Mobile Services (ST 2010)

Axel Küpper | Technische Universität Berlin | Service-centric Networking Mobile Services – ST 2010 | 4 Mobile Internet Mobile Services (ST 2010) Cha...
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Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Mobile Services (ST 2010) Chapter 4: Mobile Internet Axel Küpper Service-centric Networking Deutsche Telekom Laboratories, TU Berlin

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Mobile Services Summer Term 2010

4 Mobile Internet 4.1 Problem Statement 4.2 Mobile IP 4.3 Network Layer Support in GPRS/UMTS

2

4.1 Problem Statement Internet Protocol - Overview Internet Protocol

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet





 



Primary protocol of the network layer used for transmission in networks that employ packet-switched data communication Packets can be sent without establishing a connection before (unlike circuitswitched communication) Packets can be lost Packets may arrive at the receiver in another order than initially sent 0

4

Version

8

IHL

12

16

Time to Live

 

20

Type of Service

Identification

Each data packet contains a header that (besides other things) fixes the IP address of the sender (source) and the address of the receiver (destination) Packet passes different routers along the way from the source to the destination Router receives a packet from a source or a previous router, gets the destination address from the IP header, and forwards the packet to the next router 24 28 Total Length

Flags

Protocol (IP)

31

Fragment Offset

Header Checksum

Source Address Destination Address Options and Padding (optional) TCP/UDP/… payload

3

4.1 Problem Statement Internet Protocol - Addressing Two-Level Classful Hierarchy



Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet



Internet is an interconnection of several networks IP addresses refer to the network a host is connected to (network prefix) and to the host within that network (host number)

Network prefix

Host number

Three-Level Subnet Hierarchy Network prefix 8, 16, or 24 bits for class A, B, or C network prefixes

Subnet number

24, 16, or 8 bits for class A, B, or C host number

Two-Level Classful Hierarchy

Three-Level Subnet Hierarchy







Initial addressing scheme for fixing the length of network prefixes and number of hosts within a network Class A  



Class B  



8-bit network prefix for 126 networks 16,777,214 hosts per network 16-bit prefix for 16,384 networks 65,534 hosts per network

Class C  

24-bit prefix for 2,097,152 networks 254 hosts per network

Host number

Division of Class A, B, and C networks into smaller subnetworks that have a common, designated IP addressing routing index  Subnet mask fixes the length of the prefix (sum of length of network prefix and subnet number)  Breaks a network into smaller realms that may use existing network address space more efficiently

4

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

4.1 Problem Statement Routing Example (I)

Host B Destination 128.9.1.2 128.9.1.0 DEFAULT

Subnet mask Route to 255.255.255.255 SELF 255.255.255.0 LAN 0 128.9.1.1

Host A Destination 128.8.1.2 128.8.0.0 128.9.00

Subnet mask 255.255.255.255 255.255.0.0 255.255.0.0

Route to SELF LAN 0 128.8.1.1

Router Destination 128.8.1.1 128.9.1.1 128.9.2.1 128.8.0.0 128.9.1.0 128.9.2.0

Subnet mask 255.255.255.255 255.255.255.255 255.255.255.255 255.255.0.0 255.255.255.0 255.255.255.0

Route to SELF SELF SELF LAN 0 LAN 1 LAN 2

128.8 network LAN 0

Host C Destination 128.9.2.2 128.9.2.0 DEFAULT

Subnet mask Route to 255.255.255.255 SELF 255.255.255.0 LAN 0 128.9.2.1

Host A LAN 0

LAN 0

Router

Host B 128.9.1 subnet

 

LAN 2

LAN 1

LAN 0

Host C 128.9.2 subnet

Problem: IP addresses contain routing information (network/subnet ID fixed by the subnet mask) What happens if Host C moves from the 128.8 network to the 128.9.1 subnet? 5

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

4.1 Problem Statement Routing Example (II)

Host C Destination 128.9.1.3 128.9.1.0 DEFAULT

Subnet mask Route to 255.255.255.255 SELF 255.255.255.0 LAN 0 128.9.1.1

Host B Destination 128.9.1.2 128.9.1.0 DEFAULT

Subnet mask Route to 255.255.255.255 SELF 255.255.255.0 LAN 0 128.9.1.1

Host A Destination 128.8.1.2 128.8.0.0 128.9.00

Subnet mask 255.255.255.255 255.255.0.0 255.255.0.0

Route to SELF LAN 0 128.8.1.1

Router Destination 128.8.1.1 128.9.1.1 128.9.2.1 128.8.0.0 128.9.1.0 128.9.2.0

Subnet mask 255.255.255.255 255.255.255.255 255.255.255.255 255.255.0.0 255.255.255.0 255.255.255.0

Route to SELF SELF SELF LAN 0 LAN 1 LAN 2

128.8 network LAN 0

Host A

Host C LAN 0 LAN 0 LAN 0

Router

Host B 128.9.1 subnet





LAN 2

LAN 1

128.9.2 subnet

Because an IP address is not only a reference to a particular host, but also addresses the network and subnet the host is connected to, a host gets a new IP address when getting connected to another network Original Internet Protocol does not support mobility!

