Communication Networks - Technische Universität Ilmenaumidas1.e-technik.tu-ilmenau.de/~webkn/Webdaten/Lehre/WS2019... · Packets may be called blocks, cells, datagrams, data units,

Communication Networks

Chapter 7 – Connection Oriented Packet Data Networks

Communication Networks - 7. Connection Oriented PDNs 236

Overview

1. Fundamentals of Connection-Oriented Packet Switching

2. X.25

a) X.21

b) High-Level Data Link Control (HDLC)

c) X.25 Layer 3

3. Frame Relay

4. Asynchronous Transfer Mode (ATM)


7.1 Fundamentals

Packet Switching

• Circuit switching was designed for voice• Packet switching was designed for data Information transmitted in small packets Packets contain user data and control info

user data may be part of a larger message control info includes routing (addressing) info

Packets are received, stored briefly (buffered) and passed on to the next node


Packet Switching


7.1 Fundamentals

AE

SwitchingSystem

End System(User) End System

(User)Application Data

Application Data

7.1 Fundamentals

Packet-Switched Networks

• In packet-switched networks, data is packetized prior to transmission Each packet is a group of bits organized in a predetermined structure Each packet contains data bits as well as additional overhead information to ensure

error-free transmission to intended recipients Packets may be called blocks, cells, datagrams, data units, or frames


Packet-Switching Advantages and Disadvantages

Advantages• Single link shared by multiple senders and

receivers• No occupied links• Different data rates at sender and

receiver possible• Establishment of packet-priority systems• Charging by the volume of data (number

of packets) transmitted rather than connection time

Disadvantages• Variable, unforeseeable transmission

delays caused by packet processing and packet queues at packet switches

• Variable packet sizes leading to longer packet processing times at packet switches

• Overhead data in packets leading to lower data transmission efficiency and throughput than in circuit-switched networks


7.1 Fundamentals

Virtual Circuit


7.1 Fundamentals

AE

SwitchingSystem

End System(User) End System

(User)3 2 1

Virtual Circuit vs. Datagram

Virtual circuit• network can provide sequencing and

error control• packets are forwarded more quickly• less reliable in case of link or switch

failure

Datagram• no call setup phase• more flexible• more fault-tolerant, but no QoS


7.1 Fundamentals

(Real) Circuit vs. Virtual Circuit

Real Circuit• Connection-oriented• All information use the same path ordered delivery

• Resources dedicated to single connection

• Delay only depending on propagation delay of physical signal

• No overhead

Virtual Circuit• Connection-oriented• All Packets use the same path ordered delivery

• Resources shared between different connections

• Delays due to traffic on the path and delay caused by forwarding nodes

• Overhead due to packet header


7.1 Fundamentals

Event Timing


7.1 Fundamentals

According to Stallings

CR

CRCR

CC

User Data

CR

CRCR

Pkt 1Pkt 2Pkt 3

Pkt 1Pkt 2Pkt 3

Pkt 1Pkt 2Pkt 3

Pkt 1Pkt 2Pkt 3

Pkt 1Pkt 2Pkt 3

Pkt 1Pkt 2Pkt 3

ACKACK

ACK

CCCC

CC

(a) Circuit Switching (b) Virtual Circuit Packet Switching (c) Datagram Packet Switching

7.2 X.25

ITU-T Recommendation X.25

• ITU-T standard for interface between host and packet switched network:„Interface between Data Terminal Equipment and Data Circuit Terminating Equipment for Terminals Operating in the Packet Mode on Public Data Network”

• almost universal on packet switched networks and packet switching in ISDN• defines three layers

Physical Link Packet


7.2 X.25

Characteristics of X.25

• Virtual connections

Permanent virtual connections

Switched virtual connections

Several virtual connections at the same time (up to 4096)

• End-to-end flow control

• According to the ISO/OSI Basic Reference Model:

Physical layer: X.21

Transmission of data frames: HDLC

Switching: X.25


X.25 & the OSI Reference Model


7.2 X.25

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Network Layer

Data Link Layer

Physical Layer

Packet Layer Protocol (PLP)

X.21 Layer: RS-232

High-Level Data Link Control (HDLC)

