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Packets Reviewed

A packet is a unit of information transmitted as a whole from one network device to another.

During the transmission and reception process, appropriate information is added and subtracted to and from each packet.

Packet Structure

All packets have the same 3 basic parts:
Header
Contains the source and destination address
Data
Transported Data
Trailer
Error correction data

Minimum Packet Contents

Source and destination addresses.
Alert signal.
Data being transmitted.
Error correction data.

Protocols
Rules and procedures for communicating.
A set of protocols that work together is called a protocol stack or protocol suite.

Common protocol stacks include:

TCP/IP
IPX/SPX
NWLink

Protocol Classifications
Certain classifications can be applied to all protocols.

Connection or connectionless orientation.
Routable or noroutable.

Connectionless vs. Connection Oriented

Connectionless protocols place data on the media and assume that it will get through. (i.e. the Mailbox Model)
Reliable but could be more reliable
Fast

Connection oriented protocols establish a connection between the two computers.

More reliable
Slower

Routable vs. Nonroutable Protocols

The network layer of the OSI model is responsible for moving data across networks.
Moving data between networks is called routing.
Network level protocols are routable, other protocols, such as Transport protocols are not.

Enterprise Protocols

TCP/IP and IPX/SPX are routable protocols well suited for large networks.
NetBEUI however is nonroutable.
It is a small fast transport level protocol well suited for small networks.
Sometimes, collections of separate protocols form protocol groups.

Major Protocol Groups

Application, Session, and Presentation layers combine into the Applications Major Group.
Transport Layer becomes the Transport Group.
Network, Data Link, and Physical layers, combine into the Network Major Group.

Application Group Protocols

Operate at the OSI model's upper layers
Provide application to application services.
Common application protocols include:
SMTP
FTP
SNMP

Transport Protocols

Ensure reliable data delivery.
Common transport protocols include:
TCP
SPX and NWLink
ATP
NetBIOS/NetBEUI

Network Protocols
Provide addressing and routing information, error checking.
Also called link services.
Common Network Protocols include:

IP
IPX
DLC

Microsoft's Protocol Stack
NetBIOS and NetBEUI are two of six components in the Microsoft Protocol Stack.

In order from the top they are:
Redirector
SMB
NetBIOS
NetBEUI
NDIS
NIC Driver
Physical

Microsoft Protocol Suite

Redirector interprets requests from the computer
Keeps request local or remote.
If the service is remote, it passes the request to the SMB (Server Message Block).
The SMB passes information between networked computers.
NetBIOS operates at the Session layer to establish and maintain connections.
NetBEUI works at the Transport layer
Manages communications
Each computer in a NetBIOS network has a 15 character name that is used for identification.

NWLink

Microsoft's 32 bit IPX/SPX implementation.
NWLink works with particular Ethernet frame type(s).
For communications to be effective, all frame types must be identified to NWLink.

Auto Frame Detect

Note that auto frame detect will only detect one frame type.
If everything seems okay and communications is not occurring, check the frame type.

Frame Types

EthernetII DEC
802.2 Novell 3.12 and later
Industry standard. 802.3 Compliant.
802.3 Novel 3.11 and earlier
SNAP Apple

TCP/IP
While it predates the ISO model, its protocols and functions are similar.
Utilizes small, specialized protocols.
IP provides source and destination addressing and routing.
Connectionless datagram protocol that is fast but not reliable.

TCP/IP Protocol Components

ARP Address Resolution Protocol
Translates logical (IP) addresses to a physical MAC address.
TCP Transmission Control Protocol (TCP)
Transport protocol that accepts messages of any length from an upper-layer protocol and provides transportation to a TCP peer.
UDP User Datagram Protocol (UDP)
A connectionless Transport layer protocol.
DNS Domain Name System
A Transport layer, name to address resolution protocol. Keeps a list of system's NetBIOS names and their IP addresses.
Telnet
A remote terminal emulation program.
SMTP Simple Mail Transport Program
Mail protocol that operates at all upper layers.
RIP Routing Information Protocol
Uses distance vector algorithm to select the best path for a packet.
OPSF Open Shortest Path First
Determines best path through network

IP Address
Logical address
32 bits, 4 bytes, long.
Each byte can be represented by a decimal number from 0 to 255.

IP Address Representation

Each IP addresses is represented by four octets separated by periods, that is, 126.107.7.109
Part of the address denotes the network that the computer resides on. The other part of the address denotes the computer itself.

Address Classes

Classfull TCP/IP addressing includes several classes.
Class A addresses
Begin with a number between 1 and 126.
Can have 16,387,064 hosts.
Class B addresses
Begin with a number between 128 and 191
Can have 64,516 hosts per address
Class C addresses
First three octets begin with a number between 192 and 223.
Can have 254 hosts.

Certain address, such as those beginning with 127, are reserved for special purposes.

Subnet Mask

Determines which part of the IP address denotes the network and which part the host.
All computers on the same network must use the same subnet mask.

Dynamic Host Configuration Program

DHCP is defined as a server that assigns IP addresses from an address pool to each computer as it signs onto a network.
Makes moving computers easier.
Included with NT Server.

Media Access Methods

Defines when computers can access the shared network cable or data channel.
Provides additional assurance that data reaches its destination by preventing two or more computers from simultaneously accessing the cable.

Major Access Methods

Contention
CSMA/CD -- Ethernet
CSMA/CA -- Apple's Local Talk
Token Passing
Token Ring, FDDI, ARCNet
Demand Priority
100VG-AnyLAN
Polling
PDP 11, SNA