Jaringan Komputer

(1)

Data Komunikasi

oleh

(2)

OSI Layer

7 Layer/OSI

Application

Presentation

Session

Transport

Network

Data-link

Physical

Application

Transport

Network

Data-link

Physical

(3)

Application

• Contoh : Email, HTTP, dsb

Data Header

(4)

Presentation & Session

• Security, Compression

• RPC, RMI

Data Header

Payload Header

Data Header

Header

(5)

Transport

• PL = PayLoad

• TCP, UDP Protocol

Payload Header

PL PL PL PL PL PL PL

Dumy

PL 4

PL

1 7 PL

PL 2

PL 3

PL 5

(6)

Transport Layer Analogi

• Paket besar dibagi-bagi menjadi paket-paket yang

lebih kecil

• Masing-masing paket diberi nomor sesuai dengan

urutannya

Header

1 2

4 3

6 5

2

3 1

4

(7)

Network Layer

• Address pada Network Layer dinamakan : Logical Address • Address terdiri dari : Source Address (alamat IP pengirim,

mis:172.16.180.16), dan Destination Address (alamat IP penerima, mis: 192.234.13.201)

PL 4

PL

1 7 PL

PL 2

PL 3

PL 5

PL 6

(8)

Network Layer Analogi

• Router

2

3 1

4

6 5

Pengirim Penerima

4

(9)

Data-link

Paket kecil

PL Address PL Address PL Address PL Address PL Address PL Address

Paket besar

• Address pada Data-link disebut: Physical Address

• Address terdiri atas: Source Address (Alamat Asal), dan Destination Address (Alamat Tujuan)

(10)

Data-link

• Jika ukuran paket besar

• Jika ukuran paket kecil

Pengirim Penerima

Pengirim Penerima Asal

Tujuan

Asal

Tujuan

Pengirim Penerima

Asal

Tujuan

(11)

Physical Layer

• Hub, repeater

PC PC

0 1

(12)

Contoh

ALI INUL R1 DIDI

R2

R3 BUDI IPANG

(13)

Contoh

ALI INUL R1 DIDI

R2

R3 BUDI IPANG

YF YF YF YF ALI BUDI Peng irim Pene rima 202 205 101 102 103 202 205 405 600

502 606 608

(14)

Contoh

ALI INUL R1 DIDI

R2

R3 BUDI IPANG

YF YF YF YF ALI BUDI ALI BUDI Peng irim Pene rima 600 606 101 102 103 202 205 405 600

(15)

Internetwork

• An

internetwork

is a collection of individual

(16)

Local-area networks (LANs) evolved around the PC revolution. LANs enabled multiple users in a relatively small geographical area to

exchange files and messages, as well as access shared resources such as file servers and printers.

Wide-area networks (WANs) interconnect LANs with geographically

dispersed users to create connectivity. Some of the technologies used for connecting LANs include T1, T3, ATM, ISDN, ADSL, Frame Relay, radio links, and others. New methods of connecting dispersed LANs are

(17)

Internetworking Challenges

• Implementing a functional internetwork is

no simple task. Many challenges must be

faced, especially in the areas of

connectivity, reliability, network

(18)

Open System Interconnection

Reference Model

• The Open System Interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a

software application in another computer.

• The OSI reference model is a conceptual model composed of seven layers, each specifying particular network

functions.

• The model was developed by the International

Organization for Standardization (ISO) in 1984, and it is now considered the primary architectural model for

(19)

(20)

Open System Interconnection

Reference Model

• The seven layers of the OSI reference model can be

divided into two categories: upper layers and lower layers. • The upper layers of the OSI model deal with application

issues and generally are implemented only in software. The highest layer, the application layer, is closest to the end

user.

• The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are

implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network

(21)

(22)

OSI Model Physical Layer

• The physical layer defines the electrical,

mechanical, procedural, and functional

specifications for activating, maintaining, and

deactivating the physical link between

communicating network systems. Physical layer

specifications define characteristics such as

(23)

OSI Model Physical Layer

(24)

OSI Model Data Link Layer

• The data link layer provides reliable transit of data across a physical network link. Different data link layer specifications define different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control.

• Physical addressing (as opposed to network addressing) defines how devices are addressed at the data link layer.

• Network topology consists of the data link layer specifications that often define how devices are to be physically connected, such as in a bus or a ring topology.

• Error notification alerts upper-layer protocols that a transmission error has occurred, and the sequencing of data frames reorders frames that are transmitted out of sequence.

(25)

OSI Model Data Link Layer

• The Institute of Electrical and Electronics Engineers (IEEE) has subdivided the data link layer into two

sublayers: Logical Link Control (LLC) and Media Access

(26)

OSI Model Data Link Layer

• The Logical Link Control (LLC) sublayer of the data link layer manages communications between devices over a single link of a network.

• LLC is defined in the IEEE 802.2 specification and supports both

connectionless and connection-oriented services used by higher-layer protocols. IEEE 802.2 defines a number of fields in data link layer frames that enable multiple higher-layer protocols to share a single physical data link.

(27)

OSI Model Network Layer

• The network layer defines the network address,

which differs from the MAC address. Some

network layer implementations, such as the

Internet Protocol (IP), define network addresses in

a way that route selection can be determined

(28)

OSI Model Transport Layer

• The transport layer accepts data from the session layer and segments the data for transport across the network.

• Generally, the transport layer is responsible for making sure that the data is delivered error-free and in the proper sequence. Flow control generally occurs at the transport layer.

• Flow control manages data transmission between devices so that the transmitting device does not send more data than the receiving device can process.

(29)

OSI Model Session Layer

• The session layer establishes, manages, and terminates communication sessions.

