1. CPEG 514 Lecture 11 Asynchronous Transfer Mode (ATM)2

2. Outline ATM Introduction Virtual Circuit Setup – PVC vs. SVC
Quality of Service and Congestion Control
IP over ATM
ATM and Frame Relay interworking
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3. ATM Network (integrated voice, video, and data services)
Private
Carrier to carrier
Is not really common
Integrated via IP
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4. ATM Standards ITU-T, ATM Forum, IETF
User-to-Network Interface (UNI) 2.0
UNI 3.0, UNI 3.1, UNI 4.0
Network-to-Network Interface (NNI)
PNNI
Private NNI
Public-Network Node Interface
RFC 2684 (Multiprotocol encapsulation over ATM)
LAN Emulation (LANE)
Multiprotocol over ATM (MPoA)
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5. Synchronous vs. Asynchronous
ATM- cell switching technology (asynchronous)
NO clock synch between xmt/rcv
TDM – circuit switching technology (synchronous)
clock synch between xmt/rcv
ATM is more efficient than TDM. (why?)
TDM: dedicated time slots.
ATM: time slots are available on demand with information identifying the destination address of the transmission contained in the header of each ATM cell.
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6. ATM Network Components
If i/f is not ATM, the switch would have to do the interworking function
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7. ATM PCI NIC (ATM to the desktop)
Network
ATM OC-3c
OC-3 155Mbps
Price: $605 (cf. how much is Gigabit-E NIC?)
Should remember OC-3 speed
Number of T1 on OC-3, 28 T1s
Q: is there still a market for ATM to the desktop? why?
Ethernet is cheaper even at the Gbps, 1Gb Ethernet = $30, 100 BaseT = $7-10
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8. ATM UNI, PNNI, and NNI
NNI?
PNNI
Is there a public ATM? Is there a public Frame Relay?
Private NNI (PNNI): connecting two private networks through a public one.
or Inside the same carrier’s network
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9. ATM Cell Format
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10. ATM Cell Format Generic Flow Control (GFC) – typically not used.
Virtual Path Identifier (VPI) – 8 (UNI) or 12 (NNI) bits
Virtual Channel Identifier (VCI) – 16 bits
Payload Type (PT)— 3 bits
first bit: user data (0) or control data (1)
second bit: Congestion Indicator 0 = no congestion, 1 = congestion),
Set to 1 if pkt encountered congestion
third bit: whether the cell is the last cell (1) in a series of AAL5 frame
Cell Loss Priority (CLP)—Indicates whether the cell should be discarded (1) if it encounters extreme congestion as it moves through the network.
Similar to - DE (Discard Eligibility in Frame Relay)
Header Error Control (HEC)—checksum on the first 4 bytes of the header.
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11. ATM PVC and SVC
PVC (permanent virtual circuit ) allows direct connectivity between sites, and is similar to a leased line.
+++ guarantees availability of a connection
+++ does not require call setup procedures between switches.
--- requires manual setup between the source and the destination.
--- no network resiliency/Flexibility is available with PVC.
SVC (Switched virtual circuits) is created and released dynamically and remains in use only as long as data is being transferred. In this sense, it is similar to a telephone call. Dynamic call control requires a signaling protocol between the ATM endpoint and the ATM switch.
+++ connection flexibility
+++ call setup that can be handled automatically by a networking device.
--- the extra time and overhead required to set up the connection.
--- network management and trouble shooting due to dynamic nature of SVC
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12. ATM Virtual Connections
ATM switching is based on VPI/VCI
However, VPI+VPI is not called ATM address.
VPI/VCI has local significance only at the port level of the ATM switch.
NSAP is ATM’s address
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13. ATM Physical Layer Up 8 T1s as one link using IMA ATM over T1
ATM over multiple T1 - Inverse Multiplexing over ATM (IMA)
Up 8 T1s as one link using IMA
ATM over DS3, OC-3, OC-12, OC-48, and OC-192
Note: Marconi bought Fore Switch in 2000.
Q; What is the max speed for Frame Relay? Up to 30Mbps
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14. ATM Switching video data audio data For PVC, table done Manually10 11 P1
data 20 P3 21 P4 P2
audio 10 12 P5
data 30 30
IN/port
VPI/VCI
OUT/port P1
0/10 P3
0/11
0/20 P4
0/21 P2
0/12
0/30 P5
For PVC, table done Manually
SVC, table is done dynamically/on-demand
Audio and Video having the same VPI, that is OK and does not need to be.
