LECTURE 5: Wide Area Networks (WANs) CIS484 Summer 2015 Instructor: Dr. Song Xing Department of Information Systems California State University, Los Angeles Outlines Introduction to WAN Point-to-point WANs Switched WANs 2 1
WAN Background Industry convention describes a Wide Area Network (WAN) as a network that spans a large geographical distance. WAN Network traversing some distance, connecting LANs Transmission methods dependent on business needs The largest example of a WAN is the public Internet, but many other types of WANs exist. Wide area networking is sometimes referred to as enterprise networking. 3 WAN Background (cont.) Wide area networking developed from the way businesses first used computer networks to exchange information internally, beginning in the mid-1970s. Several architectural features distinguished these networks from modern WANs. WANs now support voice, data, and multimedia information; use open network protocols; and often are offered over a public network such as the Internet. 4 2
WAN Essentials WAN Network traversing some distance, connecting LANs Transmission methods dependent on business needs WAN and LAN common properties Client-host communications for resource sharing, use the same protocols from Layer 3 and higher of the OSI/Internet model, packet-switched digitized data WAN and LAN differences Layers 1 and 2 in access methods, topologies, and media LAN wiring: private WAN wiring: public through NSPs (network service providers) LAN And WAN Connectivity WAN site: Individual geographic locations WAN link: WAN site to WAN site connection 6 3
WAN Purposes Link sites (usually) within the same corporation Remote access for individuals who are off-site Internet access for individuals or firms 7 WAN Speeds WANs are Characterized by High Cost and Low Speeds WANs speeds are slow because longdistance transmission is costly. High cost per bit transmitted compared to LANs Typical WAN speeds: 128 kbps to several megabits per second. This speed usually is aggregate throughput shared by many users. Much slower than LAN speeds (100 Mbps to 10 Gbps for wired LAN). 8 4
WAN Technologies Technologies for Individual Internet Access DSL lines Cable modems etc Site-to-Site Transmission within a Firm Private line networks (Point-to-point WANs) Public switched data networks (PSDNs) Metropolitan Area Ethernet Virtual Private Networks (VPNs) 9 WAN Systems Point-to-point WANs Switched WANs 10 5
Outlines Introduction to WAN Point-to-point WANs Leased line networks SONET Switched WANs Frame Relay ATM Metropolitan Area Ethernet 11 Point-to-point WAN A point-to-point WAN connects two remote devices using a line available from a public network such as a telephone network. We discuss T-lines, and SONET here. Traditional modem technology, DSL line, cable modem willed be discussed on Lecture #6. 12 6
Leased (Private ) Services First, if you need a faster service, or need one that is always on to connect computer systems, you can get a leased line service. A T-1 (or T1) service gives you a 1.544 Mbps rate and is used by businesses to connect their in-house telephone systems (PBX) and data networks to the outside world. Second, long-distance carrier system was designed to transmit voice signals over high-capacity transmission links (e.g. optical fiber, coaxial cable, and microwave). Part of the evolution of these networks to digital technology has been the adoption of synchronous TDM transmission structures. The basis of the TDM hierarchy is the T-1 transmission format. 13 Recall Synchronous Time-Division Multiplexing (TDM) Used in digital transmission Requires data rate of the shared medium to exceed data rate of individual signals to be transmitted Multiple signals take turns over the shared medium Slices of data are organized into frames Used in the modern digital telephone system US, Canada, Japan: DS-0, DS-1 (T-1), DS-3 (T-3),... Europe, elsewhere: E-1, E3, Time Frame 1 Frame 2 Frame 3 14 7
Leased Characteristics Point-to-point circuits Always on High speeds: 64 kbps (rare) to several gigabits per second Circuits with reserved capacity Leased for a minimum period of time Physical layer operation offered by telephone companies Examples: T lines, SONET 15 Private Networks Using Leased If a company such as a bank wants a dedicated transmission path between its branches for private digital communication lines, the company has the option of leasing dedicated private lines from a network provider. A private leased line is not shared with other customers of the network provider, so it can guarantee performance and availability to some degree. 16 8
