ATM - Overview• ATM is a high-bandwidth switching and multiplexing technology that combines the benefits of circuit switching (ensuring minimum transmission delay and guaranteed bandwidth) with the benefits of packet switching (providing flexibility and efficiency in handling intermittent traffic).
ATM - Overview• ATM technology supports the following types of communications services: – Circuit emulation (CE) services—CE service is an on-demand, connection- oriented, constant bit rate ATM transport service. This service has stringent end-to-end timing requirements, and the user chooses the desired bandwidth and quality of services during connection setup. CE services traditionally provide the equivalent of a dedicated line for such communications applications as video conferencing and multimedia. – Frame Relay services—Frame Relay is an industry-standard, switched data link layer protocol used for handling multiple virtual circuits by means of HDLC encapsulation between connected devices. Due to its relative efficiency, Frame Relay has to some extent superseded X.25 packet-switching technologies. – Switched Multimegabit Data Services (SMDS)—SMDS is a high-speed, packet- switched, datagram-based WAN technology offered typically by telephone companies. – Cell relay services (CRS)—CRS is a networking technology based on the use of small, fixed-length packets (cells) that can be processed and switched in hardware at very high speeds. CRS is the basis for several high-speed networking protocols, including ATM, SMDS, and IEEE 802.6.
ATM Technology• Frame Relay, SMDS, and CRS are "fastpacket" transmission technologies that are playing a prominent role in communications of the 1990s. A generic ATM platform can support all three of these fastpacket technologies, as well as CE services.• A network that supports cell relay services is based on user data units called cells. Such cells are formatted according to a standard layout and sent sequentially in a connection-oriented manner (by means of an established communications path) to remote destinations in the network.• Cell relay services are being used for emerging multimedia and video conferencing applications that require both high transmission capacities and a guaranteed quality of service (QoS). For such applications, cell relay technology provides the most efficient means for transporting data expediently and reliably through the network.• Hence, cell relay services are generally regarded as the best data multiplexing technology available for todays current and emerging communications needs. ATM combines its unique strengths with those inherent in existing data communications and telecommunications applications.
ATM – Cell Relay Sevices• Typically, cell relay services support two types of network connections: – Permanent virtual connections (PVCs)—A PVC is a logical (rather than a physical) connection between two communicating ATM peers. Such a connection is typically established by a network administrator. Thus, a PVC is a non-switched connection that is established beforehand (pre-provisioned manually) to satisfy a standing need for network services. User applications that require an on-going, specific level of transmission bandwidth typically use PVCs for interconnectivity. Such connections are static in nature, that is, they remain in service until changed by the user, a network administrator, or a network management application. – Switched virtual connections (SVCs)— An SVC is a switched connection that is established by means of a defined and standardized ATM signaling protocol. Such connections are set up dynamically ("on demand") across the network, as required by the users communications applications.
ATM Technology• The power and flexibility of ATM derive from two primary attributes: – ATM supports very high-speed interfaces in a single data transmission and switching fabric – ATM supports the multiplexing of multiple traffic types—data, voice, and video.• Consequently, ATM affords the following benefits to network users: – Provides flexible access to and efficient use of network resources – Provides scalable framework for growing the network – Enables highly integrated communications capabilities and services
Benefits of ATM• ATM Benefits ATM technology offers the following primary benefits: – Bandwidth efficiency—ATM efficiently supports the aggregate transmission requirements of a network by allocating bandwidth on demand, based on actual user needs. Bandwidth allocation is accomplished without administrative intervention. Furthermore, network bandwidth is scalable to meet future user needs for higher transmission rates. – Scalability —ATM is highly flexible, accommodating a wide range of traffic types, traffic rates, and communications applications. ATM interface standards exist for data rates as low as 1.544 Mbps (DS1) and as high as 2.4 Gbps (SONET). – Application transparency—The fixed-length size of an ATM cell is an effective compromise between the typically lengthy packets of data communications applications and the short, repetitive frames of telecommunications (voice) applications.
