Post on 15-Oct-2021
CPEG 514
CPEG 514
Lecture 11
Asynchronous Transfer
Mode (ATM)
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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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ATM Network (integrated voice, video, and data services)
Private Carrier to carrier Is not really common Integrated via IP
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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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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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ATM Network Components
ATM Network
ATM?
If i/f is not ATM, the switch would have to do the interworking function
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ATM PCI NIC
(ATM to the desktop)
http://www.techstore.com/Item.aspx?sku=227610TD&sgd=330d316d317d314d315
Price: $605 (cf. how much is Gigabit-E NIC?)
ATM Network
ATM OC-3c OC-3 155Mbps
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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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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ATM Cell Format
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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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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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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.
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ATM Physical Layer 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
http://www.nwfusion.com/edge/news/2002/1002marconi.html
Note: Marconi bought Fore Switch in 2000.
Q; What is the max speed for Frame Relay? Up to 30Mbps
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ATM Switching 10
20
video
data
10
30
audio
data
11
21
12
30
P1
P2
P3
P5
P4
IN/port VPI/VCI OUT/port VPI/VCI
P1 0/10 P3 0/11
P1 0/20 P4 0/21
P2 0/10 P4 0/12
P2 0/30 P5 0/30
For PVC, table done Manually SVC, table is done dynamically/on-demand
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ATM Reference Model
AAL
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ATM Protocol Layers
ATM
Applications
ATM Adaptive
Layer (AAL)
ATM
Layer
Physical
Layer
ATM
Layer
Physical
Layer
ATM
Applications
ATM Adaptive
Layer (AAL)
ATM
Layer
Physical
Layer
ATM End Station ATM Switch ATM End Station
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ATM Adaptation Layer 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)
Physical
ATM
AAL
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AAL1
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?
Payload = 47
SAR Hdr
Convergence Sublayer Sends 47 bytes to SAR Which adds 1 byte of SAR hdr
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AAL5
CPCS-PDU Payload
Padding (0-47)
CPCS-UU (1)
CPI (1)
Length (2)
CRC (4)
up to 216 -1
why do we need padding?
CPCS: Common Part Convergence Sublayer PDU: Protocol Data Unit UU: User-to-user interface information CPI: Common Part Indicator
48 bytes (0..47) Cell payload To make the Full PDU Divisible by 48 Bytes And divide it Evenly into 48 byte segments
Carries upper other Protocols inside CPCS payload (i.e. tcp/ip, ethernet
8 byte trailer
CPCS Payload Not including PAD
Trailer alignment to 32 bit
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ATM Segmentation and Reassembly (SAR)
AAL5 Frame
Cell1 Cell2 H H Celln H H:5-bytes
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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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ATM Connection Establishment
Goal: setup VPI/VCI between any two ATM devices
A
B
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ATM UNI Signaling (Q.2931) - SVC
SETUP
ALERT
CONNECT
ATM End Device
ATM Switch
ATM Switch
ATM End Device
Why do we need this signaling protocol?
Connection Established, control, mgmt, Does it look familiar (Q.931)?
PROCEEDING PROCEEDING
SETUP
SETUP
ALERT
ALERT CONNECT
CONNECT
VPI/VCI Will be Setup For each Direction
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Signaling VCI (VPI=0)
(UNI)
Q; What is the VPI/VCI in the ATM Q.2931 SETUP message? VPI= 0 VCI = 5
e.g. VPI =0, VCI for connection establishment signaling
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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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PVC or SVC 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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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
VBR
UBR
PCR
SCR
Service
Bit Rate
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ATM QoS 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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IP over ATM Protocol (RFC 2684)
ATM
802.3: IEEE Media Access Control layer (also know as Ethernet)
802.3
PHY PHY
802.3 802.3
RFC 2684
ATM
PHY
IP
AAL5
802.3
PHY
IP
PHY
802.3 802.3
RFC 2684
ATM
PHY
AAL5
192.168.1.10/24 192.168.1.11/24
Both ATM and Ethernet Switching
Same Subnet Then we are Using switches
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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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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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ATM/FR Network Interworking (FRF.5)
p1r1 p1r3
ATM Core Network
FR (T1)
FR (T1)
OC-3
FRF.5 Convert FR
frames to ATM cells
FRF.5 Convert ATM cells to FR
frames
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ATM/FR Network Interworking (FRF.5)
p1r1 p1r3
PHY
FR
ULP
PHY
FR FR-SSCS
AAL5
ATM
PHY
FR-SSCS
AAL5
ATM
PHY
PHY
FR
PHY
FR
ULP
FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function
ATM/FR IWF ATM/FR IWF
ATM Core
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ATM/FR Network Interworking (FRF.8)
p1r1 p1r3
PHY
FR
RFC2427
PHY
FR FR-SSCS
AAL5
ATM
PHY
ATM
PHY PHY
ATM
IP
FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function
ATM ATM/FR IWF
IP
RFC2684
AAL5
(FRF .8)
FR ATM
ATM Core