6

4.1 Problem Statement Solutions for Mobility Support in the Internet Problem: TCP connection cannot survive IP address change

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

   

TCP connections are identified by the tuple (source address, source port, destination address, destination port) TCP connection cannot survive any address change Solution: inform all communication partners of the mobile node about the new address Drawback: requires modification of existing, proven protocol software

Problem: Mobile hosts acting as servers are not reachable after an address change  

Solution #1: simply assign a new, topologically correct address after the movement Drawback: nobody knows about this new address – it is almost impossible to find a host on the Internet that has just changed its address



Solution #2: Use of Dynamic DNS (DynDNS) for updating the mapping between a logical domain name and an IP address Drawback: because of caching methods, DynDNS is not able to cope with frequent updates

  

Solution #3: create dedicated routes for a mobile node Drawback: routing tables are based on network prefixes – storing entries of millions of mobile nodes would not scale 7

4.2 Mobile IP Components and Addresses (I) MN

CoA

Home Network

Router HA

Router FA

Foreign Network

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Internet CN Router

Mobile Node (MN)

Home Network



 



Mobile device that moves to other networks and for which mobility support is to be provided Keeps its IP address and can continuously communicate with any other system in the Internet as long as link-layer connectivity is given

Correspondent Node (CN)  

Communication partner of the MN May invoke services offered by the MN



Subnet the MN belongs to Responsible for assigning an IP address to the MN No mobility support required inside the home network

Foreign Network 

Current subnet the MN visits and which is not the home network

8

4.2 Mobile IP Components and Addresses (II) MN

CoA

Home Network

Router HA

Router FA

Foreign Network

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Internet CN Router

Foreign Agent

Foreign Agent CoA



 



Implemented in the router of the foreign network Acts a tunnel endpoint that decapsulates packets and forwards them to the MN

CoA is an IP address referring to the FA FA is tunnel endpoint and forwards packets to the MN

Care-of Address (CoA)   

IP address associated with the MN in the foreign network IP packets sent to the MN are delivered to the CoA, not directly to the MN‘s IP address CoA marks the tunnel endpoint

9

4.2 Mobile IP Basic Procedure MN

CoA

Home Network

2

Router HA

Router FA

3

Foreign Network

4 Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Internet CN

1

Router

CN → HA 

 2

1

CN transmits an IP datagram destined to the MN, with MN’s home address in the IP header IP datagram is routed to the home network of the MN

 3

FA → MN 

HA → FA  

At the home network, IP datagram is intercepted by the HA HA encapsulates the datagram inside a new IP datagram with the MN’s CoA in its header

4

Encapsulated IP datagram is retransmitted and routed to the FA

FA decapsulates the original IP datagram and delivers it to the MN across the foreign network

MN → CN 

When the MN sends a reply to CN, the associated datagram travels directly across the Internet to the CN

10

4.2 Mobile IP Alternative: “FA Inside” Co-located CoA

Home Network

2

Router HA

3

Router

MN

Foreign Network

4 Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Internet CN

  

 

1

Router

Initial version of Mobile IP worked only with a FA in the foreign network Alternative proposal: MN may act as its own FA Tunnel is established between HA and MN, and MN is addressed by a Co-located CoA Advantage: no enhancements need to made in the foreign network Disadvantage: scarcity of IP addresses (if MN received a permanent address)

Co-located CoA   

CoA is assigned to the MN, and hence is topologically correct May be acquired using DHCP May be assigned as a long-term address for use when the MN visits the foreign network

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4.2 Mobile IP How to Detect the Entering of a New Network? (I)

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet



HAs and FAs periodically broadcast their presence using an Agent Advertisement Message (extension of ICMP messages) MNs listen to the broadcast …  … to detect whether they entered a new subnet  … to detect whether the new subnet is their home or foreign network  … to receive special features of the new subnet  … to receive a CoA if they entered a new foreign network

Agent Solicitations  

Agent Advertisements are only broadcast periodically MN may explicitly solicit for an Agent Advertisement Message if it needs it immediately

