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

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