5/27/2023 0 Comments Network framer![]() J0 Section trace byte (0x01 for compatibility, 0xCC is default) On the Cisco 12000 Series Engine 2 POS line cards, the value now changes automatically when the framing type is configured (Cisco bug ID CSCdm62748). Originally, with SDH framing, the ss bits needed manual reconfiguration with the pos flag s1s0 2 command. This table illustrates well-known values for these bits: Binary ValueĪU3/4 - Most implementations in Europe use 3. A POS interface configured with SDH framing typically sends ss = 10. ![]() A transmitting POS interface configured with SONET framing sends ss = 00, and a receiving SONET device ignores these bits, because they are used to indicate payload mapping type information, which is communicated through other fields. The s1s0 bits or flag is unused in SONET. There are two major AU types, which are listed here:ĪU-3 operates in the same way as three sets of H1, H2, and H3 pointers would operate in channelized STS-3 frames.ĪU-4 operates like a single set of pointers in Synchronous Transport Signal-3c (STS-3c) concatenated frames. The ITU-T G.709 standard (or G.707, which combines G.707, G.708, and G.709) describes the AU pointer. SDH uses these bits to form the Administrative Unit (AU) field. One more difference between SONET and SDH framing is the value of the s0 and s1 bits (s is for size), which are bits 5 and 6 in SONET's H1 byte. The POs framing command enables you to set framing to SONET Optical Carrier (OC) or SDH STM. Refer to ATM Control Cells Illustrated - Idle Cells, Unassigned Cells, IMA Filler Cells and Invalid Cells for more information. Issue this command in interface configuration mode in order to configure for Synchronous Transport Module-level 1 (STM-1): Router(config-if)# atm sonet stm-4 In Synchronous Transport Signal-Xc (STS-Xc) mode, the ATM interface sends unassigned cells for cell-rate decoupling. More specifically, in Synchronous Transport Module-X (STM-X) mode, an ATM interface sends idle cells for cell-rate decoupling. The ATM forum specifies the use of idle cells if unassigned cells are not generated. In ATM environments, the key difference between SONET and SDH framing modes is the type of cell transmission when no user or data cells are available. The ITU-T defines cell delineation mechanisms in its I.432 Recommendation. The purpose of these cells is to ensure proper cell decoupling or cell delineation, which enables a receiving ATM interface to recognize the start of each new cell. The International Telecommunications Union (ITU-T) defines the format of unassigned and idle cells in its I.361 Recommendation. Refer to Troubleshooting Guide for Synchronous Digital Hierarchy for more information. The overhead of SDH framing is illustrated here. Specific overhead bytes, and the content of Automatic Protection Systems (APS) messages transmitted in the K1/K2 bytes are different. Both SONET and SDH use 0x16 and 0xCF for POS. The values of the C2 Path Overhead (POH) byte are slightly different. SDH uses the terms path, multiplex section, and regenerator section while SONET uses the terms section, line, and path. SONET and SDH use different terms to describe the three layers. Some key differences between SONET and SDH are listed here: In many cases, the SDH definitions of some overhead messages are more general in nature, and their SONET equivalents are more tuned to the operating conditions within North America. SONET and SDH have relatively minor, but still important differences between them, mostly in terminology. Refer to Cisco Technical Tips Conventions for more information on document conventions. ![]() This document is not restricted to specific software and hardware versions. There are no specific requirements for this document. Note: A detailed discussion of SONET and SDH differences is outside the scope of this document. Currently, SONET is more widely used in North America, while SDH is more widely deployed in Europe. This document reviews the basic differences in the framing used with Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) in an Asynchronous Transfer Mode (ATM) environment, and in a Packet over SONET (POS) environment.
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