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Chapter 9ATM Networks
Why ATM? BISDN Reference Model
ATM LayerATM Adaptation Layer
ATM SignalingPNNI Routing
Classical IP over ATM
Chapter 9ATM Networks
Why ATM?
The Integrated Services Vision Initially telephone network all-analog
Transmission & Switching Gradual transition to all-digital core
1960’s: transmission in backbone became digital 1970’s: switching became digital Subscriber loop from customer to network remained analog
Integrated Services Vision: Network should be digital end-to-end Network should support all services: telephone, data, video
Three attempts at achieving Integrated Services Network ISDN in 1980s ATM/BISDN in 1990’s Internet in 2000’s
Basic rate interface (BRI): 2B+D
BRI
PRI
BRI
PRI
Circuit-switched network
Private channel-switched network
Signalingnetwork
Packet-switched networks
Integrated Services Digital Network (ISDN)
Primary rate interface (PRI): 23B+D
ISDN: Integrated access to end-to-end digital communication services through a standard set of user-to-network interfaces
Network consisted of separate networks for voice, data, signaling
B=64 kbpsD=16 kbps
Broadband ISDN
BISDN: A single universal network that is flexible enough to provide all user services in a uniform manner ISDN not enough: Needed 10s to 100s Mbps for LAN
interconnect and for digital TV
Synchronous Transfer Mode (connections at nx64 kbps) was initial candidate for BISDN, but
Asynchronous Transfer Mode (ATM) chosen Multiplexing & switching framework connection-oriented virtual circuits fixed-length packets, “cells”, with short headers
Benefits of ATM Network infrastructure and management simplified
by using a single transfer mode for the network Expected to cover LAN, MAN, and WAN
Extensive bandwidth management capabilities SONET-like grooming capabilities, but at arbitrary
bandwidth granularities
ATM is not limited by speed or distance limitations 50-600 Mbps the sweet spot for ATM
QoS attributes of ATM allow it to carry voice, data, and video thus making it suitable for an integrated services network.
ATM Anticipated Scope All information transferred by network that handles 53-byte cells Scalable in terms of speed Switched approach operates in LAN, MAN, or WAN
ATM fibre backboneWide Area Network (WAN)
ATM fibre backboneWide Area Network (WAN)
supercomputersupercomputer
wirelessinterface
wirelessinterface
multimediaterminal
local areanetwork(LAN)
local areanetwork(LAN)
User informationNetwork header
5 bytes 48 bytes
videoserver
data base
ATMAdaptation
Layer
ATMAdaptation
Layer
ATM Network
Video PacketVoiceVideo PacketVoice
ATM Networking
AAL converts Info into Cells
A/D AAL
Voice
s1 , s2 …
Digital voice samples
cells
AALDataBursty variable-length
packets
cells
A/D AAL
Video
… Compression
compressed frames
picture frames
cells
Connection setup establishes virtual circuit by setting pointers in tables in path across network
All cells for a connection follow the same path Abbreviated header identifies connection Cells queue for transmission at ATM switches & multiplexers Fixed and Variable bit rates possible, negotiated during call set-up Delay and loss performance negotiated prior to connection setup
Cell-Switching – Virtual Circuit
Switches
Cells
Destination
Source
Cells
Cells
Cells
Switch carries out table translation and routing
ATM switches can be implemented using shared memory,shared backplanes, or self-routing multi-stage fabrics
ATM Switching
2
3
N
1
Switch
N
1
5
6
video
video
voice
data
25
32
3261
75
67
39
67
N
1
32
video 75
voice
data
video
……
…
32
25 32
61
39
67
67
1
2
N
1
2
N
Packet traffic multiplexed onto input lines
Demultiplexed at input port
Forwarded to output port
Multiplexing in ATM Switches
