Chapter 9
ATM Networks
Why ATM?
BISDN Reference Model
ATM Layer
ATM Adaptation Layer
ATM Signaling
PNNI Routing
Classical IP over ATM
Chapter 9
ATM 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
Integrated Services Digital
Network (ISDN)


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
Circuitswitched
network
BRI
PRI
Private channelswitched network
Packetswitched
networks
B=64 kbps
D=16 kbps
Basic rate interface
(BRI): 2B+D
BRI
PRI
Primary rate interface
Signaling
network
(PRI): 23B+D
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


Extensive bandwidth management capabilities


SONET-like grooming capabilities, but at arbitrary
bandwidth granularities
ATM is not limited by speed or distance limitations


Expected to cover LAN, MAN, and WAN
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
5 bytes
Network header
local area
network
(LAN)
wireless
interface
48 bytes
User information

multimedia
terminal
data
base
ATM fibre backbone
Wide Area Network (WAN)
video
server
wireless
interface
supercomputer
ATM Networking
Voice Video Packet
Voice Video Packet
ATM
Adaptation
Layer
ATM
Adaptation
Layer
ATM Network
AAL converts Info into Cells
Voice
AAL
A/D
s1 , s2 …
cells
Digital voice samples
Video
A/D
Compression
…
picture
frames
Data
AAL
cells
compressed
frames
AAL
Bursty variable-length
packets
cells
Cell-Switching – Virtual Circuit
Cells
Cells
Cells
Source
Cells
Switches






Destination
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
ATM Switching
Switch carries out table translation and routing
1
…
Switch
5 video 25
…
6 data 32
N
voice 32
video 61
25
32
N
1
75
32
61
3
2
39
67
67
voice 67
video 67
2
data 39
3
…
1
video 75
ATM switches can be implemented using shared memory,
shared backplanes, or self-routing multi-stage fabrics
N
Multiplexing in ATM Switches



Packet traffic
multiplexed onto
input lines
Demultiplexed at
input port
Forwarded to
output port
1
1
2
2
N
N
ATM Support for Multiple QoS
Levels
VCs
with
different TDs
&
different
QoS reqts






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
Chapter 9
ATM Networks
BISDN Reference Model
BISDN Reference Model
Management Planes
Higher Layers
ATM Adaptation Layer
ATM Layer
Physical Layer
Plane Management
Layer Management
Control Plane User Plane
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
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 Layered Architecture
Higher Layers
Higher Layers
ATM Adaptation Layer
(AAL)
ATM Adaptation Layer
(AAL)
ATM Network Layer
ATM Network Layer
ATM Network Layer
Physical Layer
Physical Layer
Physical Layer
USER
NETWORK
USER
ATM Layered Architecture
Higher Layers
ATM Adaptation Layer
(AAL)
ATM Network Layer
Physical Layer
ATM 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 Interfaces
X
Public ATM
network A
X
X
X
NNI
X
B-ICI
X
Public
UNI
Public ATM
network B
X
X
Private
NNI
UNI: User-Network Interface
NNI: Network-Network Interface
B-ICI: Broadband Inter-carrier i/f
X
Private
UNI
Private
ATM
network
Public
UNI
The ATM Physical Layer
TC Sublayer:

Transmission
convergence
sublayer
Physical medium
dependent
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
Private UNI Physical Layers
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
UTP = Unshielded twisted pair
MMF = Multimode fiber
STP = Shielded twisted pair
SMF = Single-mode pair
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 9
ATM 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): shorterterm connections established in response to
customer requests
ATM Virtual Connections



Virtual Channel Connections: virtual circuit
Virtual Path Connections: bundle of virtual connections
ATM Header contains virtual connection information:

8-bit Virtual Path Identifier
Virtual paths

16-bit Virtual Channel Identifier
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
ATM cell header
The ATM Cell
GFC (4 bits)
VPI (4 bits)
VPI (4 bits)
VCI (4 bits)
Virtual Path Identifier