Link Access Procedure Balanced

X.25 Protocol Stack

ITU-T X.25 Recommendation


7.2 X.25

Packet Level Procedures

Physical Level Procedures

Frame Level Procedures

Layers 4-7End-to-End Connections

Layer 3X.25-3

Packet Interface

(Virtual Connections)

Layer 2HDLC (LAPB)

Data Link Interface

Layer 1X.21

Physical Interface

DTE DTE/DCE Interface DCE/Network

ISO/OSI layerson top of X.25

7.2 X.25

X.25 – Physical Layer

• Interface between station node link• Two ends are distinct Data Terminal Equipment DTE (user equipment) Data Circuit-terminating Equipment DCE (node)

• Physical layer specification is X.21• Can substitute alternative such as EIA-232


7.2 X.25

X.21 Interface

• X.21 covers the first three layers of the ISO/OSI BRM: Electrical and mechanical interface Error detection and

correction Circuit switching


DTE PIN CCITT-IDENTIFICATION DCEG/P Signal ground or common return

⇒ Ga DTE common return ⇒

⇐ Gb DCE common return ⇐

⇒ T Transmit ⇒

⇐ R Receive ⇐

⇒ C Control ⇒

⇐ I Indication ⇐

⇐ S Signal element timing ⇐

⇐ B Byte timing (frame timing) ⇐

7.2 X.25

X.25 – Data Link Layer

• Link Access Protocol Balanced (LAPB) Subset of High-Level Data Link Control (HDLC) Hybrid topology

• Reliable transfer of data over one link• Information sent as a sequence of frames


7.2 X.25

High-Level Data Link Control (HDLC)

• Bit-oriented, code-transparent Data Link Protocol• Half and full duplex mode• Point-to-point and point-to-multipoint configuration• Symmetrical and asymmetrical configuration• Piggybacking of acknowledgements• Flow control based on “Sliding Window”• Variants of HDLC:

IBM‘s SDLC (Synchronous Data Link Control) LAPB (Link Access Procedure, Balanced) as used by X.25 LAPD (ISDN, Link Access Procedure for the D-Channel) LLC (IEEE 802.2, Logical Link Control) PPP (Point-to-Point Protocol)


7.2 X.25

HDLC: Configurations

• Two types of stations: Primary station (sending commands); Secondary station (sending responses). Combined (hybrid) stations are possible, too,

• Information flow alternatives: Unbalanced control: Selecting

Primary station requests secondary station to receive data. Unbalanced control: Polling

Primary station requests secondary station to send data. Balanced control

Two hybrid station may send commands or responses.


HDLC: Point-to-Point Topology


7.2 X.25

HDLCHybridStation

HDLCHybridStation

Balanced link configuration

HDLC: Point-to-Multipoint Topology


7.2 X.25

HDLCPrimaryStation

HDLCSecondary

Station

HDLCSecondary

Station

HDLCSecondary

Station

Unbalanced link configuration

7.2 X.25

HDLC: Operating Modes

• Normal Response Mode (NRM) Unbalanced configuration in which only the primary terminal may initiate data transfer. The secondary terminal transmits data only in response to commands from the primary

terminal. The primary terminal polls the secondary terminal(s) to determine whether they have data to

transmit, and then selects one to transmit.• Asynchronous Response Mode (ARM)

Unbalanced configuration in which secondary terminals may transmit without permission from the primary terminal.

However, the primary terminal still retains responsibility for line initialization, error recovery, and logical disconnect.

• Asynchronous Balanced Mode (ABM) Balanced configuration in which either station may initiate the transmission.


