high speed networks lecture 5
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High Speed Networks
Lecture 5
Uday Prakash
Uday3prakash@ gmail.com
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2
Traditional Telephone Network VS
Integrated Digital Network
Traditional Telephone Networks
Separately designed and administrated transmission and switchingsystems
Demultiplexing and demodulating are necessary at each switchingcenter
A repeated process results in an accommodation of noise as well as cost
Integration of transmission and switching systems Achievable when both systems are digital
Using PCM modulation and TDM multiplexing
Switching without decoding along the way Separate multiplex/demultiplex channel banks are not required
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History of ISDN
Developed by CCITT (Comate Consultative International
Telephonique Telegraphs) to limitation of POTS (Plane old
Telephone system).
Original document was I.120 version in 1984.
Early 1990s produced NI-1version.
Every country has its own ISDN standards, called National
ISDN standards (NIs).
More recently NI-2 also manufactures worked with phonecompanies to simplify ordering.
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Integrated Digital Network
AnalogNetworks
DigitalNetworks
Low capacity copper cables---high capacity optical fibers. Electromechanical analog space division switching system-
Electronic digital time division switching
Channel associated signaling--common channel signaling.
Reduced network configuration More than one connection to the upper level of hierarchy
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Voice Communication over an
Analog Telephone Network
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Voice and Data Communication
over an Analog Telephone Network
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Analog and Digital Services
over the Telephone Network
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The Integrated Digital Network
Analog telephone network
Space-divisionswitch
Multiplex and modulate signalsDemultiplex and demodulate signals
PCM: pulse-code modulation
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Integrated Digital Network
Digital refers to its purely
digital transmission
Use of an analog telephone modem
for Internet access requires that
ISPs modem which converts thedigital content to analog signals
before sending it and the user's
modem then converts those signals
back to digital when receiving.
When connecting withISDN there is no digital to
analog conversion.
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Integrated Digital Network
Switching Network
Data links used for common channel signalling
between digital exchanges form a separate
signalling networks.
As signalling network uses transmission bearer
network channels, synchronizing network is
deserved to synchronize all PCM frames, to avoid
congestion.
Administrative network is to used to connect the
remote operations and management centers to the
nodes of the PSTN.
All these four networks uses the channels in the
basic transmission bearer network.
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ISDN
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Integrated Services Digital Network
Support a wide range of voice and non-voice
applications in the same network
Service integration for provision of a range of
services using a limited set of connection types
and multipurpose user-network interface
arrangements.
Support applications including Switched
(circuit switched, packet switched or their
concatenation) and non-switched connections.
Modem is not necessary, as it supports digitaltransmission of all types of data (including
voice). This also results in very short call setup
time between two ISDN subscribers.
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Evolution of ISDN I.120
Transition from existing network to a comprehensive ISDN may require a
period of time extending over one or more decades.
Interworking must be done during this period.
Based on concept developed for IDNs, involving progressively
incorporating additional functions and network features. In the evolution of ISDN, digital end to end connectivity will be obtained
via plant and equipment used in existing networks, such as digital
transmission, time-division multiplexing switching and/or space division
multiplex switching.
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NETE0510: Communication Media andData Communications 14
Principles of ISDN1. Support of voice and non-voice applications using a limited
set of standardized facilities Defines the purpose of ISDN and the means of achieving it
2. Support for switched and non-switched applications
Both circuit-switched and packet-switched connections
Support non-switched services in the form of dedicated lines
3. Reliance on 64-kbps connections
Fundamental block of ISDN
64 kbps were chosen because it was the standard rate for digitized
voice
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NETE0510: Communication Media andData Communications 15
Principles of ISDN (contd)4. Intelligence in the network
Sophisticated serviced beyond simple setup a circuit-switched call
Sophisticated network management and maintenance capabilities
Use of SS7 ( (common channel) signaling system number 7) and intelligentswitching nodes in the network
SS7 is a set of telephonysignaling protocols which are used to set up the vastmajority of the world's
public switched telephone network telephone calls.
