06_tm3110eu01tm_0002_ip

IP Internet Protocol for GPRS Siemens

TM3110EU01TM_00021

Contents

1 Generalities 3

2 IP-Datagram Structure 11

3 Exercise 37

4 Solution 41

IP Internet Protocol for GPRS

Siemens IP Internet Protocol for GPRS

TM3110EU01TM_00022


TM3110EU01TM_00023

1 Generalities


TM3110EU01TM_00024

The Internet Protocol (IP) is designed for the use in interconnected systems ofpacket-switched computer communication networks. IP provides services fortransmitting blocks of datagrams from sources to destinations, where sources anddestinations are hosts identified by addresses of fixed length. IP also provides basicfacilities for fragmentation and reassemble of long datagrams and type of service,which means the quality of service of the data transmission. The two basic functionsof IP are addressing and fragmentation.

The internet modules on a transmission path use the addresses carried in theinternet header to transmit internet datagrams toward their destinations. Theselection of a path for transmission is called routing. The internet modules use fieldsin the internet header to fragment and reassemble internet datagrams whennecessary for transmission through "small packet" networks. The model of operationis that an internet module resides in each host engaged in internet communicationand in each gateway that interconnects networks. These modules share commonrules for interpreting address fields and for fragmenting and assembling internetdatagrams. In addition, these modules (especially in gateways) have procedures formaking routing decisions and other functions.

IP treats each internet datagram as an independent entity unrelated to any otherinternet datagram. There are no connections or logical circuits (virtual or otherwise)via the internet.

The Internet Protocol is specifically limited in scope, to provide the functionsnecessary to deliver a package of bits (an IP datagram) from a source to adestination host over an interconnected system of networks. There are nomechanisms to improve end-to-end data reliability, flow control, sequencing, or otherservices commonly found in host-to-host protocols. IP can capitalize on the servicesof its supporting networks to provide various types and qualities of service.

IP does not provide a reliable communication facility. There are no acknowledgmentsneither end-to-end nor hop-by-hop. There is no error control for data, only a headerchecksum. There are no retransmissions. There is no flow control.

Errors detected may be reported via the Internet Control Message Protocol (ICMP)which is implemented in the internet protocol module.


TM3110EU01TM_00025

Connectionless datagram service

Addressing

Fragmentation and Reassembly

Type of Service

Tasks of IP

Fig. 1 Tasks of IP

End-to-End Data Reliability

Flow Control

Sequencing

Reliable Communication Facility

Acknowledgements

Error Control for Data

Retransmissions

No Mechanisms for:

Fig. 2 "Drawbacks" of IP


TM3110EU01TM_00026

The tasks of the physical and data link layer of OSI are provided by the networkaccess level in TCP/IP.

The three highest layer in OSI are combined in the application level of TCP/IP.


TM3110EU01TM_00027

Physical

Data Link

Network

Transport

Session

Presentation

Transport

Internet

Network Access

ISO OSI Reference Model

Application

TCP/IP Architecture

Application

Fig. 3 ISO OSI 7 layer reference model versus TCP/IP architecture


TM3110EU01TM_00028

The figure on the right shows a more detailed view about the TCP/IP protocol stack.

ARP Address Resolution Protocol

FTP File Transfer Protocol

ICMP Internet Control Message Protocol

IGMP Internet Group Management Protocol

IPv4 Internet Protocol version 4

NFS Network File System

RARP Reverse Address Resolution Protocol

SMTP Simple Mail Transfer Protocol

TCP Transmission Control Protocol

TFTP Trivial File Transfer Protocol

UDP User Datagram Protocol


TM3110EU01TM_00029

Network

Device

Driver

Physical

Media

RARPARP

IP IGMPICMP

UDPTCP

NFSTFTPSMTPFTP Application

Transport

Network

Network

Interface

Fig. 4 TCP/IP architecture


TM3110EU01TM_000210


TM3110EU01TM_000211

2 IP-Datagram Structure


TM3110EU01TM_000212

The IP headers size can range from 20 Bytes (when no options are included) to 64Bytes (when options and padding bits are included).

The following IP parameters belong to the header of a IP datagram:

IP Version and IP Header Length

Type of Service

Total Length

Identification, Flags and Fragment Offset

Time to Live

Protocol

Header Checksum

Source and Destination Addresses

Options and Padding bits (these are optional contents).

On the following pages a detailed descriptions explains the parameters.