7.2 X.25

HDLC: Frame Format

• HDLC frame fields include: Flag: used to delimit the beginning and end of a packet Address: specifies the address of the intended packet recipient or sender Control: transports packet type, sequence numbers and retransmission requests Frame check: used for error checking. CRC-16 or a 16-bit checksum may be used

with HDLC frames


Flag Address Control Frame CheckSequence FlagData

(Optional Octets)

8 bits 8 bits 8 bits 16 bits 8 bitsn bits (variable)

HDLC: Control Field


7.2 X.25

Flag Address Control Frame CheckSequence FlagData

(Optional Octets)

01111110 8 bits 8 bits 16 bits 01111110n bits (variable)

1 0 S SS Frame[S=Supervisory]P/F N(R)

1 1 M MU Frame[U=Unnumbered]P/F M M M

0I Frame[I=Information]P/FN(S) P/F N(R)

HDLC: I Frame and S Frame

I Frame

• Information Frame(both command or response) I (Information)

S Frame

• Supervisory Frame(both command or response)containing sequence number RR (Receive Ready) S S = 0 0 RNR (Receive not ready) S S = 0 1 REJ (Reject) S S = 1 0 SREJ (Selective Reject) S S = 1 1


7.2 X.25

0 N(S) P/F N(R) 1 0 S S P/F N(R)

HDLC: U Frame

Unnumbered Commands

• SNRM .............Set NRM• SARM ............. Set ARM• SABM ............. Set ABM• DISC ............... Disconnect• SNRME ...........Set extended NRM• SARME ....……..Set extended ARM• SABME ...………Set extended ABM• SIM .................Set Initialization Mode• UP .................. Unnumbered Poll• UI ................... Unnumbered Information• XID ................. Exchange Identification• RSET ...............Reset• TEST ............... Test

Unnumbered Responses

• UA .................. Unnumbered Acknowledgment• FRMR ............. Frame Reject• DM .................Disconnect Mode• RIM ................ Request Initialization Mode• RD .................. Request Disconnect• UI ................... Unnumbered Information• XID ................. Exchange Identification• TEST ............... Test


7.2 X.25

HDLC: MSC


7.2 X.25

Primary Station Secondary Station

Set NormalResponse Mode

Transfer of 3I Frames

Transfer of 7Additional

I FramesThen Awaiting

Acknowledgement

Data Transfer

Acknowledgment

Transfer of 2 I Framesincl. Acknowledgment

Ack without Data

Notation: <Command/Response, [N(S),] P/F, N(R)>half duplex mode,

Modulo 8, Window Size 7

7.2 X.25

X.25 – Packet Switching

• Provides logical connections (virtual circuit or virtual connection) between subscribers

• All data in this connection form a single stream between the end stations• All packets follow the same path through the network• Established permanently or on demand


7.2 X.25

Virtual Circuits

• Call setup packets Used to establish virtual circuits Identify the (currently) best path to the destination through the network

• Virtual circuit details stored in virtual circuit tables at packet switches• Logical channel = path followed by the packets in a virtual circuit Identified by logical channel number when created

• Two major types of virtual circuits: Switched virtual circuits (SVCs): similar to temporary circuit-switched connections Permanent virtual circuits (PVCs): similar to a leased, circuit-switched connection

Once a PVC is allocated, no call setup or call clearing is needed the logical circuit is permanently stored in virtual circuit tables


X.25: Packet• General Format Identifier (GFI)

to identify packet format• Logical Channel Identifier (LCI)

to identify the logical channel the packet belongs to

• Packet Controlto specify packet type and additional control information


7.2 X.25

Start of Frame (Flag)AddressControl

Logical ChannelPacket Control

Frame Check Sequence

End of Frame (Flag)

User Information

TransmissionDirection

According toHDLC-LAPB

According to X.25

According tohigher layersand application

According toHDLC-LAPB

LAPBControlHeader

X.25Packet Header

User Information

LAPBControl

Trailer

Time

GFI

7.2 X.25

X.25: Packet Header

• General Format Identifier, GFI: Bit 5 and 6 = Sequence numbering scheme: 01 = Modulo 8; 10 = Modulo 128 Bit 7 = Delivery Confirmation Bit Bit 8 = Data Qualifier Bit (for important control information) Bits 7 and 8 only relevant for special packet types

• Logical Channel Identifier, LCI: Divided into group and number (which is not important…) 212 = 4096 logical channels might be simultaneously active on one subscriber line

• Packet Type Identification: Currently 22 different packet types Packet for data exchange: 1st Bit in Octet 3 = 0 All other packets: 1st Bit in Octet 3 = 1


