Networking and Data Communications

Network standards

A set of network standards developed by the IEEE. They include:

IEEE 802.1 IEEE 802.2 IEEE 802.3 IEEE 802.4 IEEE 802.5 IEEE 802.6

IEEE 802.1

IEEE 802.1 : Standards related to network management.

Network management refers to the broad subject of managing computer networks.

There exists a wide variety of software and hardware products that help network system administrators manage a network.

Network management covers a wide area, including:

Security: Ensuring that the network is protected from unauthorized users.

Performance: Eliminating bottlenecks in the network. Reliability: Making sure the network is available to

users and responding to hardware and software malfunctions.

IEEE 802.2 IEEE 802.2: General standard for the data link layer in the

OSI Reference Model. The IEEE divides this layer into two sublayers:

The logical link control (LLC) layer and The media access control (MAC) layer.

The Media Access Control Layer is one of two sublayers that make up the Data Link Layer of the OSI model.

The MAC layer varies for different network types and is defined by standards IEEE 802.3 through IEEE 802.5.

The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.

The MAC sublayer uses MAC protocols to ensure that signals sent from different stations across the same channel don't collide.

IEEE 802.3

IEEE 802.3: Defines the MAC layer for bus networks that use CSMA/CD.

IEEE 802.4

IEEE 802.4: Defines the MAC layer for bus networks that use a token-passing mechanism (token bus networks).

Token bus networks A type of local-area network (LAN) that has a bus

topology and uses a token -passing mechanism to regulate traffic on the bus.

A token bus network is very similar to a token ring network, the main difference being that the endpoints of the bus do not meet to form a physical ring.

Token bus networks are defined by the IEEE 802.4 standard.

IEEE 802.5 and IEEE 802.6

IEEE 802.5 IEEE 802.5: Defines the MAC layer

for token-ring networks.

IEEE 802.6 IEEE 802.6: Standard for

Metropolitan Area Networks (MANs).

OSI Model

The International Standards Organization (ISO) developed the OSI (Open Systems Interconnection) model.

It divides network communication into seven layers Layers 1-4 are considered the lower layers, and

mostly concern themselves with moving data around. Layers 5-7, the upper layers, contain application-level

data. Networks operate on one basic principle: "pass it on."

Each layer takes care of a very specific job, and then passes the data onto the next layer.

OSI Model

OSI Model Layer 1

Layer one is simply wiring, fiber, network cards, and anything else that is used to make two network devices communicate

Network troubleshooting will often lead to a layer one issue.

OSI Layers

OSI Model Layer 2

Bridge and Switch, and MAC address all operate at layer 2

Hubs live in layer 1 land, since they are simply electronic devices with zero layer 2

The layer 2 translates data frames into bits for layer 1 processing.

OSI Layers

•Provides connectivity and path selection between two host

•Provides Logical address

•No error correction, best effort delivery.

OSI Model Layer 3

If you are talking about router and an IP address, you're dealing with layer 3 and "packets" instead of layer 2's "frames."

Everything about routing is handled in layer 3. Addressing and routing is the main goal of this layer.

OSI Layers

OSI Model Layer 3

Layer 4, the transport layer, handles messaging. Layer 4 data units are also called packets.

This layer is responsible for getting the entire message, so it must keep track of fragmentation, out-of-order packets.

Another way to think of layer 4 is that it provides end-to-end management of communication.

Some protocols, like TCP, do a very good job of making sure the communication is reliable.

OSI Layers

Peer-to-Peer Communication

TCP/IP Model

Encapsulation

Names for Data at Each Layer

LOCAL AND WIDE AREA NETWORKS

LAN Technologies

LAN (Local Area Network) refers to a group of computers interconnected into a network so that they are able to communicate, exchange information and share resources (e.g. printers, application programs, database etc).

In other words, the same computer resources can be used by multiple users in the network, regardless of the physical location of the resources.

Media Access Control methods

There are different types of Media Access Control methods in a LAN: Ethernet Token ring Fast ethernet FDDI

Ethernet

Ethernet is a 10Mbps LAN that uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol to control access network.

