Transcript ATM Tutorial

ATM Tutorial
Paul Chen
April, 2000
1
Outlines
1. ATM Basics and Reference Model
2. Concepts of VP and VC
3. ATM Protocol Stack
4. QoS Concept
5. Network Congestion and Policing
6. ATM and SONET
7. ATM OAM Principle
8. ATM Adaptation Layer (AAL)
9. ATM Network Management and MIB
10. References
2
Why Interest in ATM?
Both LAN and WAN Technology
One
International
Standard
Standards
Based
ATM
Scaleable
in Speeds
Mbit
Gbit
Voice/Data/Video
3
ATM and B-ISDN Relationship
• ATM is the foundation technology for
Broadband-ISDN
• B-ISDN is the universe of services that will be
made possible by the use of ATM technology
VOICE
DATA
VIDEO
4
Broadband Protocol Model
Management Plane
User Plane
Signaling
(VBR)
CO (VBR)
CBR
Other VBR
e.g.
e.g.
e.g.
DS1 DS3 VBR Video Frame Relay
X.25
Voice
Other
Services
Upper Layer 2
AAL
ATM
SONET/SDH
PDH
5
Functions B-ISDN Layers
End
Station
ATM
Switch
A A P
A T H
L M Y
P A P
H T H
Y M Y
End
Station
P A A
H T A
Y M L
ATM
Cells
• Adaptation Layer (AAL): Inserts/extracts information
into 48 byte payload
• ATM Layer: Adds/removes 5 byte header to payload
• Physical Layer: Converts to appropriate electrical
or optical format
6
History of ATM
ITU-T
Launches
B-ISDN
Project
53 Byte Cell
Standardized
(June 1989)
1985
Public WAN
Services
Launched
ATM
Forum
Chartered
1987
1989
ATM
Products
Introduced
1991
1993
Anchorage Accord
Interoperability
based on ATMF
Specifications
(April 1996)
1995
1997
7
Comparison of ATM with other
Technologies
CONVENTIONAL
LAN
CONVENTIONAL
TELECOM
ATM
TRAFFIC TYPE
DATA
VOICE
DATA, VOICE,
VIDEO
TRANSMISSION
UNIT
VARIABLE
PACKET
FIXED FRAME
FIXED CELL
UP TO G BPS
UP TO G BPS
M BPS TO G BPS
CONNECTION
LESS
CONNECTIONORIENTED
BEST EFFORT
GUARANTEED
CONNECTIONORIENTED
DEFINED
CLASSES
SHARED
DEDICATED
RATE
CONNECTION
TYPE
DELIVERY OF
TRAFFIC
ACCESS
DEDICATED
8
Anatomy of an ATM Cell
8
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
7
6
5
4
GFC (UNI) OR VPI (NNI)
3
2
1
VPI
VCI
VPI
Header
VCI
VCI
PTI
CLP
HEC
Payload
48
Bytes
9
Virtual Circuits
First we have the cable...
Next, ATM Addressing Defines Paths...
• VP’s
Then Channels.
