atm networks: an overview
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21-1©2005 Raj JainCSE473sWashington University in St. Louis
ATM Networks: ATM Networks: An OverviewAn Overview
Raj Jain Washington UniversitySaint Louis, MO 63131
Jain@cse.wustl.eduThese slides are available on-line at:
http://www.cse.wustl.edu/~jain/cse473-05/
21-2©2005 Raj JainCSE473sWashington University in St. Louis
q ATM vs Phone Networks and Data Networksq ATM Protocol Layersq Cell Header Format, AALs q Physical Media q Service Classes: CBR, VBR,ABR, UBR, GFR
OverviewOverview
21-3©2005 Raj JainCSE473sWashington University in St. Louis
ATMATM
q ATM Net = Data Net + Phone Netq Combination of Internet method of
communication (packet switching) and phone companies� method (circuit switching)
ATM
21-4©2005 Raj JainCSE473sWashington University in St. Louis
ATM vs Phone NetworksATM vs Phone Networks
q Legacy 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 automated setup.
125 μs
21-5©2005 Raj JainCSE473sWashington University in St. Louis
ATM vs Data NetworksATM vs Data Networks
q Signaling: Internet Protocol (IP) was connectionless.You could not reserve bandwidth in advance.ATM is connection-oriented. You declare your needs before using the network.
q PNNI: Path based on quality of service (QoS)q Switching: In IP, each packet is addressed and
processed individually. q Traffic Management: Loss based in IP.
ATM has newer traffic management technology.Required for high-speed and variable demands.
q Cells: Fixed size or small size. Not important
21-7©2005 Raj JainCSE473sWashington University in St. Louis
PrivateNNI
Private
UNI
ATM InterfacesATM Interfaces
Computer PrivateSwitch
PublicSwitch
RouterDigitalService
Unit
DXI
B-ICI
PublicUNI
Public
NNI
PrivateUNI
PrivateSwitch
PublicSwitch
Carriers
PublicSwitch
Carrier
Computer
21-8©2005 Raj JainCSE473sWashington University in St. Louis
ATM InterfacesATM Interfaces
q User to Network Interface (UNI): Public UNI, Private UNI
q Network to Node Interface (NNI): q Private NNI (P-NNI)q Public NNI =Inter-Switching System Interface (ISSI)
Intra-LATA ISSI (Regional Bell Operating Co)q Inter-LATA ISSI (Inter-exchange Carriers)
⇒ Broadband Inter-Carrier Interface (B-ICI)q Data Exchange Interface (DXI)
Between routers and ATM Digital Service Units (DSU)
21-9©2005 Raj JainCSE473sWashington University in St. Louis
ATM Layer
ATM Adaptation
Layer
PhysicalLayer
ATM Layer
PhysicalLayer
ATM Layer
ATM Adaptation
Layer
PhysicalLayer
End System
Switch
Protocol LayersProtocol Layers
HigherLayer
End System
HigherLayer
21-10©2005 Raj JainCSE473sWashington University in St. Louis
Protocol LayersProtocol Layers
q The ATM Adaptation Layerq How to break messages to cells
q The ATM Layerq Transmission/Switching/Receptionq Congestion Control/Buffer managementq Cell header generation/removal at
source/destinationq Cell address translationq Sequential delivery
21-11©2005 Raj JainCSE473sWashington University in St. Louis
Virtual Circuit NumbersVirtual Circuit Numbers
q Each cell has a circuit numberq Circuit number determines the cell�s queuing and
forwardingq Circuits have be set up before useq Circuits are called Virtual Circuits (VCs)
PBXPBX PBXPBX
1 3 5 2 3
21-12©2005 Raj JainCSE473sWashington University in St. Louis
Cell Header FormatCell Header Format
q GFC = Generic Flow Controlq (Was used in UNI but not in NNI)
q VPI/VCI = 0/0 ⇒ Idle cell; 0/n ⇒ Signalingq HEC: 1 + x + x2 + x8
VCI PTIHeader Error Check (HEC)
VCIVPI VCI
GFC/VPI VPI
CLP
Payload
21-13©2005 Raj JainCSE473sWashington University in St. Louis
Path vs ChannelsPath vs Channelsq 24/28-bit connection identifier
