Download - SDH-Part IV (Next Generation)
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1EETAC 3B
SDH IV: NG-SDH3B. BACHELOR IN TELEMATICS ENGINEERING
Cristina Cervell i [email protected]
Contents2
Functional Architecture: network elements and topology
SDH Basics
SDH Transport Services
Protection Mechanisms
Synchronization
Next Generation SDH
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2SDH challenges
Fine granularity to accommodate all potential clients stream rates.
How to use bandwidth efficiently for both voice and data traffic.
New services and applications based on IP, mobile, multimedia, DVB,
SAN, Ethernet or VPN, demanding long haul transport.
SDH/SONET networks offer features for long-haul transport, that
include: Resiliency, Reliability, Scalability, Built-in protection and
Management.
The data packet transport (Ethernet, IP, DVB) was a challenge for
SDH.
This is because these services are connectionless, use statistical
multiplexing, and can be best-effort technologies.
This is the opposite of SDH which is predictable and based on time
division multiplexing (TDM).
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Next Generation SDH (NG-SDH)
The drive to SDH Next Generation development was:
The desire to find one simple encapsulation method that was capable of
accommodating any data packet protocols.
Secondly, the need to use bandwidth accurately.
Solution: A new adaptation protocol layer is required and a new
mapping mechanism for controlling the bandwidth use.
Next-generation SDH is the evolution and enhancement of existing SDH
networks.
It improves network efficiency and broadband service potential.
SDH Next Generation enables transporting data efficiently, without
needing to replace the installed equipment base.
The only change needed to update the network is to replace the edge
nodes.
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3Components of NG-SDH
VCAT: Virtual Concatenation (ITU-T G.707)
LCAS: Link Capacity Adjustment Scheme (ITU-T G.7042)
GFP: Generic Frame Procedure (ITU-T G.7041)
These functions are implemented on the new MSSP nodes which
are located at the edges of the network
They interact with the client data packets that are aggregated
over the SDH/SONET backplane that continues unchanged
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NG-SDH Architecture
Protocols Architecture
MSSP: Multi Service Switching Platform: include SDH multiplexing add-drop,
Ethernet ports, packets multiplexing and switching , WDM, switching TDM...
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G.7041
, G.7042G.707/783
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4Next Generation SDH Network Elements7
Multiservice Provisioning Platform (MSPP)
A Multiservice Provisioning Platform (MSPP) is basically
the result of legacy ADM and TDM interfaces, to a type of
access node that includes a set of:
Legacy TDM interfaces
Data interfaces, such as Ethernet, GE, Fibre Channel or DVB
NG SDH functionalities such as GFP, VCAT and LCAS
Optical interfaces from STM-0 to STM-64
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5Multiservice Transport Platform (MSTP)
A Multiservice Transport Platform (MSTP) is basically a
MSPP with DWDM functions to drop selected wavelengths
at a site that will provide higher aggregated capacity to
multiplex and to transport client signals
MSTP allows to integrate SDH, TDM and data services, with
efficient WDM transport and wavelength switching
Typically, MSTPs are installed in the metro core network
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Multiservice Switching Platform (MSSP)
A Multiservice Switching Platform (MSSP) is the NG equivalent
cross-connect, performing efficient traffic grooming and
switching at STM-N levels but also at VC level.
MSSP should support more than just data service, namely true
data services multiplexing and switching.
Large MSPP systems, which have switching and grooming capacity
of at least 300 Gbps.
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6Current MSPP: unifying MSPP & MSTP
Example: the ONS 15454SDH provides TDM solutions with interfaces such
as E1, E3 and DS3, data solutions with 10/100/1000 Ethernet solutions with
STM1 to STM64 optical transport bit rates in both gray and DWDM (ITU
compatible) wavelengths. Capabilities:
Aggregation and transport of services from E1 to STM64
Flexible architecture with multirate (SFP-based) Ethernet and optical modules
Metro Ethernet Forum (MEF) Certified ELINE and ELAN
10 Gb Ethernet modules
Flexible networking support including rings, linear point-to point, linear add/drop, star, and
hybrid topologies
Restoration choices: SNCP, 2-fiber and 4-fiber MS SPR,
1+1 APS, unprotected span, and Ciscos Path Protected Mesh Networking (PPMN)
Compact footprint for deployment flexibility
(3 can fit in a 2000mm ETSI rack/cabinet).