VCI (8 bits)
VCI (4 bits)
PT (3 bits)
CLP
(1 bit)
8-bits: 256 VC bundles
Virtual Channel Identifier

HEC (8 bits)
16 bits: 65,536 VCs/VP
Payload Type Indicator


Payload
(48 bytes)

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

GFC-undefined
UNI cells has GFC field
NNI cells allocate these 4 bits to VPI; 4096 VPs
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 at
Network Control Center
ATM
Switch


ATM
Switch
Operator “manually” sets up VPI/VCI tables at
switches and terminals
Long set-up time, long-lived connections
ATM Switched Virtual Connections
ATM
Switch


ATM
Switch
Terminals and switches use pre-defined VPI/VCI to
setup connections dynamically, on-demand
Signalling protocol used to communicate with callprocessing system
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

Cell Loss Ratio (CLR): fraction of cells that are lost


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
probability density of cell delay

Determined by buffer priority

D0
Peak-to-Peak CDV
Dmax
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.
ATM Service Categories
Cell transfer services provided by ATM Network
CBR
VBR
VBR
real-time
non-real-time
Cell Loss
Rate
Cell Transfer
Delay
Cell Delay
Variation
Traffic
Descriptors
specified
specified
PCR/CDVT
SCR/BT
PCR/CDVT
Constant Bit Rate
Variable Bit Rate
Available Bit Rate
Unspecified Bit Rate
UBR
unspecified
unspecified
unspecified
specified
Flow Control
CBR =
VBR =
ABR =
UBR =
ABR
no
PCR =
CDVT =
SCR =
BT =
PCR/CDVT
& others
yes
PCR/CDVT
no
Peak Cell Rate
Cell Delay Variation Tolerance
Sustainable Cell Rate
Burst Tolerance
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



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



Generic Cell Rate Algorithm can be used for UPC; related to the leakybucket algorithm
Non-conforming cells can be tagged (CLP=1) or dropped
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 9
ATM 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
Connection
Mode
B
A
required
constant
D
C
not required
variable
connection-oriented
Class A = circuit emulation
Class B = variable bit-rate video
Class C & D = packet transmission
connectionless
AAL Protocol Structure
Higher Layers
Service Specific
Convergence
Sublayer
AAL
Layer
Convergence
Sublayer
Common Part
Segmentation
and
Reassembly
Sublayer
ATM
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
AAL1

Provides constant bit rate transfer
Higher layer
b1
b2
b3
Convergence
sublayer
CS PDUs
47
47
47
SAR PDUs
SAR sublayer
1
47
47
H
H
5
H
H
H
1
ATM layer
…
User data stream
48
5
1
47
ATM Cells
H
48
5
48
AAL1


4 bits
4 bits
SN
SNP
8 bits
Pointer
optional
46 or 47 octets
Payload
Convergence Sublayer:
 Adaptation to cell-delay variation, constant bit rate delivery AALSDUs
 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
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.
2.
Insert parity cell every 15 cells, correct lost cell
Interleaving of 124 cells, correct up to 4 cell
losses
AAL1 PDUs
SAR PDU header
CSI
1 bit
SNP
Seq. Count
3 bit
4 bits
4 bits
SN
SNP
4 bits
46 or 47 octets
Pointer
optional
8 bits
AAL 1
Pointer
1 Byte
Payload
46 Bytes
CS PDU with pointer in structured data transfer
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
Low bit rate
Short voice packets
Mobile
switching
ATM cells
office
AAL2
Higher layer
P3
P2
P1
This example
assumes 24 byte
packets
Service specific
convergence
sublayer
Assume null
Common part
convergence
sublayer
H
3
H
24
3
H
24
3
SAR sublayer
24
PAD
1
ATM layer
Add 3-byte
header to each
user packet
H
5
1
47
47
H
48
5
48
Segment into SAR
PDUs
AAL2 Common Part CS PDU