• Communication sessions consist of service requests and service responses that occur between applications located in different network devices.

• These requests and responses are coordinated by protocols implemented at the session layer.

(30)

OSI Model Presentation Layer

• The presentation layer provides a variety of

coding and conversion functions that are applied

to application layer data.

• Common data representation formats, or the use of

standard image, sound, and video formats, enable

the interchange of application data between

different types of computer systems.

• Conversion schemes are used to exchange

(31)

• Standard data compression schemes enable

data that is compressed at the source device

to be properly decompressed at the

destination.

(32)

• Presentation layer implementations are not typically associated with a particular protocol stack. Some

well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG). QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for video compression and coding.

• Among the well-known graphic image formats are

Graphics Interchange Format (GIF), Joint Photographic Experts Group (JPEG), and Tagged Image File Format (TIFF). GIF is a standard for compressing and coding

(33)

OSI Model Application Layer

• The application layer is the OSI layer closest to the end user

• This layer interacts with software applications that implement a communicating component.

• Application layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication.

• Some examples of application layer implementations

(34)

OSI Model Application Layer

• When identifying communication partners, the application layer determines the identity and availability of

communication partners for an application with data to transmit.

• When determining resource availability, the application layer must decide whether sufficient network resources for the requested communication exist.

• In synchronizing communication, all communication

(35)

Information Formats

Data from Upper-Layer Entities Makes Up the Data Link Layer Frame

(36)

Information Formats

• A frame is an information unit whose source and

destination are data link layer entities.

• A packet is an information unit whose source and destination are network layer entities.

• The term datagram usually refers to an information unit whose source and destination are network layer entities that use connectionless network service.

• The term segment usually refers to an information unit whose source and destination are transport layer entities. • A message is an information unit whose source and

destination entities exist above the network layer (often at the application layer).

(37)

ISO Hierarchy of Networks

• Large networks typically are organized as

hierarchies. A hierarchical organization provides

such advantages as ease of management,

flexibility, and a reduction in unnecessary traffic.

• ISO has adopted a number of terminology

conventions for addressing network entities,

– end system (ES)

– intermediate system (IS),

(38)

• Typical ESs include such devices as terminals, personal computers, and printers.

• An IS performs routing or other traffic-forwarding functions, such devices as routers, switches, and bridges. Two types of IS networks exist: intradomain IS and interdomain IS. An intradomain IS

communicates within a single autonomous system, while an interdomain IS communicates within and between autonomous systems.

• An area is a logical group of network segments and their attached

devices. Areas are subdivisions of autonomous systems (AS's). An AS is a collection of networks under a common administration that share a common routing strategy. Autonomous systems are subdivided into areas, and an AS is sometimes called a domain.

(39)

(40)

Connection-Oriented and

Connectionless Network

• Connection-oriented services must first establish a connection with the desired service before passing any data. A connectionless service can send the data without any need to establish a connection first.

• Connection-oriented service involves three phases: connection establishment, data transfer, and connection termination

• Connection-oriented services must negotiate a connection, transfer data, and tear down the connection, whereas a connectionless transfer can simply send the data without the added overhead of creating and tearing down a connection.

(41)

LAN

(42)

LAN-Local Area Network

• A LAN

is a high-speed data network that covers a

relatively small geographic area. It typically

connects workstations, personal computers,

printers, servers, and other devices.

• LANs offer computer users many advantages,

including shared access to devices and

(43)

(44)

LAN Media-Access Methods

• two main ways:

– carrier sense multiple access collision detect (CSMA/CD)

– token passing

• CSMA/CD (Ethernet), when a device has data to send, it first listens to see if any other device is currently using the network. If not, it starts sending its data. After finishing its transmission, it listens again to see if a collision occurred. A collision occurs when two devices send data

(45)

LAN Media-Access Methods

(46)

LAN Transmission Methods

• LAN data transmissions fall into three

classifications: unicast, multicast, and broadcast.

• In a

unicast transmission, a single packet is sent

from the source to a destination on a network.

• A multicast transmission consists of a single data

packet that is copied and sent to a specific subset

of nodes on the network.

(47)

LAN Topologies

• LAN topologies define the manner in which

network devices are organized.

• Four common LAN topologies exist:

– bus, – ring, – star, – tree.

(48)

(49)

LAN Devices

• Devices commonly used in LANs include

– repeaters,

– hubs,

– LAN extenders,

– bridges,

(50)

WAN-wide-area network

• A WAN

is a data communications network that

covers a relatively broad geographic area and that

often uses transmission facilities provided by

common carriers, such as telephone companies.

• WAN technologies generally function at the lower

three layers of the OSI reference model: the

(51)

WAN-wide-area network

WAN

(52)

Point-to-Point Links

• A point-to-point link

provides a single,

(53)

Circuit Switching

•

Switched circuits allow data connections

that can be initiated when needed and

terminated when communication is

complete. This works much like a normal

telephone line works for voice

communication. Integrated Services Digital

Network (ISDN) is a good example of

(54)

(55)

Packet Switching

• Packet switching is a WAN technology in which users share common carrier resources.

• In a packet switching setup, networks have connections into the carrier's network, and many customers share the carrier's network. The carrier can then create virtual

circuits between customers' sites by which packets of data are delivered from one to the other through the network.

• Some examples of packet-switching networks include Asynchronous Transfer Mode (ATM), Frame Relay,

Switched Multimegabit Data Services (SMDS), and X.25. Figure

(56)

(57)

WAN Virtual Circuits

• A

virtual circuit

is a logical circuit created

within a shared network between two

network devices. Two types of virtual

circuits exist:

(58)

SVC

•

SVCs are virtual circuits that are

dynamically established on demand and

terminated when transmission is complete.

