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General Pseudo-wires for TDM & Packet
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General Pseudo-wires for TDM & Packet
Tuan
Several Example Transmission Services
Core
MPLS PE
L2 VPNL2 VPNL3 VPNL3 VPN
AggregationIP/MPLSEthernet
BSC
EoMPLSL3
CES
VoD Servers
WiFi / WiMax Access Points
3G
Off Air
Bcast
BRAS
InternetInternet
ATM-BASED CESPart 1
Introduction
In the development of ATM (or Broadband) standards, AAL1 found its niche as a way to allow ATM to replace Time Division Multiplexing (TDM)
circuits at fixed rates such as 1.536 Mbps (T1) or 2.048 Mbps (E1).
The use of AAL1 was subsequently extended to allow replacement of 64K circuits (or traditional digital voice circuits),
providing a means to convey voice on ATM backbones instead of TDM infrastructures.
AAL1 was not initially developed to optimize Voice-over-ATM applications, but is considered a de facto standard in the absence of a real specification.
ATM Layers
ATM-PDU
ATM-SDU
ATM.DATA. Indication
ATM.DATA. Request
Indicate
Request
ATM Adaptation Layer (AAL)
ATM Layer
Physical layer (PHY)
ATM-SDU: ATM Service Data Unit (48 bytes of user data including ALL Header)
Higher layers
Application information
Video Data Voice
Applications
Convert to correct electrical or optical format
Forward (or receive) cell through network
Conversion to (from) ATM data types
ATM-PDU: ATM Process Data Unit (53 byte cells)
To (from) ATM switch
Role of AAL
Mask specifics of ATM transport from user application, e.g. maps the services from their native format into fixed length ATM cells and back (SAR -
segmentation and reassembly) takes care of jitter, error checking, removal of corrupted cells (CS convergence
sublayer; service specific) Expected that different applications will have different AALs (for simpler network
management, number is kept at a minimum)
Emulates PDH connections over ATM network: E1/DS1,
CES
Unstructured Structured
Base Nx64 Nx64 w/CAS
E1 E3 DS1 DS3 J1 E1 DS1 J1 E1 DS1 J1
Unstructured Service
The E1/DS1, E3/DS3, J1 stream (bit by bit) is encapsulated in the AAL1 frame and transmitted via ATM network
The internal structure of the PDH signal is not considered by the ATM network Any PDH framing can be supported Clock recovery methods
Synchronous Asynchronous
ATM networkCESIWF
ATM wirtual connection (CBR)
ATM interface
CESIWF
TDM device TDM device
Structured Service
Nx64 kbps channels can be transmisted via the ATM network Up to 30 in case of E1 interface can be transmited Up 24 in case of DS1 interface can be transmited
Clock recovery method Synchronous The PDH framing must comply with G.704 standard Two service types
Without Signalling With Channel Associated Signalling (w/ CAS )
ATM networkCESIWF
ATM wirtual connection (CBR)
ATM access interfaces
CESIWF
TDM device TDM device
CESIWF
TDM device
TDM interface( E1 ot T1)
TDM interface( E1 ot T1)
TDM interface( E1 ot T1)
AAL1 Frame
Checks for mis-sequencing (using a 3-bit counter) and Allows regeneration of the original clock timing at the receiver side (e.g. using a 4-bit
Residual Time Stamp transmitted over 8 cells).
47 bytes payload4-bitSN
4-bitsSNP
AAL1 frame
CSI sequence count CRC Parity
SN - sequence numberSNP - sequence number protectionCSI - Convergence sublayer indicator
AAL1 Protocol
AAL1 Frameseven
AAL1 Framesodd
0|0
SN frame number (0-7)SN|CSI CSI valid PTR fieldPTR field points at the beginning of TDM frame(in curent or next ATM cell)
1|a
2|0
3|b
4|1|PTR
5|c
6|0
7|d
abcd SRTS value
Next TDM frame
AAL2
(not yet agreed by ITU) checks for mis-sequencing and allows regeneration of the original clock timing at the receiver side.
The IT field indicates either the position of the segment in relation to a submitted message, or whether the segment contains timing or other information.
3 segment types are: BOM, COM and EOM. The LI field indicates the number of useful bytes in segment. FEC provides error detection, and some limited correction.
