Overview Multiplexing techniques Circuit switching

OverviewMultiplexing techniques Circuit switching

Space Division (SDM) - Digital Cross ConnectFrequency Division (FDM) Origins of packet switching

Time Division (TDM) Introduction to:

Addressing - Frame relaySwitching - X.25

Point-to-point - Fast Packetpoint-to-multipoint - ATMspace divisiontime divisionaddressfrequency

Multiplexing TechnologiesMultiplexing defines the means by which multiple streams of information from multiple users share a common physical transmission medium all of which may require some or all of the bandwidth at any given time.Switching takes multiple instances of a physical transmission medium, each containing multiplexed information streams, and rearranges the information streams between the input and output of the switch.

Multiplexer DefinedThe multiplexing function shares many inputs to a single output. The demultiplexing function has one input which must be distributed to many outputs.Refer to Figure 6.1 (p. 189)The overall speed on the access side interfaces is generally less than that on the trunk side.Multiplexing techniques can be used to share a physical medium between multiple users at two different sites over a private line with each pair of users requiring some or all of the bandwidth at any given time.

Multiplexing Methods

Space Division Multiplexing

It can be facilitated by mechanical patch panels, or by optical and electronic patch panelsIt is being replaced by space division switching or other types of multiplexingAn example of SDM is seen where multiple cables interconnect equipment.

Frequency Division Multiplexing (FDM)Many analog conversations are multiplexed onto the same cable, or radio spectrum,by modulating each signal by a carrier frequency.Refer to Figure 6.2 (p. 190)FDM multiplexes 12 voice-grade, full-duplex channels into a single 48-kHz bandwidth group by translating each voiceband signal’s carrier frequency.One variation of FDM is Wavelength Division Multiplexing (WDM) based on Fiber technology.Refer to Figure 6.3 (p. 191)

Time Division Multiplexing (TDM)TDM allows multiple users to share a digital transmission medium by using preallocated time slots.Refer to Figure 6.4 (p. 193)Time slots are dedicated to a single user, whether data is being transmitted or the user is idle. The same time slots are dedicated to the same user in the same order for every frame transmitted.Different time slots are dedicated to different channel sources, such as voice channels, data, or video.Multiplexer inputs can carry simultaneously asynchronous and synchronous data

Time Division Multiplexing (TDM) (Continue….)

All transmissions through multiplexers are point-to-pointA single T1 circuit can be configured for 24 to 196 allocated channels.Each channel uses 64 kbpsRefer to Figure 6.5 (p. 194)

Address or Label MultiplexingA common name for address multiplexing is Asynchronous Time Division Multiplexing (ATDM)Examples: SNA, DECNET, X.25, Frame Relay, ATMStatistical Time Division Multiplexing (STDM) dynamically assigns time slots only to users who need data transmission.The net effect is an increase in overall throughput for users since time slots are “reserved” or dedicated to individual users.Refer to Figure 6.6 (p. 194)Concentrator is a type of block-oriented multiplexer.Concentrators transmit blocks of information for each user as needed,

adding an address to each block to identify the user.

Address or Label Multiplexing (Continue…)Concentrators utilizing this technique are called Asynchronous Time Division Multiplexers (ATDMs).The primary difference between concentrator and multiplexing is that concentrators have additional intelligence to understand the contents of the data being passed and can route the information streams based upon the data within them.

Types of Multiplexers

There are four types of multiplexers used in data network designs:

Access multiplexerNetwork multiplexerDrop-and-insert multiplexerAggregator multiplexor

Most forms of multiplexing are protocol-transparent and protocol-independent.Refer to Figure 6.7 (p. 197)

Access or Channel Bank MultiplexersThey provide the first level of user access to the multiplexer network. These devices typically reside on the user or customer premisesThey provide network access for a variety of user asynchronous and synchronous, low- and high-speed inputs including: Data telephone, LAN, Low-speed video, terminal.Access multiplexers usually provide one or more T1 trunks to the next class of larger multiplexers, the backbone multiplexer.

Access or Channel Bank Multiplexers (continue…)There are two versions:

Fractional T1 multiplexerSubRate Data multiplexer

Refer to Figure 6.8 (p. 198)Refer to Figure 6.9 (p. 199)Both versions optimize the use of access trunks for multiple low-speed users.

Network MultiplexersThey support T1 on the access side and T3 or higher on the network side.They offer larger capacity, reroute capability, and configuration capabilityPrivate and public data transport network backbones are built using network multiplexers.Refer to Figure 6.10 (p. 200)

Aggregator MultiplexersThey combine multiple T1 channels into higher-bandwidth pipes for transmission.

