Chapter 9 Outline

Chapter 9 Outline

Chapter 9 Outline

I.Network Architectures

A.A specific network’s architecture involves the network’s physical configuration, logical operation, structure, procedures, data formats, protocols, and other components.

B.The two main categories of network architecture are LANs and WANs.

1.LANs, or local area networks, are smaller in size and geographic coverage and consist of two or more connected devices.

2.WANs, or wide area networks, cover more geographic area and consist of two or more systems in geographically separated areas connected by leased lines, radio waves, satellite relays, microwaves, or even dial-up connections.

C.The following terms describe emerging, specialized network structures that are classified based on size and use:

1.CAN – Campus Area Network (also referred to as a Campus Wide Area Network), a network connecting any number of buildings in an office or university complex.

2.Intranet – A “private” network only accessible to authorized users.

3.Internet – “The global network” connecting millions of systems and users.

4.MAN – Metropolitan Area Network, a network designed for a specific geographic locality such as a town or city.

5.SAN – Storage Area Network, a high-speed network connecting a variety of storage devices such as tape systems, RAID arrays, optical drives, and file servers.

6.VLAN – Virtual Local Area Network, a logical network allowing systems on different physical networks to interact as if they were connected to the same physical network.

7.Client-Server – A network where powerful, dedicated systems called servers provide resources to individual workstations or clients.

8.Peer-to-Peer – A network where every system is treated as an equal, such as a home network.

II.Network Topology

A.A major component of every network’s architecture is its topology – how the network is physically or logically arranged.

B.The main classes of network topologies are: star, ring, bus, and mixed.

1.Star – Network components are connected to a central point.

2.Bus – Network components are connected to the same cable, often called “the bus” or “the backbone.”

3.Ring – Network components are connected to each other in a closed loop with each device directly connected to two other devices.

C.Larger networks, such as those inside an office complex, may use more than one topology at the same time.

D.With recent advances in technology, these topology definitions often break down. To avoid confusion, many people use topology definitions to apply only to the physical layout of the network, focusing on how the devices are connected to the network.

III.Network Protocols

A.A protocol is a format for exchanging or transmitting data between systems. It defines a number of parameters such as the data compression method, the type of error checking to use, and mechanisms for systems to signal when they have finished receiving or transmitting data.

B.Some of the common protocols are:

1.AppleTalk – The communications protocol developed by Apple to connect Macintosh computers and printers.

2.Asynchronous Transfer Mode (ATM) – A protocol based on transferring data in fixed size packets, which ensures that no single data type monopolizes the available bandwidth.

3.DECnet – A protocol developed by Digital Equipment Corporation to connect PDP and VAX systems.

4.Ethernet – The LAN protocol developed jointly by Xerox, DEC, and Intel. It is the most widely implemented LAN standard.

5.Fiber Distributed Data Interface (FDDI) – The protocol for sending digital data over fiber optic cabling.

6.Internet Protocols (IP) – The protocols for managing and transmitting data between packet-switched computer networks.

7.Internetwork Packet Exchange (IPX) – The networking protocol used by Novell NetWare operating systems.

8.Netware – The LAN protocol developed by Novell Corporation.

9.Signaling System 7 (SS7) – The telecommunications protocol used between PBXes to handle tasks such as call setup, routing, and teardown.

10.Systems Network Architecture (SNA) – A set of network protocols developed by IBM, originally used to connect IBM’s mainframe systems.

11.Token Ring – A LAN protocol developed by IBM where systems must possess the network “token” before transmitting data.

12.Transmission Control Protocol/Internet Protocol (TCP/IP) – The collection of communication protocols used to connect hosts on the Internet.

13.X.25 – A protocol developed by the Comité Consultatif International Téléphonique et Télégraphique (CCITT) for use in packet-switched networks.

C.In most cases, communications protocols were developed around the Open System Interconnection (OSI) model, or OSI Reference Model, which is an ISO standardfor worldwide communications. It defines a framework for implementing protocols in seven distinct layers.

1.Within the OSI model, control is passed from one layer to another (top down) before it exits one system and enters another system where control is passed bottom-up to complete the communications cycle.

2.Most protocols only loosely follow the OSI model. Several protocols combine one or more layers into a single function.

3.The OSI model also provides a certain level of abstraction and isolation for each layer since each layer only needs to know how to interact with the layer above and below it. Figure 9-6 shows the different layers of the OSI model.