• VC’s
10
SONET and ATM Channels
Transport Overhead
Transport Overhead
Path Overhead
Path Overhead
STS-1
(DS3)
STS-1
(DS3)
VT1.5
DS1
STS-1
28 VT1.5
11
Virtual Paths & Virtual Channels
VCs
VP
VCs
VP
Physical
Transmission
Link
VP
VCs
VP
VCs
• VPI: Virtual Path Identifier
– 4,096 at NNI and 256 at UNI
• VCI: Virtual Channel Identifier
– 65,536
• Both used to route cells through network
– Unique on link-by-link basis
– Interpreted at each switch
12
ATM Connections
• ATM is virtual connection-oriented; there must always be
a virtual connection established before cells can be sent
• Connections can be established:
›› Administratively as PVCs
– Lowest common denominator for Interoperability for
devices not supporting UNI 3.x signaling
›› Dynamically as SVCs
– Implies ATM signaling capability
13
ATM Switches are easily Scaleable
in Speed
• ATM protocol is connection-oriented
– once connection is set up, cells are quickly switched in hardware
by using VPI/VCI at very high speeds
• Uses fixed cell length
– Allows switch hardware to be optimized around a fixed length cell
• Uses SONET as physical layer interface
– Scales to high speed and is defined and deployed at Gigabit rates
14
Logical ATM Switch Fabric
ATM Switch Ingress Path
from
interface
PHY
receive
termination
Connection
Lookup
OAM
Processing
Policing
Buffering,
Queueing
& Scheduling
to
queue
ATM Layer
Processing
Physical/TC
Layer
Processing
ATM Switch Egress Path
from
queue
Fabric
receive
termination
Connection
Lookup
Buffering,
Queueing
& Scheduling
OAM
Policing
(EFCI)
to
interface
ATM Layer
Processing
Internal
Loopback
15
Concept –
VPs and VCs in the Network
VP2
Link 1
Link 1
NN 1
VP2
VP3
Link 2
Link 1
VP3
VC8
VC11
VC8
VC11
VC21
VC21
VC11
VC2
VC2
VC11
VP8
VP5
VP5
VP8
VP6
CPN 1
VP6
VC7
User/Network
Interface
(UNI)
VC2
VP3
Link 3
Link 2
CPN 2
VP5
Link 4
Network Node
Interface
(NNI)
User/Network
Interface
(UNI)
Link 1
VP3
VP5
CPN 3
VC7
VP2
Link 2
Link 1
VP2
VC2
VC9
Routing Concept in
an ATM Network
VC9
VP1
NN 2
Link 3
Link 2
VP1
16
ATM Protocol Stack
ISO
Model
(OSI)
Layer 3
(Network)
MAC
Service Access
Point (SAP)
AAL - SAP
(Not part
of ATM)
Service Specific Functions (SSCS)
• Provide additional functions as required
for specific services (can be null)
Common Part Convergence Sublayer (CPCS)
• Builds header and trailer records onto user data frame
• Assures integrity at the frame level
Sublayer
Boundary
Layer 2
(Link)
Higher
Layers
ATM
Adaptation
Layer (AAL)
Segmentation and Reassembly (SAR)
• Converts CPCS frames into cells
• Adds cell headers and trailers to provide integrity at the cell level
Service Access Point (SAP)
Cell
Switching
ATM Layer
Transmission Convergence Sublayer
• HEC generation and checking
• Transmission frame adaptation
Layer 1
(Physical)
• Cell delineation
• Decoupling of Cell Rate
(ITU systems)
Physical
Layer
Physical Media Dependant Sublayer
• Encoding for transmission
• Timing and synchronization
• Transmission (Electrical/Optical)
17
Concept - QoS
• QoS is associated with a VCC that specifies an average
bandwidth as well as a maximum bandwidth
• QoS is provisioned for a VPC or VCC (VCCs within the
VPC may have a lower QoS than the VPC)
• QoS parameters include:
–
–
–
–
–
–
Cell Transfer Delay (Network Latency)
Cell Delay Variation (Jitter)
Cell Transfer Capacity (Speed - average and peak allowed rates)
Cell Error Ratio
Cell Loss Ratio