45 bytes payload4-bitSN
4-bits IT
AAL2 frame
SN - Sequence numberIT - Information typeLI - Length indicatorFEC - Forward error control
6-bitLI
10-bits FEC
AAL5
much simpler than AAL3/4. A bit in the cell header (PT) indicates when the last bit of the PDU is transmitted.
higher layer data frame
padpayload
5-byteheader
48-bytepayload
... 5-byteheaderup to 40-bytepayload
ATM cell
ATMlayer
convergencesub-layer
higherlayers
8 bytetrailer
CRClengthCPIUUUU- AAL layer user-to-user identifierCPI- common part identifier 1 1 2 4
Structured service with CAS
...
A B C D A B C DA B C D
Block structure N=3
First TDM frame
Second TDM Frame
Last TDM frame(from superframe)
Signalling block
Signalling bits for first TDM channel
Signalling bits for third TDM channel Signalling bits for second TDM channel
AAL1 pointer
First TDM channel
Second TDM channel
Third TDM channle
MPLS BASEDPart 2
General
The MPLS-based PSN Packets with RFC4553/Y.1413 Stds
DA SAType 8847
Tunnel Label
PW LabelControlWord
TDM Payload
DA SAType 8847
Transport Label
Interworking Label
ControlWord
TDM Payload
DA SAType 8847
Tunnel Label
VC LabelControlWord
TDM Payload
Type 8100
VLAN Tags (optional)
Type 8100
VLAN Tags (optional)
Type 8100
VLAN Tags (optional)
RTP (optional)
RTP (optional)
RTP (optional)
L2 Header
Tunnel & VC labels
Ethernet Frame Header Format Extensions
3-bit Priority1-bit CFI
SA (6-byte)
12-bit VLAN ID
Canonical Format Indicator (CFI)
DA (6-byte)Length/Type = 802.1Q
Tag Type (2-byte) Tag Control Information
(2-byte) Length/Type
(2-byte)
DA SAType 8847
Type 8100
VLAN Tags (optional)
MPLS Label as in the RFC3032
3-bit Exp. 1-bit SLabel ID 8-bit TTL
MPLS Label (Tunnel/Transport or VC/Interworking/PW Label)
IP BASEDPart 3
The IP-based PSN packets with RFC4553/Y.1453 Stds
DA SAIP
HeaderControl Word (CW)
TDM Payload
UDP Header
UDP Header(PW demultiplexing layer)
Common interworking indicators
TDM Payload
DA SAType 800
IP Header
L2TPv3 Header(PW demultiplexing layer)
Common interworking indicators
TDM Payload
DA SAType 8100
IP Header
VLAN Tags (optional)
Type 800
Type 8100
VLAN Tags (optional)
Type 800
Type 8100
VLAN Tags (optional)
RTP (optional)
RTP (optional)
RTP (optional)
IP & L2TPv3/UDP HDRs
L2 Header
Encapsulation format without the use of RTP (ITU-T Y.1453)
IP version IHL
IP ToS
Total Length
Identification
Flags
Fragment Offset
Time to Live (TTL)
Protocol
IP header checksum
Source IP address
Destination IP address
Source UDP port number
Destination UDP port number
UDP length
UDP checksum
18 45
1
2
3-4
5-6
67
Fragment Offset 7
8
9
10
11-12
13-16
17-20
21-22
23-24
25-26
27-28
Reserved L R M
FRAG Length
Sequence Number
Adapted Payload
29
30
31-32
33-N
ETHERNET BASEDPart 4
An Ethernet-based PSN with MEF-8 std
DA SAVLAN Tags (optional)
Ethertype 88d8
ECIDControlWord
TDM Payload
RTP (optional)
FCS
TDM PSEUDOWIRESPart 5
Generic PW Encapsulation
Payload Options: SAToP used for structure-agnostic transport of TDM bit-streams (DS1/E1, DS3/E3) TDMoIP - AAL1 used for preconfigured setup TDMoIP - AAL2 used for dynamic bandwidth CESoPSN used for structure-locked encapsulation HDLC used for CCS signaling (e.g., SS7).
PSN (MPLS, UDP/IP, L2TPv3/IP, Ethernet)
Optional RTP header
Control Word
Payload (SAToP , CESoPSN , HDLC, TDMoIP - AAL1, TDMoIP - AAL2)
SAToP PW Payload
Packet size must be defined during the the PW setup.