When an endstation (network device) transmits data, every endstation on the LAN receives it.

Each endstation checks the data packet to see whether the destination address matches its own address.

If the addresses match, the endstation accepts and processes the packet.

If they do not match, it disregards the packet. If two endstations transmit data simultaneously, a collision occurs and the result is a composite, garbled message.

All endstations on the network, including the transmitting endstations, detect the collision and ignore the message.

Each endstation that wants to transmit waits a random amount of time and then attempts to transmit again

Token Ring It is a method operating in a ring topology. Devices on a Token Ring network get access to the

media through token passing. Token and data pass to each station on the ring. The

devices pass the token around the ring until one of the computer who wants to transmit data , takes the token and replaces it with a frame.

Each device passes the frame to the next device, until the frame reaches its destination.

As the frame passes to the intended recipient, the recipient sets certain bits in the frame to indicate that it received the frame.

The original sender of the frame strips the frame data off the ring and issues a new token

NETWORK ACCESS METHODS

CSMA/CD This stands for "carrier-sense multiple access with collision

detection. It is a method used on ethernet networks whereby all

computers on the network check the cable for traffic before attempting to transmit a packet.

Each device senses whether the line is idle and therefore available to be used

If more than 1 transmits at the same time then there will be a collision and both computers will wait a random amount of time and retransmit.

Collision

A collision is the result of two devices on the same Ethernet network attempting to transmit data at exactly the same time

The network detects the "collision" of the two transmitted packets and discards them both

Collisions are a natural occurrence on Ethernets.


CSMA/CA Stands for "carrier-sense multiple access with

collision avoidance". In CSMA/CA, as soon as a node receives a packet

that is to be sent, it checks to be sure the channel is clear (no other node is transmitting at the time).

If the channel is clear, then the packet is sent.


If the channel is not clear, the node waits for a randomly chosen period of time, and then checks again to see if the channel is clear.

This period of time is called the backoff factor, and is counted down by a backoff counter. If the channel is clear when the backoff counter reaches zero, the node transmits the packet.

If the channel is not clear when the backoff counter reaches zero, the backoff factor is set again, and the process is repeated.


TOKEN PASSING Token passing uses a token, or series of bits, to grant a

device permission to transmit over the network Token passing is the access method used by token ring

networks. With this method, a packet called a token is passed around

the network. A computer that wishes to transmit must wait until it can take

control of the token, allowing only one computer to transmit at a time.

When its transmission is complete, the device passes the token along to the next device in the topology.


DEMAND PRIORITY The repeaters, bridges, routers or hubs search the network

for requests that are waiting to be sent. If 2 or more requests are received by the network hardware

at once, the data with the highest priority is sent Priority for different data types can be controlled by the

administrator. A real advantage is that computers can receive and transmit

at the same time with this access method .

Fast Ethernet

This is an extension of 10Mbps Ethernet standard and supports speed upto 100Mbps.

The access method used is CSMA/CD. For physical connections Star wiring

topology is used. Fast Ethernet is becoming very popular as

an upgradation from 10Mbps Ethernet LAN to Fast Ethernet LAN is quite easy.

FDDI (Fiber Distributed Data Interface):

FDDI provides data speed at 100Mbps which is faster than Token Ring and Ethernet LANs . FDDI comprise two independent, counter-rotating rings : a primary ring and a secondary ring.

Data flows in opposite directions on the rings.

The counter-rotating ring architecture prevents data loss in the event of a link failure, a node failure

This technology is usually implemented for a backbone network.

Carrier sense multiple access networks collision

detection (CSMA/CD) This stands for "carrier-sense multiple access with collision

detection. It is a method used on ethernet networks whereby all

computers on the network check the cable for traffic before attempting to transmit a packet.

Each device senses whether the line is idle and therefore available to be used

If more than 1 transmits at the same time then there will be a collision and both computers will wait a random amount of time and retransmit.

If the channel is not clear, the node waits for a randomly chosen period of time, and then checks again to see if the channel is clear.

This period of time is called the backoff factor, and is counted down by a backoff counter. If the channel is clear when the backoff counter reaches zero, the node transmits the packet.

