Section 6 Networking Protocols

Communications

Networking Protocols

Professor Izhak Rubin

Electrical Engineering Department

UCLA

[email protected]

© 2014-2015 by Professor Izhak Rubin

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Layered Communications

Networking Protocol Structure

Each layer provides a well defined targeted service

Ordering: a layer provides a service to the layer above it and receives a service from the layer below it

Intelligent message operations/processing between layer-i peer entities

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PDUs and SDUs

Protocol Data Unit (PDU) – a message unit as it is intelligently processed (and understood) by peer layer entities Layer i PDU is intelligently understood and processed by

layer i entities

Service Data Unit (SDU) – a message entities, accompanied by primitives (directives) that is transacted between neighboring layers Such transactions can involve an acknowledging

handshake

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Layer Services and Interfaces

N-service provider

(N-1)- service provider

N – service Entity

N – service Entity

N – service User

N – service User

N-service access points (SAPs)

N-service protocol

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Interlayer Communications

Primitives for Confirmed Services

Requesting user Accepting user

Service request

Service confirmation

Service indication

Service response

time

Confirmed services consist of four primitives

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The Open Systems Interconnect

(OSI) Reference Model

Application L7

Presentation L6

Session L5

Transport L4

Network L3

Link L2

Physical L1

Application

Session

Transport

Network

Link

Physical

Presentation

Network

Link

Physical

Network

Link

Physical

L3 Packet, routing

Frame, link level Error and flow control

Symbol, Signal; mechanical and electrical Ifs and Transmission Comm

User

Ex: compression. encryption, conversion

Notes (and service examples):

ETE Multiplexing, error And flow controls

Ex: connection dialogue rules and sync.

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Layer 7: Application layer

The application layer is the seventh level of the seven-layer OSI model. It interfaces directly to and performs common application services for the application processes; it also issues requests to the presentation layer. Note carefully that this layer provides services to user-defined application processes, and not to the end user. For example, it defines a file transfer protocol, but the end user must go through an application process to invoke file transfer. The OSI model does not include human interfaces.

The common application services sublayer provides functional elements including the Remote Operations Service Element (comparable to Internet Remote Procedure Call), Association Control, and Transaction Processing (according to the ACID requirements).

Above the common application service sublayer are functions meaningful to user application programs, such as messaging (X.400), directory (X.500), file transfer (FTAM), virtual terminal (VTAM), and batch job manipulation (JTAM).

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Layer 6: Presentation layer

The Presentation layer transforms the data to provide a standard interface for the Application layer. MIME encoding, data encryption and similar manipulation of the presentation are done at this layer to present the data as a service or protocol developer sees fit. Examples of this layer are converting an EBCDIC-coded text file to an ASCII-coded file, or serializing objects and other data structures into and out of XML.

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Layer 5: Session layer

The Session layer controls the dialogues/connections (sessions) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for either full-duplex or half-duplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. The OSI model made this layer responsible for "graceful close" of sessions, which is a property of TCP, and also for session checkpointing and recovery, which is not usually used in the Internet protocols suite.

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Layer 4: Transport layer

The Transport layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers.

The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control.

Some protocols are state and connection oriented. This means that the transport layer can keep track of the segments and retransmit those that fail.

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Transport layer (Cont.)

The best known example of a layer 4 protocol is the Transmission Control Protocol (TCP).

The transport layer is the layer that converts messages into TCP segments or User Datagram Protocol (UDP), Stream Control Transmission Protocol (SCTP), etc. packets.

Perhaps an easy way to visualize the Transport Layer is to compare it with a Post Office, which deals with the dispatch and classification of mail and parcels sent.

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Transport layer (Cont.)

Do remember, however, that a post office

manages the outer envelope of mail. Higher

layers may have the equivalent of double

envelopes, such as cryptographic Presentation

services that can be read by the addressee only.

Roughly speaking, tunneling protocols operate at

the transport layer, such as carrying non-IP

protocols such as IBM's SNA or Novell's IPX over an

IP network, or end-to-end encryption with IPsec.

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Layer 3: Network layer

The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport layer.

The Network layer performs network routing functions, and might also perform fragmentation and reassembly, and report delivery errors.

Routers operate at this layer—sending data throughout the extended network and making the Internet possible.

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Network layer (Cont.)

This is a logical addressing scheme – values are chosen by the network engineer.

The addressing scheme is hierarchical.

The best known example of a layer 3 protocol is the Internet Protocol (IP).

Perhaps it's easier to visualize this layer as managing the sequence of human carriers taking a letter from the sender to the local post office, trucks that carry sacks of mail to other post offices or airports, airplanes that carry airmail between major cities, trucks that distribute mail sacks in a city, and carriers that take a letter to its destinations.