•

Communication over an SVC consists of

three phases:

–

circuit establishment,

–

data transfer, and

(59)

SVC

• The establishment phase involves creating

the virtual circuit between the source and

destination devices.

• Data transfer involves transmitting data

between the devices over the virtual circuit

• The circuit termination phase involves

(60)

PVC

•

PVC is a permanently established virtual

circuit that consists of one mode: data

(61)

Ethernet

(62)

Ethernet

• The term Ethernet _{refers to the family of local-area}

network (LAN) products covered by the IEEE 802.3 standard. Three data rates are currently defined for operation over optical fiber and twisted-pair cables:

• 10 Mbps—10Base-T Ethernet • 100 Mbps—Fast Ethernet

• 1000 Mbps—Gigabit Ethernet

(63)

Ethernet

Ethernet Network Topologies

and Structures

• LANs take on many topological configurations,

but regardless of their size or complexity, all will

be a combination of only three basic

interconnection structures or network building

blocks

• point-to-point interconnection

• coaxial bus structure, Segment lengths were limited to 500 meters, and up to 100 stations could be connected to a single segment

(64)

Ethernet

(65)

Ethernet

IEEE 802.3 to ISO

(66)

Ethernet

IEEE 802.3 to ISO

• The MAC-client sublayer may be one of the

following:

• Logical Link Control (LLC), if the unit is a DTE. This

sublayer 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.

(67)

Ethernet

IEEE 802.3 to ISO

MAC and Physical Layer

(68)

Ethernet

The Ethernet MAC Sublayer

• The MAC sublayer 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

(69)

Ethernet

Frame Format

IEEE 802.3 Data Frame Format

PRE 7 SOF 1 DA 6 SA 6 Type 2 Data 1500 FCS 4

Ethernet Data Frame Format Ethernet Data Frame Format

(70)

Ethernet

Frame Format

• Preamble (PRE)—Consists of 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 physical layers with the incoming bit stream. • Start-of-frame delimiter (SOF)—Consists of 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)—Consists of 6 bytes. The DA field

identifies which station(s) should receive the frame. The left-most bit in the DA field indicates whether the address is an individual address (indicated by a 0) or a group address (indicated by a 1). The second bit from the left indicates whether the DA is globally administered

(indicated by a 0) or locally administered (indicated by a 1). The

(71)

Ethernet

Frame Format

• Source addresses (SA)—Consists of 6 bytes. The SA field identifies the sending station. The SA is always an

individual address and the left-most bit in the SA field is always 0.

• Length/Type—Consists of 2 bytes (0600<=type-Eth, 0600>length-802.3).

– Ethernet menggunakan Type untuk menentukan protokol di atasnya, seperti IP(0800),IPX, dsb. Panjang data untuk Ethernet max, yaitu 1500 bytes (=05DC).

(72)

Ethernet

Ethernet Frame Format

• Data—Is a sequence of n _{bytes of any value, where}n _is

less than or equal to 1500. If the length of the Data field is less than 46, the Data field must be extended by adding a filler (a pad) sufficient to bring the Data field length to 46 bytes.

• Frame check sequence (FCS)—_{Consists of 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. The FCS is generated over the DA, SA,

(73)

Ethernet

Frame Transmission

Whenever an end station MAC receives a transmit-frame request with the accompanying address and data

information from the LLC sublayer, the MAC begins the transmission sequence by transferring the LLC information into the MAC frame buffer.

• The preamble and start-of-frame delimiter are inserted in the PRE and SOF fields.

• The destination and source addresses are inserted into the address fields.

• The LLC data bytes are counted, and the number of bytes is inserted into the Length/Type field.

• The LLC data bytes are inserted into the Data field. If the number of LLC data bytes is less than 46, a pad is added to bring the Data field length up to 46.

(74)

Ethernet

Half-Duplex Transmission—

The CSMA/CD Access Method

• Carrier sense—Each station continuously listens for traffic on the medium to determine when gaps between frame transmissions occur. • Multiple access—Stations may begin transmitting any time they

detect that the network is quiet (there is no traffic).

(75)

Token Ring

Token Ring/IEEE 802.5

(76)

Token Ring

(77)

Token Ring

(78)

Token Ring

Physical Connections

(79)

Token Ring

Token Ring Operation

• Token Ring and IEEE 802.5 are two principal examples of

token-passing networks (FDDI is the other). Token-token-passing networks move a small frame, called a token, around the network.

• Possession of the token grants the right to transmit. If a node receiving the token has no information to send, it passes the token to the next end station. Each station can hold the token for a maximum period of time • If a station possessing the token does have information to transmit, 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 to transmit, 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 (unless the ring supports early token release), which means that other stations wanting to transmit must wait. Therefore, collisions cannot occur in Token Ring networks. If early token release is

(80)

Token Ring

Priority System

• Token Ring networks use a sophisticated priority system that permits certain user-designated, high-priority stations to use the network more frequently. Token Ring frames have two fields that control priority: the priority field and the reservation field.

• Only stations with a priority equal to or higher than the priority value contained in a token can seize that token. After the token is seized and changed to an information frame, only stations with a priority value higher than that of the transmitting station can reserve the token for the next pass around the network. When the next token is generated, it

includes the higher priority of the reserving station. Stations that raise a token's priority level must reinstate the previous priority after their

(81)

Token Ring

Frame Format

• Token Ring and IEEE 802.5 support two basic frame types: • tokens

• data/command frames.

• Tokens are 3 bytes in length and consist of a start delimiter, an access control byte, and an end delimiter.

• Data frames carry information for upper-layer protocols

(82)

(83)

Token Ring

Token Frame Fields

• Start delimiter—Alerts each station of the arrival of a token (or

data/command frame). This field includes signals that distinguish the byte from the rest of the frame by violating the encoding scheme used elsewhere in the frame.

