Networking Review

CIS 278 Spring 2004

Learning in CIS

• "Education is not the filling of a pail, but the lighting of a fire."

• William Butler Yeats

OSI Model

OSI Model

• The Application layer is where the tools are located to support a class of software we are familiar with. An example would be SMTP, an application used by most email software like Outlook and Netscape Mail to carry email from source to destination.

OSI Model

• The Presentation layer is the encoding layer. It is responsible for providing the data in the proper format. For example, text can be presented in many formats, including ASCII and ANSI. A picture can be displayed using either JPEG or PICT. It’s the same information, only the encoding technique is different.

OSI Model

• The Session layer establishes the dialogue between applications. In a Telnet session, it defines the login procedure and maintains that conversation until the parties log out or disconnect, then it handles the disconnect process.

OSI Model

• The Transport layer handles the delivery of complete messages from one network to another. It keeps all message packets in order, manages the flow of the data, and offers a level of error detection and correction.

OSI Model

• The Network layer delivers packets from one network to another. It deals with routing and addressing of packets. This is the Internetworking layer, and is associated with a router.

OSI Model

• The Data Link layer deals with frames within a network. It doesn’t understand going from one network to another. It provides a local form of addressing (like MAC addresses), and offers another layer of error detection and correction that’s used within a network. This layer is associated with Bridges and Switches

OSI Model• The Physical layer looks at bits. It address

issues like the number of pins on a connector, the signal type (eg control or data), encoding scheme (eg Manchester Encoding), and signal level (eg 5 volts or 12 volts). It has nothing to do with addressing. To define a network type like Ethernet requires both the Physical and Data Link layers. This layer is associated with a Repeater.

TCP/IP Modelhttp://www.unm.edu/~network/presentations/course/chap2/sld018.htm

Comparison of OSI and TCP/IPhttp://dast.nlanr.net/Training/DCWJuly99/kai_tcpip/sld005.htm

Comparison of OSI and TCP/IPhttp://www.microsoft.com/windows2000/en/server/help/sag_TCPIP_ovr_model.htm

Encapsulation

Network Hardware

• Networks have evolved over time, but today we chiefly use Hubs to interconnect our LAN devices using a star topology, providing one port per device. These hubs are usually either Ethernet Repeaters or Switches.

Network Hardware

Hub

ServerTower PCTower PCTower PC

Network Hardware

• Repeaters keep devices all on a single collision domain. Everything connected to the same repeater is on the same network, regardless of which port it is connected to.

• Switches provide a separate collision domain for each port, but provide a single broadcast domain, all within the same network.

Network Hardware

• Routers are placed at the end of a network to provide access to another network. They are Internetworking devices.

Ethernet

• There are lots of different LAN types, including ARCnet, Token Ring, FDDI, and ATM, However, in this class we will chiefly work with Ethernet.

Ethernet

• An Ethernet definition from Webopedia:• A local-area network (LAN) architecture

developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard... Ethernet uses … CSMA/CD …. It is one of the most widely implemented LAN standards.

Ethernet

• Webopedia definition, continued:

• A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second.

• (10Gbps is also now available)

Ethernet• The original Ethernet was based on a single

coaxial cable to which all devices were attached. These days we mostly use a hub, UTP cable and a star topology.

Ethernet

ServerTower PCTower PCTower PC

Ethernet

• Frames come in a variety of formats, including Ethernet_II, 802.3, 802.2 and SNAP. Each differs slightly from the next and they are all more-or-less equivalent. The important part is that all devices on a network must use the same frame format.

Ethernet

• Frame addressing uses the 48 bit MAC address (Media Access Control). The address is typically displayed in hexadecimal, with six two digit fields of 8 bits each separated by colons. E.g. 00:80:c7:a8:f0:3d. A broadcast frame is addressed with all 1s. In hex it looks like this: ff:ff:ff:ff:ff:ff.

Ethernet

• Ethernet at the physical layer is identified with a standardized format that often indicates data rate, signaling type, and the maximum length of cable in hundreds of meters. Examples would be 10base5 and 100baseT. These specifications are often driven by the cable selection.