Private Networks Using Leased (cont.) These dedicated lines may run terrestrially over fiber-optic cables or high-grade twisted pair, via undersea fiber-optic cables, or even via satellite for international communications or remote areas that do not have adequate terrestrial telecommunications. The primary disadvantage of a private network is cost, because a single enterprise bears the entire cost of the lines. 17 Private Networks Using Leased (cont.) 18 9
T Rates 19 Leased Speeds North American Digital Hierarchy Speed Typical Transmission Medium 56 kbps 56 kbps 2-Pair Data-Grade UTP T1 1.544 Mbps 2-Pair Data-Grade UTP 56 kbps leased lines are hardly used today because they are so slow. T1 lines are very widely used because they are in the speed range of greatest corporate demand 128 kbps to a few megabits per second. 20 10
Leased Speeds (Cont.) North American Digital Hierarchy Typical Transmission Speed Medium T1 1.544 Mbps 2-Pair Data-Grade UTP Fractional T1 Bonded T1s (multiple T1s acting as a single line) 128 kbps, 256 kbps, 384 kbps, 512 kbps, 768 kbps A few multiples of 1.544 Mbps 2-Pair Data-Grade UTP 2-Pair Data-Grade UTP T1 lines are very widely used. Fractional T1 lines offer lower speeds for companies that need them. Two or three T1 lines can be bonded for higher speeds. T1, Fractional T1, and Bonded T1s are the most widely used leased lines. 21 Leased Speeds (Cont.) North American Digital Hierarchy T1 T3 Speed Typical Transmission Medium 1.544 Mbps 2-Pair Data-Grade UTP 44.736 Mbps Optical Fiber The jump from T1 to T3 speeds is extremely large. Few firms need T3 speeds, and they only need these speeds for some of their leased lines. Some carriers offer fractional T3 lines to bridge the T1-T3 gap. T3 lines and all faster leased lines use optical fiber. 22 11
Leased Speeds (Cont.) CEPT Hierarchy Speed Typical Transmission Medium 64 kbps 64 kbps 2-Pair Data-Grade UTP E1 E3 2.048 Mbps 2-Pair Data-Grade UTP 34.368 Mbps Optical Fiber In Europe, most countries use the CEPT hierarchy. CEPT: European Conference of Postal and Telecommunications Administrations E1 lines are slightly faster than T1 lines E3 lines are slightly slower than T3 lines 23 Outlines Introduction to WAN Point-to-point WANs Leased line networks SONET Switched WANs Frame Relay ATM Metropolitan Area Ethernet 24 12
SONET/SDH The high bandwidths of fiber-optic cable are suitable for today s highest data rate technologies (such as video conferencing) and for carrying large numbers of lower-rate technologies at the same time. ANSI created a set of standards called SONET (Synchronous Optical Network) to handle the use of fiber-optic cables for high-speed digital transmission. Synchronous Digital Hierarchy (SDH), a compatible version, has been published by ITU-T. SONET and SDH are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber cables. 25 SONET (Synchronous Optical Network) Specifies framing and multiplexing techniques at the physical layer of the OSI/Internet model Four key strengths WAN technology integration Fast data transfer rates Simple link additions, removals High degree of fault tolerance Double-ring topology over fiber-optic cable: one used as the working ring and the other as the backup ring in different direction. 26 13
SONET (Synchronous Optical Network) (cont.) Synchronous It means data being transmitted and received by nodes must conform to a timing scheme. A clock maintain s time for all nodes on a network. A receiving node in synchronous communications recognizes that it should be receiving data by looking at the time on the clock. Advantage Interoperability: used to aggregate multiple T1s,T3s, or ISDN lines. Also used as the underlying technology for ATM transmission. 27 A SONET Ring 28 14
SONET/SDH Speeds OC3/STM1 OC12/STM4 OC48/STM16 OC192/STM64 Speed (Mbps) Typical Transmission Medium 155.52 Optical Fiber 622.08 Optical Fiber 2,488.32 Optical Fiber 9,953.28 Optical Fiber OC768/STM256 39,813.12 Optical Fiber For speeds above 50 Mbps, the world uses one technology called SONET in the United States, SDH in Europe. SONET speeds measured in OC numbers, SDH in STM numbers. Speeds are multiples of 51.84 Mbps. Used mostly by carriers. 29 Leased Networks for Voice Site A Leased Voice Networks PBX Have a PBX at Each Site OC3 Leased Site B T1 Leased Site D Site C T3 Leased 256 kbps Leased T1 Leased T1 Leased T1 Leased Site E 30 15
