Network

GATEWAY: Convert from one protocol to another (Transport Layer) A computer that performs pro

tocol conversion between different types of networks or applications. e.g.

A TCP/IP packet	can be converted to (vice verse)	a NetWare IPX packet
AppleTalk	to	DECnet
From SNA	to	AppleTalk

Gateways work at layer 4 and above the OSI model.

A computer that acts as a go-between two or more networks that use the same protocols. The gateway functions as an entry/exit point to the network.

Transport protocol conversion may not be required, but some from of processing is typically performed.

ROUTER: IP, IPX, SNA, DECnet, AppleTalk (Network Layer) A device that forwards data packets from one local area network(LAN) or wide area network (WAN) to another. Routers are used to segment LANs in order to balance traffic within workgroups and to filter traffic for security puposes and policy management. Routers are also used at the edge of the network to connect remote offices.

HUB: Shared, Switch (Data Link) A central connecting device in a network that joins communications lines together in a star configuration. Passive hubs are just connecting units that add nothing to the data passing through them.

Active hubs also are called "multiport repiters", regenerate the data bits in order maintain a strong signal. Hubs by default are 10BaseT twisted pair Ethernet as will as Token Ring networks. (the daisy chain cabling in 10Base5 and 10Base2 coaxial Ethernets I believe still under DECnet control)

A common mistake is calling a HUB "MAU". A Multi-Station Access Unit (MAU) is only for Token Rings

Multiple media hubs interconnect different types of Ethernets (twisted pair, coax and optical fiber) and can bridge between Ethernet, Token Ring, FDDI, and ATM topologies.

A hub can host a CPU board and network operating system and it can be turn into a file server or a type of network control processor to perform LAN emulation. The new models allows you to customize them allowing for the insertion of bridgin, routing and switching modules.

SWITCH: (Data Link) Mechanical or electronic device that directs the flow of electrical or optical signals from ose side to the other.

Switches with more than two ports, such as a LAN switch or PBX, are able to route traffic.

LAN Switch: A network device that cross connects stations or LAN segments. LAN switches are available for Ethernet, Fast Ethernet, Token Ring and FDDI. A LAN switch is also know as a frame switch.

ATM switches are generally considered a category by themselves. Network switches are increasingly replacing shared media hubs in order to increase bandwidth. e.g. a 16-ort 10BaseT hub hsares the total 10 Mbps bandwidth with all 16 attached nodes. By replacing the hub with a switch, each sender/receiver pair has the full 10 Mbps capacity. Each port on the switch can give full bandwidth to a single server or client station or it can be connected to a hub with several stations.

BRIDGE: Segment LANs or Convert between Ethernet & Token Ring (Data Link) A device that conencts two local area networks and allows them to exchange data, even though they may have different topologies or communications protocols.

REPEATER: Regenerate signals to span longer distances (Data Link)

We live in an age of rapidly expanding technology. Harnessing the power and potential of complex thinking machines will help us achieve the fantastic world we only now read about in Sciences Fiction.

Computer science is a discipline that examines the myriad of computer applications.

Computer Sciences ranges from mathematical work, to experimental work.

Computing languages and systems are being designed to interact faster with hardware creating a breed of people dedicated to designing algorithms, computer systems, super computers to solve problems.

Computer Sciences Degree

Data Structures and Algorithms
Assembly Language
Programming C, C++
Analysis of Algorithms
Graphical Software
Design and Implementation
Systems Software
Artificial Intelligence
Databases Administration
Introduction to Mathematical ModelingNumerical Analysis

TIP 1

PowerPoint; Save a Presentation for Overheads and 35mm Slides:
Overhead transparencies and 35 mm slides have slightly different dimensions than computer displays, so your slides must be proportioned correctly to have information properly positioned on the screen. The Page Setup dialog box allows you to size and orient a presentation's slides for an output medium you select. To do this:
1. Open the PowerPoint presentation that you want to use

2. Click File>> Page Setup…
3. In the Page Setup dialog box, in the "Slides sized for:" drop down list, select Overhead or 35mm Slides .
4. Notice that the slide width changes according to the option you choose.
5. Click OK.

Ports and Protocols

You should review the ports and protocols listed in this appendix to prevent interruption of service when implementing a firewall. The following is a list of ports and protocols for Microsoft Windows 2000 services.

