networking note 4 5th sem

7/30/2019 Networking Note 4 5th Sem

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STATIC

Static routing is not really a protocol, simply the process of manually entering routesinto the routing table via a configuration file that is loaded when the routing device

starts up. As an alternative, these routes can be enterd by a network administratorwho configures the routes. Since these routes don't change after they are configured

(unless a human changes them) they are called 'static' routes.

Static routing is the simplest form ofrouting, but it is a manual process and does notwork well when the routing information has to be changed frequently or needs to be

configfured on a large number ofrouting devices (routers). Static routing also doesnot handle outages or down connections well because any route that is configured

manually must be reconfigured manually to fix or repair any lost connectivity.

DYNAMIC

Dynamic routing protocols are software applications that dynamically discovernetwork destinations and how to get to them.

A router will 'learn' routes to all directly connected networks first. It will then learnroutes from other routers that run the same routing protocol. The router will then

sort through it's list ofroutes and select one or more 'best' routes for each networkdestination it knows or has learned.

Dynamic protocols will then distribute this 'best route' information to other routersrunning the same routing protocol, thereby extending the information on what

networks exist and can be reached. This gives dynamic routing protocols the abilityto adapt to logical network topology changes, equipment failures or network outages

'on the fly'.

Message Switching

Message Switching, also known as store-and-forward switching, refers to a switching

technique involving transmission of messages from node to node through a network.The message is stored at each node until such time as a forwarding path is available.

Ethernet is a family offrame-based computer networking technologies for local area

networks (LANs). The name comes from the physical concept of the ether. It definesa number of wiring and signaling standards for the Physical Layer of the OSI

networking model, through means of network access at the Media Access Control(MAC) /Data Link Layer, and a common addressing format.

IEEE 802.3 is a collection ofIEEE standards defining the Physical Layer and DataLink Layer's media access control (MAC) sublayer of wired Ethernet. This is generally

a LAN technology with some WAN applications. Physical connections are madebetween nodes and/or infrastructure devices (hubs, switches, routers) by various

types of copper or fiber cable.

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Ethernet: IEEE 802.3 Local Area Network (LAN) protocols

Ethernet protocols refer to the family of local-area network (LAN) covered by theIEEE 802.3. In the Ethernet standard, there are two modes of operation: half-duplex

and full-duplex modes. In the half duplex mode, data are transmitted using thepopular Carrier-Sense Multiple Access/Collision Detection (CSMA/CD) protocol on a

shared medium. The main disadvantages of the half-duplex are the efficiency anddistance limitation, in which the link distance is limited by the minimum MAC framesize. This restriction reduces the efficiency drastically for high-rate transmission.

Therefore, the carrier extension technique is used to ensure the minimum frame sizeof 512 bytes in Gigabit Ethernet to achieve a reasonable link distance.

The Ethernet system consists of three basic elements: 1. the physical medium usedto carry Ethernet signals between computers, 2. a set of medium access control rules

embedded in each Ethernet interface that allow multiple computers to fairly arbitrateaccess to the shared Ethernet channel, and 3. an Ethernet frame that consists of a

standardized set of bits used to carry data over the system.

As with all IEEE 802 protocols, the ISO data link layer is divided into two IEEE 802sublayers, the Media Access Control (MAC) sublayer and the MAC-client sublayer.The IEEE 802.3 physical layer corresponds to the ISO physical layer.

The MAC sub-layer has two primary responsibilities:

Data encapsulation, including frame assembly before transmission, and frame

parsing/error detection during and after reception

Media access control, including initiation of frame transmission and recovery

from transmission failure

The MAC-client sub-layer may be one of the following:

Logical Link Control (LLC), which provides the interface between the Ethernet

MAC and the upper layers in the protocol stack of the end station. The LLC

sublayer is defined by IEEE 802.2 standards.

Bridge entity, which provides LAN-to-LAN interfaces between LANs that use

the same protocol (for example, Ethernet to Ethernet) and also betweendifferent protocols (for example, Ethernet to Token Ring). Bridge entities are

defined by IEEE 802.1 standards.

Each Ethernet-equipped computer operates independently of all other stations on the

network: there is no central controller. All stations attached to an Ethernet areconnected to a shared signaling system, also called the medium. To send data a

station first listens to the channel, and when the channel is idle the station transmitsits data in the form of an Ethernet frame, or packet.

After each frame transmission, all stations on the network must contend equally forthe next frame transmission opportunity. Access to the shared channel is determined

by the medium access control (MAC) mechanism embedded in the Ethernet interfacelocated in each station. The medium access control mechanism is based on a system

called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

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As each Ethernet frame is sent onto the shared signal channel, all Ethernet interfaceslook at the destination address. If the destination address of the frame matches with

the interface address, the frame will be read entirely and be delivered to thenetworking software running on that computer. All other network interfaces will stop

reading the frame when they discover that the destination address does not matchtheir own address.

