OCAM9 Flashcards
What is SONET?
A mature, Time Division Multiplexing (TDM) based system for optical communication transport. It was developed by the Exchange Carriers Standards Association (ECSA) and is now supported by the American National Standards Institute (ANSI). Before SONET there was no common optical transport protocol.
Why was SONET developed?
SONET was developed to create a common transport protocol for use by the Regional Bell operating Companies (RBOCs) and Inter-exchange Carriers (IXCs). Voice was the primary type of traffic for SONET so its framing and lines have been defined based on this so has a rate of 64Kbps
What has SONET evolved to support?
Can now transport ATM, frame relay, ethernet, fibre channel and video
RBOCs and IXCs suffered from what pitfalls before SONET?
1) Optical transport technologies were as hoc proprietary
2) needed fixed TDM multiplex/ demultiplex equipment at all provider add/drop locations
3) No efficient or cost effective electrical signal distance extension mechanism
4) Limited provider-provider interconnection or complications
5) Each provider used different suppliers = different technologies = lack of common transport equipment
6) Lack of common management and control plane for provider transport
7) Restoration and protection guarantees were very complex
What were the initial benefits of SONET?
1) Highly reliable and resilient transport and defined carrier grade resilience with 50ms switch time and 99.999% availability
2) High speed line rate interfaces allows for huge capacity gains
3) Reduction in equipment and real estate costs
4) Reduced complexity, especially between provider and handoffs
5) Simplified management as they were now defined
6) Simplified multi-vendor equipment interconnection and deployments
7) Flexible architecture accommodating new applications and supports variety of line rates
8) Simplified provisioning
What is TDM?
TDM allocates bandwidth into time slots and uses them as traffic carrying containers to transport digital signals over a fixed and constant line rate
Describe SONET TDM
1) Signals mapped into time slot containers that are dedicated along the entire communication path
2) Framing occurs at line rate of the optical carrier -n, even when no signals to transport
3) Digital signals must be mapped end to end as a circuit to be carried over a SONET network
4) Oversubscription is not inherent of TDM due to fixed time slot allocations
5) Scaling and upgrades are costly and complex
6) SLAs are inherently guaranteed and easy to support
7) Bandwidth inefficiencies exist for non traditional traffic types (i.e ethernet over SONET)
How is SONET framed?
Synchronous Transport Signal (STS-1) is the basic framing unit of SONET transmission. STS-1 operates at 51.84mbps and is a timeslot for transporting signals. STS-1 is an electrical multiplexing construct. Each multiple of STS-n is a linear increment of 51.84mbps
What are the functional areas of STS-1?
1) Management overhead - Path, Section and Line Overhead or POH, SOH and LOH
2) Synchronous Payload Envelope (SPE) - carries customer signals
What is Path Overhead?
POH includes 9 bytes of STS POH and 5 bytes of Virtual Tributary (VT) POH. POH is accessed, generated and processed by the incoming tributary card/module.
What is Section Overhead?
SOH has 9 bytes of overhead processed at each regeneration point and supports the functions such as framing the signal and performance monitoring.
What is Line Overhead?
LOH has 18 bytes of overhead accessed, generated and processed at the add/drop OC-n optic. Supports functions such as locating SPE in Fram, multiplexing or concatenating signals, performance monitoring, automatic protection switching and line maintenance
What is SONET Overhead Termination?
1) SOH is added or removed at ingress or egress regeneration points
2) LOH is added or removed at the ingress or egress of the SONET optical line
3) POH is added or removed at the ingress or egress of the tributary optic or mapper
What can a 49.536 Mbps STS-1 Synchronous Payload Envelope carry?
1) 28 DS-1s
2) 1 DS-3
3) 21 E1 2.048 Mbps signals
4) smaller combinations of DS-1 and E-1s
What cannot fit onto an STS-1 frame?
1) 100Mb Ethernet
2) Gigabit ethernet
3) Fibre channel
4) FICON
5) Video
