future of sdh

SDH Future & Industry Trends SDH Strengths & Weaknesses Strengths Weaknesses

Highly reliable (50ms restoration time) Complex

Variety of standardized rates & well-organized set of standards

Rates are fixed & large multiples of the basic rate (STM-1,4,16,64)

Fully supported long-haul needs Not very adaptive to packet switching

Comprehensive management Multiplexing is not dynamic

Supports multiplexing of lower rates data streams (T1, E1)

Adds cost and management overhead to the physical layer (vs. IPoDWDM)

Voice/data agnostic Additional footprint at the CO

Additional equipment (vs. IPoDWDM)

Advancements in NG-SDH

Advancements in NG-SDH •  Conventional SDH/SONET has several limitations:

1.  Traffic carried in streams with fixed speeds (e.g. STM-16, E4 etc.) 2.  Lack of built in capability to dynamically alter speed ofstreams

according to usage

•  SDH/SONET originally designed for circuit-switched voice

traffic:

1.  Unsuitable for asynchronous packet-switched bursty data traffic 2.  Four-fold capacity increase increments (e.g. from STM-1 to STM-4) Þ

Inflexible provision of capacity to users

•  Facing competition from data-centric standards (e.g. Ethernet)


Carrier choices: § Invest in a new parallel data-centric network infrastructure? OR § … maximize reuse of existing SDH/SONET networks • Tried and tested • Excellent management features • Resilient design configurations (e.g. SNCP rings) • Reduce capital expenditure • Extending network’s lifespan


•  With datagram applications explosion allowed by IP and other packet switch technologies, solutions for the transport of data over SDH systems were developed to enable flexible and reliable data transport over SDH.

•  The techniques involved in providing these solution are:

1.  Generic Framing Procedure (GFP) 2.  Virtual Concatenation (VCAT) 3.  Link Capacity Adjustment Scheme (LCAS)

•  These upgrades only needed at source and destination terminal equipment of required service:

–  Intermediate equipment do not need to be aware and can

interoperate with upgraded equipment –  Enables operators to make only partial network upgrades on

as-needed basis


Generic Framing Procedure (GFP) •  GFP is a framing procedure that allows mapping of octet-aligned,

variable- length payloads from higher-layer client signals into octet-synchronous paths over a transport network like SDH/SONET. The client signals can be protocol data unit (PDU) oriented (like IP/PPP or Ethernet Media Access Control) or can be block-code oriented (like fiber channel).

•  There are two modes of GFP: Framed Generic Framing GFP and Transparent GFP.


Virtual concatenation (VCAT) •  Virtual concatenation is a mechanism that provides flexible

and effective use of SDH payload. originally, SDH was first defined as a voice-optimized digital hierarchy for the transport of 64-kb/s-based TDM service. The capacity of payload was rigidly defined for PDH service accommodation.

•  VCAT breaks the limitation incurred by this rigidity via the

definition of payloads with flexible bandwidth. It “virtually” concatenates several payloads to provide a payload with flexible bandwidth, appropriate for data service accommodation such as Ethernet.


VCAT: The GbE over SDH case –  According to the conventional SDH specifications, VC-4-16c must

be used to accommodate GbE signals at full speed. Since VC-4-16c capacity is 2.4 Gb/s, however, 1.4 Gb/s capacity is wasted.

–  If VC-4-4c is used to avoid bandwidth wastage, full-speed accommodation cannot be achieved. GbE could be suitably accommodated if a contiguously concatenated payload VC-4-7c with 1.05 Gb/s capacity were defined.


VCAT: The GbE over SDH case

–  If VC-4-4c is used, every node in the network would need to handle this newly defined VC-4-7c signal, which would not be practical because such a concatenated payload is not supported by legacy SDH equipment.

–  Using VCAT, seven independent VC-4 payloads are virtually

concatenated to provide VC-4-7v payload (suffix v stands for virtual) with 1.05 Gb/s bandwidth, which is perfectly suitable for GbE accommodation.


