Network Access and Transmission Methods Chapter 10

Objectives In this chapter, you will learn to: Recognize simple and complex physical topologies used in data networks Describe Ethernet and the CSMA/CD network access method Understand the different types of Ethernet access methods Describe the techniques used in the Token Ring, ATM, and FDDI network access methods Identify the main characteristics of network transmission methods, such as X.25, Frame Relay, T-Carriers, ISDN, DSL, cable, and SONET

Bus

Ring

Star

Hybrid Physical Topologies

Mesh Topologies

Network Access Methods

Ethernet A network access method originally developed by Xerox in the 1970s and later improved by Xerox, Digital Equipment Corporation (DEC), and Intel. Can run on a variety of network media, including both wireline and wireless channels Uses packet switching

Ethernet Baseband - a transmission form in which digital signals are sent through direct current (DC) pulses applied to the wire. Multiple Access - refers to the fact that Ethernet nodes can be connected to a network and can monitor and issue traffic. CSMA/CD - Rules for communication used by shared Ethernet networks.

Ethernet

Ethernet Frames - each frame contains a 14-byte header and a 4-byte frame check sequence (FCS) field. 10BaseT - a physical layer standard for networks that use baseband transmission and twisted pair media and can achieve 10 Mbps throughput.

Ethernet

10BaseF - a physical layer standard for networks that use baseband transmission. 100BaseT - uses baseband transmission and multimode fiber cabling and can achieve 100 Mbps throughput. 100BaseF - specifies a network capable of 100 Mbps throughput that uses baseband transmission and fiber optic cabling. Switched Ethernet - enables multiple nodes to simultaneously transmit and receive data over different network segments.

Ethernet

Token Ring Transmits at either 4, 16, or 100 Mbps over STP or UTP. Uses the token-passing routine and a star- ring hybrid physical topology. High Speed Token Ring (HSTR) - can use either twisted pair or fiber cable as its transmission medium.

FDDI A network access method whose standard was originally specified by ANSI in the mid-1980s and later refined by ISO. Uses a double ring of multimode or single mode fiber to transmit data speeds of up to 100 Mbps.

FDDI

ATM Asynchronous Transfer Mode (ATM) - a standard that describes both a network access method and a multiplexing technique. Cells - consist of 48 bytes of data plus a five- byte header for a 53-byte packet. Virtual circuits - logical connections between network nodes.

ATM Quality of Service (QoS) - a standard that specifies that data will be delivered within a certain time period after its transmission. Compatibility - ATM cells can support multiple types of higher-layer protocols, including TCP/IP and IPX/SPX.

Network Transmission Methods X.25 and Frame Relay - a set of protocols designed for long-distance data transmission and standardized by the ITU in the mid-1970s. Frame Relay - an updated, digital version of X.25 that also relies on packet switching. It does not guarantee the delivery of data.

Network Transmission Methods

ISDN An international standard, established by the ITU for transmitting data over digital lines. All ISDN connections are based on two types of channels: B Channels: employ circuit-switching techniques to carry voice, video and other types of data over the ISDN connection. D Channels: employ packet switching techniques to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals.

Basic Rate Interface

Primary Rate Interface

T-Carrier Services The general name for a group of transmission methods that includes T1s, fractional T1s, and T3s. T-carriers are examples of dedicated leased lines. They are also private lines.

Types of T-Carriers Signal level - the T-carrier’s Physical layer electrical signaling characteristics as defined by ANSI standards in the early 1980s. T1 Circuit - can carry the equivalent of 672 voice or data channels, giving a maximum data throughput of Mbps.

Types of T-Carriers

T-Carrier Connectivity Transmission Media - T1 technology can use unshielded or shielded twisted-pair copper wiring. CSU/DSU (Channel Service Unit/Data Service Unit) - the connection point for a T- carrier line at the customer’s site. CSU: provides termination monitoring. DSU: converts the digital signals used by bridges, routers and multiplexers into the digital signal sent via the cabling.

T-Carrier Connectivity

Multiplexers

DACS

DSL Uses advanced data modulation techniques to achieve extraordinary throughput over regular phone lines. Downstream - data traveling from the telecommunications carrier’s end office. Upstream - data traveling from the customer to the carrier’s end office. Types of DSL Asymmetrical: downstream throughput is usually much higher than upstream throughput. Symmetrical - provides equal capacity for data traveling both upstream and downstream.

DSL

DSL Connectivity

Cable Modem Technology

SONET and SDH

Summary Three simple physical topologies exist: bus, star, and ring. Ethernet is a network access method that uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to determine how multiple nodes share a single channel. Token Ring is a network access method originally designed by IBM and now specified by IEEE in its project. Digital subscriber line (DSL) is a transmission method that uses advanced data modulation techniques to achieve extraordinary throughput over regular phone lines. It comes in several different varieties.