5441336593

SubSystem	SSN
HLR	6
VLR	7
MSC	8
AuC	10

Table 1: Subsystem SSNs

The SSN are static depending on the type of node, in table 1 we show some of the SSNs used in SS7. SSNs rangę from 0-255. SCCP provides both connectionless and connection-oriented messaging and use segmenta-tion/reassembly to divide and join messages that are big.

TCAP is short for Transaction Capabilities Application Part and is used for communication between subsystems at the top level in the SS7 stack. TCAP manages the Communications between the subsystems and can join many messages into one logical transaction. TCAP can handle many con-current transactions between subsystems and maintains transaction IDs to set them apart. Since we are using SS7 over IP we use SCTP. SCTP is short for Stream Constrol Transmission Protocol and is used as a transport layer protocol. It was developed by the SigTran group when they found that the existing IP-transport protocols was not able to fulfill the reliability demands for telecoms. SCTP can be used in any IP network. MTP Level 3 User Adaption layer was developed by SigTran. In figurę 3 M3UA is shown in context, it enables SCTP.

Finally we have MAP, which stands for Mobile Application Part. MAP enables the application nodes in the GSM network to communicate with each other. MAP plays a vital part in this thesis. See section 4.5 for morę information on how we used MAP to build the HLR. There are other protocols in the SS7 stack such as DTAP, BSS-MAP, TUP and ISUP. They are used for procedures such as cali handling and will thus not be used here.

2.3 SMS

SMS is a seryice which enables sending and receiving of application layer text messages in the network. The messages cannot be longer than 160 characters, in many countries the encoding of the characters leads to even shorter messages (for instance messages encoded in Urdu (Pakistan) can not be longer than 70 characters). To deal with this constraint, longer messages can be segmented into many smaller. The service can be used by operators who wish to inform their subscribers of temporary campaigns or offers. The main use for the service is between subscribers who wish to communicate, but it can also be used between different application level nodes. For SMS to work there is a number of signaling messages sent between many different nodes to get the message to the recipient. The HLR is situated roughly in