Chapter 5 network and transport layers
Download
1 / 85

Chapter 5: Network and Transport Layers - PowerPoint PPT Presentation

Chapter 5: Network and Transport Layers Outlines Network Protocols and TCP/IP Networking Addressing Routing Network flow control and QoS Network Protocols and TCP/IP Transmission Control Protocol/ Internet Protocol (TCP/IP)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentation

Chapter 5: Network and Transport Layers

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 5: Network and Transport Layers


Outlines

  • Network Protocols and TCP/IP

  • Networking Addressing

  • Routing

  • Network flow control and QoS


Network Protocols and TCP/IP


Transmission Control Protocol/ Internet Protocol (TCP/IP)

The Transmission Control Protocol/ Internet Protocol (TCP/IP) was developed for the U.S. Dept of Defense’s Advanced Research Project Agency Network (ARPANET) in 1974.

TCP/IP allows reasonable efficient and error-free transmission.


TCP/IP

TCP/IP has two parts:

  • TCP - performs packetizing: TCP is only active at the sender and receiver.

  • IP - performs routing and addressing.

    A typical TCP packet has 192-bit (24-byte) header of control information.


TCP/IP

Two forms of IP are currently in use:

  • IPv4 also has a 192-bit (24-byte) header.

  • IPv6 has a 320-bit (40-byte) header.

    The primary reason for the increase in packet size is an increase in the address size from 32 bits to 128 bits, due to the dramatic growth in the usage of the Internet.

    The size of the message field depends on the data link layer protocol used. TCP/IP is commonly combined with Ethernet.


TCP Packet

1

2

3

4

5

6

7

8

9

10

11

User Data

1Source ID16 bits

2Destination ID16 bits

3Sequence number32 bits

4ACK number32 bits

5Header length4 bits

6Unused6 bits

7Flags6 bits

8Flow control16 bits

9CRC 1616 bits

10Urgent pointer16 bits

11Options16 bits


IP Packet version

IP4

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1Version number4 bits

2Header length4 bits

3Type of Service8 bits

4Total length16 bits

5Identifiers16 bits

6Flags3 bits

7Packet offset13 bits

8Hop limit8 bits

9Protocol8 bits

10 CRC 16 16 bits

11Source address32 bits

12Destination Address32 bits

13 Optionsvaries

14User datavaries

15Flow name24 bits

16Next header8 bits

IP6

1

15

4

16

8

11 (128 bits)

12 (128 bits)

14


*History of IPng Effort

  • By the Winter of 1992 the Internet community had developed four separate proposals for IPng. These were "CNAT", "IP Encaps", "Nimrod", and "Simple CLNP". By December 1992 three more proposals followed; "The P Internet Protocol" (PIP), "The Simple Internet Protocol" (SIP) and "TP/IX". In the Spring of 1992 the "Simple CLNP" evolved into "TCP and UDP with Bigger Addresses" (TUBA) and "IP Encaps" evolved into "IP Address Encapsulation" (IPAE).

  • By the fall of 1993, IPAE merged with SIP while still maintaining the name SIP. This group later merged with PIP and the resulting working group called themselves "Simple Internet Protocol Plus" (SIPP). At about the same time the TP/IX Working Group changed its name to "Common Architecture for the Internet" (CATNIP).

  • The IPng area directors made a recommendation for an IPng in July of 1994 [RFC 1752].

  • The formal name of IPng is IPv6


Why Need IPv6?

  • Internet Growth

    • Network numbers and size

    • Traffic management

  • Quality of Services (QoS)

  • Internet Transition

    • Routing

    • Addressing

  • No question that an IPv6 is needed, but when


Other Protocols

  • Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)

    • Developed by Xerox in the 1970s. It is primary network protocol used by Novell NetWare. Novell has replaced IPX/SPX with TCP/IP.

  • X.25

    • ITU-T’s standard for WAN. Mature standard. Seldom used in north America.

  • System Network Architecture (SNA)

    • IBM developed SNA in 1974. It is used on IBM’s mainframes. It is hard to integrate SNA with other networks.