Leased Networks for Data Site A Router Leased Data Networks Have a Router at Each Site Site B OC3 Private T1 Leased Site D Site C T3 Leased 256 kbps Leased Site E T1 Leased T1Leased T1 Leased 31 Full Mesh Topologies for Leased Data Networks Site A Full Mesh Topology Site B OC3 Leased In a full mesh topology, there is a leased line between each pair of sites T1 Leased T3 Leased T3 Leased Highly reliable Highly expensive T1 Leased Site C Site D 32 16
Pure Hub-and-spoke Topology Site A In a Pure Hub-and-Spoke Topology, There is Only One for Each Site Site B Site C Site D Less Expensive, but No Redundancy for Reliability Site E 33 Pure Hub-and-Spoke Topologies for Leased Data Networks Site A In a pure hub-and-spoke topology, there is Pure Only Hub-and-Spoke one leased line Topology from the hub site (Site A) to each other site. OC3 Leased Site B Very inexpensive. Very unreliable. T3 Leased T3 Leased Site D Site C 34 17
Mixture of Two Topologies Site A Most Firms Mix the Two Topologies To Balance Cost and Reliability OC3 Leased Site B 256 kbps Leased Site D Site C T3 Leased 256 kbps Leased T1 Leased T1 Leased Site E 35 Outlines Introduction to WAN Point-to-point WANs Leased line networks SONET Switched WANs Frame Relay ATM Metropolitan Area Ethernet 36 18
Switched WANs The backbone networks in the Internet can be switched WANs. A switched WAN is a wide area network that covers a large area (a state or a country) and provides access at several points to the users. Inside the network, there is a mesh of point-to-point networks that connects switches (routers). The switches (routers), multiple port connectors, allow the connection of several inputs and outputs. Switched WAN technology differs from LAN technology in many ways. We discuss the Public Switched Data Networks here. 37 Leased Network Versus Public Switched Data Network Leased Network Use many leased lines, which must span long distances between sites. Company must design and operate its leased line network. It is very expensive. 38 19
Leased Network Versus Public Switched Data Network (cont.) Public Switched Data Network (PSDN) The idea is to outsource site-to-site networking to a PSDN carrier. PSDN carrier provides planning, switching, and operation of the network. Total cost of technology, service, and management usually lower than leased line networks. The PSDN central core is shown as a cloud to indicate that the user firm does not have to know how the network operates because the PSDN handles all of the details. Companies merely need access devices at their sites and a single leased line from each site to the PSDN carrier s nearest point of presence (pop). 39 Public Switched Data Network (PSDN) You only need one leased line from each site to the PSDN carrier s nearest point of presence (POP). 40 20
PSDN Cloud 41 LANs Connected to PSDN Cloud Through T-carrier s 42 21
PSDN Switches The internal cloud network is a mesh of switches. This creates multiple alternative paths. This gives reliability. However, Mesh switching is slow because each switch must evaluate available alternative paths and select the best one. 43 Virtual Circuits Solution in PSDN Virtual circuit is a single path (data link) between two stations. Before communication begins between sites, the PSDN computes a best path called a virtual circuit. All frames travel along this virtual circuit. Only a single possible path, so switching is fast and inexpensive. Virtual Circuit Virtual Circuit 44 22
PSDN Switching Table Example Switching table has virtual circuit number instead of data link layer MAC addresses Frame header has a VC number, NOT a destination MAC address. Hence, only a single possible path. Each switch looks up the VC number in its switching table, sends the frame out the indicated port. Switch A Switching Table So switching is fast and inexpensive. Virtual Circuit port Frame with VC number 47 47 2 A 270 3 B 982 3 5 1 Virtual Circuit 47 C Virtual Circuit 47 D Figure 6-25 E 45 PVCs and SVCs A software-defined (virtual) path is set between two devices on the public switched network, and the devices are expected to exchange information. Switched virtual circuits (SVCs) Permanent virtual circuits (PVCs) 46 23
