ATM?
This tutorial is for professionals who are not familiar with ATM.
It focuses on ATM (Asynchronous Transfer Mode)
communication technology. The ATM layered model is
presented along with ATM terminology and traffic descriptors.
Basic ATM concepts such as Permanent Virtual Circuits,
Switch Virtual Circuits, and Network to Network interfaces are
also covered.
This is a technical discussion of basic ATM standards.
Abstract

4.  Introduction to ATM
 Layered Model
 Physical Layer
 ATM Layer
 ATM Adaptation Layer
 ATM Addressing
 ILMI Registration
 Permanent Virtual Circuits
 Switched Virtual Circuits
 QoS
 Connection Types
 Conclusion
Agenda

5. An industry group that formulates implementations
of standards for ATM
Networking equipment vendors
Service providers
Network users
Over 600 total members
IBM is a Principal Member
IBM/ISSC and IBM Global Network (Advantis) are User
Members
Many Auditing Members
Contributions
IBM has made over 10 % of the technical contributions
http://www.atmforum.com
ATM Forum

6. Current LAN technologies have reached their limit:
Available bandwidth is shared
Fewer users per LAN segment increases topology complexity
Time dependent traffic incompatible with shared media
Shared media is leaving the stage to switching:
Provides dedicated bandwidth for high-demand WS
Static switching: per module - per port
Dynamic switching: based on LAN address
Ultimate: cell switching - ATM
Why ATM?

7. New High Speed Environment
New
Network
Architecture
High-Bandwidth
Applications
New
Technology
Different Traffic
Types
Voice, video, data integration
Bursty traffic
Isochronous
Timing sensitive
Multipoint
PDH
Sonet/SDH (OCx, STM-1)
Cell Relay (ATM)
SMDS/CBDS
Lower Costs / High Quality Fiber
LAN Interconnect
Client/Server
Image
Distributed Computing
Multimedia
Medical Imaging
Video Distribution

8. Multimedia Applications
Kiosks
 Retail
merchandizing
 Public information
services
Business Desktop
 Annotated mail
documents
 Image, video
archives
 Conferencing
 Training
 News bulletins
Audio/Video Distribution
(Media on Demand)
 Entertainment
 News
 Education
 Information
 Business
Simulation & Imaging
Medical
 Patient records
 Diagnosis
Engineering
 Design
 Modeling
Manufacturing
 Process control
 Monitoring
 Training
Media production
 Animation
 A/V Development
 Entertainment
 Advertising
 Theme Parks
The World Wide Web

9. Multimedia Isochronous Requirements
FRAME FRAME FRAME FRAME FRAME
FRAME FRAME FRAME FRAME FRAME
FRAME FRAME FRAME FRAME FRAME
FRAME FRAME FRAME FRAME FRAME
FRAME FRAME FRAME FRAME FRAME
t t t t
T=
/
Latency
Latency
Jitter
Skew
Sender
Receiver
Receiver
Video
Audio
Skew
Network delay
Synchronization
between flows
Uneven arrival

10. Bandwidth
Scalable speed up to 1.2 Gbps (and higher)
Dedicated bandwidth
Full duplex
Topology
Scalable
Physical logical segmentation
Multimedia requirements
Isochronous
Bandwidth on demand
Deployment
Industry driven standard evolution (ATM Forum)
Aggressive price/performance expectations
ATM Meets New Requirements

11. ATM supports voice, data, video
Cell switching
53-byte cells (5-byte header + 48 bytes data)
Small cells to minimize cell delay
Low-error rate links (primarily optical)
Defined as part of Broadband-ISDN standards
No error recovery in network
Only error detection and some correction
Error recovery is responsibility of end device
Connection oriented
Guaranteed sequential delivery
No room in a cell header for a destination ATM address
Instead using circuit identifier (VPI/VCI)
Key Concepts

12. One Network for All Information
Data
Video
Voice
Multimedia
Integrated Services
Digital
Pipe Up To Gigabit
Speeds
Cells
Voice Data Video
 ATM Moves Cells
 Low Delay
 Low Delay
Variation
 Very High Speeds