The Message Field Size

Maximum Ethernet packet size = 1492

TCP message field

1492 - 24 (TCP header) - 24 (IPv4 header) = 1444


Addressing


Types of addresses

Address Example SoftwareExample Address

Application LayerWeb browserike.ba.ttu.edu

(also called domain name)

Network LayerTCP/IP129.118.49.189

Data Link LayerEthernet00-A0-C9-96-1D-90


Addressing

The network layer determines the best route through the network to the final destination.

Based on this routing, the network layer identifies the data link layer address of the next computer to which the message should be sent.


Assigning Addresses

In general, the data link layer address is permanently encoded in each network card, and as part of the hardware that cannot be changed.

Network layer addresses are generally assigned by software. Every network layer software package usually has a configuration file that specifies the network layer address for that computer.


Assigning Addresses

Application layer addresses (or server addresses) are also assigned by a software configuration file. Virtually all servers have an application layer address, but most client computers do not.

Network layer addresses and application layer addresses go hand in hand. ike.ba.ttu.edu - means 129.118.49.189 at the network layer.)


How IP Addresses Distributed

  • Internet Corporation for Assigned Names and Numbers (ICANN) oversees the Internet Assigned Numbers Authority (IANA) and controls how the Net's 4.29 billion IP addresses are used.

  • IANA distributes address space to three geographically diverse Regional Internet Registries (RIRs) and encourage three RIRs to operate so that addresses remain unique, are mapped efficiently, and are treated as a precious resource.

  • Three RIRs dole out available pools of IP based on a shared criteria. All deploy numerical address space to ISPs, local registries, and in some cases small users.


IP Address Allocation

IANA

InterNIC

America

RIPE

Europe

APNIC

Asia

National

Regional

Consumer


Three RIRs

  • American Registry for Internet Numbers (ARIN)

  • Reseaux IP Europeen (RIPE)

  • Asia Pacific Network Information Centre (APNIC)


Internet Addresses

InterNIC is responsible for network layer addresses (IP addresses) and application layer addresses or domain names (www.ttu.edu).

There are five classes of Internet addresses.

Classes A, B, and C are available to organizations

Class D and E are reserved for special purposes and are not assigned to organizations.


Internet Address Classes

  • Class A (/8 address)

    • The first digit is fixed, ranging 1-126 (01-7E), 16 million addresses

    • 127.x.x.x is reserved for loopback

  • Class B (/16 address)

    • First two bytes are fixed with the first digit ranging 128-191 (80-BF), 65,000 addresses.

  • Class C (/24 address)

    • First 3 bytes are fixed, with the first digit ranging 192-223 (C0-DF), 254 addresses.

  • Class D & E

    • The first digit is 224-239 (E0-EF) and 240-255 (F0-FF) respectively.

    • Reserved for special purposes and not available to organizations.


Internet Address Classes

Ranges of the first byte for different classes:

224 239

126

128

191

192 223

1

240 255

1/2

1/4

1/8

1/16

1/16

Class A

Class B

Class D Class E

Class C

Class A: 0xxxxxxx

Class B: 10xxxxxx.xxxxxxxx

Class C: 110xxxxx.xxxxxxxx.xxxxxxxx

Class D: 1110xxxx.xxxxxxxx.xxxxxxxx

Class E: 1111xxxx.xxxxxxxx.xxxxxxxx

Note:

The IP addresses with the first

byte as 0 and 127 are reserved


Internet Address Classes

# of Addresses

Class Available Addr-Structure Example Available#

Class A 16 millionFirst byte fixed50.x.x.x127

Organization assigns

last three bytes

Class B 65kFirst two bytes fixed128.192.x.x16k

Organization assigns

last two bytes

Class C 254First three bytes fixed192.1.56.x2 millions

Organization assigns

last byte


Internet Addresses

The Internet is quickly running out of addresses. Although there are more than 1 billion possible addresses, the fact that they are assigned in sets (or groups) significantly restricts the number of usable addresses.

