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MToP in the RAN

Mobile Transport over Pseudowires

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Introduction

Q. What is Mobile Transport over Pseudowires (MToP)?
A. Mobile Transport over Pwsudowires is the Cisco® solution for converged packet-based Radio Access Network (RAN) aggregation between edge aggregation sites and the network core. Existing time-division multiplexing (TDM) backhaul cannot cost-effectively grow to allow advanced data and video services to be delivered to aggregation and preaggregation sites. MToP uses standards-based Multiprotocol Label Switching (MPLS) technology to extend the packet-based core already deployed at many carriers to the edge of the network. This provides a solution that is flexible and cost-effective and allows operators to evolve to a packet-based network while still maintaining the easy operational familiarity and resiliency of the existing TDM-based network.
Q. How is MToP different from the Cisco Optimized RAN (RAN-O) solution?
A. MToP provides flexible, standards-based transport over any MPLS infrastructure for TDM-based circuits. This allows operators to evolve to a packet-based network, allowing for flexible bandwidth provisioning and new service offerings, while reducing cost in expensive TDM equipment.

MToP and RAN-O are both IP-based but operate differently. Cisco IP RAN Optimization delivers IP connectivity for Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications Service (UMTS) RAN backhaul links by examining the traffic and minimizing and aggregating bandwidth for GSM Abis and the UMTS Terrestrial Radio Access Network (UTRAN) Iub interfaces. RAN-O also provides an operator with the ability to easily use alternative forms of backhaul for data services, such as DSL or WiMAX, while helping ensure that voice traffic is carried over T1/E1 lines. GSM traffic is optimized up to 50 percent, and UMTS traffic is compressed 15 to 90 percent, so operators can potentially transport the same level of GSM and/or UMTS traffic with half the number of T1/E1 links

RAN-O and MToP are complementary solutions that can be used independently or together as desired to maximize RAN backhaul efficiency.

Q. What new hardware is being introduced to provide MToP?
A. Cisco is adding two new multiservice shared port adapters (SPAs) to our I-Flex portfolio (SPA interface processors [SIPs] and SPAs). The following interfaces are being introduced:

• 24-port channelized T1/E1/J1

• 1-port channelized OC3/STM1

These SPAs provide bit-transparent data transport that is completely protocol-independent. This allows network administrators to make use of their existing IP/MPLS network to provide leased-line emulation services or to carry data streams or protocols that do not meet the format requirements of other multiservice platform interfaces. In addition, these SPAs can be used for low-speed ATM services, including IMThe SPAs are the first Cisco router interfaces designed to meet the emerging standards for Circuit Emulation Services over Packet Switched Networks (CESoPSN) and Structure-Agnostic transport over Packet (SAToP) transport.

The first platform to support these new SPAs is the Cisco 7600 using the SIP-400 running Cisco IOS® Software Release 12.2.33SRB. Additional Cisco routing platforms will support these SPAs in the future.

Technical Details

Q. What are the primary features of this solution?
A. For complete information, refer to the data sheet at http://www.cisco.com/en/US/products/hw/routers/ps368/products_relevant_interfaces_and_modules.html.

A summary of the CEoP SPA features includes:

• 24 ports of channelized T1/E1/J1 or 1 port of channelized OC3/STM1 per SPA depending on the model

• Bit-transparent data transport

• Protocol-independent data transport

• Supports CEoP PWE (CESoPSN and SAToP) transport using Real-Time Transport Protocol (RTP)

• Quality of service (QoS) using MPLS EXP

• Configurable payload size

• Synchronous, differential, and adaptive clock recovery schemes, with clock accuracy target of 15 ppb

• Configurable jitter buffer up to 320 milliseconds

• Configurable idle pattern

• Support for ATM traffic classes: UBR, UBR+, VBR-nrt, VBR-rt, CBR

• Support for ATM QoS: VC and VP shaping

• Support for ATM IMA

• Support for ATM PWE (VC and VP mode cell relay)

• Support for ATM UNI

• SONET/SDH fault, performance monitoring

• VP to VP switching

• VC to VC switching

• ATM IMA (24T1/E1, 1xchOC3)

• Online insertion and removal (OIR) supported on Cisco 7600 platforms

• Overall SPA status LED

• Per-port status LEDs

Additional Features of the SPA

• Unframed (unstructured) T1/E1 transport

• N x 64 kbps and N x 56 kbps framed T1 transport

• N x 64 kbps framed E1 transport

• Grooming of up to 24 (T1) or 31 (E1) separate data streams, each able to terminate on a separate network destination