• Access-control byte—Contains the Priority field (the most significant 3 bits) and

the Reservation field (the least significant 3 bits), as well as a token bit (used to differentiate a token from a data/command frame) and a

monitor bit (used by the active monitor to determine whether a frame is circling the ring endlessly).

(84)

Token Ring

Data/Command Frame Fields

• Start delimiter—Alerts each station of the arrival of a token (or

data/command frame). This field includes signals that distinguish the byte from the rest of the frame by violating the encoding scheme used elsewhere in the frame.

• Access-control byte—Contains the Priority field (the most significant 3 bits) and

the Reservation field (the least significant 3 bits), as well as a token bit (used to differentiate a token from a data/command frame) and a

monitor bit (used by the active monitor to determine whether a frame is circling the ring endlessly).

(85)

Token Ring

Data/Command Frame Fields

• Destination and source addresses—Consists of two 6-byte address fields that identify the destination and source station addresses.

• Data—Indicates that the length of field is limited by the ring token holding time, which defines the maximum time a station can hold the token.

• Frame-check sequence (FCS)—Is filed by the source station with a calculated value dependent on the frame contents. The destination station recalculates the value to determine whether the frame was damaged in transit. If so, the frame is discarded.

• End Delimiter—Signals the end of the token or data/command frame. The end delimiter also contains bits to indicate a damaged frame and identify the frame that is the last in a logical sequence.

(86)

Frame Relay 1

Frame Relay

(87)

Frame Relay 2

Frame Relay

•

Frame Relay

is a high-performance WAN

protocol that operates at the physical and

data link layers of the OSI reference model.

• Frame Relay originally was designed for

(88)

Frame Relay 3

Packet Switching

• Frame Relay is based on packet-switched

technology.

• The following two techniques are used in

packet-switching technology:

(89)

Frame Relay 4

Frame Relay Devices

• Devices attached to a Frame Relay WAN fall into the following two general categories:

– Data terminal equipment (DTE)

– Data circuit-terminating equipment (DCE)

• Examples of DTE devices are terminals, personal computers, routers, and bridges.

• DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to provide clocking and

(90)

Frame Relay 5

(91)

Frame Relay 6

Frame Relay Virtual Circuits

• Frame Relay provides connection-oriented data link layer

communication.

• This service is implemented by using a Frame Relay virtual circuit, which is a logical connection created between two data terminal equipment (DTE) devices across a Frame Relay packet-switched

network (PSN).

• Virtual circuits provide a bidirectional communication path from one DTE device to another and are uniquely identified by a data-link

connection identifier (DLCI).

• A number of virtual circuits can be multiplexed into a single physical circuit for transmission across the network.

• A virtual circuit can pass through any number of intermediate DCE devices (switches) located within the Frame Relay PSN.

(92)

Frame Relay 7

Switched Virtual Circuits

• Switched virtual circuits (SVCs) are temporary

connections used in situations requiring only

sporadic data transfer between DTE devices across

the Frame Relay network.

• Call setup—The virtual circuit between two Frame Relay DTE devices is established.

• Data transfer—Data is transmitted between the DTE devices over the virtual circuit.

• Idle—The connection between DTE devices is still active, but no data is transferred. If an SVC remains in an idle state for a defined period of time, the call can be terminated.

(93)

Frame Relay 8

Switched Virtual Circuits

•

Few manufacturers

of Frame Relay DCE

equipment support switched virtual circuit

connections. Therefore, their actual deployment is

minimal in today's Frame Relay networks.

•

Previously not widely supported

by Frame

Relay equipment, SVCs are now the norm.

(94)

Frame Relay 9

Permanent Virtual Circuits

• Permanent virtual circuits (PVCs) are permanently

established connections that are used for frequent and consistent data transfers between DTE devices across the Frame Relay network.

• Communication across a PVC does not require the call setup and termination states that are used with SVCs.

• Data transfer—Data is transmitted between the DTE devices over the virtual circuit.

• Idle—The connection between DTE devices is active, but no data is transferred. Unlike SVCs, PVCs will not be terminated under any circumstances when in an idle state.

(95)

Frame Relay 10

Data-Link Connection

Identifier

• Frame Relay virtual circuits are identified by

data-link connection identifiers (DLCIs)

. DLCI values

typically are assigned by the Frame Relay service

provider (for example, the telephone company).

• Frame Relay DLCIs have local significance,

(96)

Frame Relay 11

Data-Link Connection

Identifier

(97)

Frame Relay 12

Congestion-Control

Mechanisms

• Frame Relay reduces network overhead by implementing simple congestion-notification mechanisms rather than explicit, per-virtual-circuit flow control.

• Frame Relay implements two congestion-notification mechanisms:

– Forward-explicit congestion notification (FECN) – Backward-explicit congestion notification (BECN)

• FECN and BECN each is controlled by a single bit contained in the Frame Relay frame header.

• The Frame Relay frame header also contains a Discard Eligibility (DE) bit, which is used to identify less

(98)

Frame Relay 13

Congestion-Control

Mechanisms

• The FECN bit is part of the Address field in the Frame Relay frame header.

• The FECN mechanism is initiated when a DTE device sends Frame Relay frames into the network.

If the network is congested, DCE devices (switches) set the value of the frames' FECN bit to 1. When the frames reach the destination DTE device, the Address field (with the FECN bit set) indicates that the frame experienced congestion in the path from source to destination. The DTE device can relay this

information to a higher-layer protocol for processing. Depending on the implementation, flow control may be initiated, or the indication may be ignored.

