Chapter 12: Wide Area Networks. Business Data Communications, 4e. Wide Area Networking Issues. Trend towards distributed processing architectures to support applications and organizational needs. Expansion of wide area networking technologies and services available to meet those needs.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Chapter 12:Wide Area Networks Business Data Communications, 4e
Wide Area Networking Issues • Trend towards distributed processing architectures to support applications and organizational needs. • Expansion of wide area networking technologies and services available to meet those needs.
WAN Alternatives SMDS: Switched Mulitmegabit Data Service
Frame Relay Characteristics • Designed to eliminate excessive X.25 overhead • Control signaling takes place on a separate logical connection (nodes don’t need state tables for each call) • Multiplexing/switching take place at layer 2, eliminating a layer of processing • No hop-by-hop flow/error control
ATM - Asynchronous Transfer Mode • Also known as cell relay • Faster than X.25, more streamlined than frame relay • Supports data rates several orders of magnitude greater than frame relay • Data on logical connection is organized into fixed-size packets, called cells. • No link-by-link error control or flow control.
Virtual Channels & Virtual Paths • Logical connections in ATM are virtual channels • analogous to a virtual circuit in X.25 or a frame relay logical connection • used for connections between two end users, user-network exchange (control signaling), and network-network exchange (network management and routing) • A virtual path is a bundle of virtual channels that have the same endpoints.
Advantages of Virtual Paths • Simplified network architecture • Increased network performance and reliability • Reduced processing and short connection setup time • Enhanced network services
Virtual-Path/Virtual-Channel Characteristics • Quality of service • Cell loss ratio, Cell delay variation • Switched and semi-permanent virtual-channel connections • Cell sequence integrity • Traffic parameter negotiation and usage monitoring - average rate, peak rate, burstiness, peak duration
ATM Cell Format UNI NNI
ATM Cell Header • GFC (Generic Flow Control): 4 bits • Control of cell flow at local user-network interface • Virtual Path Identifier (VPI) • 8 bits at UNI, 12 bits at NNI • Virtual Channel Identifier (VCI) : 16 bits • VCI functions much as a service access point. • Payload Type (PT) : 3 bits • Type of information • Cell Loss Priority (CLP): 1 bit • 0: Relative high priority • Header Error Control (HEC): 8 bits • To correct single-bit errors And to detect double-bit errors
ATM Bit Rate Services • Constant bit rate (CBR) • Fixed data rate • Variable bit rate (VBR) • Sustained rate for normal use • Faster burst rate at peak periods • Available bit rate (ABR) • Guaranteed minimum rate • Unspecified bit rate (UBR) • Best-effort service Leased line Voice/video On-line sessions E-mail