The IP address shortage was one of the reasons behind the IPv6, providing in theory, 3.2 x 1038 possible addresses.

How to apply for IP address?


Subnets

Assign IP addresses to specific computers so that all computers on the same local area network have a similar address.

Each LAN that is logically grouped together by IP number is called a TCP/IP subnet.

Benefit:

  • allows it to be connected to the Internet with a single shared network address

  • an necessary use of the limited number of network numbers

  • Overload Internet routing tables on gateways outside the organization


Gateway

146.7.11.1

128.192.254.2


Subnet Mask

Subnet mask enables a computer to determine which computers are on the same subnet. This is very important for message routing.

E.g.

IP address: 129.118.49.189

Subnet mask:255.255.255.0

IP address: 129.118.49.x is for the computers in the same subnet


Subnet

Subnet with partial bytes addresses.

E.g. 129.118.49.1 to 129.118.49.126

  • Subnet mask: 255.255.255.128

  • Subnet address: 129.118.49.0

  • Subnet broadcast address: 129.118.49.127


Subnet

IP address:

129.118.49.1111000 0001.0111 0110.0011 0001.0110 1111

Subnet mask:

255.255.192.01111 1111.1111 1111.1100 0000.0000 0000

The IP prefix1000 0001.0111 0110.00

Destination IP:

129.118.51.2541000 0001.0111 0110.0011 0011.0110 1111

Destination IP:

128.83.127.11000 0000.0101 0011.0111 1111.0000 0001


128

192

192

224

224

240

240

248

248

252

252

254

255

Subnet Mask Template

Broadcast Address

150.1.0.0

255

255

0

0

Host Address

150

1

128 64 32 16 8 4 2 1

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

1 0 0 1 0 1 1 0

0 0 0 0 0 0 0 1

Network ID–Class B

128

Mask Numbers

Possible Subnet Address


Dynamic Addressing

An address assignment problem:

Each time the computer is moved, or its network is assigned a new address, the software on each individual computer must be updated.

Solution: dynamic addressing

With this approach, a server is designated to supply a network layer address to a computer each time the computer connects to the network.


Dynamic Addressing

Two standards for dynamic addressing are commonly used in TCP/IP networks:

  • Bootstrap Protocol (bootp) for dial-up networks (1985)

  • Dynamic Host Control Protocol (DHCP) for non-dial-up networks (1993)


Dynamic Addressing

The Bootp or DHCP server can be configured to assign the same network layer address to the computer each time it requests an address or it can lease the address to the computer by picking the “next available” network layer address from a list of authorized addresses.

Dynamic addressing greatly simplifies network management in non-dial-up networks too.


Address Resolution

Address resolution:

The sender translates the application layer address (or server name) of the destination into a network layer address; and in turn translates that into a data link layer address.

Two approaches used in TCP/IP:

  • Server address resolution

  • Data link layer address resolution.


Server Name Resolution

Domain Name Service (DNS)

Used for translating application layer addresses into network layer addresses.

InterNIC

Keeps the name and IP addresses of the name server that will provide DNS information for your address classes.


Domain Name System

  • 32-bit IP addresses have two drawbacks

    • Routers can’t keep track of every network path

    • Users can’t remember dotted decimals easily

  • Domain names address these problems by providing a name for each network domain (hosts under the control of a given entity)


*DNS Database

  • Hierarchical database containing name, IP address, and related information for hosts

  • Provides name-to-address directory services

  • Key features:

    • Variable-depth hierarchy. Unlimited levels

    • Distributed database. Scattered throughout the Internet and private intranet.

    • Distribution controlled by the database. Thousands of separately managed zones managed by separate administrators


Server Name Resolution

Server address resolution process:

  • TCP/IP sends a special TCP-level packet to the nearest DNS server asking for the requesting computer the IP address that matches the Internet address provided.

  • If the DNS does not have the answer for the request, it will forward the request to another DNS.

    This is why it sometimes takes a long time to access certain sites.