13. Why 53 Bytes?
64 + 5 32 + 4
48 + 5
U.S. Telco wanted 64 Bytes for Efficiency
Europe wanted 32 Bytes to avoid echo cancellation equipment
Compromise reached in ITU-TS Study Group in 1989

14. ATM Layered Architecture
Adaptation Layer
ATM Layer
Physical Layer
ATM Switch
C
P
S
w
ATM User Device ATM User Device
Adaptation Layer
ATM Layer
Physical Layer

15. Consists of two sublayers:
Transmission Convergence Sublayer
HEC Generation
Cell Scrambling/Descrambling
Cell Delineation (HEC)
Path Signal Identification
Frequency Justification/ Pointer Processing
Multiplexing
Scrambling Descrambling
Transmission frame generation/recovery
Physical Media Dependent Sublayer
Encoding for transmission
Timing and synchronization
Transmission (electrical/optica)
Physical Layer 155 Mpbs

16. OVERHEAD
Maintenance
& Operations
CELL CELL CELL CELL CELL CELL
CELL CELL CELL CELL CELL
CELL CELL
....
....
SDH or SONET Framing - STS 3C
270 Columns
9 Rows
9 Bytes
125 U secs
1 Synchrounous Payload
Data Envelope
(1 floating column of overhead)
9 x 260 x 8 / 125 u secs = 149.76 Mpbs
May be interleaved to get STS 12 and higher

17. ATM Forum Physical Interfaces

18. Cell creation (53 Octets)
Transfer of fixed size ATM Service Data Units (SDU)
Data - 48 Bytes
SDU Type - PTI
Requested/Received Cell Loss Priority - CLP
Congestion Experience - EFCN
According to traffic contract
QoS
traffic parameters
conformance definition
Multiplexing/demultiplexing - multiple ATM connections
with QoS requirements
Generic flow control
ATM Layer

19. ATM User-Network Interface (UNI) Cell
BIT
1
2
3
4
5
6
53
GFC VPI
VPI VCI
VCI
VCI PT CLP
HEC
CELL PAYLOAD
(48 OCTETS)
1
4
5
8
GFC - Generic Flow Control
VPI - Virtual Path Identifier
VCI - Virtual Channel Identifier
PT - Payload Type
CLP - Call Loss Priority
HEC - Header Error Control

20. ATM Network to Network Interface (NNI) Cell
BIT
1
2
3
4
5
6
53
VPI VPI
VPI VCI
VCI
VCI PT CLP
HEC
CELL PAYLOAD
(48 OCTETS)
1
4
5
8
VPI - Virtual Path Identifier
VCI - Virtual Channel Identifier
PT - Payload Type
CLP - Call Loss Priority
HEC - Header Error Control

21. 5 classes defined
 A - circuit emulation (e.g. voice)
 Constant bit rate, connection oriented, timing
 Emulates a leased line
 Iintended for constant rate voice and video applications.
 B - variable bit-rate service (e.g. compressed voice and video)
 Variable bit rate, connection oriented, timing
 Intended for voice and video traffic
 Basically isochronous at the level of end-user presentation
 May becoded as variable-rate information.
 C - connection-oriented data
 Variable bit rate, connection oriented
 traditional data traffic as known in an SNA or X.25 network
 D - connectionless data
 Variable bit rate, connectionless
 could beused for example to carry TCP/IP or LAN interconnection traffic where
the protocol in use is inherently connectionless
 X - connection oriented
 User defined bandwidth and QoS, VBR or CBR
ATM Adaptation Layer

22. AAL-1: Constant bit rate services (circuit emulation)
Voice, video,...
AAL-2: Variable bit rate Compressed voice, coded video
Not yet defined
AAL-3/4: Traditional data and image
Very complex (derived from SMDS)
AAL-5: Traditional data and image
Simple - what everyone will use
AAL Types

23. AAL 5 Operation
User Data
User Data Fill Trailer
SAR PDU
SAR PDU
SAR PDU
ATM Adaptation Layer
ATM Layer
SAR PDU
SAR PDU
5 Bytes
5 Bytes
5 Bytes SAR PDU
Step 1
1.) Pad such that SDU
PLUS 8-byte trailer will
be a multiple of 48
2) Add Trailer
Step 2
Segment into 48 Bytes
Step 3
Add 5 Byte Header and
mark the last one with an
EOM bit
x
Service Interface