If the network is congested, DCE devices (switches) set the value of the frames' FECN bit to 1. When the frames reach the destination DTE device, the Address field (with the FECN bit set) indicates that the frame experienced congestion in the path from source to destination. The DTE device can relay this

(99)

Frame Relay 14

Congestion-Control

Mechanisms

• The BECN bit is part of the Address field in the Frame Relay frame header.

• DCE devices set the value of the BECN bit to 1 in frames traveling in the opposite direction of frames with their

FECN bit set.

• This informs the receiving DTE device that a particular path through the network is congested.

(100)

Frame Relay 15

Frame Relay Discard

Eligibility

• The DE bit is part of the Address field in the Frame Relay frame header.

• The Discard Eligibility (DE) bit is used to indicate that a frame has lower importance than other frames.

• DTE devices can set the value of the DE bit of a frame to 1 to indicate that the frame has lower importance than other frames.

(101)

Frame Relay 16

Frame Relay Error Checking

• Frame Relay uses a common error-checking

mechanism known as the cyclic redundancy check

(CRC).

• The CRC compares two calculated values to

determine whether errors occurred during the

transmission from source to destination.

• Frame Relay reduces network overhead by

(102)

Frame Relay 17

Frame Relay

Local Management Interface

• The Local Management Interface (LMI) is a set of enhancements to the basic Frame Relay specification

• The LMI global addressing extension gives Frame Relay (DLCI) values global rather than local significance. DLCI values become DTE addresses that are unique in the Frame Relay WAN.

• LMI virtual circuit status messages provide

communication and synchronization between Frame Relay DTE and DCE devices. These messages are used to

(103)

Frame Relay 18

Frame Relay Network

Implementation

• A common private Frame Relay network

implementation is to equip a T1 multiplexer with

both

Frame Relay

and

non-Frame Relay

interfaces.

• Frame Relay traffic is forwarded out the Frame

Relay interface and onto the data network.

• Non-Frame Relay traffic is forwarded to the

appropriate application or service, such as a

private branch exchange (PBX) for telephone

(104)

Frame Relay 19

(105)

Frame Relay 20

Public Carrier-Provided

Networks

• In public carrier-provided Frame Relay networks, the

Frame Relay switching equipment is located in the central offices of a telecommunications carrier.

• Subscribers are charged based on their network use but are relieved from administering and maintaining the Frame Relay network equipment and service.

• DCE equipment either will be customer-owned or perhaps will be owned by the telecommunications provider as a service to the customer. Generally, the DCE equipment also is owned by the telecommunications provider.

(106)

Frame Relay 21

Private Enterprise Networks

• More frequently, organizations worldwide are

deploying private Frame Relay networks.

• In private Frame Relay networks, the

administration and maintenance of the network are

the responsibilities of the enterprise (a private

company).

(107)

Frame Relay 22

Frame Relay Frame Formats

• Flags indicate the beginning and end of the frame. • Three primary components make up

the Frame Relay frame: the header and address area, the user-data portion, and the frame check sequence (FCS).

(108)

Frame Relay 23

Frame Relay Frame Formats

• Flags—Delimits the beginning and end of the frame. The value of this field is always the same and is represented either as the hexadecimal number 7E or as the binary number 01111110.

• Address—Contains the following information:

– DLCI

– Extended Address (EA)

– C/R

– Congestion Control

• (FECN)

• (BECN)

(109)

Frame Relay 24

• DLCI—The 10-bit DLCI is the essence of the Frame

Relay header. This value represents the virtual connection between the DTE device and the switch. Each virtual

connection that is multiplexed onto the physical channel will be represented by a unique DLCI. The DLCI values have local significance only, which means that they are unique only to the physical channel on which they reside. Therefore, devices at opposite ends of a connection can use different DLCI values to refer to the same virtual

(110)

Frame Relay 25

Frame Relay Frame Formats

(111)

Frame Relay 26

• C/R—The C/R is the bit that follows the most significant DLCI byte in the Address field. The C/R bit is not

currently defined.

• Congestion Control—This consists of the 3 bits that control the Frame Relay congestion-notification

(112)

Frame Relay 27

• Forward-explicit congestion notification (FECN) is a

single-bit field that can be set to a value of 1 by a switch to indicate to an end DTE device, such as a router, that

congestion was experienced in the direction of the frame transmission from source to destination. The primary benefit of the use of the FECN and BECN fields is the

capability of higher-layer protocols to react intelligently to these congestion indicators. Today, DECnet and OSI are the only higher-layer protocols that implement these

(113)

Frame Relay 28

Frame Relay Frame Formats

• Backward-explicit congestion notification (BECN) is a single-bit field that, when set to a value of 1 by a

switch, indicates that congestion was experienced in the network in the direction opposite of the frame

transmission from source to destination.

• Discard eligibility (DE) is set by the DTE device, such as a router, to indicate that the marked frame is of

lesser importance relative to other frames being transmitted. Frames that are marked as "discard

eligible" should be discarded before other frames in a congested network. This allows for a basic

(114)

Frame Relay 29

Frame Relay Frame Formats

•

Data

—Contains encapsulated upper-layer data.

Each frame in this variable-length field includes a

user data or payload field that will vary in length

up to

16,000 octets

. This field serves to transport

the higher-layer protocol packet (PDU) through a

Frame Relay network.

•

Frame Check Sequence

—Ensures the integrity

of transmitted data. This value is computed by the

source device and verified by the receiver to

(115)

Frame Relay 30

LMI Frame Format

• Flag—Delimits the beginning and end of the frame.

• LMI DLCI—Identifies the frame as an LMI frame instead of a basic Frame Relay frame. The LMI-specific DLCI

(116)

Frame Relay 31

LMI Frame Format

• Unnumbered Information Indicator—Sets the poll/final bit to zero.

