Transcript Asynchronous Transfer Mode Networks

Asynchronous Transfer Mode
Networks
Nirmala Shenoy
Information Technology Department
Rochester Institute of Technology
updated 12/2001
1
Asynchronous Transfer Mode
• Scope
–
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Purpose
Cells vs packets
Topology
Virtual connections
VP and VPC switching
ATM layers
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Asynchronous Transfer Mode
• Scope
–
–
–
–
–
–
–
Delays in ATM networks
Service & QoS
Traffic control
UNI
B-ICI
Switch fabric
ATM addressing
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Asynchronous Transfer Mode
• Purpose
– Cells over frames
– Optimal use of transmission and equipment
technology
– Interface with various packet switching
networks
– WAN connectivity
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Asynchronous Transfer Mode
• Purpose
– Easy and inexpensive implementation
– Support exiting telecommunication hierarchies
• Local loops, local providers, long distance carriers
– Connection oriented – reliable and predictable
delivery especially for real-time application
– protocol functions from sw to hw
– High-speed low delay packet switching for all
types of traffic
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Asynchronous Transfer Mode
Cell vs Frames
Frames - Packets
• Current packet sizes- 200bytes to 64kbytes
• Elaborate software at intermediate nodes to
accommodate variable size packets
• Variable header evaluations
• Packets to be checked for integrity
• Non-uniformity of service for different types of
packet networks
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Asynchronous Transfer Mode
Packets
• Consistent data rate delivery not possible
• In-time delivery for some packets
– Real-time packets may be smaller compared to
data packets
Cells
• Predictable processing
• Uniformity guaranteed
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Asynchronous Transfer Mode
Cells
• Deterministic delays = n*cell transmission
• High speed + small cell size = continuous
stream effect
• Cells handled as cells not as bit stream –
faster
• Fixed cells – more hardware implementable
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Asynchronous Transfer Mode
Asynchronous TDM
A3
A2
B2
B1
C3
C2
A1
C3
B2
A3
C2
B1
A2
C1
A1
MUX
C1
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Asynchronous Transfer Mode
Topology
Private ATM
switch
Public ATM
switch
CPE
End
point
Public
UNI
SW
ATM
Network
SW
Private
UNI
SW
SW
End
Point
SW
Public
UNI
ATM end
point
NNI
NNI
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End
Point
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Asynchronous Transfer Mode
Topology
– Similar to ISDN has all reference points and
functional groupings (b tag)
– Public and private UNI may use different
different interfaces & schemes
– ATM can be used as a LAN, WAN, hub
– interconnecting networks, backbone
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Asynchronous Transfer Mode
Virtual connections
• Transmission Path
– Physical connection between two points
– Switches and end points or between switches
• Virtual Path
– Transmission path is divided into several
virtual paths
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Asynchronous Transfer Mode
Virtual connections
– The set of all virtual path = transmission
path
• Virtual circuit
– A single message flow circuit
– A number of virtual circuits make a virtual
path
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Asynchronous Transfer Mode
Virtual connections – relationship
VC
VC
VC
VP
Transmission
Path
VC
VP
VC
VP
VP
VC
VC
VC
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Asynchronous Transfer Mode
Virtual connections – relationship
End
Point
ATM
Network
VC
VC
VP
VP
End
point
VC
SW
SW
SW
VC
VP
VC
VC
SW
VC
End
Point
End
Point
VP
VP
End
Point
End
Point
End
Point
VC
End
Point
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Asynchronous Transfer Mode
Virtual connections – relationship
• VPI & VCI
VCI =21
VCI =21
VCI =45
VPI=14
VCI =32
VPI=18
Unique Virtual
connection id
VPI=14, VCI=21
VPI=14 VCI =45
VPI =18
VCI =32
VC I=45
VCI=45
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Asynchronous Transfer Mode
Virtual connections set-up
• PVC – permanent virtual circuit
– Negotiated with the network on long term
basis
• SVC – switched virtual circuit
– On per call basis
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Asynchronous Transfer Mode
Virtual connections set-up
Set up message
Call processing
Call processing
connect
Connect ack
Connect ack
Data interchange
End pt
Release
Release
Release
complete
Release
complete
Ingress
Node
ATM network
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Egress
Node
End pt
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Asynchronous Transfer Mode
VP switching
Input
Interface VPI
1
153
67 153
1
VCI VPI
2
Output
interface VPI
3
140
4
SW
3
67 140
VCI VPI
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Asynchronous Transfer Mode
VPC switching – VP & VC switching
Input
Interface VPI
1
153
-
VCI
67
67 153
1
VCI VPI
2
Output
interface VPI
3
140
-
VCI
92
4
SW
3
92 140
VCI VPI
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Asynchronous Transfer Mode
ATM layers
– ATM Adaptation Layer – AAL
• Convergence Sub layer
• Segmentation and Reassembly sub layer
– ATM Layer
– Physical layer
• SONET/SDH
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Asynchronous Transfer Mode
ATM layers & the OSI layers
– ATM layer performs layers 2 & 3 functions
of the OSI layers
– AAL combines, 2,4 and 5 of the OSI layers
– Not adhering to the OSI layers
• OSI layers getting obsolete?
