Integrated Services; Introduction ATM

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Integrated Services;


Introduction ATM

Dr. Farid Farahmand


Integrated Services


Integrated Services Data Networks


Initiated to combine all services


Allowing access to and transporting
information between private and
public networks


Transporting all information in digital
format over a common
communications systems


Once the analog information is
digitized, it is treated the same!


Providing integrated services requires


Facilities (transmission media)


Protocols (organizing and regulating
the flow of data)



Examples


X.25 User
-
to
-
Network Interface


Integrated services digital Network
(ISDN)


Digital subscriber line (DSL)


Asynchronous transfer mode (ATM)


Frame relay (FR)



Private

Public

Private

Integrated Services

ISDN

LAN

MAN

WAN

Interconnecting different networks
through Public Telephone Network
or Public Data Network managed
by different carriers
-

all digitally

ATM Basics


Defined in 1988 by ITU
-
T as a part of BISDN (Broadband ISDN)


Data can exist and enter BISDN asynchronously


Govern by ATM Forum


Supports video, sound, image, high
-
quality multimedia


Seamless and can be used on LAN and WAN


Intended to replace T1 yet not as successful as predicted


Unlike TDM, ATM does not assign any time slots to a given user


dynamically allocates ATM cells when user equipment wishes to transmit
information


Statistical packet Switching

TDM Circuit switching

High quality

Broadband
services

ATM Basics


Cell Based


The cell is comprised of 53 bytes (octet).


Five of the bytes make up the header field and the remaining


contains error checking


48 bytes form the user information field


error checking is done in upper layers


Shorter assembly time


less delay


Easier buffer management and less processing/packet


supports both circuit switched and packet switched services


circuit mode

services


packet mode
services


Connection oriented service


Uses virtual paths


Supports different data rates from 16Kbps and up (OC
-
12)


ATM 5
-
Byte Header Structure


VCI

16 bits of
virtual circuit identifier

that is used, in conjunction
with the VPI, to identify the

destination of a cell
-

to identify the
next
destination
of a cell as it passes through a series of switch routers on its
way to its destination.


VPI

8 bits of
virtual path identifier

that is used, in conjunction
with the VCI; A virtual path consists of multiple virtual channels to
the same endpoint.


PT

3 bits of
payload type
. The first bit indicates whether the cell
contains user
data

or
control data
.


CLP

1 bit of
congestion loss priority

that indicates whether the cell
should be
discarded
if it encounters extreme congestion as it moves
through the network.


HEC

8 bits of
header error control

that are a checksum calculated
only on the header itself.


GFC

4 bits of
generic flow control

that are used to provide local
functions, such as identifying multiple stations that share a single ATM
interface. The GFC field is typically not used and is set to a default
value.


Virtual Connections


VCI

16 bits of
virtual circuit identifier

that is used, in conjunction with
the VPI, to identify the

destination of a cell
-

to identify the
next
destination
of a cell as it passes through a series of switch routers on
its way to its destination.


VPI

8 bits of
virtual path identifier

that is used, in conjunction with the
VCI; A virtual path
consists of multiple virtual channels
to the same
endpoint.


http://www.tekelec.com/ss7/protocols/atm10.asp

ATM Network Components


ATM End
-
point (end
-
systems)


Constitute source and destination


Can be a PC with ATM NIC or special devices


Supports multiple interfaces


ATM Switches (switch fabric)


Responsible for routing cells through public or private owned
networks


ATM Switching Paths


ATM transmission media (twisted
-
pair, optical fiber link, etc.)

ATM Network Components

ATM Endpoint

Implementation

From the

ATM Switch

Interfaces:

UNI

(user
-
to
-
network interface


within the same network

NNI (network
-
to
-
network interface)

ATM Protocol Stack


Physical Layer


Transmission Convergence Sub
-
layer


Header error control


Cell rate control


Generating recovery cell


Physical Medium Dependent


Means of accessing to the transmission media


Specifying the actual bit rate


Cell Layer


Control flow


Produce/extract cell headers


Translating VPI and VCI


ATM Adaptation Layer


Convergence sub
-
layer


Placing bits into a common format


Cell sequencing


Identifies class of service


Segment and Assembly sub
-
later


Placing data format into ATM cells and de
-
segmenting data cells


ATM Protocol Stack

ATM Adaptation Layer (AAL)


The part of the ATM protocol that breaks up
application
packets

into ATM cells


There are four types of AALs


AAL
-
1

Connection
-
oriented, Constant Bit Rate (CBR), such as DS1
and DS3.


AAL
-
2

Connection
-
oriented, Variable Bit Rate (VBR).


AAL
-
3/4

Connection
-
oriented and connectionless, Available Bit
Rate (ABR).


AAL
-
5

Connection
-
oriented, Unspecified Bit Rate (UBR). Least
amount of error checking and retransmission.


AAL
-
6

Connection
-
oriented, MPEG
-
2 video streams

ATM Traffic Types

Low Latency

Used for time sensitive data


Bursty traffic



No delivery guarantee

Best effort based



Traffic in ATM Switches


Blocking



Switch Fabric


Head
-
of
-
line Blocking


Buffering


Input


Output


Traffic Engineering


Sources



Miller Text book


Tomasi Text Book

TCP/IP Stack Protocol

Extra Credit