UNIT-V SPECIAL & HIGH SPEED NETWORKS & NETWORK DEVICES:

FDDI : access method , addressing, electrical specification, frame format, comparison of FDDI-I & FDDI-II DQDB & WAN implementation. × .25 networks its features. Frame Relay: operation, congestion control & frame format. SONET / SDH : layers , frame & application. Internet & related software’s NETSCAPE & MOSAIC . Networking devices: Repeaters, Bridge Routers & Gateways.

FDDI : access method , addressing, electrical specification: Basic principle- • TOKEN RING NETWORK LIKE IEEE 802.5 • TOKEN: A SPECIAL SEQUENCE OF BITS • TOKEN CIRCULATES AROUND THE RING • A STATION REMOVES THE TOKEN FROM RING BEFORE TRANSMISSION • AFTER TRANSMISSION, THE STATION RETURNS THE TOKEN TO THE RING • COLLISIONS ARE PREVENTED AS THERE IS ONLY ONE TOKEN IN THE RING

The American National Standards Institute (ANSI) developed the Fiber Distributed Data Interface (FDDI)

standard in the mid-1980s to meet the growing need for a reliable and fast networking system to accommodate

distributed applications. FDDI uses a ring network design, but, unlike the traditional 802.5 standard, FDDI uses

a dual ring technology for fault tolerance. Because of the dual ring design, FDDI is not susceptible to a single

cable failure like the regular 802.5 IEEE standard. Figure 1.8 shows an FDDI network with a dual ring

configuration.

Figure 1.8. FDDI network.

As with any of the other standards, FDDI has specific characteristics:

Speed FDDI transmits data at 100Mbps and higher.

Topology FDDI uses a dual ring topology for fault-tolerant reasons.

Media FDDI uses fiber-optic cable that enables data transmissions that exceed two kilometers.

Additionally, it is possible to use FDDI protocols over copper wire known as the Copper Distributed

Data Interface (CDDI).

Access method Similar to 802.5, FDDI uses a token-passing access method.

Table 1.7 summarizes each of the wired standards discussed in the previous sections.

Table 1.7. IEEE 802 Network Standards

Standard Speed

Physical

Topology Logical Topology Media Access Method

802.3 10Mbps Bus and Star Coaxial and twisted

pair

CSMA/CD

802.3u 100Mbps (Fast

Ethernet)

Star Bus Twisted pair CSMA/CD

802.3z 1000Mbps Star Bus Twisted pair CSMA/CD

802.3ae 10-Gigabit Backbone

connections

N/A Fiber/Not

Required

802.5 4Mbps and

16Mbps

Star Ring Twisted pair Token passing

FDDI 100Mbps Dual ring Ring Fiber-optic Twisted

pair (CDDI).

Token passing

frame format

The following descriptions summarize the FDDI data frame and token fields illustrated in Figure 9.

Preamble---A unique sequence that prepares each station for an upcoming frame.

Start Delimiter---Indicates the beginning of a frame by employing a signaling pattern that differentiates it from

the rest of the frame.

Frame Control---Indicates the size of the address fields and whether the frame contains asynchronous or

synchronous data, among other control information.

Destination Address---Contains a unicast (singular), multicast (group), or broadcast (every station) address. As

with Ethernet and Token Ring addresses, FDDI destination addresses are 6 bytes long.

Source Address---Identifies the single station that sent the frame. As with Ethernet and Token Ring addresses,

FDDI source addresses are 6 bytes long.

Data---Contains either information destined for an upper-layer protocol or control information.

Frame Check Sequence (FCS)---Filed by the source station with a calculated cyclic redundancy check value

dependent on frame contents (as with Token Ring and Ethernet). The destination address recalculates the value

to determine whether the frame was damaged in transit. If so, the frame is discarded.

End Delimiter---Contains unique symbols, which cannot be data symbols, that indicate the end of the frame.

Frame Status---Allows the source station to determine whether an error occurred and whether the frame was

recognized and copied by a receiving station.

comparison of FDDI-I & FDDI-II . 1. FDDI-I standard is designed to need to send real-time video or other information that cannot tolerate delay in

the network design. FDDI-Ⅱ require all nodes in the Internet FDDI-Ⅱ use FDDI-Ⅱ, otherwise it becomes FDDI. Now FDDI workstation must be connected to their online.