• BITS support

• Configurable clock source

• T1/E1 line diagnostic loopbacks (local line, local payload, and network payload)

Q. What standards do the CEoP SPAs support?
A. Refer to the data sheet for complete specifications, but primary standards that are supported include:

• Jitter and wander compliant to ITU G.823/824 traffic interface

• Compliant to IETF draft-ietf-pwe3-cesopsn-07.txt: structure-aware TDM CESoPSN

• Compliant to IETF RFC 4553: SAToP

Q. How is network synchronization achieved for emulated circuits over a packet-based infrastructure, since accurate clocking is critical to help ensure data integrity?
A. The CEoP SPAs support three options for achieving proper clocking and synchronization of the network when deploying circuit emulation services over packet network. They are:

• Synchronous mode: In this option, a GPS or BITS clock source is available to be fed into the edge router to clock the packets for transmission. The clock is received from a line interface and is used by the router to transmit the TDM frames, received from the packet network to the final destination.

• Differential clocking mode: Often a GPS or a BITS clock source may not be available for service providers at every possible site, such as a remote cell site. However, they may have a common clock source, which is fed into all the elements of the network. In this scenario, the system will use the common clock source as well as observe the time stamps received from the CEoP PWE packets received from the packet network and calculate the differential to recover an accurate clock. This recovered clock reference is then used to transmit the TDM frames.

• Adaptive clocking mode: In some deployments, there is no common clock or GPS/BITS source available at the remote site. The edge router has to completely rely on the incoming packet stream from the IP/MPLS network to calculate the clocking reference. The clock accuracy, thus derived, should be of very high quality, compliant to the 3GPP mobile standards (accuracy of 15 ppb or higher). This is called the adaptive clock recovery mode. The central office will be using a primary clock source reference, and the receiving site will derive the clock based on the incoming CEoP PWE packets.

Q. Can a clock be received on one T1/E1 and be sent out on behalf of all the other T1/E1s on an OC3/STM1 interface?
A. Yes. SSU/BITS clocking is supported on the CEoP SPAs. This means that any T1/E1 on any CEoP SPAs on the same router can be a clock source for all channels.
Q. Can we send the clock from one set of 24 E1 ports to a remote set of E1 ports (one-to-one port mapping) for clocking and traffic?
A. Yes. This is the standard CEoP application  
Q. What happens if there is a severe disruption in packet network and the adaptive clock recover algorithm is not able to provide good clock?
A. The clock will then go over to "holdover" mode. This mode references the last known good clock quality to clock out the data. After the clock recovery is established, the SPA will move from holdover to sync mode. If there is a fiber/line cut, causing loss to data to be sent on the TDM side, a LOS or LOP is declared on the TDM side.
Q. What are the QoS requirements for transporting the CEoP packets?
A. QoS plays an important role in carrying the CEoP packets across IP/MPLS networks. CEoP packets should be treated with the highest priority and lowest latency, just as voice-over-IP (VoIP) packets are treated. This helps ensure the fastest/least latency-inducing path for the CEoP packets end to end.

Table 1 compares CEoP and VoIP services.

Table 1. VoIP vs. CEoP

Similarities

Differences
• Real time applications
• Delay sensitive
• Dejitter buffer
• Synchronization required
• Uses RTP/UDP packets
• Packet drops not acceptable for CEoP
• CEoP has lower delay because no DSP is involved
• No codec, fax/modem detection, and echo cancellation for CEoP (bit transparency)
• Serial interfaces for CEoP
• CEoP supports adaptive clocking for synchronization
• Configurable packet/payload sizes

Q. What is the status of interoperability tests?
A. For CESoPSN or SAToP PWE, we are planning to be interoperable with vendors who comply with IETF RFCs and drafts relating to CEoP.

For ATM, we are planning to be interoperable with current ATM implementations on Cisco routers.

Availability and Ordering

Q. What part numbers should be ordered to purchase these new SPAs?
A. The single port OC3/STM 1 SPA has the following part number:

• SPA-CHOC3-CE-ATM 

The 24-port T1/E1 SPA uses the following part number(s):

• SPA-24CHT1-CE-ATM

• CABLE-24T1E1 (cable)

Q. How much are the CEoP SPAs?
A. Contact your local Cisco sales team for price information.
Q. When will the CEoP SPAs be available?
A. Contact your local Cisco sales team for availability information.