When it comes to how signals flow over the set of media segments that make up anEthernet system, it helps to understand the topology of the system. The signal

topology of the Ethernet is also known as the logical topology, to distinguish it fromthe actual physical layout of the media cables. The logical topology of an Ethernet

provides a single channel (or bus) that carries Ethernet signals to all stations.

Multiple Ethernet segments can be linked together to form a larger Ethernet LAN

using a signal amplifying and retiming device called a repeater. Through the use ofrepeaters, a given Ethernet system of multiple segments can grow as a "non-rooted

branching tree." Non-rooted" means that the resulting system of linked segmentsmay grow in any direction, and does not have a specific root segment. Most

importantly, segments must never be connected in a loop. Every segment in thesystem must have two ends, since the Ethernet system will not operate correctly in

the presence of loop paths.

Even though the media segments may be physically connected in a star pattern, withmultiple segments attached to a repeater, the logical topology is still that of a single

Ethernet channel that carries signals to all stations.

Protocol Structure - Ethernet: IEEE 802.3 Local Area Network protocols Thebasic IEEE 802.3 Ethernet MAC Data Frame for 10/100Mbps Ethernet:

7 1 6 6 2 46-1500bytes 4

Pre SFD DA SA Length Type Data unit + pad FCS

Preamble (PRE)- 7 bytes. The PRE is an alternating pattern of ones and

zeros that tells receiving stations that a frame is coming, and that provides a

means to synchronize the frame-reception portions of receiving physicallayers with the incoming bit stream.

Start-of-frame delimiter (SFD)- 1 byte. The SOF is an alternating pattern

of ones and zeros, ending with two consecutive 1-bits indicating that the next

bit is the left-most bit in the left-most byte of the destination address.

Destination address (DA)- 6 bytes. The DA field identifies which station(s)

should receive the frame..

Source addresses (SA)- 6 bytes. The SA field identifies the sending station.

Length/Type- 2 bytes. This field indicates either the number of MAC-client

data bytes that are contained in the data field of the frame, or the frame type

ID if the frame is assembled using an optional format.

Data- Is a sequence of n bytes (46=< n =


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Frame check sequence (FCS)- 4 bytes. This sequence contains a 32-bit

cyclic redundancy check (CRC) value, which is created by the sending MAC

and is recalculated by the receiving MAC to check for damaged frames.

Token bus network

Token passing in a Token bus network

Token bus is a network implementing the

token ring protocol over a "virtual ring" on acoaxial cable. A token is passed around the

network nodes and only the nodepossessing the token may transmit. If a

node doesn't have anything to send, thetoken is passed on to the next node on the

virtual ring. Each node must know the

address of its neighbor in the ring, so aspecial protocol is needed to notify the

other nodes of connections to, anddisconnections from, the ring.

Token bus was standardized by IEEE standard 802.4. It is mainly used for industrial

applications. Token bus was used by GM (General Motors) for their ManufacturingAutomation Protocol (MAP) standardization effort. This is an application of the

concepts used in token ring networks. The main difference is that the endpoints ofthe bus do not meet to form a physical ring. The IEEE 802.4 Working Group is

disbanded. In order to guarantee the packet delay and transmission in Token busprotocol, a modified Token bus was proposed in Manufacturing Automation Systems

and flexible manufacturing system (FMS)

Stations should not starve

Assign priorities to frames

Solution is token bus.

Each station knows its neighbors

Special control frame is a token

Owner of the token can send

After sending, should pass token to neighbor

Collisions are avoided

IEEE 802.4 defines the media access control (MAC) layer for bus networks that use a

token-passing mechanism (token bus networks). This is an application of the

concepts used in token ring networks. The main difference is that the endpoints ofthe bus do not meet to form a physical ring. The IEEE 802.4 Working Group isdisbanded.

Token Ring: IEEE 802.5 LAN Protocol

Token Ring is a LAN protocol defined in the IEEE 802.5 where all stations areconnected in a ring and each station can directly hear transmissions only from its

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immediate neighbor. Permission to transmit is granted by a message (token) thatcirculates around the ring.

Token Ring as defined in IEEE 802.5 is originated from the IBM Token Ring LAN

technologies. Both are based on the Token Passing technologies. While them differ inminor ways but generally compatible with each other.

Token-passing networksmove a small frame, called a token, around the network.

Possession of the token grants the right to transmit. If a node receiving the tokenhas no information to send, it seizes the token, alters 1 bit of the token (which turns

the token into a start-of-frame sequence), appends the information that it wants totransmit, and sends this information to the next station on the ring. While the

information frame is circling the ring, no token is on the network, which means thatother stations wanting to transmit must wait. Therefore, collisions cannot occur in

Token Ring networks.

