AREN

Networking in the K-12 Community

Rick Bagwell

Nichols Research

Alabama Research and Education Network

(Formerly the Alabama Supercomputer Network)

AREN

• Ethernet – Shared, Switched, Fast, Gigabit

• Token Ring

• FDDI (Fiber Distributed Data Interface)

• ATM (Asynchronous Transfer Mode)

Local Area Network Options (LAN)

AREN

Ethernet Types

• Ethernet – 10Base-T (100m, Unshielded Twisted Pair = UTP)

– 10Base-2 (~200m, Coax)

– 10Base-5 (500m, Coax)

– 10Base-FL (2000m=2km, Multimode Fiber)

• Fast Ethernet – 100Base-TX (100m over CAT5 UTP)

– 100Base-FX (2000m=2km over MM Fiber)

• Gigabit Ethernet – 1000Base-SX (300m over MM Fiber)

– 1000Base-LX (550m over MM Fiber, 3000m over SM Fiber)

AREN

Ethernet

• 10 Mbps

• CSMA/CD – Carrier Sense Multiple Access with Collision Detection

• Can be configured with cable, hubs, or switches

AREN

Common Ethernet Topologies (non-segmented)

Ethernet

IBM Compatible IBM Compatible Server

Mac IIWorkstation

ComputerComputer ComputerComputer

Hub Hub

Hub

ComputerComputer

Computer

Computer

Computer

Computer

Stackable Hubs

AREN

Limitations of Cascaded Hub Topology

• Distance limitations of UTP or Fiber• Network size limited by the 5-4-3 rule

– just remember hosts cannot talk to each other if they are connected through more than 4 hubs or repeaters

• One Broadcast Domain – collisions likely as number of hosts increases

• Users generally don’t know about the 5-4-3 rule and just keep on adding hubs at random points

AREN

Limitations of Stacked Hub Topology

• All hosts must be within 100m of the stack when using UTP

• Using fiber to overcome distance limitations is useful for MDF to IDF connections but is cost prohibitive to the desktop

• “Stackables” use proprietary interconnects• One broadcast domain

AREN

Limitations of 10Base-2 and 10Base-5

• Difficult to troubleshoot– Terminations, Terminations, Terminations

• 5-4-3 rule must be strictly enforced

• Cable infrastructure does not support upgrades to Fast or Gigabit Ethernet.

• Difficult to troubleshoot– Terminations, Terminations, Terminations

AREN

Ethernet: The Next Generation

• Layer 2 switches (Ethernet, FastE, GigE)– Switching decisions are made based on MAC address

– Segments network into separate traffic domains

– Broadcasts are still heard by all hosts

– Does not affect IP subnetting

129.66.32.4

129.66.32.1 129.66.32.2

Ethernet Switch

Ethernet Hub

129.66.32.3

AREN

Ethernet: The Next Generation (cont.)• Layer 3 switches (Ethernet, FastE, GigE)

– Switching decisions are made based on MAC and IP addresses

– High-speed ASIC-based routing

– Can usually be configured as Layer2/Layer3 switches on a per-port basis

– Layer 3 switching takes place between subnets

199.88.72.15

129.66.32.1 129.66.32.2

Ethernet Switch ing Router

Ethernet Hub

207.157.18.2

AREN

Ethernet: The Next Generation (cont. again)

• Layer 4 “switches” (Ethernet, FastE, GigE)– Switching decisions are based on Application, MAC and IP

addresses

– Can usually be configured as Layer2/3/4 switches on a per-port basis

– Layer 3 switching takes place between subnets

– Layer 4 “switching” is used to provide QoS and multimedia

services

199.88.17.2

129.66.32.1 129.66.32.2

Ethernet Switch ing Router

Ethernet Hub

207.157.13.9

AREN

Ethernet Network Design Pointers

• Use Ethernet switching as much as possible– Limit the number of hosts sharing a switched port

– Switched to the desktop is nice but expensive

• Use Layer 3 switching (routing) for large (>200 hosts) networks and high-performance.

• Use Fiber between MDF and IDFs when distance exceeds 100m (300ft to be conservative)

• Do NOT use Fiber to the desktop unless you are made of money

AREN

How do I connect my schools to each other and to the Internet?

• The same general answer applies for almost every choice of WAN connection technology.– Routers at each school are connected via some WAN technology

to the other routers in the school system

– Schools are on different IP subnets

• Internet access – Usually obtained for the school system by connecting a single

location to the Internet with a high-speed connection.

– Other schools in the system can access the Internet by routing through the central location.

– Can be purchased on a school by school basis • This option can be MUCH more expensive and likely gains little, if

anything, in the way of performance.

