Pseudowires Solutions

1
Pseudowires Solutions Advanced

• Presented by
• Merav Shenkar
• E-mail merav_s_at_rad.com

2
Agenda

• Introduction
• PW protocols for different services
• The PW Challenges
• PSN QoS
• Throughput Delay
• PW OAM- connectivity confirmation
• Fault propagation
• Clock

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PW Protocols for different Services
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TDM PW Services

• Unframed TDMoIP or SAToP over PSN
• E1/T1 line is a 2.048/1.544 Mbps bit stream
• Full transparency to the TDM traffic
• No Multi-Bundling
• End-to-End framing sync
• TDMoIP standard IETF ietf-pwe3-tdmoip
• SAToP standard draft-ietf-pwe3-satop.txt-
  Structure-Agnostic TDM over Packet

PBX
PBX
PW-GW
PW-GW
ETH
ETH
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TDM PW Services cont.

• Framed TDMoIP or CESoPSN
• Framed E1/T1
• Multi-Bundling
• TS0/Fbit Termination
• Local framing sync
• TDMoIP standard IETF ietf-pwe3-tdmoip
• CESoPSN draft-ietf-pwe3-cesopsn.txt -
  Structure-Aware TDM Circuit Emulation Service
  over PSN

PBX
PBX
PW-GW
PW-GW
ETH
ETH
Framing Sync
Framing Sync
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TDM PW Encapsulation Format
Tunnel Label (4)
MPLS
TDMCW (4)
IP
UDP
UDP Header (8)

• Overhead size
• IP 46 bytes
• MPLS 30 bytes
• UDP 50 bytes
• HDLC encapsulation is done according to IP/MPLS
  RFC 4618

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TDMoIP Payload Size

• TDMoIP Unframed/Framed payload size is between
  48-1440 bytesnx48 bytes (where n1,2,3,,30)
• CESoPSN SAToP payload size is between 32-512
  bytesaccording to the number of TS in a
  bundle(configurable)
• Payload configurationN Number of Time Slots
  in a bundle
• L Packet payload size in bytes
• L should be multiple integer (m) of number of
  Time Slots in the bundle (N)
• L m x N
• HDLCoIP mechanism monitors the data stream until
  a frame (data) is detected (flag)

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3G ATM Based Services

• ATMoPSN
• Mapping of ATM cells to packets
• Transparent backhaul of lub over packet based
  network
• End-to-End QoS is maintained
• 11 n1 mapping modes
• Standard draft-IETF-PWE3-atm-encap

Node B
ATMoPSN GW
ATMoPSN GW
RNC
n E1 IMA/ STM-1
PSN
ATM
Node B
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ATMoPSN
Cell Header
MPLS Type(2)
TunnelLabel(4)
PW Label (4)
ATM CW (3)
ETH(12)
ATM Payload
CRC(4)
ATM CW(3)
CellHeader

• Overhead size
• IP 45 bytes
• MPLS 29 bytes

Cell Header In VCC mode 1 byte per cell, In
VPC mode 3 bytes per cell Control word Has
a different format for each PW type (optional for
some PW types)
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Multiple Cells Concatenation Format

• ATM Payload size
• Up to 29 cells in a single frame
• Cell concatenation reduces overhead

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Pseudowire Standards
Application Standard IETF Product
TDM PW TDMoIP Ietf-pwe3-tdmoip IPmux-11 IPmux-14 IPmux-8/16 Gmux-2000 LA-110
TDM PW CESoPSN Ietf-pwe3-cesopsn ACE-3xxx LA-110 LA-130
TDM PW SAToP draft-ietf-pwe3-satop ACE-3xxx LA-110 LA-130
ATMoPSN ATM service transport ietf-pwe3-atm-encap ACE-3xxx LA-110 LA-130
HDLCoPSN HDLC transport RFC 4618 LA-110
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The PW Challenges
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PSN QoS
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QoS over PSN

• Challenge
• Traffic coming from the native services ports
  (ATM/TDM) contains a certain QoS which should be
  kept across the PSN
• Solution
• The PSN GW scheduler should decide which packet
  will be sent first towards the PSN network
• Convert the native service priority into
  priority over PSN

PSN GW
UBR
VCC
CBR
PSN
VCC
E1
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ETH Scheduling TX Queue Assignment

• User traffic priority should be also prioritized
  internally by the PW GW when transmitted to the
  PSN
• The internal prioritization will be done using
  ETH Tx queues with different priority levels
• The user should decide which service will get the
  highest priority within the PW-GW. for example
• Clock traffic highest priority Tx queue
• ETH data traffic lowest priority queue

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PSN QoS

• TDM/ATM QoS are mapped to PSN QoS
• Ethernet networks
• VLAN ID or VLAN priority
• VLAN can be optionally added to every
  encapsulation mode for CoS differentiation and
  QoS marking
• MPLS networks
• EXP bits of the MPLS label on both inner and
  outer label
• IP networks
• ToS/DSCP
• ToS bit marking per PW

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Throughput Delay
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Throughput Delay

• Challenge
• Encapsulating the native service payload over PSN
  transparently adds an overhead and delay
• Solution
• Provide a mechanism to control PW bandwidth
  utilization and delay

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PSN Bandwidth Utilization

• The output BW of the PW GW is governed by setting
  the PW frames payload size.
• Typically the PW overhead introduced by the PW
  protocol has a fixed size, while the payload size
  is user configurable.
• Increasing the payload size would reduce the
  ratio between the overhead and the frame size.
• The larger the payload size the better smaller
  the BW utilization over the PSN.

