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
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
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
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
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
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
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)