5. Layered protocol architecture
User access to ISDN protocol is a layered architecture that can be mappedto OSI model
Standards can be developed independently for various layers andfunctions
6. Variety of configurations More than one physical configuration is possible for implementing ISDN
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ISDN Services
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Broad aspects of ISDN in I.121
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ISDN protocols
E-series protocols Telephone networkstandards for ISDN.
I-series protocols Specify ISDN concepts
and interfaces. Q-series protocols Standards for ISDN
switching and signaling.
Operate at the physical, data link, and networklayers of the OSI reference model
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Integrated Services Digital Network Standard interfaces between the user an
d the network include functional units,as:
1. Exchange Termination(ET) End userconnectivity.
2. Line Termination (LT)---BRI or PRI accessprovisioning.
3. Network Termination(NT1)-terminatesaccess line at customers end.
4. Network Termination(NT2)---enablesswitching functions to be performed.
5. Terminal Equipment (TE1)provisioning offunction required to handle layer 1, 2 & 3protocols.
6. Terminal Equipment(TE2)
providesfunctions corresponding to capabilities ofexisting equipments which do not conformto ITU-T standards.
7. Terminal Adapter (TA)converts layer1,2&3 protocols of TE2 into those of TE1,to enable equipment on TE2 to operateover the ISDN.
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ISDN Reference Points-interfaces
U - Two wire cable that connects thecustomers equipment to thetelecommunications provider
R - Point between non-ISDN equipment (TE2)and the TA
S - Four-wire cable from TE1 or TA to theNT1 or NT2
T - Point between NT1 and NT2
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Analogy
NT-1 (Network Terminator-1)An NT-1 is an interface box that converts ISDNdata into something a PC can understand (andvice versa). It works a little like a cable TVdescrambler for ISDN signals, and is oftenbuilt into ISDN adapters.
TA (Terminal Adapter)
This chunk of hardware converts the data itreceives over ISDN to a form your computercan understand. Sometimes mistakenly calledan ISDN modem or a digital modem, aterminal adapter handles data digitally anddoes not need to modulate or demodulate an
analog signal. Terminal adapters can be aninternal board or an external board thatconnects to the computer through the serialport.
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The User Interface
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The User Interface (contd) User has access to ISDN via a local interface to a digital pipe.
Pipes of various sizes are available to satisfy different needs
Pipe to the users promises has a fixed capacity but the traffic on the pipemay be a variable mix up to the capacity limit
ISDN requires control signals to instruct how to sort out the time-
multiplexed data and provide the required services Control signals are multiplexed onto the same digital pipe.
Recommendation from I.410: more than one size of pipe is needed
A single terminal (e.g. a residential telephone)
Multiple terminals (e.g. a residential telephone, PC, and alarm system)
A network of devices attached to a LAN or PBX (ISDN gateway)
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The User Interface (contd)
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ISDN Protocols at the user-network interface
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ISDN Architecture
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ISDN Architecture (contd) Physical interface provides a standardized means of attaching
to the network
The interface supports a basic service consisting of three time-multiplexed channels, two at 64 kbps and one at 16 kbps
In addition, there is a primary service that provide multiple64-kbps channels
An interface is defined between the customers terminalequipment (TE) and a device on the customers premises,known as a network termination (NT)
The subscriber loop is the physical path from the subscribersNT to the ISDN central office Must support full-duplex digital transmission for both basic and
primary data rates
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ISDN Protocol Operating OSI Layers 1 Through3
Physical layer ISDN protocols BRI (ITU-T I.430) / PRI (ITU-T I.431)
Defines two ISDN physical layer frame formats
Inbound (local exchange to ISDN customer)
Outbound (ISDN customer to local exchange )
Data link layer ISDN protocols
LAPD signaling protocol (ITU-T Q.920 for BRI and Q.921 for PRI) for transmitting
control and signaling information over the D channel
LAPD frame format similar to ISO HDLC frame format
Network layer ISDN protocols
ITU-T I.930 and ITU-T Q.931 defines switching and signaling methods using the D
channel.