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Asynchronous Transfer Mode
ATM Planes
control
Q.2931
SAAL
SSCF – service specific
coordination
function
SSCOP – service
specific connectionoriented protcol
user
management
voice, video, data
LMI, OAM
SSCF
SSCOP
ATM
AAL
AAL
AAL
ATM
SDH, SONET, DS1, ES1 etc
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Asynchronous Transfer Mode
• ATM Adaptation Layer – at the end
points
• ATM & Physical layer through the
AAL
AAL
network
ATM
ATM
ATM
ATM
PHY
PHY
PHY
PHY
EP
SW
SW
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EP
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Asynchronous Transfer Mode
• ATM Adaptation Layer – application specific
• Classification of traffic
– Class A – constant bit rate
– Class B - variable bit rate, connection oriented,
timing requirements
– Class C- Variable Bit Rate, connection oriented,
timing not required
– Class D – Variable Bit Rate, connectionless, timing
not required
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Asynchronous Transfer Mode
• ATM Adaptation Layer
– AAL1 – to support Class A
– AAL2 – Class B – later for voice
– AAL3/4 – connection oriented data &
connectionless data, Class C & D
– AAL5 – signaling – data
• Simple and most popular
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL1
– Convergence Sub layer
– Segments PDU from upper layer to 47 byte
segments
– Passes to SAR
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL1
– Segmentation And Reassembly layer –SAR
– adds a 1 byte header
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•
•
•
1bit CSI – convergence sublayer id
3 bits – sequence count
3 bits – CRC on the above
1 bit parity
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Asynchronous Transfer Mode
• Delays and real-time service support
• Transmission efficiency = Li/(Li+Lo)
– Li – information field length
– Lo – length of control header
• Variable SDU – Li can be large
– Processing delays at switch
• Fixed SDU – predictable delays
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Asynchronous Transfer Mode
• Transmission delay
– To provide for time transparency
• Circuit emulation for some applications
– Responsibility of the AAL
• Buffering schemes
– Delay at sender end
• Convergence and reassembly – C/S1
• At the receiver end C/S2
– Propagation Delay – PD 4-5 sec per Km
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Asynchronous Transfer Mode
• Transmission delay
– Cell loss
• Loss of one cell – 4-16 msec
– Switching Delay – SD – fixed 2-100 sec
– Delays to overcome jitter
– Queuing Delay – traffic peaks
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Asynchronous Transfer Mode
• Transmission delay
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–
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–
C/S = 12000 sec (6000  sec at each end)
PD = 2000  sec
SD= 72  sec (24  sec for each switch –3)
QD =225  sec (total for 3 switch)
• Predominant PD and C/S
• C/S can be higher if some other layers
include more mapping & convergence
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL3/4
– Convergence sub layer
User data <=65,536 bytes
T
BT
BA
Convergence
sub-layer
PAD
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AL ET L
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL3/4
– Convergence Sub layer bits
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T – type
BT – Begin Tag
BA – Buffer Allocation
PAD- padding to proper multiple size
AL – align trailer to 4 bytes
ET – End Tag
L – length of data unit
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL3/4
– Segmentation and Reassembly sub layer
Convergence layer PDU
Convergence
sub-layer
44 bytes
44 bytes
44 bytes
Header 2
bytes
ST
CSI
2
1
Trailer 2
bytes
SC MID
3
LI
10
6
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SAR sublayer
CRC
10
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL3/4
– SAR sub layer bits
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•
•
•
•
ST – segment type
CSI – convergence sublayer identifier
SC - Sequence count
MID – Multiplexing identifier
LI – length indicator
CRC updated 12/2001
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL5
– SEAL – Simple and Efficient Adaptation Layer
– Assumes most sequencing and error control if
required are provided by end system ULP
– Convergence
PAD UU T L CRC
sub-layer
48 bytes
48 bytes
48 bytes
SAR sub-layer
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Asynchronous Transfer Mode
• ATM Adaptation Layer- AAL5
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–
–
–
UU – user-to user id
T – type
L- length
CRC - checksum
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Asynchronous Transfer Mode
• ATM layer
–
5 bytes header
48 bytes from AAL
GFC/VPI
ATM cell
VPI
VPI
VCI
VCI
VCI
VCI
PT
CLP
HEC
48 bytes payload
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Asynchronous Transfer Mode
• ATM layer
– PT – payload type (3 bits) – 1st bit
• User Data – 0
• Management data – 1
– User data
• 2nd bit 0- no congestion, 1 congestion
• 3rd bit – 0 no signaling, 1 signaling bit