Header
Header
PW Frame
Payload
Payload
PW Frame
Payload
PW Frame
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Packetization Delay

• Packetization Delay (PD) The time it takes the
  PSN-GW to fill the payload with the incoming
  TDM/ATM traffic
• The larger the payload, the longer it will take
  to fill up and transmit the PW frame.
• The PD is the interval between two consecutive PW
  frames

Overhead
PW Frame
Overhead
PW Frame
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Triggers for Packet Transmission

• A PW frame will be sent towards the PSN under the
  following conditions
• TDMoIP/CESoPSN/SAToP
• The configurable payload size is filled with TDM
  frames.
• ATMoPSN
• Payload is filled with ATM cells (1-29 cells per
  frame)
• The timeout mechanism expires (between 100
  5000000 mSec)
• Detection of AAL5 SDU bit1 triggers packet
  transmission

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PD Vs. Bandwidth/PPS
5.5ms
5.1 Mbps
2.2 Mbps
0.2ms
This graph describes the BW consumption and PD
values for a full Unframed E1.
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TDMoIP Calculator
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CESoPSN SAToP Calculator
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ATMoPSN Calculator
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PW OAM-Connectivity Verification
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Connectivity Verification

• Challenge
• PSN networks have no inherent connectivity
  verification mechanism between two end points.
• Solution
• Provide path fault detection for an emulated PW
  over PSN
• Allow detecting faults occur on the remote end,
  in order to prevent IP/ETH network flooding
• Enable the use of redundancy

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TDM PWs

• TDM PWs generate constant traffic over the PSN
  (regardless of the TDM traffic)
• Therefore, there is no need for keep-alive
  messages during steady state
• During device failure condition, we need to stop
  traffic transmission in order to prevent PSN
  flooding.
• The PW GW will initiate a keep alive messages
  based on TDMoIP OAM protocol, just in case a
  failure was detected

5 OAM messages
PW
PSN
PW-GW
PW-GW
Wait 2 sec for an answer and then stop
transmission
TDMoIP OAM RADs proprietary Operation
Administration and Maintenance protocol
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ATM PWs

• Since ATM PWs based on a statistical network, a
  keep alive messages are required in order to
  verify the PW connectivity.
• PW-GWs sends BFD messages messages periodically
  between PW, based on VCCV-BFD (Bidirectional
  Forwarding Detection)

BFD
BFD
state down
PW
PSN
PW-GW
PW-GW
Complies with draft-ietf-pwe3-vccv
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Fault Propagation
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Fault Propagation

• Challenges
• Alarms on the legacy services network should be
  propagated over the PSN transparently.
• Impairments on the PSN network should be
  forwarded to the legacy services network.
• Solution Provide alarm forwarding mechanism
  between the native ATM/TDM network to the PSN and
  vise versa.

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PSN TDM/ATM

• PSN impairments (marked with ) can be
• TDM-PW Packet loss,Jitter buffer
  underflow/overflows
• ATM-PW ETH Link down or BFD control message is
  not received
• As a result the PW GW 2 will generate alarms on
  the Attachment Circuit (AC)
• TDM PW AIS/Trunk condition
• ATM PW AIS OAM
• In addition PW GW 2 will signal the remote PW GW
  1 on the local PSN fault

Trunk condition/ AIS
PW-GW 2
PW-GW 1
PSN
TDM/ATM CE
TDM/ATM CE
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TDM/ATM to PSN

• The local PW-GW enters a forward defects state
  when one of the below are detected on the TDM/ATM
  network
• LOS/ LOF/ AIS/ RDI
• The PW-GW 1 reports on local failure to the
  remote PW-GW 2
• PW GW 2 propagate the relevant alarm on the
  Attachment Circuit

PW-GW 2
PW-GW 1
PSN
TDM/ATM CE
TDM/ATM CE
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Synchronization and Clock Distribution
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Synchronization and Clock Distribution

• Challenge
• PSN networks are by nature asynchronous with
  statistical behavior, thus, can not provide the
  clock source.
• Solution
• Develop a mechanism which can recover synchronous
  clock over PSN networks.

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Synchronization and Clock Distribution
Clock distributed over the PSN
3G RNC
C.STM-1 ATM
E1/T1
PSN-GW
Node B
PSN-GW
Packet Switched Network
Clock
FE
GbE
2G BSC
E1/T1
TDM E1/T1
BTS

• Central unit distributes local clock source
  through the PSN
• Remote device recovers the clock and distributes
  to the radio stations
• Clock recovery performance
• Complies to G.823/4 Traffic interface G.8261
• Frequency Accuracy better than 16 ppb
• Hold over mechanism in case of clock stream
  failure

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thank you
for your attention
Merav Shenkar BroadBand Access team Email
merav_s_at_rad.com
www.rad.com