Cell Misinsertion Rate
18
Concept - ATM Service Categories
• Constant Bit Rate (CBR)
– Includes traffic where a continuous stream of bits at a
predefined constant rate is transported through the
network (e.g., T1 circuit, voice)
– Low latency, low jitter, low errors and cell loss
• Realtime Variable Bit Rate (rt-VBR)
– Like CBR in the sense that we want low latency, low jitter,
low errors and cell loss but the rate the bits can transmit
varies (e.g., compressed video, voice)
• Non-realtime Variable Bit Rate (nrt-VBR)
– Like rt-VBR except ‘some’ latency and jitter might not cause a
problem (e.g., one-way TV distribution)
19
Concept - ATM Service Categories
• Unspecified Bit Rate (UBR)
– Provides ‘best effort’ delivery of data. Good for end-to-end
applications that have flow control (high cell loss, high jitter and
latency)
• Available Bit Rate (ABR)
– Has guaranteed delivery but not delivery time (Limited cell loss,
high jitter and latency)
– ABR has many other parameters and a technique (RM cell) to
manage this resource beyond the scope of this presentation
20
Application Areas for ATM
Service Categories
Application
Area
Critical Data
LAN interconnection
LAN emulation
Data
Transport/interworking
(IP-FR-SMDS)
Circuit Emulation-PABX
POTS/ISDN
-video conference
Compressed Video/Audio
CBR
rt-VBR
nrt-VRB
ABR
UBR
xx
x
xxx
x
N/S
x
x
xx
xxx
xx
x
x
xx
xxx
xx
xxx
xx
N/S
N/S
N/S
N/S
N/S
xxx
x
xxx
xx
xx
x
1-way TV Distribution
x
xx
xxx
N/S
N/S
Interactive Multimedia
xxx
xxx
xx
xx
x
Score to indicate the ‘advantage’:
Optimum: xxx Good: xx Fair: x
N/S: Not Suitable
Not Quoted: Presently considered not applicable with advantage
(might be shown in the future)
21
Concept Network Congestion & Policing
•
•
•
When congestion happens on ATM networks - Cell gets
discarded!!!
One mechanism to control congestion is to ‘police’ packets as
they enter the network (i.e., UNI) or are passed between Nodes
(i.e., NNI)
Types of policing controls include:
– Generic Flow Control (GFC) - Instructs the ATM network to employ
a flow control algorithm for cells in this connection.
– Call Admission Control (CAC) - Done during establishing a
channel; makes sure the requested bandwidth exists and that the
QoS can be provided.
– Traffic Policing and Shaping - Usage/Network Parameter Control
(UPC/NPC)
22
Concept Network Congestion & Policing
• Checks the rate of the cells at the input to
ensure that arriving cells meet the ‘traffic
profile’ (bandwidth and QoS) specifications.
If not, it can discard the cell or mark the cell
as eligible for discard.
• Algorithm to determine if a cell should be
discarded is called ‘Leaky bucket’.
– Explicit Forward Congestion Indicator
(EFCI) - If node is becoming congested,
it marks the cells. The end station then
hopefully throttles its traffic.
23
PVC - Manual Set Up
Console or
NMS GUI
VPI/VCI
14/1055
14/1055
9/47
9/47
• Pre-established connections
• Permanent
• No signaling required
24
SVC - Automatic Set Up
Connect to B
OK
OK
Terminal B
Connect to B
Connect to B
Terminal A
OK
OK
• Uses UNI 3.0/3.1 signaling
– VPI/VCI = 0/5
• Automatic
• Transparent to User
25
ATM Network Interfaces
Public NNI
B-ICI
WAN
WAN
FUNI
Router
Remote
Site
Service
Provider
Public
UNI
Private
UNI
Customer
Premises
Private
NNI
Private
UNI
26
Public NNI
• Network Node Interface (NNI)
– The interface at a network node which is used to