TM3110EU01TM_000213

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 90 1 2 3 4 5 6 7 8 9 0 1

0 1 2 3

Version IHL Type of Service Total Length

Identification Flags Fragment Offset

Time to Live Protocol Header Checksum

Source Address

Destination Address

Options Padding

Data

20 b

yte

s

Fig. 5 IP datagram


TM3110EU01TM_000214

The IP Version parameter indicates the version of the used internet protocol. At themoment, usually V4 is used.

The IP Header Length (IHL) indicates the length of the IP header in multiple of 32bits. The minimum IP header length is 20 Bytes, whilst the maximal IP header lengthis 64 octets.

If the option attributes are also contained, the IHL gives the length of the IP headerincluding the padding bits.


TM3110EU01TM_000215

IP Version

Versionnumber

Keyword Version

0 reserved

1-3 unassigned

4 IP Internet Protocol (i.e. IPv4)

5 ST ST datagram mode

6 SIP Simple Internet Protocol (i.e. IPv6)

7 TP/IX The next Internet

8 PIP The P Internet Protocol

9 TUBA TUBA

10-14 unassigned

15 reserved

Fig. 6 IP version


TM3110EU01TM_000216

The Type of Service (TOS) provides an indication of the abstract parameters of thequality of service desired. These parameters are used to guide the selection of theactual service parameters when transmitting a datagram through a particularnetwork. Several networks offer service precedence, which somehow treats highprecedence traffic as more important than other traffic (generally by accepting onlytraffic above certain precedence at time of high load). The major choice is a threeway tradeoff between

low-delay

high-reliability

high-throughput

low cost.

The use of the Delay, Throughput, and Reliability indications may increase the cost(in some sense) of the service. In many networks better performance for one of theseparameters is coupled with worse performance on another. Except for very unusualcases at most two of these three indications should be set.

The network control precedence designation is intended to be used within a networkonly. The actual use and control of that designation is up to each network. The inter-network control designation is intended for use by gateway control originators only. Ifthe actual use of these precedence designations is of concern to a particularnetwork, it is the responsibility of that network to control the access to, and use of,those precedence designations.

Total Length is the length of the datagram, measured in octets, including internetheader and data. The parameter Total Length is contained in 16bits.

This field allows the length of a datagram of up to 65,535 octets. Such longdatagrams are practically not usable for most hosts and networks. The minimumrequirement for all hosts is, to accept datagrams of up to 576 octets (whether theyarrive completely or in fragments, i.e. in case of fragmentation, the Total Lengthindicates the size of the fragment). It is recommended that hosts only senddatagrams larger than 576 octets if they have assurance that the destination isprepared to accept the larger datagrams.

The number 576 is selected to allow a reasonable sized data block to be transmittedin addition to the required header information. For example, this size allows a datablock of 512 octets plus 64 header octets to fit in a datagram. The maximal internetheader is 60 octets, and a typical internet header is 20 octets, allowing a margin forheaders of higher level protocols.


TM3110EU01TM_000217

Bit Parameter Values

0-2 Precedence 111 - Network Control110 - Internetwork Control101 - CRITIC / ECP100 - Flash Override011 - Flash010 - Immediate001 - Priority000 - Routine

3 Delay (D) 0 = Normal Delay1 = Low Delay

4 Throughput (T) 0 = Normal Throughput1 = High Throughput

5 Reliability (R) 0 = Normal Reliability1 = High Reliability

6 Costs 0 = Normal Costs1 = Low Costs

7 Reversed forFuture Use

0 1 2 3 4 5 6 7

Precedence D RT C 0

bits

Fig. 7 Type of service


TM3110EU01TM_000218

The Identification parameter is used to distinguish the fragments of one datagramfrom those of another datagram. The originating protocol module of an internetdatagram sets the identification field to a value that must be unique for that source-destination pair and protocol for the time the datagram will be active in the internetsystem. The originating protocol module of a complete datagram sets the fragmentoffset to zero in the first fragment and the More Fragments flag to zero if the lastfragment is transmitted.

Flags:

The flags are used to control the fragmentation of the IP datagram. Fragmentationmay be allowed (DF=0) or not (DF=1). The bit MF indicates (if fragmentation occurs)if further fragments have to be received later on (MF=1) or not (MF=0).

Bit Parameter Values

Bit 0: 0 reserved, must be zero

Bit 1 DF 0 = May Fragment

1 = Dont Fragment

Bit 2: MF 0 = Last Fragment

1 = More Fragments

Fragment Offset:

This field indicates where in the datagram this fragment belongs. The fragment offsetis measured in units of 8 octets (64 bits). The first fragment has offset zero.