Call Admission Control based on Traffic Descriptors & QoS Reqts Cell streams policed at User Network Interface Cell Enqueueing Policy, Cell Transmission Scheduling, Flow
Control Generalized Processor Sharing, Weighted Fair Queueing, etc. Multiplexing Gain Cell Multiplexing implies Delay, Jitter, Loss
VCswith
different TDs&
differentQoS reqts
ATM Support for Multiple QoS Levels
Chapter 9ATM Networks
BISDN Reference Model
BISDN Reference Model
User Plane: transfer of user information; flow control; error recovery
Control Plane: setting up, management, and release of connections
Layer Management Plane: management of layer entities & OAM
Plane Management: management of all the planes
Physical Layer
ATM Layer
ATM Adaptation Layer
Higher Layers
User PlaneControl Plane
Management Planes
Layer M
anag
emen
tP
lane M
anag
emen
t
Planes Explained
Three types of logical networks are involved in delivering communication services User Network: transfers user information Control (Signaling) Network: carries signaling
messages to establish, maintain, terminate connections
Management Network: carries management information: monitoring information, alarms and usage statistics
A separate protocol stack, “plane”, is defined for each of these three networks
ATM Adaptation Layer (AAL)
ATM Network Layer
Physical Layer
Higher Layers
ATM Adaptation Layer (AAL)
ATM Network Layer
Physical Layer
Higher Layers
ATM Network Layer
Physical Layer
USER NETWORK USER
ATM Layered Architecture
ATM Layered ArchitectureATM Adaptation Layer
standard interface to higher layers adaptation functions end-to-end between end systems segmentation into cells and reassembly
ATM Layer Transfer of Cells Cell-Header Generation/Extraction VPI/VCI Translation Cell multiplexing/demultiplexing Flow and congestion control
Physical Layer Cell stream / bit stream conversion Digital transmission
ATM Adaptation Layer (AAL)
ATM Network Layer
Physical Layer
Higher Layers
ATM Interfaces
X
X
X
X
X
X
X
X
X
Private UNI
Public UNI
NNI
Private NNI
Private ATM
network
Public UNI B-ICI
Public UNIPublic ATM network A
Public ATM network B
UNI: User-Network InterfaceNNI: Network-Network InterfaceB-ICI: Broadband Inter-carrier i/f
The ATM Physical Layer
TC Sublayer: Cell Delineation Header Error Checking Cell Rate Decoupling
(Insertion of Idle Cells) Specific to PMD
PMD Sublayer: Line code Connectors Re-use of existing physical
layer standards
Transmission
convergence sublayer
Physical medium dependent sublayer
Private UNI Physical Layers
UTP = Unshielded twisted pair STP = Shielded twisted pair MMF = Multimode fiber SMF = Single-mode pair
Frame format Bit rate Media
Cell stream 25.6 Mbps UTP-3
STS-1 51.84 Mbps UTP-3
FDDI 100 Mbps MMF
STS-3c, STM-1 155.52 Mbps UTP-3, UTP-5, STP, SMF, MMF coaxial pair
Cell stream 155.52 Mbps MMF, STP
STS-12, STM-4 622.08 Mbps SMF, MMF
Public UNI Physical Layers
Frame format Bit rate Media
DS-1 1.655 Mbps Twisted pair
DS-3 44.736 Mbps Coaxial
STS-3c, STM-1 155.52 Mbps SMF
E-1 2.048 Mbps Twisted pair
Coaxial
E3 34.368 Mbps Coaxial
J2 6.312 Mbps Coaxial
Chapter 9ATM Networks
ATM Layer
The ATM Layer
Concerned with sequenced transfer of cells across network connections
ATM Connections Point-to-Point: unidirectional or bidirectional Point-to-Multipoint: unidirectional Permanent Virtual Connections (PVC): long-term
connections to provision bandwidth between endpoints in an ATM network
Switched Virtual Connections (SVC): shorter-term connections established in response to customer requests
Virtual Channel Connections: virtual circuit Virtual Path Connections: bundle of virtual connections ATM Header contains virtual connection information:
8-bit Virtual Path Identifier 16-bit Virtual Channel Identifier
ATM Virtual Connections
Virtual paths
Virtual channels
Why 53 Bytes?