VPI/VCI have local significance at the port level.
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15. ATM Reference Model
AAL
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16. ATM Protocol Layers ATM Switch ATM Applications ATM Applications
ATM Adaptive
Layer (AAL)
ATM Adaptive
Layer (AAL)
ATM
Layer
ATM
Layer
ATM
Layer
Physical
Layer
Physical
Layer
Physical
Layer
ATM Switch
ATM End Station
ATM End Station
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17. ATM Adaptation Layer AAL1: AAL5: AAL ATM Physical
Function: Add control information and break Protocol Data Unit (PDU) into cells
Segmentation and Reassembly (SAR)
AAL1:
Designed for voice application
Constant Bit Rate (CBR)
Circuit Emulation Service (CES) (emulates TDM circuit)
AAL2 (Not covered in this class)
Variable Bit Rate (VBR)
VBR-rt (voice)
VBR-nrt (data)
AAL5:
Designed for data application
Unspecified Bit Rate (UBR)
AAL
ATM
Physical
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18. AAL1 Convergence Sublayer Sends 47 bytes to SAR
Which adds 1 byte of SAR hdr
SAR
Hdr
Payload = 47
SN: Sequence Number
1 bit Convergence Sublayer Indicator (Clock recovery) +
3 bit Sequence Count (for entire PDU from convergence sublayer)
SNP: Sequence Number Protection:
3 bit CRC for the SN +
Last bit, parity check for the previous 7 bits (SN and CRC)
Q: How much overhead in an AAL1 cell?
A cell has 47bytes * 8 bits/byte = 376 bits
G.7111
DS0 at 64kbps
64000bits/sec
20ms has 64000/20 = 1280bits which needs 1280/376 = 4 cells
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19. AAL5 CPCS-PDU Payload Padding (0-47) CPCS-UU (1) CPI (1) Length (2)
Carries upper other
Protocols inside CPCS
payload (i.e. tcp/ip, ethernet
CPCS-PDU Payload
up to
Padding (0-47)
why do we need padding?
8 byte
trailer
CPCS-UU (1)
CPI (1)
Trailer alignment to 32 bit
Length (2)
CPCS Payload
Not including PAD
48 bytes (0..47)
Cell payload
To make the
Full PDU
Divisible by 48
Bytes
And divide it
Evenly into
48 byte segments
CRC (4)
CPCS: Common Part Convergence Sublayer
PDU: Protocol Data Unit
UU: User-to-user interface information
CPI: Common Part Indicator
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20. ATM Segmentation and Reassembly (SAR)
H:5-bytes H
Cell1 H
Cell2 H
Celln
AAL5 Frame
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21. ATM NSAP Address
This is required for NNI, but it is rarely used.
Note NSAP has global significance while VPI/VCI is an addressing scheme that has local significance only.
ATM NNI: same issue with Frame Relay.
NSAP: Network Service Access Point based on E.164 (phone #)
20 bytes
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22. ATM Connection Establishment
Goal: setup VPI/VCI between any two ATM devices
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23. ATM UNI Signaling (Q.2931) - SVC
End Device
ATM
Switch
ATM
Switch
ATM
End Device
SETUP
SETUP
SETUP
VPI/VCI
Will be
Setup
For each
Direction
PROCEEDING
PROCEEDING
ALERT
ALERT
CONNECT
ALERT
CONNECT
CONNECT
Why do we need this signaling protocol?
Connection Established, control, mgmt,
Does it look familiar (Q.931)?
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24. Signaling VCI (VPI=0) (UNI)
e.g. VPI =0, VCI for connection establishment signaling
Q; What is the VPI/VCI in the ATM Q.2931 SETUP message?
VPI= 0 VCI = 5
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25. ATM ILMI (mgmt plain)
Integrated Local Management Interface (ILMI) enables devices to determine status of components at the other end of a physical link and to negotiate a common set of operational parameters to ensure interoperability.
ILMI operates over a reserved VCC of VPI = X, VCI = 16.