24. ATM Layered Model
Management Plane
User Plane
Control
Plane
User
Layer
ATM
Standard
ATM Adaption Layer
ATM Layer
Physical Layer
Signalling
& Control
Class A Class B Class C Class D
Constant Bit
Rate Circuit
Emulation
Variable Bit
Rate
Audio/Video
Connection
Oriented
Services
Connection-
less
Services
AAL1 AAL2 AAL3/4 or AAL5
 ATM Adaptation Layer takes frames and adds header/trailer to create 48-byte PDU to
have ATM Layer create 53-byte cell
 Protocols above ATM Adaptation Layer not defined by ATM standards

25. CONTROL PLANE FUNCTIONS
 ATM Forum V3.0 ,V3.1 (UNI)
– SVC, PVC
– Point to point and Point to multipoint
– Anycast addresses (4.0 feature)
– Interworking 3.0 3.1
 PNNI Phase 1
– Single level hierarchy
– Soft PVCs
– Crankback
 Path Selection
– Generic CAC
– On demand and Precomputed routing
– Widest Path and Shortest path
– Load balancing
– Tuneable to specific network conditions

26. LANE Software Layer
Layered Interfaces
Higher Layer Protocols
LLC or Bridge Relay function
LAN Emulation Entity
Q2931
Connection Mgt.
SAAL
AAL
(NULL SSCS)
AAL5 Common Part
ATM
PHY
Layer
Mgt.
LUNI
Network
Layer
Data
Link
Layer
Physical
Layer

27. LE will use
ATM Adaptation Layer 5 (AAL5) to segment and reassemble
its Protocol Data Units (PDU)
AAL5 Message Mode Service and non-assured operation
Service Specific CS is NULL
QoS class 0 (best effort) (not required)
 Bearer Classes BCOB-X or BCOB-C for incoming calls
 BCOB-X for outgoing calls
Point to point VCCs (SVC)
Point-to-multipoint services (if available) for multicast services
End system must "initialize" to find its ATM @
ATM Network Assumptions

28. ATM Address
AFI DCC HO DSP ESI
S
E
L
AFI ICD HO DSP ESI
S
E
L
39 - DCC Data Country Code ISO-3166
47 - ICD International Code Descriptor ISO-6523
AFI
E.164
telephone number
HO DSP ESI
S
E
L
45 - E.164 ISDN in their International Format
AFI authority and format identifier
HO DSP high order domain specific part
ESI end system identifier
SEL vendor selector

29. ICD / GOSIP Encodings
AFI ICD HO DSP ESI
S
E
L
47 - ICD International Code Descriptor ISO-6523
D
F
I
AA reserved RDN Area
470005 80FFEA000000xxxxyyyy
DFI Domain Format Identifier
AA Administrative Authority
RDN Routing Domain Number

30. SNMP Interface
Access UNI V3.X MIB
Address Registration
ATM UNI V3.X MIB
Physical Layer
ATM Layer
ATM Layer Statistics
Virtual Path Connection
Virtual Channel Connection
Default VPI=0 VCI=16
Interim Local Management Interface

31. Address Registration Using ILMI
Network Prefix
Table
Address
Table
User Side Network Side
UNI
1) Initialize Network Prefix Table
2) Issue ColdStart trap
3) Issue GET Address Table
4) Update Network Prefix Table
5) Append ESI/SEL
6) SET ATM Address
1) Initialize Address Table
2) SET Network Prefix
3) Update Address Table
C
P
S
w
40.00.03.50.00.01
39.99.99.99.99.99.99.00.00.99.99.01.05
39.99.99.99.99.99.99.00.00.99.99.01.05.40.00.03.50.00.01.00

32. Connection Relationships
Physical
Link
VP
VC
VP = Virtual Path
VC = Virtual Channel
VC
VC VC
VC
VC
VP
VP VP
VP
VP
- A bundle of Virtual Channels
- All the Virtual Channels have the same endpoints
- A unidirectional communication capability for the
transport of ATM cells