More Fragments Flag Fragment Offset Description

1 0 First Fragment

1 >0 Middle Fragment

0 >0 Last Fragment

0 0 Only Fragment


TM3110EU01TM_000219

Identification

16 bits

to ensure correct reassembly of fragments

Flags

controls fragmentation

Fragment Offset

13 bits

measures in 8 octets (64 bits) the offset of

the datagram fragment

DF0 MF

210

Fig. 8 Identification, flags and fragment offset


TM3110EU01TM_000220

Fragmentation

The fragmentation of a datagram is necessary when the transport network is not ableto send the complete datagram in one frame. The IP fragmentation and reassemblyprocedures need to be able to split a datagram into an almost arbitrary number ofpieces that can be later reassembled by the remote node.

The receiver of the fragments uses the identification field to ensure that fragmentsof different datagrams are not mixed. So, the identification field is used to distinguishthe fragments of one datagram from those of another. The originating protocolmodule of an IP datagram sets the identification field to a value that must be uniquefor that source-destination pair and protocol for the time the datagram will be active inthe internet system.

The fragment offset field tells the receiver the position of a fragment in the originaldatagram. The fragment offset and length determine the portion of the originaldatagram covered by this fragment.

The more-fragments flag indicates (by being reset) the last fragment. Theinformation out of these fields is sufficient to reassemble datagrams correctly. Adatagram marked with the flag "don't fragment" is discarded in case the transportnetwork is not able to deliver it as one frame via the underlying physical layer.

The size limit of a datagram that can be transported by the transport network isknown as the Maximum Transmission Unit (MTU). For example, the Ethernetsystem has a maximum data size (MTU) of 1500 octets or X.25 of 128 octets.

To fragment an IP datagram, the IP module (for example in a gateway) creates twonew IP datagrams and copies the content of the IP header from the original datagraminto the IP header of the fragmented datagrams. The data of the original datagram isdivided into two portions on an 8 octet (64 bit) boundary (the second portion mightnot be an integral multiple of 8 octets, but the first must be).

The first portion of the data is placed in the first new IP datagram, and the total lengthfield is set to the length of the first datagram. The more-fragments flag is set to one.The fragmentation offset becomes the value 0.

The second portion of the data is placed in the second new IP datagram, and thetotal length field is set to the length of the second datagram. The more-fragments flagcarries the same value as the complete datagram, in our case the value 0. Thefragment offset field of the second new internet datagram is set to the value of thatfield in the complete datagram plus offset as number of data Bytes divided by 8.

This procedure can be generalized for an n-way split, rather than the two-way splitdescribed.

To assemble the fragments of an internet datagram, an internet protocol module (forexample at a destination host) combines internet datagrams that all have the samevalue for the four fields: identification, source, destination, and protocol. Thecombination is done by placing the data portion of each fragment in the relativeposition indicated by the fragment offset in the fragment's internet header. The firstfragment will have the fragment offset zero, and the last fragment will have the more-fragments flag reset to zero.


TM3110EU01TM_000221

ID:1234

Length: 1620

MF=0

Fragmentation

Offset:0

Length1600 Bytes

ID:1234

Length: 1500

MF=1

Fragmentation

Offset:0

Length1480 Bytes

ID:1234

Length: 140

MF=0

Fragmentation

Offset:185

Length

120 Bytes

Large IP

Datagram

Fragment 1

Fragment 2

Header Data

Fig. 9 Example for a fragmentation


TM3110EU01TM_000222

The time to live field indicates the maximum time the datagram is allowed to remainin the internet system. If this field contains the value zero, then the datagram must bedestroyed. This field is modified in internet header processing. The time is measuredin units of seconds, but since every module that processes a datagram mustdecrease the TTL by at least one even if it process the datagram in less than asecond, the TTL must be thought of only as an upper bound on the time a datagrammay exist. The intention is to cause undeliverable datagrams to be discarded, and tobound the maximum datagram lifetime.

The Protocol parameter is an 8 bit parameter. It indicates the next level protocolused in the data portion of the internet datagram. RFC 1700 defines the values to beused in this field, but some of the more common protocols are shown on the rightfigure.