ATM – User benefits• ATM affords the following user benefits: – Provides timely access to network resources – Supports message traffic of variable length – Provides higher transmission speeds – Provides self-routing capabilities for multiple traffic types – Supports new data communications and telecommuncations applications – Offers guaranteed network access for voice and video applications – Enables users to request a desired level and quality of service – Provides protection mechanisms against network congestion conditions
VLAN/LANE• What Is a VLAN?• Well, the reality of the work environment today is that personnel is always changing. Employees move departments; they switch projects. Keeping up with these changes can consume significant network administration time. VLANs address the end-to-end mobility needs that businesses require.• Traditionally, routers have been used to limit the broadcast domains of workgroups. While routers provide well-defined boundaries between LAN segments,• they introduce the following problems: - Lack of scalability (e.g., restrictive addressing on subnets) - Lack of security (e.g., within shared segments) - Insufficient bandwidth use (e.g., extra traffic results when segmentation of the network is based upon physical location and not necessarily by workgroups or interest group) - Lack of flexibility (e.g., cost reconfigurations are required when users are moved)
VLANE• Virtual LAN, or VLAN, technology solves these problems because it enables switches and routers to configure logical topologies on top of the physical network infrastructure. Logical topologies allow any arbitrary collection of LAN segments within a network to be combined into an autonomous user group, appearing as a single LAN.
VLAN - Functionality• A VLAN can be defined as a logical LAN segment that spans different physical LANs. VLANs provide traffic separation and logical network partitioning.• VLANs logically segment the physical LAN infrastructure into different subnets (broadcast domains for Ethernet) so that broadcast frames are switched only between ports within the same VLAN.• A VLAN is a logical grouping of network devices (users) connected to the port(s) on a LAN switch. A VLAN creates a single broadcast domain and is treated like a subnet.• Unlike a traditional segment or workgroup, you can create a VLAN to group users by their work functions, departments, the applications used, or the protocols shared irrespective of the users’ work location (for example, an AppleTalk network that you want to separate from the rest of the switched network).• VLAN implementation is most often done in the switch software.
Remove the Physical BoundariesConceptually, VLANs provide greater segmentation and organizational flexibility. VLANtechnology allows you to group switch ports and the users connected to them intologically defined communities of interest. These groupings can be coworkers within thesame department, a cross-functional product team, or diverse users sharing the samenetwork application or software (such as Lotus Notes users).
VLAN Benefits• VLANs provide many internetworking benefits that are compelling. – Reduced administrative costs—Members of a VLAN group can be geographically dispersed. Members might be related because of their job functions or type of data that they use rather than the physical location of their workspace. – The power of VLANs comes from the fact that adds, moves, and changes can be achieved simply by configuring a port into the appropriate VLAN. Expensive, time-consuming recabling to extend connectivity in a switched LAN environment, or host reconfiguration and re-addressing is no longer necessary, because network management can be used to logically “drag and drop” a user from one VLAN group to another. – Better management and control of broadcast activity—A VLAN solves the scalability problems often found in a large flat network by breaking a single broadcast domain into several smaller broadcast domains or VLAN groups. All broadcast and multicast traffic is contained within each smaller domain.
X.25• X.25 networks implement the internationally accepted ITU-T standard governing the operation of packet switching networks. Transmission links are used only when needed.• X.25 was designed almost 20 years ago when network link quality was relatively unstable. It performs error checking along each hop from source node to destination node.• The bandwidth is typically between 9.6Kbps and 64Kbps.• X.25 is widely available in many parts of the world including North America, Europe, and Asia. There is a large installed base of X.25 devices.
FRAME RELAY• Frame Relay provides a standard interface to the wide-area network for bridges, routers, front-end processors (FEPs), and other LAN devices.• A Frame Relay interface is designed to act like a wide-area LAN- it relays data frames directly to their destinations at very high speeds.• Frame Relay frames travel over predetermined virtual circuit paths, are self-routing, and arrive at their destination in the correct order.• Frame Relay is designed to handle the LAN-type bursty traffic efficiently.• The guaranteed bandwidth (known as committed information rate or CIR) is typically between 56 Kbps and 1.544 Mbps. The cost is normally not distance-sensitive.
FDDI (Fiber Distributed Data Interface)• FDDI (Fiber Distributed Data Interface) has found its niche as a reliable, high-speed backbone for mission critical and high traffic networks.• It can transport data at a rate of 100 megabits per second, and can support up to 500 stations on a single network.• FDDI was designed to run through fiber cables, transmitting light pulses to convey information between stations, but it can also run on copper using electrical signals.