• Protocol Discriminator—Always contains a value indicating that the frame is an LMI frame.

• Call Reference—Always contains zeros. This field currently is not used for any purpose.

• Message Type—Labels the frame as one of the following message types:

– Status-inquiry message—Allows a user device to inquire about the status of the network.

(117)

Frame Relay 32

LMI Frame Format

•

Information Elements

—Contains a variable

number of individual information elements (IEs).

IEs consist of the following fields:

– IE Identifier—Uniquely identifies the IE. – IE Length—Indicates the length of the IE. – Data—Consists of 1 or more bytes containing

encapsulated upper-layer data.

(118)

switching

Bridging and Switching

Yudhie Kurnia M.

Bridges and switches are data communications devices that operate

(119)

switching

Bridging and Switching

• Bridging and switching occur at the link layer, which controls data flow, handles transmission errors, provides physical (as opposed to logical) addressing, and manages access to the physical medium.

• Bridges and switches are not complicated devices. They analyze incoming frames, make forwarding decisions

based on information contained in the frames, and forward the frames toward the destination.

• Bridges are capable of filtering frames based on any Layer 2 fields. For example, a bridge can be programmed to

(120)

switching

Bridging and Switching

• Bridges are generally used to segment a LAN into a couple of smaller segments. Switches are generally used to segment a large LAN into many smaller segments.

• Bridges generally have only a few ports for LAN connectivity, whereas switches generally have many.

• Switches can also be used to connect LANs with different media—for example, a 10-Mbps Ethernet LAN and a 100-Mbps Ethernet LAN can be connected using a switch.

• Some switches support cut-through switching, which reduces latency and delays in the network, while bridges support only

store-and-forward traffic switching.

(121)

switching

Types of Bridges

•

Local bridges

provide a direct connection

between multiple LAN segments in the

same area.

(122)

switching

Types of Bridges

(123)

switching

Bridges

• Some bridges are

MAC-layer bridges, which bridge between homogeneous

networks (for example, IEEE 802.3 and IEEE 802.3),

• other bridges can translate between different link layer protocols (for

(124)

switching

Types of Switches

• Switches can use different forwarding techniques—two of these are store-and-forward switching and cut-through switching.

• In store-and-forward switching, an entire frame must be received before it is forwarded.

• Cut-through switching allows the switch to begin forwarding the frame when enough of the frame is received to make a

forwarding decision. This reduces the latency through the switch.

• Store-and-forward switching gives the switch the opportunity to evaluate the frame for errors before forwarding it.

(125)

switching

ATM Switch

•

Asynchronous Transfer Mode (ATM) switches

provide high-speed switching and scalable

bandwidths in the workgroup, the enterprise

network backbone, and the wide area.

• ATM switches support voice, video, and data

(126)

switching

ATM Switch

(127)

switching

LAN Switch

•

LAN switches

are used to interconnect

multiple LAN segments.

• LAN switching provides dedicated,

collision-free communication between

network devices, with support for multiple

simultaneous conversations.

(128)

switching

LAN Switch

(129)

Transparent Bridge 1

Transparent Bridging

(130)

Transparent Bridging

• Transparent bridges were first developed at Digital Equipment Corporation (Digital) in

the early 1980s.

• Work into the IEEE 802.1 standard. Transparent bridges are very popular in Ethernet/IEEE 802.3 networks.

• When transparent bridges are powered on, they learn the workstation locations by analyzing the source address of incoming frames from all attached networks.

• If a bridge sees a frame arrive on port 1 from Host A, the bridge concludes that Host A can be reached through the segment connected to port 1. Through this process,

(131)

Address Learning

• Host 1 (MAC: 00:00:8c:01:11:11) mengirim frame ke Host 3 (MAC:

00:00:8c:01:22:22)

• Switch menerima frame tersebut melalui port E0. Switch kemudian

[image:131.792.89.591.67.313.2]

(132)

Address Learning

• Switch tidak tahu di mana letak Host 3. Switch mem-broadcast ke semua port-nya

• Host 3 menerima frame tersebut, dan memberi jawaban (response) ke Host 1

• Switch menerima jawaban dari Host 3 yang ditujukan ke Host 1 via port E2. Switch kemudian mencatat bahwa Host 3 terletak di port E2 ke dalam tabelnya.

(133)

Operation

• The bridge uses its table as the basis for traffic forwarding. • When a frame is received on one of the bridge's interfaces,

the bridge looks up the frame's destination address in its internal table.

• If the table contains an association between the destination address and any of the bridge's ports aside from the one on which the frame was received, the frame is forwarded out the indicated port.

(134)

Virtual Circuit Switching

0 1 3 2 0 1 3 2 0 1 3 2 5 11 4 7 Switch 3 Host B Switch 2 Host A Switch 1

•Explicit connection setup (and tear-down) phase

•Subsequence packets follow same circuit

•Sometimes called connection-oriented model

(135)

Virtual Circuit Switching

• Connection setup

Untuk menyambungkan antara A dan B, NA menset suatu nilai VCI yang belum dipakai. Sebagai contoh,

VCI=5 diberikan untuk link dari A ke switch 1. VCI=11 untuk link dari switch 1 ke switch 2 VCI=7 untuk link dari switch 2 ke switch 3 VCI=4 untuk link dari switch 3 ke B

• Data Transfer

(136)

Datagram Switching

• No connection setup phase

• Each packet forwarded independently • Sometimes called connectionless model

0 1 3 2 0 1 3 2 0 1 3 2

(137)

Bridging Loops

• Without a bridge-to-bridge protocol, the transparent-bridge algorithm fails when multiple paths of bridges and local-area networks (LANs) exist between any two LANs in the internetwork

A

(138)

Bridging Loops

• Suppose that Host A sends a frame to Host B. Both bridges receive the frame and correctly learn that Host B is on

segment 2. Each bridge then forwards the frame onto segment 2.