Carrier Class Reliability
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Components of NG-SDH
GFP: Generic Frame Procedure (ITU-T G.7041)
VCAT: Virtual Concatenation (ITU-T G.707)
LCAS: Link Capacity Adjustment Scheme (ITU-T G.7042)
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7GFP (Generic Framing Procedure)
GFP (Generic Frame Procedure) G.7041
A standard mechanism of generic multiplexing and framing for transparent
transport of user data over SDH or OTN (G.709) networks.
Valid for framing any protocol.
Two modes of encapsulation (Framed and Transparent).
Frame oriented GFP-F.
Code oriented GFP-T (Optimized for low-latency, constant bit-rate applications)
(e.g., SAN or digital video delivery).
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GFP
GFP-F
GFP-F entirely maps one complete client frame into a single GFP frame.
Idle packets are not transmitted resulting in more efficient transport.
GFP-F is used where the client signal is framed or packetized by the client protocol e.g., Ethernet, PPP/IP and HDLC-like protocols.
To perform the encapsulation process it is necessary to receive the complete client packet, therefore this procedure increases the latency. It is optimized for bandwidth efficiency at the expense of latency.
Specific mechanisms are required to transport each type of protocol.
GFP-T
Transparent GFP (GFP-T) is a protocol-independent encapsulation method in which all client code words are decoded and mapped into GFP frames.
The frames are transmitted immediately without waiting for the entire client data packet to be received.
Low latency.
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GFP Frame15
GFP-F Mode16
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9VCAT (Virtual Concatenation) G.707, G.783, Y.1322
Resolves the granularity problem of SDH adapting transmission speed to
user requirements by using virtual concatenation.
User data mapped to groups of virtual containers. Inverse multiplexing (G.805)
Optimizes the use of SDH network
Virtual Concatenation offers the user a granular bandwidth choice, optimizing
the use of network resources.
Better efficiency of the SDH network
Transparency in the SDH network
Individual VC are beared as traditional virtual containers.
Core nodes are transparent to VCAT.
End nodes must support VCAT functionalities.
Receiver node reassembles the user frame and must compensate the delay
differences of each path. Delay correction has a maximum limit of 512 ms.
Suitable for continental networks.
Terminology: VC-n-Xv with n = {4,3,12} and X according to provided
service
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Contiguous vs Virtual Concatenation18
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VCAT (Virtual Concatenation)
VCAT: Efficiency in data transmission
Service Rate Contiguous
Containers
Virtual Containers
Ethernet 10 Mbps VC-3 20,66% VC-12-5v 92%
Fast Ethernet 100 Mbps VC-4 66,77% VC-3-2v 100%
Gigabit Ethernet 1 Gbps VC-4-16c 41,73% VC-3-21v 98,43%
VC-4-7v 95,39%
ESCON 160 Mbps VC-4-4c 26,7% VC-3-4v 82,67%
Fibre Channel 850 Mbps VC-4-16c 35,47% VC-4-6v 94,6%
Fibre Channel 1.7 Gbps VC-4 16c 70,95% VC-4-12v 94,59%
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VCAT Efficiency
Example: Fast Ethernet (100 Mb/s)
Contiguous concatenation: VC-4
VC-4 (without POH): 260x9x8 bits, T=125 s 149.76Mb/s
Virtual concatenation: VC-3-2v
VC-3 (without POH): 84x9x8 bits, T=125 s 48.384 Mb/s
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VCAT (Virtual Concatenation)
Data Transport
Different containers of the same VCG (Virtual Container Group)
are independently transmitted
Frames arrive out of phase at the sink due to different paths.
Differential delay compensation required at sink.
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VCAT (Virtual Concatenation)
Differential delay is caused by:
geographically large ring with VC-ns from the same VC-n-Xv
routed around the ring in different directions, delay is mainly due
to fiber propagation (~5 s/km)
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Y VC-ns
(Y
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VCAT (Virtual Concatenation)
Differential delay is caused by:
networks with diversely routed path protected VC-ns, delay is
mainly due to fiber propagation (~5 s/km)
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End to end traffic: VC-n-Xv
Y VC-nson working path
(X-Y) VC-nson Protection path
Transportnetwork
Protectionpath
Working path
LCAS (Link Capacity Adjustment Scheme)
G.7042. Provides soft protection and a mechanism for load
sharing. Is an extension of virtual concatenation.
Designed to manage the bandwidth allocation of a VCAT path.
LCAS can add and remove members of a VCG that control a VCAT
channel. LCAS cannot adapt the size of the VCAT channel according
to the traffic pattern.
Dynamic bandwidth
Allows bandwidth changes during the service.
BW can be managed adding or dropping VC of VCG.
Protection and failure tolerance
Increases availability of VC from failures or changes.
