Chapter 7

Backbone Network

Announcements and OutlineAnnouncements• Grades for Assessment 2 and Assessment 2 Review Posted• Exercise 6 due tonight before midnight• Design Quiz will be moved from Tuesday to Thursday

• Tuesday – finish Chapter 8 (Wide Area Network) & start on designing networks

OutlineBackbone Network Components

Switches, Routers, Gateways

Backbone Network ArchitecturesBackbone Best Practices Improving backbone performance

2Copyright 2010 John Wiley & Sons, Inc

Backbone Networks

High speed networks linking an organization’s LANs Making information transfer possible between

departments Use high speed circuits to connect LANs Provide connections to other backbones, MANs, and

WANs

Sometimes referred to as An enterprise network A campus network

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Backbone Network Components

Network cable Functions in the same way as in LANs Optical fiber - more commonly chosen because it

provides higher data rates

Hardware devices Computers or special purpose devices used for

interconnecting networks• Switches• Routers • Gateways

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Backbone Network Devices

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Switches

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Switches

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Routers

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Routers

Operations Operates at the network layer Examines the destination address of the network layer Strips off the data link layer packet Chooses the “best” route for a packet (via routing

tables) Forwards only those messages that need to go to other

networks

Compared to Switches Performs more processing Processes only messages specifically addressed to it Recognizes that message is specifically addressed to it

before message is passed to network layer for processing

Builds new data link layer packet for transmitted packets

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Backbone Network Architectures

Identifies the way backbone interconnects LANs

Manages way packets from one network move through the backbone to other networks

Three layers:

1.

2.

3.

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Backbone Network Design Layers

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Fundamental Backbone Architectures

Switched Backbones: most common type of backbone, used in distribution layer, used in new buildings, sometimes in core layer, can be rack or chassis based.

Routed Backbones: move packets along backbone on basis of network layer address, typically using bus, Ethernet 100Base-T, sometimes called subnetted backbone

Virtual LANs: networks in which computers are assigned into LAN segments by software rather than by hardware; can be single switch or multiswitch VLANs. Very popular technology.

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Switched Backbone

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Inse

Switched Backbones

Replaces the many routers of other designs

Advantages:

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Rack-Mounted Switched Backbones

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Rack-Based Switched Backbones

Places all network switch equipment physically in one “rack” room Easy maintenance and upgrade Requires more cable, but usually small part of overall

cost

Main Distribution Facility (MDF) or Central Distribution Facility (CDF) Another name for the rack room Place where many cables come together Patch cables used to connect devices on the rack

Easier to move computers among LANs

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Main Distribution Facility (MDF)

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Rack Room

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Chassis-Based Switched Backbones

Use a “chassis” switch instead of a rack Enables administrators to plug modules into switch Modules can vary in nature, router or 4-port 100Base T

switch• Example of a chassis switch with 710 Mbps capacity

– 5 10Base-T hubs, 2 10Base-T switches (8 ports each)– 1 100Base-T switch (4 ports), 100Base-T router– ( 5 x 10) + (2 x 10 x 8) + (4 x 100) + 100 = 710

Mbps

Advantage is flexibility Enables users to plug modules directly into the switch Simple to add new modules

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Routed Backbone

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Routed Backbones

Move packets using network layer addresses

Commonly used at the core layer

LANs can use different data link layer protocols

Main advantage

Main disadvantages

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Virtual LANs (VLANs)

A new type of LAN-BN architecture Made possible by high-speed intelligent switches Computers assigned to LAN segments by software

Often faster and provide more flexible network management Much easier to assign computers to different segments

More complex and so far usually used for larger networks

Basic VLAN designs: Single switch VLANs Multi-switch VLANs

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VLAN-based Backbone

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Multi-switch VLAN-Based Backbone

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How VLANs Work

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Each computer is assigned into a VLAN that has a VLAN ID

Each VLAN ID is matched to a traditional IP subnet• Each computer gets an IP address from that switch

• Similar to how DHCP operates

Computers are assigned into the VLAN based on physical port they are plugged into

Multiswitch VLAN Operations

Same as single switch VLAN, except uses several switches, perhaps in core between buildings

Inter-switch protocols Must be able to identify the VLAN to which the packet

belongs

Use IEEE 802.1q (an emerging standard) When a packet needs to go from one switch to another

• 16-byte VLAN tag inserted into the 802.3 packet by the sending switch

When the IEEE 802.1q packet reaches its destination switch

• Its header (VLAN tag) stripped off and Ethernet packet inside is sent to its destination computer

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VLAN Operating Characteristics

Advantages of VLANs Faster performance: Allow precise management of traffic

flow and ability to allocate resources to different type of applications

Traffic prioritization (via 802.1q VLAN tag)• Include in the tag: a priority code based on 802.1q• Can have QoS capability at MAC level

– Similar to RSVP and QoS capabilities at network and transport layers

Drawbacks Cost Management complexity Some “bleeding edge” technology issues to consider

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Recommendations for Backbone Design

Best architecture

Best technology:

Ideal design:

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Chapter 8

Wide Area Networks

8.1 Introduction

Wide area networks (WANs)

Typically built by using leased circuits from common carriers such as AT&T

8.1 Introduction (Cont.)

Regulation of services Federal Communications Commission (FCC) in the US Canadian Radio Television and Telecomm Commission

(CRTC) in Canada Public Utilities Commission (PUC) in each state

Common Carriers Local Exchange Carriers (LECs) like Verizon Interexchange Carriers (IXCs) like Sprint