Permanent Virtual Circuits (PVCs) Once defined, require no additional set-up procedures, meaning that the route of links does not have to be recreated kept in place for months or years Always available as they are permanent Require virtual circuit identifiers for each communication Between a firm s sites (which rarely change) 47 Switched Virtual Circuits (SVCs) Similar in concept to a dial-up circuit switched connection Temporarily set up the route of links a circuit takes, meaning only for the duration of the communication Require a setup procedure for each communication Set up at beginning of a communication session Taken down at the end of the session More expensive than PVCs. 48 24
PSDN Standards X.25 Frame Relay ATM Metro Ethernet/Carrier Ethernet 49 Outlines Introduction to WAN Point-to-point WANs Leased line networks SONET Switched WANs Frame Relay ATM Metro Ethernet/Carrier Ethernet 50 25
Frame Relay (FR) Consider the follow scenario. A business wants a fast, permanent connection to another site. It wants a system designed for data and not voice. What should the business use? The answer is frame relay. Frame relay is the leased service that can provide a high-speed connection for data transfer between two points either locally or over long distances. Historically, frame relay originated as an improvement over an older WAN technology known as X.25. 51 Frame Relay (FR) (cont.) The frame relay network is owned and operated by the service provider but is used by the customer. This service uses packets, called frames, with a variable number of bits that are switched throughout the WAN until they reach their destination. The frame relay standard uses a different format from other WAN standards. Functions in the Data Link Layer. Information Technology in Theory 52 26
Frame Relay (FR) (Cont.) Use high-speed digital backbone links to achieve very high transmission rates (up to 45 Mbps or even higher). Encryption techniques used to transmit data between frame relay switches, providing very good security. Permanent connection, always available. Low error rates during transmission. Usually less expensive than a network of leased lines Use virtual circuits to reduce cost. 53 A WAN using Frame Relay 54 27
A Business Connecting to the Frame Relay Network Via a Local Connection A business only has to connect itself to the local frame relay port via local telephone lines or leased lines. Once the data reaches the local frame relay port, the frame relay network, or cloud, transmits the data to the other side. 55 Frame Relay Connections Relies on packet switching and virtual connection technology (PVC) to transmit data packets. Supports variable length packets. PVCs (Permanent Virtual Circuits ) are created by the provider of the frame relay service. Utilizes two layers: physical and data link. The user uses a high-speed access line (leased line) to connect its company to a port on the POP, which is the entryway to the frame relay network. Multiple PVCs (one to each other site) are multiplexed over a site s single leased line and single POP port. The high-speed access line, the port, and the PVC should all be chosen to support a desired transmission speed. 56 28
A Frame Relay Connection Between Two Cities 57 Frame Relay Network Elements Customer Premises A 1. Access Device DSU CSU 2. T-Leased Access to POP Switch 4. Two PVCs PVC 2 PVCs 1&2 POP PVC 1 3. Port Speed Charge at POP Switch PVC 1 PVC 2 PVC 1 Customer Premises B Customer Premises C 58 29
Frame Relay Network Access Devices (FRAD & Router) Site A Access Device (Frame Relay Access Device) T1/T3 CSU/DSU at Physical Layer T1 PC Frame Relay, ATM at Data Link Layer Site B Access Device (Router) T1/T3 CSU/DSU at Physical Layer T3 Server Frame Relay, ATM at Data Link Layer 59 CSU and DSU Channel service unit (CSU) is the end-point of the digital access line. keeps the access line open and active protects the access line from unapproved voltage levels, etc. coming from the firm Data service unit (DSU) converts signals from access device into the type of signal required by the leased access line. Access devices may be a router or a dedicated Frame Relay Access Device (FRAD) to disassemble and reassemble packets DSU 60 30
More About CSU/DSU Customers who access the Internet or another type of WANs are connected to an edge router. A CSU/DSU is an important network component between the edge router and the dedicated transmission line. 61 Frame Relay Network PVCs Frame Relay PVC Numbers are called data link control indicators (DLCIs) Usually 10 bits long 2 10 or 1,024 possible PVCs from each site Multiplexed over the single leased line to the POP Leased line must be fast enough to handle the combined PVC speeds Site 1 POP Leased PVC 1-2 PSDN PVC 1-3 Site 2 Site 3 62 31
