| The broadband networks of US telecommunications | | | | Transparent GFP is used for applications that are |
| carriers are fiber optics networks using SONET | | | | sensitive to latency. In this encapsulation, all code |
| (Synchronous Optical Network) and WDM | | | | words from the physical interface are transmitted. |
| (Wavelength Division Multiplexing) technologies. | | | | Transparent GFP is primarily targeted at Storage |
| SONET uses TDM (Time Division Multiplexing) to | | | | Area Networks (SANs) where latency is very |
| multiplex data streams of different rates in electrical | | | | important and the delays associated with frame |
| domain and then converts the electrical signals to | | | | based GFP cannot be tolerated. With Virtual |
| optical signals to be transported over optical fiber. | | | | Concatenation and GFP, the required inter-working |
| SONET transmission systems payload can transport | | | | function for Ethernet (LAN) to the Telco network |
| data streams of rates from T1 (1.544 Mb/s), T3 | | | | (WAN) is eliminated. This reduces the complexity of |
| (44.736 Mb/s), OC-3 (155.52 Mb/s) to OC-192 (10 Gb | | | | establishing a ubiquitous Ethernet between the |
| s). WDM enables multiple optical signals with different | | | | customer networks and the Telco SONET network. |
| wavelengths to be multiplexed and transported over | | | | Since SONET payload can transport data streams |
| a single optical fiber. Since each SONET signal uses a | | | | from T1 to OC-192, the Telco SONET network can |
| different wavelength, hence multiple SONET signals | | | | provide carrier Ethernet services at various rates |
| can be transported over an optical fiber using WDM. | | | | from 1.5 Mb/s to 10 Gb/s using GFP and virtual |
| Ethernets are defined according to data rates. There | | | | concatenation. The first type of carrier Ethernet is |
| are 10Mb/s, 100 Mb/s, 1 Gb/s and 10 Gb/s Ethernet. | | | | E-LINE or Private Lease Line. E-LINE is a point-to-point |
| Since SONET is optimized for TDM traffic (Voice), it | | | | Ethernet connection between any two locations |
| does not match the optimal rate for transporting a | | | | within a metropolitan area. E-LINE provides reliability, |
| typical Ethernet data stream. To increase the | | | | rate guarantee and security of SONET network as |
| efficiency of transporting Ethernet over SONET, two | | | | well as adjustable bandwidth using LCAS protocol. |
| new technology standards are introduced, namely | | | | There is also E-LINE that is similar to Virtual Lease |
| Virtual Concatenation and Generic Framing Procedure. | | | | Line where many customers share the same |
| Virtual Concatenation allows SONET channels to | | | | transport bandwidth using Ethernet over MPLS |
| multiplex in arbitrary arrangement to address the | | | | protocol (EoMPLS) with lower QoS (Quality of |
| bandwidth mismatch between Ethernet and SONET. | | | | Services) than Private Lease Line. Hence, E-Line can |
| Custom-sized SONET pipes are created using multiple | | | | be used to create a Private Network or a Virtual |
| STS-1/STS-3 as well as virtual tributaries (VT-1.5 | | | | Private Network (VPN). |
| VT-2). Each SONET channel is routed independently | | | | The second type of carrier Ethernet is E-LAN. E-LAN |
| and transparently through the network. This enables | | | | is an Ethernet service that can connect multiple |
| SONET pipes to be right-sized for Ethernet transport. | | | | locations. E-LAN resembles a multi-point service with |
| The capability of dynamic bandwidth allocation of | | | | any-to-any connection. E-LAN is used to provide |
| virtual concatenation channel, LCAS (Link Capacity | | | | interconnection capability between multiple |
| Adjustment Scheme), is also developed. | | | | organization sites within a metropolitan area. From the |
| Generic Framing Procedure (GFP) is a simple | | | | subscriber standpoint, E-LAN makes the carrier |
| adaptation scheme that extends the ability of SONET | | | | Ethernet looks like a LAN. Just like E-LINE, E-LAN can |
| to carry different types of traffic. Frame based GFP | | | | also be shared by many customers using the EoMPLS |
| permits the transport of frame oriented traffic for | | | | protocol. Hence E-LAN can be used to create a |
| connections where efficiency and flexibility is | | | | Private LAN or a Virtual Private LAN Service (VPLS). |
| important, such as Ethernet and IP over PPP. | | | | |