The effect of delay on packet voice influenced selection of cell size
The packetization delay grows with the cell size @64kbps: packetization delay = cell size * 125 sec
If delay is too long, echo cancellation equipment needs to be introduced
Europe has short transmission lines and no echo cancellers so it proposed 32 byte payload
U.S. has long transmission lines and echo cancellers in place, so it proposed 64 byte payload
Compromise: 48 byte payload
The ATM Cell
GFC-undefinedUNI cells has GFC fieldNNI cells allocate these 4 bits to VPI; 4096 VPs
GFC (4 bits) VPI (4 bits)
VPI (4 bits) VCI (4 bits)
VCI (8 bits)
VCI (4 bits) PT (3 bits)CLP
(1 bit)
HEC (8 bits)AT
M c
ell h
eade
r
Payload (48 bytes)
Virtual Path Identifier 8-bits: 256 VC bundles
Virtual Channel Identifier 16 bits: 65,536 VCs/VP
Payload Type Indicator Bit 3: data vs. OAM cell Bit 2: Congestion indication in
data cells Bit 1: Carried transparently end-
to-end; Used in AAL5
Cell Loss Priority if 1, cell can be discarded by
network
Header Error Check
The HEC only covers the 5 bytes of the header to protect against cell misdelivery
Since VPI/VCI changes at every switch, HEC must be recomputed
HEC used for cell delineation Two modes: Header Error Detection / Correction Generating Polynomial: g(x)=x8+ x2+ x+ 1 The pattern 01010101 is XORed to r(x); keeps idle cells
from having HEC=0 and preventing cell delineation The pattern 01010101 is XORed to r(x) in received
header prior to error checking
ATM Permanent Virtual Connections
Operator “manually” sets up VPI/VCI tables at switches and terminals
Long set-up time, long-lived connections
ATMSwitch
ATMSwitch
Operator atNetwork Control Center
ATM Switched Virtual Connections
Terminals and switches use pre-defined VPI/VCI to setup connections dynamically, on-demand
Signalling protocol used to communicate with call-processing system
ATMSwitch
ATMSwitch
Traffic Contract
During connection setup the user and the network negotiate two sets of parameters for a connection
Traffic descriptor: the user specifies the traffic that it will expect the network to transfer on its behalf
QoS requirements: the user specifies the type of network performance that is required by its cells
Traffic Contract The user is expected to conform to traffic descriptor The network is expected to deliver on its QoS
commitments
Quality of Service Parameters
Six QoS parameters are defined Three are intrinsic to network performance and are
not negotiated during connection setup: Cell error ratio: fraction of delivered cells that
contain bit errors Cell mis-insertion ratio: average number of
cells/second that are misdelivered Severely errored cell block ratio: M or more out of N
cells are lost, in error, or misdelivered
Negotiable QoS Parameters
D0 Peak-to-Peak CDVDmax
prob
abili
ty d
ensi
ty o
f ce
ll de
lay
Cell Loss Ratio (CLR): fraction of cells that are lost Determined by buffer priority
Cell Transfer Delay (CTD): negotiate “maximum delay” Dmax: 1- of cells have delay less than Dmax Determined by cell scheduling
Cell Delay Variation (CDV): Peak-to-Peak variation: Dmax-D0
Traffic Descriptors Peak Cell Rate: rate in cells/second that a source
is never allowed to exceed Sustainable Cell Rate: average cell rate produced
by the source over a long time interval Maximum Burst Size: maximum number of
consecutive cells that may be transmitted by a source at the peak cell rate (PCR)
Minimum Cell Rate: minimum average cell rate, in cells per second, that the source is always allowed to send
Cell Delay Variation Tolerance: cell delay variation that must be tolerated for in a given connection.