AREN

Typical School System Network

Core Router

CSU/DSU

CSU/DSU

CSU/DSU

CSU/DSU

CSU/DSU

In te rne t

Router

CSU/DSU

Ethernet

IBM Com patible

IBM Com patible

IBM Com patible

AREN

Wide Area Network Options (WAN)

– DS1 (a.k.a T1)– Fractional DS1 (Frac. T1)– Frame Relay– Cable Modem– ISDN– xDSL– Private/Leased Fiber (or copper)– Wireless

AREN

What is a “T1” and how does it work ??

• High speed “phone” line– digital– 1.544Mbps (if all 24 channels are used)– 24 “phone” lines

• Used by phone companies between COs

• Used by businesses between offices

• Used by Networking folks for Data

AREN

Advantages and Disadvantages of T1 Lines for School System Networking

• Advantages:– Reasonable WAN speed (1.5Mbps)

– An educational tariff is available for T1s in Alabama.

– Full T1’s are almost always less expensive than Frame Relay (due to the edu. Tariff)

– Telco is responsible for insuring that the line stays operational • Disadvantages:

– Bandwidth is limited (1.5Mbps)

– Requires more router ports at central site than Frame Relay• but large systems can use Channelized DS3

AREN

What is Frame Relay and how does it work ??

• Circuit switched network technology• You purchase access to the “cloud”

– usually a T1 or fractional T1

• Virtual connections are made across the cloud to connect schools (PVCs)

• A Committed Information Rate (CIR) can be purchased that guarantees a level of performance

AREN

Frame Relay Example

S choo l A

S choo l B

S ys temC en tra lO ffice

Fram e C loud

T1

T1

AREN

Advantages and Disadvantages of Frame Relay for School System Networking

• Advantages:– Reasonable WAN speed (64kbps -- 1.5Mbps)

• When T1 or Fract. T1 is the transport

– Buy bandwidth only when you need it ****

– One serial port at the central site can support multiple incoming PVCs

– Telco is responsible for insuring connectivity

• Disadvantages:– No educational tariff is currently available in Alabama.

– Full T1’s are almost always less expensive than Frame Relay (due to the edu. Tariff)

• This is true even when low CIRs or no CIRs are compared to T1s

AREN

Cable Modems and xDSL

• High-speed (256kbps -- 10Mbps) wide area connectivity that can be used to connect schools or for Internet access

• Usually only available in the larger cities (Huntsville, Birmingham, Montgomery, Mobile)

• Too early to recommend or dismiss as a technology for school system use– Both Cable Modem systems and xDSL can and often are over-

subscribed

– Some sort of service level agreement should be obtained before either of these technologies are considered

AREN

ISDN (Integrated Services Digital Network)

• Designed to be a digital phone service– BRI: 2B+D (Basic Rate Interface)

– PRI: 23B+D (Primary Rate Interface)

• Telco’s frown on “nailing up” ISDN connections• Limited bandwidth (64-128kbps for BRI)• Good solution for “dial backup”

– if you can afford dial backup

AREN

Private or Leased Fiber Optic Lines

• My personal favorite

• Extremely high bandwidth available (1Gbps is easily obtained)

• Can economically use Fast Ethernet over such and infrastructure (100Mbps)

• No recurring costs (T1 min. is $240.00 per month)

• Must either obtain right-of-way or have existing fiber donated by telco or power company

AREN

Wireless WAN/MAN

• Good solution in Flat areas or when a mountain is nearby– line of sight is required !!!

• High Bandwidth solutions are available (2Mbps--155Mbps)

• 10Mbps is now very economical

• No recurring cost (unless leased)

• Leasing provides insurance against malfunction or the weather

• My second choice if fiber is unavailable

AREN

Unconventional Wisdom(at least some people would say so)

• Never use managed Ethernet hubs– most of the functionality is never used

– much more expensive than “dumb” hubs

– exception to this rule: VLANs on hubs

• The only use for Fiber Optics is between IDFs and the MDF when the distance is over 300ft

• Almost never buy Frame Relay for connecting schools in a single system to each other (Educational T1s are cheaper).

• Always compare all WAN options (T1, Frame, Fiber, Wireless, etc.)

• Use network appliances and/or LINUX systems for Internet servers.

• Having a trained Network Manager makes ALL the difference– Don’t have to rely completely on vendors and contractors

• Get network advice from someone other than the vendor before purchasing

AREN

Contact Information

Rick BagwellNetwork EngineerNichols Research Corporation(Contractor for AREN)

Voice: (256) 971-7432FAX: (256) 971-7491Email: Rick@asc.edu -or- bagwellr@nichols.com