• Host B will receive two copies of the frame (once from bridge 1 and once from bridge 2)

• Each bridge now believes that Host A resides on the same segment as Host B.

(139)

Bridging Loops

• Host A's initial frame is a broadcast. Both bridges forward the frames endlessly, using all available network

bandwidth and blocking the transmission of other packets on both segments.

• A loop implies the existence of multiple paths through the internetwork, and a network with multiple paths from

(140)

Spanning-Tree

• The spanning-tree algorithm (STA) was developed by

Digital Equipment Corporation, and published in the IEEE 802.1d specification.

• The STA designates a loop-free subset of the network's topology by placing those bridge ports that, if active, would create loops into a standby (blocking) condition. The STA uses a conclusion from graph theory as a basis for constructing a loop-free subset of the network's

topology. Graph theory states the following:

(141)

Spanning-Tree

• STA akan memilih satu bridge sebagai root di dalam network.

• The STA calls for each bridge to be assigned a unique identifier.

• Typically, this identifier is one of the bridge's MAC addresses, plus an administratively assigned priority. • Each port in every bridge also is assigned a unique

identifier (within that bridge), which is typically its own MAC address.

(142)

Spanning-Tree

Root bridge

Designated port

Root port A

B

S1

S2 A

B

(143)

Seleksi Root Bridge

• Komunikasi antar bridge menggunakan

BPDUs (Brige Protocol Data Units)

• Root bridge dipilih berdasarkan kombinasi

nilai priority dan MAC address. Jika dua

bridge mempunyai nilai pritoritas yang

sama, maka bridge dengan MAC address

lebih kecil akan dipilih sebagai root.

(144)

Seleksi Designated Port

• Untuk menentukan designated port, harus dilihat path cost-nya.

• STA cost adalah cost total berdasarkan pada bandwidth suatu link. 100 100 10 Mbps 10 19 100 Mbps 1 4 1 Gbps 1 2 10 Gbps

Original IEEE Cost New IEEE Cost

(145)

Spanning-Tree

• The spanning-tree calculation occurs when the bridge is powered up and whenever a topology change is detected.

• Configuration messages contain information identifying the bridge that is presumed to be the root (root identifier) and the distance from the sending bridge to the root bridge (root path cost).

• Configuration messages also contain the bridge and port identifier of the sending bridge, as well as the age of information contained in the configuration message.

Switch/Bridge

(146)

BPDU Frame Format

• Transparent bridges exchange configuration messages and

topology-change messages.

• Configuration messages are sent between bridges to establish a network topology.

(147)

Frame Format

• Protocol Identifier—Contains the value zero. • Version—Contains the value zero.

• Message Type—Contains the value zero.

• Flag—Contains 1 byte, of which only 2 bits are used. The topology-change (TC) least significant bit signals a

topology change. The topology-change acknowledgment (TCA) most significant bit is set to acknowledge receipt of a configuration message with the TC bit set.

• Root ID—Identifies the root bridge by listing its 2-byte priority followed by its

(148)

Frame Format

• Root Path Cost—Contains the cost of the path from the bridge sending the configuration message to the root

bridge.

• Bridge ID—Identifies the priority and ID of the bridge sending the message.

• Port ID—Identifies the port from which the configuration message was sent. This field allows loops created by

multiple attached bridges to be detected and handled.

• Message Age—Specifies the amount of time since the root sent the configuration message on which the current

(149)

Frame Format

• Maximum Age—Indicates when the current configuration message should be deleted.

• Hello Time—Provides the time period between root bridge configuration messages.

• Forward Delay—Provides the length of time that bridges should wait before transitioning to a new state after a

topology change. If a bridge transitions too soon, not all network links might be ready to change their state, and loops can result

Topology-change messages consist of only 4 bytes. These include a Protocol-Identifier field, which contains the

(150)

Contoh STA

• Dengan melihat MAC dan priority-nya, kita bisa tentukan bahwa root bridge

adalah 1900A

A

B

1900A

MAC: 0c:00:c8:11:00:00 Default priority: 32768

1900B

1900C

1900A 1900B 1900C 100BaseT 10BaseT Port 0 Port 0

Port 1 Port 1

(151)

Contoh STA

• Untuk menentukan root ports pada switch 1900B dan 1900C, harus diperhatikan cost-nya. Karena dua-duanya lewat port 0 terhubung jalur 100Mbps (yang adalah yang terbaik), maka port 0 pada 1900B adalah root port, dan port 0 pada 1900C adalah juga root port.

• Penentuan designated port. Semua port milik root bridge adalah designated port. Walaupun 1900B dan 1900C

mempunyai cost yang sama ke root bridge, designated port ditentukan pada 1900B, karena 1900B mempunyai ID

yang lebih kecil.

(152)

Contoh STA

A B Root Bridge MAC: 0c:00:c8:11:00:00 Default priority: 32768

MAC: 0c:00:c8:11:11:11

Default priority: 32768 MAC: 0c:00:c8:22:22:22_{Default priority: 32768}

1900A

1900B 1900C

100BaseT

10BaseT

Port 0, Designated port

Port 0, Root port

Port 1, Designated port Port 1, blocked Port 0, Root port

B _C

A B

(153)

Spanning Tree States

•

Blocking

, tidak mem-forward frame, tapi

mendengarkan BPDUs. (Jika switch baru saja on,

semua port dalam status blocking)

•

Listening

, mendengarkan BPDU

•

Learning

, mempelajari MAC address dan

membangun tabel filter/forwarding, tapi belum

mem-forward frame

(154)

Mode switch LAN

• Store and Forward. Suatu frame telah diterima lengkap di dalam buffer Switch, CRC dijalankan, dan alamat tujuan dilihat dari tabel untuk diteruskan

• Cut-through. Switch menerima alamat tujuan, melihat ke dalam tabelnya, kemudian berdasar tabel itu

memforwardkan frame.