Frame Relay Setup Example Consider a company that has four office locations and currently has six leased lines interconnecting the four locations. To install frame relay, the company would ask for six PVCs in place of the six leased lines. The company would also need four high speed access lines and four ports connecting the four locations to the frame relay cloud. Cost less than six leased lines as using multiple PVCs on a single physical line. 63 Solution 1: Six Leased s Used to Interconnect a Company s Four Locations 64 32
Solution 2: a Frame Relay Network Used to Interconnect a Company s Four Locations 65 Frame Relay Vs. The Internet Frame relay has many advantages over the Internet, including guaranteed throughput, minimum delay, and better security. The Internet (or public Internet) has the advantage of being practically everywhere, cheaper, and simpler to create connections (no PVCs necessary). 66 33
Internet Services Many businesses use the infrastructure of the public Internet to communicate internally and with customers and suppliers. Using the Internet and other shared public WANs is much more cost effective than using dedicated private networks. 67 Outlines Introduction to WAN Point-to-point WANs Leased line networks SONET Switched WANs Frame Relay ATM Metro Ethernet/Carrier Ethernet 68 34
Cell Networks Many of the problems associated with frame internetworking are solved by adopting cell networking. A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-size block of information. ATM is a PSDN system using fixed-length cells. 69 Problem of Multiplexing Using Different Frame Sizes The variety of frame sizes make traffic unpredictable by switches, multiplexers, and routers. Another problem is that of providing consistent data rate delivery when frame sizes are unpredictable and can vary so dramatically. What happens when line1 uses large frames (usually data frames) while line 2 uses very small frames (the norm for audio and video information)? 70 35
Multiplexing Using Cells Message frames are segmented into cells. Each cell is the same size and all are small. All data are loaded into identical cells that can be transmitted with complete predictability and uniformity. The cells from the two lines are interleaved so that none suffers a long delay. 71 Multiplexing Using Cells (cont.) Another point is that the high speed of the links coupled with the small cells means that, despite interleaving, cells from each line arrive at their respective destinations in an approximation of a continuous stream. In this way, a cell network can handle realtime transmissions such as a phone call, even video conferencing, without the parties being aware of the segmentation or multiplexing at all. 72 36
Asynchronous Transfer Mode (ATM) Asynchronous Transfer Mode (ATM) is the cell relay WAN (Wide Area Network) designed by the ATM Forum and adopted by the ITU-T (International Telecommunication Union-Telecommunication Standards Sector). It uses asynchronous time-division multiplexing (TDM)-that is why it is called Asynchronous Transfer Mode to multiplex cells coming from different channels. 73 Time Division Multiplexing (TDM) TDM is a digital multiplexing technique for combining several low-rate channels into one high-rate one. Medium sharing is accomplished by dividing available transmission time on a medium among users (channels). Divides the transmission time into several slots. Each user (channel) s message is divided into small units. A round of data units from each user (channel) is collected into a TDM frame. If we have N users (channels), a TDM frame is divided into N time slots and one slot is allocated for each unit, one for each input line. 74 37
Recall Synchronous TDM The original TDM. The multiplexor accepts input from attached devices in a round-robin fashion and transmit the data in a never ending pattern. T1/T3 and ISDN telephone lines are common examples of synchronous TDM. 75 Synchronous TDM Problem If a device has nothing to transmit, the multiplexor must still insert a piece of data from that device into the multiplexed stream, wasting the time slot. 76 38