FDDI-Ⅱ using frequency division multiplexing technology to guarantee multimedia communication frequency band into a dedicated transmission lines.

2. Fiber Distributed Data Interface (FDDI) provides a 100 Mbit/s optical standard for data transmission in a local

area network that can extend in range up to 200 kilometers (120 mi). Although FDDI logical topology is a ring-based token network, it does not use the IEEE 802.5 token ring protocol as its basis; instead, its protocol is derived from the IEEE 802.4 token bus timed token protocol. In addition to covering large geographical areas, FDDI local area networks can support thousands of users. As a standard underlying medium it uses optical fiber, although it can use copper cable, in which case it may be referred to as CDDI (Copper Distributed Data Interface). FDDI offers both a Dual-Attached Station (DAS), counter-rotating token ring topology and a Single-Attached Station (SAS), token bus passing ring topology.It is also a double ring transmitting in two directions, so transmission is possible if ring is broken.

FDDI-II is a more recent development of FDDI that has added support for circuit-switched services

thereby enabling FDDI-II to carry both voice and video signals as well. This means that it is admirably

suited to large scale ISP Internet backbone implementation scenarios as it provides for scalability,

coverage, geographical spanning (particularly now that modern fiber-optic cabling has overcome signal

attenuation and regeneration issues), fault tolerance (the redundant secondary ring), speed, bandwidth

(multi-mode fiber-optics), cost effectiveness, improved security (particularly in comparison with copper

and wireless)

DQDB & WAN implementation.

In telecommunication, a distributed-queue dual-bus network (DQDB) is a distributed multi-access network that (a) supports integrated communications using a dual bus and distributed queuing, (b) provides access to local or metropolitan area networks, and (c) supports connectionless data transfer, connection-oriented data transfer, and isochronous communications, such as voice communications. IEEE 802.6 is an example of a network providing DQDB access methods.

• IEEE 802.3 to 802.5 protocols are only suited for “small” LANs. They cannot be used for very large but non-wide area networks. IEEE 802.6 DQDB is designed for MANs It can cover an entire city, up to 160 km at a rate of 44.736 Mbps – Basic rule: if you want to send something to one of your right-hand neighbours, use upper busA; otherwise, lower bus B – Direction of flow on a bus points to downstream. Fixed-size 53-byte cells with 44-byte payload are used, similar to ATM – Stream of cells flows down on a bus. Each cell has a busy (B) bit and request (R) bit. If a cell is occupied, its B bit is 1. You make a request by setting a cell’s R bit (if it is zero) to 1 • Unlike 802.3 to 802.5 where a user transmits at first chance, DQDB MAC is non greedy • Users queue up in the order they became ready to send and transmit in FIFO order • This is achieved without a central queue control, hence called distributed queue Data link layer consists of three sublayers – Security sublayer manages encryption,decryption, and key management, crucial for privacy and security – Service-specific convergence replaceslogical link control, providing seamlessly interface for network layer that may haveboth datagram protocols and ATM

× .25 networks its features.- X.25 is an ITU-T standard protocol suite for packet switched wide area network (WAN) communication. An X.25 WAN consists of packet-switching exchange (PSE) nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links. X.25 is a family of protocols that was popular during the 1980s with telecommunications companies and in financial transaction systems such as automated teller machines. X.25 was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts and finalized in a publication known as The Orange Book in 1976. While X.25 has been, to a large extent, replaced by less complex protocols, especially the Internet protocol (IP), the service is still used and available in niche and legacy applications. Architecture The general concept of X.25 was to create a universal and global packet-switched network. Much of the X.25 system is a description of the rigorous error correction needed to achieve this, as well as more efficient sharing of capital-intensive physical resources. The X.25 specification defines only the interface between a subscriber (DTE) and an X.25 network (DCE). X.75, a very similar protocol to X.25, defines the interface between two X.25 networks to allow connections to traverse two or more networks. X.25 details The network may allow the selection of the maximal length in range 16 to 4096 octets (2n values only) per virtual circuit by negotiation as part of the call setup procedure. The maximal length may be different at the two ends of the virtual circuit.