Octet 1

Octet 2

Octet 3

Bit 8 7 6 5 4 3 2 1GFI

Q D 0 1Logical Channel

Group (LCG)Logical Channel Number (LCN)

Packet Type Identification

X.25: Encapsulation


7.2 X.25

Data

DataPacketHeader

InformationControlAddressFlag FCS Flag

Bit stream according to X.21

Direction of Transmission

Layer 3

Layer 2

Layer 1

7.2 X.25

Error Correction

• Node-to-node (aka hop-to-hop or point-to-point) error detection and correction• Each packet is checked for errors at each packet switch before being forwarded to

the next hop on its path• If no errors are detected, an ACK is sent to the previous hop• If errors are detected, a NAK is sent to the previous hop which triggers

retransmission of the packet• Store-and-forward: packets are stored at switching nodes until positive

acknowledgements are received


7.2 X.25

X.25: Network Access Protocol

• Packet multiplexing on layer 3 Packets are delivered in statistical time multiplex in demand 4096 different layer 3 virtual connections use one physical link and one HDLC connection Virtual connections are differentiated by the Logical Channel Identifier

• Packet multiplexing at the interface between DCE and DTE:


Bidirectional Packet Flow

Packet belonging to logical channel “N”

DCE

1 1 4 3

2 1 3

N

Logical Channel Virtual Connection between DTE A and…

1 DTE B

2 DTE C

3 DTE D

4 DTE CA

7.2 X.25

X.25: Logical Channels and Identifiers

• Logical Channel Identifiers, LCIs LCIs group all packets that belong to a virtual X.25 connection on a network link Both directions use the same identifier LCIs are valid on a single link only The subscriber only knows the LCIs on the subscriber line LCIs are used for packet multiplexing

• On all links of a virtual connection, different LCIs are used• All LCIs are independent of each other


7.2 X.25

X25: Assignment of LCI

• Assignment of Logical Channel Identifiers: For each link independently During connection establishment by the initiating entity

• Call collision: Incoming Call Request and Outgoing Call Request using the same LCI Avoidance by a special LCI allocation method

• Logical Channel Identifiers are grouped for Permanent Virtual Circuits (PVC) for incoming only Switched Virtual Circuits (SVC) for outgoing only Switched Virtual Circuits (SVC) for incoming and outgoing Switched Virtual Circuits (SVC)


X.25: Allocation of LCIsIncoming Calls increase the LCIOutgoing Calls decrease the LCI


7.2 X.25

LCI Usage

0 not available

1 … High Number PVC for permanentvirtual circuits

… --

LIC (Low Number Incoming Calls)…

HIC (High Number Incoming Calls)

for incomingswitched virtualcircuits

… --

LTC (Low Number Two Way Calls)…

HTC (High Number Two Way Calls)

for both incomingand outgoingswitched virtual circuits

… --

LOC (Low Number Outgoing Calls)…

HOC (High Number Outgoing Calls)

for outgoingswitched virtualcircuits

… 4095 --

Currentlynot used

LCIs

7.2 X.25

X.25: Local Character of LCIs

• Complete addresses of sender and receiver only during connection setup

• Packets assigned to current virtual connection by an LCI valid only on single link

• No relation between the network addresses of the DTEs and the LCIs to be used

• A new virtual connection is assigned a currently unused (temporary) LCI several independent virtual connections between the same two DTEs possible


X.25 Network

1 2 3 52 3711 4095DTE C

... ... ...

1

49

28122813

4095

......

...

DTE A

1

7172

2177

4095

......

...