The information frame circulates the ring until it reaches the intended destination

station, which copies the information for further processing. The information frame

continues to circle the ring and is finally removed when it reaches the sendingstation. The sending station can check the returning frame to see whether the framewas seen and subsequently copied by the destination.

Unlike Ethernet CSMA/CD networks, token-passing networks are deterministic, whichmeans that it is possible to calculate the maximum time that will pass before any

end station will be capable of transmitting. This feature and several reliabilityfeatures make Token Ring networks ideal for applications in which delay must be

predictable and robust network operation is important.

The Fiber Distributed-Data Interface (FDDI) also uses the Token Passing protocol.

Protocol Structure - Token Ring: IEEE 802.5 LAN Protocol

1 2 3 9 15bytes

SDEL AC FC Destination address Source address

Route information 0-30 bytes

Information (LLC or MAC) variable

FCS (4 bytes) EDEL (1) FS(1)

SDEL / EDEL - Starting Delimiter / Ending Delimiter. Both the SDEL and EDEL

have intentional Manchester code violations in certain bit positions so that thestart and end of a frame can never be accidentally recognized in the middle of

other data.

AC - Access control field Contains the Priority fields.

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FC - Frame control field indicates whether the frame contains data or control

information

Destination address - Destination station address.

Source address - Source station address.

Route information - The field with routing control, route descriptor and

routing type information.

Information - The Information field may be LLC or MAC. FCS - Frame check sequence.

Frame status - Contains bits that may be set on by the recipient of the frame

to signal recognition of the address and whether the frame was successfully

copied.

In the Integrated Services Digital Network (ISDN), the D-channel is the channel that

carries control and signalling information. (The "D" stands for "delta" channel.) TheB-channel ("B" for "bearer") carries the main data.

In ISDN, there are two levels of service: the Basic Rate Interface, intended for thehome and small enterprise, and the Primary Rate Interface, for larger users. Bothrates include a number of B- (bearer) channels and a D- (delta) channel. The B-

channels carry data, voice, and other services. The D-channel carries control andsignaling information.

The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The

Primary Rate Interface consists of 23 B-channels and one 64- Kpbs D channel in theUnited States or 30 B-channels and 1 D-channel in Europe.

Protocol Structure - ISDN: Integrated Services Digital Network

Below is the general structure of the ISDN frame:

8 7 6 5 4 3 2 1

Protocol discriminator

0 0 0 0 Length of reference call value

Flag Call reference value

0 Message type

Other information elements as required

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Protocol discriminator - The protocol used to encode the remainder of the

Layer.

Length of call reference value - Defines the length of the next field. The

Call reference may be one or two octets long depending on the size of the

value being encoded.

Flag - Set to zero for messages sent by the party that allocated the call

reference value; otherwise set to one. Call reference value - An arbitrary value that is allocated for the duration of

the specific session, which identifies the call between the device maintainingthe call and the ISDN switch.

Message type - Defines the primary purpose of the frame. The message

type may be one octet or two octets (for network specific messages). When

there is more than one octet, the first octet is coded as eight zeros. Acomplete list of message types is given in ISDN Message Types below.

ISDN Information Elements - there are two types of information elements:

single octet and variable length. Single octet information elements- the

single octet information element appears as follows:

8 7 6 5 4 3 2 1

1 Information element identifier Information element

Variable length information elements - The following is format and the

variable length information element:

8 7 6 5 4 3 2

1

0Information element identifier

Length of information elements

Information elements (multiple bytes)

The information element identifier identifies the chosen element and is unique only

within the given Codeset. The length of the information element informs the receiveras to the amount of the following octets belonging to each information element.

ISDN Message Types - The possible ISDN message types: Call Establishment,

Call Information Phase, Call Clearing, and Miscellaneous.

Codeset - Three main Codesets are defined. In each Codeset, a section of the

information elements are defined by the associated variant of the protocol:

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Codeset 0 The default code, referring to the CCITT set of information elements.

Codeset 5 The national specific Codeset.

Codeset 6 The network specific Codeset.

CPE - Customer Premises Equipment - refers to all ISDN compatible equipmentconnected at the user sight. Examples of devices are telephone, PC, Telex, Facsimile,

etc. The exception is the FCC definition of NT1. The FCC views the NT1 as a CPEbecause it is on the customer sight, but the CCITT views NT1 as part of the network.

Consequently the network reference point of the network boundary is dependent onthe variant in use.

ISDN Channels B, D and H - The three logical digital communication channels of

ISDN perform the following functions:

B-Channel Carries user service information including: digital data, video, and voice.