Data terminal equipment constructs control packets which are encapsulated into data packets. The packets are sent to the data circuit-terminating equipment, using LAPB Protocol. Data circuit-terminating equipment strips the layer-2 headers in order to encapsulate packets to the internal network protocol.

Features and Benefits

Full STREAMS compatibility for implementation in a native UNIX System V Release 3 or 4 kernel Portable Streams Environment (PSE) for platforms which do not support a native Streams environment Full compatibility with UIT-T and ISO standards, including UIT-T 1993 X.25 Included Sub-Network Dependent Convergence Functions (SNDCF) module allowing connection less network

Layers (IP, CLNP, ...) to access X.25 services Included Asynchronous HDLC module for operation over asynchronous lines Full dynamic run-time configuration per interface Extensive local network management functions (configuration, line monitoring, statistics, and alarms handling) Comprehensive porting and testing Toolkit

Technical Specifications

Sub-Network Dependent Convergence Functions (SNDCF)

Connection Less DLPI user interface Full compliance with all encapsulation modes defined in RFC 1356 Address mapping through local mapping tables or DDN algorithm. Can be disabled for direct addressing mode Full support for Idle and Holding timers

X.25 Packet Level

Full support for UIT-T 1980, 1984, 1988, and 1993 standards Full support for ISO 8208 standard, including all additional timers

Up to 4096 PVCs and or SVCs per physical line DTE or DCE (point to point only) modes of operation Modulo 8 or modulo 128 numbering Automatic run time parameters negotiation through Registration packets Full support for Reject packets and packet retransmission Extended address format support Extensive listening facilities to wait for incoming calls with flexible listening criteria on called and calling addresses

and user data Extensive local network management functions (configuration, line monitoring, statistics, billing records

generation, and alarms handling)

X.25 Frame Level

Full support for UIT-T 1980, 1984, 1988, and 1993 standards Full support for ISO 7776 standard DTE or DCE modes of operation with optional automatic selection at run time Modulo 8 or modulo 128 numbering Support for LAP-B and LAP-D protocols and frame formats Extensive local network management functions (configuration, line monitoring, statistics, and alarms handling)

Asynchronous HDLC (AHD)

Software HDLC framing and transparency for operations over an asynchronous line Compliant with RFC 1662 and OSI 3309, Addendum 2, 1992 standards

Serial Driver

Synchronous HDLC mode of operation Asynchronous mode of operation for framing oriented Upper Layers (SLIP, AHD, or PPP) UIT-T V.25bis dial up support Flexible junction signal monitoring functions

Frame Relay: operation, congestion control & frame format.

Frame Relay was originally designed for use on Integrated Services Digital

Network (ISDN) Usually considered a replacement for X.25 using more advanced digital and fiber

optic connections Does not perform error correction at intermediate nodes making it faster than

X.25 When an error is detected (FCS) the frame is discarded and correction is

left up to higher layer protocols Original standard proposed in 1984 but widespread acceptance did not occur

until the late 1980’s Service Description Standard (ITU-T I.233)

Overall service description and specifications, Connection Management

Core Aspects (ITU-T Q.922) Frame Format, Field Functions, Congestion Control

Signaling (ITU-T Q.933) Establishing and Releasing switched connections and status of

permanent connections SONET / SDH : layers , frame & application.

Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized

multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or highly coherent

light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical

interface. The method was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for

transporting large amounts of telephone calls and data traffic over the same fiber without synchronization

problems. SONET generic criteria are detailed in Telcordia Technologies Generic Requirements document GR-

253-CORE. Generic criteria applicable to SONET and other transmission systems (e.g., asynchronous fiber

optic systems or digital radio systems) are found in Telcordia GR-499-CORE.

SONET and SDH, which are essentially the same, were originally designed to transport circuit mode

communications (e.g., DS1, DS3) from a variety of different sources, but they were primarily designed to

support real-time, uncompressed, circuit-switched voice encoded in PCM format. The primary difficulty in

doing this prior to SONET/SDH was that the synchronization sources of these various circuits were different.

