Telecommunication Networks and Systemswajda/3Y_TNaS/TNaS_L3_ATM_AAL_KW_2018_… ·...
Transcript of Telecommunication Networks and Systemswajda/3Y_TNaS/TNaS_L3_ATM_AAL_KW_2018_… ·...
Telecommunication
Networks and SystemsNetworks and Systems
AAL (ATM Adaptation Layer)
Krzysztof Wajda
Department of Telecommunications, AGH-USTNovember, 2018
Outline
• Motivation to introduce so many AAL versions
• Description of AAL1-AAL5
• Interworking between AAL and • Interworking between AAL and applications (also: higher layers)
Concepts:
• application requirements
• traffic classes
•
Lecture scope
• low-level support for service
differentiation
AAL LayerAAL Layer(ATM Adaptation layer)
This is an interim layer between higherlayers (applications) and ATM layer,
main functions: error detection and
AAL Layer
main functions: error detection and reaction, recognition of lost and wrongpackets, flow control, bit timing.
class A class B class C class D
Synchroniza-tion betweenterminals
required Not required
bitstream constant variable
Service classes
bitstream constant variable
Connectionmode
Connection-oriented Conn.less
AAL type 1 2 3/4 i 5 type 5
• Matching the size and features of application PDUs with transport features of ATM networks,
• Error correction,
• Synchronization.
CS functions
• Synchronization.
• Transformation of higher layers PDUs into SDU (and in opposite way)
n+1 layer PDUn+1
SAR functions
n layer
n-1 layer
SDUnPCIn
+
PDUn
SDUn-1
AAL1
• Transfer of data in CBR (connection-oriented CBR service),
• Decreasing the effect of cell jitter,
• Reaction for lost or out-of-order cells,
• Clock frequency recovery inside receiver,• Clock frequency recovery inside receiver,
• Monitoring and error recovery service for control field of AAL called SNP.
cell header SN SNP SAR-PDU payload
SAR-PDU header
SAR-PDU for AAL1
SAR-PDU
SN
SNP
= Sequence Number
= Sequence Number Protection
(4 bits)
(4 bits)
• The most significant bit of SN field is used for special purposes
• 3 other bits of SN field constitute cell counter modulo 8
SAR-PDU header
counter modulo 8
• Pole SNP field secures whole SAR-PDU header
SN-field SNP-field
SAR-PDU header for AAL1
SpecialPurposeIndication
Sequence NumberCount
CRCParityBit(Even)
AAL1 - summary
Single bits, bytes
47 bytes
Higher layers
Convergence sublayer
(CS)
Segmentation and
48 bytes
53 bytes
Segmentation and
reassembly sublayer
(SAR)
ATM layer
• Transfer of data in VBR (connection-oriented real-time service),
• CS-PDUs with variable length,
• For long time without precise specification for AAL2,
AAL2
for AAL2,
• For voice services, mobile systems,
• Error correction for audio and video services
• Synchronization of terminals by sending time stamps
CS sublayer functions for AAL2
sending time stamps
• Service for lost and out-of-sequence cells
cell header SN IT SAR-PDU payload
SAR-PDU header
SAR-PDU
SAR-PDU trailer
LI CRC
SAR-PDU structure for AAL2
SAR-PDU
SN = Sequence number
= Information Type
LI
CRC
= Length Indicator
= Cyclic Redundancy Check
IT
• Transfer of data in VBR (connection-oriented real-time service),
• Synchronization between sender and receiver is not necessary,
• Two modes of operation:
AAL3
• Two modes of operation: – framed mode, message mode,
– streaming mode,
• Monitoring and service of errors in AAL (CRC field in SAR-PDU).
AAL3/4 - summary
SN SNPSAR-PDU
Informacja użyteczna
nagłówek1-bajtowy
47 bajtów
b) Struktura danych podwarstwy SAR dla AAL typ 2
ST IT LI CRCSAR-PDU
Informacja użyteczna
nagłówek1-bajtowy
45 bajtów
a) Struktura danych podwarstwy SAR dla AAL typ 1
zakończenie2-bajtowe
AAL1 - 4 - summary
nagłówek1-bajtowy
ST SN MIDSAR-PDU
Informacja użyteczna
44 bajty
c) Struktura danych podwarstwy SAR dla AAL typ 3
d) Struktura danych podwarstwy SAR dla AAL typ 4
zakończenie2-bajtowe
ST SN ResSAR-PDU
Informacja użyteczna
nagłówek2-bajtowy
44 bajty zakończenie2-bajtowe
SN ( - 4 bity) - numer kolejnySNP ( - 4 bity) - ochrona SNIT ( - 4 bity) - typ informacjiLI ( - 6 bitów) - wskaźnik, długościCRC ( - 10 bitów) - ciąg kontrolny kodu cyklicznegoST ( - 2 bity) typ segmentuRes ( - 10 bitów) - rezerwaMID ( - 10 bitów) -identyfikator multipleksowania
Sequence NumberSequence Number Protection
Information TypeLength Indicator
Cyclic-Redundancy-CheckSegment TypeReservedMultiplexing IDentification
LI CRC
LI CRC
• Universal version of AAL, covering functions of AAL3/4 and more. VBR mode, connection-oriented, without synchronization,
AAL5 - summary
• Without numbering of subsequent cells,
• No retransmission,
• SEAL (Simple and Efficient Adaptation Layer),
ATM cell header SAR-PDU payload
SAR-PDU for AAL5
SAR-PDU
CS-PDU trailer
CRCLFCFPADUser data
CS-PDU
CS sublayer
Split of CS-PDU into cells
= Cyclic Redundancy CheckCRC
PAD = Pad field (0 to 47 bytes)
LF = Length Field (2 bytes)CF = Control Field (2 bytes)
(4 bytes)
ATM cell(AAL5)
SAR sublayer
ATM cell(AAL5)
ATM cell(AAL5)
ATM cell(AAL5)
PT
Summary
• Flexible but complicated concept of AAL,
• Extensive and explicit service specification,
• AAL5 mostly used.• AAL5 mostly used.
• ATM Forum standards• ITU-T Recommendations
• D. Ginsburg, „ATM. Solutions for enterprise networking”, Addison-Wesley,
Bibliography
enterprise networking”, Addison-Wesley, 1999• Lecture notes: http://www.kt.agh.edu.pl/~wajda/students/telecommunication-networks-and-
systems/
Thank you!