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DCC Solution for SONET/SDH Systems White Paper Version 1.0, October 2003

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DCC Solutions for

SONET/SDH Systems

Version 1.0 October 2003

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DCC Solution for SONET/SDH Systems White Paper Version 1.0, October 2003

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COPYRIGHT

This material is the property of OpenCon Systems, Inc. Unauthorized distribution is prohibited

Copyright 2003 OpenCon Systems, Inc.

All Rights Reserved

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Table of Contents

1. OVERVIEW 4

2. SONET/SDH DATA COMMUNICATION CHANNEL 6

3. SONET/SDH DCC PROTOCOL STACKS 7

4. DCC SUBSYSTEM REQUIREMENTS 12

5. DCC NETWORK CONFIGURATIONS 14

5.1 End-to-End OSI-7 Layer Communication 14

4.1. TCP-IP to OSI-7 Mediation 15

5.2 IP Tunneling 17

6. OCS DCC PACKAGE 19

7. REFERENCES 20

8. ABBREVIATIONS 21

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1. Overview

Each SONET/SDH frame includes two Data Communication Channels (DCC) called Section DCC and Line DCC for transporting management messages between NEs and between NEs and Management systems. These in-band data communication channels enable service providers’ Operation Support Systems (OSS) to manage SONET/SDH Network Elements (NE) without the need for an expensive out-of-band data communication network.

SONET/SDH is the most widely used transport technology in carrier’s network today and deployment of SONET/SDH based network equipment continues to grow as carriers extend the reach of fiber from central offices to business locations. As the size of SONET/SDH networks grow and as carriers start deploying systems from different vendors, managing these networks have become increasingly difficult and complicated. To reduce the cost and complexity of managing these networks, carriers rely on embedded Data Communication Channels (DCC) within a SONET/SDH frame and expect vendors to provide equipments that are interoperable with the SONET equipments that are already deployed in their networks. To ensure interoperability with the equipment deployed in the network, SONET/SDH vendors have to support DCC standards such as Telcordia’s GR-253 and ITU G.7712.

Telcordia’s GR-253-CORE standard defines the interfaces and the communication protocols required for transporting information over DCC. The following is a summary of Telcordia requirements pertaining to DCC:

• Communication interfaces::

(a) Data Communication Channel, X.25 interface (b) Local Communication Network (LCN)

• OSI 7-layer Protocol Stacks

• SONET-specific Naming Resolution Protocol: Terminal IDentification (TID) Address

Resolution Protocol (TARP)

• Network Management Protocols: Transaction Language-1 (TL-1) or Common Management Information Protocol (CMIP)

• Generic File Management System

With the explosive growth of packet-based traffic in the service provider’s network, the SONET/SDH equipment vendors have started to incorporate packet network interfaces such as Ethernet into their equipment to transport packet-based traffic over SONET/SDH network. Unlike circuit switched traffic, packet switched traffic is bursty in nature and requires IP based signaling protocols to dynamically set up and tear down payload paths between the NEs in the network. SONET/SDH network elements that support packet interfaces are generally managed by IP based protocols such as SNMP and HTTP. To manage these types of next generation SONET/SDH network elements, the embedded DCC channel has to carry IP based management messages and has to interoperate at the DCC level with legacy network elements that are capable of transporting OSI-based messages through DCC. To address this interoperability problem at the DCC level, ITU G.7712 has defined the following three DCC network domains:

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• OSI DCC network • IP DCC • OSI+IP DCC network

IP Tunneling is one of the methods recommended by ITU G.7712 for tunneling IP traffic through the OSI based DCN network. In the following subsections, we will illustrate how IP Tunneling method can be used to integrate next generation SONET/SDH systems with the legacy network elements. OCS’ standards-based, off-the-shelf DCC System Solution shortens the DCC implementation time and is designed to provide DCC interoperability with equipment from leading SONET/SDH equipment vendors such as Fujitsu, Lucent and Nortel. OCS offers two standards-based DCC packages that can be used by equipment vendors to quickly implement an interoperable DCC solution in their equipments. These two DCC packages include support for full OSI 7-Layer Stack and an OSI three layer stack (also referred to as Short Stack). Both full stack and short stack versions support IP Tunneling as per G.7712 recommendations. OCS’ solution is designed to be hardware and operating system independent and can be easily ported to most hardware/software platforms.

