Ebook Mobile communications (2nd edition): Part 2
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Ebook Mobile communications (2nd edition): Part 2
Mobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2 is Mobile IP, discussed in the first section, which adds mobility support to the internet network layer protocol IP. While systems like GSM have been designed with mobility in mind, the internet started al a time when no one had thought of mobile computers. Today's internet lacks any mechanisms to Ebook Mobile communications (2nd edition): Part 2support users traveling around the world. 11’ is the common base for thousands of applications and runs over dozens of different networks. This is theEbook Mobile communications (2nd edition): Part 2
reason for supporting mobility at the IP layer; mobile phono systems, for example, cannot offer this type of mobility for heterogeneous networks. To Mobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2 developed.Another kind of mobility, portability of equipment, is supported by the dynamic host configuration protocol (DHCP) presented in section 8.2. In former times, computers did not often change their location. Today, due to laptops or notebooks, students show up al a university with their comp Ebook Mobile communications (2nd edition): Part 2uters, and want to plug them in or use wireless access. A network administrator docs not want to configure dozens of computers every day or hand out lEbook Mobile communications (2nd edition): Part 2
ists of valid IP addresses, DNS servers, subnet prefixes, default routers etc. DHCP sets in at this point to support automatic configuration of computMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2s that are unclear as yet. How can routing lx- done in a dynamic network with permanent changes in connectivity? What if there are no dedicated routers or databases telling us where a node currently is? The last section deals with some approaches offering routing by extending standard algorithms kno Ebook Mobile communications (2nd edition): Part 2wn from the internet. Knowledge of the current situation of the physical medium or of the current location can be utilized.303304Mobile communicationsEbook Mobile communications (2nd edition): Part 2
8.1Mobile IPThe following gives an overall view of Mobile IP, and the extensions needed for the internet to support the mobility of hosts. A good refeMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2t formats, mechanisms, discussions of the protocol and alternatives etc. in detail. The new version of Mobile 11’ does not involve major changes in the basic architecture but corrects some minor problems (RFC 3344, Perkins, 2002). The following material requires some familiarity with Internet protoc Ebook Mobile communications (2nd edition): Part 2ols, especially IP. A very good overview which includes detailed descriptions of classical Internet protocols is given in Stevens (1994). Many new appEbook Mobile communications (2nd edition): Part 2
roaches related to Internet protocols, applications, and architectures can be found in Kurose (2003).8.1.1Goals, assumptions and requirementsAs shown Mobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2ons of users. So why not simply use a mobile computer in the internet?1 he reason is quite simple: you will not receive a single packet as soon as you leave your home network, i.c., the network your computer is configured for, and reconnect your computer (wireless or wired) al another place (if no a Ebook Mobile communications (2nd edition): Part 2dditional mechanisms are available). 1 he reason for this is quite simple if you consider routing mechanisms on the internet. A host sends an 11’ packEbook Mobile communications (2nd edition): Part 2
et with the header containing a destination address with other fields. The destination address not only determines the receiver of the packet, but alsMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2net with the network prefix 129.13.42 (unless CĨDR is used, RFC 1519, Fuller, 1993). Routers in the internet now look at the destination addresses of incoming packets and forward them according to internal look-up tables. To avoid an explosion of routing tables, only prefixes are stored and further Ebook Mobile communications (2nd edition): Part 2optimizations arc applied. A router would otherwise have to store the addresses of all computers in the internet, which is obviously not feasible. AsEbook Mobile communications (2nd edition): Part 2
long as the receiver can be reached within its physical subnet, it gets the packets; as soon as it moves outside the subnet, a packet will not reach iMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2ign to the computer a new, topologically correct IP address. This is what many users do with the help of DHCP (see section 8.2). So moving to a new location would mean assigning a new IP address, rhe problem is that nobody knows about this new address. It is almost impossible to find a (mobile) host Ebook Mobile communications (2nd edition): Part 2 on the internet which has just changed its address.Mobile network layer305One could argue that with the help of dynamic DNS (DDNS, RFC 2136, Vixie, 1Ebook Mobile communications (2nd edition): Part 2
997) an update of the mapping logical name - IP address is possible. This is what many computer users do if they have a dynamic IP address and still wMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2tivation, are important if a user wants to offer services from a mobile node, i.e., the node should act as server. Typically, the 11’ address Is of no special interest for service usage: in this case DHCP is sufficient. Another motivation for pennanent IP addresses is emergency communication with pe Ebook Mobile communications (2nd edition): Part 2rmanent and quick reachability via the same IP address.So what about dynamically adapting the IP address with regard to the current location? lhe probEbook Mobile communications (2nd edition): Part 2
lem is that the domain name system (DNS) needs some time before it updates the internal tables necessary to map a logical name to an IP address. Ulis Mobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2odes moving at the same lime. DNS could never present a consistent view of names and addresses, as it uses caching lo improve scalability. Il is simply loo expensive to update quickly.There is a severe problem with higher layer protocols like TCP which roly on IP addresses. Changing lhe IP address w Ebook Mobile communications (2nd edition): Part 2hile slill having a TCP connection open means breaking the connection. A TCP connection is identified by the tuple (source IP address, source port, deEbook Mobile communications (2nd edition): Part 2
stination IP address, destination port), also known as a socket pair la socket consists of address and port). Therefore, a TCP connection cannot surviMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2so have to notify all communication partners about the new address.Another approach is the creation of specific routes to the mobile node. Routers always choose the best-fitting prefix for the routing decision. If a router now has an entry for a prefix 129.13.42 and an address 129.13.42.99, it would Ebook Mobile communications (2nd edition): Part 2 choose the port associated with the latter for forwarding, if a packet with the destination address 129.13.42.99 comes in. While it is theoreticallyEbook Mobile communications (2nd edition): Part 2
possible to change routing tables all over the world to create specific routes to a mobile node, this does not scale at all with the number of nodes iMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2ware support, the latter is typically a piece of software which cannot handle the burden of frequent updates. Routers are the 'brains' of the internet, holding the whole net together. No service provider or system administrator would allow changes to the routing tables, probably sacrificing stabilit Ebook Mobile communications (2nd edition): Part 2y, just to provide mobility for individual users.8.1.1.2RequirementsSince the quick ‘solutions' obviously did not work, a more general architecture haEbook Mobile communications (2nd edition): Part 2
d to be designed. Many field trials and proprietary systems finally led to mobile II’ as a standard to enable mobility in the internet. Several requirMobile network layer8This chapter introduces protocols and mechanisms developed for the network layer to support mobility. The most prominent example Ebook Mobile communications (2nd edition): Part 2unning TCP/IP and connected to the internet, is huge. A new standard cannot introduce changes for applications or network protocols already in use. People still want to use their favorite browser for ttw and do not want to change applications just for mobility, the same holds for operating systems. Ebook Mobile communications (2nd edition): Part 2Mobile IP has to be integrated into existing operating systems or at least work with them (today it is available for many platforms). Routers within tEbook Mobile communications (2nd edition): Part 2
he internet should not necessarily require other software. While it is possible to enhance the capabilities of some routers to support mobility, it isGọi ngay
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