Port	TCP/UDP	Service Name
42	TCP	WINS Replication
47	TCP	GRE for PPTP
53	UDP	DNS Name Resolution
53	TCP	DNS
67	UDP	DHCP Lease (BOOTP)
68	UDP	DHCP Lease
88	UDP	Kerberos
135	TCP	Location Service (RPC, RPC EP Mapper, WINS Manager, DHCP Manager, MS DTC)
137	UDP	NetBIOS Name Service (Logon Sequence, Windows NT 4.0 Trusts, Windows NT 4.0 Secure Channel, Pass Through Validation, Browsing, Printing)
137	TCP	WINS Registration
138	UDP	NetBIOS Datagram Service (Logon Sequence, Windows NT 4.0 Trusts, Windows NT 4.0 Directory Replication, Windows NT 4.0 Secure Channel, Pass Through Validation, NetLogon, Browsing, Printing)
139	TCP	NetBIOS Session Service (NBT, SMB, File Sharing, Printing, Logon Sequence, Windows NT 4.0 Trusts, Windows NT 4.0 Directory Replication, Windows NT 4.0 Secure Channel, Pass Through Validation, Windows NT 4.0 Administration Tools [Server Manager, User Manager, Event Viewer, Registry Editor, Diagnostics, Performance Monitor, DNS Administrator])
389	TCP/UDP	LDAP
500	TCP/UDP	ISAKMP/Oakley negotiation traffic (IPSec)
522	TCP	User Location Store
636	TCP/UDP	LDAP (over TLS/SSL)
750	UDP	Kerberos Authentication
750	TCP	Kerberos Authentication
751	UDP	Kerberos Authentication
751	TCP	Kerberos Authentication
752	UDP	Kerberos Password Server
753	UDP	Kerberos User Registration Server
754	TCP	Kerberos Slave Propagation
888	TCP	Logon and Environment Passing
Dynamic	TCP	Directory Replication
1109	TCP	POP with Kerberos
1723	TCP	PPTP Control Channel (IP Protocol 47 – GRE)
2053	TCP	Kerberos de-multiplexor
2105	TCP	Kerberos encrypted login
3268		Global Catalog
3269		Global Catalog
3389	RDP	Terminal Services

The following is a list of ports and protocols for Microsoft Exchange 2000 Server services.

Port	TCP/UDP	Service Name
25	TCP	SMTP
80	TCP	HTTP
102	TCP	MTA – X.400 over TCP/IP
110	TCP	POP3
119	TCP	NNTP
135	TCP	Client/Server Communication, RPC, Exchange Administration
143	TCP	IMAP4
389	TCP	LDAP
443	TCP	HTTP (SSL)
465	TCP	SMTP (SSL)
563	TCP	NNTP (SSL)
636	TCP	LDAP (SSL)
993	TCP	IMAP4 (SSL)
995	TCP	POP3 (SSL)
1720	TCP	H.323 Call Setup
1731	TCP	Audio Call Control
2980	TCP/UDP	Instant Messaging Service
Dynamic	TCP	H.323 Call Control
Dynamic	TCP	H.323 Call (RTP Over UDP)

 

Computer Architecture

A von Neumann Architecture computer has five parts: an arithmetic-logic unit, a control unit, a memory, some form of input/output and a bus that provides a data path between these parts.

A von Neumann Architecture computer performs or emulates the following sequence of steps:

• 1) Fetch the next instruction from memory at the address in the program counter.
• 2) Add the length of the instruction to the program counter.
• 3) Decode the instruction using the control unit. The control unit commands the rest of the computer to perform some operation. The instruction may change the address in the program counter, permitting repetitive operations. The instruction may also change the program counter only if some arithmetic condition is true, giving the effect of a decision, which can be calculated to any degree of complexity by the preceding arithmetic and logic.
• 4) Go back to step 1.

Very few computers have a pure von Neumann architecture. Most computers add another step to check for interrupts, electronic events that could occur at any time. An interrupt resembles the ring of a telephone, calling a person away from some lengthy task. Interrupts let a computer do other things while it waits for events.

Von Neumann computers spend a lot of time moving data to and from the memory, and this slows the computer (this problem is called von Neumann bottleneck ) So, engineers often separate the bus into two or more busses, usually one for instructions, and the other for data.