Lesson 10

Okay, work has been hectic this week so once again I am only getting to this on a Friday! Gotta do it now as I expect to be in Forries before 3!


Quick recap:

802.3 – Ethernet

802.5 – Ring

802.11(x) – Wireless

Key Acronyms:

• FHSS – Frequency Hopping Spread Spectrum

• DSSS - Direct Sequence Spread Spectrum

• Multiplexing – send and receive on same channel

Wireless:

• 802.11

o Has transmission speeds of 1 or 2 Mbps

o Radio frequency of 2.4GHz

o One variation uses FHSS and one uses DSSS

• 802.11.a

o Speeds up to 54Mbps

o 5 GHz band

o Transmission typically at 6, 12 or 24Mbps

o Uses orthogonal frequency division multiplexing (OFDM)

o Range roughly 20 metres

• 802.11b

o Speed – 11Mbps

o 2.4GHz

o Range 100 metres

• 802.11g

o Speed 54Mbps

o 2.5GHz

o Average speeds 20-25Mbps

o Range – 100 metres

• 802.11n

o Speeds up to 300Mbps

o Two streams so 600Mbps

o 2.4GHz or 5GHz frequency

Channels in 802.11b/g Implementation:

Overlap in the radio signals or bleeding can occur when these overlap between adjacent accesses points and clients. The best channels to use to avoid this are channels: 1, 6 and 11.

802.11 Modes:

You get infrastructure and ad hoc modes

Infrastructure mode is when the WAP is hardwired to the network (server) and the workstations connect wirelessly. Uses BSS (basic service set) or ESS (Extended service set) as the protocol

Ad hoc is when the workstations connect to the WAP wirelessly and there is no hardwired backbone. This uses the protocol IBSS (independent basic service set)

WLAN Architecture: see page 190, not important.

Protocols:

• BSS (Basic Service Set)

o One access point connected to a wired network and has one or more wireless stations or clients. A BSS is also referred to as Infrastructure mode as it requires an access point in order to transmit data

• ESS (Extended Service Set)

o The ESS comprises two or more BSS’s that are connected to a common distribution system such as a wired network. An ESS must contain at least two wireless access points operating in infrastructure mode, which allows clients to use their AP depending on the locations of the wireless station or point.

• ESSID (Extended Service Set ID)

o The ESSID is the name that identifies a wireless network or wireless access point so that you can identify the networks clearly.

• IBSS (Independent Basic Service Set

o IBSS does not contain an AP. It is a peer to peer network in which each wireless station or client has its own wireless network adapter and each acts as both client and wireless AP.

802.11 BEACONS

Beacon frames are management frames that are only 50 bytes long. They are used to start and maintain wireless communication. They contain information about the communication process such as the STA and SSID, channel number and security protocol.

Wire Equivalent Privacy (WEP)

• To prevent eavesdropping, IEEE 802.11 WEP defines and algorithm that gives authorised users the same level of security they would on a wired network.

WIFI Protected Access (WPA)

• WPA is a Wi-Fi standard that was designed to improve upon the security flaws of WEP. WPA2 is an upgrade and includes all the 802.11 mandatory standards.

• It improves data encryption through the Temporal Key Integrity Protocol (TKIP).

• WPA adds AES a cipher based CCMP encryption for even greater security.

• User authentication, considered poor over WEP through the EAP (Extensible Authentication Protocol). WEP regulates access to the wireless network based on the computers specific MAC address which is relatively easy to sniff or spoof.

• EAP is built on a more secure public key encryption system to ensure that only the authorised network users can access the network.

Wireless Authentication Methods:

Authentication Method Description

Open System This uses null authentication

Shared Key This authentication method verifies the identity of a station by using a WEP key. Both the station and the AP must be configured to use the data encryption and the same WEP key

802.1x and EAP This authentication method authenticates the user and not the station. A RADIUS server is used – Remote Authentication Dial In Server – the user dials in to the server which disconnects the call and will return the call and reconnect.

Bluetooth

• This is not a network service, it is peer-to-peer

• Bluetooth 1.1 is a wireless protocol used to communicate form device to device in a small area up to 10 metres, transfer is approximately 1Mbps.

• Bluetooth 1.2 increases speed to 2.1-3Mbps and the range increases to about 30 metres.

Networking with TCP/IP

Families and Protocols:

• Successful network communications hinges on them sharing a network protocol to perform various functions related to that communication.

• Network protocols are classified into general families that share common features.

Network Protocols:

Network communications between computers is provided by a network protocol – rules by which network operations are conducted.

There are the following Protocols:

• Network and transport layer protocols

• Application – Presentation- and session layer Protocols

Protocol Bindings:

Assigning a protocol to a network interface card (NIC) is referred to as protocol binding. Multiple protocols can be bound to a single NIC. The NIC can use any of the protocols that are bound to it to communicate with other nodes on the network.

Binding order:

A network interface bound with multiple protocols attempts to connect to a receiving node by testing its available protocols, one by one until it finds a protocol that the receiving node answers.

The TCP/IP Protocol:

This is a protocol suite which works at the network and transport layers of the OSI model. Providing the protocol family functions of reliability, connection and routing.

TCP/IP

The transmission Control/Internet protocol (TCP/IP) is a non-proprietary, routable network protocol suit that enables computers to communicate over all types of networks. TCP/IP is the native protocol of the Internet and is required for Internet connectivity.

IPv4 Addresses:

An IPv4 Address is a 32 bit binary number assigned to a computer on a TCP/IP Network. The 32 bit binary IP Address is usually separated by dots into four 8 bit octets.

• Binary = 11010000.01111011.00101101.00010010

• Decimal = 208.123.45.18

Dotted decimal Notation – this is how TCP/IP address is usually displayed!

An IP address is like a mailing address:

Some of the numbers in the IP address identify the network segment on which computer resides, just as a person mailing address uses a street name etc.

Binary and Decimal Conversion:

Binary is a base 2 numbering system in which any bit in the number is either 1 or 0


Standard Speed Frequency Approximate Range

802.11 1-2Mbps 2.4GHz      100 metres

802.11a 54Mbps 5GHZ        20 metres

802.11b 11Mbps 2.4GHz     100 metres

802.11g 54Mbps 2.4GHz     100 metres

802.11n 300Mbps 2.4 or 5MHz 70 metres


Well that is it for now - see you all tomorrow.