TM3110EU01TM_000223

Parameter Time to Live

Indicates the upper-bound lifetime of a datagram

8 bits

set by the sender

reduced on hop-to-hop basis

datagram is destroyed when the TTL = 0

Fig. 10 Time to live

Decimalvalue

Keyword Protocol

0 Reserved

1 ICMP Internet Control Message

2 IGMP Internet Group Management

3 GGP Gateway-to-Gateway

4 IP IP in IP (encasulation)

6 TCP Transmission Control

8 EGP Exterior Gateway Protocol

17 UDP User Datagram

29 ISO-TP4 ISO Transport Protocol Class 4

45 IDRP Inter-Domain Routing Protocol

46 RSVP Reservation Protocol

70 VISA VISA Protocol

80 ISO-IP ISO Internet Protocol

83 VINES VINES

88 IGRP IGRP (CISCO)

92 MTP Multicast Transport Protocol

94 IPIP IP-within-IP Encapsulation Protocol

95 MICP Mobile Internetworking Control Pro.

97 ETHERIP Ethernet-within-IP Encapsulation

Fig. 11 Protocol


TM3110EU01TM_000224

The Header Checksum provides a verification that the information used inprocessing internet datagram has been transmitted correctly. The data may containerrors. If the header checksum fails, the internet datagram is discarded at once bythe entity which detects the error.

The checksum is build on the header only. Since some header fields change (e.g.time to live), the checksum is recomputed and verified at each point where theinternet header is processed.

The checksum algorithm calculates as follows: the checksum field is the 16 bitone's complement of the one's complement sum of all 16 bit words in the header. Forpurposes of computing the checksum, the value of the checksum field is zero. This isa simple to compute checksum and experimental evidence indicates it is adequate,but it is provisional and may be replaced by a CRC procedure, depending on furtherexperience.

Source IP address

The IP address of the sender of the IP datagram (32 bits).

Destination IP address

The IP address of the host to which this datagram is to be sent (32 bits).

For better readability the values of the address fields are written in dotted decimalmanner. Each dot represents the border of an octet.


TM3110EU01TM_000225

Header Checksum

Verifies that the datagram has been sent correctly

16 bits

calculated only over the header

Verified and recomputed on hop-by-hop basis

if header checksum fails, datagram is discarded

Fig. 12 Header checksum

Source Address: 32 bits

Destination Address: 32 bits

Dotted decimal notation, (e.g. 195.24.1.2)

Hexadecimal: 0x C3 18 01 02

0 31

Example of an IP address:

1100 0011 0001 1000 0000 0001 0000 0010

Fig. 13 Address parameters


TM3110EU01TM_000226

Address classes

5 types of Address classes are defined which cover different address ranges:

Class Address Range

A 000.000.000.000 - 127.255.255.255

B 128.000.000.000 - 191.255.255.255

C 192.000.000.000 - 223.255.255.255

D 224.000.000.000 - 239.255.255.255

E 240.000.000.000 - 255.255.255.255

To provide for flexibility in assigning addresses to networks and allow for the largenumber of small to intermediate sized networks the interpretation of the address fieldis coded to specify a small number of networks with a large number of host, amoderate number of networks with a moderate number of hosts, and a large numberof networks with a small number of hosts. In addition there is an escape code forextended addressing mode.

A value of zero in the network field means that network. This is only used in certainICMP messages. The extended addressing mode is undefined. Both of thesefeatures are reserved for future use.

The local address, assigned by the local network, must allow for a single physicalhost to act as several distinct internet hosts. That is, there must be a mappingbetween internet host addresses and network/host interfaces that allows severalinternet addresses to correspond to one interface. It must also be allowed for a hostto have several physical interfaces and to treat the datagrams from several of themas if they were all addressed to a single host.


TM3110EU01TM_000227

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 90 1 2 3 4 5 6 7 8 9 0 1

0 1 2 3

0 Network ID Host ID

1 0 Network ID Host ID

1 1 0 Network ID Host ID

Class A

Class B

Class C

1 11 0 Host group addressClass D

1 1 1 1 Reserved for experimental protocolClass E

Fig. 14 Address classes


TM3110EU01TM_000228

Option

The options, as the name says, are an optional part in IP datagrams. The functionmust be implemented in all IP modules (host and gateways). The option field isvariable in length. There may be zero or more options. We distinguish two cases forthe format of an option:

A single octet of option-type.

An option-type octet, an option-length octet, and the actual option-data octets.

The option-length octet counts the option-type octet and the option-length octet aswell as the option-data octets.

The End of Option indicates the end of the option list. This might not coincide withthe end of the internet header according to the internet header length. The field maybe copied, introduced, or deleted on fragmentation, or for any other reason.