33. Permanent Virtual Circuits (PVC)
C
P
S
w
1
5
5
1
5
5
Similar to LEASED Lines
Statically Defined
No Standard for Defining
VPI=0, VCI = 33 VPI=0, VCI = 33
VPI=0, VCI = 33 VPI=0, VCI = 34
Connection Table
Port VPI/VCI Port VPI/VCI
1, 1 0/33 15, 1 0/33
1,2 0/33 17,2 0/34

34. Switched Virtual Circuits (SVC)
C
P
S
w
6
2
2
1
5
5
C
P
S
w 1
5
5
6
2
2
PNNI-1
VP=2
ATM Address
39.01.01.....01
ATM Address
39.01.02.....02
Switch A Switch B
Connection Table A
Port VPI/VCI Port VPI/VCI
1, 2 0/33 17, 2 2/305
Connection Table B
Port VPI/VCI Port VPI/VCI
1, 2 2/305 17, 2 0/34
Call (39.01.02.....02)
VPI=0, VCI=33
VPI=0, VCI=34
VPI=2, VCI=305
 Similar to Dial Up Lines
 Dynamically Defined
 Q2931 Signaling Standard
OC-12

35. ATM CALL SET UP / CALL RELEASE
RELEASE COMPLETE
CONNECT
SET UP
SET UP
CONNECT
CONNECT ACK
CONNECT ACK
RELEASE
RELEASE COMPLETE
RELEASE
CALL PROCEEDING
CALL PROCEEDING
C
P
S
w

36. POINT to MULTIPOINT
C
P
S
w
SET UP
SET UP
SET UP
CONNECT
CONNECT
CONNECT
ADD PARY ACK
ADD PARTY

37. Quality of Service
Reserved Bandwidth (RB)
Used by ATM native applications:
At call setup application knows how much is needed and how
The network:
 Guarantees the bandwidth
 Assigns priorities
 Performs policing and reshaping
Non-Reserved Bandwidth (NRB)
Used for support of current (LAN) applications
The network:
 Performs "best effort" switching
 Packets transmitted after service for RB
 Applies back-pressure to sender
Flow Control is for NRB Only!!!
 If a RB connection sticks with its traffic contract it has guarenteed bandwidth.
 If a RB connection violates its traffic contract and the queue backs up POLICING takes
place. Cells are discarded.

38. Constant Bit Rate (CBR) - circuit emulation
 Continuous stream of bits -- 64 kbps, for example
 Very low delay and very low delay variation
Real-Time Variable Bit Rate (rt-VBR)
 Very tight bounds on delay
 Not have very tight bounds on cell loss
Non-Real-Time Variable Bit Rate (nrt-VBR)
 Complement of rt-VBR
 Not as interested in delay
 No Cell Loss
Unspecified Bit Rate (UBR)
 No guarantees
Available Bit Rate (ABR)
 Flow control
 Very low cell loss within the network
General QoS Service Catagories

39. Buffer Management and Traffic Management Determine:
What Traffic Enters the Network,
 At What Rate, and
 Whether the Traffic Gets to Its Destination(s)
Actual Throughput Seen By the Users
Quality of Service Seen By the Users
Throughput and QoS

40. Reshaping Traffic
Reshaping - Evenly spacing ATM cells to conform to allocated
bandwidth rates
25Mbps
25Mbps
100Mbps
Queue
90 Mbps

41. Policing Traffic
Policing - associated with RB traffic. Throwing away cells that
do not meet the Traffic contract.
100 Mbps peak
shallow
queue
90 Mbps
Traffic
Contract
BIT
Bucket

42. Policing, Tagging, and Discarding Are Determined By:
Cell Loss Priority (CLP)
Traffic Control Descriptors
Traffic Contract Enforcement Methods
Congestion Thresholds Are Not User Setable
Discard Methods:
EPD - Early Packet Discard
PPD - Partial Packet Discard
RED - Random Early Detect
Traffic Enforcement

43. GCRAs Are Also Referred to as Dual Leaky Buckets
Each Virtual Circuit Has Two GCRAs Defined
A GCRA Is Defined to Monitor One of the Following Options:
CLP=0, CLP=1, or CLP=0+1:
For the Following Characteristics (Based on QoS):
 PCR
 PCR + SCR
 PCR + SCR + MBS
 SCR + MBS
For Each GCRA, an Enforcement Mode Is Also Selected:
Static Enforcement - Discards Cells Regardless of Available
Bandwidth
Congestion Based Enforcement - Discards Cells Only If There
Is Congestion
Generic Cell Rate Algorithms (GCRAs)