Max length CPCS PDU


CID (8 bits)
CPS packet
header
PPT
(2 bits)
LI (6 bits)
UUI (3 bits)
Channel ID





3: OAM cell
≠3: application cell
User-to-user indication



Payload length – 1
Packet payload type

Payload
Identifies user
Length Indicator

HEC (5 bits)
64 bytes
End-to-end info for
application cells
End-to-end for AAL mgmt
when OAM cell
Error detection

g(x)=x5+x2+1
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)

Cell Header
Start field (STF)
OSF (6 bits)
SN
P
(1 bit)
(1 bit)


Sequence Number



CPS-PDU
payload
0 or 1
Parity bit
PAD

PAD
From end of the
field to start of
first CPCS PDU
or to start of PAD
Max CPCS PDU
may span 2 SDUs
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
AAL 3/4
Higher layer
Information
User message
Service specific
convergence
sublayer
Common part
convergence
sublayer
Assume null
H
2 44
T
4
4
…
SAR sublayer
ATM layer
PAD
Information
Pad message to
multiple of 4 bytes.
Add header and trailer.
2
2 44
2
2 44
…
2
Each SAR-PDU
consists of 2-byte
header, 2-byte trailer,
and 44-byte payload.
AAL3/4 Common Part CS PDU
User Data
Trailer
Header
CPI Btag BASize
1
1

2
(bytes)
1 - 65,535
(bytes)
Common Part Indicator


CPCS - PDU Payload
How subsequent fields are to
be interpreted
Beginning Tag & Ending Tag

Used to match header & trailer
at destination

0-3 1


1
2
(bytes)
Buffer Allocation size:


Pad AL Etag Length
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
AAL3/4 SAR PDU
Trailer
(2 bytes)
Header
(2 bytes)
ST SN MID
2 4
(bits)

44
(bytes)
Segment Type





10
10 Beginning of Message
00 Continuation
01 End of Message
11 Single segment Message
Sequence Number

LI CRC
SAR - PDU Payload
Of SAR PDU within CPCS PDU
6 10
(bits)

MID allows SAR sublayer multiplexing


Length Indicator: size of payload



Up to 210 AAL users on 1 ATM VC
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 AAL3/4
Higher layer
Service specific
convergence
sublayer
Common part
convergence and
SAR sublayers
P1
Assume two packets
from different users
P2
MID = b
MID = a
CPCS
SAR
CPCS
SAR


SPDUA2
SPDUB2
SPDUA1
SPDUB1
Each packet is
segmented separately.
SAR PDUs identified
by MID.
Interleaver
ATM layer
Interleaved cells
Cells from two
packets are
interleaved.
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
AAL5
Higher layer
Information

Service specific
convergence
sublayer


Common part
convergence
sublayer
PAD
Information
T

…
SAR sublayer
48
(0)
48
(0)
48
(1)
…
ATM layer
PTI = 0
PTI = 0
PTI = 1
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
AAL5 Common Part CS PDU
Information
0 - 65,535
(bytes)




Pad UU CPI Length CRC
0-47
1
1
(bytes)
2
4
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 Process
Signaling application
Message
Message
SSCF maps SSCOP
service to service required
by SSCF user
SSCF
SSCS
SSCOP
CSCP and SAR
of AAL 5
ATM layer
Message
T
As per AAL 5
…
SSCOP identifies gaps in
SDU sequence and
requests retransmissions
(Selective Repeat ARQ)
AAL 5 provides nonassured service
SSCOP PDU
Information
0 - 65,535
(bytes)





SN
Type
0-3 2
2
4
24
(bytes)(bits)(bits) (bits) (bits)
Padding: 0-3 bytes
Pad Length Indicator
Reserved (unassigned)
PDU type


Pad PL RSVD PDU
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


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


Voice, video, connectionless data
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 Capabilities
Sublayer
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
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
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
CPCS
SAR
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
Central Office
User Premise
splitter
ATM
Subscriber
loop
ADSL
IP
PPPoE
AAL5
ATM
ADSL
Telephone
Switch
splitter
Telephone
Network
ATM
Network
DSL Access Mux