The No Operation Option may be used between options, for example, to align thebeginning of a subsequent option on a 32 bit boundary. It may be copied, introduced,or deleted on fragmentation, or for any other reason.

The Security Option provides a way for hosts to send security, handling restrictions,and TCC (closed user group) parameters. This field must be copied onfragmentation. This option appears at most once in a datagram.

The Loose source and record route (LSRR) Option provides a means for thesource of an internet datagram to supply routing information to be used by thegateways in forwarding the datagram to the destination, and to record the routeinformation.

The Strict Source and Record Route (SSRR) Option provides a means for thesource of an internet datagram to supply routing information to be used by thegateways in forwarding the datagram to the destination, and to record the routeinformation.

The Record Route Option provides a means to record the route of an internetdatagram.

The Stream Identifier Option provides a way for the 16-bit SATNET streamidentifier to be carried through networks that do not support the stream concept.

The Internet Timestamp Option permits to accumulate Timestamps of all Gateways(optional with IP address), or a subset of them.


TM3110EU01TM_000229

Options

Option Type

Option Number

End of Option

No Operation

Security

Loose Source

Strict Source

Record Route

Stream Identifier

Internet Timestamp

Fig. 15 Options


TM3110EU01TM_000230

On the right figure, there is an example for an IP header.


TM3110EU01TM_000231

Vers.=4 IHL=5 Type of Service Total Length=112

Identification=0Flag

=2Fragment Offset=0

Time to Live=64 Protocol=6 Header Checksum

Source Address = 255.255.0.1

Destination Address = 17.34.0.68

Data

Fig. 16 Example internet header


TM3110EU01TM_000232

The figure on the right shows the transmission plane for GPRS.

IP is used for

end-to-end traffic between the mobile subscriber and the Internet Service Providerand for

routing the user packets between GGSN and SGSN on the Gn interface, as well asto the internet service provider on the Gi interface.


TM3110EU01TM_000233

xGSN

MS BSS SGSNGbUm Gn Gi

GSM RF

MAC

RLC

LLC

SNDCP

IP

Appli-cation

Frame

Relay

RFC

1490

IP

Appli-

cation

GGSN ISP

BSS

SIEMENS

NIXDORF

RFC

1490

IP

UDP/

TCP

GTP

Frame Relay

RFC

1490

IP

IP

Relay

Frame

Relay

Network

Service

BSSGP

GSM RF

MAC

RLC

Relay

Frame Relay

Network

Service

BSSGP

LLC

SNDCP

RFC

1490

IP

UDP/

TCP

GTP

Relay

Fig. 17 GPRS transmission plane


TM3110EU01TM_000234

The figures on the right show examples the principal usage of IP on the interfaces Gband Gi.


TM3110EU01TM_000235

FTP Data

FTP DataTCP

Header

TCP DataIP

Header

IP DataSN-Data SNDCP Frame

IP Datagram

TCP Segment

SNDCP message

IP Protocol

TCP Protocol

Fig. 18 IP at the Gb-interface

FTP Data

FTP DataTCP

Header

TCP DataIP

Header

IP DataRFC

1490

IP Datagram

TCP Segment

Frame Relay

IP Protocol

TCP Protocol

FTP Client

Frame

RelayCRC

Fig. 19 IP at the Gi-interface


TM3110EU01TM_000236


TM3110EU01TM_000237

3 Exercise


TM3110EU01TM_000238


TM3110EU01TM_000239

Exercise

1. What is the min/max length of a datagram?

2. Which flag has to be set when fragmentation is not allowed?

3. What is the Maximum Transmission Unit when the transport network is FrameRelay?

4. To which class of address belongs the following address: 195.12.12.12?

5. Which GPRS Interfaces are based on IP?


TM3110EU01TM_000240


TM3110EU01TM_000241

4 Solution


TM3110EU01TM_000242


TM3110EU01TM_000243

Solution

1. What is the min/max length of a datagram?

Minimum 576 Bytes / maximum 65.535 Bytes

2. Which flag has to be set when fragmentation is not allowed?

DF-flag set to one means "Don't fragment"

3. What is the Maximum Transmission Unit when the transport network is FrameRelay?

1600 Bytes

4. To which class of address belongs the following address: 195.12.12.12?

Class C

5. Which GPRS Interfaces are based on IP?

The Gb- and Gn/Gi-interface


TM3110EU01TM_000244

IP Internet Protocol for GPRSGeneralitiesIP-Datagram StructureExerciseSolution

Documents

06_tm3110eu01tm_0002_ip