• Fragment-free. Kadang disebut dengan modified Cut-through. Mencheck 64 bytes pertama (karena ada

(155)

IP Addressing

(156)

28 December 2009 IP Addressing 2

Host Addressing

12

2

7 1

12

10 7

11

3 7

1

Network 1

Network 2

(157)

Host Addressing

• Setiap host di dalam suatu network punya alamat (ID) yang unique

• Ada kemungkinan suatu host punya alamat yang sama dengan host lain tetapi berada di network yang berbeda

• Ada banyak jaringan. Setiap jaringan harus diberi ID (alamat) untuk membedakan antara jaringan yang satu dengan jaringan yang lain, jika jaringan-jaringan tersebut saling berhubungan. • Di dalam Jaringan Global, suatu host ada dua alamat:

– Alamat Jaringan (Network Address/Network Number)) – Alamat Host (Host Address/Host Number)

• ID suatu host secara global ditulis dengan cara : alamat network terlebih dahulu, diikuti dengan alamat host. Contoh:

3.12 -> 3 adalah alamat network

(158)

Host Addressing

1.12

1.2

1.7 1.1

2.12

2.10 2.7

2.11

3.3 3.7

3.1

Network 1

Network 2

Network 3

(159)

Biner ke Desimal

1 1 1 1 1 1 1 1

= 1.27 _{+ 1.2}6 _{+ 1.2}5 _{+ 1.2}4 _{+ 1.2}3 _{+ 1.2}2 _{+ 1.2}1 _{+ 1.2}0

= 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255

1 1 0 0 0 0 0 1

= 1.27 _{+ 1.2}6 _{+ 0.2}5 _{+ 0.2}4 _{+ 0.2}3 _{+ 0.2}2 _{+ 0.2}1 _{+ 1.2}0

(160)

IP Addressing

• Dipakai di Internet

• Pengalamatan IP berdasarkan IP versi 4 (IPv4)

• Setiap host mempunyai ID (Network Number dan Host Number) sebanyak 32 bit. Contoh:

1010 0011 1001 0000 1010 1010 0101 1000

Network Number Host Number

• Di seluruh dunia secara administratif ada 232 _alamat

internet, dikurangi dengan alamat broadcast dan lain-lain • Alamat sebanyak itu saat ini masih kurang. Penyelesaian:

(161)

IP Addressing

• Membaca bit biner terlalu sulit

• Alamat IP suatu host dibaca 8 bit demi 8 bit dan

setiap 8 bit tersebut dikonversi ke desimal

1010 0011 1001 0000 1010 1010 0101 1000

(162)

Klasifikasi Jaringan Internet

• Perancang Internet mengklasifikasi jaringan

berdasarkan pada ukuran jaringan

• Sekelompok kecil jaringan mempunyai

anggota host yang sangat banyak (Class A)

• Di lain pihak, banyak jaringan yang

(163)

(164)

• Contoh alamat IP suatu PC:

202.46.249.33

– Host dari jaringan klas C

– SubNet mask = 255.255.255.0

– Alamat Network (Network Number,NN) = 202.46.249.0

– Alamat Broadcast pada network tersebut (multicast_{) =}

202.46.249.255

(165)

Klasifikasi Jaringan Internet

• Subnet mask digunakan untuk mendapatkan Network Number dengan meng-AND kan dengan alamat IP suatu host

– Alamat IP = 1100 1010 0010 1110 1111 1001 0010 0001 202.46.249.33

– SubNet mask = 1111 1111 1111 1111 1111 1111 0000 0000 255.255.255.0

(166)

• Class A

(167)

• Class C

(168)

ipconfig

(169)

Alamat IP terpakai

Kegunaan Alamat

Private Network (Class C) 192.168.0.0 – 192.168.255.255

Private Network (Class B) 172.16.0.0 – 172.31.255.255

Private Network (Class A) 10.0.0.0 – 10.255.255.255

broadcast 255.255.255.255

Ke semua host dalam network ini (multicast)

HN semua 1 (202.46.249.255)

Maksudnya host ini HN semua 0 (202.46.249.0)

localhost 127.0.0.1

Maksudnya semua network NN semua 1 (255.255.53.5)

Maksudnya network ini atau segment ini

(170)

Subnetting

• Subnetting adalah membagi suatu network

menjadi sub-sub network yang lebih kecil

• Cara kerja subnetwork mirip dengan cara

kerja pada network, hanya pada skala yang

lebih kecil

(171)

Subnetting

• Hanya 8 bit yang tersedia untuk host klas C

• Subnet mask secara default untuk network class C adalah

= 255.255.255.0 0000 0000

1111 1111 1111 1111

1111 1111

• Subnet mask untuk subnetting bisa menjadi

(172)

Subnetting

• Sebagai contoh, kita ambil 255.255.255.192 subnetting

210.12.3.6 210.12.3.x

210.12.3.x

210.12.3.x 210.12.3.x

210.12.3.x 210.12.3.x 210.12.3.x

210.12.3.x

NN = 210.12.3.0 HN = 210.12.3.1 –

(173)

Subnetting

• Network klas C terdapat 254 host

• Subnetting x.x.x.192 = x.x.x.1100 0000

– 2 bit (11) untuk subnetting, terdapat = 22 _{–2 = 2 subnet. Bit semua}