Broadband ISDN and ATM

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Broadband ISDN and ATM

• ??? ???
• Jmpark_at_cs.chonbuk.ac.kr

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Contents

• Introduction to B-ISDN and ATM
• The B-ISDN ATM Reference Model
• Physical Layer in ATM
• Virtual Circuits versus Circuit Switching
• Transmission in ATM Networks
• ATM Switches ( Knockout, Batcher-Banyan )
• Data Link Layer in ATM

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• Network Layer in ATM
• Cell Formats
• Connection Setup
• Routing and Switching
• Service Categories
• Quality of Service
• Congestion Control
• ATM LANs
• ATM AAL Layer Protocols
• Structure of the ATM Adaptation Layer
• AAL 1, AAL 2, AAL 3 / 4, AAL 5
• Comparison of AAL Protocols
• Service Specific Connection-Oriented
  Protocol(SSCOP)

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1. Introduction to B-ISDN ATM

• B-ISDN(Broadband Integrated Services Digital
  Network)
• A single physical network integrates variety of
  services
• Problems
• QoS Requirements for services widely different
• Voice Real time(low delay jitter), tolerates
  occasional losses
• Data Usually no real-time requirements,
  error-free, guaranteed delivery
• Video High bandwidth, low delay and jitter
• Traffic characteristics also widely different
• Certain applications require synchronization
  among multiple traffic streams

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• ATM(Asynchronous Transfer Mode)
• Underlying technology that makes B-ISDN possible
• Transmit all information in small, fixed size
  packet (ATM cell)
• Cell switching technology
• Flexible and handle both constant(audio, video)
  and variable(data) rate traffic
• Easier than traditional multiplexing techniques
  using fiber optics
• Broadcasting(television distribution)
• Connection-oriented Cell order is guaranteed
• Intended speed 155 Mbps, 622 Mbps, gigabit
  speeds later
• 155 Mbps(exact choice) made for compatibility
  with ATTs SONET

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B-ISDN ATM Reference Model
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• Physical Layer(deals with physical medium)
• Voltage, bit timing, various other issues.
• Designed to be independent of the transmission
  medium
• ATM Layer(deals with cells and cell transport)
• Defines the layout of a cell
• Establishment and release of virtual circuits
• Congestion control
• AAL Layer(ATM Adaptation Layer)
• Allows users to send packets larger than a cell
• Segments packets, transmits the cells
  individually, and reassembles then at the other
  end
• User plane
• Deals with data transport, flow control, error
  correction, and other user functions
• Control plane is concerned with connection
  management

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2. Physical Layer in ATM

• B-ISDN service Compromise between circuit and
  packet switching
• Virtual Circuits
• Connection oriented
• Implemented internally with packet switching
• Connection Types
• Permanent virtual circuits (No setup time)
• Switched virtual circuits (Like telephone call)
• Circuit establishment
• The route is chosen from source to destination
• All switch along the way make table entries so
  they can route any packet on that virtual circuit

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Transmission in ATM Network

• Synchronous transmission mode
• Asynchronous transmission mode
• Not required that the stream of cells coming out
  of a computer be continuous(Gaps between the data
  cells are filled by idle cells)
• Does not standardize the format for transmitting
  cells
• All ATM links are point-to-point(unidirectional)
• Multicasting Enter a switch on one line and
  exit it on multiple lines

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ATM Switches

• General Model for an ATM cell switch
• ATM switches are generally synchronous
• Cell arrive on the input lines asynchronously
• Master clock marks the beginning of a cycle
• Common goal
• Switch all cells with as low a discard rate as
  possible
• Never reorder the cells on a virtual circuit

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• Input queueing head-of-line blocking
• Output queueing

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The Knockout Switch

• Output queueing

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Batcher-Banyan Switch
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3. Data Link Layer in ATM

• TC(Transmission Convergence) sublayer
• Cell Transmission
• takes a sequence of cells
• add HEC to each one ( HEC Header Error Control
  )
• convert the result to bit stream
• match the bit stream to the speed of the
  underlying physical transmission system by
  inserting OAM cells as filler
• OAM Operation And Maintenance
• Cell Reception
• takes an incoming bit stream
• locates cell boundaries
• verifies the header
• processes the OAM cells
• passes the data cell up to the ATM layer