Automatically decreases link capacity if a VC path has a failure,
increasing when repaired.
Protection mechanism applies efficiently to packet transmission.
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LCAS (Link Capacity Adjustment Scheme)25
Source to Sink messages:
Multi-Frame Indicator (MFI) keeps the multiframe
sequence.
Sequence Indicator (SQ) indicates members sequence to
reassemble correctly the client signal that was split and
sent through several paths.
Control (CTRL) protocol messages which can be fixed,
add, norm, eos, idle, and dnu.
Group Identification (GID) is a constant value for all
members of a VCG.
Sink to Source include:
Member Status (MST), which indicates to source each
member status: fail or OK.
Re-Sequence Acknowledge (RS-Ack) is an ack of
renumbering after a new eos member
LCAS Applications
VCAT bandwidth allocation. LCAS enables the resizing of the VCAT pipe
in use when it receives an order from the NMS to increase or decrease the
size.
Network Resilience. In the case of a partial failure of one path, LCAS
reconfigures the connection using the members still up and able to continue
carrying traffic.
Asymmetric Configurations. LCAS is a unidirectional protocol allowing the
provision of asymmetric bandwidth between two MSSP nodes to configure
asymmetric links
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Services over GFP27
NG SDH Application: EoSDH (EoS)
The Keys to Ethernet Services Success
Rapid return on investment. Recoup CAPEX in under a year, model deployed
leverages legacy transport infrastructure.
Legacy compatibility and interoperability. Leverage the installed base of
transport and packet services infrastructure
Bandwidth efficiency. Ethernet must be transported as efficiently as possible,
with options for statistical multiplexing and efficient mapping to SDH/SONET
transport bandwidth.
Resiliency. Solution with strict protection and restoration capabilities equivalent
to services carried over a SDH/SONET infrastructure.
Comparable profiles to existing Layer 2 services. Customers have expectations
of service quality, service guarantees, security and service flexibility that must
be matched by Ethernet.
End-to-end management, monitoring and provisioning.
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Ethernet Service provided with LCAS/VCAT29
Ethernet service
The MEF (Metro Ethernet Forum) has defined the following
three basic Ethernet connectivity services within and between
metro areas:
E-Line (point-to-point)
E-LAN (multipoint-to-multipoint)
E-Tree (rooted-multipoint)
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E-Line
Ethernet Private Line (EPL): Provides dedicated bandwidth and
guaranteed throughput across a point-to-point connection. EPL is analogous
to a "circuit-like service such as an E1 service which is permanently
reserved and dedicated for an enterprise customer.
Ethernet Virtual Private Line services (EVPL): Dedicated point-to-point
VPN service connecting two customer sites over a shared bandwidth
supporting statistical multiplexing and oversubscription. It takes advantage
of Ethernet's lower-cost bandwidth to share resources amongst multiple
customers. The EVPL service is aware of service attributes and can offer
different QoS (delay, jitter, and frame loss), thus introducing a service
differentiation offering to customers.
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EPL EVPL
E-LAN
Ethernet Private LAN (EPLAN): An E-LAN service that provides
multipoint connectivity over dedicated bandwidth. This service
provides high-speed LAN interconnection amongst multiple customer
sites which appear to be linked by a LAN segment.
Ethernet Virtual Private LAN (EVPLAN): Provides a packet-based
service that delivers secure any-to-any connectivity across a shared
infrastructure supporting statistical multiplexing and oversubscription.
EVPLAN service supports multipoint-to-multipoint connectivity and
point-to-multipoint service.
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EPLAN and EVPLAN 3 connectivity examples33
Mesh connectivityTraffic hauled to centralized
switching point(s)
Switching at network edge (hub and spoke)
Ethernet service
The following metro Ethernet service delivery technologies can
be used:
Ethernet over SONET/SDH (EoS)
Ethernet Leased Line over SONET/SDH (EoS LL)
Switched Ethernet (Layer 2) over SONET/SDH (SW EoS)
Ethernet over DWDM (EoWDM)
Ethernet over Fiber (EoF)/Ethernet transport
Resilient Packet Rings (RPR)
Provider Backbone Transport (PBT)/PBB-TE
Ethernet over MPLS (EoMPLS)/T-MPLS
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Ethernet Leased Line over SONET/SDH
Typically used for Ethernet private line applications, Ethernet over
SONET/SDH.
EPL is a point-to-point service with a native Ethernet interface. EPL was
developed as a packet data transport solution which would allow the
use of the existing deployed SONET/SDH infrastructure.