interconnect with another network node
• SONET/SDH interface is preferred
– ANSI T1.105-1995 and ITU-T G.707 March 1996
• Provides ATM mapping to 10 Gbps and beyond
• Let’s review SONET
27
STS- 1 Frame with ATM
87 Bytes
3 Bytes
3 Bytes
Section
Overhead
Line
6 Bytes Overhead
1X9
Byte
1X9
Byte
1X9
Byte
P
a
t
h
F
I
X
F
I
X
O
v
e
r
h
e
a
d
S
t
u
f
f
ATM
Payload
48.384
Mbps
S
t
u
f
f
51.84 Mbps
28
STS-3c Frame Structure
9 Bytes
261 Bytes
H
3 Bytes
Section
Overhead
6 Bytes
Line
Overhead
…
H
P
a
t
h
O
v
e
r
h
e
a
d
ATM Payload
149.76 Mbps
…
H
53 Bytes
155.52 Mbps
H
ATM Cell
29
STS-48c Frame Structure
15
Bytes
144 Bytes
4160 Bytes
H
3 Bytes
Section
Overhead
6 Bytes
Line
Overhead
P
a
t
h
O
v
e
r
h
e
a
d
F
i
x
e
d
S
t
u
f
f
…
H
ATM Payload
2.39616 Gbps
…
H
4176 Bytes
2.48832 Gbps
30
Fault Management Example
STE
PTE
Terminal
Repeater
X
LTE
ATM Switch
ATM Switch
ADM
VP
VC
LOS
Line AIS (AIS-L)
STS Path AIS (AIS-P)
VP-AIS
VC-AIS
RDI-L (formally Line FERF)
RDI-P (formally STS Yellow)
VP-RDI
VC-RDI
LOS- Loss of Signal
AIS- Alarm Indication Signal
RDI- Remote Defect Indication
FERF- Far End Receive Failure
31
ATMOperation and Maintenance Principles
• Fault Management, using AIS, RDI, continuity check and
loopback OAM cells.
• Performance management, using forward monitoring
and backward reporting OAM cells.
• Activation/deactivation of performance monitoring
and/or continuity check, using activation/deactivation
OAM cells.
• System management OAM cells for use by end-systems
only.
32
Concept - OAM
• Operations, Administration and Maintenance (OAM)
• ATM allows the maintenance/test operation to be
performed on a VPC or VCC.
• These operations are performed on a selected basis;
they can span segments or can be end-to-end.
• Types of maintenance/test operations:
– Performance Monitoring - a VPC or VCC is monitored to ensure
the connection is not congested or has degraded (forward and
backward monitoring are provided)
– Failure detection (AIS, RDI)
– PM and Failure Reporting (RDI, PM results)
– Facility Protection of VPCs
– Fault Isolation (continuity checks and loopbacks)
33
I.610Operation and Maintenance Flows
• Physical Layer Mechanism
– F1: SONET Section Level
– F2: SONET Line Level
– F3: SONET Path Level
• ATM Layer Mechanism
– F4: Virtual Path Level
• End to end F4 flow
• Segment F4 flow
– F5: Virtual Channel Level
• End to end F5 flow
• Segment F5 flow
34
Fault Management Example
Using F1 - F5 Flows
STE
PTE
LOS
Terminal
Repeater
X
F1
F2 (AIS-L)
LTE
ATM Switch
ATM Switch
ADM
VP
VC
F3 (AIS-P)
F4 (VP-AIS)
F5 (VC-AIS)
F2 (RDI-L)
F3 (RDI-P)
F4 (VP-RDI)
F5 (VC-RDI)
35
Example of Mechanism
for OAM Flows
VCC
endpoint
VP cross-connect
VC cross-connect
VCC
endpoint
AAL
AAL
Physical layer
connecting point
ATM
PL
PL
PL
ATM
ATM
ATM
ATM
ATM
PL
PL
PL
PL
PL
VCI 1
VCI 1
VCI 2
VCI 2
Virtual channel OAM cell indicated by PT identifier F5
VPI 1
VPI 1
VPI 2
VPI 2
Virtual path connection uses VCI(=3/4) for OAM F4
Transmission path F3
F1, F2
F1, F2
Trans path F3
F1, F2
VPI 3
VPI 3
VPC - OAM F4
Trans path F3
F1, F2
36
Layered Model of AIS & RDI
VC-AIS (F5)
VP-AIS (F4)
AIS-P (F3)
AIS-L (F2)
(F1)
VC
VC-RDI (F5)
VP
VP-RDI (F4)
PATH
RDI-P (F3)
LINE
RDI-L (F2)
SECTION
(BIP-8 PM, F1)
PHYSICAL
(Layer to layer indications)
(Peer to peer indications)
37
The ATM Adaptation Layer
The AAL process is the most important feature of the ATM
Communications process...
