OSI Reference Model and Security COMP 423. The Physical Layer Establish and terminate the physical and logical connections to the media Manage the flow.

OSI Reference Model and Security

COMP 423

The Physical Layer

• Establish and terminate the physical and logical connections to the media

• Manage the flow and communication on the media

• Embed the message onto the signal carried across the physical media

Network Media Type Description Comments

Coaxial Cable One of the first LAN media. Channel medium – it can only carry one message in one direction.

Fiber-Optic cable Essentially a tube with an ultra-pure glass or plastic core that carries light waves. The single-mode cable provides data transmission rate of approximately 10 gigabits per second over distances of up to approximately 35 miles.

To send multiple simultaneous signals, networks use a multimode variant. Multimode transmission speeds are up to 100 Mbps for up to 2 miles, up to 1 Gbps for approximately 500 yards, and up to 10 Gbps for up to approximately 1/5 mile (300 yards).

Twisted Pair Wire One of the most dominant cabling types in use today. UTP has no supplemental shielding, and because the twisting only provides minimal protection, the cable has a maximum effective limit of approximately 100 yards.

When installing networks in buildings under construction, it is most beneficial to install networks using physical cable like UTP. UPT is easy to work with, reliable, less subject to interception or eavesdropping, and relatively inexpensive.

Wireless LAN The most common alternative when installing physical cable in existing buildings becomes too difficult and expensive. The standard for wireless networks falls under IEEE 802.11 – Wireless Local Area Networks (WLAN). WANs use one of three architectures – peer-to-peer (P2P), basic service set, or extended service set.

Wireless LANs (also called WLANs, or the brand name Wi-Fi) are thought by many in the IT industry to be inherently insecure. The radio transmissions used for the wireless network interface between computing devices and access point (Aps) can be intercepted by any receiver within range. To prevent this, the networks must use some form of cryptographic security control.

Bluetooth A wireless technology not covered under the 802.11 standard. Is a de facto industry standard for short-range wireless communications between devices.

To secure Bluetooth-enabled devices you must: 1) turn off Bluetooth when you do not intend to use it and 2) refuse incoming communications paring requests unless you know who the requestor is.

Infrared A wireless technique for data connections between personal devices, like personal digital assistans (PDAs) and laptops.

The Infrared Data Association (IrDA) defined several standards for short-range infrared connections (typically less than 1 meter). Older IR LANs mounted central Aps in the ceiling, but these were quickly replaced with 802.11 alternatives.

Data Link Layer• Primary networking support layer• Provides addressing, packetizing, media access control,

error control, and some flow control for the local network.

• In LANs, it handles client-to-client and client-to-server communications

• Divided in two sublayers– Logical Link Control

• Primarily designed to support multiplexing and demultiplexing protocols

– Media Access Control • Designed to manage access to the communications media(which

clients are allowed to transmit and when)

DLL Protocols

– Ethernet (IEEE standard 802.3)• Wired networks

– Wi-Fi (IEEE 802.11)• Wireless networks

Network Layer

• Primary layer for communications between networks. Has three key functions:– Packetizing– Addressing– Routing

Network Layer

• Packetizing – Takes the segments sent from the transport layer

and organizes them into one or more packets for transmission across a network

Network Layer

• Addressing – Uniquely identify a destination across multiple

networks.

Network Layer

• Routing – The process of moving a Network layer packet

across multiple networks.

Transport Layer

• The primary function of the Transport Layer is to provide reliable end-to-end transfer of date between user applications.

• Error control• Flow control

Session Layer

• Responsible for establishing, maintaining, and terminating communications sessions between to systems.

• Regulates whether communications are preformed in:– Simplex mode– Half-duplex mode– Full-duplex mode

Presentation Layer

• Responsible for data translation and encryption functions.

Application Layer

• The user is provided with a number of services, perhaps most aptly called application protocols.– E-mail (SMTP & POP)– World Wide Web (HTTP and HTTPS)– File transfer (FTP and SFTP)

TCP/IP Layers compared to OSI Layers

OSI Layers Included Protocols TCP/IP Layers

Application SNMPTFTPNFSDNSBOOTP

FTPTelnetFingerSMTPPOP

ApplicationPresentation

Session

Transport UDP TCP Host-to-Host Transport

Network IP Internet

Data Link Network Interface CardsNetwork InterfacePhysical Transmission Media