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