Note: With Q.921/Q.931 the second digit indicates the OSI layer.
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ISDN Physical Layer
ISDN physical-layer frame formats are 48 bits long, of which 36 bits represent data
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ISDN Data Link Layer
Frame format is very similar to that of HDLC
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ISDN Network Layer
Two Layer 3 specifications are used for ISDN signaling: ITU-T I.450 (also known as ITU-T Q.930) ITU-T I.451 (also known as ITU-T Q.931)
Together, these protocols support: User-to-user circuit-switched connections
User-to-user packet-switched connections
A variety of standards for: Call establishment
Call termination
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Call Reference Field
Information Elements
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Information Element Types
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Addressing in ISDN
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ISDN Encapsulation
The two most common encapsulations: PPP
HDLC
ISDN defaults to HDLC.
PPP is much more robust. Open standard specified by RFC 1661
Supported by most vendors
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Channels of ISDN
B (Barrier or Bearer) Channel carries voice, data, video etc. This Channel functions at a constant 64 kbps. This channel can be usedfor packet and circuit switching applications.
64k bps per channel
The two B channels can be inverse multiplexed or boded together Achieve a maximum aggregate communication speed of 128 Kbps
D (Denial or Delta) channel is used to convey user signaling messages. This type channel used out of band signaling . This meansthat network related signals are carried on a separate channel than used data.
16 Kbps Entire bandwidth is not used for signaling purpose
Excess of 9.6 Kbps is available for packet switched data transmission applications
Excess bandwidth usage Climate control, security alarm system etc.
D Channel is packet switched Excess capacity can be utilized for packet switched applications
H channels have a considerably higher transfer rate than B channels. These channels effectively meet the needs of real time videoconferencing, digital quality audio and other services requiring a much higher bandwidth. H channel sustains rates of approximately1920 mbps.
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Integrated Services Digital Network
Something more(Supplementary
services) than the services carried by
PSTN.
In PRI, less than 30 or 23 channels
can be provided to obtain channels
with greater digit rates for broad
applications, as:
H0 channel at 384 kbps.
H11 channel at 1536 kbps(for 1.544
Mbps access.
H12 channel at 1920 kbps(for 2.048
Mbps access).
BRI standardized as ITU-T I.420
PRI standardized as ITU-T I.421
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Basic Rate Interface Basic Rate Interface (BRI)
Two 64 Kbps B channels, one 16 Kbps D channel, and 48 Kbps worth of framing andsynchronization.
Available data bandwidth: 128 Kbps (2 x 64 Kbps)
User bandwidth: 144 Kbps (128 Kbps + a 16 Kbps D channel)
Total line capacity: 192 Kbps (144 Kbps + 48 Kbps framing)
Each B channel can be used for separate applications Such as Internet and Voice
Allows individual B channels to be aggregated together into aMultilink channel
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Inverse Multiplexing of B Channels
B (64 Kbps)
B (64 Kbps)
128 Kbps 128 Kbps
Inverse Multiplexers
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BRI Frame
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Primary Rate Interface
Primary Rate Interface (PRI) A PRI connection can assign various 64 Kbps channels to both ISDN and analog modem connections
B channels can be combined together to increase the aggregate communication speed
North America and JapanPRI service has 23 64 Kbps B channels, one 64 Kbps D channel, and 8Kbps of synchronization and framing for a total bit rate of up to 1.544 Mbps (same as T1)
Europe, Australia, and other parts of the worldPRI service has 30 64 Kbps B channels, one 64 Kbps Dchannel, and 64 Kbps of framing and synchronization for a total bit rate of up to 2.048 Mbps (same asE1)
Aggregate speed of PRI from all 23 B channels and the single D Channel is computed as follows: 23 * 64 + 64 + xx = 1.544 Mbps
Each B channel to be used for separate applications including voice, data andInternet
Multiple B channels can be Multilinked together
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Bonding of B Channels or BOD
(Bandwidth on Demand)
B (64 Kbps)
B (64 Kbps)
64- 128 Kbps 64- 128 Kbps
Inverse Multiplexers with Dynamic Bonding
Channel Bonded on Demand
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PRI Frame
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Benefits of ISDN The principle benefits of ISDN to the customer can be
expressed in terms ofcost savings and flexibility
Integrated voice and data means that the user does not haveto buy multiple services to meet multiple needs
Access charges to a single line only
Purchasing services based on actual needs
Product diversity, low price, and wide availability ofequipment.