M12 Multiplexer: 4 DS1s to the rate of DS2M13 Multiplexer: 28 DS1s to the rate of DS3M23 Multiplexer: 7 DS2s to the rate of DS3M22 and M44 Multiplexers: configuration management and rerouting capability of 22 and 44 channelsMX3 Multiplexer: different combinations of DS1s and DS2s to the rate of DS3

Note that syncrhonization of the aggregate circuits within many of these multiplexers is not supported by many vendors

Drop-and-Insert MultiplexerThey are special-purpose multiplexers designed to drop and insert low-speed channels in and out of a high-speed multiplexed channel like a T1.Channel speeds dropped and inserted are typically 56 or 64kbps. Each DS0 is demultiplexed and remultiplexed for transmission.Refer to Figure 6.12 (p. 202)

Switching Techniques

Space Division Switching

It delivers a signal from one physical interface to another physical interface.Classical space division switch fabrics have been built from electromechanical and electronic elements with the crosspoint function.Refer to Figure 6.15 (p. 207)

Time Division Switching

The operation of current digital telephone switches may be viewed as being made up of an interconnected network of special-purpose computers called Time Division Switches (TDS).The TDS is effectively a very special-purpose computer designed to operate at very high speeds.Refer to Figure 6.16 (p. 208)

Address Switching

Address switching operates on a data stream in which data is organized into packets, each with a header and a payload. The header contains address information that is used in switching decisions at each node.All possible connection topologies can be implemented: point-to-point, point-to-multipoint, multipoint-to-point, and multipoint-to-multipoint.Refer to Figure 6.17 (p. 208)

Frequency/Wavelength SwitchingIt translates signals from one carrier frequency (wavelength) to another.Currently Optical Fiber networks use this methodThe optical end system nodes transmit on at least one wavelength and receive on at least one wavelength. The wavelengths for transmission and reception are currently tunable in a time frame on the order of milliseconds, with an objective of microseconds.Refer to Figure 6.18 (p. 210)

The Matrix SwitchThey provide a simplistic form of T1 multiplexing and offer the capability to switch ports similar to a cross-connect.They are composed of a high-speed bus for connection between ports.They are controlled and switched through a central network-management center, and can manage the entire network from a single point.The drawback is the possibility of failure, which would bring down the entire network.Refer to Figure 6.20 (p. 212)

Packet Switching TechnologiesPacket-switching allows multiple users to share data-network facilities and bandwidth, rather than providing specific amounts of dedicated bandwidth to each user.The traffic passed by packet-switched networks is “bursty” in nature, and therefore can be aggregated statistically to maximize the use of on-demand bandwidth resources.Due to the connectionless characteristic of packet switching, the intelligence of the network nodes will route packets around failed links.Quick interview of packet switching technologies

X.25 - Fast PacketFrame relay - ATM

X.25Access speeds range up to 56 kbpsContains error detection and correctionConnectionless service using connection-oriented virtual circuitsGood for time-insensitive data transmission but poor for connection-oriented and time-sensitive voice and video.Employs a queuing scheme for buffering and transmission of dataAllows numerous virtual circuits on the same physical path, and can transport packet sizes up to 4,096 bytesPermanent Virtual Circuits and Switched Virtual Circuits are supported.Traffic can be prioritizedOld technology

Frame RelayIt is a connection-oriented service employing PVCs and SVCs.Frames can vary in size and bandwidthMultiple sessions can take place over a single physical circuitIt is only a transport service (no error control or correction)It must be transmitted over reliable fiber-optic transmission media with low bit-error ratios

Fast PacketIt is not a defined standard, protocol, or service.Fast packet is a backbone technology which combines attributes of both circuit switching and packet switching.It can accommodate both delay-sensitive traffic as well as data traffic not affected by variable delay.It offers low network delay and high network resources efficiencyIt provides protocol transparencyFast packet technologies typically use advanced fiber-optic transport media, such as T3 and SONET.

Asynchronous Transfer Mode (ATM)ATM is another form of fast packet switching.Fixed size packets called cellsIt provides two types of connection:

Virtual channelVirtual path

It allows for the transmission for data, voice, and video traffic simultaneously over high-bandwidth circuits.Full dublex 155.52 MbpsAsymmetrical transmission from subscriber to network at 155.52 Mbps in one direction and 622.08 Mbps in the otherFull-dublex 622.08 Mbps service.

Cisco

Switching Technologies

ObjectivesDescribe layer-2 switchingDescribe address learning in layer-2 SwitchesUnderstand when a layer-2 switch will forward or filter a frameDescribe network loop problems in layer-2 switched networksDescribe the Spanning-Tree ProtocolList the LAN switch types and describe how they work with layer-2 switches

Layer-2 SwitchingHardware basedProvides the following:

Hardware-based bridging (MAC)Wire speedLow latencyLow cost

Layer-2 Switching

LimitationsBridging vs LAN SwitchingThree Switch Functions at Layer 2Address Learning

How Switches Learn Hosts’ Locations

Layer-2 Switching

Forward/Filter DecisionsBroadcast & Multicast Frames

Loop Avoidance

Broadcast Storms

Multiple Frame Copies

Spanning-Tree Protocol (SPT)

Purpose

History

STP Operations

Function

How does it do this?

