Virtual Circuit Networks: Frame Relay And ATM UNIT 5 Chapter 18 Forouzan

ATM(Asynchronous Transfer Mode) ( pg.nu.523 F) A streamlined packet transfer interface similarities to packet switching transfers data in discrete chunks supports multiple logical connections over a single physical interface ATM uses fixed sized packets called cells. It provides with minimal error and flow control Data rates of 25.6Mbps to Mbps Speeds on ATM networks can reach 10 Gbps.Gbps

Application Area

Pg.Nu.526 F

TP,VPs and VCs Virtual connections TP: Transmission path – link between two switches VP: Virtual Path – Contains several VCs VC: Virtual Circuit

ATM Cell( pg.nu.528 F )

ATM Layers

ATM Layer (pg.nu. 531)

ATM Headers (pg.nu.531)

ATM Cell Header Format ATM Cell Header—UNI Format ATM Cell Header—NNI Format

X.25 Packet Switching WAN X.25 Packet Switching WAN

X.25 Was the first popular packet switched network Allowed for the setup of data connections at speeds between 300bps to about 56kbps. Uses the “Virtual Circuit” concept. Connection oriented packet switch. Still used for low bandwidth transactions credit cards / Point-of-Sale (POS) transactions.

Frame Layer and Packet Layer Domains

X.25 Devices Data terminal equipment (DTE) terminating equipment for a specific network typically are located on the premises of a customer Examples: terminals, personal computers, routers, and bridges Data circuit-terminating equipment (DCE) carrier-owned internetworking devices to provide clocking and switching services in a network actually transmit data through the WAN

Key points on X.25 Was developed as a packet switching protocol. Standard includes Layer 1,2,3 Limited in bandwidth Not optimized for high quality links. Not optimized for TCP / IP transport

Frame Relay(pg. no 517)

What is Frame Relay? High-performance WAN protocol Operates at the physical and data link layers Originally designed for use across ISDN interfaces.(Integrated Service Digital n/w) An example of packet-switched technology described as a streamlined version of X.25

Frame Relay versus Pure Mesh T-Line Network

Features Of Frame Relay Higher Speed: Operates at a higher speed 1.544Mbps & recently Mbps. Backbone Network: Operates in just physical & data link layers. Bursty data: frame relay allows bursty data. Larger frame size: It allows frame size of 9000 bytes, which accommodate all LAN frame sizes. Less expensive No flow control or error control.

Frame Relay Network

Frame Relay Layers

Comparing Layers in Frame Relay and X.25

Frame Relay Frame

BECN(Backward Explicit Congestion Notification) BECN assumes the source can reduce congestion by slowing down the transmission of data.

FECN(Forward Explicit Congestion Notification) FECN notifies the receiver that congestion is occurring. It can then be more patient and not request so much data.

Four Cases of Congestion

Integrated Services Digital Network (ISDN)

ISDN ISDN in concept is the integration of both analog or voice data together with digital data over the same network. Abbreviation of integrated services digital network, an international communication standard for sending voice, video and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second).

ISDN Another alternative to using analog telephones lines to establish a connection is ISDN. Speed is one advantage ISDN has over telephone line connections. ISDN network is a switched digital network consisting of ISDN Switches. Each node in the network is identified by hierarchical ISDN address which is of 15 digits. ISDN user accesses network through a set of standard interfaces provided by ISDN User Interfaces.

ISDN Services Bearer services – provide the means to transfer information (voice, data, video) between users without the network manipulating the content of that information. Belongs to the first 3 layers of the OSI model. Teleservices – the network may change or process the contents of the data. correspond to layers 4-7 of the OSI model rely on the facilities of bearer services Supplementary services – provide additional functionality to the bearer services and teleservices.

ISDN Services

Analog and Digital Services over the Telephone Network 3 types of customers – the first one is the most prominent

Integrated Digital Network (IDN) A combination of networks available for different purposes. Access to these networks is by digital pipes digital pipes – time-multiplexed channels sharing very-high-speed paths.

Integrated Services Digital Network (ISDN) ISDN incorporates all communication connections in a home or building into a single interface With ISDN all customer services will become digital rather than analog.

Subscriber Access to the ISDN Subscriber loops – organized into multiple channels of different sizes B channel basic user channel Can carry any type of digital info in Full-duplex mode Carries transmissions end-to-end D channel Primary function is to carry control signaling for the B channel Acts like an operator between the user and the network at the network layer ChannelData Rates (Kbps) Bearer (B)64 Data (D)16, 64 Hybrid (H)384 (H0), 1536(H11), 1920(H12) H Channels - For high data rate applications such as video, teleconferencing and so on

Two Types of Digital Subscriber Loops Basic rate interface (BRI)(Applicable for home users) Primary rate interface (PRI)(Applicable for corporate customers.) Each type is suited to a different level of customer needs Both include one D channel and some number of either B or H channels

Basic Rate Interface (BRI) Designed to meet the needs of residential and small-office customers The same twisted pair local loop that delivers analog transmission can be used to handle digital transmission

Primary Rate Interface (PRI) PRI was designed to be compatible with existing T-1 lines In Europe, the PRI includes 30 B channels and 2 D channels = capacity of Mbps – the capacity of E-1 line

Functional Grouping NT – network termination TE – terminal equipment NT1 Controls the physical & electrical termination of the ISDN at the user’s premises Connects the user’s internal system to the digital subscriber loop Organizes the data stream from a connected subscriber into frames that can be sent over the digital pipe Translates the frames received from the network into a format usable by the subscriber’s devices. Similar to the physical layer of OSI model Defines the function of each type of equipment

NT2 ( ex. Digital PBX, LAN) Performs functions at the physical (multiplexing), data link (flow control), network layers (packetizing) of the OSI model Provides intermediate signal processing between the data-generating devices and an NT1 Used primarily to interface between a multiuser system and an NT1 in a PRI.

TE1 – same thing as DTE Any device that supports the ISDN standards Ex. Digital telephones,integrated voice/data terminals TE2 Any non-ISDN device Ex. Terminal workstation, regular telephone Can be used with the help of Terminal Adapter (TA)

Reference Points Label used to identify individual interfaces between two elements of an ISDN installation Defines the functions of the connections

ISDN Layers

ISDN Layers for B and D Channels