Business Data Communications

1. Business Data Communications Chapter Six Backbone and Metropolitan Area Network Fundamentals

2. Primary Learning Objectives • Define backbone and metropolitan area networks • Differentiate between horizontal and vertical network segments • Recognize the function of a backbone network protocol • Understand the advantages and disadvantages of distributed and collapsed backbones • Explain the concept of backbone fault tolerance • List examples of backbone design considerations • Identify common backbone problems • Describe Switched Multimegabit Data Services

3. Backbone and Metropolitan Area Networks • A backbone network (BN): • Connects other networks of an organization • Networks connected are typically LANs • Generally spans a building or campus • Has its own address • A metropolitan area network (MAN): • Is often used to connects BNs • Generally spans a city • Is sometimes viewed as a citywide backbone • Has its own address • The distinction between BNs and MANs is blurring

4. Horizontal and Vertical Networks • Each individual LAN is called a network segment • A network segment may be horizontal or vertical • Horizontal networks are configured on a single floor • Vertical networks are configured on multiple floors • Whether horizontal or vertical, network segments are usually connected to each other by means of a backbone network

5. A Horizontal Network

6. A Vertical Network

7. Connecting to a backbone

8. Backbone Network Protocols • BNs most often support high traffic demand for connected LANs • Therefore a BN generally uses a protocol that provides higher throughput than the protocol used by the connected LANs • Gigabit Ethernet: • Is a common protocol choice for BNs • In its initial form was labeled 802.3z by the IEEE • Supports 1 Gbps (billion bits per second) • Does not change the underlying Ethernet format • Is both half- and full-duplex capable • ATM and Frame Relay are also possible BN protocols

9. Distributed and Collapsed Backbones • In addition to having a protocol, BNs have an architecture • Two common types of BN architecture are: • Distributed • Collapsed • Factors that influence the BN architecture choice include: • Business need • Condition of the facility or physical plant • The way that users need to communicate • Budget • Placement of networked devices

10. Distributed Backbones • “Distributed” implies “in more than one location” • A Distributed Backbone: • Runs throughout the entire facility • Uses a central cable • Requires its own protocol • Is its own network • Is usually connected to network segments, LANs, by switches and/or routers • Can have directly connected devices that are part of the BN

11. Distributed Backbones Each router will have two network addresses

12. Distributed Backbones • When configured with multiple routers, may need to pass traffic through several routers for that traffic to reach its final destination • Going through several routers can result in traffic delay • Internetwork traffic can be expected to increase when more routers are used • Require that each network segment have its own cabling and connecting device to the distributed backbone, adding to expense

13. Distributed Backbones • Are generally more complex than collapsed backbones, resulting in more complicated: • Security • Maintenance • Monitoring • Allow the placing of commonly needed networked devices or resources directly onto the backbone • May be the only viable solution for a business, depending on the facility and layout of network segments

14. Distributed Backbone with a Directly Connected DB Server

15. Collapsed Backbones • Use a single central device, namely a router or switch, to which network segments are connected • This central router or switch is in essence the backbone • Connect network segments to the collapsed backbone, using other hubs, switches, or routers • Generally reduce cabling needs, however: • Connected devices must be able to support cable segment lengths that span the distance to the collapsed backbone • Legacy networks using lower grade UTP may not be collapsed-backbone compatible

16. Collapsed Backbones • Do not require a protocol different from that of connected network segments • Having one protocol can make network administration easier • However, depending on how the backbone needs to be used relative to traffic demands, having one protocol may not be an advantage • Utilize a “backplane”--a high-speed communications bus--in the switch or router

17. Collapsed Backbones • Use fiber optic cabling to connect network segments to a collapsed backbone’s backplane • Fiber allows network segments to be widely scattered across a building or campus • Might not allow legacy Ethernet networks to utilize the collapsed backbone architecture • Pass internetwork traffic through only one device • Centralize security, monitoring, and maintenance • Can achieve significant cost savings

18. Collapsed Backbones Internetwork traffic passes through only one connecting device, in this example a switch, to its ultimate destination

19. Distributed versus Collapsed

20. Backbone Fault Tolerance • “Fault tolerance” is the capability of a technology to recover in the event of an error, failure, or some other unexpected event • Backbones, because they connect and provide communication to various segments of an enterprise, must be fault tolerant • Resource redundancy is a common means of providing fault tolerance

21. A Simplified Redundant Backbone

22. Backbone Fault Tolerance • Redundant backbones also allow for traffic load balancing • By permitting placement of half of all network segments onto one or the other backbone, duplicate backbones allow internetworking traffic to be shared or balanced • Duplicating the backbone can be done in whole or in part, based on cost and need • Documentation is also part of recovery procedures

23. Backbone Design Considerations • Internal versus external wiring • Identification and labeling of all backbone networks, devices, wiring • Knowledge of collision domain boundaries • An enterprise with a mix of Ethernet networks (such as Standard, Fast, Gigabit) might have a mix of collision domains • Wiring closets • Data centers

24. Backbone Design Considerations

25. Backbone Design Considerations

26. Wiring Closet Design

27. A few Good Tools

28. Common Gigabit Backbone Problems • Packet errors • Early collision • Late collision • Runts • Giants and jabbering • Broadcast storms

29. Common Gigabit Backbone Problems • Cable errors: • Near-end cross talk • Attenuation • Impedance • Attenuation to cross talk • Capacitance • Cable length

30. Common Gigabit Backbone Problems • Network Interface Card errors: • Improper configuration – diagnostic software • Physical failure • Connectivity testing with ping: • Based on ICMP • Various vendor implementations • Echo_Request • Echo_Reply • Time-to-live

31. Common Gigabit Backbone Problems

32. Switched Multimegabit Data Services - SMDS • Were designed specifically for MANs • Support exchanging data between: • LANs in different parts of a city • Network segments over a large campus • Provide packet-switched datagram delivery • Are associated with a common carrier’s SMDS network • Require subscribers to pay only when they use the common carrier’s network

33. In Summary • The distinction between BNs and MANs is blurring • BNs are critical in connecting the various network segments of an organization • BNs have both a protocol and architecture: • Gigabit Ethernet is a popular BN protocol • Two BN architectures are distributed or collapsed • Fault tolerance is important for the backbone • Common Gigabit backbone problems include packet, cable, and NIC errors • SMDS is associated particularly with MANs