ATM Multiplexing ATM multiplexers fill a slot with a cell from any input channel that has a cell. The slot is empty if none of the channels has a cell to send. Note: at the first tick of the clock, channel 2 has no cell (empty input slot), so the multiplexer fills the slot with a cell from the third channel. 77 ATM Features Widely adopted for the Public Switched Telephone Network core. Also provided as a PSDN service. ATM is a universal integrated carrier of voice, data, audio, and video. ATM formats information into fixed-length packets, called cells. ATM cells are small and have total length of 53 bytes. ATM is a connection-oriented WAN approach; it establishes an end-to-end virtual connection between the transmission device and destination device before transmission begins. ATM s fixed transmission delays, virtual circuits, and fixed cell size are beneficial for low latency applications. 78 39
ATM vs. Frame Relay ATM and Frame Relay are two commonly used PSDNs. ATM is the fastest and most powerful PSDN. ATM is a very high-speed cell-switching service, similar in a number of ways to frame relay. Both require a user to create a virtual circuit with a provider. Difference between ATM and Frame Relay: ATM is capable of speeds up to 622 Mbps (even Giga bps) while frame relay s maximum is typically 45 Mbps. ATM uses fixed-length cell; Frame relay uses variablelength packets (frames). 79 Cell Relay Technology Functions in the Data Link Layer. ATM uses cell relay technology. Cell relay is a data transmission technology based on transmitting data in relatively small, fixed-size packets or cells. Cell relay systems can reliably carry live video and audio because cells of fixed size arrive in more predictable way than systems with packets or frames of varying size. 80 40
ATM Network Architecture ATM is a cell-switched network. The user access devices, called the endpoints, are connected through a user-tonetwork interface (UNI) to the ATM switches. ATM uses switches to route the cell from a source endpoint to the destination endpoint. The ATM switches are connected through network-to-network interfaces (NNIs). 81 ATM Network Architecture (cont.) 82 41
Multiple Inputs Aggregated onto a Single ATM UNI 83 How ATM Works ATM data travels over a connection called a virtual channel (VC) connection. To better manage VCs, a VC must travel over a virtual path (VP) connection. A VP is a bundle of VCs that have the same endpoints. 84 42
TP, VPs, and VCs TP: Transmission Path 85 TP, VPs, and VCs (cont.) A TP is the physical connection (wire, cable, satellite, and so on) between an endpoint and a switch or between two switches. Switch city TP set of all freeways connect the two cities. A VP provides a connection or a set of connections between two switches. VP a freeway that connect two cities. All cells belonging to a single message follow the same virtual circuit (VC) and remain in their original order until they reach their destination. VC lanes of a freeway 86 43
Example of VPs and VCs Eight endpoints are communicating using four VCs. VC1 and VC2 seem to share the same virtual path from Switch I to Switch III, so it is reasonable to bundle VC1 & VC2 together to form VP1. Similarly, it is also reasonable to bundle VC3 & VC4 together to form VP2. VP1 contains VC1 and VC2. VP2 contains VC3 and VC4. 87 ATM Identifiers Note that a virtual connection is defined by a pair of numbers: the VPI (Virtual Path Identifier) and the VCI (Virtual Circuit Identifier) 88 44
Connection Identifiers 89 ATM Cell Fixed length (53 bytes) frame allows simpler and therefore faster processing at switches. For instance, switch does not have to do calculations to figure out how much buffer space it will need for a cell, as is the case with Frame Relay s variable-size frame. 53 bytes 5 bytes of header 48 bytes of payload (data) Fixed length frames are called cells. 90 45
An ATM Cell 91 ATM Cells (Cont.) Short cell length limits latency at each switch. Switches may have to wait until the entire frame arrives before processing it and sending it back out. With shorter frames, there is less latency at each switch along the path Important in continent-wide WANs that require cells to pass through many switches Especially important for voice/video, which is highly latency-intolerant. 92 46
Routing with a ATM Switch ATM switch routes the cell using both the VPIs and the VCIs. Note: in this example, the switch changes the VPI and VCI in the cell header from 153 to 140 and from 67 to 92, respectively. 93 ATM QoS Besides its high speeds, ATM can support different traffic classes to provide different levels of service to prevent congestion. Negotiate with the network for a particular QoS: Before making a connection, user requests how much bandwidth is needed, or if connection needs to be real-time. Network checks to see if it can satisfy user request. If user request can be satisfied, connection is established. If a user does not need a high bandwidth or real-time, a simpler, cheaper connection is created. 94 47