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• Locating the cell boundaries
• HUNT Shifting bits into the shift registers one
  at a time looking for a valid HEC
• PRESYNCH shifts in the next 424 bits(5-bytes)
  without examining them

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4. Network Layer in ATM Network

• Connection-oriented layer
• Basic element virtual circuit(virtual channel)
• Unusual for a connection-oriented protocol
• Does not provide any acknowledgements
• Used for real-time traffic(audio, video)
• Guarantee cells sent will never arrive out of
  order
• Supports a two-level connection hierarchy

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Cell Formats

• UNI(User-Network Interface)
• Define boundary between a host and an ATM
  network(between the customer and the carrier)
• NNI(Network-Network Interface)
• Define boundary between two ATM switches
• GFC General Flow Control PTI Payload Type
• VPI Virtual Path Identifier CLP Cell Loss
  Priority
• VCI Virtual Channel Identification HEC
  Header Error Check

40 bits
40 bits
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• GFC flow control or priority
• VPI select a particular virtual path
• VCI select a particular virtual circuit
• PTI define the type of payload
• CLP set by host to differentiate between
  high-priority traffic and low-priority traffic
• HEC checksum over the header

Payload type Meaning
000 User data cell, no congestion, cell type 0
001 User data cell, no congestion, cell type 1
010 User data cell, congestion experienced, cell type 0
011 User data cell, congestion experienced, cell type 1
100 Maintenance information between adjacent switches
101 Maintenance information between source and destination switch
110 Resource Management cell(used for ABR congestion control)
111 Reserved for future function
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Connection Setup

• Messages used for connection establishment and
  release
• ATM address
• 20 bytes(based on OSI addresses)
• Byte 1 indicate which of three formats the
  address is in
• Bytes 2-3 country(alternatively, international
  organization)
• Bytes 4 format of the rest of the address
  3-byte(authority), 2-byte(domain),
  2-byte(area), 6-byte(address)
• 15 digit decimal ISDN telephone number

Message Meaning when sent by host Meaning when sent by network
SETUP Please establish a circuit Incoming call
CALL PROCEEDING I saw the incoming call Your call request will be attempted
CONNECT I accept the incoming call Your call request was accepted
CONNECT ACK Thanks for accepting Thanks for making the call
RELEASE Please terminate the call The other side has had enough
RELEASE COMPLETE Ack for release Ack for release
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Connection setup in an ATM network
Connection release
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Routing and Switching

• Route on VPI field, but not VCI field
• Exception route on VCI at the final hop in each
  direction
• Advantage
• No new routing decisions have to be made
• Routing of individual cells is easier when all
  VCs for a given path are always in the same
  bundles
• Easier to switch a whole group of VCs
• Easier for carriers to offer closed user
  groups(private network) to corporate customers

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• Examples Rerouting a VP reroutes all of its VCs

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Service Categories

• The ATM service categories
• Characteristics of the ATM service categories

Class Description Example
CBR Constant bit rate T1 circuit
RT-VBR Variable bit rate real time Real-time videoconference
NRT-VBR Variable bit rate non-real time Multimedia email
ABR Available bit rate Browsing the Web
UBR Unspecified bit rate Background file transfer
Service characteristic CBR RT-VBR NRT-VBR ABR UBR
Bandwidth guarantee Yes Yes Yes Optional No
Suitable for real-time traffic Yes Yes No No No
Suitable for bursty traffic No No Yes Yes Yes
Feedback about congestion No No No Yes No
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Quality of Service

• Some of the quality of service parameters

Parameter Acronym Meaning
Peak cell rate PCR Maximum rate at which cells will be sent
Sustained cell rate SCR The long-term average cell rate
Minimum cell rate MCR The minimum acceptable cell rate
Cell delay variation tolerance CDVT The maximum acceptable cell jitter
Cell loss ratio CLR Fraction of cells lost or delivered too late
Cell transfer delay CTD How long delivery takes(mean and maximum)
Cell delay variation CDV The variance in cell delivery times
Cell error rate CER Fraction of cells delivered without error
Severely-errored cell block ratio SECBR Fraction of blocks garbled
Cell misinsertion rate CMR Fraction of cells delivered to wrong destination
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• The probability density function for cell arrival
  times

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Congestion Control

• Admission Control.
• Must describe the traffic to be offered and the
  service expected.
• Check to see if it is possible to handle this
  connection.
• If no route can be located, the call is rejected.
• Denying admission should be done fairly.
• Resource Reservation.
• Reserving resources in advance, usually at call
  setup time.
• Bandwidth can be reserved by having the SETUP
  message along each line it traverses.
• Rate-Based Congestion Control.
• CBR and VBR No dynamic congestion control are
  possible( real-time ).
• UBR Nobody cares.
• ABR How congestion should be detected,
  signaled, and controlled ?