    IP addresses are then temporarily stored in a server address table.


Data Link Layer Address Resolution

In order to actually send a message, the network layer software must know the data link layer of the destination computer.

In the case of a distant computer, the network layer would route the message by selecting a path through the network that would ultimately lead to the destination.


Data Link Layer Address Resolution

The process:

  • TCP/IP software sends a broadcast message (using Address-Resolution-Protocol or ARP) to all computers in its subnet requesting the data link layer address.

  • The computer with the right IP address responds with its data link layer address

  • The message is sent to the destination computer


Routing


Routing

There are many possible routes or paths a message can take to get from one computer to another.

Routing

The process of determining the route or path through the network that a message will travel from the sender to the receiver.

Routing table

The routing information on each router, which specifies how message will travel through the network.

Types of routing:

Centralized routing

Decentralized routing: Static routing, Dynamic routing


Routing


Routing Table for Computer B

Destination Route

AA

CC

DA

EE

FE

GC


Static Routing

  • Static Routing

    • The routing table is developed by the network manager, and changes are made only when computers are added or removed from network.


Dynamic Routing

Dynamic Routing (adaptive routing)

  • An initial routing table is developed by the network manager, but is continuously updated by the computers themselves to reflect changing network conditions, such as network traffic.

  • Used when there are multiple routes through a network and it is important to select the best (or fastest) route, in order to route messages away from traffic on busy circuits.


Dynamic Routing

Commonly used dynamic routing protocols

  • Routing Information Protocol (RIP) - used by the network manager to develop the routing table.

  • Border Gateway Protocol (BGP). A dynamic exterior routing protocol for the Internet.

  • Internet Control Message Protocol (ICMP) - used on the internet with TCP/IP.

  • Open Shortest Path First (OSPF) uses the number of computers in a route as well as network traffic and error rates to select the best route.

  • Enhanced Interior Gateway Routing Protocol (EIGRP) – a dynamic link state interior routing protocol and commonly used inside an organization.


Dynamic Routing

Routing Information Protocol (RIP)

  • When new computers are added, it counts the number of computers in the possible routes to the destination and selects the rout with the least number.

  • Computers using RIP send broadcast messages every minute or so to announce routing state.

  • It is used by TCP/IP and IPX/SPX.


Dynamic routing

  • Border Gateway Protocol (BGP)

    • A dynamic routing protocol used on the Internet to exchange routing information between autonomous systems – the large sections of the Internet. It is seldom used inside companies

    • Large, complex and hard to administer


Dynamic Routing

Internet Control Message Protocol (ICMP)

  • Uses both broadcast messages and the messages to specific computers to exchange routing information

  • Only used by TPC/IP


Dynamic Routing

Open Shortest Path First (OSPF)

  • More efficient than RIP because it normally doesn’t use broadcast messages. Instead it selectively sends status update messages directly to selected computers

  • Used by TCP/IP


Dynamic routing

  • Enhanced Interior Gateway Routing Protocol (EIGRP)

    • A dynamic link state interior routing protocol developed by CISCO

    • Commonly used inside an organization

    • Computers/routers store their own routing table and their neighbors’ routing tables


Dynamic Routing

Two drawbacks to Dynamic Routing.

  • It requires more processing by each computer in the network than centralized or static routing.

  • The transmission of status information “wastes” network capacity.


Connectionless vs. Connection-Oriented Routing

Two ways a group of packets can be routed:

  • Connectionless routing

    • Each packet is treated separately and makes its own way through the network.

  • Connection-Oriented routing

    • Sets up a virtual circuit between the sender and receiver. Appears to use point-to-point circuit-switching, but actually uses store-and-forward.

    • Has greater overhead than connectionless, due to the routing information.


Connectionless vs. Connection-Oriented Routing

Virtual Circuit

  • Appears to the application software to use a point-to-point circuit

  • The network layer makes one routing decision and all packets follow the same route


Connectionless vs. Connection-Oriented Routing

TCP/IP vs. UPD/IP

  • TCP/IP is used for connection-oriented routing

    • TCP establishes the virtual circuit and IP routes the messages.

