CS457/557 - Computer Networks: Chapter 5 - Local Area Network Concepts and Architectures

Objectives

Understand how access methodologies, logical topologies, and physical topologies combine to form alternative network architectures
Understand the similarities, differences, advantages, and disadvantages to current network architectures such as Ethernet, token ring, and FDDI.
Understand the similarities, differences, advantages, and disadvantages of emerging high-speed network architectures such as 100BaseT, 100VG-AnyLAN, ISO-Ethernet, gigabit Ethernet, fibre channel, and LAN-based ATM.
Understand the value of the OSI model in the analysis of network architecture alternatives
Understand how proper LAN analysis can help determine which network architecture is most appropriate in any given situation.

What is a Local Area Network?

How is a Local Area Network Implemented?

Networking Hardware

network interface card
hub

Networking Software

client
server

Networking Media

Why are Local Area Networks Implemented?

Business

The overall business needs/perspectives. Recognition of information as a corporate asset. Save money. Increase productivity. Increase data accessabililty. Provide more bandwidth to the desktop. Reliable, easy to use information systems. Well supported information systems.

Identify the business activities. General information requirements. Resource sharing of printers, CD-ROMs, communication links, FAXs, and modems. File sharing and application sharing. Distributed data access and shared databases. Extended communications through: Inter-LAN, micro to mainframe links, and wide area network links.

Business Analysis Questions. See Fig. 4-5

Application

Application Programs. Network printing, network backup, network security, network management, network resource optimization, workgroup software, remote access/control software, connectivity / gateway software, productivity software, MAC integration software

Data

Database management languages. SQL. Database types. multiuser (file server), client / server (database server). Back-end databases: ORACLE, SYBASE. Front-end database tools. Database servers. Gupta, Netware, NT

Network

File transfer software. Laplink, Interlnk. Printer sharing networks: Black-box Zero-slot LANs. LANtastic-Z. Peer-to-peer systems LANtastic, Netware Lite, WFWG. Fully-integerated LANs Netware, Banyan Vines, NT, Appletalk, Pathworks LANs and LAN look-alikes

Business Analysis Questions

	Current	2-3 years	5 years
User Issues How many users? What are their business activities? What is the budgeted cost/user? Comprehensive cost of ownership? What are the security needs? What are the support issues?
Local Communications Required speed?
Resource sharing? How many CD-ROMs, printers, modems and FAXs are to be shared? What is the greatest distance from the server to each service?
File Sharing Is printer / queue management required? How many simultaneous users?
Application Sharing What is the number and type of required applications? Are e-mail services required?
Distributed Data Access
LAN Management/Administration
Extended Communications

Network Applications: What can a LAN do for you?

Network Application	Issues
Network Printing	Printers share print requests, buffered and spooled, Queue / device management
Network Backup	Match hardware/software to your needs and network. check out restore features. schedule unattended backups. generation of LOG reports. hardware dependencies and capacities.
Network Security	virus control. additional user ID/password protection. encryption. user authentication. Automatic logout of inactive terminals
Network Management	network monitors. Diagnostic and analysis tools. Administrative concerns.
Network Resource Optimization. Configuration and Inventory Management	Hardware and software inventory database. Reporting and query capabilities. Planning and network configuration tools. Monitoring and network alarm capabilities
Remote Access control software. Connectivity / Gateway software	See chapter 6
Groupware	Workflow automation. Interactive work document review. Information sharing. Group schedules. Enhanced e-mail.

Categorizing LAN Architectures: The OSI Model Revisited

Layer Name

Example of Protocols or Standards

Comments

7 Application

X.400, X.500

utilities that support end-user application programs

6 Presentation

encryption, code translation, compression

5 Session

establishes, maintains, and terminates sessions between applications

4 Transport

TCP, UDP, SPX

provides reliability (end-to-end recovery and flow control)

3 Network

IP, IPX

establishes, maintains, and terminates end-to-end network links

2 Data Link

Logical link control sublayer
Media access control sublayer	CSMA/CD - IEEE 802.3 IEEE 802.4 - Token Bus IEEE 802.5 - token Ring Arcnet

delivers reliability for point-to-point connections [built into NICs]

Physical

RS-232-C, 10Base-T, 10Base-2, 10Base-5, 10Base-F

establishes, maintains, and terminates physical connections

The Local Area Network Architecture Model

Access Methodology

CSMA/CD (Carrier Sense Multiple Access / Collision Detection)
Token Passing

Logical Topologies

sequential (ring)
broadcast

Physical Topologies

Bus
Star (requires a hub, concentrator, MAU(multiple access unit))
Ring
Tree

Ethernet Standards

developed by Robert Metcalfe [founder of 3Com) in early 80s - first Ethernet standard in 1981 [Digital-Intel-Xerox]
Ethernet II developed in 1982 followed by IEEE 802.3