0 Standard ICMP message



Agent Advertisement Message

Extensions for Mobile IP

Agent Advertisement

4

8

12

Type

Code

#Addresses

Addr. Size

16

20

24 28 Checksum

31

Lifetime

Router address 1 Preference level 1

Router address 2 Preference level 2

Type=16

Sequence number

Lentgh

Registration lifetime

RBHFMGrT

reserved

CoA 1 CoA 2

12

4.2 Mobile IP How to Detect the Entering of a New Network? (II)

Use of lifetime field 







MN receiving an Agent Advertisement Message from an agent records the lifetime field as a timer If the timer expires before the MN has received the next message, it assumes that it has lost contact to that agent If, in the meantime, it has received an AA message from another agent (and that advertisement has not yet expired), the MN registers with this new agent If it has not received an AA message, MN uses Agent Solicitation

Use of network prefix 



MN checks whether any newly received AA is on the same network as the MN’s current CoA If not, MN assumes that it has moved and may register with the agent whose advertisement it has just received. Old Router FA

New Router FA

MN

Agent Advertisement

AA Broadcast

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet



MN may move from one subnet to another without the IP layer being aware of it Agent discovery process enables the MN to detect such a move

AA Solicitation



Agent Advertisement Agent Advertisement Agent Advertisement Agent Advertisement

Agent Solicitation Agent Advertisement

13

4.2 Mobile IP Registration with a Foreign Network Registration via the FA:

Registration directly with the HA:

Foreign Network

Home Network

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

MN

Router FA

Router HA

MN Registration Request

1 Registration

Registration 2 Request Registration 3 Registration Reply Reply 4

Request



1 2 3 4

Once an MN has detected that it entered a (new) foreign network, it has to register with the FA and alert the HA. MN sends a registration request to the FA FA relays request to the HA HA accepts or denies request and sends a registration reply to the FA FA forwards reply to the MN

Router HA

Registration Reply



If the MN uses a co-located CoA, then it registers directly with its HA

14

4.2 Mobile IP Tunneling and Encapsulation (I) Tunnel

Encapsulation/Decapsulation





Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet





 

Establishes a virtual pipe for data packets between a tunnel entry and a tunnel endpoint Packets entering a tunnel are forwarded inside the tunnel and leave the tunnel unchanged Tunneling, i.e., sending a packet through a tunnel is achieved by using encapsulation Whole tunnel is considered as single hop from the packet’s point of view Tunneling allows the MN to behave as if it were attached directly to the home network Original IP header New IP header

OR

Outer header

 



Encapsulation: mechanism of taking a packet consisting of packet header and data and putting it into the data part of the new packet Decapsulation: taking a packet out of the data part of another packet Encapsulation/decapsulation are operations typically performed when a packet is transferred from a higher protocol layer to a lower one (or from a lower layer to a higher layer respectively) Mobile IP uses encapsulation/decapsulation within the same layer

Original data New data

Inner header

Original data

15

4.2 Mobile IP Tunneling and Encapsulation (II) IP-in-IP Encapsulation 0

4

Version

8

IHL

12

16

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Version

20

Type of Service

Identification Time to Live

Minimal Encapsulation 24 28 Total Length

Flags

IP-in-IP

31

0

4

8 IHL

Version

Fragment Offset

12

16

Time to Live

Min. Encaps.

24

Flags

Header Checksum

Source Address (HA Address)

Destination Address (Care-of Address)

Destination Address (Care-of Address)

Identification Time to Live

Total Length

Type of Service

IPv4

Flags

IPv4

Fragment Offset

S

reserved

31

Fragment Offset

Source Address (HA Address)

IHL

28

Total Length

Type of Service

Identification

Header Checksum

20

Header Checksum

Destination Address (Home Address of MN)

Header Checksum

Source Address (CN Address, is not present if S=0)

Source Address (CN Address)

TCP/UDP/… payload

Destination Address (Home address of MN) TCP/UDP/… payload

  

Simple encapsulation of one IP packet into another one Mandatory of Mobile IP Drawback: several redundant fields

 

Removes redundant fields Source address in the inner header is omitted if original sender is identical to the HA 16

4.2 Mobile IP HA Realizations MN

CoA

Home Network

Router HA

Router FA

Foreign Network

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Internet CN Router

Home Agent (HA)

HA Realization #2







Tunnel for packets toward the MN starts at the HA HA maintains a location registry, which stores the CoA of all MNs that have their origins in the home network



HA could be implemented on an arbitrary node in the subnet Disadvantage: double crossing of the router by all packets if the MN is in a foreign network

HA Realization #1

HA Realization #3







HA is implemented on a router that is responsible for the home network Good solution as all packets have to pass the router anyway



No home network, but only a virtual home network represented by a router and all MNs are always connected to foreign networks HA is again implemented on the router

17

4.2 Mobile IP Optimization (I)

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Router HA

Router FA CN MN

Problem: Triangular Routing   

With basic Mobile IP, all packets to the MN have to go through the HA May cause unnecessary overhead for the network between CN and HA, but also between HA and CoA, depending on the current location of the MN Figure: although the communicating computers might only be a few meters away, the packets have to travel around the world