This meant that each circuit was actually operating at a slightly different rate and with different phase.

SONET/SDH allowed for the simultaneous transport of many different circuits of differing origin within a

single framing protocol. SONET/SDH is not itself a communications protocol per se, but a transport protocol.

Due to SONET/SDH's essential protocol neutrality and transport-oriented features, SONET/SDH was the

obvious choice for transporting the fixed length Asynchronous Transfer Mode (ATM) frames also known as

cells. It quickly evolved mapping structures and concatenated payload containers to transport ATM

connections. In other words, for ATM (and eventually other protocols such as Ethernet), the internal complex

structure previously used to transport circuit-oriented connections was removed and replaced with a large and

concatenated frame (such as OC-3c) into which ATM cells, IP packets, or Ethernet frames are placed.

Racks of Alcatel STM-16 SDH add-drop multiplexers

Both SDH and SONET are widely used today: SONET in the United States and Canada, and SDH in the rest of

the world. Although the SONET standards were developed before SDH, it is considered a variation of SDH

because of SDH's greater worldwide market penetration.

The SDH standard was originally defined by the European Telecommunications Standards Institute (ETSI), and

is formalized as International Telecommunication Union (ITU) standards G.707, G.783, G.784, and G.803. The

SONET standard was defined by Telcordia and American National Standards Institute (ANSI) standard T1.105.

SDH frame

An STM-1 frame. The first nine columns contain the overhead and the pointers. For the sake of simplicity, the frame is

shown as a rectangular structure of 270 columns and nine rows but the protocol does not transmit the bytes in this

order.

For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and nine rows. The first three

rows and nine columns contain regenerator section overhead (RSOH) and the last five rows and nine columns contain

multiplex section overhead (MSOH). The fourth row from the top contains pointers.

The STM-1 (Synchronous Transport Module, level 1) frame is the basic transmission format for SDH—the first

level of the synchronous digital hierarchy. The STM-1 frame is transmitted in exactly 125 µs, therefore, there

are 8,000 frames per second on a 155.52 Mbit/s OC-3 fiber-optic circuit.The STM-1 frame consists of overhead

and pointers plus information payload. The first nine columns of each frame make up the Section Overhead and

Administrative Unit Pointers, and the last 261 columns make up the Information Payload. The pointers (H1, H2,

H3 bytes) identify administrative units (AU) within the information payload. Thus, an OC-3 circuit can carry

150.336 Mbit/s of payload, after accounting for the overhead.

Carried within the information payload, which has its own frame structure of nine rows and 261 columns, are

administrative units identified by pointers. Also within the administrative unit are one or more virtual containers

(VCs). VCs contain path overhead and VC payload. The first column is for path overhead; it is followed by the

payload container, which can itself carry other containers. Administrative units can have any phase alignment

within the STM frame, and this alignment is indicated by the pointer in row four.

The section overhead (SOH) of a STM-1 signal is divided into two parts: the regenerator section overhead

(RSOH) and the multiplex section overhead (MSOH). The overheads contain information from the transmission

system itself, which is used for a wide range of management functions, such as monitoring transmission quality,

detecting failures, managing alarms, data communication channels, service channels, etc.

The STM frame is continuous and is transmitted in a serial fashion: byte-by-byte, row-by-row.

SONET/SDH and relationship to 10 Gigabit Ethernet

Another type of high-speed data networking circuit is 10 Gigabit Ethernet (10GbE). The Gigabit Ethernet

Alliance created two 10 Gigabit Ethernet variants: a local area variant (LAN PHY) with a line rate of 10.3125

Gbit/s, and a wide area variant (WAN PHY) with the same line rate as OC-192/STM-64 (9,953,280 kbit/s). The

WAN PHY variant encapsulates Ethernet data using a lightweight SDH/SONET frame, so as to be compatible

at a low level with equipment designed to carry SDH/SONET signals, whereas the LAN PHY variant

encapsulates Ethernet data using 64B/66B line coding.