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• Rate-based solution
• After every k data cells, transmits a special RM
  cell
• RM(Resource Management) cell
• Travels along the same path as the data cells
• Contains ER(Explicit Rate).
• When it gets the destination, it is examined,
  updated, and sent back
• Congestion control mechanism
• Overloaded switches generate RM cells and ship
  them back to the sender
• Overloaded switches set the middle PTI bit

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ATM LANs

• How to provide connectionless LAN service over
  the ATM network
• Introduce a connectionless server into the
  network
• Every host has a (potential) ATM virtual circuit
  to every other host

LES LAN Emulation Server BUS
Broadcast/Unknown Server
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5. ATM ALL Layer Protocol

• AAL ATM Adaptation Layer
• Goal
• Provide useful services to application programs
• Shield application programs from the mechanical
  processing
• Original service classes supported by AAL(now
  obsolete)
• Defined four protocols to handle services(AAL 1
  AAL4)

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Structure of the ATM Adaptation Layer

• ATM adaptation layer
• Convergence sublayer
• Provide the interface to the application
• Service specific part
• Common part
• SAR(Segmentation And Reassembly) sublayer
• Sender add header and trailers to the data
• Receiver reassemble the cells into message

Convergence sublayer (service specific part)
Convergence sublayer (common part)
Segmentation reassembly sublayer
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AAL 1

• Used for transmitting class A traffic
• Simple, connection-oriented, real-time constant
  bit rate
• Ex. Uncompressed audio and video
• CS sublayer
• Break up the input message or stream into 46- or
  47- byte unit
• Does not have any protocol header
• Cell format
• SN(Sequence Number), SNP(Sequence Number
  Protection checksum)
• P cell used when message boundaries must be
  preserved

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AAL 2

• Used for transmitting class B traffic
• Rate can vary strongly in time
• Message boundary preserved
• Ex. Compressed audio or video
• As in AAL1, the CS sublayer does not have a
  protocol header
• Cell format
• 1-byte header, 2-byte trailer, 45-byte data bytes
• IT(Information Type) indicate that cell is the
  start, middle, or end
• LI(Length Indicator) tells how big the payload
  is

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AAL 3/4

• Protocols for classes C and D
• Stream or message mode
• Message mode Boundaries are preserved
• Stream mode Boundaries are not preserved
• Multiplexing of several sessions onto one virtual
  circuit

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• AAL 3 / 4 CS sublayer message format
• CPI(Common Part Indicator) Message type
• Btag, Etag Used to frame message
• BA size, Length Payload length
• Cell format ST(Segment Type), MID(Multiplexing
  ID)

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AAL 5

• SEAL(Simple Efficient Adaptation Layer)
• Service
• Reliable service, Unreliable service
• Unicast and Multicast(not guaranteed) are
  supported
• Supports message mode and stream mode
• CS sublayer
• UU(User to User) available for a higher layer
  for its own purpose
• Sequencing, multiplexing
• Length Payload length(not counting padding)
• SAR sublayer does not add headers or trailers

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Comparison of AAL Protocols

• Some difference between the various AAL protocols

Item AAL 1 AAL 2 AAL 3/4 AAL 5
Service class A B C/D C/D
Multiplexing No No Yes No
Message delimiting None None Btag/Etag Bit in PTI
Advance buffer allocation No No Yes No
User bytes available 0 0 0 1
CS padding 0 0 32-Bit word 0-47 bytes
CS protocol overhead(bytes) 0 0 8 8
CS checksum None None None 32 Bits
SAR payload bytes 46-47 45 44 48
SAR protocol overhead(bytes) 1-2 3 4 0
SAR checksum None None 10 Bits None
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SSCOP

• AAL protocols does not provide for simple
  end-to-end reliable transport connections
• SSCOP
• Service Specific Connection-Oriented Protocol
• Used for control, not for data transmission
• Fundamentally a dynamic sliding window protocol
• No piggybacking
• Periodically, sender asks to send back the bit
  map giving the window status