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Asynchronous Transfer Mode
• ATM layer
– Management data – 1st bit = 1
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•
•
•
00 – link associated
01 – end-to-end management
10 – resource management
11 – reserved
– CLP – cell loss priority bit
– HEC- header error correction/detection
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Asynchronous Transfer Mode
• Services supported over ATM
– CBR
– VBR
• rt, nrt
– ABR
– UBR
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Asynchronous Transfer Mode
capacity
• Utilization of bandwidth by Services
ABR & UBR
VBR
CBR
time
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Asynchronous Transfer Mode
• Quality of Service QoS
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User oriented
SCR – Sustained Cell Rate
PCR – Peak Cell Rate
MCR – Minimum Cell Rate
CVDT – cell variation delay tolerance
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Asynchronous Transfer Mode
• Quality of Service QoS
–
–
–
–
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Network oriented
CLR – cell loss ratio
CTD – cell transfer delay
CDV – cell delay variation
CER – Cell Error Ratio
• Traffic Descriptors
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Asynchronous Transfer Mode
• Network parameters
– Error Free Cells arriving before a specified
time T are successfully delivered cells
– Lost cells if it arrives after time T or
discarded, header error
– Mis-inserted cells due to wrong header
– Severely damaged cells
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Asynchronous Transfer Mode
• Allocation of
resources
Service request
Request denied
no
Bw available
yes
no
Path generation
phase
Alternate paths?
no
Bw available on each
trunk
yes
Link allocation
phase
no
VPI/VCI successfully
allocated
yes
no
Qos guarantees
OK?
yes
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Grant
connection
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Asynchronous Transfer Mode
•
•
•
•
Traffic control
CBR – Peak cell rate – pcr
VBR – pcr, scr and maximum burst size
Burst tolerance - BT
– BT = (MBS – 1)/(1/SCR – 1/PCR)
• Generic cell rate algorithm
– Virtual scheduling
– Continuous leaky bucket
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Asynchronous Transfer Mode
• Virtual scheduling algorithm
– Theoretical Arrival Time TAT is the expected
arrival time
– Cell arriving before TAT + L is confirming
– Cell arrival time is ta, then TAT is set to ta if
it was a confirming cell
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Asynchronous Transfer Mode
• ATM at the UNI
– Supports symmetric and asymmetric
connections
– bandwidth allocation independent in the 2
directions
– Negotiation of QoS
–
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Asynchronous Transfer Mode
• ATM at the UNI
– Identification of end-to-end capabilities
– Client registration
• Address, administrative information exchange
across the UNI
• Facilitate network administrator
– A number of messages defined to facilitate
the above
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Asynchronous Transfer Mode
• ATM B-ICI – Inter carrier interface
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–
–
–
Internetworking specification
ITU-T -> NNI based on SDH
ATM Forum – B-ICI based on SONET , DS3
To accommodate
•
•
•
•
Frame Relay
Cell relay service as ATM cells
Circuit emulation service DS1, DS3
SMDS
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Asynchronous Transfer Mode
input
• Switch fabric – crossbar switch
output
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Asynchronous Transfer Mode
input
• Switch fabric – Knockout switch
output
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Asynchronous Transfer Mode
• Switch fabric – Knockout switch
– To avoid collisions at switch
• Two input cells to one output
– Uses distributors and queues
– n2 crossover points still required
• n – number of inputs/outputs
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Asynchronous Transfer Mode
• Switch fabric – Banyan switch
0
Left bit
0
A1
1
middle bit
0
B1
1
right bit
0
C1
1
1
2
1
A2
3
4
0
1
B2
0
1
0
C2
1
2
3
A3
5
6
A4
7
0
0
1
B3
0
1
B4
0
1
0
1
C3
0
1
4
5
C4
0
1
6
7
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Asynchronous Transfer Mode
• Switch fabric – Batcher Banyan switch
Left bit
0
A1
middle bit right bit
0
0
B1
1
1
0
C1
1
1
4
0
Trap module
3
Batcher Switch
1
2
A2
1
B2
0
1
C2
0
1
2
3
A3
0
1
B3
0
1
C3
0
1
A4
0
1
B4
0
1
4
5
5
6
0
C4
0
1
6
7
7
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Asynchronous Transfer Mode
• ATM Addressing
– OSI model
– Initial Domain Part – IDP
• Authority Format Identifier
– DCC ATM format
– ICD ATM format
– E.164 format
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Asynchronous Transfer Mode
• ATM Addressing
• Initial Domain Identifier
• Domain Specific Part
–
–
–
–
–
–
DFI
AA – administrative authority
RD – routing domain id
Area
ESI – end system id
SEL – ULP entities – not used in ATM network
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