CBRVBR
real-timeVBR
non-real-timeABR UBR
Cell LossRate
Cell TransferDelay
Cell DelayVariation
TrafficDescriptors
Flow Control
specified
specified
specified
unspecified
unspecified
unspecified
PCR/CDVTPCR/CDVT
SCR/BTPCR/CDVT
& othersPCR/CDVT
no yes no
CBR = Constant Bit RateVBR = Variable Bit RateABR = Available Bit RateUBR = Unspecified Bit Rate
PCR = Peak Cell RateCDVT = Cell Delay Variation Tolerance SCR = Sustainable Cell Rate BT = Burst Tolerance
Cell transfer services provided by ATM Network
ATM Service Categories
Multiplexing & QoS Guarantees
ATM provides per-connection QoS guarantees Many cell flows are multiplexed onto a common stream, so
how are guarantees delivered? CBR: scheduler must ensure transmission opportunities are
regularly available for each connection Real-time VBR: expect some multiplexing gain from
combining VBR flows; however need to meet delay and loss requirements
Non-real-time VBR: can attempt higher multiplexing gains, subject only to loss requirement
UBR: no guarantees, but excellent performance at light traffic ABR: some degree of guarantee: low CLR if source
responds to network feedback; MCR can be negotiated
Traffic Contract & Call Admission Control
Traffic contract: includes the ATM service category, the traffic descriptors, and the QoS requirements
Connection admission control (CAC) determines whether request for a connection should be accepted or rejected Each switch in path must determine whether it can accommodate
new flow and still meet commitments to existing flows; if yes, resources allocated
CAC is not standardized, each operator is free to select own procedures Different degrees of overbooking possible to attain different
multiplexing gains Different types of tariffs for service offerings
Policing, Traffic Shaping, and Congestion Control
QoS guarantees are valid only if the user traffic conforms to the connection contract
Usage parameter control (UPC) is the process of enforcing the traffic agreement at the UNI Generic Cell Rate Algorithm can be used for UPC; related to the leaky-
bucket algorithm Non-conforming cells can be tagged (CLP=1) or dropped
Traffic shaping can be used by source to ensure that its traffic complies to the connection contract Token bucket can be used for shaping
Congestion control CLP=1 cells are dropped first when congestion occurs ABR connections must respond to congestion feedback information that
is received from the network These topics were discussed in Chapter 7
Chapter 9ATM Networks
ATM Adaptation Layer
ATM Adaptation Layer AAL: end-to-end protocol to adapt the cell transfer service provided by ATM network to the
requirements of specific application classes Includes conversion to cells and back, and additional adaptation functions, e.g. timing recovery,
reliable transfer ITU defined the following service classes
Class
End-to-End Timing
Bit Rate
ConnectionMode
A B C D
required not required
constant variable
connection-oriented connectionless
Class A = circuit emulationClass B = variable bit-rate videoClass C & D = packet transmission
AAL Protocol Structure
AAL has two sublayers: Segmentation &
Reassembly Segments PDUs into cell
payloads; Reassembles PDUs from received cell payloads
Convergence Common Part: packet framing
and error detection functions required by all AAL users
Specific Part: functions that depend on specific requirements of AAL user classes
ATM
Higher Layers
Segmentation and
Reassembly Sublayer
AAL Layer
Convergence Sublayer
Common Part
Service Specific Convergence
Sublayer
AAL1
Higher layer User data stream
Convergence sublayer
SAR sublayer
ATM layer
CS PDUs
SAR PDUs
ATM Cells
…
47 47 47
1 47 1 47 1 47
H H H
5 48
H
5 48
H
5 48
H
b1 b2 b3
Provides constant bit rate transfer
AAL1
Convergence Sublayer: Adaptation to cell-delay variation, constant bit rate delivery AAL-
SDUs Detection of lost or out-of-sequence cells Source clock recovery Forward error correction on user data Forward error correction on Sequence Number (SN)
1-bit CS to indicate pointer (used for partially-filled cells) 3-bit sequence count
Time-stamp option uses 4 consecutive CS bits for residual TS SAR: Add 1-byte header to 47-byte payload
SN SNP
4 bits 4 bitsPointeroptional
46 or 47 octets
Payload
8 bits
AAL1 services
Structured & Unstructured Transfer Unstructured: take bits from T1 and group into
8-bit bytes; since T1 frame has 193 bits, bytes are never aligned to frame
Structured: take 24 T1 bytes and map into CS PDUs; use CS PDU pointer to indicate beginning of T1 frame
Forward error control options:1. Insert parity cell every 15 cells, correct lost cell2. Interleaving of 124 cells, correct up to 4 cell
losses
SAR PDU header
CS PDU with pointer in structured data transfer
AAL 1 Pointer
1 Byte
CSI SNPSeq. Count
1 bit 3 bit 4 bits
SN SNP
4 bits 4 bitsPointeroptional
46 or 47 octets
Payload
8 bits
AAL1 PDUs
46 Bytes
AAL2
New AAL2 intended for bandwidth-efficient transfer of low-bit rate, short-packet traffic with low-delay requirement
Adds third level of multiplexing to the VP/VC hierarchy of ATM, so low-bit-rate users can share an ATM connection.