Payload size can be in the range of 40 1550 bytes
SAToP does not assume alignment to any underlying structure imposed by TDM framing
All SAToP implementations must support the following N:
E1 - 256 bytes
T1- 192 bytes
E3 and T3 1024 bytes
But may use any value for N
Optional Octet aligned T1 SAToP payload consists of a number of 25-byte sub frames, each sub frame
carrying 193 bits of TDM data and afterwards 7 bits of padding (zeros)
N native TDM Octets
Payload (N )CWPSN
CESoPSN Payload Basic NxDS0 service
N number of DSO channels in a frame (bundle).
L Packet payload size in bytes
L = m*N (m integer)
D - packetization latency (msec)
L = 8*N*D
Frame #mFrame #1 Frame #2
PayloadCWPSN
Timeslot 1 Timeslot 2 Timeslot N Timeslot 1 Timeslot 2 Timeslot N Timeslot 1 Timeslot 2 Timeslot N
TDM PW Control Word
0 0 0 0 / FORMID (4 b) Was used to indicate TDMoIP mode (AAL1, AAL1 - CAS, AAL2, HDLC) Ensures differentiation between IP and PW packets for MPLS PSNs (first nibble MUST be set to zero when PSN is
MPLS)
Flags (4 b) L bit (Local failure) R bit (Remote failure) M defect Modifier optional used to supplement the meaning of L bit
FRG in CESoPSN FRG bits MUST be used to indicate first, intermediate and last fragment 00 indicates that the entire (un-fragmented) payload is carried in a single packet 01 indicates the packet carrying the first fragment
10 indicates the packet carrying the last fragment 11 indicates a packet carrying an intermediate fragment
Length (6 b) used when packet may be padded by L2 Sequence Number (16 b) used to detect packet loss / mis-ordering
ReservedSet to Zero L R M FRG Length SN (Sequence Number)
540 6 8 10 16 31
PayloadCWPSN
TDMoIP AAL1 Payload Formats
C - Indicates if there is a pointer in the 2nd octet of the cell. When set, a pointer exists.
SN - sequence number CRC - Error cyclic redundancy code on C and SN P- Even parity bit on C, SN and CRC or the even byte parity LSB for the sequence number
octet (P format cells only)
E - (P format cells only) Even byte parity MSB for pointer octetNote: P format cells add a 7-bit pointer which delineates the boundaries of the encapsulated
data.
OR
C SN CRC P 47-OctetPayload Non-P Format
C SN CRC P E P Format (Structured AAL1 Only)
Payload (up to 30 AAL1 Subframes) CWPSN
Pointer 46-OctetPayload
Interworking between ATM CES and TDMoIP/MPLS
AAL1 PDU
AAL1 SAR
ATMIP/MPLS
AAL1 PDUIP/MPLSATM ATM ATMTDMoIP/MPLSATM CES SAR
IP/MPLS-based CES
SONET/SDHFramer
T1/J1/E1 FramersTU/VT MappersM13 MuxesT3 Framers
optics
AAL1 SAR/CESStructured & Unstructured
Preserve existing Layer 2 ATM Infrastructure
NP TM & Policing
IP/MPLSInterworking
Software Upgrade to IP/MPLS Infrastructure
TDM Framer
TDM Framer
TDM Framer
Sonet Framer
HDLC Engine
IMA Engine
AAL1 Engine
TDMoIP AAL2 Payload
CID Channel (timeslot) identifier unique for the connection. Values below 15 are reserved therefore there are 248 possible CID values
LI Length indicator, one less than the length of the payload in octets UUI User-to-user indication, the higher layer (application) identifier and counter HEC Header error control
CID LI UUI HEC Payload
Payload (up to 31 AAL2 Subframes) CWPSN
CID LI UUI HEC Payload
TDMoIP HDLC Payload
HDLC PDU is transported in its entirety excluding: HDLC flags CRC Bit/Byte stuffing
Zero Bit Deletion
Flags Data CRC 16 Flags
HDLC Frame in TDM
PayloadCWPSN
PACKET PSEUDOWIRESPart 6
HDLC PW
HDLC Pseudo-wire
HDLC PW Layering Structure:
HDLC Control Word:
PSN (MPLS, UDP/IP, Ethernet) PW Header
Control Word (optional)
HDLC Service Payload
ReservedSet to Zero 0 0
540 6 7 10 16 31
PayloadCWPSN
0 0
8
RES Length SN (Sequence Number)
HDLC Pseudo-wire (contd)
HDLC Payload:
HDLC PDU is transported in its entirety excluding: HDLC flags
FCS
Bit/Byte stuffing
Flag Data FCS Flags
PayloadCWPSN
ATM PW
ATM PW Layering Structure
PSN Transport Header Varies depending on particular tunneling technology. Used to transport encapsulated ATM information through packet network.