44. Dual Leaky Buckets (GCRAs)
VCC
VCC
PCR
Dependent on Traffic
Descriptor or Class
#1
#2
Monitor
 Based on CLP = 0, 1, or 0+1
Enforcement
 Static or Congestion Based

45. BASIC CONTROL POINT FUNCTIONS
ROUTING
B
CALL B
?
?
SIGNALLING
?

46. UNI 3.0 & 3.1
User Network Interface
PNNI Phase 1.0 (Single Peer Group)
Network to Network Interface
Network Node Interface
Establish VCs That Meet Requested Bandwidth and QoS
Enable the Network to Scale to Hundreds (or Thousands) of
Nodes
Interim Inter-Switch Signaling Protocol (IISP)
Interoperability With Older ATM Switches
No topology or resource information gets passed
Manually configure Static routing only.
PNNI Phase Zero
Connection Types

47. Current PNNI-1
CLUSTERING : 2 LEVELS HIERARCHY
STANDARD or PRE-STANDARD INTERFACES
UNI UNI
IISP
SSI
-Signalling:UNI*
-Routing:OSPF
-Signalling:UNI*
-Routing:Static

48. PATH SELECTION CBR, VBR
A D
C
B
x
5040
510
2520
510
x
'On demand routing'
Path computation is done at Call set up time
1-Links not satisfying QOS are pruned
(GCAC)
Pruning takes in account asymmetry
2-Shortest path on the Administrative weight
Network designer control
3-If equal shortest paths : Widest path on
AvCR
Load balancing
Widest path: width of path determined by narrowest link in path
AvCR: Available Cell Rate

49. PATH SELECTION UBR
'Precomputed routing'
Paths are precomputed as a
background task
optimise Call Set-up late
Network designer can select either:
- Widest path on MaxCR
optimise load balancing
or
- Shortest path on Admin. weight
followed by Widest path
optimise network resources and
allow network designer control
A D
C
B
5040
5040
5040
5040
5040
Widest path: width of path determined by narrowest link in path
MaxCR: Maximum Cell Rate

50. The Future!!!
L
L
L
TOPOLOGY AGGREGATION
CONCEPT OF 'HIERARCHY'

51. Conclusion
ATM provides:
Scalable network bandwidth
Simplified network design
Consolidation of disparate networks
Seamless connectivity from LAN to WAN
Multi-media support
Migration from installed base
Concerns
Standards still emerging
 Multimedia
Public WAN deployment lagging

52.  AAL. ATM Adaptation Layer
 AIX . IBM's implementation of the UNIX operating system
 ARP Address Resolution Protocol
 API. Application Programming Interface
 ATM. Asynchronous Transfer Mode
 BUS. Broadcast and Unknown Server
 IP. Internet Protocol
 ILMI. Interim Local Management Interface
 LAN. Local Area Network
 LANE. LAN Emulation
 LEC. LAN Emulation Client
 LES. Lan Emulation Server
 LIS Logical IP Subnet
 MAC. Part of Data Link Layer
 MIB. Management Information Base
 MSS. Multiprotocol Switch Services
 NDIS. Network Driver Interface Specification
 NNI. Network Node Interface
 ODI. Open Data-link Interface
Acronyms

53.  PVC. Permanent Virtual Connection
 QOS Quality of Service
 RFC. Request For Comments
 RISC. Reduced Instruction-Set Computer
SNMP. Simple Network Management Protocol
SSCS Service Specific Convergence Subsystem
SSI. Switch-to-Switch Interface
SVC. Switched Virtual Connection
SVN. Switched Virtual Networking
TCP/IP. Transmission Control Protocol/Internet Protocol
UNI. User-Network Interface
VC. VIRTUAL CONNECTION
VCC. Virtual Channel Connection
VCI. Virtual Channel Identifier (in ATM cell header)
VPI. Virtual Path Identifier
WAN. Wide Area Network
WG. Work Group
Acronyms (continued)