18

4.2 Mobile IP Optimization (II)   

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

1

Binding request  

2

Used by the HA to inform the CN about the current location of the MN Contains the MN’s fixed address and CoA

Binding acknowledgement 

4

Any CN that wants to know the current location of an MN sends a binding request to the HA If HA is allowed to disclose the MN’s location, it returns a binding update

Binding update  

3

Idea: Optimize routing by informing the CN of the current location of the MN Binding cache: part of the local routing table of the CN Introduction of four additional messages

CN returns an acknowledgement after receiving an update

Binding warning   

If an FA decapsulates a packet for an MN, but is not the MN’s current FA, it sends a warning to the CN Warning contains the MN’s fixed home address After receiving a warning, the CN knows that the MN has probably moved, and initiates a 19 binding request

4.2 Mobile IP Optimization (III)

CN

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Data

3 ACK

Router HA

Data Update 2

Data

Old Router FA

New Router FA

MN

Data

Data Registration

Update

MN changes location

ACK Data Data

1

Warning 4

Request

Data

Update 2

3

ACK Data Data

20

4.3 Network Layer Support in GPRS/UMTS GPRS/UMTS Basic Procedures GERAN

Packet-switched domain

UE BTS

BSC

SGSN

GGSN

Internet

GPRS Attach Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

Connection Setup (Activation of a PDP Context) Transmission of the User Data



Before data can be transmitted between the UE and an external host, some preparations are necessary  UE must be introduced to the network  Appropriate SGSN must be found (according to the user’s location)  Features and capabilities of the data service must be negotiated  An GGSN must be selected and a setup between UE and GGSN has to be established  Path for routing data packets has to prepared for tunneling



Three procedures  GPRS Attach  Activation of PDP Context  Data Transfer

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet

4.3 Network Layer Support in GPRS/UMTS PDP Context PDP Context

Access Point Name (APN)

  



 



PDP: Packet Data Protocol Describes characteristics of the session Contains routing information for packet transfer between a UE and a GGSN to have access to an external packetswitching network Stored in the mobile station, the SGSN, and the GGSN Once a mobile station has an active PDP context, it is visible for the external network and can send and receive packets Each UE may be assigned several PDP contexts for …  … getting access to different networks  … different services  … different charging methods



Logical name for the desired data network Refers to the GGSN enabling access to that network

PDP type 

Type of the packet network used (e.g., IPv4 or IPv6)

PDP address   

Address assigned to the mobile station (e.g. an IP address) Static address: permanent IP address of UE Dynamic address: dynamically assigned, usually for the duration of a session

QoS class 

Four QoS parameters: service precedence, reliability, delay, and throughput

4.3 Network Layer Support in GPRS/UMTS GPRS/UMTS Packet Addresses Packet Data Protocol (PDP) Address

Packet TMSI (P-TMSI)





Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet







Address of a UE in the format of the used PDP (e.g., IP address) Static  UE permanently owns a PDP address assigned by the operator of the user’s home GSM network Dynamic  UE is assigned a new PDP address whenever it attaches to the network  Dynamic Home-PLMN Address: Dynamic address assigned by the user’s home PLMN  Dynamic Visited-PLMN Address: dynamic address assigned by the operator of the visited PLMN GGSN is responsible for the allocation and deactivation of PDP addresses

 

Assigned during an GPRS attach procedure and after a location update Used to page the UE when packets have to be delivered Mapping between PDP address and PTMSI by the SGSN makes the transmission of packets between GGSN and UE possible

Routing Area Identifier (RAI) 



In order to optimize location management, GSM location areas are subdivided into several routing areas RAI is transmitted from the MS to the network instead of the LAI

4.3 Network Layer Support in GPRS/UMTS Quality of Service Quality of Service Classes

Reliability





Required to support diverse applications (ranging from real-time video conferencing to E-Mail) Enable operators to offer different billing options

Axel Küpper | Technische Universität Berlin | Service-centric Networking

Mobile Services – ST 2010 | 4 Mobile Internet



Service precedence 

Reliability of a service with regard to probability of packet loss, packet duplication, wrong sequencing, packet corruption

Delay 

Priority of a service in relation to other services (high, normal, low)

Maximum values for mean and 95% delay with regard to end-to-end delay between UEs or between a UE and the serving GGSN

Throughput  Rel. class

Lost packet

1 2 3

10-9 10-4 10-2

Probability Duplicated Out of sequ. packet packet 10-9 10-5 10-5

10-9 10-6 10-5

Peak bit rate and mean bit rate Seconds Corrupted packet

Mean delay

95% delay

Delay class

10-9 10-9 10-2

< 0.5