AAL 2 ATM cells
Low bit rate Short voice packets
Mobile switching
office
AAL2Higher layer
This example assumes 24 byte packets
Common part convergence
sublayer
SAR sublayer
ATM layer
1 47
5 48
H
P3
Service specific convergence
sublayer
P2P1
Assume null
1 47
3 243 243 24
PAD
5 48
H
Add 3-byte header to each user packet
Segment into SAR PDUs
H H H
CPS packet header
LI (6 bits)PPT
(2 bits)
CID (8 bits)
UUI (3 bits) HEC (5 bits)
Payload
AAL2 Common Part CS PDU
Max length CPCS PDU 64 bytes
Channel ID Identifies user
Length Indicator Payload length – 1
Packet payload type 3: OAM cell ≠3: application cell
User-to-user indication End-to-end info for
application cells End-to-end for AAL mgmt
when OAM cell Error detection
g(x)=x5+x2+1
Start field (STF)
CPS-PDU payload
OSF (6 bits)SN (1 bit)
Cell Header
PAD
P (1 bit)
Packing ATM SDU in AAL2 CPCS PDU’s concatenated, segmented into 48 byte chunks,
and packed into ATM SDU’s ATM SDU format: Offset Field (6 bits)
From end of the field to start of first CPCS PDU or to start of PAD
Max CPCS PDU may span 2 SDUs
Sequence Number 0 or 1
Parity bit PAD
0-47 bytes
AAL3/4 Why 3 / 4 ?
AAL3: For connection-oriented transfer of data AAL4: For connectionless transfer of data
All connectionless packets use the same VPI/VCI at the UNI Multiplexing ID (MID) introduced to distinguish connectionless packets
AAL3 and AAL4 combined into AAL that can be used for connection-oriented or connectionless transfer
AAL3/4 allows multiple users to be multiplexed and interleaved in the same ATM VC Message mode: single user message segmented into ATM
payloads Stream mode: one or more messages segmented into ATM
payloads and delivered without indication of boundaries Assured mode: error-free delivery of messages Non-Assured mode: messages may be delivered in error, or not at
all
Higher layer
Common part convergence
sublayer
SAR sublayer
ATM layer
Service specific convergence
sublayer
Information
Assume null
TPAD
User message
Pad message to multiple of 4 bytes. Add header and trailer.
Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload.
H
4 4
2 44 2 2 44 2 2 44 2
…
…
Information
AAL 3/4
CPI Btag BASize CPCS - PDU Payload
1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes)
AL Etag LengthPad
Header Trailer
AAL3/4 Common Part CS PDU
Common Part Indicator How subsequent fields are to
be interpreted Beginning Tag & Ending Tag
Used to match header & trailer at destination
Buffer Allocation size: Buffer size required at destination
Length: of payload PAD: aligns trailer to 32-bit boundary Alignment: byte of 0s to make trailer 32
bits long
User Data
ST SN MID SAR - PDU Payload
2 4 10 44 6 10 (bits)
(bytes) (bits)
LI CRC
Header (2 bytes)
Trailer (2 bytes)
AAL3/4 SAR PDU
Segment Type 10 Beginning of Message 00 Continuation 01 End of Message 11 Single segment Message
Sequence Number Of SAR PDU within CPCS PDU
MID allows SAR sublayer multiplexing Up to 210 AAL users on 1 ATM VC
Length Indicator: size of payload Except for last cell, all cells have LI=44 Last cell has LI = 4 to 44
Each cell payload has 10-bit CRC
Multiplexing in AAL3/4Higher layer Assume two packets
from different users
Common part convergence and SAR sublayers
ATM layer
Service specific convergence
sublayer
P2P1
Each packet is segmented separately. SAR PDUs identified by MID.
Cells from two packets are interleaved.
Interleaved cells
MID = bMID = a
CPCS SAR
CPCS SAR
Interleaver
SPDUA2
SPDUA1
SPDUB2
SPDUB1
AAL3/4 Overhead
8 bytes added to each message at CPCS sublayer
Each ATM payload has 4 out of 48 bytes additional overhead
9 bytes out of 53 ATM cell bytes overhead Too much overhead! Let to development of AAL5
Higher layer
Common part convergence
sublayer
SAR sublayer
ATM layerPTI = 0
Service specific convergence
sublayer
48 (1)
Information
TPAD
…
…
Information
48 (0)
48 (0)
PTI = 0 PTI = 1
AAL5
Simpler than AAL3/4
48 bytes payload Single packet at
a time per VCI PTI in ATM
header indicates last cell for a given packet
Information
0 - 65,535 0-47 1 1 2 4 (bytes) (bytes)
UU CPI Length CRCPad
AAL5 Common Part CS PDU
User-to-User: 1 byte CPI aligns trailer to 8 bytes Length: 2 bytes to indicate length of CPCS PDU
payload 40-byte CRC
Signaling AAL
AAL standard for BISDN control plane Provides reliable transport for signaling messages
exchanged among endsystems and switches to set up ATM VCs.
