Evolution of the Network Computing Model


Mainframe:  IBM, Honeywell, CDC

Client/Server: Novell, Banyan, Windows NT 4/2000



Peer-to-Peer (Distributed): NetBEUI, Windows in Workgroups, Napster, SETI


Network Topologies




Star-Bus (Hybrid):

Mesh (Full, Partial):


Network Layers






Common Network Operating Systems (NOSs)


Microsoft Win9x/ME:

Microsoft NT/2000/XP/.NET:

Novell 3.x:

Novell 4.x:

Novell 5.x:

Novell 6.x:




DoD Model: Early 1970s


Process/Application:           Negotiation

Host-to-Host:                       Encapsulation (TCP, UDP, SPX)

Internet:                                 Encapsulation (IP, IPX)

Network Access:                  Encapsulation (E’net, Token Ring, FDDI, HDLC, PPP) / Electrical & Optical


OSI Model: Mid to Late 1970s


Application:          Negotiation

Presentation:         Negotiation

Session:                 Negotiation

Transport:             Encapsulation (TCP, UDP, SPX)

Network:                Encapsulation (IP, IPX)

Data Link:              Encapsulation (E’net, Token Ring, FDDI, HDLC, PPP)

Physical:                Electrical or Optical signals


Application Layer:


Simple Mail Transfer Protocol (SMTP)

BootP/Dynamic Host Configuration Protocol (DHCP)

File Transfer Protocol (FTP)

HyperText Transfer Protocol (HTTP)

Simple Network Management Protocol (SNMP)

Domain Name Service (DNS)


Server Message Block Protocol (SMB)

Kerberos (Authentication Protocol for Win2K)


Network File System (NFS) – also placed at the Session Layer by some

SAMBA (SMB Emulator)

Network Information System (NIS/NIS+)

Kerberos (Authentication Protocol)


Novell Core Protocols (NCP)


AppleTalk Filing Protocol


X.400 (International Addressing Standard)

X.500 (International Directory Standard)

LDAP (lightweight Directory Access Protocol)


Presentation Layer:

                Character sets used (ASCII, EBCDIC, Unicode)

File formats (JPEG, MPEG, MIDI, bitstream, text, formatted text)




Session Layer: (Separates application data)

Network File System (NFS)

Structured Query Language (SQL)

Remote Procedure Calls (RPC)

X Window

AppleTalk Session Protocol (ASP)

Digital Network Architecture Session Control Protocol (DNA SCP)


Transport: (The protocol data unit or PDU is called a segment at this layer)

Breaks Large Pieces of Higher-level Data into Segments of Size Appropriate to the Network

Flow Control (Negotiate receive buffer sizes, Identify ports to be used, Set up sequence numbers)

Tracking Remote Window

Sending Acknowledgements


Network: (The PDU is called a packet at this layer)

                Logical Addressing

Identify Routes

Determine Costs to Remote Networks

Routers Operate Primarily at the Network Layer with Increasing levels of Transport Function

(They learn the network layer addresses in the network and how to reach them.  They make additional decisions based on Transport Layer data)

(Routers do not know the addresses of individual hosts except to form frames to send to hosts)


Data Link: (The PDU is called a frame at this layer)

                Identify the Higher-level Stack to Receive the Data (TCP/IP, IPX/SPX, DecNet, IBM SNA)

Ensure Hardware Data Addressing (non-logical)

Set Bitstream Format (Canonical vs. non-Canonical)

Switches Operate Primarily at the Data Link Layer (i.e. They learn the Data Link addresses of attached stations, but know nothing of the Network Layer Addresses).

End Users Do Not Control Data Link Addressing


Physical (PHY):

Set Transmission Characteristics

Optical Wavelength, Pulse Intensity, Pulse Duration, Pulse Frequency

Electrical Voltage, Pulse Duration, Pulse Frequency, Pulse Encoding

Cable Characteristics such as Connectors, Resistance, Diameter (FO), Maximum/Minimum Lengths

Hubs Operate at the PHY (They reshape pulses only)


Major Networking Protocols:

TCP/IP – Open Standard, Routable, Protocol of the Internet

IPX/SPX – Proprietary (Novell), Routable

NetBEUI – Proprietary (IBM/Microsoft), Non-routable

AppleTalk – Proprietary (Apple), Routable

Data Link Control (DLC) – Proprietary (IBM), Non-routable

DECNet – Proprietary (Digital/Compaq/HP), Routable

Local Area Transport (LAT) – Proprietary (Digital/Compaq/HP), Non-routable

Systems Network Architecture (SNA) – Proprietary (IBM), Non-routable


Communication Types:

Connection-oriented – registered letter – TCP, SPX

Connectionless – postcard – UDP, IPX



Primary Protocol Suite

Internet Protocol (IP): Logical addressing and routing

Address Resolution Protocol (ARP): Connect logical IP addresses to “real” hardware addresses on the network

Transmission Control Protocol (TCP): Packages application data for reliable transport