However, 10 Gigabit Ethernet does not explicitly provide any interoperability at the bitstream level with other

SDH/SONET systems. This differs from WDM system transponders, including both coarse and dense

wavelength-division multiplexing systems (CWDM and DWDM) that currently support OC-192 SONET

signals, which can normally support thin-SONET–framed 10 Gigabit Ethernet.

The basic unit of transmission

The basic unit of framing in SDH is a STM-1 (Synchronous Transport Module, level 1), which operates at

155.520 megabits per second (Mbit/s). SONET refers to this basic unit as an STS-3c (Synchronous Transport

Signal 3, concatenated) or OC-3c, depending on whether the signal is carried electrically (STS) or optically

(OC), but its high-level functionality, frame size, and bit-rate are the same as STM-1.

SONET offers an additional basic unit of transmission, the STS-1 (Synchronous Transport Signal 1) or OC-1,

operating at 51.84 Mbit/s—exactly one third of an STM-1/STS-3c/OC-3c carrier. This speed is dictated by the

bandwidth requirements for PCM-encoded telephonic voice signals: at this rate, an STS-1/OC-1 circuit can

carry the bandwidth equivalent of a standard DS-3 channel, which can carry 672 64-kbit/s voice channels.

Internet & related software’s NETSCAPE

Netscape Communications (formerly known as Netscape Communications Corporation and commonly known

as Netscape) is a US computer services company, best known for Netscape Navigator, its web browser. When it

was an independent company, its headquarters were in Mountain View, California.[1]

The name Netscape was a

trademark of Cisco Systems.[2]

Netscape's web browser was once dominant in terms of usage share, but lost most of that share to Internet

Explorer during the first browser war. By the end of 2006, the usage share of Netscape browsers had fallen,

from over 90% in the mid 1990s, to less than 1%.

Netscape is credited with developing the Secure Sockets Layer Protocol (SSL) for securing online

communication, which is still widely used,[3]

as well as JavaScript, the most widely used language for client-

side scripting of web pages.

Netscape stock traded between 1995 and 2003, subsequently as a subsidiary of AOL. However, it became a

holding company following AOL's purchase of Netscape in 1998. The Netscape brand is still extensively used

by AOL. Some services currently offered under the Netscape brand, other than the web browser, include a

discount Internet service provider and a popular social news website. In December 2007, AOL announced it

would no longer be updating the Netscape browser. Tom Drapeau, director of AOL's Netscape Brand,

announced that the company would stop supporting Netscape software products as of March 1, 2008.[4]

The

decision met mixed reactions from communities, with many arguing that the termination of product support is

significantly belated. Internet security site Security Watch stated that a trend of infrequent security updates for

AOL's Netscape caused the browser to become a "security liability", specifically the 2005–2007 versions,

Netscape Browser 8.[5]

Asa Dotzler, one of Firefox's original bug testers, greeted the news with "good riddance"

in his blog post, but praised the various members of the Netscape team over the years for enabling the creation

of Mozilla in 1998.[6]

Others protested and petitioned AOL to continue providing vital security fixes to

unknowing or loyal users of its software, as well as protection of a well-known brand.

MOSAIC

Mosaic is the web browser credited with popularizing the World Wide Web. It was also a client for earlier

protocols such as FTP, NNTP, and gopher. Its clean, easily understood user interface, reliability, Windows port

and simple installation all contributed to making it the application that opened up the Web to the general

public.[3]

Mosaic was also the first browser to display images inline with text instead of displaying images in a

separate window.[4]

While often described as the first graphical web browser, Mosaic was preceded by

WorldWideWeb and the lesser-known Erwise[5]

and ViolaWWW.

Mosaic was developed at the National Center for Supercomputing Applications (NCSA)[4]

at the University of

Illinois Urbana-Champaign beginning in late 1992. NCSA released the browser in 1993,[6]

and officially

discontinued development and support on January 7, 1997.[7]

However, it can still be downloaded from

NCSA.[8]

Fifteen years after Mosaic's introduction, the most popular contemporary browsers, Internet Explorer, Mozilla

Firefox and Google Chrome, retain many of the characteristics of the original Mosaic graphical user interface

(GUI) and interactive experience.

