Wholesale: Products & Services

Synchronous Service Transport (SST) - V17.0

History Log

Product Description

Synchronous Service Transport (SST) is a point-to-point dedicated bandwidth Private Line that uses fiber optics and Synchronous Optical Network (SONET) technology for transmission.

Current SONET bandwidths offered are:

  • OC3 at 155.52 Megabit per second (Mbps)
  • OC12 at 622.08 Mbps
  • OC24 at 1.244 Gigabits per second (Gbps)
  • OC48 at 2.48832 Gbps
  • OC192 at 9.952 Gbps

Current Ethernet over Sonet (EoS) bandwidths offered are:

  • 10 Mbps
  • 50 Mbps
  • 100 Mbps
  • 150 Mbps
  • 300 Mbps
  • 450 Mbps
  • 600 Mbps
  • 1 Gbps

Synchronous Service Transport (SST) is a high capacity connection designed to transport large volumes of information.

Synchronous Service Transport (SST) satisfies the customers ever increasing bandwidth needs for voice, data and video transport. Customers' transport needs grow from Digital Signal Level 0 (DS0), to Digital Signal Level 1 (DS1) and to Digital Signal Level 3 (DS3), and the next logical step is SST which provides higher bandwidth SONET and Ethernet over SONET interfaces.


Synchronous Service Transport (SST) is available where facilities exist throughout CenturyLink QC.

Terms and Conditions

Terms and Conditions for Synchronous Service Transport (SST) are set forth in the CenturyLink Corporation Rates and Services Schedule (QC RSS No.1) and/or state tariffs located in Tariffs/Catalogs/Price Lists.

Technical Publications

Technical characteristics, including Network Channel /Network Channel Interface (NC/NCI™) codes, are described in Technical Publication, Synchronous Service Transport (Synchronous Optical Transport), 77346.


Rate Structure

Recurring charges are comprised of the following rate elements:

  • Central Office (CO) Node
  • Remote Central Office (RCO) Node (Grandparented)
  • CO Port
  • Remote Node
  • Remote Port
  • Ethernet Port
  • Ethernet Bandwidth
  • Central Office Connecting Channel
  • Port-to-Port Connecting Arrangement (Grandparented)
  • CO multiplexing options
  • OC96 Optical Drop Capability (Grandparented)
  • OC48 Electrical Drop Capability (Grandparented)
  • Virtual Tributary (VT) Mux Port

A non-recurring charge may or may not apply depending upon the element and the chosen length of the fixed period rate plan.

Additional rate structure information can be found in the Statement of Generally Available Terms and Conditions (SGAT), the access tariff, or your Interconnection Agreement.


Rates are available in Exhibit A or the specific rate sheet in your Interconnection Agreement.

Tariffs, Rates and Services Schedule (RSS), Regulations and Policies

Tariffs, RSS, regulations and policies are located in the interstate QC RSS No.1 or the state specific Tariffs/Catalogs/Price Lists.

Optional Features

Current Service

  • Loop Protection: The Central Office Node includes a working and protect pair from the Serving Wire Center (SWC) to the end-user. Whenever possible, the working and protect pair are separated by 25 feet or more. There are times when it is not economically feasible to provide this separation, or when the user wants some form of "insurance" or "rebate guarantee"; when this requirement exists, then Self-Healing Alternate Route Protection (SHARP) is available.
  • Channelized vs. Concatenated: SONET breaks the delivered signal into smaller units called Synchronous Transport Signals (STS). Each STS includes one Synchronous Payload Envelope (SPE)--slightly larger than a DS3-plus overhead used for maintenance, provisioning and alarming. When used in this manner, the SST service is said to be a "Channelized Optical Service". When the data to be transported cannot be broken into the smaller SPE size, the data can be interleaved into three STSs, or concatenated to '"look" like a single data stream. The three STS channels will still carry the Line and Section Overhead, but only the first STS will have Path Overhead. Channelization will normally be used with the Gather/Distribute application; either Channelization or Concatenation may be used for the Fat Pipe and Transport Facility applications. A customer may request an SST system which will provide Channelized Optical Service. Channelized Optical Service allows a customer to channelize the SST as needed and CenturyLink equipment will sense the channelization and provide the service accordingly. CenturyLink accomplishes this by using a feature called auto-concatenation. Auto-concatenation is limited to OC12 and OC48 systems, and may be requested by using appropriate NC codes delineated in CenturyLink Tech Pub 77346. Auto-concatenation is limited to services supported by specific existing network equipment, and is not available for all requests.
  • Specific Issues dealing with Concatenation: For most applications, the concatenated service terminates on a Router or an Asynchronous Transfer Mode (ATM) switch. Rarely are these SONET-compatible. The Router or ATM device will accept the SONET signal, but ignores the overhead. Without the overhead, the SONET system does not know when an error exists and when to switch to the protect side. Additionally, the Router and ATM devices usually do not have a port for the protect fiber. When route protection is required, the user must buy a Remote Node to interface to the SONET network. There will still be a single pair between the Remote Node and the Customer Premis Equipment (CPE); however, that is usually in the protected environment of the equipment room. If a user asks to terminate the concatenated signal in non-SONET equipment, then the Service Guarantees do not apply.
  • Ethernet circuits can ride an SST system via the use of Ethernet interfaces. CenturyLink supports 10 Mbps Ethernet, 100 Mbps Ethernet and 1Gbps, Mbps Ethernet interfaces. Ethernet Bandwidth speeds of 10Mbps, 50Mbps, 100Mbps, 150Mbps, 300Mbps, 450Mbps, 600Mbps and 1Gbps are available using the Ethernet Ports. Typically, an Ethernet circuit will have Ethernet interfaces at both ends of the circuit. However, CenturyLink can support circuits that have an Ethernet interface at one end and a SONET interface at the other end.


