Data Communication Network

333: DISCUSS THE FUNDAMENTALS OF NETWORKING

333: DISCUSS THE FUNDAMENTALS OF NETWORKING

1. Discuss networking concepts (20 hrs)

2. Discuss hardware & software requirement to setup a Local Area Network (20 hrs)

333.1: Discuss networking concepts PERFORMANCE STANDARD

◦ Given a scenario, identify correctly the hardware and services required for a Network

Objectives:◦ Define a Node/Host ◦ Discuss functional & geographical relationship among

nodes◦ Discuss services provided by a common carrier such as

Leased line Switched line

◦ Describe switching techniques Circuit Message Packet

◦ Discuss ISO/OSl reference model◦ Explain network communication protocols

SKILL AREA 331.1.3

Discuss services provided by a

common carrier

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Carriers You can only install wires on your own property

◦ Called your customer premises

To send signals between sites or to customers, you must use a carrier

Carriers transport data and voice traffic between customer premises, charging a price for their services

Receive rights of way from the government to lay wires and radio links

CarrierCustomerPremises

Computer network nodes

In data communication, a physical network node may either be a data circuit-terminating equipment (DCE) such as a modem, hub, bridge or switch or a data terminal equipment (DTE) such as a digital telephone handset, a printer or a host computer, for example a router, a workstation or a server.

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Types of Traditional Telephone Circuits

Dial-Up Service (Any-to-Any) Leased Lines

◦ Point-to-point only◦ Cheaper for high volumes of use

Leased Line

SwitchedDial-UpService

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Uses POTS (Plain Old Telephone System) Dial up networking technology provides PCs and

other network devices access to a LAN or WAN via standard telephone lines.

Dial up Internet service providers offer subscription plans for home computer users.

Provides a low cost need based access. Bandwidth 33.6 /56 Kbps. Types of dial up services include V.34 and

V.90 modem as well as Integrated Services Digital Network (ISDN). Dial up systems utilize special-purpose network protocols like Point-to-Point Protocol (PPP).

Dial-up

To use a dial up Internet connection, a client modem calls another modem located at the Internet Service Provider (ISP). The modems transfer network information over the telephone until one modem or the other disconnects.

When the popularity of the Internet exploded in the 1990s, dial up was the most common form of Internet access due mainly to its low cost to setup. However, the performance of dial up networking is relatively poor due to the limitations of traditional modem technology. V.90 modem dial up supports less than 56 Kbps bandwidth and ISDN handles approximately 128Kbps.

Many home users are currently replacing their dial up services with high-speed broadband technologies that operate at much higher speeds.

Dial-up

Dial-up

A leased line connects two locations for private voice and/or data telecommunication service.

It is not a dedicated cable, a leased line is actually a reserved circuit between two points. 

Permanent telephone connection between two points Organization ‘owns’ the leased line – not shared with

anyone else. Leased lines can span short or long distances. Quality of service is assured Line access is assured Line is always active Fixed monthly fee Fees based on distance and speed of connection

Leased Lines

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Leased Line Service

Customer Premises A Customer Premises B

SwitchingOffice

SwitchingOffice

SwitchingOffice

TrunkLine

TrunkLine

LocalLoop Local

Loop

Leased LinesMay Pass ThroughMultiple Switches,Even MultipleCarriers

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Leased Lines Leased Lines are Circuits

◦ Often goes through multiple switches and trunk lines

◦ Looks to user like a simple direct link

◦ Limited to point-to-point communication Limits who you can talk to

◦ Carriers offer leased lines at an attractive price per bit sent to keep high-volume customers

Switch Trunk Line

Leased Line

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Leased Line Meshes If you have several sites, you need a mesh

of leased lines among sites

Leased Line

Mesh

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Leased Line Speeds Largest Demand is 56 kbps to a few Mbps

56 kbps (sometimes 64 kbps) digital leased lines◦ DS0 signaling

T1 (1.544 Mbps) digital leased lines◦ 24 times effective capacity of 56 kbps◦ Only about 3-5 times cost of 56 kbps◦ DS1 signaling

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Leased Line Speeds Fractional T1

◦ Fraction of T1’s speed and price◦ Often 128, 256, 384 kbps

T3: is the next step◦ 44.7 Mbps in U.S.