SAAL: common part & a service-specific part Service specific part:
service-specific connection-oriented protocol (SSCOP) Service-Specific Coordination Function (SSCF).
SSCF supports the signaling applications (UNI and NNI).
SAAL ProcessSignaling application
SSCF
CSCP and SAR of AAL 5
ATM layer
SSCS
SSCF maps SSCOP service to service required by SSCF user
Message
SSCOP identifies gaps in SDU sequence and requests retransmissions (Selective Repeat ARQ)
AAL 5 provides non-assured service
…
As per AAL 5
SSCOP
Message
Message T
Information
0 - 65,535 0-3 2 2 4 24 (bytes) (bytes)(bits)(bits) (bits) (bits)
PL RSVD PDU SN Type
Pad
SSCOP PDU
Padding: 0-3 bytes Pad Length Indicator Reserved (unassigned) PDU type
Sequenced data message; poll and control messages 24-bit sequence number for large delay-bandwidth product Depends on error detection provided by AAL5
Applications, AALs, and ATM Service Categories
Applications impose requirements Voice, video, connectionless data
AALs provide segmentation & reassembly, and possibly additional adaptation functions AAL1, AAL2, AAL3/4, AAL5, SAAL
ATM service category provides cell transfer with certain QoS attributes CBR, rt-VBR, nrt-VBR, UBR, ABR
Overall system requirements determine what combination of AAL and ATM service category is used
Application Requirements
Feature
transfer granularity
stream message
bit rate constant variable
reliability non-assured assured
accuracy error tolerant error intolerant
delay sensitivity delay/jitter sensitive delay/jitter insensitive
multiplexing single user multiple users
payload efficiency
bandwidth inexpensive
bandwidth expensive
Summary of AAL CapabilitiesSublayer Feature AAL1 AAL2 AAL3/4 AAL5 SAAL
SSCS Forward Error Control optional optional optional optional no
ARQ no no optional optional SSCOP
Timing Recovery optional optional no optional no
CPCS Multiplexing no 8-bit CID 10-bit MID no no
Framing Structure yes no no no no
Message Delimiting no yes yes PTI PTI
Advance Buffer Alloc no no yes no no
User-to-User Indication no 3 bits no 1 byte no
Overhead 0 3 bytes 8 bytes 8 bytes 4 bytes
Padding 0 0 4 bytes 0-44 byte 0-47 byte
Checksum no no no 32 bit 32 bit
Sequence Numbers no no no no 24-bit
SAR Payload/Overhead 46-47 byte 47 bytes 44 bytes 48 bytes 48 bytes
Overhead 1-2 bytes 1 byte 4 bytes 0 bytes 0
Checksum no no 10 bits no no
Timing Information optional no no no no
Sequence Numbers 3-bit 1 bit 4 bit no no
Examples: Voice and Video
Voice AAL1 for individual PCM
voice calls AAL1 with structured
transfer for nx64 kbps AAL2 for low-bit-rate
cellular voice AAL5 for inexpensive
voice
CBR MPEG2 Video Timing recovery at AAL
or at MPEG systems layer?
Error detection & correction at which layer?