How the Adaptation process is carried out depends on the type
of service to be transported...
AAL TYPE SERVICE TYPE
COMMENTS
AAL1
Isochronous Traffic like DS0,
DS1s, DS3s to carry Voice
For data services, compressed
Audio / Video, etc.
Bursty data over long periods
AAL2
AAL3
AAL4
AAL5
Constant Bit Rate
CBR
Variable Bit Rate
VBR
Connection-Oriented
for VBR Data
Transfer
Connectionless VBR
Data Transfer
Simplified AAL
For short, bursty data (SMDS…)
Mainly for point-to-point
38
Classes of ATM Service
CLASS A
Timing Relation Between
Source & Destination
Bit Rate
Connection Mode
AAL Types
CLASS B
Required
CLASS D
Not Required
Constant
Variable
CONNECTION ORIENTED
1
CLASS C
2
CONNECTION-LESS
3/4, 5
3/4
39
The AAL Process
AAL is divided
into two
sublayers:
USER INFORMATION
CS Process
CS-PDU
1) CONVERGENCE
SUBLAYER
2) SEGMENTATION &
REASSEMBLY SUBLAYER
CS-PDU
CS-PDU
SAR Process
SAR-PDU
SAR-PDU
SAR-PDU
SAR-PDU
These two sublayers convert the user information into 48-byte cell
payloads. Each sublayer produces a Protocol Data Unit (PDU).
The CS-PDU is variable length while the SAR-PDU is always 48 bytes.
40
AAL-1 Processing
Payload
Header
SN Field
4 Bits
1
CSI
2 3 4
Sequence
Count
SNP Field
4 Bits
1 2 3
CRC
PDU Payload (47 Octets)
4
Parity
SN: Sequence Number
SNP: Sequence Number Protection
CSI: Convergence Sublayer Indicator
41
AAL-2 Processing
CPS-Packet
Header (3 octets)
CPS-Packet
Payload (1 to 45/64 octets)
CPS-Packet
Cell Header
(5 octets)
Start Field
(1 Octet)
CPS-PDU Payload( up
to 47 octets and pad)
CPS-PDU
ATM Cell
Each AAL2 user generates CPS packets with a 3-octet packet header and a variable
length payload. The CPS sublayer collects CPS packets from AAL2 users multiplexed
onto the same VCC over a specified interval of time, forming CPS-PDU, comprised of
48 octets worth of CPS packets.
42
The AAL Process:
AAL 3/4 CS-PDU
CS-PDU
CPI
BTag
BASize Information
Pad
AL
ETag Length
CPI: Common Point Indicator - 1 Byte
BTag: Beginning Tag - 1 Byte
BA Size: Buffer Allocation Size - 2 Bytes
Info Payload: Length of Payload (Max: 65, 535 Bytes)
Pad: Up to 3 Bytes - used to align CS-PDU length
AL: Alignment - 1 Byte
ETag: End Tag - 1 Byte
Length: 2 Bytes
43
AAL 3/4
CPI BTag BASize
AAL SEVICE DATA UNIT
AAL - SDU
44 Bytes
BOM
SequenceSequence
Type
Number
2 BITS
4 BITS
MID
10 BITS
2 Bytes
Payload
Al
Fill Length ETag
44 Bytes
Length
Indicator
6 BITS
CRC
10 BITS
2 Bytes
Convergence
Sublayer
Protocol
Length Data Unit:
CS-PDU
44 Bytes
Payload
COM
Payload
EOM
Segmentation &
Reassembly
Protocol Data
Unit:
SAR-PDU
MID: Message Identifier
BOM: Beginning of message
BASIZE: Buffer Allocation Size
COM: Continuation of message CRC: Cyclic Redundancy Check BTAG: Beginning Tag
EOM: End of message
EOM: End of message
ETAG: End Tag
44
The AAL Process:
AAL5 CPCS-PDU
CPCS-PDU
CPCS-PDU