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2. SONET/SDH Data Communication Channel Section DCC is based on three (3) bytes embedded in the SONET frame. These bytes are termed D1, D2 and D3 in the transport overhead of the Synchronous Transport Signal “1” (STS-1) frame. Figure 1 shows the structure of the STS-1 frame.

1 byte 1 byte 1 byte 87 columns A1 A2 J0/Z0 B1 E1 F1 D1 D2 D3 H1 H2 H3 B2 K1 K2 D4 D5 D6 D7 D8 D9 D10 D11 D12

S1/Z1 M0 or M1/Z2

E2

STS-1 payload capacity (9 × 87 bytes)

Figure 1: STS-1 Frame Structure

There are 27 bytes in the transport overhead part of the STS-1 frame. They provide many features for standard-based SONET equipment such as Automatic Protection Switching (APS). Bytes D1, D2 and D3 provide the “Section Data Communication Channel” for message-based administration, monitoring, alarm maintenance and other communication needs. The Section DCC bandwidth is 192 Kbit/s between each pair of SONET section termination equipment. Any SONET equipment that can extract these 3 bytes from the STS-1 frame overhead and process them is considered to support a DCC interface. Bytes D4 through D12 form another embedded data communication channel within SONET/SDH frame and are referred to as Line DCC. The bandwidth of Line DCC is 576 Kbit/s. Most of the SONET equipment vendors extract and process only SDCC overhead bytes.

Transport Overhead

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3. SONET/SDH DCC Protocol Stacks In order to exchange SONET/SDH network management information between OSSs and SONET/SDH NEs, a standards based management framework is needed. Telcordia has defined in GR-253-CORE standards, a network management architecture for exchanging SONET/SDH operations messages. In practice, SONET/SDH operations communications architectures will vary depending on deployment configurations and applications supported by the network. Figure 2, shows an example of the SONET /SDH Operations Communications Architecture.

SONET/SDH Ring

NMS-1 NMS-2

EMS

Data Communications Network

ADM

ADM ADM

ADM

Terminal Terminal

Terminal

TerminalTerminal

Terminal

LAN HUBGNE

GNE

GNE: Gateway NE

ADM: Add-drop Multiplexer

EMS: Element Management System

NMS: Network Management System

Figure 2: Example SONET/SDH Network

Figure 2, shows the SONET/SDH network that includes SONET/SDH Add-drop multiplexers (ADM) and Terminals. As illustrated in the Figure, the network management systems use wide area Data Communication Network (e.g., X.25) to manage elements in the SONET/SDH network. Figure 2, also illustrates the configuration where two network elements communicate with each other via an intra-site Local Area Network (LAN). Figure 3, illustrates the protocol stacks for the X.25 DCN, the DCC and the intra-site LAN. In all three cases, it is assumed that OSI based protocols are used for communication.

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Stack A: OS (X.25 DCN)

Stack B: NE (DCC)

Stack C: NE (LAN)

TL1 CMISE ROSE

TL1 CMISE ROSE

TL1 CMISE ROSE

Application

ACSE

ACSE

ACSE

Presentation ASN.1/BER ASN.1/BER ASN.1/BER Session Kernel/Full Duplex Kernel/Full Duplex Kernel/Full Duplex Transport TP4 TP4 TP4

CLNP CLNP CLNP Network X.25

ES-IS IS-IS

ES-IS IS-IS

LLC1 Data Link LAPB LAPD CSMA/CD

Physical EIA-232-D V.35

DCC AUI 10BASE2 10BASE-T

Figure 3: Protocol Components of OSI-7 layer DCC

On top of these three stacks are the TL-1 and Common Management Information Service Element (CMISE) management applications. In this example, both TL-1 and CMISE applications are implemented on top of OSI-7 protocols. v TL-1 is easily the most widely used protocol in telecommunication management today.

Most telecommunication elements in North America today are managed using TL-1. TL-1 was designed to be a human readable machine language for craft operators and operations personnel. In the 1980s, Telcordia adopted TL-1 as the network element management protocol for their Network Monitoring and Analysis (NMA) system. NMA is a fault management OSS wide ly used by Regional Bell Operating Company (RBOCs). One of the pre-requisites for deployment in a network owned by RBOCs, is that the equipment must support TL-1 and should be manageable by NMA and other OSSs used by RBOCs.

v CMISE is the service element built on CMIP.

