Migration of TDM networks towards unified packet infrastructures Wolfgang Fischer
What is TDM migration Two different aspects Transport of native TDM traffic over a packet network infrastructure: Circuit Emulation Applications leased lines with native TDM traffic (e.g., legacy PBXs) mobile backhaul (2G) interconnection of legacy voice switches in SP networks support for SCADA applications in utility networks Elimination of legacy PDH and SDH equipment Migration of native packet-based services from TDM infrastructure (leased lines) to packet network infrastructure Applications leased lines with packet-only traffic (e.g., MPLS VPNs) mobile backhaul (3G) modernization of utility networks (introduction of sensors and actors with Ethernet interfaces) Keep PDH/SDH access interfaces where appropriate
Drivers for TDM migration Overwhelming majority of traffic is packet-based Significant OPEX penalty for operating multiple disjoint service / technology specific networks Coarse granularity of fixed TDM bitrates: 64kbps, 2Mbps, 34Mbps, 155Mbps, 622Mbps, vs. variable or fixed bitrates without strict granularity for packet technology No statistical multiplexing in TDM networks Technological evolution has focused on packet technology (Ethernet, IP, MPLS) for many years technology has become more cost effective, uses less power and space, and has more functionality than TDM technology, compared at the same speeds ADMs operate at VC-4 granularity, and DCSs at E1/VC-12 granularity hierarchy in equipment deployment No further evolution of TDM systems obsolescence Significant real estate and power savings elimination of equipment hierarchies Integrated multi-service networks have to be implemented as packet networks
Example SP metro office - TDM vs. packet 750m 2 75m 2 Legacy: DCS, M13, ADM, WDM, etc. - modernized network Legacy Optimized Transport Space 100 Racks 10 Racks Power 200kW 50kW Cost of Space and Power $975,000 $124,000 OpEx Savings $3M/year for large office $250M/year network-wide
TDM Services across legacy TDM networks Mobile E1 POS DC Leased line Corporate Utility Microwave links Railways E1/E3/STM-1 E1/STM-1 STM-1/STM-4 E1/E3/STM-1 PDH / SDH Aggregation ADM STM-4 STM-16 SNCP Ring ADM DXC DXC STM-64 Network DXC E1/STM-1 FCoS ADM BSC / MSC / RNC Landing stations STM-16/STM-64 Network
TDM Services across legacy TDM networks SDH Circuit 1000s of E1/E3/STM-1/STM-4 Low Order TDM Switching TDM Customer Premises STM-1-16 DXC DXC DXC STM-1-64 Long Haul Transport IP Customer Premise ADM ADM ADM E3/STM-1 STM-16/-64 ROADM ROADM ROADM Service Edges High Order SDH Switching
TDM Services across packet networks Mobile E1 Ethernet DC Leased line Corporate Utility Microwave links E1/E3/STM-1 E1/STM-1 STM-1/STM-4 E1/E3/STM-1 node node node node node / OTN Network Full IP/MPLS network node FCoE node Railways Landing stations STM-16/STM-64 E1/STM-1 BSC / MSC /RNC
TDM Services across packet networks Circuit Emulation Pseudowire Primary LSP Backup LSP TDM Customer Premises STM-1-16 Circuit Emulation Endpoint STM-1-64 Modernized TDM Customer IP Customer Premise Modernized IP Customer 10GE 10GE Node Node Node E3/STM-1 Service Edges Long Haul Transport ROADM ROADM ROADM Pseudo-Wire OTU4 MPLS Transport Bi-directional LSPs with 1:1 Path Protection (Working / Protect LSP)
TDM over OTN instead of packet? For efficient support of TDM services a granularity down to 2Mbps (E1) is required ODU0 @ 1.24Gbps is the lowest bitrate level in OTN To transport TDM traffic over OTN TDM structures up to STM-16 would have to be maintained this defeats the idea of TDM migration transport will provide arbitrarily small granularity and efficient multiplexing, including statistical multiplexing OTN will be used to create flexibility in DWDM-based transport networks with speeds of 10 100Gbps+ per wavelength
Challenges and solutions to TDM migration Standards for Circuit Emulation Structure Agnostic TDM over (SAToP, RFC 4553) E1, E3 Circuit Emulation Protocol (CEP, RFC 4842) - SDH container Circuit Emulation Service over Switched Networks (CESoPSN, RFC 5086) - Frame aware n*64k Clocking Synchronous Ethernet (SyncE) for frequency synchronization, Precision timing protocol (PTP, IEEE 1588) for phase synchronization Resource allocation Resource reservation for pseudowires using FlexLSPs, and strict prioritization Protection Reservation of bi-directional working and standby FlexLSPs, wrap-around for sub-50ms reaction to local failures
Summary SDH and PDH transmission equipment is up for replacement Most traffic is packet-oriented Consolidated networks will be packet-based Remaining TDM traffic will be circuit-emulated Legacy TDM access interfaces will terminate on packet access nodes