ATM by sitimuslikhah65

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									ATM Asynchronous

  Transfer Mode
Voice                                 Data Bursty


                                      variable-lengt
                                      h packets
AAL                                        AAL
                                           cells
    A/D                               Copyright ©2000 The
s                                        McGraw Hill
     s   …
                                          Companies
1, 2

Digital voice samples
Video
    Compression                          Leon-Garcia &
                                            Widjaja:
                                        Communication
                                       Networks Figure 9.3

                            c
                            o
                            m
                            pressed
picture frames
frames
              cells
              AAL
              cells
                        …
           Asynchronous Transfer Mode (ATM)



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               4              3    2     1   4     3    2    1     4       3   2 1
               AT                                                      `
               M                                  4     3    1     3 2         2 1
                  GFC (4 bits) VPI VPI (4 bits) VCI (4                       CLP (1
                  (4 bits) VCI (4         bits) VCI (8 bits) PT (3 bit)
                  bits)                     jaja: HEC (8 Networks
                                          bits) Communicationbits) Figure 7.37
Copyright ©2000 The McGraw Hill Companies
                                          Payload (48 bytes)
          ATM
• ATM standard (defined
by CCITT) is widely accepted
by common carriers as mode
of operation for
communication – particularly BISDN
• ATM is a form of cell switching using
small fixed-sized packets.

          Basic ATM Cell Format

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           Assumptions for ATM
            Conceptual Model
. ATM network will be organized as a
    hierarchy. User’s equipment connects to
    networks via a UNI (User-Network Interface).
              Connections  between      provided
              networks are made through NNI
              (Network-Network Interface).
    2. ATM will be connection-oriented.
           A connection (a channel)
           must be established before
           any cells are sent.
     Assumptions for ATM
    Conceptual Model (cont.)
• two levels of ATM connections are
      defined: virtual path
      connections virtual channel
      connections
    These are indicated by the two
    fields in the cell header:
     virtual path identifier VPI virtual
           channel identifier VCI
                                        Private ATM
Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.5
ATM Virtual
Connections


   Virtual Paths
   Physical Link



Copyright ©2000 The McGraw
Hill Companies Leon-Garcia &
   Widjaja: Communication
     Networks Figure 7.40
     Assumptions for ATM
    Conceptual Model (cont.)
3. Vast majority of ATM networks
will run on optical fiber networks
with extremely low error rates.
4. ATM supports low cost
attachments
 • This decision lead to a significant
 decision – to prohibit cell reordering in
 ATM networks.
 • ATM switch design is more difficult.
                              UNI Cell Format

ATM cell             4                 3     2     1     4       3    2     1     4        3    2 1
                     AT                                                                `
 header
                     M                                         4      3     1     3 2           2 1
                     GFC (4 bits) VPI VPI (4 bits) VCI (4                                      CLP (1
                                                                                               bit)
                     (4 bits) VCI (4  bits) VCI (8 bits) PT (3
                     bits)            bits) HEC (8 bits)
                                      Payload (48 bytes)




                     2             4 10                              44                                                            6 10
                     (bits)                                          (bytes)                                         (bits)
                     Copyright ©2000 The McGraw Hill Companies       Leon-Garcia & Widjaja: Communication Networks   Figure 9.16



Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.7
                                       Copyri
        ATM Cell Switching               ght
                                       ©2000
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                                       Figure
                                        7.38
                             5


                                  3


                              6


                                  N

                                         1
                             N
                                  …
                                a
        VP3
                  VP5 a b



                                           Sw =
                                           switch
                                    Sw 4




                                             b
c
                            c
d
                                    Copyright ©2000 The
                                    McGraw          Hill
e VP2                               Companies
                                    Leon-Garcia      &
                                    Widjaja:
                                    Communication
                                    Networks




              VP1 ATM d
        ATM Protocol                   l   h
                                       a   e
         Architecture                  y   r
                                       e   e
• ATM Adaptation Layer (AAL) –         r
the protocol for packaging data into   s   b
cells is collectively referred to as       e
AAL.                                   s   ?
• Must efficiently package higher      h
level data such as voice samples,      o
video frames and datagram packets      u
into a series of cells.                l
                                       d
  Issue: How many adaptation           t
Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.2
             User User information information         Network
                                                     Copyright ©2000 The
                                                        McGraw Hill


        …
End system

                                                 E
                                                 n
                                                 d
                                                         Companies
                                                 s     Leon-Garcia &
                                                          Widjaja:
                                                 y    Communication
                                                     Networks Figure 9.4
                                                 s
                                                 t




                                                 e
                                                 m
  ATM Architecture
{original}
• CCITT envisioned four classes of
   applications (A-D) requiring four
   distinct adaptation layers (1-4)
   which would be optimized for an
   application class:
A. Constant bit-rate applications CBR
   B. Variable bit-rate applications VBR
   C. Connection-oriented data
   applications
   D. Connectionless data application
      ATM Architecture
• The AAL is further divided into:
• The Convergence Sublayer (CS) – to
manage flow of data to and from SAR
sublayer.
• The Segmentation and Reassembly
Sublayer (SAR)