User Datagram Protocol (UDP): Packages application data for quick, not-necessarily reliable transport

Large Number of Support Protocols: ICMP, DNS, DHCP, SMTP, FTP, Telnet, TFTP, RIP

Uses 32-bit (4-byte) addresses and network masks

Class A – 8-bit (1-byte) network mask of 1’s with the remainder 0’s; 126 networks of approx. 16,000,000 hosts

Class B – 16-bit (2-byte) network mask; about 16,000 networks with approximately 65,000 hosts

Class C – 24-bit (3-byte) network mask; approximately 2,000,000 networks with 254 hosts



Primary Protocol Suite:

Internet Packet eXchange (IPX): Logical addressing and routing

Sequenced Packet eXchange (SPX): Session setup and management

Support Protocols: NCP, NLSP, IPX RIP

Uses 80-bit (10-byte) address: a 32-bit/4-byte administrator-assigned network number and the 48-bit/6-byte MAC address of the network adapter


Directory Services:

Banyan Vines: Street Talk

Novell: Netware 4.x, Novell Directory Service (NDS)


Microsoft: NTDS (SAM) for NT, Active Directory (A.D.) for Windows 2000


Lightweight Directory Access Protocol (LDAP)


Network Hardware:



Local Area Networks (LANs): Locally owned and managed

Wide Area Networks (WANs): Leased from a vendor, managed by the vendor, links LAN pieces (the Internet)

Network Access Points (NAPs): Owned by large telco providers, used by ISPs to exchange traffic, generically used for all internet exchanges



NICs and Drivers: NDIS (Microsoft) and ODI (Novell)

Repeaters and Hubs:

Layer 1, reshape pulses

No knowledge of traffic

Bridges and Switches:

Layer 2

Knowledge of attached hardware devices (MAC addresses)

Spanning Tree Protocol

Bridging loops and packet amplification

Bridge Protocol Data Units

Routers (and Brouters):

Layer 3

Knowledge of networks within the universe

Limited knowledge of local hardware addresses

Variety of Routing Protocols (RIP, OSPF, BGP4, IPX RIP, NLSP, AppleTalk RTMP)

Distance Vector Protocols

Link State Protocols



Patch Panels/Wall Jacks:



Serial: 9-pin, 25-pin, Data Terminal Equipment (DTE), Data Circuit Terminating Equipment (DCE), 115 kbps

Parallel: Printers

Universal Serial Bus: v.2 60 - MB/sec, daisy-chainable to 127 devices

FireWire (IEEE 1394): 1394b - 400 MB/sec, daisy-chainable to 63 devces

Small Computer Systems Interface (SCSI)

SCSI-1: 25-pin connector, 8-bit bus, DB form factor, 4 Mbps, not daisy-chainable must use SCSI-2 cables to daisy-chain)

SCSI-2 (“wide”): 50-pin connector, 8-bit bus, Centronics 50 form factor, 4 Mbps, daisy-chainable

SCSI-3 (“ultra-wide”): 68-pin connector, 16-bit bus, Centronics 68 form factor, 80 Mbps (120?), daisy-chainable




                Coaxial cable: 50 Ohm, RG-8/RG-11 (10Base5), RG-58 (10Base2), BNC connectors for 10BASE2, screw connectors for 10BASE5

Shielded Twisted Pair (STP): each ground/signal pair encased in a conducting shield, token ring and gigabit E’net Cat7

Unshielded Twisted Pair (UTP): several categories (“CatX”) for different levels of service

Cat1: telephony, only

Cat2: four pairs, data to 4 Mbps, UTP token ring

Cat3: Four twisted pairs, data to 10 Mbps, classical star-topology E’net 10BASE-T, beware split cable plants

Cat4: Four twisted pairs, data to 16 Mbps, later token ring

Cat5: Four twisted pairs, data to 100 Mbps, 100BASE-TX fast E’net

Cat5e: Improved Cat5 to work with gigabit E’net

Cat6: Four twisted pairs, data to 1 gigabit, rigid cable with fixed pair geometry from end to end

Cat7: Four twisted pairs, shielded, improved gigabit performance

Register Jack 45 (RJ-45): 8-wire connector with form factor similar to a telephone jack (RJ-11)

Register Jack 21 (RJ-11): High-density, 50-pin telco jack, multiplexes 12 lines into one connector



Multimode (MM): 62.5 micron/125 micron, short haul

Single-mode (SM): 6 micron/125 micron, long haul



ST: Bayonet connector style, individual fiber

SC: Snap connector style, individual fiber

MTRJ: Snap style, fiber pair


                LASER: Longer wavelength systems (infrared), SM cable, long haul

                LED: Shorter wavelength systems (visible) tend to be LED, MM cable, short haul



The most important protocol available today is 802.11b

Direct Sequence Spread Spectrum (Hedy Lamar)

Operates at 11 Mbps under optimum conditions

As reception degrades (distance, obstacles) less sophisticated coding is switched in, which reduces the bit rate.

See http://www.networkcomputing.com/1115/1115ws2.html