Selecting a Root Bridge

Process

Spanning-Tree Port States

Port states

Convergence

Selecting the Designated Port

Process

Spanning-Tree Operations

LAN Switch TypesStore and Forward

Cut-through

FragmentFree

Spanning Tree Example

Different Switching Modes within a Frame

SummaryDescribed layer-2 switchingDescribed address learning in layer-2 SwitchesStated when a layer-2 switch will forward or filter a frameDescribed network loop problems in layer-2 switched networksDescribed the Spanning-Tree ProtocolListed the LAN switch types and describe how they work with layer-2 switches

Cisco

Internet Protocol

ObjectivesDescribe the different classes of IP addressesPerform subnetting for an internetworkConfigure IP address in an internetworkVerify IP addresses and configuration

The DoD and OSI Models

Process/Application Layer Protocols

Telnet

File Transfer Protocol (FTP)

Trivial File Transfer Protocol (TFTP)

Network File System (NFS)

Line Printer Daemon (LPD)

Process/Application Layer Protocols

X Window

Simple Network Management Protocol (SNMP)

Domain Name Service (DNS)

Dynamic Host Configuration Protocol (DHCP)

Host-to Host Layer ProtocolsPurpose

ProtocolsTransmission Control Protocol (TCP)User Datagram Protocol (UDP)

The TCP/IP Protocol Suite

TCP Segment Format

UDP Segment

Key ConceptsTCP

SequencedReliableConnection-orientedVirtual circuit

UDPUnsequencedUnreliableConnectionlessLow overhead

Port NumbersPurposePort Numbers:

< 1024: “Well-known port numbers” Defined in RFC 1700; linked to specific applications or

protocols

> 1024: Dynamically assigned Used by upper layers to communicate between hosts

Port Numbers for TCP & UDP

Internet Layer ProtocolsInternet Protocol (IP)

Internet Control Message Protocol (ICMP)

Address Resolution Protocol (ARP)

Reverse Address Resolution Protocol (RARP)

IP Header

The Protocol Field in an IP Header

Local APR Broadcast

RARP Broadcast

Summary of the Three Classes of Networks

IP AddressingWhat is it?Terminology

Bit: one digit: 1 or 0Byte: 7 or 8 digitsOctet: Always 8 bits (base-8 addressing)Network Address: Used to send packets to a remote networkBroadcast Address: Sends information to all nodes on a network

All networks: 255.255.255.255 All nodes: 172.16.255.255 All subnets & hosts: 10.255.255.255

Hierarchical IP Addressing Scheme

IP addresses = 32 bitsDivided into 4 sections or octets or bytesEach byte containing 8 bits

Depicting IP addresses: Dotted decimal: 172.16.30.56 Binary: 10101100.00010000.00011110.00111000 Hexadecimal: 82 39 1E 38

Network AddressingBackgroundNetwork Address Range: Class ANetwork Address Range: Class BNetwork Address Range: Class CNetwork Address Ranges: Classes D & ENetwork Addresses: Special Purpose

Class A AddressesStructure

NetworkNetwork.node.node.node

Class A Valid Host IDs10.0.0.0 All host bits off10.255.255.255 All host bits onValid hosts = 10.0.0.1 - 10.255.255.254

0’s & 255s are valid hosts but hosts bits cannot all be off or on at the same time!

224-2 = 222

Class B AddressesStructure

NetworkNetwork.NetworkNetwork.node.node

Class B Valid Host IDs172.16.0.0 All host bits off172.16.255.255 All host bits onValid hosts = 172.16.0.1 - 172.16.255.254

0’s & 255s are valid hosts but hosts bits cannot all be off or on at the same time!

216-2 = 214

Class C AddressesStructure

NetworkNetwork.NetworkNetwork.NetworkNetwork.node

Class C Valid Host IDs192.168.100.0 All host bits off192.168.100.255 All host bits onValid hosts = 192.168.100.1 - 192.168.100.254

0’s & 255s are valid hosts but hosts bits cannot all be off or on at the same time!

28-2 = 26

SubnettingBenefits

Creating subnetworks

Understanding the Powers of 2

Subnet Masks

Subnetting Class C AddressesClass C address = 8 bitsSubnetting =

10000000 = 128 11000000 = 192 11100000 = 224 11110000 = 240 11111000 = 248 11111100 = 252 11111110 = 254

RulesCannot have only 1 bit for subnetting

Subnets 128 & 254 are illegal

The Binary Method

The Alternate Method1. How many subnets does the subnet mask produce?

2. How many valid hosts per subnet?

3. What are the valid subnets?

4. What are the valid hosts in each subnet?

5. What is the broadcast address of each subnet?

Subnetting Practice ExamplesClass C

Class B

Class A

SummaryDescribed the different classes of IP addressesPerformed subnetting for an internetworkConfigured IP address in an internetworkVerified IP addresses and configuration