Netscape Navigator was later developed by Netscape, which employed many of the original Mosaic authors;

however, it intentionally shared no code with Mosaic. Netscape Navigator's code descendant is Mozilla.[9]

Networking devices: Repeaters Repeaters and hubs-A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs

longer than 100 meters. A repeater with multiple ports is known as a hub. Repeaters work on the Physical Layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay which can affect network communication when there are several repeaters in a row. Many network architectures limit the number of repeaters that can be used in a row (e.g. Ethernet's 5-4-3 rule).

Today, repeaters and hubs have been made mostly obsolete by switches

A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances. Repeaters are used to boost signals in coaxial and twisted pair cable and in fiber optics. A network hub is one such device. An optical communications repeater is a piece of equipment that receives an optical signal, converts that signal into an electrical one, regenerates it, and then retransmits an optical signal. In contrast, Optical amplifiers are often used in transcontinental and submarine communications cables, because the signal loss over such distances would be unacceptable without them. Radio repeaters are used in radio communication services. Radio repeaters are also used extensively in broadcasting, where they are known as broadcast relay stations. A digipeater is a blend meaning "digital repeater", particularly used in amateur radio. Store and forward digipeaters generally receive a packet radio transmission and then retransmit it on the same frequency. When providing a point-to-point telecom link using radio beyond line of sight, one uses repeaters in a microwave radio relay. A reflector, often on a mountaintop, that relays such signals around an obstacle, is called a passive repeater.

Bridge

Bridges come in three basic types:

Local bridges: Directly connect LANs

Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote

bridges, where the connecting link is slower than the end networks, largely have been replaced with

routers.

Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

A Bridge is a box with ports (usually two) to LAN segments. It operates in promiscuous mode at the data link

layer (i.e. at the level of frames, not signals), it examines all frames and it recognizes where they came from,

and where they are going to. It selectively (frame filtering) transfers frames from any port to other ports. It

does not propagate noise signals and defective frames as it was the case for repeaters (at the physical layer). It

adaptively recognizes which machines are reacheable from a port. It reduces traffic on each port and it improves

security since each port will only transmit frames directed to nodes reacheable from that port (thus one does not

overhear irrelevant traffic).

Bridges are normally used to connect LAN segments within a limited geographic area (local bridges), like a

building or a campus. But they are also used in the network of an enterprise to interconnect LANs: a bridge in a

LAN is connected through some long distance channel (for example, a line provided by a common carrier) to a

bridge in a distant LAN (remote bridges). Usually bridges connect segments using the same data link protocol,

but some modern bridges can convert between different data link protocols (for example, ethernet and token

ring).

Bridges can be transparent (usually in Ethernet lans), also called spanning tree bridges, where the aim is to

minimize all work required to set up a bridge and have instead the hardware and software set up the bridge with

the information required for routing frames correctly. Or bridges can be source routing bridges (usually in

token ring lans) where the route from sender to receiver are preset at the sender and included in the frame. We

will only discuss transparent bridges.

All the nodes reacheable from a node through segments and bridges will receive broadcast messages sent by

that node. They constitute the broadcast domain of the given node.

Bridges are able to filter frames on the basis of any information available at the data link level in the frame. For

example, since an Ethernet frame has a field with information about the higher level protocol used in the data

portion of the frame, a bridge could be programmed to filter out frames that use selected protocols.

Routers A router is a box (usually a regular computer) with (at least) two ports, used to connect also dissimilar

networks. It differs from bridges since it operates at the network level. [It will also use different addresses. For

example a bridge may use Ethernet addresses while a router uses IP addresses.] It does all the transformations

that may be required by the transfer of packets across the networks it connects. Routing involves two basic

activities: running routing algorithms to determine routes, as expresed by routing tables, and using the routing

tables to move packets across the network. The latter activity is easier and it is called switching. Routing tables

contain information that will indicate for each packet on the basis of its final destination (usually an IP address)

where to go next (next-hop forwarding) as to the port to be used and the physical address of the next router.

Cycles can exist in the graph that has routers as nodes and ports as edges. The routing tables are built to work

well also in the presence of cycles. It is important that routing tables be not too large.