Features Benefits
  • With multiple capacities and interfaces, SST can be provisioned to meet most customer needs
  • Compatible
  • SST can transport most Private Line services, packet services, and Switched services
  • Reliable SONET has redundancy built in at every level, customer down time is almost nonexistent.
  • Although SST requires funding approval before a sale is made, it is rarely denied, and service can be installed throughout the CenturyLink QC.
  • Customer Appeal
  • Because of the wide range of bandwidths and interfaces, SST is popular in all areas of the Business and Wholesale Markets
  • Applications

    Synchronous Service Transport (SST) applications fit into three broad categories:

    • Gather/Distribute
    • Fat Pipe
    • Transport Facility


    Fat Pipe
    This is strictly a point-to-point transport of a large amount of data that exceeds the current capacities of DS3. An example of this is a large business doing design and manufacture in multiple locations, which needs a high-speed connection between the computer facilities.

    Transport Facility
    This application is unique to SST. Many of the new data protocols need a broadband delivery system, and SST becomes that transport mechanism.


    Product Prerequisites

    If you are an Interexchange Carrier (IXC), Internet & Data (ISP) or Wireless Service Provider (WSP) and have questions regarding your contract with CenturyLink, contact your Account Team / Sales Executives and Service Managers for more information.


    Prior to submitting your Access Service Request (ASR), contact your Account Team / Sales Executives and Service Managers to request a facilities check. If facilities are not available, then your CenturyLink Account Team representative will submit a Notification of Potential Sale. In the event a facility build is required, additional information regarding the equipment and space requirements at the customer premise are found in the Customer Premise Site Visit Requirements for Fiber Based Services.

    Contract Process: Interstate SST must be purchased under contract.


    Synchronous Service Transport (SST) service requests are submitted using the following Access Service Ordering Guidelines (ASOG) forms:

    • Access Service Request
    • Administrative
    • Transport Request
    • Service Address Location Information Form

    Field entry requirements are described in the Access Service Request (ASR) Forms.

    Contact your Account Team / Sales Executives and Service Managers for information.

    Ethernet Over SONET (EoS) and Channelized Optical Service

    CenturyLink requires that all order requests for Ethernet Over SONET (EoS) and Channelized Optical Service go through the AQCB pre-order process before you submit your service request. The AQCB inquiry is reviewed to ensure that the equipment deployed for your SONET system supports EoS or can automatically reconfigure Channelized Optical Service, and to determine any additional requirements that might be necessary to provide the service. Contact your CenturyLink account team to initiate the pre-order request; they will provide you with the AQCB inquiry number to include on your service request.

    If an AQCB ID number has been provided to you, that information must be populated into the VTA field after the contract term period: i.e. "36 AQCBID#".

    Provisioning and Installation

    On a new service where facilities do not exist, the time between sale and cut-over takes 90 to 180 days. New services where facilities exist should take between 20 and 90 days.

    Service for SST assumes using existing facilities. If facilities are not available, then a Business Case for funding is submitted for review and either granted or denied. SST has disclosed interfaces at the DS1, DS3, OC3, OC12 and OC48 level.

    Maintenance and Repair

    Contact your Account Team / Sales Executives and Service Managers for information.


    Carrier Access Billing System (CABS) billing is described in Billing Information - Carrier Access Billing System (CABS).

    Contact your Account Team / Sales Executives and Service Managers for information.


    View CenturyLink courses by clicking on Course Catalog .


    CenturyLink contact information is located in Wholesale Customer Contacts.


    Contact your Account Team / Sales Executives and Service Managers for information.

    Frequently Asked Questions (FAQs)

    1. What are concatenated services?
    Concatenation is a special way of formatting SONET's STSs (Optical or Electrical). STSs are given time slots next to each other, as opposed to being interleaved with other STSs. Also, multiple STSs share one header. The resulting increase in useable bandwidth is usually too small to be a driver of the purchase. However, customers need concatenated services for particular applications. OCn services without ports are not necessarily concatenated, but concatenated service cannot be "Channelized" using ports.

    2. Can CenturyLink connect SST with other systems?
    Yes. SST allows for many different protocols and is often purchased to connect with ATM or other systems. SST Service Guarantees apply only to the SONET portion of the total circuit.

    3. If a CenturyLink customer owns its own premise equipment and will not purchase CenturyLink's SST Remote Node, does SST still have a working and protect path?
    SST pricing includes a protect path. However, termination of the protect path, as well as SST service guarantees, depends on the customer's equipment and its configuration.

    4. Because SST comes with a protect path, when must the customer pay for SHARP?

    • The SHARP option is a service that includes a diversely routed protect path and Service Guarantees that are in addition to the underlying service (SST, DS3, DS1). Protect path SHARP can also be provided without a guarantee.
    • If the customer expects SHARP guarantees, CenturyLink must charge for SHARP and a Remote Node.
    • When separated facilities are not available, but are promised to the customer (must be built for the customer), CenturyLink must charge for that promise of diversely routed protection.
    • CenturyLink may provision SST's protect path over a separate route if facilities are available, or to satisfy Network initiatives. CenturyLink would not charge for SHARP, but the customer does not get the SHARP service, the guarantee of diverse routing, or the additional SHARP service guarantees.

    Last Update: January 30, 2017

    NC/NCI™ is a Trademark of Telcordia Technologies, Inc.