s), ITU-R (radio), and ITU-D (developing nations). IV (initialization vector) In cryptography, a block of bits that is required to allow a stream cipher or a block cipher executed in any of several streaming modes to produce a unique stream independent from other streams produced by the same encryption key, without having to go through a rekeying process. IXC (interexchange carrier) A long-distance telephone company that offers circuit- switched, leased-line, or packet-switched service. IXP (Internet exchange point) A physical infrastructure that allows different ISPs to exchange Internet traffic between their networks by means of mutual peering agreements, which allow traffic to be exchanged without cost. jack A device used generally for terminating the permanent wiring of a circuit, access to which is obtained by the insertion of a plug. J-carrier The Japanese standard of the PDH, a TDM digital transmission system. J-carrier is a PCM system that uses 64Kbps per channel as the basis of the hierarchy. Higher levels reflect aggre- gation of the 64Kbps channels. J-1 is a 1.544Mbps 24-channel communications circuit; J-2 is 6.312Mbps 96-channel communications circuit; J-3 is a 32.064Mbps 480-channel communications circuit; J-4 is a 97.728Mbps 1,440-channel communications circuit; and J-5 is a 565.148Mbps 8,192-channel communications circuit. jitter The slight movement of a transmission signal in time or phase that can introduce errors and loss of synchronization for high-speed synchronous communications. JPEG (Joint Pictures Expert Group) An international standard used primarily for still image compression. JTACS (Japanese Total Access Communication Systems) A Japanese wireless system that operates in the 800MHz to 900MHz band. JTAPI (Java TAPI) JTAPI (Java TAPI) An extensible object-oriented API that supports telephony call control. jumper A patch cable or wire used to establish a circuit, often temporarily, for testing or diagnostics. Ka-band The portion of the electromagnetic spectrum allotted for satellite transm