  • UDP/IP is used for connectionless routing

    • The TCP packet is replaced with a User Datagram Protocol (UDP) packet.


Multicast

Unicasting

The usual transmission between two computers.

Broadcasting

Sending messages to all computers on a LAN or subnet.

Multicasting

Sending the same message to a group of computers temporarily in a class D IP address.


Broadcast

Individual

transfers

Clients

Host


Multicast

Could be one packet that all receive or

replicated by routers in the network

Data replicated

by the network

Clients

Host

Multicast

Infrastructure

One transfer


Multicast

Computers wishing to participate in a multicast send a message to the sending computer or some other computer performing routing along the way using a special type of TCP-level packet called Internet Group Management Protocol (IGMP).

Each multicast group is temporarily assigned a special Class D IP address to identify the group, thus allowing a restricted broadcast of messages to this specific group.


*TCP/IP

Application

Presentation

Session

TELNET FTP SMTP DNS SNMP DHCP

RIP

RTP

RTCP

Transmission

Control Protocol

User Datagram

Protocol

Transport

OSPF

ICMP

IGMP

Internet Protocol

Network

ARP

Data link

Physical

Ethernet

Token Bus

Token Ring

FDDI


Flow control and QoS


Quality of Service

Quality of Service (QoS):

  • The idea that transmission quality (rates, error rates, bandwidth and jitter) can be measured, improved, and, to some extent, guaranteed in advance.

    QoS routing:

  • A special type of connection-oriented dynamic routing in which different messages or packets are assigned different priorities.


Categories of Traffic

  • Elastic traffic, such as FTP, email, etc

    • Allow fluctuating bandwidth, the total transmission time is important

    • The data must correctly transmitted

    • Service quality concerns mainly in transmission delay and error control.

  • Real-time traffic, such as videoconferencing.

    • Demands certain bandwidth with isochronous features

    • Tolerates some level of errors.

    • Service quality criteria include: Throughput, Delay, Delay variation (jitter), and Packet loss.


Routing at Routers

  • Bandwidth schedule

    • First in first out

    • Round robin

    • Prioritization

  • Queue management

    • Packet discard policy

    • Congestion control

Packet arrival

Packet forward

Packet Drop


Network Congestion

  • What is traffic congestion?

    • The buffer in a forwarding device overflows. This results packet losses and incur retransmission. The transmission will worsen the situation.

  • Network congestion control is very important in flow management


Internet Flow Control

  • Internet flow control algorithm

    • Slow start, congestion avoidance

  • Router queue management

    • Random early detection (RED) for packet dropping

  • Data flow scheduling

    • FIFO, round robin, priority queueing, weighted fair queueing


Internet Flow Control

  • Slow Start algorithm (RFC2001). To avoid router running out of space

    • Two windows: advertised window by receiver and congestion window by sender. The congestion window is flow control imposed by the sender, while the advertised window is flow control imposed by the receiver.

    • The congestion window is initialized to one segment. Each time an ACK is received, the congestion window is increased by one segment. The sender can transmit up to the minimum of the congestion window and the advertised window.

    • The sender starts by transmitting one segment and waiting for its ACK. When that ACK is received, the congestion window is incremented from one to two, and two segments can be sent.

    • When each of those two segments is acknowledged, the congestion window is increased to four. This provides an exponential growth.

    • At some point the capacity of the internet can be reached, and an intermediate router will start discarding packets. This tells the sender that its congestion window has gotten too large.


Internet Flow Control

  • Congestion Avoidance (RFC2001)

    • Sets congestion window to one segment.

    • When congestion occurs (indicated by a timeout or the reception of duplicate ACKs), one-half of the current window size (the minimum of congestion window and the receiver's advertised window, but at least two segments) is saved as X.

    • When new data is acknowledged by the other end, increase congestion window, but the way it increases depends on whether TCP is performing slow start or congestion avoidance. If congestion window is less than or equal to X, TCP is in slow start; otherwise TCP is performing congestion avoidance.