Think of fragmentation as splitting a large document into smaller envelopes for shipping, or, in the case of the network layer, splitting an application or transport record into packets.

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Layer 2: Data Link layer

The Data Link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical layer.

The best known example of this is Ethernet.

This layer manages the interaction of devices with a shared medium. (MAC sub-layer)

Other examples of data link protocols are HDLC and ADCCP for point-to-point or packet-switched networks and Aloha for local area networks.

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Data Link layer (Cont.)

On IEEE 802 local area networks, and some non-IEEE 802 networks such as FDDI, this layer may be split into a Media Access Control (MAC) layer and the IEEE 802.2 Logical Link Control (LLC) layer.

It arranges bits from the physical layer into logical chunks of data, known as frames.

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Data Link layer (Cont.)

This is the layer at which the bridges

and switches operate.

Connectivity is provided only among

locally attached network nodes

forming layer 2 domains for unicast or

broadcast forwarding.

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Data Link layer (Cont.)

The data link layer might implement a sliding window flow control and acknowledgment mechanism to provide reliable delivery of frames;

that is the case for SDLC and HDLC, and derivatives of HDLC such as LAPB and LAPD.

Only error detection, not flow control using sliding window, is present in modern data link protocols such as Point-to-Point Protocol (PPP),

On local area networks, the IEEE 802.2 LLC layer is often not used for most protocols on Ethernet, and, on other local area networks, its flow control and acknowledgment mechanisms are rarely used.

Sliding window flow control and acknowledgment is used at the transport layers by protocols such as TCP.

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Layer 1: Physical layer

The Physical layer defines all the electrical and physical specifications for devices.

In particular, it defines the relationship between a device and a physical medium.

This includes the layout of pins, voltages, and cable specifications.

Hubs, repeaters, network adapters and Host Bus Adapters (HBAs used in Storage Area Networks) are physical-layer devices.

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Physical layer (Cont.)

To understand the function of the physical layer in contrast to the functions of the data link layer, think of the physical layer as concerned primarily with the interaction of a single device with a medium, where the data link layer is concerned more with the interactions of multiple devices (i.e., at least two) with a shared medium.

The physical layer will tell one device how to transmit to the medium, and another device how to receive from it, but not, with modern protocols, how to gain access to the medium.

Older physical layer standards such as RS-232 do use physical wires to control access to the medium.

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Physical layer (Cont.)

The major functions and services performed by the physical layer are:

* Establishment and termination of a connection to a communications medium.

* Participation in the process whereby the communication resources are effectively shared among multiple users. For example, contention resolution and flow control.

* Modulation, or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and fiber optic) or over a radio link.

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Physical layer (Cont.)

Parallel SCSI buses operate in this layer, although it must be remembered that the logical SCSI protocol is a transport-layer protocol that runs over this bus.

Ethernet incorporates both this layer and the data-link layer.

The same applies to other local-area networks, such as Token ring, FDDI, and IEEE 802.11, as well as personal area networks such as Bluetooth.

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Information Flow in a Layered system in a

datagram packet switching network

L7 PDU L7

L6 PDU L6

L5 PDU L5

H4 M L4

H3 H4 M L3

H2 H3 H4 M T2

L2

Physical L1 Physical

H2 H3 H4 M T2

Physical Physical

H2 H3 H4 M T2

H2 H3 H4 M T2

H3 H4 M H3 H4 M H3 H4 M

H4 M

L5 PDU

L6 PDU

L7 PDU

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X.21 Digital Interface

DTE DCE

T (Transport)

C (Control)

R (Receive)

I (Indication)

S (Signal, Bit Timing)

B (Byte Timing, Optional)

GA (DTE Common Return)

G (Ground)

Specification for DTE to DCE call setup and clearance (1976)

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Data Link Control Protocols

Link layer communications

Typical services: SAP, Error control, flow control, sequencing

Protocol types:

Asynchronous (e.g., teletype, RS232C)

Synchronous character oriented (e.g., BSC)

Synchronous bit oriented (e.g., SDLC, HDLC, X.25, LAP, LAPB and other)

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Full Duplex Data Link Control such as: SDLC, HDLC, LAP

Frame types (e.g., SDLC)

Information frame

Supervisory command frame

Non-sequenced format frame

Illustrative Information Frame format:

Flag Address Control Text (payload) Check Seq. Flag

8 bits 8 bits 8 bits variable 8,16,32 bits 8 bits

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DLCP: Control Field

ARQ (Go Back N) Error control oriented

control field:

Send count (3 bits) = sequence number for

sent frame

Receive count (3 bits) = sequence number

of next frame expected to receive

Piggyback batch ACK

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Network Layer Services:

Datagram vs. Virtual Circuit

Initial Setup:

Datagram: None

VCS: Employed

Destination address:

Datagram: Required in every packet

VCS: used during connection setup phase

Error handling:

Datagram: Performed by host

VCS: Performed by network; transparent to host

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Datagram vs. Virtual Circuit

(Cont.)