ATM QoS (Cont.) ATM provides strong QoS guarantees for voice/video traffic (latency, jitter, etc.) However, ATM usually offers few or no QoS guarantees for data traffic get what is left over after capacity reserved for voice/video QoS 95 Sample ATM Applications 96 48
ATM on a Large Multi-LAN 97 Advantages and Disadvantages of ATM Advantages Very high speeds and the different classes of service. Disadvantages Potentially high costs (both equipment and support) and a high level of complexity. 98 49
Outlines Introduction to WAN Point-to-point WANs Leased line networks SONET Switched WANs Frame Relay ATM Metro Ethernet/Carrier Ethernet 99 Metro Ethernet/Carrier Ethernet Metropolitan area network (MAN): a city and its environs MANs have smaller distances than national or international WANs, so lower prices and higher speeds Why not use Ethernet as a WAN connection? Hence, the idea of Metro Ethernet was born originally to connect subscribers and businesses in the metropolitan area networks (MANs). Later, it evolved into Carrier Ethernet. Ethernet is moving beyond the LAN Moving into the metropolitan area network (within a single urban area) 100 50
Metro Ethernet/Carrier Ethernet (Cont.) Used for connectivity to the public Internet, and also used for connectivity between corporate sites that are separated geographically. Cheaper than ATM for high speeds. Familiar technology so easy to manage. Eliminates a layer of complexity from WAN access, thus reducing configuration requirements. Speeds of 1 Mbps to 100 Mbps and low prices Carrier can provision or reprovision service speed rapidly to meet periods of high demand Growing rapidly compared to Frame Relay and ATM. 101 Carrier Ethernet Ethernet service is provided by the Carrier Ethernet provider and is delivered at the User-network Interface (UNI) where the Customer Equipment (CE) attaches to the network. A UNI or User-Network Interface is defined by the MEF as the demarcation point between the customer equipment and the service provider. Generally, the UNI is an Ethernet physical interface operating at 10Mbps, 100Mbps, 1Gbps, or 10Gbps. 51
Ethernet Service Types The MEF (Metro Ethernet Forum) developed the Ethernet Service Definition framework, which defines the Ethernet service types. These services are based on the types of the EVC or Ethernet Virtual Connection. An EVC is defined by MEF as an association of two or more UNIs which essentially creates a logical path that connects two or more subscriber sites. An EVC creates a protection and data privacy for the subscriber sites on the same EVC and prevents data transfer between subscriber sites that are not part of the same EVC. The UNI and EVC relationship 52
Three Ethernet Service Types From the EVC types, the MEF derived the following three Ethernet service types: 1. Ethernet Service (E-) Point-to-Point Ethernet service based on a point-to-point EVC. 2. Ethernet LAN Service (E-LAN) Multipoint-to- Multipoint service based on a Multipoint-to-Multipoint EVC. 3. Ethernet Tree Service (E-Tree) Point-to-Multipoint service based on a Routed-Multipoint EVC. E- Service Type E- service type provides a point-to-point Ethernet Virtual Connection between two UNIs or subscriber sites as shown. It is analogous to a dedicated leased line or a Frame Relay PVC. This type of Carrier Ethernet service is the most popular one of all due to its simplicity. The Internet service is usually provided using the E- service type. 53
E-LAN Service type The E-LAN service type can provide connectivity to 2 or more subscriber sites using the same EVC as shown This type of service is more advantageous when adding new subscriber sites as they can be added to the same multipoint EVC without disturbing the existing subscriber sites on same EVC. E-Tree Service Type E-Tree service type provides more of a Hub-and- Spoke environment or in this case a Root-and-Leaf environment. 54
E-Tree Service Type (cont.) The E-Tree provides traffic separation between subscriber sites. Traffic from any leaf can only be sent to and received from a root. Traffic can never be forwarded directly to other leaves in the EVC. This service type is geared towards ISPs that want to provide multicast type service like video on demand. 55