If the channel is not clear when the backoff counter reaches zero, the backoff factor is set again, and the process is repeated.

Collision

A collision is the result of two devices on the same Ethernet network attempting to transmit data at exactly the same time

The network detects the "collision" of the two transmitted packets and discards them both

Collisions are a natural occurrence on Ethernets.

Circuit Switching vs. Packet Switching

In circuit-switching, this path is decided upon before the data transmission starts.

The system decides on which route to follow, based on a resource-optimizing algorithm, and transmission goes according to the path.

For the whole length of the communication session between the two communicating bodies, the route is dedicated and exclusive, and released only when the session terminates.

Packet-switching

In packet-switching, the packets are sent towards the destination irrespective of each other.

Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached.

Each packet finds its way using the information it carries, such as the source and destination IP addresses.

Mobile Computing

Mobile Computing is becoming increasingly important due to the rise in the number of portable computers and the desire to have continuous network connectivity to the Internet irrespective of the physical location of the node.

IP requires the location of any host connected to the Internet to be uniquely identified by an assigned IP address.

Updated IP Requirements

A mobile node must be able to communicate with other nodes after changing its link-layer point of attachment to the Internet, yet without changing its IP address.

A mobile node must be able to communicate with other nodes that do not implement mobility functions.

Need for the Mobile IP Design

IP address of a host consists of two parts:

(i) The higher order bits of the address determine the network on which the host resides;

(ii) The remaining low-order bits determine the host number.

IP decides the next-hop by determining the network information from the destination IP address of the packet.


On the other hand, higher level layers like TCP maintain information about connections that are indexed by a quadruplet containing the IP addresses of both the endpoints and the port numbers

Thus, while trying to support mobility on the Internet under the existing protocol suite, we are faced with two mutually conflicting requirements:


(i) a mobile node has to change its IP address whenever it changes its point of attachment, so that packets destined to the node are routed correctly,

(ii) to maintain existing TCP connections, the mobile node has to keep its IP address the same. Changing the IP address will cause the connection to be disrupted and lost.

What is Mobile IP?

Mobile IP is an internet protocol designed to support host mobility.

Mobile IP, the standard proposed by IETF, is designed to enable mobile computers to stay connected to the Internet regardless of their location and without changing their IP address.

Mobile IP is a standard protocol that builds on the Internet Protocol by making mobility transparent to applications and higher level protocols like TCP.

What is Mobile IP? It solves the problem by allowing each mobile

node to have two IP addresses and by transparently maintaining the binding between the two addresses.

One of the IP addresses is the permanent home address that is assigned at the home network and is used to identify communication endpoints.

The other is a temporary care-of address that represents the current location of the host.

Mobile IP Functional Entities

Mobile IP introduces new functional entities that include:

A mobile node host or router that changes its point of attachment from one network to another maintains all existing communications by using its home IP address

A home agent server or router on the home network of a mobile node intercepts datagrams that are destined for the mobile node

Maintains current information on the location of the mobile node

Delivers the datagrams to the care-of address

Mobile IP Functional Entities

A foreign agent server or router on the foreign network that the mobile node visits Provides host routing services to the

mobile node Provides a care-of address to the

mobile node Provides “first-hop” routing services for

the mobile node

Mobile IP topology

Mobile IP topology

The correspondent node (node on any network) sends a datagram to the mobile node by using the mobile node’s home address (normal IP communication).

If the mobile node is not on its home network, the home agent knows to intercept the datagram.

The home agent forwards the datagram to the foreign agent. The home agent must “tunnel” the datagram so that the foreign agent’s IP address appears in the outer IP header.

The network routes the datagram as it would any other datagram. The foreign agent receives the datagram, sees it contains the datagram originally

addressed to the mobile node, and delivers it to the mobile node. Datagrams sent from the mobile node to its correspondent node are sent through the

foreign agent by normal IP routing procedures. Either the foreign agent forwards the mobile node’s datagram to its router as it would any other datagram, or if the agents are using a reverse tunnel, the foreign agent “tunnels” the mobile node’s datagram to the home agent, which then sends it to the correspondent node exactly as it would any other datagram.

