Chapter 5 Hardware Layers Backbone Networks Networking in the Internet Age by Alan Dennis 1 Copyright 2002 John Wiley Sons Inc Copyright John Wiley Sons Inc All rights reserved Reproduction or translation of this work beyond that named in Section 117 of the United States Copyright Act without the express written consent of the copyright owner is unlawful Requests for further information should be addressed to the Permissions Department John Wiley Sons Inc Adopters of the textbook are granted permission to make back up copies for their own use only to make copies for distribution to students of the course the textbook is used in and to modify this material to best suit their instructional needs Under no circumstances can copies be made for resale The Publisher assumes no responsibility for errors omissions or damages caused by the use of these programs or from the use of the information contained herein 2 Chapter 5 Learning Objectives Understand hierarchical backbones and the devices they use Understand flat backbones and the devices they use Understand collapsed backbones and the devices they use Understand VLANs and the devices they use Be familiar with FDDI Be familiar with ATM Understand the best practice recommendations for backbone design 3 Chapter 5 Outline Introduction Backbone Architectures Hierarchical backbones Flat backbones Collapsed backbones Virtual LANs Fiber Distributed Data Interface Topology Medium Access Control Error Control Message Delineation Data Transmission in the Physical Layer Asynchronous Transfer Mode Topology Medium Access Control Error Control Message Delineation Data Transmission in the Physical Layer ATMs and LANs The Best Practice Backbone Design Architectures Effective Data Rates Conversion Between Protocols Recommendations 4 Introduction 5 Backbone Networks Backbone networks are high speed networks that link an organization s LANs and also provide connections to other backbones MANs WANs and the Internet A backbone that connects backbones in several buildings is also often called a campus network A backbone is also sometimes called an enterprise network if it connects all the networks within a company especially if this includes large WAN segments 6 Backbone Architecture Layers Figure 5 1 Network designers view networks as made of three technology layers The access layer which is the technology used in LANs The distribution layer which is the part of the backbone that connects the LANs together The core layer connects different backbone networks together often between buildings Some organizations are not large enough to have a core layer In such cases their backbone only spans the distribution layer 7 Figure 5 1 Backbone network design layers 8 Backbone Architectures 9 Backbone Network Types There are four basic types of backbone networks Hierarchical Backbones Flat Backbones Collapsed Backbones Virtual LANs 10 Hierarchical Backbones Figure 5 2 shows an example of a distribution layer hierarchical backbone Each LAN is a separate and isolated network connected by a TCP IP gateway usually a router to a shared media backbone network Within the LANs messages are sent based on the data link layer addresses To move between LANs message traffic needs to be sent specifically to the router which forwards the message based on its network layer address 11 Figure 5 2 Hierarchical backbone architecture 12 Flat Backbones Figure 5 3 gives an example of a distribution layer flat backbone with a bus topology With a flat backbone LANs are connected using bridges or layer 2 switches Packets are forwarded based on their data link layer addresses making the entire flat backbone a single subnet Flat backbones using bridges were developed in the mid 1980s to reduce costs because at the time routers were very expensive Bridges have now become obsolete and are typically replaced by layer 2 switches which have continued to fall in price 13 Figure 5 3 Flat backbone architecture 14 Collapsed Backbones Figure 5 4 Collapsed backbones use a star topology usually with a high speed switch at the center Collapsed backbones can use either layer 2 switches or layer 3 routing switches The two main advantages are 1 each connection to the switch becomes a separate point to point circuit also giving much higher performance from 200 600 higher 2 the network has far fewer devices and so is much simpler to manage Two minor disadvantages are 1 use more cable and the cable runs for longer distances 2 if the central switch fails the network goes down 15 Figure 5 4 Collapsed backbone architecture 16 Rack Mounted Collapsed Backbones Rack mounted backbones collapse the backbone into a single room called a main distribution facility MDF where networking equipment is connected and mounted on equipment racks Figure 5 5 Devices are connected using short patch cables Moving computers between LANs is relatively simple since equipment is all in the same location 17 Fig 5 5 Rack mounted collapsed backbone architecture 18 Chassis based Collapsed Backbones Chassis switch designs include a number of open slots and have an internal capacity capable of supporting all active modules A variety of modules i e card mounted networking devices can be inserted into these slots providing a high level flexibility in network configuration By turning the backbone into an internal bus chassis switches also can provide very high performance speeds capable of aggregate data rates in the Gbps range 19 Figure 5 7 Central Parking s collapsed backbone 20 Virtual LANs VLANs are a new type of LAN BN architecture using intelligent high speed switches Unlike other LAN types which physically connect computers to LAN segments VLANs assign computers to LAN segments by software VLANs have been standardized as IEEE802 1q and IEEE802 1p The two basic designs are Single switch VLANs Multiswitch VLANs 21 Single Switch VLANs Figure 5 8 With single switch VLANs computers are assigned to VLANs using special software but physically connected together using a large physical switch Computers can be assigned to VLANs in four ways Port based VLANs assign computers according to the VLAN switch port to which they are attached MAC based VLANs assign computers according to each computer s data link layer address IP based VLANs assign computers using their IP address Application based VLANs assign computers depending on the application that the computer typically uses This has the advantage of allowing precise allocation of network capacity 22