Layered Communication Building Blocks Hardware Layers in LAN

Layered Communication Building Blocks: Hardware Layers in LAN

Multi-layer Network Models The process of transferring a message between sender and receiver is more easily implemented by breaking it down into simpler components. Instead of a single layer, a group of layers are used, dividing up the tasks required for network communications. The best known network model is the OSI models.

The OSI Networking Reference Model OSI= Open Systems Interconnect. Created by the International Standards Organization (ISO) in 1984 as a network standards framework. The model’s seven layers from high to low are: n n n n 7. 6. 5. 4. 3. 2. 1. Application Presentation Session Transport Network Data Link Physical

Application Layers The application layers are the user’s connection to the network and include the application software and other software used to connect the application to the network: n n n 7. Application: provides a set of utilities used by application programs. 6. Presentation: formats data for presentation to the user, provides data interfaces, data compression and translation between different data formats. 5. Session: responsible for initiating, maintaining and terminating each logical session between sender and receiver.

Internetwork Layers The internetwork layers connect applications to the network and as well as determine the best route for sending messages between sender and receiver. n n 4. Transport: deals with end-to-end issues such as segmenting the message for network transport, and maintaining the logical connections between sender and receiver. 3. Network: responsible for making routing decisions.

Hardware Layers The hardware layers move messages from one computer or device to another. n n 2. Data Link: deals with message delineation, error control and network medium access control. 1. Physical: defines how individual bits are formatted to be transmitted through the network.

How the layers fit together in practice

Message Transmission Using Layers Network model layers use protocols, i. e. , sets of rules to define how to communicate at each layer and how to interface with adjacent layers. Generally, outgoing messages travel down all network layers. Before sending a message to the next layer, each layer places it in an envelope of overhead information related to that layer (encapsulation). At the receiving end, messages travels up through the network layers, each layer removing the envelopes added when the message was sent.

Message transmission using layers

Why Standards? Standards provide a fixed way for hardware and/or software systems to communicate. For example, USB enables two pieces of equipment to interface even though they are manufactured by different companies. By allowing hardware and software from different companies to interconnect, standards help promote competition.

Some Major Standards Making Bodies ISO: International Organization for Standardization (http: //www. iso. ch) ITU-T: International Telecommunications Union —Telecom Group (http: //www. itu. int) ANSI: American National Standards Institute (http: //www. ansi. org) IEEE: Institute of Electrical and Electronic Engineers (http: //standards. ieee. org) IETF: Internet Engineering Task Force (http: //www. ietf. org)

Layers & Standards Layer Common Standards 5. Application layer HTTP, HTML (Web) MPEG, H. 323 (audio/video) IMAP, POP (e-mail) 4. Transport layer TCP (Internet) SPX (Novell LANs) 3. Network layer IP (Internet) IPX (Novell LANs) 2. Data link layer Ethernet (LAN) PPP (dial-up via modem) 1. Physical layer RS-232 c cable (LAN) Category 5 twisted pair (LAN) V. 92 (56 kbps modem)

Topology refers to the geometric layout of the network. A logical topology is how the networks conceptually Physical topology refers to how the network is physically connected.

Topology determines type of equipment to purchase and how to manage network When designing a network, you must understand different topologies Consider growth and security requirements Good design grows and adapts as needs change

Standard Topologies Today’s network designs are based on three topologies: n n n Bus consists of series of computers connected along a single cable segment Ring connects computers to form a loop Star connects computers via central connection point

Terminated Bus Network

Cable Break

Ring Network

Star Topology

Ethernet’s two forms, shared and switched Ethernet, use bus and star logical topologies, respectively.

Hub Operation Ethernet Hub Station A 1 -44 -D 5 -1 F-AA-4 C transmits a bit. D 4 -47 -55 -C 4 -B 6 -9 F C 3 -2 D-55 -3 B-A 9 -4 F A 1 -44 -D 5 -1 F-AA-4 C B 2 -CD-13 -5 B-E 4 -65

Hub Operation Ethernet Hub broadcasts the bit out all ports. D 4 -47 -55 -C 4 -B 6 -9 F C 3 -2 D-55 -3 B-A 9 -4 F A 1 -44 -D 5 -1 F-AA-4 C B 2 -CD-13 -5 B-E 4 -65

Switches Networking devices that manage network connections between any pair of star-wired devices on a network Does not broadcast; forwards the message to the intended computer Offer greater bandwidth (not shared)

Switch Operation Ethernet Switch Station A 1 -44 -D 5 -1 F-AA-4 C transmits a bit. D 4 -47 -55 -C 4 -B 6 -9 F On Switch Port 13 A 1 -44 -D 5 -1 F-AA-4 C On Switch Port 10 B 2 -CD-13 -5 B-E 4 -65 On Switch Port 11 C 3 -2 D-55 -3 B-A 9 -4 F On Switch Port 13