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Bit Rates for Different Applications
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Conversational (or Interactive) Services Real time end to end information transfer
Can be bidirectional or Unidirectional.
Telephone, Tele-education, video conferencing etc.
Messaging Services Communication via storage units (mailbox etc)
Emails, Video Mails Retrieval Services
Provide users with capability to retrieve information stored elsewhere
High Resolution Image Retrieval, Document Retrieval Services.
Distributed Services Video and Audio transmission services.
Electronic Newspaper
Video Services: TV Program Distribution
Digital Video Library
B-ISDN Services
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B-ISDN Access Schemes
R i f Vi l
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Requirements of Virtual
Circuit Technology for B-ISDN
Performance Requirements
Support for flexible bandwidth (Variable Access Rate)
Limited Error Rate
Bit Error Rate < 10-7 to 10-10
Packet Loss Rate < 10-5 to 10-7
Limited Delay and Delay Variation (Jitter)
delay < 25 ms for telephony limited delay for real-time applications
limited delay-variation for voice communication
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ATM : Solution for B-ISDN
Suitable for both real-time and non real-time
applications
Suitable for both loss-sensitive and loss-insensitive
applications Seamless networking
LAN to MAN to WAN
to carry Voice, Telephony, Multimedia, Data traffic
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ATM Concepts
ATM is based on Virtual Circuit Technology
Virtual Circuits have many advantages over
Datagram and Circuit Switching
Similar to Circuit Switching, ATM uses signalingprotocol to establish Circuit before data
communication commences.
Unlike Circuit Switching, ATM is based on
Statistical Multiplexing (Similar to Packet
Switching)
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ATM Concepts
In order delivery of Cells due to Virtual circuits No error protection or flow control on a link by link basis
Links are assumed to be high quality with low bit error rate
Preventive actions: Proper resource allocation and queue
dimensioning to reduce packet loss End-to-End error protection and recovery.
Flow control by input rate control and capacityreservation
Congestion control : Avoid congestion Drop cells when congestion occurs
Fixed size packets called Cells size 53 bytes = 48 bytes payload + 5 bytes header
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Cell Size
Based on :
Transmission efficiency
End-to-end delay
Packetization delay
Transmission delay
Switching delay
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Why Small Cells ?
Overhead Delay
%Ove
rhead
Delay(m
s)
Payload (bytes)
0 20 60 80
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Cell Size: 32 bytes or 64 bytes?