7 / Application Layer / Program level communication.
6 / Presentation Layer / Performs data conversion functions when needed.
5 / Session Layer / Establishes and maintains communications channels.
4 / Transport Layer / Handles end-to-end transmission and integrity of transmitted data.
3 / Network Layer / Routes data from one system to another.
2 / Data Link Layer / Handles the physical passing of data from one system to another.
1 / Physical Layer / Manages the transmission and reception of data on the network media.


1.When data is broken up into smaller pieces for transmission, the smaller pieces are called packets. Each protocol has its definition of a packet – dictating how much data can be carried, what information is stored where, and how the packet should be interpreted by another system.

2.A standard packet structure is a crucial element in a protocol definition. Without a standard packet structure, systems would not be able to interpret the information they receive from other systems. The different components of a packet include:

a)IP packets, also called datagrams, which have two main sections: the header and the data section (sometimes called the payload).

b)The header section contains all the information needed to describe the packet such as:

(1)What kind of packet it is (protocol version number).

(2)How large the header of the packet is (packet header length).

(3)How to process the packet (type of service telling the network whether or not to use options such as minimize delay, maximize throughput, maximize reliability, and minimize cost).

(4)How large the entire packet is (overall length of the packet – as this is a 16-bit field, the maximum size of an IP packet is 65,535 bytes, but in practice, most packets are around 1500 bytes).

(5)A unique identifier so this packet can be distinguished from other packets.

(6)Whether or not this packet is part of a longer data stream and should be handled relative to other packets.

(7)A description of where this packet fits into the data stream as compared to other packets (the fragment offset).

(8)A checksum of the packet header (to minimize the potential for data corruption during transmission).

(9)Where the packet is from (Source IP address such as

(10)Where the packet is going (Destination IP address such as

(11)Option flags that govern security and handling restrictions, whether or not to record the route this packet has taken, and whether or not to record timestamps.

(12)The data this packet carries.

E.TCP versus UDP

1.The Transmission Control Protocol (TCP)and User Datagram Protocol (UDP) run on the IP network protocol. As separate protocols, they have their own packet definitions, capabilities, and advantages. The most important difference between TCP and UDP is the concept of “guaranteed” reliability and delivery.

2.UDP is known as a “connectionless” protocol as it has very few error recovery services and no guarantee of packet delivery.

a)With UDP, packets are created and sent. The sender, however, does not know if the packets were successfully received or whether or not they were received in order.

b)UDP is an unreliable protocol and is often only used for network services that are not affected by the dropped packet.

c)UDP is an “efficient” protocol in terms of content delivery versus overhead. With the UDP protocol, more time and space is dedicated to content, or data, delivery than other protocols such as TCP. This makes UDP preferred for streaming protocols as more of the available bandwidth and resources are used for data delivery than with other protocols.

3.TCP is a “connection-oriented” protocol and was specifically designed to allow for a reliable connection between two hosts exchanging data. It was designed to ensure that packets are processed in the same order as they were sent.

a)As part of the TCP protocol, each packet has a sequence number to show where that packet fits into the overall conversation.

b)With the sequence numbers, packets can arrive in any order and at different times and the receiving system will still know the correct order for processing the packets.

c)The sequence numbers also informs the receiving system if packets are missing so that the receiving system can then request re-transmission of missing packets from the sender to fill in any gaps.

4.As part of the connection, the TCP protocol requires that systems follow a specific pattern when establishing communications. This pattern is often called the “three-way handshake” consisting of a sequence of the following steps:

a)The originating host (usually called the client) sends a SYN (synchronize) packet to the destination host (usually called the server) which tells the server what port the client wants to connect and the initial packet sequence number of the client.

b)Next, the server sends a SYN/ACK (synchronize/acknowledge) packet back to the client which tells the client “I received your request” and also contains the server’s initial packet sequence number.

c)Finally, the client responds to the server with an ACK packet to complete the connection establishment process.

F.The Internet Control Message Protocol (ICMP) is a control and information protocol. It is used by network devices to determine things like a remote network’s availability, length of time to reach a remote network, and the best route for packets to take when traveling to that remote network.

1.ICMP can also be used to handle the flow of traffic, indicating other network devices to “slow down” transmission speeds if packets are coming in too fast.

2.ICMP, like UDP, is a connectionless protocol and was designed to carry small messages quickly with minimal overhead or impact to bandwidth.

a)ICMP packets are sent using the same header structure as IP packets with the Protocol Field set to “1” to indicate it is an ICMP packet.

b)Each packet also contains a “type” which indicates what type of ICMP message it is as well as a “code” field which tells what the message really means.