DTE

B

X.25: Packet „Call Request”


7.2 X.25

LCGGFI0 0 0 1

LCNPacket Type

0 0 0 0 1 0 1 1Address Length of

Called DTEAddress Length of

Calling DTE

Addresses of DTEs (calling, called) 0 0 0 0

Length of Performance Features0 0

Performance Features

Short information of calling user

Octet 1

2

3

4

8 7 6 5 4 3 2 1Bit

7.2 X.25

X.25: Connection Setup (1)

• Connection setup at the calling DTE: Selection of a currently unused LCI according to allocation rules Creation of a „Call Request“ packet:

Entry of LCIEntry of (complete) DTE addresses

− Destination Address and Source Address− Length of Address might go up to 15 digits

Entry of requested performance features, e.g.:− Reverse Charging Acceptance− Throughput Class− Transmission Rate

Short User Data


7.2 X.25

X.25: Connection Setup (2)

X.25 “Call Request“ packet encapsulated into an HDLC Information Frame Packet sent to the DCE to which the initiating DTE is connected DCE is forwarding the packet into the network which is responsible for delivering it to

the receiving DCE Receiving DCE is transmitting an X.25 „Incoming Call” Packet with an accordingly

selected LCI to the called DTE


7.2 X.25

X.25: Phases

• Three Phases: Connection Establishment Phase:

finished with the arrival of a „Call Connected” Packet at the calling DTE Data Phase:

Full duplex, bidirectional data transmission Disconnection Phase:

finished with the arrival of a „Clear Confirmation” Packets at the DTE that wanted to disconnect


Establishment PhaseEstablishment Phase

X.25: Message Sequence Chart

The arrival of a „Clear Confirmation” packet at the called entity might notnecessarily be the result of a „Clear Confirmation” packet of the calling entity


7.2 X.25

Interface of calling DTE/DCE Interface of called DTE/DCE

Call Request Packet IncomingCall Packet

Call Accepted PacketCallConnected Packet

Data Packet

Data Packet

Data Packet

Data Packet

Data PacketData Packet

ClearIndication Packet Clear Request Packet

Clear ConfirmationPacket

ClearConfirmation Packet Disconnection Phase

Data Phase

Disconnection Phase

Data Phase

7.2 X.25

X.25: Data Packet

• Sequence numbers either Modulo 8 or Modulo 128• Virtual connections always end-to-end: Sequence numbers for sequence guarantees and acknowledgements just like in HDLC Sequence numbers used end-to-end and not only on one link

• Control information of the data packet: P(S):

Packet Send Sequence Number

P(R): Packet Receive Sequence Number

M-Bit (More Data Bit): Several packets belong to the same context E.g. a segmented transport layer PDU


7.2 X.25

X.25: Data Packet

• Sequence numbers are Modulo 8:


Octet GFIQ D 0 1 LCG

LCN

P(R) M P(S) 0

Bit 8 7 6 5 4 3 2 1

User Information(e.g. transport layer PDU)

2

3

4

1

...

7.2 X.25

Issues with X.25

• Key features include: Call control packets: in band signaling Multiplexing of virtual circuits at layer 3 Both layers 2 and 3 include flow and error control

• Considerable overhead• Not appropriate for modern digital systems with high reliability


7.2 X.25

Important X.25 PDN Standards

X.25: defines interface between DTE and DCE in public data networksX.21: specifies the interface between user terminal equipment and

PDN packet-switching nodesX.3: specifies packet assembly/disassembly processesX.28: governs asynchronous dial-up access to PDNsX.29: governs synchronous dial-up access to PDNsX.75: defines the interface between different public packet-switching

networks, both domestic and internationalX.121: defines a global addressing scheme for PDNs


7.3 Frame Relay

Advancement: Frame Relay

• Influenced by: Requests for higher throughput / bandwidth Lower error rates on the physical medium supersedes extensive error detection and

correction mechanisms as in X.25

• Standardization: Initial proposals for the standardization of Frame Relay presented to the Consultative

Committee on International Telephone and Telegraph (CCITT) in 1984 ITU-T Standard I.122: „Packet Mode Bearer Services for ISDN”

In 1990, Cisco, Digital Equipment Corporation (DEC), Northern Telecom, and StrataCom formed a consortium to focus on Frame Relay technology development:“Frame Relay Specification with Extensions”

Establishment of Frame Relay Forum, which is now the Broadband Forum (http://www.broadband-forum.org/)


Frame Relay: Frame


7.3 Frame Relay

Flag Information FCS Flag

Frame Header

DLCI

8 7 6 5 4 3 2 1

C/REA

8 7 6 5 4 3 2 1 Bit

DLCI

FECNBECN

DE EADLCI = Data Link Connection IdentifierC/R = Command/Response FieldFECN = Forward Explicit Congestion NotificationBECN = Backward Explicit Congestion NotificationDE = Discard Eligibility IndicatorEA = Address Field Extension Bit