VCAT: The GbE over SDH case –  There is no need to add VCAT capability to every node of a SDH

network as the implementation of VCAT is limited to multiplexing nodes.

–  There is no restriction on which STM-N signals should be used.

The seven payloads may or may not reside in the same STM-N contiguously, or may even reside at different STM-N interfaces. Within the network, they are treated as seven separate and independent VC-4 payloads.

Advancements in NG-SDH VCAT: The GbE over SDH case

–  The individual containers can follow different paths in the network, with different delays, and they need to be reassembled at the end points, taking into account the different path delays.

•  Another feature of VCAT provides a way to partition SONET/SDH

bandwidth into several sub-rates, each of which being capable of accommodating different services.

Advancements in NG-SDH Link Capacity Adjustment Scheme (LCAS) •  LCAS is a method to dynamically increase or decrease the bandwidth

of virtual concatenated containers. •  Note that VCAT can be used without LCAS, but LCAS only possible

with VCGs, therefore requires VCAT

•  LCAS allows carriers to assign and utilize the bandwidth of the virtual concatenated group (VCG) more efficiently and flexibly in a hitless (i.e. w/o service interruption) manner. This brings bandwidth-on-demand capability for data clients like Ethernet when mapped into TDM containers to provision:

- Time-of-day demands - Special events - Pay-as-you-grow - Introducing new service granularities

Advancements in NG-SDH Link Capacity Adjustment Scheme (LCAS) •  LCAS enables removal of failed VCG members and eventual

member reinstatement without affecting services •  LCAS could be used to enhance other functions such as:

–  Load Sharing –  Congestion avoidance –  QoS differentiation

Advancements in NG-SDH Overview

SDH Future & Industry Trends Conclusion

•  SDH is not the most efficient means to transport data traffic. Enterprises and service providers are or will be moving away from SDH for their regular data applications.

•  The industry trends for data network are moving from multiple layers (IP over ATM over SDH over Optical to IP over Optical) to two layers network. The IP over optical network provides higher speed and lower complexity and overhead, hence, lower cost.

•  Today’s data network in Saudi Aramco has overlapping functionality among all layers. Multiplexing, protection and management occur at every layer, hence, complexity, wasted bandwidth, and trouble shooting time are increased.

•  The current evolution of data networking to provide voice (VoIP), data, and video services over high bit rates (thru 10GbE) QoS enabled-network (using MPLS) in a highly resilient and long-haul enabled optical environment (using advanced DWDM technology) is overcoming the shortcomings of the traditional Ethernet including: limited manageability options, slow restoration times (in seconds), and shorter-reach distances with increasing bit rates.

SDH Future & Industry Trends

Higher Speed, Lower cost, complexity and overhead

IP Over ATM

ATM

SDH

IP

Fiber/DWDM

Multiplexing, protection and management at every layer

IP Over SDH

IP

SDH

Fiber/DWDM

IP Over Optical

IP

Fiber/DWDM

SDH Future & Industry Trends • As shown below, the network layers are becoming more integrated with the improvement of VoIP, IP, DWDM, and Ethernet Technologies, which will gradually lead to abandoning the services of SDH and ATM.

Migration of Services

Transition Plan to IP Network

1/10GE / DWDM

CAMPUS LAN

Video Conference

SCADA, Voice, Radio

Optical Switches

Soft Switch

Target IT Network IP Based

CAMPUS LAN

Access Layer

SDH

VSAT

IMUX/DACS

10Gbps SDH/DWDM

Video Conference

DCO

SEC/STC

INTERNET

NETWORK MANAGEME

NT

ATM SWITCH

10Gbps SDH/DWDM

622Mbps & 2.4Gbps SDH (1+1)

Digital M/W

Data, Voice

Data, Voice, Radio

OTN

Backbone Router

SCADA

Data

Telephone

Radio

2.4Gbps or less SDH Backbone

Layer

High-Speed Backbone Layer

Current IT Network TDM Based

future of sdh

Documents