Administrators may enable or disable ILMI at will, but it is highly recommended to enable it. Doing so allows the devices to determine the highest UNI interface level to operate (3.0, 3.1, 4.0), UNI vs. NNI, as well as numerous other items.
Furthermore, ILMI allows devices to share information such as NSAP addresses, peer interface names, and IP addresses.
Without ILMI, many of these parameters must be manually configured for the ATM attached devices to operate correctly.
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26. PVC or SVC Core (SVC) vs. Access (PVC)
Q1: What is the purpose of PVC and SVC?
Q2: What are differences between PVC and SVC?
Q3: For data services, is it better to use PVC or SVC?
Core (SVC) vs. Access (PVC)
Using the dynamic setup in the core would be easier
Q4: For voice services, is it better to use PVC or SVC?
Core (PVC – trunks are already there) vs. Access (SVC)
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27. ATM Quality of Service (QoS)
CBR: Constant Bit Rate
Guaranteed transmission rate EMULATING TDM circuit
VBR: Variable Bit Rate (Requires QoS attention)
rtVBR and nrtVBR (rt = real time)
Peak Cell Rate (PCR) – MAX allowed data rate
The maximum cell rate at which the user will transmit
Sustained Cell Rate (SCR) – allowable cell rate over time
Max Burst Size (MBR)
Minimum Cell Rate (MCR)
UBR: Unspecified Bit Rate
No guarantee, best effort
CBR
Service
Bit Rate
PCR
VBR
SCR
UBR
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28. ATM QoS ABR: Available Bit Rate
How does a carrier ensure that QOS can be met?
Connection Admission Control (CAC)
Procedure for determining whether each new SETUP request should be granted or denied based on current network conditions
Usage Parameter Control (UPC)
Procedure for verifying whether customer is conforming to their contractual Traffic Parameters. PER the SLA
Resource Management (RM)
Procedure for notifying ABR users when they should slow down
ABR: Available Bit Rate
Selective Cell Discard (SCD)
Procedure for discarding cells (CLP=1)during congestion.
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29. IP over ATM Protocol (RFC 2684)
/24
/24
ATM
Both ATM and
Ethernet Switching IP IP
802.3
802.3
802.3
802.3
802.3
802.3
PHY
PHY
RFC 2684
RFC 2684
PHY
PHY
AAL5
AAL5
Same Subnet
Then we are
Using switches
Need to remember protocol stack
ATM
ATM
PHY
PHY
802.3: IEEE Media Access Control layer (also know as Ethernet)
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30. Frame Relay and ATM Interworking
Frame Relay is an access technology, and it is rarely used on the carrier backbone (core).
The backbone is usually the ATM network, slowly migrating to IP/MPLS backbone.
How is Frame Relay carried over the ATM network?
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31. ATM/FR IWF
Frame Relay Service Specific Convergence Sublayer (FR-SSCS) uses the same PDU format as Frame Relay (Q.922) minus the FCS and FLAG.
FR traffic parameters (FECN, BECN, and DI) are maintained in FR-SSCS PDU.
FRF.5 supports both one-to-one (one DLCI to one VPI/VCI) and many-to-one (many DLCIs to one VPI/VCI) mappings.
Q: is DLCI in FR-SSCS used for addressing?
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32. ATM/FR Network Interworking (FRF.5)
p1r1
p1r3 FR
(T1) FR
(T1)
OC-3
ATM Core Network
FRF.5
Convert FR frames
to ATM cells
FRF.5
Convert ATM cells to FR frames
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33. ATM/FR Network Interworking (FRF.5)
FR-SSCS: Frame Relay Service Specific Convergence Sublayer
IWF: Interworking Function
ATM Core
p1r1
p1r3
ATM/FR IWF
ATM/FR IWF
ULP
ULP FR FR FR
FR-SSCS
FR-SSCS FR
PHY
PHY
PHY
AAL5
AAL5
PHY
ATM
ATM
PHY
PHY
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34. ATM/FR Network Interworking (FRF.8)
FR-SSCS: Frame Relay Service Specific Convergence Sublayer
IWF: Interworking Function
ATM
Core
p1r1
p1r3 FR
ATM
ATM
ATM/FR IWF IP IP
RFC2427
(FRF .8) FR FR
FR-SSCS
RFC2684
PHY
PHY
AAL5
AAL5
ATM
ATM
ATM
PHY
PHY
PHY
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