    – responsible for breaking data into
    cells at the sender and reassembling
    cells into larger data units at the
    receiver.
                                            ATM layer
                                        Physical medium



Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.6
      ATM Architecture                      (als   d
                                            o
        {original}                          ref    E
                                            err    f
• The AAL interface was initially defined   ed     f
as classes A-D with SAP (service access     to     i
points) for AAL1-4.                         as     c
• AAL3 and AAL4 were so similar that        SE     i
they were merged into AAL3/4.               AL     e
                                            –      n
  • The data communications                 the    t
  community concluded that AAL3/4           Si
  was not suitable for data                 mp     A
  communications applications and they      le     d
  pushed for standardization of AAL5        an     a
ptation Layer).
• AAL2 was not deployed.
    ATM Service Categories
    {revised}
Class Description Example

 CBR Constant Bit Rate T1 circuit RT-VBR Real
         Time Variable Bit Rate Real-time
            videoconferencing NRT-VBR
Non-real-time Variable Bit Rate Multimedia email
ABR Available Bit Rate Browsing the Web UBR
Unspecified Bit Rate Background file
transfer
                                            m    n
    QoS, PVC, and SVC                            e
                                            a
• Quality of Service requirements are       n    c
  handled at connection time and is              t
                                            a    i
          viewed as part of                 g    o
  signaling.                                e    n
  • ATM provides permanent virtual          r    s
  connections and switched virtual
  connections.                           –       (
                                         Swit    S
  – Permanent    Virtual   Connections
                                         ched    V
  (PVC)
                                         Virtu   C
     permanent connections set up        al      )
     manually    by      network         Con
set up and released on demand by
the end user via signaling
procedures.
AAL 1 Payload

(b) CS PDU with
pointer in structured
data transfer
(a) SAR PDU
header

   1 bit 3 bits 4 bits



  Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.11
             AAL 1                                                 AT
                                                                   M
                                                                   laye
                                                                   r
    Higher layer User data stream                                  5 48
…                                                                  5 48
                b    b   b
                                                                   5 48
                    1 2 3

                                                        C
                                                        S
                                                       SAR
                                                        sublayer
                                                       P
                             1 47 1 47 1 47
                                               47 47   D
                                              47
                                                       U
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                               sublayer                            Networ
                                                                   ks
 AAL 3/4
  CS and                  CPI      Btag   (
 SAR PDUs
(a) CPCS-PDU
format
      Header

                                          b
                                     T
                                          y
                                     r
                                     a    t
                          BASize          e
                           CPCS -PDU i
                            Payload l     s
                                     e    )
                                   11r
                                   21     (
Pad                                -65,   b
                                 A 535    y
                                 L0-3     t
                                   11     e
                                 E        s
                                   2
                                 t
                                          )
                                 a (byt
               g Length            es)
                                                                          LI
                                                                                 (
                                                                                 b
                                                                                 )

                                                    (2 bytes) (2 bytes)
                                                                                 S
                                                                                 A
                                                                                 R
                                                                          ST SN MID

                                                                          SAR -PDUP
                                                                          Payload
                                                                                 D
                                                                                 U
                                              format Trailer

        Header
4         3   2   1   4   3   2   1   4       3    2 1
AT                                        `
M                         4   3   1   3 2          2 1
GFC (4 bits) VPI VPI (4 bits) VCI (4              CLP (1
                                                  bit)
(4 bits) VCI (4  bits) VCI (8 bits) PT (3
bits)            bits) HEC (8 bits)
                 Payload (48 bytes)
                     AAL 3/4
Higher layer

                                 User message
         Service specific convergence sublayer




                                  Assume null




                                                 P
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                      h
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                      a
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                  sube
                  lay r
                  er
Common part
convergence

              4




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                                               Copyright s
                                               ©2000 The
                                               McGraw t
                                               Hill      s
                                               Companies
                                               Leon-Garci
                                               a        &
               …                               Widjaja:
                                               Communic
                                               ation
                                    of         Networks

                   2-
                   by 2 44 2 2 44 2
                         2 44 2
                   te           trailer, and
                         44-byte payload.
                   head
                   er, 2-byte
SAR sublayer




 ATM layer
               …
                                                             F
                                                             i
                      AAL 5                      SAR
                                                 For

  Convergent
Sublayer Format

Pad



UU CPI

Length

                                             C
                                             R
                                             C    mat
Information
                                                  Copyright
0 -65,535     0-47 1 1 2 4 (bytes) (bytes)       ©2000 The
                                                  McGraw
                                                    Hill
                                                 Companies
                                                 Leon-Garci
a & Widjaja: Communication Networks Figure 9.19
                           AAL 5
                          Higher layer
Service specific convergence




                               Assume null sublayer
             Common part convergence sublayer
 SAR sublayer
                   48


                                                               48
    48
     (0)

    (0) (1)




 ATM layer
 PTI = 1
 PTI = 0 PTI = 0
                                 Leon-Garcia & Widjaja:   Communication
                                 Networks Figure 9.18

								
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