New HDLC Variant: LAPF (Link Access Procedure, Frame Mode)

Frame Relay: Topology


7.3 Frame Relay

Frame Relay-Network

A

BC

Router

Router

Router

Router

LAN 1

LAN 2

LAN 3

LAN 4

DLCI 3

7.3 Frame Relay

Frame Relay: Explicit Congestion Notification

Congestion avoidance policy:• Forward Explicit Congestion Notification FECN bit set to 1 to indicate that congestion was experienced in the direction

of the frame transmission, so it informs the destination that congestion has occurred

• Backwards Explicit Congestion Notification BECN bit set to 1 to indicate that congestion was experienced in the network

in the direction opposite of the frame transmission, so it informs the sender that congestion has occurred


Comparison Frame Relay – X.25


7.3 Frame Relay

X.25

Throughput slow(200 kbit/s – 2 Mbit/s)

Latency

JitterError Detection &

CorrectionFunctionality

high

No countermeasure

Special mechanisms(retransmission on layer 2 and 3)

complex

Frame Relayfast

(2Mbit/s typically, 45 Mbit/s max)low

(due to less overhead)

No countermeasure

Responsibility of higher layers

simple

• Frame Relay discards frames (in congestion or with wrong FCS) – higher layers have to correct this problem.• Isochronous transmission is not possible with both protocols.

Comparison Frame Relay –X.25Taken from „The Basic Guide toFrame Relay Networking“ (Frame Relay Forum, http://www.frforum.com)


7.3 Frame Relay

7.4 ATM

Broadband Applications According to ITU-T

• Interactive Services Conversational Services

e.g. video conferencing, interactive work on shared documents Messaging Services

e.g. transfer of multimedia messages (videos, high resolution pictures) Retrieval Services

e.g. video on demand, access to high resolution pictures• Distribution Services ... without User Individual Presentation Control (Broadcast Services)

e.g. television broadcast ... with User Individual Presentation Control

e.g. Broadband videotext


Traffic

STM – Synchronous Transfer Mode

Isochronous data traffic (constant data rate and constant latency)

Example: Narrowband-ISDN Circuit-switched communication

channels

ATM – Asynchronous Transfer Mode

Transport of small data packets(ATM cells)

Data rate and latency are variable, but guarantees are possible

Packet-switched communication(connection-oriented: virtual channels)


7.4 ATM

7.4 ATM

ATM: Principle

• Technology for backbone networks• Statistical (asynchronous, demand-driven) time multiplex (ATDM)• Cell header includes identifier of virtual connection• Mixing of different cell rates possible

Different throughput for different virtual connections• Support of variable data rates:

Guaranteed base rate Bursty traffic possible, if there are enough resources

• ATM cell:


Cell Header User Data

5 Octets 48 Octets

7.4 ATM

ATM: Multiplexing

• Advantages of small size of ATM cells: Easy Multiplexing of different streams Support for different bit rates Support of different services

• Easy processing of ATM cells: High data rates Complex end systems, network equipment can be kept simple


ATM ist a fundamental concept,on which different networks can be based

ConstantBit Rate

VariableBit Rate

155 Mbit/s

7.4 ATM

ATM: Cell Header (UNI)

• GFC (Generic Flow Control): local control functions such as identification of several terminals connected to the same ATM interface

• VPI, VCI (see next slide)• PT (Payload Type): type of data in the information field

(user data or control data)• CLP (Cell Loss Priority): determines whether a cell can

be preferentially deleted or not in case of a transmission bottleneck. Cells with CLP=0 have higher priority than cells with CLP=1.