CMIP defines the format and protocol for exchanging management messages between different OSSs and NEs so that each party can understand the messages sent from the other side. Despite gaining much press and some implementations by workstation vendors, CMIP has not been embedded in many network elements. A possible reason is the lack of an important, widely used OSS that supports CMIP. Another contributing factor may be the failure of the OSI family of protocols to become the dominant networking protocol suite.

v TARP is another special protocol in the SONET management framework. TID is used in the TL-1 language to identify each NE in the network. In a TL-1 managed SONET network, each node including the OSS and the NEs are assigned a unique TID. TARP1 provides the function to translate the TID into a network address used by CLNP for routing and relaying.

v OSI Short Stack

Prior to standardization based on OSI-7 layer protocols, number of vendors had implemented their own version of OSI-3 layer stack, popularly known as the “short stack”. Therefore, interoperability at the DCC level was impossible between SONET equipment from different vendors utilizing the “proprietary short stack” DCC solution. Due to cost considerations, some vendors, especially

1 OCS worked with Fujitsu to propose TARP protocol to SONET Interoperability Forum (SIF), which was later adopted by Telcordia as part of GR-253 standard

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Terminal equipment vendors are reluctant to implement full OSI-7 layer stack in their equipment as required by GR-253 standard. OSI short stack solution based on lower three OSI layer protocols enables vendors to implement a cost effective DCC solution that would provide interoperability with OSI-7 layer DCC solution. There are two versions of OSI short stack as illustrated in Figure 4. OSI short stack based on X.25/LAPB can be used for communicating with OSS but cannot be used for communication between NEs over DCC.

Stack A: OS

(X.25 DCN) Stack B: NE

(DCC) Application TL-1 TL-1 Transport

CLNP CLNP Network X.25

ES-IS, IS-IS

Data Link LAPB LAPD

Physical EIA-232-D V.35

DCC

Figure 4:Protocol Components of the Short Stack DCC

v Dual Stack As indicated in the earlier section, the next generation SONET/SDH network elements support IP based protocols for signaling and management. Some of these NEs support only IP based protocols. These NEs cannot interwork at the DCC level with the legacy NEs that support only OSI based protocols. To overcome this DCC interoperability problem, some vendors support both OSI and IP protocol stacks in their NEs. To transport an IP packet through a network based on OSI-only network elements, the IP packet is encapsulated with OSI network layer protocol header and tunneled through the OSI network until it reaches the exit point in the OSI network, where the encapsulation header is removed and the IP packet is sent over the IP-only network towards its destination. Figure 5, illustrates the protocol stacks used by a network element in an IP-only network and a network element with a dual stack.

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Physical

Link

Application

Presentation

Network

Session

Transport

DCC

Presentation

IS-IS,ES-IS,CLNP

Session

TARP

TP4

ACSE

TL1 FTAMROSE

CMIP

OSI Only StackIP Only Stack

DCC X.25LAN

TCP UDP

HTTP, FTPTelnet, TL1

SNMPv1/v2/v3RMON

IPv4 ICMPARP

OSPFRIP

DCC LAN

PPP overHDLC

(RFC1661)LLC1

DCC RS-449/V.35LAN

LAPD X.25LAPBLLC1

Figure 5: IP-only and OSI-only Protocol Stack Components

Figure 6, illustrates the protocol components used in the implementation of a Dual Stack with encapsulation module for tunneling OSI traffic into IP-only domain and IP traffic into OSI-only domain.

TCP UDP

HTTP, FTPTelnet, TL1

SNMPv1/v2/v3RMON

IPv4OSPFRIP

ES-IS,IS-IS

Presentation

CLNP

Session

TARP

TP4

ACSE

TL1 FTAMROSE

CMIP

Tunneling(GRE)

Physical

Link

Application

Presentation

Network

Session

Transport

Dual Stack

DCC RS-449V.35LAN

PPP over HDLC/LAPD LLC1 LAPB

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Figure 6: Dual Stack Protocol Components

v TCP-IP to OSI Mediation

High capacity SONET/SDH network elements with hundreds of network interfaces and cross-connects tend to generate large number of messages to report performance data periodically to the OSS. These network elements also tend to generate large number of alarms/events when a failure such as fiber cut occurs in the network. If messages from number of these high capacity SONET/SDH network elements are channeled through a slow X.25 link from the GNE in the network to the NMS, the buffers in the GNE will overflow resulting in loss of important alarm/event messages from the NE. Replacing the slow X.25 based link from GNE to OSS with high-speed link such as ATM or Frame Relay would require an external OSI router. OSI routers are generally more expensive than IP based routers and furthermore, service providers have an extensive IP based data network infrastructure that connects their network operations center to most of the central offices where the GNEs are located. Therefore, service providers generally prefer to use their existing IP based data network infrastructure to manage the SONET/SDH network elements. To achieve this goal, the GNE must support TL1/TCP-IP to TL1/OSI-7layer mediation. Figure 7, below illustrates the protocol components required to support such a function in GNE.