IV.Packet Delivery

A.Packet delivery can be divided into two sections: local and remote packet delivery.

1.Local delivery applies to packets being sent out on a local network while remote delivery applies to packets being delivered to a remote system, such as across the Internet.

2.The biggest difference in local and remote delivery is how packets are addressed. These addresses are usually called Media Access Control (MAC) addresses for local packet delivery and IP addresses for remote packet delivery.

B.Local packet delivery.

1.Packets delivered on a local network, such as an office LAN, are usually sent using the destination systems hardware address, or MAC address.

2.The MAC address is a unique hardware address that is assigned to a device or network card by the manufacturer and each manufacturer is assigned a specific block of MAC addresses to prevent two devices from sharing the same MAC address. MAC addresses are usually expressed as six pairs of hexadecimal digits. An example of a MAC address is “00:07:e9:7c:c8:aa.”

3.For a system to send data to another system on the local network, it must first find out the destination system’s MAC address.

4.To find another system’s MAC address, the Address Resolution Protocol (ARP) is used, which is essentially the computer’s way of finding out “who owns the blue convertible with license number 123JAK.” In most cases, systems know the IP address they wish to send, but not the MAC address.

a)Using an ARP request, the sending system sends a query.

b)This broadcast query is examined by every system on the local network, but only the system whose IP address that matches the query responds.

c)The system sends back an acknowledgement response with the MAC address.

d)The sending system then formats the packet for delivery and drops it on the network media, stamped with the MAC address of the destination workstation.

C.Remote Packet Delivery

1.Remote packet delivery is accomplished using Internet Protocol (IP) addresses. IP addresses are 32-bit numbers that are expressed as a group of four numbers (such as

2.The Domain Name Service (DNS) protocol translates names into IP addresses.

a)On entering a Web site into the location bar of the Web browser, the system sends a query to a local DNS server that essentially asks for the IP address of the specified Web site.

b)The DNS server checks its local records to locate the IP address.

c)If no match is found, the DNS server queries another higher-level domain server which checks its records and queries the server above it. The search continues till the matching record is found.

d)The name that matches the IP address is passed back down to the original computer so it can create the Web request, stamp it with the right destination IP address, and send it.

3.Before sending the packet, the system first determines if the destination IP address is on a local or remote network by forwarding the packet to a network gateway.

a)Network gateways, usually called routers, are devices that are used to interconnect networks and move packets from one network to another. The process of moving packets from one network to another is called routing.

b)Routers use forwarding tables to determine where a packet should go. When a packet reaches a router, it looks at the destination address to determine where to send the packet. If the router’s forwarding tables know where the packet should go, the router sends the packet out along the appropriate route.

c)If the router does not know where the destination network is, it forwards the packet to its defined gateway. This process is repeated and eventually, the packet reaches the router serving the network with the Web site with the original request.

d)This router determines the appropriate MAC address of the destination system and forwards the packet accordingly.


1.IP addresses are 32-bit numbers and of these 32-bits, some are used for the network portion of the address, and some for the host portion of the address. The network portion is typically called the subnet and the process of dividing the 32-bit space into networks is called subnetting.

2.Subnetting defines the network portion and the host portion of the address.

3.To interpret the 32-bit space correctly, a subnet mask is used. It tells exactly how much of the space is the network portion and how much is the host portion. When using subnet mask and IP addresses:

a)Convert the IP address and subnet mask to their binary representations.

b)Perform a bitwise AND operation to get the subnet address. The bitwise AND operation examines each set of matching bits from the binary representation of the subnet mask and the binary representation of the IP address. For each set where both the mask and address bits are 1, the result of the AND operation is a 1. If either bit is a 0, the result is a 0.

4.As per the subnet address and mask, the first three parts of the address are network related, which means that the last part of the address is the host portion.

5.Subnets are usually divided into one of the three classes:

a)Class A addresses – Support 16 million hosts on each of the 127 networks. Subnets: to ( to is reserved for loopback and is not included in the class A range).

b)Class B addresses – Support 65,000 hosts on each of the 16,000 networks. Subnets: to

c)Class C addresses – Supports 254 hosts on each of the 2,000,000 networks. Subnets: to Everything above is reserved for either multicasting or future use.

6.In addition, certain subnets are reserved for private use and are not routed across public networks.

a) to

b) to

c) to

7.When determining the valid hosts that can be placed on a particular subnet, ensure that the “all 0s” address of the host portion is reserved for the network address and the “all 1s” address of the host portion is reserved for the broadcast address of that particular subnet.