8.2 MANs/WANs Services

1) Circuit-Switched Networks

2) Dedicated-Circuit Networks

3) Packet-Switched Networks

4) Virtual Private Networks

8.21 Circuit Switched Networks – Architecture

8.21 Circuit Switched Networks

Oldest and simplest WAN approach

Uses the Public Switched Telephone Network (PSTN), or the telephone networks

Provided by common carriers

Basic types in use today: POTS (Plain Old Telephone Service)

• Via use of modems to dial-up and connect to ISPs

ISDN (Integrated Services Digital Network )• Basic Rate Interface (BRI) – 128 Kbps• Primary Rate Interface (PRI) – 1.5 Mbps

8.21 Circuit Switched Services

Simple, flexible, and inexpensive When not used intensively

Main problems Varying quality

• Each connection goes through the regular telephone network on a different circuit,

Low Data transmission rates• Up to 56 Kbps for POTS, and up to 1.5 Mbps for ISDN

An alternative Use a private dedicated circuit

• Leased from a common carrier for the user’s exclusive use 24 hrs/day, 7 days/week

8.22 Dedicated Circuit Services – Basic Architecture

8.22 Dedicated Circuits

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8.22 Ring Architecture• Reliability

• Performance

8.22 Star ArchitectureEasy to manage

Reliability

Performance

8.22 Mesh Architectures

8.22 Dedicated Services - T-Carrier

Most commonly used dedicated digital circuits in North America

Units of the T-hierarchy• T-1

• T-2

• T-3

• T-4

8.22 T-Carrier Digital Hierarchy

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T-Carrier Designation

DS Designation Data Rate

DS-0 64 Kbps

T-1 DS-1 1.544 Mbps

T-2 DS-2 6.312 Mbps

T-3 DS-3 44.376 Mbps

T-4 DS-4 274.176 Mbps

8.22 Dedicated Services - Synchronous Optical Network (SONET)

ANSI standard for optical fiber transmission in Gbps range Similar to ITU-T-based, synchronous digital hierarchy

(SDH) SDH and SONET can be easily interconnected

SONET hierarchy Begins with OC-1 (optical carrier level 1) at

51.84 Mbps Each succeeding SONET hierarchy rate is defined

as a multiple of OC-1

8.22 SONET Digital HierarchySONET Designation

SDH Designation Data Rate

OC-1 STM-0 51.84 Mbps

OC-3 STM-1 155.52 Mbps

OC-9 STM-3 466.56 Mbps

OC-12 STM-4 622.08 Mbps

OC-18 STM-6 933.12 Mbps

OC-24 STM-8 1.244 Gbps

OC-36 STM-12 1.866 Gbps

OC-48 STM-16 2.488 Gbps

OC-192 STM-64 9.952 Gbps

8.23 Packet Switched Services – Basic Architecture

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8.23 Packet Switched Services

Recap: In both circuit switched and dedicated services…

Packet switched services

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8.23 Packet Switching

Interleave packets from separate messages for transmission Most data communications consists of short burst of

data Packet switching takes advantage of this burstiness

• Interleaving bursts from many users to maximize the use of the shared network

8.23 Packet Switched - Service Protocols

• X.25• Oldest packet switched service (widely used in Europe)• Not in widespread use in North America

• Low data rates (64 Kbps) (available now at 2.048 Mbps)

• Asynchronous Transfer Mode (ATM)• Newer than X.25; also standardized• Data Rates

• Same rates as SONET: 51.8, 466.5, 622.08 Mpbs• New versions: T1 ATM (1.5 Mbps), T3 ATM (45 Mbps)

• Provides extensive QoS information • Enables setting of precise priorities among different

types of transmissions (i.e. voice, video & e-mail)

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8.23 Packet Switched - Service Protocols

• Frame Relay• Faster than X.25 but slower than ATM• NO QoS support (under development)• Common CIR speeds:

• 56, 128, 256, 384 Kbps, 1.5, 2, and 45 Mbps

• Ethernet Services• Most organizations use Ethernet and IP in the LAN and

BN.• Currently offer CIR speeds from 1 Mbps to 1 Gbps at 1/4

the cost of more traditional services• No need to translate LAN protocol (Ethernet/IP) to the

protocol used in MAN/WAN services• X.25, ATM, & Frame Relay use different protocols

requiring translation from/to LAN protocols

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8.24 Virtual Private Networks

Provides equivalent of a private packet switched network over public Internet

Provides low cost and flexibility

Disadvantages of VPNs:

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8.24 VPN – Basic Architecture

8.24 Layer 3 VPN Using IPSec

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8.24 VPN Types

Intranet VPN

Extranet VPN

Access VPN

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8.3 WAN Design Practices

Difficult to recommend best practices

Factors used

Design Practices

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8.3 MAN/WAN Services Summary

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8.3 Recommendations Best Practices MAN/WAN

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8.4 Improving Performance

MAN/WAN: Handled in the same way as improving LAN performance By checking the devices in the network, By upgrading the circuits between computers By changing the demand placed on the network

Device: • Upgrade the devices (routers) and computers that

connect backbones to the WAN • Examine the routing protocol (static or dynamic)

• Dynamic routing• Increases performance in networks with many

possible routes from one computer to another• Better suited for “bursty” traffic• Imposes an overhead cost (additional traffic)

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8.4 Improving Circuit Capacity

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8.4 Reducing Network Demand

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