D-ChannelCarries signals and data packets between the user and the network

Using the Integrated Services Digital Network (ISDN) Basic Rate Interchange (Basic

Rate Interface in ISDN) service, an NT1 (network terminating unit 1) is a device thataccepts a two-wire signal from the phone company and converts it to a four-wire

signal that sends and receives to and from devices within the home or business. Inthe U.K. and some other countries, the NT1 is located at the telephone company's

central office. In the U.S., the NT1 is a separate box at the home or business or itcan be integrated into one device. If it is a separate box, up to eight devices, such as

telephones and computers, can be attached to it. If the NT1 is built into one device,then only that one device can be served by the line coming in from the phone

company. Additional devices would require one or more additional lines.

ISDN Devices

In the context of ISDN standards, STANDARD DEVICES refers not to actualhardware, but to standard collections of functions that can usually be performed by

individual hardware units. The ISDN Standard Devices are:

Terminal Equipment (TE)

Terminal Adapter (TA)

Network Termination 1 (NT1)


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Exchange Termination (ET)


A TE is any piece of communicating equipment that complies with the ISDNstandards. Examples include: digital telephones, ISDN data terminals, Group IV Fax

machines, and ISDN-equipped computers.

In most cases, a TE should be able to provide a full Basic Rate Access (2B+D),

although some TEs may use only 1B+D or even only a D channel.


A TA is a special interface-conversion device that allows communicating devices thatdon't conform to ISDN standards to communicate over the ISDN.

The most common TAs provide Basic Rate Access and have one RJ-type modular jackfor voice and one RS-232 or V.35 connector for data (with each port able to connect

to either of the available B channels). Some TAs have a separate data connector forthe D channel.

Network Termination (NT1 and NT2)

The NT devices, NT1 and NT2, form the physical and logical boundary between the

customer's premises and the carrier's network. NT1 performs the logical interfacefunctions of switching and local-device control (local signalling). NT2 performs the

physical interface conversion between the dissimilar customer and network sides ofthe interface.

In most cases, a single device, such as a PBX or digital multiplexer, performs both

physical and logical interface functions. In ISDN terms, such a device is called NT12("NT-one-two") or simply NT.

ISDN Devices

In the context of ISDN standards, STANDARD DEVICES refers not to actualhardware, but to standard collections of functions that can usually be performed by

individual hardware units. The ISDN Standard Devices are:





Exchange Termination (ET)


A TE is any piece of communicating equipment that complies with the ISDN

standards. Examples include: digital telephones, ISDN data terminals, Group IV Faxmachines, and ISDN-equipped computers.

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In most cases, a TE should be able to provide a full Basic Rate Access (2B+D),although some TEs may use only 1B+D or even only a D channel.


A TA is a special interface-conversion device that allows communicating devices that

don't conform to ISDN standards to communicate over the ISDN.

The most common TAs provide Basic Rate Access and have one RJ-type modular jack

for voice and one RS-232 or V.35 connector for data (with each port able to connectto either of the available B channels). Some TAs have a separate data connector for

the D channel.

Network Termination (NT1 and NT2)

The NT devices, NT1 and NT2, form the physical and logical boundary between the

customer's premises and the carrier's network. NT1 performs the logical interfacefunctions of switching and local-device control (local signalling). NT2 performs the

physical interface conversion between the dissimilar customer and network sides ofthe interface.

In most cases, a single device, such as a PBX or digital multiplexer, performs both

physical and logical interface functions. In ISDN terms, such a device is called NT12("NT-one-two") or simply NT.

X.25 provides quality of service and error-free delivery, whereas, Frame Relay was

designed to relay data as quickly as possible over low error networks. Frame Relayeliminates a number of the higher-level procedures and fields used in X.25. Frame

relay was designed for use on links with error-rates far lower than available whenX.25 was designed.

X.25 prepares and sends packets, while frame relay prepares and sends frames.X.25 packets contain several fields used for error checking and flow control, most of

which are not used by Frame Relay. The frames in Frame Relay contain an expandedlink layer address field that enables frame relay nodes to direct frames to their

destinations with minimal processing. The elimination of functions and fields overX.25 allows Frame Relay to move data more quickly, but leaves more room for errors

and larger delays should data need to be retransmitted.

X.25 packet switched networks typically allocated a fixed bandwidth through the

network for each X.25 access, regardless of the current load. This resource allocationapproach, while apt for applications that require guaranteed quality of service, is

inefficient for applications that are highly dynamic in their load characteristics orwhich would benefit from a more dynamic resource allocation. Frame Relay networks

can dynamically allocate bandwidth at both the physical and logical channel level.

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networking note 4 5th sem

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