17). TCP and UDP are therefore integrated parts of all IP node realizations (as SCCP is with MTP L3 in most SS7 networks). We should therefore look at TCP, UDP, and IP as the resident layers of a {TCP UDP IP} logical network, as depicted in Fig. 3.29. This logical network realizes socket routes and is therefore, from a structural point of view, quite similar to the SCCP/MTP L3 model (in Fig. 3.28). The terms used for APi, NA, etc. are different from any other network system (what else could be expected?). 8 Note that this term is not used by the SCCP standard, which defines this way of addressing as one of several addressing methods in SCCP (e.g., global title addressing, see next section). 3.4 Route Type Examples Socket Port number range routes is 0-65535 Management Some port numbers: destPON 23: Telnet 25: SMTP 53: DNS 161: SNMP {destPON, sourcePON,.. 5060: SIP PRN=6 PRN=17 {PRN, sourceIPA, destIPA,...) T-ROs AddrPar LAN encapsulation, T-RE(TCP/UDP-user): REi->IPA,destPN T-APi(TCP/UDP): Lli->sourcePN encapsulation tunnelling, MPLS layer elements Fig. 3.29 Socket routes in IP networks. PON=port number; PRN=protocol number There are, however, functional differences as well: All applications are assigned to port numbers (in SS7, MTP L3 also supports applications). The range of port numbers is very large (0-65535). To the knowl- edge of the author, all assigned port numbers are used by "real applications," i.e., there exist no such thing as TCAP that listens to a whole set of port num- bers. TCP offers a CON service, UDP offers a CNL service. They are standardized separately, each defining its own protocol. Port numbers are normally common for both TCP and UDP (SCCP also defines both CON and CNL services, but within the context of a single and very complex protocol specification). A minor difference to CON services in SCCP is that socket routes are always referred to by {destIPA, destPortNumber} in TCP messages (in SCCP an OSI approach is used in data phase, identifying SCCP connections by a kind of con- nection id