• HEC (Header Error Control)

At NNI, the VPI field is 4 bits longer, as the GFC is not needed there


GFC VPI

VPI VCI

VCI

VCI PT CLP

HEC

1

2

3

4

5

[Byte]

Cell Header User Data

5 Octets 48 Octets

7.4 ATM

ATM: Virtual Channel and Virtual Connection

• Definition of two different connection types: Virtual Channel (VC):

unidirectional virtual connection: Virtual Path (VP):

Bundle of virtual channels with the same end points• Accordingly identified in the cell header:

Virtual Channel Identifier (VCI) Virtual Path Identifier (VPI)


VCVC

VC

... Transmission PathVP

VP

7.4 ATM

ATM: Traffic Engineering

• CBR (constant bit rate): a peak cell rate (PCR) is specified, which is constant, and a maximum jitter value

• VBR (variable bit rate):an average cell rate is specified, which can peak at a certain level for a maximum interval before being problematic (typical e.g. for MPEG streams)

• ABR (available bit rate):a minimum guaranteed rate is specified; if the rate cannot be sustained, the sender is notified

• UBR (unspecified bit rate):no guarantees, just best effort transmission


CBR

VBR

UBR

ABR

t

7.4 ATM

ATM and AAL

• ATM Layer: service-independent transport of ATM cells, multiplexing and demultiplexing• AAL Layer: ATM Adaptation Layer – support of different services


physicallayer

ATM

AAL

physicallayer

ATM

AAL

End System A End System B

ATM-Network

Service-dependentAAL connections

Service-independentATM connections

Application

7.4 ATM

ATM Networks and Broadband-ISDN

• ATM networks provide data transmission services for realtime applications for applications with variable bit rates

• Broadband-ISDN was realized as an ATM-networkin Germany: T-Net-ATM

• ATM is also applied in broadband data networks with high bit rates• ATM provides the infrastructure for IP networks

LANE (LAN Emulation) CIP (Classical IP over ATM) MPOA (Multi-Protocol over ATM)

• Standardization: ITU-T, ATM-Forum, IETF


ATM: Support of Voice and Data Services


7.4 ATM

ATM-SwitchATMSubnetwork

ATMAdaptationLayer

Services

Cells Cells Cells Cells

Packets PacketsBit Stream Bit Stream

B-ISDN Reference Model (I)

• 3-dimensional reference model• Three vertical planes

User Plane Control Plane Management Plane

• Three hierarchical Layers Physical Layer ATM Layer ATM Adaptation Layer

• Signaling information is transferred separately from the user information (Out-of-Band-Signalling)


7.4 ATM

Physical Layer

ATM Layer

ATM Adaptation Layer

Higher Layers

Management Plane

ControlPlane

UserPlane

Layer Managem

ent

Plane Managem

ent

PlanesLayers

B-ISDN Reference Model (II)


7.4 ATM

Physical layer

ATM layer

SignalingAAL AAL1 AAL2 AAL3/4

or AAL5

Signaling ClassA

ClassB

ClassC

ClassD

Controlplane

User plane

Management plane

Higherlayers

ATMadaptation layer

7.4 ATM

ATM Adaptation Layer AAL

• Different AAL for different service types• AAL0 : empty AAL = no adaptation required• AAL consists of sublayers Segmentation and Reassembly Sublayer (SAR-Sublayer) Convergence Sublayer (CS)

Common Part Convergence Sublayer (CPCS) Service Specific Convergence Sublayer (SSCS)


References

References

• Kasera, Sumit (2007): ATM Networks. Concepts and Protocols. New York: McGraw-Hill (McGraw-Hill Communications).

• Stallings, William; Case, Thomas (2012): Business Data Communications. Infrastructure, Networking and Security. 7th edition. Upper Saddle River, N.J., London: Prentice Hall; Pearson Education.

• Stallings, William (2014): Data and Computer Communications. 10th edition. Upper Saddle River, N.J.: Pearson.

• Stallings, William (1999): ISDN and Broadband ISDN with Frame Relay and ATM. 4th edition. Upper Saddle River,N.J.: Prentice Hall.

• Stamper, David A.; Case, Thomas (2003): Business Data Communications. 6th edition. Princeton, N.J.: Prentice Hall.


Documents

Communication Networks - Technische Universität Ilmenaumidas1.e-technik.tu-ilmenau.de/~webkn/Webdaten/Lehre/WS2019... · Packets may be called blocks, cells, datagrams, data units,