TCPUDP

TL1------------

Telnet

SNMPv1/v2/v3RMON

IPv4

Presentation

CLNP

Session

TARP

TP4

ACSE

TL1 FTAMROSE

CMIP

Physical

Link

Application

Presentation

Network

Session

Transport

TCP-IP to OSI Mediation in GNE

DCCLAN

LAPDLLC1

TL1 Mediation

OSS NE

Figure 7: TL1/TCP-IP to TL1/OSI-7 Mediation in GNE

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4. DCC Subsystem Requirements The protocol components and other supporting modules used in the implementation of a DCC solution is referred to a DCC subsystem in the network element. Depending on the system architecture of the NE, a DCC Subsystem can reside on a single processor or span across multiple processors. Regardless of the architecture used for implementation, a DCC subsystem generally has the following characteristics: v Support different types of communication interfaces, such as Section DCC, X.25 and LAN

Telcordia’s GR-253-CORE and ITU G.7712 have defined the following standard interfaces for SONET/SDH operations communications: Section/Line DCC, X.25 over RS-449/V.35 and 10/100Base-T.

v Support OS (Operation Systems) to NE and NE to NE communications

OS to NE communications is required by all SONET/SDH NEs to perform network operations and management functions. As illustrated in Figure 2, OS to NE communication path can be direct or indirect connection (i.e., connection thru a GNE). A direct communication path is one with no gateway or intermediate NE between the OS and NE (i.e., a dedicated physical connection or through a X.25 DCN). An indirect OS to NE communication path may consist of at least one gateway NE, intermediate NE or Mediation Device (MD) between the OS and NE.

A DCC subsystem should support both direct and indirect OS to NE interfaces. The OS to NE interface is defined in a layered fashion with the requirements of protocol support on each layer of the OSI model.

NE to NE communications are also required by all SONET/SDH NEs in order to route management information such as alarm, failure report, status and error indications to the OSSs. In order to satisfy this requirement, an interoperable network layer interface between the NEs is required.

v Support IP Tunneling

As indicated in the earlier sections, to extend the reach of IP based applications through a OSI-only DCC network, the network elements located at the boundary between IP and OSI network domains must support dual stack as illustrated in Figure 6.

v Support Software Download and Remote Memory Backup/Restoration

Memory administration is an important task of SONET/SDH operations. It includes memory backup and NE firmware management. Memory backup involves the backup and restoration of a network element’s configuration database. For faster recovery from equipment failures, service providers normally upload the configuration database from the network element and store it on a workstation or on a storage media such as CD and magnetic tape. Like any other software, the firmware used by a SONET/SDH network element is upgraded periodically to fix software bugs or to introduce new features. The process of upgrading the firmware stored in a NE is called Software Download. File transfer protocols such as FTP, TFTP and File Transfer Access Management (FTAM) are used to upload/download files between the NE and OSSs. FTP and TFTP protocols are supported by NEs, which are managed by IP based protocols and FTAM is supported by NEs, which are

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managed by OSI based protocols. NEs, which support Dual Stack use FTP for file transfer over IP based network and FTAM over OSI based network to perform software download operations.

v TCP/IP to OSI Mediation

To facilitate the management of SONET/SDH NEs over IP based DCN, GNEs must support TL1 over TCP-IP to TL1 over OSI-7 protocol mediation. If software download and remote memory backup functions are supported from NMS then the GNEs must have store and forward capability to distribute the files from NMS to NEs and vice versa. Since GNE communicates with the NMS over IP based DCN, it must support FTP protocol for file transfer purposes. GNE uses FTAM protocol to transfer files to non-GNEs.

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5. DCC Network Configurations In this section, we will examine some of the commonly used DCC network configurations and the protocol elements involved in providing an end-to-end communication over each one of the commonly used DCC network configuration.

5.1 End-to-End OSI-7 Layer Communication Figure 8, illustrates an OSI-7 layer based communication path between an OSS (NMS-1) and a SONET/SDH NE named NE-B. The communication path between NMS-1 and NE-B traverses through DCN and GNE before terminating in NE-B. It is assumed that the NMS-1 has built-in OSI-7 layer stack and uses TL1 over OSI-7 layer to manage the SONET/SDH NEs in the network. The physical link between NMS-1 and GNE is assumed to be X.25 Permanent Virtual Circuit.