First 8/12 bits: Virtual Path, Last 16 bits: Virtual Circuit
q VP service allows new VC's w/o orders to carriers
VC1VC2VC3VC1VC2VC3VC1VC2VC3
VP1
VP2
VP3
Link
21-14©2005 Raj JainCSE473sWashington University in St. Louis
VP/VC Assignment/UseVP/VC Assignment/Use
Switch
33 56Video Data
37 34VoiceData
2
1
34
5
35
56
65
766
1122
Port0/370/340/330/56
VPI/VCIIn
1/350/560/654/76
VPI/VCI3456
PortOut
21-15©2005 Raj JainCSE473sWashington University in St. Louis
Header Error ControlHeader Error Control
q 8 bit error control fieldq Calculated on remaining 32 bits of headerq Allows some error correction
21-16©2005 Raj JainCSE473sWashington University in St. Louis
HEC Operation at ReceiverHEC Operation at Receiver
CorrectionMode
DetectionMode
Multibit error detected(Cell discarded)
Single-bit error detected(correction)
No errordetected
Error detected(cell discarded)
No Errordetected
21-17©2005 Raj JainCSE473sWashington University in St. Louis
Original Classes of TrafficOriginal Classes of Traffic
Class A Class B Class C Class DTime Sync Yes Yes No NoBit Rate Constant Variable Variable VariableConnection-Oriented
Yes Yes Yes No
Examples CircuitEmulation
Comp.Video
FrameRelay
SMDS
AAL AAL1 AAL2 AAL3 AAL4
21-18©2005 Raj JainCSE473sWashington University in St. Louis
AAL 5AAL 5
q Designed for data trafficq Less overhead bits than AAL 3/4
� Simple and Efficient AAL (SEAL)q No per cell length field, No per cell CRC
PADUserPayload Length CRC-32Control
4220-64kB
10PTI bit indicates last cell
0-47
21-19©2005 Raj JainCSE473sWashington University in St. Louis
AAL2AAL2q Ideal for low bit rate voiceq Variable/constant rate voiceq Multiple users per VCq Compression and Silence suppressionq Idle channel suppression
CellHeaderCell
Header Payload 1PktHdr Payload 2 Payload 3Pkt
HdrPktHdr
Payload 1PktHdr Payload 2 Payload 3Pkt
HdrPktHdr
Payload 1 Payload 2 Payload 3
21-20©2005 Raj JainCSE473sWashington University in St. Louis
Physical MediaPhysical Media
q Multimode Fiber: 100 Mbps using 4b/5b, 155 Mbps SONET STS-3c, 155 Mbps 8b/10b
q Single-mode Fiber: 155 Mbps STS-3c, 622 Mbpsq Plastic Optical Fiber: 155 Mbpsq Shielded Twisted Pair (STP): 155 Mbps 8b/10bq Coax: 45 Mbps, DS3, 155 Mbpsq Unshielded Twisted Pair (UTP)
q UTP-3 (phone wire) at 25.6, 51.84, 155 Mbpsq UTP-5 (Data grade UTP) at 155 Mbps
q DS1, DS3, STS-3c, STM-1, E1, E3, J2, n × T1
21-22©2005 Raj JainCSE473sWashington University in St. Louis
Classes of ServiceClasses of Serviceq ABR (Available bit rate):
Source follows network feedback. Max throughput with minimum loss.
q UBR (Unspecified bit rate): User sends whenever it wants. No feedback. No guarantee. Cells may be dropped during congestion.
q CBR (Constant bit rate): User declares required rate.Throughput, delay and delay variation guaranteed.
q VBR (Variable bit rate): Declare avg and max rate.q rt-VBR (Real-time): Conferencing.
Max delay guaranteed.q nrt-VBR (non-real time): Stored video.
21-24©2005 Raj JainCSE473sWashington University in St. Louis
Guaranteed Frame Rate (GFR)Guaranteed Frame Rate (GFR)
q UBR with minimum cell rate (MCR) ⇒ UBR+q Frame based service
q Complete frames are accepted or discarded in the switch
q Traffic shaping is frame based. All cells of the frame have the same cell loss priority (CLP)
q All frames below MCR are given CLP =0 service. All frames above MCR are given best effort (CLP =1) service.
21-25©2005 Raj JainCSE473sWashington University in St. Louis
SummarySummary
q ATM Overview: History, Why and Whatq Protocol Layers: AAL, ATM, Physical layers, Cell
formatq Interfaces: PNNI, NNI, B-ICI, DXIq ABR, CBR, VBR, UBR, GFR
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