Ethernet

• Ethernet cable comes in a variety of forms, including wireless, several coaxial cables, and several fiber optic cables. Each cable type has a choice of connector type. The format specified defines what kind of cable and connector you will be using.

Ethernet

• Ethernet cabling assumes serial communication. That means one bit at a time. When Ethernet uses coaxial cable there is a single data path, so communication is half duplex. Twisted pair or fiber optic cable both use separate transmit and receive paths, so there is a potential for full duplex communication.

Ethernet

• Ethernet twisted pair cabling uses balanced signaling, so there is a transmit pair and receive pair.

• On a UTP cable used for Category 3, 4, 5, etc. an RJ45 connector with 8 pins is used. Only 4 wires carry the signal.

• Ethernet uses straight through cables.

Ethernet

• Since Ethernet uses straight through cables (pin 1 on one end connects to pin 1 on the other end, 2 to 2, 3 to 3, etc.), the idea of DTE and DCE is used.

• Individual signals are paired in such a way that they will carry the signal best.

• A standard straight cable connects from a host (DTE) to a hub (DCE).

Ethernet

• You can connect directly from a host directly to another host for a 2 node Ethernet network.

• You can connect directly from a hub to another hub in order to enlarge your network.

• In these cases, a crossover cable must be used.

Ethernet

• A crossover cable is used when a DTE talks directly to a DTE, or DCE to a DCE.

• To build this cable, take the transmit pair from each end of a cable and connect them to the receive pins on the other end of the cable.

• Hubs often have a crossover function built in.

EthernetCompliments of Charles Spurgeon

Ethernet

• A rollover, or rolled cable is used by Cisco as a terminal cable. It is constructed by crossing all signals; pin 1 to pin 8, pin 2 to pin 7, etc. Cisco assumes you have an RJ45 jack on your PC as a serial port. However most PCs use a 9 pin connector for serial communications, so an RJ45 to 9 pin adapter must also be used.

EthernetCompliments of Cables Online.com

Cisco Product Hierarchy

• Cisco uses the concept of Core Layer, Distribution Layer, and Access Layer to identify the target use for its products. They are Cisco terms and although they are not standardized the concept is valid. Suffice it to say that some places in your network will experience higher traffic rates than other places, so you buy appropriately sized hardware.

Ethernet

• Ethernet uses Differential Manchester Encoding as its signaling method.

• This technique ensures synchronization, but it experiences more transitions than some other signaling techniques, thus limiting the maximum data rate.

• The bit is identified by the presence or absence of a transition at the beginning of the bit time.

EthernetData Communications & Computer Networks, by Curt White

Internetworking

• Connecting one network to another typically involves a link from the telephone network.

• These digital telephone lines use twisted pair cable and run at a multiple of 64 Kbps

• They are called T carrier services. A T-1 line provides a 1.544 Mbps point-to-point connection.

Internetworking

• T-carrier services are charged based on distance and data rate.

• Delivery is typically copper, using an RJ48 connector (which has the same physical configuration as an RJ45 connector).

• These are four wire services rather than the analog phone line which uses two wires.

Internetworking

• ISDN (a switched service) and DSL (a similar, but non-switched service) are also used to provide connectivity between nodes.

Internetworking

• A digital line might instead terminate at an intermediary WAN to carry traffic to a destination.

• Some WAN technology examples would be Frame Relay, X.25, and the Internet.

Internetworking

• MANs may use SMDS (Switched Multimegabit Data Service) for high speed network connections over short distances within range of these local networks. They are typically not accessed via the telephone company.

Internetworking

• To access T-services we need:

• a router to provide addressing and layer 3 services

• A data conversion device like a CSU/DSU to convert the data from a LAN format to a format compatible with the telephone company.

Tools

• For next week, look for these tools:• T-Stripper http://www.idealindustries.com/ht/WireStrippers.nsf

• Punch tool http://www.action-electronics.com/paladin.htm

• RJ45 crimper http://www.9thtee.com/networking.htm

• Screwdriver• Wire cutters http://www.beadshop.com/wirecutter.html