SONET/SDH Ring

NMS-1 NMS-2

EMS

Data Communications Network

ADM

ADMADM

ADM

Terminal Terminal

Terminal

TerminalTerminal

Terminal

LAN HUBGNE

GNE

GNE: Gateway NE

ADM: Add-drop Multiplexer

EMS: Element Management System

NMS: Network Management System

OSS

NE-A

NE-B

Figure 8: OSS to NE Communication thru OSI Network

Figure 9, illustrates the protocol components involved in the end-to-end communication between NMS-1 and NE-B. NMS-1 establishes OSI association directly with the NE-B. The GNE (NE-A) in this particular scenario is used to forward the OSI network layer PDU between NMS-1 and NE-B. If the X.25 packet size is smaller than the LAPD frame size used over the DCC links, then the GNE will segment packets from NE-B to NMS-1 so that the packets transmitted over the X.25 PVC links do not

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exceed the packet size limit.

IS-IS,ES-IS,CLNP

TARP

OSI Upper Layers

DCC

LAPD

RS-449/V.35

X.25LAPB

GNE(NE-A)

Presentation

ES-ISCLNP

Session

TARP

TP4

ACSE

TL1FTA

M ROSE

CMIP

OSS

RS-449/V.35

X.25LAPB

Presentation

IS-ISES-ISCLNP

Session

TARP

TP4

ACSE

TL1FTAM ROSE

CMIP

NE-B

DCC

LAPD

Figure 9: Protocol Components involved in OSS to NE Communication thru OSI Network

4.1. TCP-IP to OSI-7 Mediation Figure 10, illustrates the communication path between an IP based OSS (i.e., NMS-2) and an OSI-7 layer based NE (i.e., NE-B) and Figure 11 illustrates the protocol components involved in the communication path between NMS-2 and NE-B. To establish communication with NE-B, NMS-2 establishes a TCP connection to GNE (NE-A in the Figure) and sends the TL-1 message for NE-B over the established TCP connection to GNE. The GNE in turn sets up an OSI association with the NE-B and once the association is established between GNE and NE-B, the TL1 message from NMS-2 will be forwarded over the established OSI association. The TL1 mediation module in GNE uses a mapping table to establish the correspondence between TCP connections and OSI association.

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SONET/SDH Ring

NMS-1 NMS-2

EMSData Communications Network

ADM

ADMADM

ADM

Terminal Terminal

Terminal

TerminalTerminal

Terminal

LAN HUBGNE

GNE

GNE: Gateway NE

ADM: Add-drop Multiplexer

EMS: Element Management System

NMS: Network Management System

OSS

NE-A

NE-B

CISCO SYST EMS

Router

Figure 10: TL/TCP-IP to TL1/OSI-7 Mediation

TCPUDP

TL1------------

Telnet

SNMPv1/v2/v3RMON

IPv4

LAN

LLC1

GNE(NE-A)

TL1 Mediation

TCPUDP

TL1------------

Telnet

SNMPv1/v2/v3

RMON

IPv4

LAN

LLC1

Presentation

CLNP

Session

TARP

TP4

ACSE

TL1 FTAM ROSE

CMIP

DCC

LAPD

OSS(NMS-2)

Presentation

CLNP

Session

TARP

TP4

ACSE

TL1 FTAM

ROSE

CMIP

DCC

LAPD

NE-B

Figure 11: Protocol Components involved in TCP-IP to OSI-7 Mediation

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5.2 IP Tunneling Figure 12, illustrates the communication path between an EMS that manages SONET/SDH network element using IP based management protocol such as SNMP or HTTP. In this example, an EMS connected to GNE (NE-A) is assumed to manage all SONET/SDH terminals using SNMP protocol. Since the communication path between the EMS and SONET/SDH terminals go through ADMs. Some of the ADMs (e.g., NE-B and NE-C) are assumed to support only OSI-7 layer protocols over DCC. To support this type of configuration an IP tunnel is created between SONET/SDH terminal (e.g. NE-D) and GNE (NE-A). Figure 13, illustrates the protocol components involved in IP tunneling path between NE-D and GNE.

