General Pseudowires

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)



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


Type 8100


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


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


Type 800

Type 8100


Type 800

Type 8100


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



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)

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



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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General Pseudowires