Access methodology: CSMA/CD
Logical topology: broadcast
Physical topology: traditionally bus, now star

Ethernet II Frame Layout
Preamble	Destination Address	Source Address	Type	Data Unit	Frame Check Sequence
8 Octets	6 Octets	6 Octets	2 Octets	46-1500 bytes	4 Octets

IEEE 802.3 Frame Layout
Preamble	Start Frame Delimiter	Destination Address	Source Address	Length	Logical Link Control IEEE 802.2 Data	Frame Sequence Check
7 Octets	1 Octet	2 or 6 Octets	2 or 6 Octets	2 Octets	46-1500 bytes	4 Octets

IEEE 802.2 AND Ethernet SNAP(subnetwork access protocol) - headers within the data fields [used extensively by Netware to render network protocols IEEE 802 compliant

Popular Name	Standard Name	Speed	Media	Maximum Segment Length
Orange Hose Ethernet	10Base5	10Mbps	ThickCOAX	500 m [up to 100 workstations per segment & up to 5 segments can be joined)
CheapNET ThinNET	10Base2	10Mbps	ThinCOAX	185 m (30 workstations/segment; up to 5 segments can be joined)
10BaseT, CAT-3, CAT-5	10BaseT	10Mbps, 100Mbps	Unshielded Twisted Pair	100 m [maximum diameter is 2500m and up to four repeaters between end nodes]
Fiber	10BaseF	10Mbps, 100Mbps	Fiber-optic cable	1 km
Wireless (infrared)	Wireless (infrared)	10 Mbps	infrared waves	500 feet
Wireless (radio)	cellular	1.25 - 5 Mbps	radio waves	varies

Token Ring

developed bu Olaf Soderblum for IBM in 1969 [IEE 802.5 standard] - 4-16 Mbps

Access methodology: token passing
Logical topology: sequential
Physical topology: traditionally ring, now most often star

initial cost is higher

ARCNET (attached resources computer network

developed by Datapoint, Inc. - 2.5 Mbps

FDDI (Fiber distributed data interface

100 Mbps specified in 1984 by ANSI (does support IEEE 802.2 logical link control protocols)

Access methodology: modified token passing
Logical topology: sequential
Physical topology: dual counter-rotating rings

need for increased bandwidth
FDDI - Fiber distributed data interface
supplies upwards of 100 Mbps
immune ro EMI and RFI
comprised of two separate rings (with one as a backup for the other)
requires an FDDI concentrator or hub
can connect LAN upto 20 KM with repeaters every 2 KM
uses modified token passing
interoperable with Ethernet through a FDDI-Ethernet Bridge
expensive & requires special training to install
CDDI - Copper distributed data interface (STP = 100 m; UTP = 50 m)
Applications
1. Campus Backbone
2. High-bandwidth workgroups
3. High-bandwidth subworkgroup connections

HIGH-SPEED NETWORK ARCHITECTURES

100BaseT (Fast Ethernet)

100BaseTX (uses two pair of CAT5 UTP or two pair of Type 1 STP)
100BaseT4 (uses four pair of CAT3,4, or 5 UTP)
100BaseFX - uses fiber

uses same IEEE802.3 MAC sublayer frame layout (maximum network diameter is 210m with up to only 2 repeaters between end nodes)

100VG-AnyLAN

uses IEEE 802.12 standard for demand priority access; supports IEEE 802.3 and IEEE802.5 MAC layer frames (maximum network diameter is 2500m with up to 4 repeaters between end nodes); requires four pair of CAT3,4, or 5 UTP; uses round robin polling scheme

Isochronous Ethernet

uses IEEE802.9a standard; all connections are syncronized; closely related to ISDN

10BaseT mode - uses only 10Mbps P channel for Ethernet traffic
Multiservice mode - uses both the 10Mbps P channel for Ethernet traffic and the 6.144 Mbps C channel for video/multimedia
All-isochronous mode - uses all 16.144 Mbps (248 x 64 Kbps) for streaming protocols

Gigabit Ethernet (1000Base-X)

uses IEEE802.3z standard; limited to 25m in half-duplex mode; up to 2 km without CSMA/CD

Fibre Channel

uses ANSI standard X3T9.3 running at 133 Mbps to 1.062 Gbps primarily over fibre; used to connec RAID subsystems to computers

LAN-Based ATM (asynchronous transfer mode)

- 25 Mbps to several gigabits per second

Slides