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
Chapter 9
ATM 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)
AESA Address Format
(a) Data Country Code ATM format
1
3
13
AFI DCC
19
HO-DSP
ESI
IDP
20
SEL
Domain Specific Part
IDI
(b) International Code Designator ATM format
1
AFI
3
13
ICD
19
HO-DSP
ESI
IDP
20
SEL
DSP
IDI
(c) E.164 ATM format
1
AFI
9
E.164
Initial Domain Part
Initial Domain Identifier
13
19
HO-DSP
ESI
DSP
20
SEL
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.
Capabilities of UNI 4.0
Capability
Terminal
Equipment
Switching
System
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
1
2
3
Notes
This capability is optional for public networks/switching systems and is mandatory for private
networks/switching systems
Transport of the Frame Discard indication is Mandatory.
This capability is mandatory for networks/switching systems (public and private) that support
only native E.164 address formats.
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
UNI Signaling Example
UNI
UNI
Destination
Network
Source
SETUP
CALL PROCEEDING
SETUP
CALL PROCEEDING
CONNECT
CONNECT
CONNECT ACK
CONNECT ACK
RELEASE
RELEASE COMPLETE
RELEASE
RELEASE COMPLETE
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)
Network A
Network B
PNNI
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.
PNNI Signaling Example
Source
Switch
Source A
Transit
Switch
Destination
Switch
Destination B
SETUP
SETUP
SETUP
SETUP
CALL PROCEEDING
CALL PROCEEDING
CALL PROCEEDING
CALL PROCEEDING
CONNECT
CONNECT
CONNECT
CONNECT
CONNECT ACK
CONNECT ACK
CONNECT ACK
CONNECT ACK
RELEASE
RELEASE
RELEASE
RELEASE COMPLETE
RELEASE
RELEASE COMPLETE
RELEASE COMPLETE
RELEASE COMPLETE
Chapter 9
ATM 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
PNNI Routing Hierarchy


PGL passes topology summary upward in hierarchy and
downwards to its PG
Multiple levels of hierarchy allowed
Logical Link
A
B
Logical Group Node
Peer Group Leader
PG(A)
A.2
A.1
PG(A.1)
PG(B)
PG(A.2)
A.2.2
A.1.2
B.1
B.3
A.2.1
A.1.1
A.1.3
Physical Link
A.2.3
A.2.4
B.2
B.4
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)
Logical Link
A
B
Logical Group Node
Peer Group Leader
PG(A)
A.2
A.1
PG(A.1)
PG(B)
PG(A.2)
A.2.2
A.1.2
B.1
B.3
A.2.1
A.1.1
A.1.3
A.2.3
A.2.4
B.2
B.4
DTL Stacks & Pointers


DTLs organized in a stack according to level
A pointer indicates current level
From node A.1.2
From node A.2.1
DTL: [A.1, A.2] pointer-2
DTL: [A.2.1, A.2.3, A.2.4] pointer-2
DTL: [A, B] pointer-1
DTL: [A.1, A.2] pointer-2
From node A.1.1
From node A.2.4
DTL: [A, B] pointer-1
DTL:[A.1.1, A.1.2] pointer-2
DTL: [A, B] pointer-1
DTL: [A.1, A.2] pointer-1
A
B
DTL: [A, B] pointer-1
From node B.1
DTL: [B.1, B.3] pointer-2
DTL: [A, B] pointer-1
PG(A)
A.2
A.1
PG(A.1)
PG(B)
PG(A.2)
A.2.2
A.1.2
From B.3
null
B.1
B.3
A.2.1
A.1.1
A.1.3
A.2.3
A.2.4
B.2
B.4
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 9
ATM 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
Logical IP Subnetworks (LIS’s)
ATM network
LIS2
LIS3
LIS4
LIS5
LIS6
LIS1
Router
Router
Router
Router
Router
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