Chapter 7 Backbone Network

Announcements and Outline 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 Outline Backbone Network Components Switches, Routers, Gateways Backbone Network Architectures Backbone Best Practices Improving backbone performance Copyright 2010 John Wiley & Sons, Inc 2

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

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

Backbone Network Devices    

Switches

Switches

Routers

Routers Operations Compared to Switches 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

Backbone Network Architectures Identifies the way backbone interconnects LANs Manages way packets from one network move through the backbone to other networks Three layers:

Backbone Network Design Layers

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.

Switched Backbone Inse

Switched Backbones Replaces the many routers of other designs Advantages:

Rack-Mounted Switched Backbones

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

Main Distribution Facility (MDF)

Rack Room 18

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

Routed Backbone

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

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

VLAN-based Backbone

Multi-switch VLAN-Based Backbone

How VLANs Work 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

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

Recommendations for Backbone Design Best architecture Best technology: Ideal design:

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 Common Carriers 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 Circuit-Switched Networks Dedicated-Circuit Networks Packet-Switched Networks 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

8.22 Ring Architecture Reliability Performance

8.22 Star Architecture Easy 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 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 Hierarchy SONET 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 OC-1 52 Mbps $5000-25,000/mo OC-2 155 Mbps $30,000 + /mo OC-3 622 Mbps $50,000 +/mo

8.23 Packet Switched Services – Basic Architecture

8.23 Packet Switched Services Recap: In both circuit switched and dedicated services… Packet switched services

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)

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

8.24 Virtual Private Networks Provides equivalent of a private packet switched network over public Internet Provides low cost and flexibility Disadvantages of VPNs:

8.24 VPN – Basic Architecture

8.24 Layer 3 VPN Using IPSec

8.24 VPN Types Intranet VPN Extranet VPN Access VPN

8.3 WAN Design Practices Difficult to recommend best practices Factors used Design Practices

8.3 MAN/WAN Services Summary

8.3 Recommendations Best Practices MAN/WAN

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) Reduces overall network capacity Should not exceed 20%

8.4 Improving Circuit Capacity

8.4 Reducing Network Demand