Pseudo-wire Header Identifies an ATM service on a tunnel. In the case of MPLS header is one or more MPLS labels.
ATM Control Word May contain length , sequence number needed to carry the service
PSN (MPLS, UDP/IP, Ethernet) PW Header
Control Word (optional)
ATM Service Payload
ATM N-to-1 Frame Control Word
First four bits must be set to zero Length defined as the length of the Layer 2 payload plus the length of the control word if less
than 64 bytes, the length field MUST be set to the packet's length. Otherwise the length field MUST be set to zero.
ReservedSet to Zero Flags RES Length SN (Sequence Number)
40 8 10 16 31
PayloadCWPSN
Multiple Cell Concatenation
PSN overhead can be reduced by concatenating multiple cells into the same packet
The number of cells in a packet can range from a single cell to 29 cells
For a single cell -> Cell of 53 bytes is forwarded to a 94 bytes frame size (overhead is ~ 70%)
For 29 cell -> 29 Cells of 1537 bytes are forwarded to a 1466 bytes frame size no overhead (since only 1 byte of the cell header is forwarded in VC mode)
Note: calculation is based on IP PSN type without VLAN, in VC mode
The number of cells in a packet is determined by one of the following option:
Each PW is configured manually with a limit on the number of cells it will carry in a single packet
Each PW can be set with a timeout mechanism between 100 5000000 uSec
In case AAL5 mode is set to enable (supported from version 1.0), a reception of end of AAL5 frame indication triggers a packet transmission.
ATM N-to-1 Data Encapsulation
PayloadCWPSN
VPI VCI | PTI | C
11 12 27 30
ATM Cell Payload (48 bytes)
0
VPI VCI | PTI | C ATM Cell Payload (48 bytes)
FR PW
Frame Relay PW Layering Structure
MPLS Tunnel Label (s) Label is used by MPLS LSRs to forward PW packet PW Label Identifies one PW (one LSP) assigned to a frame relay VC in one direction.
Together with the MPLS Tunnel label it forms the MPLS label Stack. Frame Relay Control Word Contains protocol control information
PSN (MPLS, UDP/IP, Ethernet) PW Header
Control Word (optional)
FR Service Payload
Frame Relay Control Word
F FECN (Forward Explicit Congestion Notification) bit is copied into F bit B BECN (Backward Explicit Congestion Notification) bit is copied into B bit D DE (Discard Eligibility ) bit is copied into the D bit C Command/ Response bit is copied into C bit
ReservedSet to Zero F B
540
6 7 10 16 31
PayloadCWPSN
D C
8
RES Length SN (Sequence Number)
Frame Relay Payload Format
Frame Relay PDU is transported in its entirety excluding: Flags FCS Bit/Byte stuffing
Flags Data FCS Flags
Frame Relay Frame
PayloadCWPSN
Thank You !
General Pseudo-wires for TDM & PacketSeveral Example Transmission ServicesATM-based CESIntroductionATM LayersRole of AALEmulates PDH connections over ATM network: E1/DS1, Unstructured ServiceStructured ServiceAAL1 FrameAAL1 ProtocolAAL2AAL5Structured service with CASMPLS basedGeneralThe MPLS-based PSN Packets with RFC4553/Y.1413 StdsEthernet Frame Header Format ExtensionsMPLS Label as in the RFC3032IP basedThe IP-based PSN packets with RFC4553/Y.1453 StdsEncapsulation format without the use of RTP (ITU-T Y.1453)Ethernet basedAn Ethernet-based PSN with MEF-8 stdTDM pseudowiresGeneric PW EncapsulationSAToP PW PayloadCESoPSN Payload Basic NxDS0 serviceTDM PW Control WordTDMoIP AAL1 Payload FormatsInterworking between ATM CES and TDMoIP/MPLSIP/MPLS-based CESTDMoIP AAL2 PayloadTDMoIP HDLC PayloadPacket pseudowiresHDLC PWHDLC Pseudo-wireHDLC Pseudo-wire (contd)ATM PWATM PW Layering StructureATM N-to-1 Frame Control WordMultiple Cell ConcatenationATM N-to-1 Data EncapsulationFR PWFrame Relay PW Layering StructureFrame Relay Control WordFrame Relay Payload FormatThank You !
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