Evaluation of Routing Algorithms:

Route quality (optimality): network utilization, path length, delay, bandwidth, communication cost,

reliability

Overhead (simplicity): control messages, processing, state (i.e. memory required)

Speed of convergence to best routes

Robustness: Responsiveness to topology changes

Routing protocol characteristics:

Centralized/decentralized

Static/Dynamic

Location of decisions (hop-by-hop/Source-routing)

Frequency of decision (per packet, per session, per topology change)

Single Path/Multipath: The routing algorithm may provide alternative routes to be taken to avoid

congestion, or improve throughput, ..

Flat or Hierarchical: i.e. all routers are at the same level, or routing takes place at two levels, one to get

to the general area, the other to navigate the local neighborhood.

Protocol: Information distribution and route computation algorithm

We consider two routing algorithms, one centralized (the full topology of the network is know at each router),

Dijkstra's shortest path algorithm, and one distributed (a router only knows its neighbors), the vector

distance routing algorithm. We do not worry at this time about protocols or standards used for exchanging

routing information.

Dijkstra's Shortest Path Algorithm

Given a graph (i.e. we know its vertices and edges) with non-negative weights associated with its edges and a

designated source vertex s determine the shortest paths from s to all other vertices and their lengths. Initialize arrays R and D so that for each vertex v of the graph, R[v] = NIL,

and D[v] is infinity except for s where D[s] = 0.

Finally let the set S consist of all the vertices of the graph.

While S is not empty

Let u be an element of S with minimal D value and remove it from S.

For each element v in the neighborhood of u

Let w be D[u] + cost-of-edge[u,v];

If D[v] is greater than w then

Set D[v] to w;

Set R[v] to u;

Then for all vertices v, D[v] is the cost of the paths from s to v

(or viceversa) and R[v] is the next node (next-hop) in the optimal

path from v to s (or viceversa).

Example

The Dijkstra algorithm is run independently at each vertex after the vertex has collected all the information on

the structure of the graph. [There has to be a routing protocol (see below) to make this possible. This routing

protocol allows each node to inform all other nodes of its own identity and of its network links, its Link State.]

Routing based on Dijkstra's algorithm is called Link State Routing.

Note that Dijkstra's Algorithm creates a spanning tree with as root the node where the algorithm is run (s in the

discussion above). The algorithm will result in different trees when run at different nodes. These spanning trees

are not necessarily minimal (i.e. the sum of the cost of the branches is not minimal). For example:

Vector Distance Routing Algorithm

In this algorithm (due to Bellman and Ford), each router exchanges routing information, the Distance Vector,

with its neighbors, not with all routers. The distance vector algorithm results in the same distances as the

Dijkstra algorithm. Now each vertex s only knows itself, its neighbors, and the distance to

these neighbors. Each vertex keeps a set of triples of the form

[destination, next-hop, distance]. This set is the distance vector.

Initially this set is {[s,NIL,0]} and it is transmitted to each neighbor.

When a vertex u receives a distance vector from its neighbor v

For each triple [d,n,c] in the received distance vector

Let w = c + distance from u to neighbor v

If there is no triple of the form [d,x,y] in the distance

vector of u or

there is such a triple and (y > w or x=v) then

Remove [d,x,y], if there, and add [d,v,w] to the distance

vector of u.

When a vertex u recognizes that the link to a neighbor v has failed

Requests distance vector information from its remaining neighbors and

Recalculate the distance vector using the new neighborhood information.

A vertex sends a copy of its distance vector to its neighbors

whenever there has been a change in its own distance vector

or a failure in its neighborhood

Here is what the Vector Distance Algorithm does in the case of the graph above: Step 0:

s {[s,nil,0]}

A {[A,nil,0]}

B {[B,nil,0]}

C {[C,nil,0]}

D {[D,nil,0]}

Step 1:

s {[s,nil,0],[A,A,9],[C,C,5]}

A {[A,nil,0],[s,s,9],[B,B,1],[C,C,2]}

B {[B,nil,0],[A,A,1],[C,C,9[,[D,D,6]}

C {[C,nil,0],[s,s,5],[A,A,2],[B,B,9],[D,D,4]}

D {[D,nil,0],[C,C,4],[B,B,6]}

Step 2:

s {[s,nil,0],[A,C,7],[B,A,10],[C,C,5],[D,C,9]}

A {[A,nil,0],[s,C,7],[B,B,1],[C,C,2],[D,C,6]}

B {[B,nil,0],[s,A,10],[A,A,1],[C,A,3],[D,D,6]}

C {[C,nil,0],[s,s,5],[A,A,2],[B,A,3],[D,D,4]}

D {[D,nil,0],[s,C,9],[A,C,6],[C,C,4],[B,B,6]}

Step 3:

s {[s,nil,0],[A,C,7],[B,C,8],[C,C,5],[D,C,9]}

A {[A,nil,0],[s,C,7],[B,B,1],[C,C,2],[D,C,6]}

B {[B,nil,0],[s,A,8],[A,A,1],[C,A,3],[D,D,6]}

C {[C,nil,0],[s,s,5],[A,A,2],[B,A,3],[D,D,4]}

D {[D,nil,0],[s,C,9],[A,C,6],[C,C,4],[B,B,6]}

A problem with the distance vector algorithm is its slowness in propagating the recognition of link failures (it is

called the count to infinity problem). For example in the following graph

+---+ +---+ +---+

| A |----------| B |-----------| C |

+---+ +---+ +---+

suppose that we have the following distance vectors: At A: {[A,NIL,0], [B,B,1], [C,B,2]}

At B: {[A,A,1], [B,NIL,0], [C,C,1]}

At C: {[A,B,2], [B,B,1], [C,NIL,0]}

and the link from B to C fails. So B discards the triple [C,C,1] and recomputes the vector using the information

from A, thus it adds the triple [C,A,3]. This change in turn is propagated to A that has to change its C triple to

[C,B,4], that causes B to change to [C,A,5], .. and so on until "infinity" is reached and A and B can finally

conclude that C is unreacheable!

Note that we say that Dijkstra's algorithm is centralized because it requires the collection of global information

about the graph. In the Distance Vector algorithm instead we need only information about the local

neighborhood of a vertex.

Routing algorithms, i.e. algorithms used for computing routing tables, are implemented using routing

protocols. Examples of such protocols are RIP (Routing Information Protocol), EGP (Exterior Gateway

Protocol), IGRP (Interior Gateway Routing Protocol). The packets exchanged in the routing protocols are called

routing packets and they contain control information, i.e. they are overhead. ICMP (Internet Control Message

Protocol) is a protocol used to propagate echo and reply messages that test the reacheability of nodes in the

network, and to report loss of packets due to time expiration. IRDP (ICMP Router Discovery Protocol) is used

to identify routers and to report their identity.

Packet Switch

A packet switch is a box with a number of ports, some to other packet switches, some to computers. Usually the

connection to computers are slower than the connections to other packet switches. A packet switch is used to

interconnect networks with similar or dissimilar structures and it operates above the data link level. It is a

generic term that includes bridges, routers, and gateways, though it used to mean an IMP in the old ARPANET.

It tends to stress the switching functionality (i.e. how packets are moved across the network) above the ability to

determine routing information. A packet switch uses a store-and-forward strategy with the messages it

receives. Thus congestions in the use of a connection do not result (unless we overrun the available buffers) in

the loss of data, only in some delays. Packet switches may use hierarchical addresses, with a [switch part, port

part]. So a computer will be known by the identity of the packet switch it is connected to and of the position of

the port it uses on the switch.

Gateways

It used to mean the same as packet switch, now it usually means a device that works above the network layer and can perform complete translations between different protocol stacks.

Firewalls A firewall is an important aspect of a network with respect to security. It typically rejects access requests from unsafe sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in 'cyber' attacks for the purpose of stealing/corrupting data, planting viruses, etc.

Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow

computers to physically access a networking medium. It provides a low-level addressing system through the use of MAC

addresses.

If any thing is wrong in this then heartly sorry no responsibility of 100% accuracy

COMPILED BY- AMIT MAURYA C.S.E.6TH SEM 3RD YEAR DR. C. V. RAMAN INSTITUTE OF SCIENCE AND TECHNOLOGY