Benefits of Ethernet over SONET/SDH
Highest possible security available; using separate VC for service
delivery
High availability; relay on SDH protection and enhanced by LCAS
functionality
End-to-end simple provisioning
High granularity; guaranteed service with a minimum of 2M bandwidth
steps
Relatively inexpensive cost as add-on to existing optical networks with
spare capacity in MSPP products
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Ethernet Leased Line over SONET/SDH
Ethernet Private Line (EPL)
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Layered Architecture for EPL services37
Service Port
Switched Ethernet (Layer 2) over SONET/SDH
Switched Ethernet over SDH shares an SDH connection amongst several
customers. To ensure service quality, each customer is assigned a VLAN tag
and specific QoS through:
A committed information rate (CIR) for guaranteed bandwidth.
A peak information rate (PIR) for traffic bursts.
Traffic metering, shaping, and scheduling.
Main characteristics of Ethernet virtual services
Enables customer separation based on a logical frame identifier (VLAN tags),
and also supports Double Tagging/Q-in-Q (C-Tag and S-Tag). Double tagging
improves the scalability of the limited range of possible VLAN instances (4096).
Provides connectivity with a frame infrastructure that is shared between a
number of customers.
Performs bandwidth allocation per customer, not as a fixed allocation.
Supports statistical multiplexing of the bandwidth amongst customers.
Uses Spanning Tree Protocols to prevent loops (xSTP).
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Switched Ethernet (Layer 2) over SONET/SDH
The most basic Ethernet virtual service multiplexes multiple customer flows
within a designated infrastructure. Such Ethernet services can be referred to
as Ethernet Virtual Private Line (EVPL) or Ethernet Virtual LAN services
(EVPLAN).
Benefits of Switched Ethernet over SDH
Allows leveraging the existing network infrastructure while keeping capital
investment at a minimum and produces additional revenue-generating
opportunities.
Secures service by separate customer traffic using VLAN.
QoS support for real-time and premium services using basic CoS service
differentiation.
Resilience using xSTP restoration mechanism which provides greater than 50
msec, or relay on SDH protection and LCAS functionality in less than 50 msec.
Efficient bandwidth usage with its statistical multiplexing benefits allowing one
port to connect to multiple (up to 4,096) customer ports.
Cost-effective Provider Bridge Ethernet over SDH/SONET in point-to-point, ring,
hub-and-spoke, and mesh configurations.
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Switched Ethernet (Layer 2) over SONET/SDH40
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Recomendations ITU over SDH
G.810 Definitions and Terminology for Synchronisation
Networks.
G.811 Timing Characteristics of Primary Reference Clocks.
G.812 Timing Requeriments of Slave Clocks Suitable for Use as
Node Clocks in Synchronization Networks.
G.813 Timing Characteristics of SHD Equipment Slave Clocks.
G.825 The control of Jitter and Wander within Digital
Networks which are based on the Synchronous Digital
Hierarchy.
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Recomendations ITU over SDH
G.832 Transport of SDH Elements on PDH Networks: Frame
and Multiplexing Structures. Interoperability PDH-SDH.
G.841 Types and Characteristics of SDH Network Protection
Architectures y G.842 Interworking of SDH Network
Protection Architectures.
G.703 Physical/Electrical Characteristics of Hierarchical Digital
Interfaces.
G. 957 Optical Interfaces Of Equipments and Systems Relating
to the SDH.
G.958 Digital Line Systems Based on the SDH for Use on
Optical Fibre Cables.
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Bibliography
Gilbert Held, High Speed Digital Transmission Networking, Ed. John Wiley &Sons, 1999.
W. J. Goralski, Sonet, Ed. MacGraw-Hill, 1997.
U. Black, S. Waters, SONET & T1: Architectures for Digital Transport Networks, Ed. Prentice Hall, 1997.
G. Dobrowski, Donald W. Grise, ATM and Sonet Basics, APDG Publising, 2001.
D. Minoli, P. Johnson, E. Minoli, SONET-Based Metro Area Networks. E. MacGraw-Hill, 2002.
W. Goralski, SONET/SDH Third Edition. Ed. McGraw-Hill, 2002.
J. Philippe Vasseur, Mario Pickavet, Piet Demeester. Network Recovery : Protection and Restoration of Optical, SONET-SDH, IP, and MPLS. The Morgan Kaufmann Series in Networking. 2004.
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Additional slides44
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LCAS (Link Capacity Adjustment Scheme)
Protocol using byte H4
2ms
125s
LCAS (Link Capacity Adjustment Scheme)
Protocol using byte K4