FDDI• FDDI is highly reliable because FDDI networks consist of two counter-rotating rings. A secondary ring provides an alternate data path in the event a fault occurs on the primary ring. FDDI stations incorporate this secondary ring into the data path to route traffic around the fault.
"Dual Homed" FDDI Backbone With Ethernet Switching
FDDI - Advantages• High Speed And Deterministic Technology FDDI runs at a speed of 100 or 200 Mbps. This results in very good performance for demanding applications which need to transfer large amounts of data in a short amount of time. It is also excellent for servicing the needs of a large number of users to ensure everyone has enough bandwidth. FDDIs token-passing network results in a collision-free network which gives excellent performance even under heavy load (80% + utilization).• Long Distance With an overall ring length of up to 20 km (66,000 feet), FDDI is an excellent choice for building a building-wide or campus network interconnecting several buildings.• Fault Tolerance FDDIs dual ring archetecture and the ability to set up a network with the dual homing provides the ability to design networks which can continue to operate even if a cable run is cut or a concentrator should fail. Since FDDI has been in use for several years, the equipment has been thoroughly debugged and is exceptionally stable.• Management FDDI works with all of the popular network management platforms, and most FDDI equipment has management features built-in from the factory.• Flexibility FDDI can be used with any of four cable types, allowing the designer to use less expensive UTP or STP cable where runs are short and fiber optic cable where distances are longer and/or electrical noise is a concern.
FDDI - Disadvantage• Cost - FDDI equipment is higher in cost than other 100 Mbps network technologies. This is due to the complexity of the token passing protocol and certain royalties which must be paid for every piece of equipment manufactured.
Copper Distributed Data Interface (CDDI)• Copper Distributed Data Interface (CDDI) is the implementation of FDDI protocols over twisted-pair copper wire. Like FDDI, CDDI provides data rates of 100 Mbps and uses dual-ring architecture to provide redundancy. CDDI supports distances of about 100 meters from desktop to concentrator.• CDDI is defined by the ANSI X3T9.5 Committee. The CDDI standard is officially named the Twisted-Pair Physical Medium-Dependent (TP-PMD) standard. It is also referred to as the Twisted-Pair Distributed Data Interface (TP-DDI), consistent with the term Fiber Distributed Data Interface (FDDI). CDDI is consistent with the physical and media- access control layers defined by the ANSI standard.
CDDI TP-PMD and FDDI Specifications Adhere to Different Standards
Integrated Services Digital Network (ISDN)• ISDN is a digital service that can use asynchronous or, more commonly, synchronous transmission. ISDN can transmit data, voice, and video over existing copper phone lines.• Instead of leasing a dedicated line for high-speed digital transmission, ISDN offers the option of dialup connectivity— incurring charges only when the line is active.• ISDN provides a high-bandwidth, cost-effective solution for companies requiring light or sporadic high-speed access to either a central or branch office.• ISDN can transmit data, voice, and video over existing copper phone lines. Instead of leasing a dedicated line for high-speed digital transmission, ISDN offers the option of dialup connectivity —incurring charges only when the line is active.
ISDN – BRI and PRI• ISDN comes in two flavors, Basic Rate Interface (BRI) and Primary Rate Interface (PRI).• BRI provides two “B” or bearer channels of 64 Kbps each and one additional signaling channel called the “D” or delta channel. While it requires only one physical connection, ISDN provides two channels that remote telecommuters use to connect to the company network.• PRI provides up to 23 bearer channels of 64 Kbps each and one D channel for signaling. That’s 23 channels but with only one physical connection, which makes it an elegant solution- there’s no wiring mess (PRI service typically provides 30 bearer channels outside the U.S. and Canada). You’ll want to use PRI at your central site if you plan to have many ISDN dial-in clients.
SONET/SDH• SONET/SDH are point-to-point synchronous networks that use TDM multiplexing across a ring or mesh physical topology. These provide the Physical layer foundation for FDDI, SMDS, and ATM implementations.• SONET/SDH are true optical implementations. They take advantage of the bandwidth and high reliability of the fiber optic medium. Because they are typically WAN standards, SONET/SDH use point-to-point connection types. The point-to-point architecture makes the standards ideal for high and centralized systems or WAN backbones.