Europe has E Series◦ E1: 2.048 Mbps◦ E3: 34 Mbps

SONET/SDH lines offer very high speeds◦ 156 Mbps, 622 Mbps, 2.5 Gbps, 10 Gbps

Advantages of Leased Line Flexible level of connection based upon

your business requirements Synchronous service where upstream and

downstream speeds are the same Private network offers reduced security

risks as it does not use the public network

Service Level Agreement provides peace of mind

Managed service

Firewalls on Leased Lines Increased threats of Internet misuse has

prompted companies to add firewalls to private leased lines to filter traffic coming into their network

The firewall filters traffic based on rules Can block several types of attacks Can monitor network traffic Can not protect against virus attacks

Digital Subscriber Lines (DSLs) Can Use Instead of Traditional Leased Lines

◦ Less expensive

HDSL (High-Speed DSL)◦ Symmetrical: Same speed in each direction

◦ HDSL: 768 kbps (Half a T1) on a single twisted pair

◦ HDSL2: 1.544 Mbps (T1) on a single twisted pair

Digital Subscriber Line Normal Leased Lines Used Data Grade

Wires◦ High-quality, high-cost◦ Two pairs (one in each direction)

DSLs Normally Use Voice Grade Copper◦ Not designed for high-speed data◦ So sometimes works poorly◦ Usually one pair (ADSL, HDSL)◦ Sometimes two pairs (HDSL2)

Problems of Leased Lines With many sites, meshes are expensive and

difficult to manage

With N sites, N*(N-1)/2 leased lines for a mesh◦ May not need all links, but usually use many

User firm must handle switching and ongoing management

◦ Expensive because this requires planning and the hiring, training, and retention of a WAN staff

Sites Lines

5 1010 4525 300

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T1 Leased Lines Voice Requirements

◦ Analog voice signal is encoded as a 64 kbps data stream

◦ 8 bits per sample

◦ 8,000 samples per second

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T1 Leased Lines T1 lines are designed to multiplex 24 voice

channels of 64 kbps each

T1 lines use time division multiplexing (TDM)◦ Time is divided into 8,000 frames per second

One frame for each sampling period

◦ Each frame is divided into 24 8-bit slots One for each channel’s sample in that time period (24 x 8) 192 bits Plus one framing bit for 193 bits per frame

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T1 Leased Lines Speed Calculation

◦ 193 bits per frame◦ 8,000 frames per second◦ 1.544 Mbps

Framing Bit◦ One per frame◦ 8,000 per second◦ Used to carry supervisory information (in groups

of 12 or 24 framing bits)

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PSDNs Public Switched Data Networks

◦ Designed for data rather than voice

◦ Site-to-site switching is handled for you

◦ You merely connect each site to the PSDN “cloud” (No need to know internal details)

PSDN

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PSDNs Connect each site to the PSDN using one

leased line◦ Only one leased line per site◦ With N sites, you only need N leased lines, not N*

(N-1)/2 as with a full mesh

1 LeasedLine

PSDN

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PSDNs Access Device Needed at Each Site

◦ Connects each site to access line◦ Often a router◦ Sometimes a device specific to a particular PSDN

Technology

PSDN

AccessDevice

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PSDNs Point of Presence (POP)

◦ Place where you connect to the cloud◦ May be several in a city◦ May not have any POP close◦ Need leased line to POP◦ Separate from PSDN charges

LeasedLine

PSDN

POP

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PSDNs in Perspective Simpler than Networks of Leased Lines

◦ Less staffing◦ Fewer leased lines to support

Less Expensive than Networks of Leased Lines◦ Less staffing◦ PSDN prices are very low◦ PSDN is less expensive overall◦ PSDNs are replacing many leased line mesh

networks

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Circuit-Switched PSDNs End-to-End Capacity is Guaranteed

◦ If you need it, it is always there◦ When you don’t need it, you still pay for it◦ Expensive for data traffic, which usually has short

bursts and long silences

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PSDN

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Packet-Switched PSDNs Messages are divided into small units

called packets

◦ Short packets load switches more effectively than fewer long messages

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Packet-Switched PSDNs Packet-Switched PSDNs Usually Operate at

Layer 2 (Data Link Layer for Single Subnets)

◦ Should be called frame-switched networks

◦ Still called packet-switched networks

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Packet Switched PSDNs Packets are multiplexed on trunk lines

◦ Cost of trunk lines is shared◦ Packet switching lowers transmission costs◦ Dominates PSDN service today

MultiplexedTrunk Line

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Packet Switched PSDNs: Virtual Circuits All commercial packet switched PSDNs use

virtual circuits◦ Eliminates forwarding decisions for individual packets◦ Reduces switching load, so reduces switching costs

VirtualCircuit

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Unreliable PSDNs Most commercial PSDNs are Unreliable

◦ (Only obsolete X.25 PSDN technology was reliable)

◦ No error correction at each hop between switches

◦ Reduces costs of switching

◦ Note that both virtual circuits and unreliable service reduce switching costs

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PSDN Cost Savings Packet Switching

◦ Reduces costs of transmission lines through multiplexing

Virtual Circuits◦ Reduces costs of switches because they do not

have to make decisions for each frame

Unreliability◦ Reduces costs of switches because they do not

have to do error correction

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