    • Slow start continues until TCP is halfway to where it was when congestion occurred (since it recorded half of the window size that caused the problem in step 2), and then congestion avoidance takes over.

    • Congestion avoidance dictates that congestion window be incremented a linear growth of congestion window, compared to slow start's exponential growth.


Internet transmission services

  • Best-effort services

    • The Internet treats all packet equally.

  • Integrated services (IntServ)

    • IntServ refers to mechanisms that enable users to request a particular QoS for a flow of data.

  • Differentiated Services (DiffServ)

    • DiffServ Use type-of-service in IPv4 header to indicate the required service quality.


Integrated Services

  • Routers require additional functionality to handle QoS-based service

  • IETF is developing suite of standards to support this

  • Two standards have received widespread support

    • Integrated Services Architecture (ISA): To enable the provision of QoS support over IP-based Internet.

    • Resource ReSerVation Protocol (RSVP)


Integrated Services Architecture

  • Enables provision of QoS over IP-networks

  • Features include

    • Admission Control: A new flow needs a reservation for QoS

    • Routing Algorithm: more parameters are considered other than just delay

    • Queuing Discipline: Queuing policy takes into account of different requirements

    • Discard Policy: Particularly for congestion management


*Resource Reservation Protocol (RSVP)

  • A tool for prevention of congestion through reservation of network resources

  • Can be used in unicast or multicast transmissions

  • Receivers (not senders) initiate resource reservations

  • Operation:

    • Complexity is in multicast transmission

    • RSVP uses two basic messages: Resv and Path. In multicast, Resv messages generated by one of the multicast group receivers propagate upstream through distribution tree and create soft state in routers. Once it reaches the sender, hosts are enabled to set parameters for the first hop. Path is used to provide upstream routing information and sent from senders via the down stream tree to all receivers


Differentiated Services (DiffServ)

  • Provides QoS based on user group needs rather than traffic flows

  • Can use current IPv4 octets

  • Service-Level Agreements (SLA) govern DiffServ, eliminating need for application-based assignment


IPv4 Type of Service Field

  • Allows user to provide guidance on individual datagrams

  • 3-bit precedence subfield

    • Indicates degree of urgency or priority

    • Queue Service & Congestion Control

  • 4-bit TOS subfield

    • Provides guidance on selecting next hop

    • Route selection, Network Service, & Queuing Discipline

1

2

3

4

5

6

7

0

Precedence

TOS

0


DiffServ Domains

Border component

Host

Host

Interior component


DiffServ Operation

  • Routers are either boundary nodes or interior nodes

  • Interior nodes use per-hop behavior (PHB) rules

  • Boundary nodes have PHB & traffic conditioning


Token Bucket Scheme

Max Burstiness:

RT + B

R: Token replenishment rate

B: Bucket size


TCP/IP Configuration Information

At least four pieces of information needed for a client computer TCP/IP configuration

  • IP address

  • Subnet mask

  • Gateway IP address

  • Domain name Server IP address


A TCP/IP Example


A TCP/IP Example

  • How a client access a web server in the same subnet with a known address?

  • How a client access a web server in a different subnet with a known address?

  • How a client access a web server in the same subnet with an unknown address?


Sender

Receiver

Application

Layer

Application

Layer

HTTP

Request

HTTP

Request

Transport

Layer

Transport

Layer

TCP

HTTP

Request

TCP

HTTP

Request

Network

Layer

Network

Layer

IP

TCP

HTTP

Request

IP

TCP

HTTP

Request

Data Link

Layer

Data Link

Layer

Ethernet

IP

TCP

HTTP

Request

Ethernet

IP

TCP

HTTP

Request

Physical

Layer

Physical

Layer


Data transmission using TCP/IP and Ethernet

Ethernet

packet header

IP

packet

TCP

packet

HTTP

packet

User Data

Ethernet

packet trailer

IP address

Data link layer address


ad
  • Login