Trailer
CPCS-PDU Payload
1 - 65,535
PAD CPCS-UU CPI
0- 47
1
1
Length CRC
2
4
Unit: octets
PAD: Padding
UU: User-to-User Indication
CPI: Common Part Indicator
LENGTH: CPCS-PDU Length
CRC: Cyclic Redundancy Check
CPCS: Common Part Convergence Sublayer
45
AAL-5
AAL Service Data Unit (SDU)
AAL5-SDUs
AAL5-SAP
1-65,535 octets
CPCS-PDU Payload
CPCS-PDUs
octets
CPCS-PDU
Trailer
PAD
CPCS-UU CPI Length CRC
0-47
1
1
2
4
•••
SAR
Payload
SAR
Payload
Header
5
Payload
48
Header Payload
5
48
•••
•••
SAR
Payload
Payload Type=
AAL_Indicate
Header
5
Payload
48
SAR-PDUs
ATM-SAP
Cells
Octets
46
Network Management for ATM
• The Role of SNMP - RFC-1157
• Integrated Local Management Interface - ILMI
• ILMI-MIB - ATM Forum
• AToM-MIB - RFC-2515
47
The Role of SNMP
•
The Simple Network Management Protocol (SNMP) has become widely
accept in the LAN industry as an open standard for managing
equipment from multiple vendors
•
SNMP is supported by various WAN systems vendors
•
Bellcore is using SNMP for their customer network management
capabilities
•
SNMP V2 addresses some of the bandwidth utilization, and security
issues that were present in SNMP V1
•
SNMP V3 is being defined in IETF
•
ILMI utilizes the SNMP protocol as an ‘interim solution’
•
Using RFC1577 - (IP & ARP over ATM) it is now possible to manage
ATM networks from a central (or multiple) NMS, using SNMP/UDP/IP
packets encapsulated in AAL5
48
Integrated Local
Management Interface
Beyond the Scope
of ILMI Specification
Remotely
Accessible
Agent
NETWORK MANAGEMENT
STATION or SUBSYSTEM
Remotely
Accessible
Agent
Private
UNI
UME
ATM
End-System
Public
UNI
UME UME
ILMI
(SNMP/AAL)
UME
Private
ATM Switch
ILMI
(SNMP/AAL)
UME
ILMI
(SNMP/AAL)
Public Network
ATM Switch
UME
Public UNI
UME: UNI Management Entity
49
Functions of ILMI
ILMI PERFORMS THE FOLLOWING TASKS:
Basic Configuration information
PVC Status Indication in FR/ATM Service
Interworking
ILMI Connectivity detection and auto neighbor
discovery
Address registration for SVC and PNNI
ABR attribute setting for SVC
Auto-configuration of a LAN Emulation Client - LEC
50
ILMI MIB
MIB specification in ATM UNI 3.X and 4.0
Management information includes:
Physical Layer
ATM Layer
ATM Layer Statistics
Virtual Path (VP) Connections
Virtual Channel (VC) Connections
Network Prefix
Network Address
Service Registry
51
ATM Management MIB - ATOM
Structure of the MIB groups:
Configuration
DS3 PLCP
TC Sublayer
Virtual Link Configuration
VP/VC cross-connect
Network Address
AAL Connection Performance Statistics
Reference: RFC 1695 & 2515
52
REFERENCES
• ATM Forum Documents - www.atmforum.com
• GR-1248 - Generic Requirements for Operations on ATM
NEs
• I.363 & 365 - ATM Adaptation Layer (AAL) Sublayer
• I.610 - BISDN OAM Principles and Functions
• RFC2761 - Terminology for ATM Benchmarking
53