Switch Operation Ethernet Switch A switch sends a frame out a single port— the one to the receiver D 4 -47 -55 -C 4 -B 6 -9 F On Switch Port 13 A 1 -44 -D 5 -1 F-AA-4 C On Switch Port 10 B 2 -CD-13 -5 B-E 4 -65 On Switch Port 11 C 3 -2 D-55 -3 B-A 9 -4 F On Switch Port 13

Switch Operation with Multiple Simultaneous Conversations Ethernet Switch Multiple simultaneous conversations are possible D 4 -47 -55 -C 4 -B 6 -9 F On Switch Port 13 A 1 -44 -D 5 -1 F-AA-4 C On Switch Port 10 B 2 -CD-13 -5 B-E 4 -65 On Switch Port 11 C 3 -2 D-55 -3 B-A 9 -4 F On Switch Port 13

Star Topology Star (Modern Ethernet) Switch Only one possible path between two stations Extended Star or Hierarchy (Modern Ethernet) Root Switch

Mesh Topology A C Multiple alternative paths between two stations Path ABD B D Path ACD

Network Interface Cards Network interface cards, also called network adapters NICs are part of both the physical and data link layer and include a unique data link layer address (MAC address), placed in them by their manufacturer. Before sending data onto the network, the network card also organizes data into frames and then sends them out on the network. Notebook computers often use NICs that are plugged into the PCMCIA port.

NIC Allows the Computer and the Network Cable to Communicate Note: Gigabit Ethernet uses parallel transmission

Ethernet NIC

Cables Each computer is physically connected to the network using a cable. The cables used on Ethernet LANs are either twisted-pair or optical fiber cables. Data can flow through cables in one of three modes: n One way only (simplex) n Both ways, one way at a time (half-duplex) n Both ways at the same time (full-duplex)

Simplex, half-duplex, and full-duplex transmissions

General Cable Characteristics Bandwidth rating (Mbps) Maximum segment length Interference susceptibility: EMI (electromagnetic interference), RFI (radio frequency interference) Connection hardware Cable grade: cabling requirements for building and fire codes Bend radius Material costs Installation costs

Twisted-Pair Cable TP is two or more pairs of insulated copper wires twisted around each other n n n Improves resistance to interference Limits crosstalk (EMI generated by wire pairs) The more twists, the better Two primary types of TP cable n n Unshielded twisted-pair (UTP) Shielded twisted pair (STP)

STP and UTP Cable

Ethernet Standards Standardization n Institute of Electrical and Electronics Engineering (IEEE) w 802 LAN/MAN Standards Committee (802 Committee) creates LAN standards n 802. 3 Working Group creates Ethernet standards n So Ethernet standards are also known as 802. 3 standards.

Ethernet Standards Physical Layer Ethernet Standards Using UTP n 802. 3 10 Base-T w 10 Mbps n 802. 3 100 Base-TX w 100 Mbps w 10/100 operation thanks to auto-sensing n 802. 3 1000 Base-T w Gigabit Ethernet

Purchasing and Installing UTP Wiring Quality Categories n n n Governed by the TIA/EIA-568 standard Categories 3, 4, 5, 5 e (enhanced), and 6 w Higher numbers indicate better quality CAT 5 e is recommended for new buildings CAT 5—for 100 Base-TX CAT 5 e—for 1000 Base-TX (Gigabit Ethernet) CAT 6—for 10 Gbs networks

Fiber-Optic Cable Uses pulses of light rather than electrical signals Immune to interference; very secure; eliminates electronic eavesdropping Excellent for high-bandwidth, high-speed, long-distance data transmissions Slender cylinder of glass fiber called core surrounded by cladding and outer sheath

Fiber-Optic Cable

Fiber-Optic Cable Each core passes signals in only one direction Most fiber-optic cable has two strands in separate cladding n May be enclosed within single sheath or jacket or may be separate cables More difficult to install and more expensive than copper media

Fiber-Optic Cables Two primary types: n Single-mode cables: cost more; span longer n distances; work with laser-based emitters Multimode cables: cost less; span shorter distances; work with light-emitting diodes (LEDs) Used for network backbone connections and with long-haul communications carrying large amounts of voice and data traffic

Full-Duplex Optical Fiber Cord Switch Fiber Cord Router A pair of fibers is needed for full-duplex (simultaneous 2 -way) transmission. Each fiber carries a signal in only one direction.

Optical Fiber Cabling Two fiber cords for full-duplex (twoway) transmission ST Connectors (Popular) SC Connectors (Recommended)

Summary Layered communication: OSI model LAN topologies Network interface cards Cable characteristics Ethernet standard: 802. 3 Twisted pair Fiber optic