End-to-end flow control:

Datagram: Not provided by network

VCS: Provided by network

Packet Sequencing:

Datagram: messages passed to host in order of

arrival

VCS: messages delivered to host in order sent

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Datagram vs. Virtual Circuit

(Cont.)

Datagram service features: rapidly adaptive

dynamic inter-networking across multiple

sub-network types; fast packet re-routing in

reacting to changes

VCS features: traffic engineering, QoS

guarantees to flows across connections,

dynamic network management through flow

admission control

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X.25 DTE-DCE Interface

X.25: DTE-DCE interface with public packet switching networks

Specifications at layers 1, 2 and 3

Principal layer 3 service: Virtual circuit switching

Signaling system for establishment of Logical Channel connections (LCI)

Secondary service: fast select datagram.

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X.25 PDUs

Flag ADDR Control Data Packet FSC Flag

N(R) P N(S) Q

Q D 0 1 LCGN LCN P(R) M P(S) Q DATA

Data Packet Seq. #

Data Packet Authorization

DLC Frame

DATA PACKET

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X.25: Signaling

Connection establishment phase: Call request packet (at calling DTE/DCE interface)

Incoming call packet (at called DTE/DCE interface)

Call accepted packet (at called DTE/DCE interface)

Call connected packet (at calling DTE/DCE interface)

Disconnect phase: Clear request packet (at interface A)

Clear indication packet (at interface B)

Clear confirmation packet (at interface B)

Clear confirmation packet (at interface A)

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Call Request Packet

Call request packet fields include:

Logical channel ID

Type = call request

Calling DTE Address Length

Called DTE Address Length

DTE Address

Facility field length

Facility field

User data

Local Area Networks

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Features

Single organization

Broadband communications

Initially: data based

Simplified switching and routing based on topological layout regularity

Star topology

Central switch; switched Ethernet; shared medium switch (backend bus system); shared memory; space switching

Bus medium and topology; passive connection to shared medium; physical layer broadcast

Ring medium; active RIU insertions; point-to-point connections of RIUs

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LAN topologies

Star Topology

Bus Topology

Ring Topology

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LAN Communications Layers

Network

Logical Link Control (LLC)

Medium Access Control (MAC)

PHY

PMD

Link

Physical

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Ethernet Frame

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Ethernet frame types

Ethernet frame types and the EtherType field

There are several types of Ethernet frames:

•The Ethernet Version 2 or Ethernet II frame, the so-called DIX frame (named after DEC, Intel, and Xerox);

this is the most common today, as it is often used directly by the Internet Protocol.

• Novell's homegrown variation of IEEE 802.3 ("raw 802.3 frame") without IEEE 802.2 LLC

• IEEE 802.2 LLC frame

• IEEE 802.2 LLC/SNAP frame

• In addition, Ethernet frames may optionally contain a IEEE 802.1Q tag to identify what VLAN it belongs to

and its IEEE 802.1p priority (quality of service). This doubles the potential number of frame types.

• The different frame types have different formats and MTU values, but can coexist on the same physical

medium.

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The most common Ethernet Frame

format: type II

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Internet Architecture and

Protocols

IEEE 802.2, PPP, LAPB, Ethernet, RS232, 802.3, 802.5 Physical/

Link Layer

ARP IP RARP

Type Code

Internet

Layer

Transport

Layer

Upper

Layer

Protocol Number

IGPs

(OSPF)

EGP TCP UDP ICMP IGMP

BGP RIP Port Number

TELNET, FTP, TFTP, BOOTP, HTTP, SNMP, SMTP

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Connectionless Datagram

Networking: The IP Datagram

Datagram Header Data

0 4 8 16 31

VERS LEN TYPE OF SERVICE TOTAL LENGTH

IDENT FLAGS FRAGMENT OFFSET

TIME PROTO HEADER CHECKSUM

SOURCE IP ADDRESS

DESTINATION IP ADDRESS

OPTIONS PADDING

DATA . . .

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IPv6: The Header

Ver. Prio. Flow Label

Payload Length Next Header Hop Limit

Source Address

Source Address

Source Address

Destination Address

Destination Address

Destination Address

Destination Address

Source Address

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TCP Segment Format

0 4 8 16 31

SOURCE PORT DESTINATION PORT

OPTIONS PADDING

DATA . . .

. . .

DATA . . .

SEQUENCE NUMBER

ACKNOWLEDGEMENT NUMBER

OFF. RES. CODE WINDOW

CHECKSUM URGENT POINTER