PERFORMANCE EVALUATION

A virtual private network VPN is a computer network in which some

of the links between nodes are carried by open connections or virtual circuits in some larger networks (such as the Internet), as opposed to running across a single private network.

The Link Layer protocols of the virtual network are said to be tunneled through the transport network.

Connection-oriented service and Connectionless service

Connection-oriented requires a session connection (analogous to a phone call) be established before any data can be sent.

This method is often called a "reliable" network service.

It can guarantee that data will arrive in the same order.

Connection-oriented services set up virtual links between end systems through a network.

Connectionless

It does not require a session connection between sender and receiver.

The sender simply starts sending packets (called datagrams) to the destination.

This service does not have the reliability of the connection-oriented method, but it is useful for periodic burst transfers.

A connectionless network provides minimal services.

Connection oriented service

Network performance characteristics

Delay Throughput

The Last Unit

Network Management

Refers to the broad subject of managing computer networks. There exists a wide variety of software and hardware products that help network system administrators manage a network. Network management covers a wide area, including: Security: Ensuring that the network is

protected from unauthorized users. Performance: Eliminating bottlenecks in the

network. Reliability: Making sure the network is

available to users and responding to hardware and software malfunctions.

Network Quality of service

Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow

For example, a required bit rate, delay, jitter, packet dropping probability and/or bit error rate may be guaranteed

Dropped packets

The routers might fail to deliver (drop) some packets if they arrive when their buffers are already full. Some, none, or all of the packets might be dropped, depending on the state of the network, and it is impossible to determine what will happen in advance.

The receiving application may ask for this information to be retransmitted, possibly causing severe delays in the overall transmission.

Delay

It might take a long time for a

packet to reach its destination, because it gets held up in long queues, or takes a less direct route to avoid congestion. In some cases, excessive delay can render an application such as VoIP or online gaming unusable.

Jitter

Packets from the source will reach the

destination with different delays. A packet's delay varies with its position in

the queues of the routers along the path between source and destination and this position can vary unpredictably.

This variation in delay is known as jitter and can seriously affect the quality of streaming audio and/or video.

Out-of-order delivery

When a collection of related packets is routed through the Internet, different packets may take different routes, each resulting in a different delay.

The result is that the packets arrive in a different order than they were sent.

Error

Sometimes packets are misdirected,

or combined together, or corrupted, while in route.

The receiver has to detect this and, just as if the packet was dropped, ask the sender to repeat itself.

Internet Service Provider (ISP)

An Internet service provider (ISP, also called Internet access provider, or IAP) is a company that offers its customers access to the Internet.

The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol datagrams, such as dial-up, DSL, cable modem, wireless or dedicated high-speed interconnects.

ISPs employ a range of technologies to enable consumers to connect to their network. The most are dial-up, DSL or ADSL, broadband wireless, cable modem, and ISDN

ISP Interconnection

Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access.

An upstream ISP usually has a larger network than the contracting ISP and/or is able to provide the contracting ISP with access to parts of the Internet the contracting ISP by itself has no access to.

Domain names and name services

A domain name is an identification label that defines a realm of administrative autonomy, authority, or control in the Internet, based on the Domain Name System (DNS).

The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains com, net and org, and the country code top-level domains (ccTLDs)

The Domain Name System (DNS)

DNS is a hierarchical naming system for computers, services, or any resource connected to the Internet or a private network.

It associates various information with domain names assigned to each of the participants.

Most importantly, it translates domain names meaningful to humans into the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices worldwide.

Network Security and Firewall

Network security consists of the provisions made in an underlying computer network infrastructure, policies adopted by the network administrator to protect the network and the network-accessible resources from unauthorized access and consistent and continuous monitoring and measurement of its effectiveness (or lack) combined together.

Firewall

A firewall is an integrated collection of security measures designed to prevent unauthorized electronic access to a networked computer system.

It is also a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all computer traffic between different security domains based upon a set of rules and other criteria

Firewall techniques

Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.

Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.

Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses

Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.

End of course

Bye, Bye!!!

Second test, when?

Networking and Data Communications

Technology

Transcript of Networking and Data Communications