Timing recovery at MPEG2 systems level and AAL5 over CBR ATM was selected
Example: ATM & ADSL
IP over PPPoE frames segmented by AAL5 into ATM cells at ADSL modem
ATM cells flow through DSLAM and ATM network to Internet Service Provider
ISP
AD
SL
AT
M
DSL Access Mux
User PremiseCentral Office
TelephoneSwitch Telephone
Network
ATMNetwork
IPPPPoEAAL5ATMADSL
splitter
splitterSubscriber
loop
Chapter 9ATM Networks
ATM Signaling
ATM Signaling
Signaling: means for dynamically setting up and releasing virtual connections in ATM
Signaling involves message exchange across: User-Network-Interface Network-Network Interface Broadband Inter-Carrier Interface
Signaling requires: Network addressing framework Protocols
ATM Addressing
Telephony E-164 Addresses For public networks Up to 15-digit E-164 (telephone) numbers In North America, 1-NPA-NXX-ABCD,
ATM End-System Addresses (AESAs) For private networks ISO Network Service Access Point (NSAP) format 20 bytes long Data Country Code (DCC) International Code Designator (ICD) E.164 (contained within the AESA format)
(c) E.164 ATM format
1 3 13 19 20
AFI DCC HO-DSP ESI SEL
IDI
(a) Data Country Code ATM format
Domain Specific Part IDP
1 3 13 19 20
AFI ICD HO-DSP ESI SEL
IDI
(b) International Code Designator ATM format
IDP DSP
1 9 13 19 20
AFI E.164 HO-DSP ESI SEL
Initial Domain Identifier
Initial Domain Part DSP
AESA Address Format
ATM Signaling
Telephone Signaling ISDN signaling (Q.931) used in call setup messages at the
user-network-interface Within the network, ISUP protocol of Signaling System #7
used to establish a connection from a source switch to a destination switch
For ATM, need UNI, NNI, & B-ICI signalling UNI: Q.2931 & ATMF UNI 4.0 NNI: ATMF PNNI based on UNI 4.0 B-ICI based on B-ISUP
UNI 4.0
ATM connections involve many more parameters than narrowband ISDN
Signaling messages carry Information Elements, that describe the user requests
Signaling messages transferred across the UNI using the services of the SAAL layer in the control plane
The signaling cells that are produced by AAL5 use the default virtual channel identified by VPI=0 and VCI=5.
Capability TerminalEquipment
SwitchingSystem
1 Point-to-Point calls M M
2 Point-to-multipoint calls O M
3 Signaling of individual QoS parameters O M
4 Leaf initiated join M M
5 ATM Anycast O O
6 ABR signaling for point-to-point calls O Note 1
7 Generic Identifier transport O O
8 Virtual UNIs O O
9 Switched virtual path (VP) service O O
10 Proxy signaling O O
11 Frame discard O O (Note 2)
12 Traffic parameter negotiation O O
13 Supplementary services - -
13.1 Direct dialing in (DDI) O O
13.2 Multiple subscriber number (MSN) O O
13.3 Calling line identification presentation (CLIP) O O
13.4 Calling line identification restriction (CLIR) O O
13.5 Connected identification presentation (COLP) O O
13.6 Connected line identification restriction (COLR) O O
13.7 Subaddressing (SUB) O Note 3
13.8 User-user siglnaling (UUS) O O
Notes
1 This capability is optional for public networks/switching systems and is mandatory for privatenetworks/switching systems
2 Transport of the Frame Discard indication is Mandatory.
3This capability is mandatory for networks/switching systems (public and private) that supportonly native E.164 address formats.
Capabilities of UNI 4.0
Signaling Messages
Meaning (when sent by host)
Meaning (when sent by network)
SETUP Requests that a call be established
Indicates an incoming call
CALL PROCEEDING
Acknowledges the incoming call
Indicates the call request will be attempted
CONNECT Indicates acceptance of the call
Indicates the call was accepted
CONNECT ACK Acknowledges acceptance of the call
Acknowledges making the call
RELEASE Requests that the call be terminated
Terminates the call
RELEASE ACK Acknowledges releasing the call
Acknowledges releasing the call
Source Destination
SETUP
SETUP
CONNECT
CONNECT
CONNECT ACK
CONNECT ACK
CALL PROCEEDING
CALL PROCEEDING
Network
UNI UNI
RELEASE
RELEASERELEASE COMPLETE
RELEASE COMPLETE
UNI Signaling Example
PNNI Signaling
ATM Forum developed PNNI for use between private ATM switches (Private Network Node
Interface) between group of private ATM switches (Private
Network-to-Network Interface)
PNNI
Network A Network B
PNNI
PNNI Protocols
A routing protocol that provides for the selection of routes that can meet QoS requirements
A signaling protocol for the exchange of messages between switches and between private networks. Based on UNI 4.0 with extensions for:
source routing crankback (a feature of the routing protocol) alternate routing of connection requests in the case of
connection setup failure. Also includes modifications in the Information
Elements to carry routing information.