Cell size of 32 and 64 bytes:
64 bytes cells have better transmission efficiency
32 bytes cells have small delay
both sizes are integer power of 2 Europe wanted 32 bytes size, US and Japan wanted
64 bytes size
Compromise: 48 bytes
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ATM Cell Format
Header :5 bytes Payload (Information) 48 bytes
GFC VPI VCI PT HEC
VPI VCI PT HEC
12 16 3 1 8 bits
CL
P
CLP
4 8 16 3 1 8 bits
at
UNI
atNNI
GFC : Generic Flow Control VPI : Virtual Path IdentifierVCI : Virtual Circuit Identifier PT : Payload TypeCLP : Cell Loss Priority HEC : Header error CheckUNI : User Network Interface NNI : Network-Network Interface
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ATM Concepts
Reduced header functionality
Provision for multiplexing, head-error detection /
correction and limited control and maintenance
function
No sequence number
No destination and source address
Header Payload
5 bytes 48 bytes
h
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Asynchronous
Multiplexing of Cells
Data
Video
Cells
Multiplexer
Packetizer
Digital Pipe
Voice
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Features of ATM
Simple queue management and Cell processing
due to the fixed size cells
Suitability for
delay sensitive and loss insensitive traffic delay insensitive and loss sensitive traffic
Quality of Service (QoS) class support
Switched Access Multiple Access Speeds (25 Mbps - 155 Mbps)
Easily Scalable
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ATM
Physical Layer
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ATM Physical Layer : Introduction
Physical medium to carry ATM cells
Two sub layers
Transmission convergence (TC) sub layer Physical Medium Dependent (PMD) sub layer
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PMD Sublayer
Physical Medium Dependent Sublayer
Fiber, Twisted pair, Coax, SONET, DS3
Functions
Bit timing Line coding
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Cell-Stream Physical Layer
cells are transmitted as a stream without any
regular framing
OAM cells are identified by VPI:0, VCI:9
Synchronization is achieved by TransmissionConvergence Sub-layer
Cell
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Physical Medium Choices
Plesiochronous Digital Hierarchy (PDH) based
Interfaces
uses existing transmission network infrastructure DS1(1.544Mbps), E1 (2.048 Mbps), E3 (34.368
Mbps) , DS3 (44.736 Mbps), E4 speeds
Cell Delineation and Synchronization with HEC
25.6 Mbps UTP
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SONET / SDH Based
Physical LayerSynchronous Optical Network: (SONET)
Synchronous Digital Hierarchy (SDH)
Lower speed ATM streams can be multiplexed overhigher speed SONET streams
SONET supports a hierarchy of digital signals with abasic rate of 51.84 Mbps
Based on Time Division Multiplexing
H4 octet in the path header indicates offset to theboundary of the first cell following H4
Parts of a cell may be carried over two successiveSONET frames
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SDH Physical Layer
for ATM The most common physical layer to transport
ATM cells in public networks
Standards are defined for encapsulation of ATMcells in SDH (SONET) frames
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SDH Physical Layer
for ATM
Total : 9 Rows * 270 Columns
STM-1/STS-3c : 9*260*8/125 sec=145.76 Mbpspayload
Path
Overhead
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Cell Delineation
Identifies cell boundaries in a cell stream
Physical layers may use their own mechanisms
SONET uses H4 pointer
CCITT Recommended HEC-based Algorithm Generic
Can be used with cell-stream when there is no framing
structure
Contrast with Marker based framing
C ll D li ti b
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Cell Delineation by
HEC Field
HUNT PRESYNC
SYNC
Incorrect HEC
correct HEC
bit-by-bitcheck
cell-by-cellcheck
consecutiveincorrect HEC
consecutivecorrect HEC
Initially HUNT state
Bit-by-bit check to match
computed HEC with thereceived HECCCITT recommendation < 7 < 6
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Cell Payload Scrambling
At source, scramble the cell payload
At receiver, descramble the cell payload
To increase the security and robustness
To protect against malicious users or unintendedsimulation of a correct HEC in the information field
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Summary
Wide range of Physical Interfaces are available :
DS1 to STS-12
ATM Cells can also be carried over (standards are
being defined) Satellite
Wireless
Two Sublayers : Convergence Sublayer andPhysical Medium Dependent sublayer
R f
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References
ITU-T ISDN standards, http://www.itu.int/rec/T-REC-I/en.
Sumit Kasera, ATM Networks-concepts and Protocols, 2e,
Tata McGraw Hill publications, ISBN-10: 0-07-058353-6.
Harry Perros, ATM Networks.
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