SONET/SDH Ring

NMS-1 NMS-2

EMS

Data Communications Network

ADM

ADMADM

ADM

Terminal Terminal

Terminal

TerminalTerminal

Terminal

LAN HUBGNE

GNE

GNE: Gateway NE

ADM: Add-drop Multiplexer

EMS: Element Management System

NMS: Network Management System

OSS

NE-A

NE-BNE-C

NE-D

Figure 12: IP Tunneling

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CLNP

DCC

LAPD

NE-C

CLNP

DCC

LAPD

NE-BNE-D

TCPUDP

HTTPFTP

Telent

SNMPv1/v2/

v3RMON

IPv4

LAN

LLC1

CLNPTunneli

ngGRE

LAPD

DCC

NE-A (GNE)

IPv4

LAN

LLC1

CLNPTunneli

ngGRE

LAPD

DCC

EMS

TCPUDP

HTTPFTP

Telent

SNMPv1/v2/v3

RMON

IPv4

LAN

LLC1

Figure 13: Protocol Components involved in an IP Tunneling Communication Path

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6. OCS DCC Package OCS offers standards-based, off-the-shelf DCC System Solution designed to shorten the DCC implementation time and to provide DCC interoperability with equipment from leading SONET/SDH equipment vendors such as Fujitsu, Lucent and Nortel. OCS offers two standards-based DCC Solutions that provide interoperability for products deployed in a SONET/SDH ring: a Full OSI 7-Layer Stack and a Short Stack DCC Subsystem. OCS’ solution is designed to be hardware and operating system independent and can be easily ported to most hardware/software platforms. OCS-DCC package is offered in two versions: as a full stack and a short stack. The full stack version incorporates all seven OSI layers as specified in GR-253 and the short stack version incorporates OSI layers one through three. Both full stack and short stack versions include API for integration with customer developed application and low-level drivers. For customers who develop SONET/SDH terminal equipment, OCS offers a package called “IP Tunneling-Lite” which includes all the components of a Short stack with the exception of IS-IS protocol. OCS-DCC package also includes the following two features:

• ITU G.7712 compliant IP Tunneling Module for IP Relay through OSI network (included in both OSI-7 layer and Short stack packages)

• NSIF-033-1999 compliant TL1 translation device (T-TD) to support TL1 over TCP/IP to

TL1 over OSI-7 layer mediation

• NSIF-033-1999 compliant File Transfer Translation Device (FT-TD) to support FTP to FTAM mediation2

2 FT-TD is an optional module in OCS-DCC package

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7. References 1. GR-253, Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria 2. ITU G.7712/Y.1703, Architecture and Specification of Data Communication Network 3. RFC-1661, Point-to-Point Protocol 4. RFC-1662, PPP in HDLC-like framing 5. RFC-2784, Generic Routing Encapsulation

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DCC Solution for SONET/SDH Systems White Paper Version 1.0, October 2003

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8. Abbreviations ACSE Association Control Service Element ARP Address Resolution Protocol ATM Asynchronous Transfer Mode BER Basic Encoding Rules CLNP Connection-less Network Layer Protocol CLNS Connection-less Network Layer Service CMISE Common Management Information Service Element CMIP Common Management Information Protocol CSMA/CD Carrier Sense Multiple Access/Collision Detection DCC Data Communications Channel DCN Data Communication Network EMS Element Management System ES End System ES IS End System to Intermediate System FR Frame Relay FTP File Transfer Protocol FTAM File Transfer, Access and Management GNE Gateway Network Element GRE Generic Routing Encapsulation HDLC High Level Data Link Control ICMP Internet Control Message Protocol ID Identifier IP Internetwork Protocol IPv4 Internetwork Protocol Version 4 IPCP Internet Protocol Control Protocol IS Intermediate System ISDN Integrated Services Digital Network ISIS Intermediate System to Intermediate System LAN Local Area Network LAPB Link Access Procedure B-Channel LAPD Link-Access Procedure D-Channel LLC1 Link Layer Control LCN Local Communications Network NE Network Element NSAP Network Service Access Point OS Operations System OSS Operations Support System OSI Open System Interface OSPF Open Shortest Path First PDU Packet Data Unit PPP Point-to-Point Protocol RFC Request For Comment ROSE Remote Operations Service Element SDH Synchronous Digital Hierarchy SONET Synchronous Optical Network STS-1 Synchronous Transport Signal-1 TARP TID Address Resolution Protocol TCP Transmission Control Protocol TL1 Transaction Language 1 WAN Wide Area Network