Source Switch
Transit Switch
Destination Switch
Source A Destination B
SETUPSETUP
SETUPSETUP
CONNECTCONNECT
CONNECT
CONNECT
CONNECT ACKCONNECT ACK
CONNECT ACKCONNECT ACK
CALL PROCEEDINGCALL PROCEEDING
CALL PROCEEDINGCALL PROCEEDING
RELEASE
RELEASE
RELEASE
RELEASE
RELEASE COMPLETE
RELEASE COMPLETE
RELEASE COMPLETE
RELEASE COMPLETE
PNNI Signaling Example
Chapter 9ATM Networks
PNNI Routing
PNNI Routing Protocol
A routing protocol for the selection of routes that can meet QoS requirements
For intra-domain and inter-domain routing Link-state approach: each node has network
topology Introduces hierarchy in the ATM network that
provides a switch: Detailed routing information in its immediate vicinity Summary information about distant destinations
PNNI Terminology
Peer Group: collection of nodes that maintain an identical view of the group
Logical Group Node: abstract representation of a peer group at a higher level in the routing hierarchy
Peer Group Leader: node in peer group that executes functions of LGN for the PG Summarizes topology info within the PG Injects summary info into higher order groups and
into the PG
A B
PG(A)
PG(B)
A.1A.2
PG(A.1) PG(A.2)
A.1.1
A.1.2
A.1.3A.2.1
A.2.2
A.2.3 A.2.4
B.1
B.2
B.3
B.4
Peer Group Leader
Logical Link
Physical Link
Logical Group Node
PNNI Routing Hierarchy PGL passes topology summary upward in hierarchy and
downwards to its PG Multiple levels of hierarchy allowed
PNNI Source Routing PNNI source node specifies entire path across its PG using designated
transit list (DTL) Rest of path specified using higher levels in the hierarchy Example: station in A.1.1 requests path to B.3 Path: (A.1.1, A.1.2, A.2, B)
A B
PG(A)
PG(B)
A.1A.2
PG(A.1) PG(A.2)
A.1.1
A.1.2
A.1.3A.2.1
A.2.2
A.2.3 A.2.4
B.1
B.2
B.3
B.4
Peer Group Leader
Logical Link
Logical Group Node
DTL Stacks & Pointers DTLs organized in a stack according to level A pointer indicates current level
From node B.1DTL: [B.1, B.3] pointer-2DTL: [A, B] pointer-1
A B
PG(A)
PG(B)
A.1A.2
PG(A.1) PG(A.2)
A.1.1
A.1.2
A.1.3A.2.1
A.2.2
A.2.3 A.2.4
B.1
B.2
B.3
B.4
From node A.1.1DTL:[A.1.1, A.1.2] pointer-2DTL: [A.1, A.2] pointer-1DTL: [A, B] pointer-1
From node A.1.2DTL: [A.1, A.2] pointer-2DTL: [A, B] pointer-1
From node A.2.1DTL: [A.2.1, A.2.3, A.2.4] pointer-2DTL: [A.1, A.2] pointer-2DTL: [A, B] pointer-1 From node A.2.4
DTL: [A, B] pointer-1
From B.3null
PNNI Features
Call setup involves connection admission control at each node PNNI uses Generic Connection Admission Control
(GCAC) to select path Call request can be blocked from lack of resources
PNNI provides for crankback & alternate routing Upon blocking, call setup is “cranked back” to creator
of DTL, which considers alternate routes from that point onwards
Chapter 9ATM Networks
Classical IP over ATM
Classical IP over ATM
Classical IP over ATM (RFC 2255) IP treats ATM as subnetwork
Logical IP subnetwork (LIS) is part of ATM network that belongs to same IP subnetwork All members of a LIS use same IP address prefix (network
# & subnetwork #) Members in same LIS communicate using ATM VC Each LIS in an ATM network operates independently of
other LIS’s in the same ATM network LIS’s communicate via routers
LIS1LIS2
LIS3 LIS4 LIS5LIS6
ATM network
RouterRouter Router
Router
Router
Logical IP Subnetworks (LIS’s)
Address Resolution Suppose host S want to send packet to host D in
same LIS Host S sends message to ATM ARP server in the LIS,
requesting ATM address corresponding to IP address of host D
(All hosts in LIS know ATM address of ATM ARP server) ATM ARP replies with ATM address, and Host S sets up
ATM connection to Host D If host D is in another LIS, host S sets up ATM
connection to the router in its LIS Router determines next hop router & sets up VC to it Packets between hosts in different LIS’s always use
intermediate routers, even if hosts are in the same ATM network